ARTIFICIAL INSEMINATION

Artificial insemination, or AI, is the process by which sperm is placed into the reproductive tract of a female for the purpose of impregnating the female by using means other than sexual intercourse or NI.

Artificial insemination is widely used for livestock breeding, especially for dairy cattle and pigs. Techniques developed for livestock have been adapted for use in humans.

Specifically, freshly ejaculated sperm, or sperm which has been frozen and thawed, is placed in the cervix (intracervical insemination – ICI) or, after washing, into the female's uterus (intrauterine insemination – IUI) by artificial means.

Artificial insemination is used in many non-human animals, including sheep, horses, cattle, pigs, dogs, pedigree animals generally, zoo animals, turkeys and even honeybees. It may be used for many reasons, including to allow a male to inseminate a much larger number of females, to allow use of genetic material from males separated by distance or time, to overcome physical breeding difficulties, to control the paternity of offspring, to synchronise births, to avoid injury incurred during natural mating, and to avoid the need to keep a male at all (such as for small numbers of females or in species whose fertile males may be difficult to manage).

Semen is collected, extended, then cooled or frozen. It can be used on site or shipped to the female's location. If frozen, the small plastic tube holding the semen is referred to as a straw. To allow the sperm to remain viable during the time before and after it is frozen, the semen is mixed with a solution containing glycerol or other cryoprotectants. An extender is a solution that allows the semen from a donor to impregnate more females by making insemination possible with fewer sperm. Antibiotics, such as streptomycin, are sometimes added to the sperm to control some bacterial venereal diseases. Before the actual insemination, estrus may be induced through the use of progestogen and another hormone (usually PMSG).

Artificial insemination of farm animals is very common in today's agriculture industry in the developed world, especially for breeding dairy cattle (75% of all inseminations[clarification needed]) and swine (up to 85% of all inseminations). It provides an economical means for a livestock breeder to improve their herds utilizing males having very desirable traits.

Although common with cattle and swine, AI is not as widely practised in the breeding of horses. A small number of equine associations in North America only accept horses that have been conceived by "natural cover" or "natural service" – the actual physical mating of a mare to a stallion. The Jockey Club being the most notable of these - no AI is allowed in Thoroughbred breeding. Other registries such as the AQHA and warmblood registries allow registration of foals created through AI, and the process is widely used allowing the breeding of mares to stallions not resident at the same facility - or even in the same country - through the use of transported frozen or cooled semen.

In 1997, Tilikum, an Orca at SeaWorld Orlando began training for AI. In early 2000, Kasatka who resides at SeaWorld San Diego was artificially inseminated using his sperm. She gave birth to Tillikum's son, Nakai, on September 1, 2001. On May 3, 2002, another female in San Diego, named Takara, bore Tilikum's calf through AI, a female named Kohana. Takara is Kasatka's oldest child and daughter.

ANTIBIOTIC RESISTANCE MECHANISMS

Antibiotic resistance can be categorized in three types:

1. Natural or intrinsic resistance

• Inaccessibility of the target (i.e. impermeability resistance due to the absence of an adequate transporter: aminoglycoside resistance in strict anaerobes)
• Multidrug efflux systems: i.e. AcrE in E. coli, MexB in P. aeruginosa
• Drug inactivation: i.e. AmpC cephalosporinase in Klebsiella 

2. Mutational resistance

• Target site modification (i.e. Streptomycin resistance: mutations in rDNA genes (rpsL), ß-lactam resistance: change in PBPs (penicillin binding proteins))
• Reduced permeability or uptake
• Metabolic by-pass (i.e trimethoprim resistance: overproduction of DHF (dihydrofolate) reductase or thi^- mutants in S. aureus)
• Derepression of multidrug efflux systems

3. Extrachromosomal or acquired resistance (Disseminated by plasmids or transposons)

• Drug inactivation (i.e. aminoglycoside-modifying enzymes, ß-lactamases, chloramphenicol acetyltransferase)
• Efflux system (i.e. tetracycline efflux)
• Target site modification (i.e. methylation in the 23S component of the 50S ribosomal subunit: Erm methylases)
• Metabolic by-pass (i.e trimethoprim resistance: resistant DHF reductase)

RESISTANCE TO AMINOGLYCOSIDE ANTIBIOTICS

Aminoglycosides (Streptomycin, kanamycin, tobramycin, amikacin,...) are compounds that are characterized by the presense of an aminocyclitol ring linked to aminosugars in their structure. Their bactericidal activity is attributed to the irreversible binding to the ribosomes although their interaction with other cellular structures and metabolic processes has also been considered. They have a broad antimicrobial spectrum. They are active against aerobic and facultative aerobic Gram-negative bacilli and some Gram-positive bacteria of which staphylococci. Aminoglycosides are not active against anaerobes and rikettsia. Spectinomycin which is an aminocyclitol devoided of aminosugars is by extension included in the familiy of aminoglycosides. It also differs from them by its bacteriostatic ativity and by its way of action. Spectinomycin acts on protein synthesis during the mRNA-ribosome interaction and it does not lead to mistranslation like aminoglycosides do.

Three mechanisms of resistance have been recognized, namely ribosome alteration, decreased permeability, and inactivation of the drugs by aminoglycoside modifying enzymes. The latter mechanism is of most clinical importance since the genes encoding aminoglycoside modifying enzymes can be disseminated by plasmids or transposons.

Ribosome alteration

High level resistance to streptomycin and spectinomycin can result from single step mutations in chromosomal genes encoding ribosomal proteins: rpsL (or strA), rpsD (or ramA or sud2), rpsE (eps or spc or spcA). Mutations in strC (or strB) generate a low-level streptomycin resistance.

Decreased permeability

Absence of or alteration in the aminoglycoside transport system, inadequate membrane potential, modification in the LPS (lipopolysacchaccarides) phenotype can result in a cross resistance to all aminoglycosides.

Inactivation of aminoglycosides

These enzymes are classified into three major classes according to the type modification: AAC (acetyltransferases), ANT (nucleotidyltransferases or adenyltransferases), APH (phosphotransferases).

RESISTANCE TO TETRACYCLINE ANTIBIOTICS

Tetracyclines (tetracycline, doxycycline, minocycline, oxtetracycline, ...) are antibiotics which inhibit the bacterial growth by stopping protein synthesis. They have been widely used for the past forty years as therapeutic agent in human and veterinary medicine but also as growth promotor in animal husbandry. The emergence of bacterial resistances to these antibiotics has nowadays limited their use. Three different specific mechanisms of tetracycline resistance have been identified so far: tetracycline efflux, ribosome protection and tetracycline modification.

Tetracycline efflux is achieved by an export protein from the major facilitator superfamily (MFS). The export protein was shown to function as an electroneutral antiport system which catalyzes the exchange of tetracycline-divalent-metal-cation complex for a proton. In Gram-negative bacteria the export protein contains 12 TMS (transmembrane fragments) whereas in Gram-positive bacteria it displays 14 TMS. Ribosome protection is mediated by a soluble protein which shares homolgy with the GTPases participating in protein synthesis, namely EF-Tu and EF-G. The third mechanism involves a cytoplasmic protein that chemically modifies tetracycline. This reaction takes only place in the presence of oxygen and NADPH and does not function in the natural host (Bacteroides). 

The two first mechanisms are the most widespread and most of their genes are normally acquired via transferable plasmids and/or transposons. These two mechanisms were observed both in aerobic and anaerobic Gram-negative or Gram-positive bacteria demonstrating their wide distribution among the bacterial kingdom. To date, about sixty-one tetracycline resistance genes have been sequenced and thirty-two classes of genes identified in non-producers and producers (Streptomyces). Each new class is identified by its inability to hybridize with any of the known tet genes under stringent conditions (Levy et al. 1989. AAC 33:1373-1374). A new nomenclature for the resistance determinants has been proposed for the future with the S. B. Levy group to coordinate the naming of the detreminants (Levy et al. 1999. AAC 43:1523-1524).

RESISTANCE TO BETA-LACTAM ANTIBIOTICS

ß-lactams belong to a family of antibiotics which is characterized by a ß-lactam ring. Penicillins, cephalosporins, clavams (or oxapenams), cephamycins and carbapenems are members of this family. The integrity of the ß-lactam ring is necessary for the activity which results in the inactivation of a set of transpeptidases that catalyze the final cross-linking reactions of peptidoglycan synthesis.


In gram positive bacteria, especially staphylococcus aureus, resistance of penicillin G is mainly through the production of beta-lactamase enzymes that break the beta-lactam ring. S.aureus secretes beta-lactamse enzyme extracellularly as inducible exoenzymes that are plasmid-mediated. The inherent resistance to penicillin G of many gram negative bacteria result from low permeability of the gram negative cell wall, lack of PBP`s, and a wide variety of beta-lactamse enzymes. Most gram negative bacteria inherently express low levels of species-specific, chromosomally mediated beta-lactamase enzyme within the periplasmic space, which sometimes contribute to resistance. These enzymes hydrolyze susceptible cephalosphorins more rapidly than penicillin G, but they hydrolyze ampicillin, carbenicillin, and beta-lactamase-resistant penicillins poorly.

Production of plasmid-mediated beta-lactamase is widespread among common gram negative primary and opportunist bacterial pathogens. The enzymes are constitutively expressed, present in the periplasmic space, and cause high-level resistamce. The majority are penicillinases rather than cephalosphorinases. The most widespread are those classified on the basis of their hydrolytic activity as TEM-type beta-lactamases, which readily hydrolyze penicillin G and ampicillin rather than methicillin, cloxacillin, or carbenicillin. The less widespread OXA-type beta-lactamases hydrolyze penicillinase-stable penicillins (oxacillin, cloxacillin, and related drugs). Beta-lactamases probably evolved from PBP`s as a protective mechanism for soil organisms exposed to beta-lactamase in nature, in which they are thought to be widespread through their production by molds. Because of transferable resistance, beta-lactamase production by pathogens is now widespread.

A major advance has been the discovery of broad-spectrum beta-lactamase-inhibitory drugs (e.g. clavulanic acid, sulbactam, tazobactam). These drugs have weak antibacterial activity but show extraordinary synergism when administered with penicillin G, ampicilin, or amoxicillin because of irreversible binding to the beta-lactamase enzymes of resistant bacteria. Other beta-;actamase inhibitors, such as cefotaxime and carbapenems, have potent antibacterial activity in their own right.

VETERINARY STUDENT SCHOLARSHIPS

Best Vet Scholarships from National Organizations and Colleges

Students aspiring to be veterinarians are truly committed to the profession and to helping animals. But veterinary programs can be unforgiving when it comes to length of time to earn the degree and cost for funding. Thankfully there are many options for scholarships.

National Organizations

We Care Paws-itive Dog Club Scholarship is available to students who are majoring in an animal-related medical field.

The Thoroughbred Scholarship is available to students who wish to pursue a career in veterinary medicine or agricultural science with an emphasis on equine medicine, racetrack management or equine business management. To be eligible, students must be 25 years of age or younger, have at least a C average in high school and must show a financial need. See the pdf.

The Saul T. Wilson Jr. Scholarship Program is for undergraduates and graduates enrolled in college full time and in good academic standing. Undergraduates must have completed at least 2 years of a 4 year pre-veterinary medicine or some other biomedical science program. Graduates must have completed no more than 1 year of study in veterinary medicine. Students must agree to work for the Animal and Plant Health Inspection Service during school breaks. See the pdf.

The American Kennel Club sponsors the Veterinary Student Scholarships to full time students enrolled at a veterinary school in the U.S. Students are selected for scholarships based on academic achievement, financial need and activities with purebred dogs or related.

School Specific

Tufts Cummings School of Veterinary Medicine in Massachusetts offers several scholarship opportunities:

• George I. Alden Scholarship Fund provides assistance to deserving students studying veterinary medicine.
• Rosamond "Darby" A. Chambers Scholarship Fund proves scholarships to veterinary medicine students.
• John F. and Georgia O'Neill Flagg Scholarship Fund for Wildlife Medicine provide assistance to students who are studying veterinary medicine with an emphasis on wildlife medicine.

Scholarship with Restrictions

Veterinary Scholarship Trust of New England awards yearly scholarships to New England (Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, or Vermont) students attending any veterinary school in the U.S. as long as they are in good standing.

U.S. Department of Health and Human Services offers scholarships for full time students who are in financial need and from disadvantaged backgrounds. Students must be enrolled in a degree program for nursing or health professions.

Association of American Veterinary Medical Colleges offers several scholarships:

• The Harold Wetterberg Foundation awards scholarships to current or past New Jersey residents who are currently enrolled in post-graduate education in the veterinary medicine field.

• The Secretary's Award for Innovations in Health Promotion and Disease Prevention is for students enrolled in a bachelor's degree program in any health science field. This is a writing competition.

• The Hill's Public Health Award is for students enrolled in a veterinary program at a college associated with the Federation of Associations of Schools of the Health Professions. This is another writing competition with veterinary medicine as the topic.

CHLAMYDIA TRACHOMATIS

Chlamydia trachomatis, an obligate intracellular human pathogen, is one of three bacterial species in the genus Chlamydia. C. trachomatis is Gram-indeterminate (i.e. cannot be stained with the Gram stain); structurally the organism is Gram-negative. Identified in 1907, C. trachomatis was the first chlamydial agent discovered in humans.

C. trachomatis includes three human biovars: trachoma (serovars A, B, Ba or C), urethritis (serovars D-K), and lymphogranuloma venereum (LGV, serovars L1, 2 and 3). Many, but not all, C. trachomatis strains have an extrachromosomal plasmid.

Chlamydia species are readily identified and distinguished from other chlamydial species using DNA-based tests.

Most strains of C. trachomatis are recognized by monoclonal antibodies (mAbs) to epitopes in the VS4 region of MOMP. However, these mAbs may also cross-react with two other Chlamydia species, C. suis and C. muridarum.

C. trachomatis is an obligate intracellular pathogen (i.e. the bacterium lives within human cells) and can cause numerous disease states in both men and women. Both sexes can display urethritis, proctitis (rectal disease and bleeding), trachoma, and infertility. The bacterium can cause prostatitis and epididymitis in men. In women, cervicitis, pelvic inflammatory disease (PID), ectopic pregnancy, and acute or chronic pelvic pain are frequent complications. C. trachomatis is also an important neonatal pathogen, where it can lead to infections of the eye (trachoma) and pulmonary complications.

C. trachomatis may be treated with any of several antibiotics: azithromycin, erythromycin or doxycycline/tetracycline.

DOXYCYCLINE

Doxycycline is a tetracycline antibiotic. It works by slowing the growth of bacteria in the body.

Doxycycline is used to treat many different bacterial infections, such as urinary tract infections, acne, gonorrhea, and chlamydia, periodontitis (gum disease), and others. Doxycycline is also used to treat blemishes, bumps, and acne-like lesions caused by rosacea. It will not treat facial redness caused by rosacea. Doxycycline may be used in combination with other medicines to treat certain amoeba infections.

Do not use doxycycline if you are pregnant. It could cause harm to the unborn baby, including permanent discoloration of the teeth later in life. Doxycycline can make birth control pills less effective. Use a second method of birth control while you are taking doxycycline to keep from getting pregnant. Doxycycline passes into breast milk and may affect bone and tooth development in a nursing baby. Do not take this medication without telling your doctor if you are breast-feeding a baby.

Do not use this medication if you are allergic to doxycycline, or to similar medicines such as demeclocycline (Declomycin), minocycline (Dynacin, Minocin, Solodyn, Vectrin), or tetracycline (Brodspec, Panmycin, Sumycin, Tetracap).

If you have liver or kidney disease, you may need a dose adjustment or special tests to safely take doxycycline.

Do not give doxycycline to a child younger than 8 years old. It can cause permanent yellowing or graying of the teeth, and it can affect a child's growth. Throw away any unused tablets or capsules when they expire or when there are no longer needed. Do not take any doxycycline after the expiration date printed on the bottle. Expired doxycycline can cause a dangerous syndrome resulting in damage to the kidneys.

Do not use doxycycline if you are allergic to doxycycline, or to similar medicines such as demeclocycline (Declomycin), minocycline (Dynacin, Minocin, Solodyn, Vectrin), or tetracycline (Brodspec, Panmycin, Sumycin, Tetracap). Before taking this medicine, tell your doctor if you have liver or kidney disease. You may not be able to take doxycycline, or you may need a dose adjustment or special tests during treatment.

If you are using doxycycline to treat gonorrhea, your doctor may test you to make sure you do not also have syphilis, another sexually transmitted disease.

Do not use doxycycline syrup (Vibramycin) without first talking to your doctor if you have asthma or are allergic to sulfites.

FDA pregnancy category D. This medication can cause harm to an unborn baby, including permanent discoloration of the teeth later in life. Do not use doxycycline without your doctor's consent if you are pregnant. Tell your doctor if you become pregnant during treatment. Doxycycline can make birth control pills less effective. Use a non-hormonal method of birth control (such as a condom, diaphragm, spermicide) to prevent pregnancy while you are taking this medication. Doxycycline passes into breast milk and may affect bone and tooth development in a nursing infant. Do not take this medication without first talking to your doctor if you are breast-feeding a baby. Children younger than 8 years old should not take doxycycline. This medication can cause permanent tooth discoloration and can also affect a child's growth.

ANIMAL WELFARE

Animal welfare is the physical and psychological state of non-human animals. The term animal welfare can also mean human concern for animal welfare or a position in a debate on animal ethics and animal rights.

Systematic concern for animal welfare can be based on awareness that non-human animals are sentient and that consideration should be given to their well-being, especially when they are used for food, in animal testing, as pets, or in other ways. These concerns can include how animals are killed for food, how they are used for scientific research, how they are kept as pets, and how human activities affect the survival of endangered species.

An ancient object of concern in some civilizations, animal welfare began to take a larger place in western public policy in 19th century Britain. Today it is a significant focus of interest or activity in veterinary science, in ethics, and in animal welfare organizations.

There are two forms of criticism of the concept of animal welfare, coming from diametrically opposite positions. One view, dating back centuries, asserts that animals are not consciously aware and hence are unable to experience poor welfare. The other view is based on the animal rights position that animals should not be regarded as property and any use of animals by humans is unacceptable. Some authorities thus treat animal welfare and animal rights as two opposing positions. Accordingly, some animal right proponents argue that the perception of better animal welfare facilitates continued and increased exploitation of animals. Others see the increasing concern for animal welfare as incremental steps towards animal rights.

Motivations to improve the welfare of animals stems from sympathy and empathy. It can also be based on self-interest. For example, animal producers might improve welfare in order to meet consumer demand for products from high welfare systems. Typically, stronger concern is given to animals that are useful to humans (farm animals, pets etc.) than those that are not (pests, wild animals etc.). The different level of sentience that various species possess, or the perception of such differences, also create a shifting level of concern. Somewhat related to this is size, with larger animals being favored.

There is some evidence to suggest that empathy is an inherited trait. Women have greater concern for animals than men in some societies, possibly the result of it being an evolutionarily beneficial trait in societies where women take care of domesticated animals while men hunt. Interestingly, more women have animal phobias than men. But animal phobias are at least partly genetically determined, and this indicates that attitudes towards animals have a genetic component. Also, children exhibit empathy for animals at a very early age , when external influences cannot be an adequate explanation.

Laws punishing cruelty to animals tend to not just be based on welfare concerns but the belief that such behavior has repercussions toward the treatment of other humans by the animal abusers. Another argument against animal cruelty is based on aesthetics.

External factors that affect people's concern for animal welfare include affluence, education, cultural heritage and religious beliefs. Increased affluence in many regions for the past few decades afforded consumers the disposable income to purchase products from high welfare systems. The adaptation of more economically efficient farming systems in these regions were at the expense of animal welfare and to the financial benefit of consumers, both of which were factors in driving the demand for higher welfare for farm animals.

Interest in animal welfare continues to grow, with increasing attention being paid to it by the media, governmental and non-governmental organizations. The volume of scientific research on animal welfare has also increased significantly.

DESCRIPTION OF IN PAPYRO

In papyro: referring to experiments or studies carried out only on paper. For example, the term may be applied to epidemiological studies that do not involve clinical subjects, such as meta-analysis. The term is similar to phrases such as in vivo, in vitro, or in silico. Like the latter, in papyro (the correct Latin is in papȳrō) has no actual Latin meaning and was constructed as an analogue to the more popular and longstanding biological sciences terms (vivo and vitro). In papyro is mutually exclusive from in vitro and in vivo, but overlaps with in silico - that is, a study carried out through computer/abstract simulations can also be considered in papyro.

DESCRIPTION OF IN SITU

In biology, in situ means to examine the phenomenon exactly in place where it occurs (i.e. without moving it to some special medium).

In the case of observations or photographs of living animals, it means that the organism was observed (and photographed) in the wild, exactly as it was found and exactly where it was found. The organism had not been not moved to another (perhaps more convenient) location such as an aquarium.

This phrase in situ when used in laboratory science such as cell science can mean something intermediate between in vivo and in vitro. For example, examining a cell within a whole organ intact and under perfusion may be in situ investigation. This would not be in vivo as the donor is sacrificed before experimentation, but it would not be the same as working with the cell alone (a common scenario for in vitro experiments).

In vitro was among the first attempts to qualitatively and quantitatively analyze natural occurrences in the lab. Eventually, the limitation of in vitro experimentation was that they were not conducted in natural environments. To compensate for this problem, in vivo experimentation allowed testing to occur in the originate organism or environment. To bridge the dichotomy of benefits associated with both methodologies, in situ experimentation allowed the controlled aspects of in vitro to become coalesced with the natural environmental compositions of in vivo experimentation.

In conservation of genetic resources, "in situ conservation" (also "on-site conservation") is the process of protecting an endangered plant or animal species in its natural habitat, as opposed to ex situ conservation (also "off-site conservation").

In oncology: for a carcinoma, in situ means that malignant cells are present as a tumor but has not metastasized, or invaded, beyond the original site where the tumor was discovered. This can happen anywhere in the body, such as the skin, breast tissue, or lung. This type of tumor can often, depending on where it is located, be removed by surgery.

In medicine in-situ means that cancer cells have not passed through the basal lamina. Basically it means the tumor has not invaded lamina propria or the deeper portions of the tissue. Because metastasis generally requires a carcinoma to 'break through' the basement membrane, chances for metastasis is very low.

DESCRIPTION OF EX VIVO

Ex vivo (Latin: out of the living) means that which takes place outside an organism . In science, ex vivo refers to experimentation or measurements done in or on tissue in an artificial environment outside the organism with the minimum alteration of natural conditions. Ex vivo conditions allow experimentation under more controlled conditions than possible in the intact organism, at the expense of altering the "natural" environment.

A primary advantage of using ex vivo tissues is the ability to perform tests or measurements that would otherwise not be possible or ethical in living subjects. Tissues may be removed in many ways, including in part, as whole organs , or as larger organ systems.

Examples of ex vivo specimen use include:

• assays;
• measurements of physical , thermal , electrical , mechanical , optical and other tissue properties, especially in various environments that may not be life-sustaining (for example, at extreme pressures or temperatures );
• realistic models for surgical procedure development;
• investigations into the interaction of different energy types with tissues;
• or as phantoms in imaging technique development.

The term ex vivo is often differentiated from the term in vitro in that the tissue or cells need not be in culture; these two terms are not necessarily synonymous.

In cell biology , ex vivo procedures often involve living cells or tissues taken from an organism and cultured in a laboratory apparatus, usually under sterile conditions with no alterations for up to 24 hours. Experiments lasting longer than this using living cells or tissue are typically considered to be in vitro . One widely performed ex vivo study is the chick chorioallantoic membrane (CAM) assay. In this assay, angiogenesis is promoted on the CAM membrane of a chicken embryo outside the organism (chicken).

DESCRIPTION OF IN VITRO

A procedure performed in vitro ( Latin : within the glass ) is performed not in a living organism but in a controlled environment, such as in a test tube or Petri dish . Many experiments in cellular biology are conducted outside of organisms or cells; because the test conditions may not correspond to the conditions inside of the organism, this may lead to results that do not correspond to the situation that arises in a living organism. Consequently, such experimental results are often annotated with in vitro , in contradistinction with in vivo .

This type of research aims at describing the effects of an experimental variable on a subset of an organism's constituent parts. It tends to focus on organs , tissues , cells , cellular components, proteins , and/or biomolecules . In vitro research is better suited than in vivo research for deducing biological mechanisms of action. With fewer variables and perceptually amplified reactions to subtle causes, results are generally more discernible.

The massive adoption of low-cost in vitro molecular biology techniques has caused a shift away from in vivo research which is more idiosyncratic and expensive in comparison to its molecular counterpart. Currently, in vitro research is vital and highly productive.

However, the controlled conditions present in the in vitro system differ significantly from those in vivo , and may give misleading results. Therefore, in vitro studies are usually followed by in vivo studies. Examples include:

• In biochemistry, non-physiological stoichiometric concentration may result in enzymatic active in a reverse direction, for example several enzymes in the Krebs cycle may appear to have incorrect nomenclature.
• DNA may adopt other configurations, such as A-DNA .
• Protein folding may differ as in a cell there is a high density of other protein and there are systems to aid in the folding, while in vitro, conditions are less clustered and not aided.

It should be pointed out that the term is historical, as currently most lab ware is disposable and made out of polypropylene (sterilizable by autoclaving, ex: microcentrifuge tubes) or clear polystyrene (ex: serological pipettes) rather than glass to ease labwork, ensure sterility, and minimize the possibility of cuts from broken glass.

DESCRIPTION OF IN VIVO

In vivo ( Latin for "within the living") is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research. In vivo testing is often employed over in vitro because it is better suited for observing the overall effects of an experiment on a living subject. This is often described by the maxim in vivo veritas.

In molecular biology in vivo is often used to refer to experimentation done in live isolated cells rather than in a whole organism, for example, cultured cells derived from biopsies. In this situation, the more specific term is ex vivo . Once cells are disrupted and individual parts are tested or analyzed, this is known as in vitro . in vivo experiment is in living; in vitro study is in test tube.

According to Christopher Lipinski and Andrew Hopkins, "Whether the aim is to discover drugs or to gain knowledge of biological systems, the nature and properties of a chemical tool cannot be considered independently of the system it is to be tested in. Compounds that bind to isolated recombinant proteins are one thing; chemical tools that can perturb cell function another; and pharmacological agents that can be tolerated by a live organism and perturb its systems are yet another. If it were simple to ascertain the properties required to develop a lead discovered in vitro to one that is active in vivo , drug discovery would be as reliable as drug manufacturing."

In the past, the guinea pig was such a commonly used in vivo experimental subject that they became part of idiomatic English: to be a guinea pig. However, they have largely been replaced by their smaller, cheaper, and faster-breeding cousins, rats and mice .

In vivo imaging provides a noninvasive method for imaging biological processes in live animals in order to understand metabolic processes, effects of drugs and disease progression. Near-infrared (NIR) fluorescent detection has proven useful for in vivo imaging in small animals. Low tissue autofluorescence at 800 nm makes it possible to use probes with NIR labels to image tumors and organs. In vivo imaging is an important tool for any research that uses animal models to study diseases, such as Alzheimer's disease.

CANINE DISTEMPER

Canine distemper is a very serious viral disease that affects animals in the families Canidae,Mustelidae, Mephitidae, Hyaenidae, Ailuridae, Procyonidae, Pinnipedia, some Viverridae and Felidae(though not domestic cats; feline distemper or panleukopenia is a different virus exclusive to cats). It is most commonly associated with domestic animals such as dogs and ferrets, although it can infect wild animals as well. It is a single-stranded RNA virus of the family paramyxovirus, and thus a close relative ofmeasles and rinderpest. Despite extensive vaccination in many regions, it remains a major disease of dogs.

INFECTION

Puppies from three to six months old are particularly susceptible. Canine distemper virus (CDV) spreads through the aerosol droplets and through contact with infected bodily fluids including nasal and ocular secretions, feces, and urine 6–22 days after exposure. It can also be spread by food and water contaminated with these fluids. The time between infection and disease is 14 to 18 days, although there can be a fever from three to six days postinfection. 

Canine distemper virus tends to orient its infection towards the lymphoid, epithelial, and nervous tissues. The virus initially replicates in the lymphatic tissue of the respiratory tract. The virus then enters the blood stream and infects the lymphatic tissue followed by respiratory, Gastrointestinal,urogenital epithelium, the Central Nervous System, and optic nerves. Therefore, the typical pathologic features of canine distemper include lymphoid depletion (causing immunosuppression and leading to secondary infections), interstitial pneumonia, encephalitis with demyelination, andhyperkeratosis of foot pads.

The mortality rate of the virus largely depends on the immune status of the infected dogs. Puppies experience the highest mortality rate where complications such as pneumonia and encephalitis are more common. In older dogs that do develop distemper encephalomyetilis, vestibular diseasemay present. Around 15% of canine inflammatory central nervous system diseases are a result of CDV.

DIAGNOSIS

The above symptoms, especially fever, respiratory signs, neurological signs, and thickened footpads found in unvaccinated dogs strongly indicate canine distemper. However, several febrile diseases match many of the symptoms of the disease and only recently has differing between canine hepatitis, herpes virus, parainfluenza and leptospirosis been possible. Thus, finding the virus by various methods in the dog's conjunctival cells gives a definitive diagnosis. In older dogs that develop distemper encephalomyetilis, diagnosis may be more difficult since many of these dogs have an adequate vaccination history. 

The most reliable test to confirm distemper is a Brush Border slide/smear of the bladder transitional epithelium of the inside lining from the bladder, stained with Dif-Quick. These cells will always have inclusions. Inclusions in these cells which will stain a carmine red color and be para nuclear in the cytoplasm of infected cells. About 90% of the bladder cells will be positive for inclusions in the early stages of distemper. This is good for at least the first 21 days from onset of the disease. After this point, it gets harder to detect as the disease progresses further in the stages and the physical clinical signs will become quite obvious.

PREVENTION

There exist a number of vaccines against canine distemper for dogs (ATCvet code: QI07AD05 and combinations) and domestic ferrets(QI20DD01), which in many jurisdictions are mandatory for pets. The type of vaccine should be approved for the type of animal being inoculated, or else the animal could actually contract the disease from the vaccine. A dog who has eaten meat infected with Rinderpest can also sometimes receive temporary immunity. Infected animals should be quarantined from other dogs for several months due to the length of time the animal may shed the virus. The virus is destroyed in the environment by routine cleaning with disinfectants, detergents, or drying. It does not survive in the environment for more than a few hours at room temperature (20–25 °C), but can survive for a few weeks in shady environments at temperatures slightly above freezing. It, along with other labile viruses, can also persist longer in serum and tissue debris.

ASPERGILLOSIS

Aspergillosis is the name given to a wide variety of diseases caused by fungi of the genusAspergillus. The most common forms are allergic bronchopulmonary aspergillosis, pulmonaryaspergilloma and invasive aspergillosis. Most humans inhale Aspergillus spores every day. Aspergillosis develops mainly in individuals who are immunocompromised, either from disease or from immunosuppressive drugs, and is a leading cause of death in acute leukemia andhematopoietic stem cell transplantation. Conversely, it may also develop as an allergic response. The most common cause is Aspergillus fumigatus.

SYMPTOMS

A fungus ball in the lungs may cause no symptoms and may be discovered only with a chest x-ray. Or it may cause repeated coughing up of blood and occasionally severe, even fatal, bleeding. A rapidly invasive Aspergillus infection in the lungs often causes cough, fever, chest pain, and difficulty breathing.

Aspergillosis affecting the deeper tissues makes a person very ill. Symptoms include fever, chills, shock, delirium, and blood clots. The person may develop kidney failure, liver failure (causing jaundice), and breathing difficulties. Death can occur quickly.

Aspergillosis of the ear canal causes itching and occasionally pain. Fluid draining overnight from the ear may leave a stain on the pillow. Aspergillosis of the sinuses causes a feeling of congestion and sometimes pain or discharge.

In addition to the symptoms, an x-ray or computerised tomography (CT) scan of the infected area provides clues for making the diagnosis. Whenever possible, a doctor sends a sample of infected material to a laboratory to confirm identification of the fungus.

DIAGNOSIS

On chest X-ray and computed tomography pulmonary aspergillosis classically manifests as an air crescent sign. In hematologic patients with invasive aspergillosis the galactomannan test can make the diagnosis in a noninvasive way.

TREATMENT

The drugs amphotericin B, caspofungin, flucytosine, itraconazole, voriconazole are used to treat this fungal infection. For severe cases of invasive aspergillosis a combination therapy of voriconazole and caspofungin is suggested as a first line treatment.

EDEMA

Edema (also spelled oedema, formerly known as dropsy) is swelling due to accumulation of excess fluid in any biological tissue. Edema has many root causes, but the mechanism is simple; fluid is drawn from the blood into the tissues when there is a higher osmotic pressure in the tissues than in the blood. (Blood normally has a higher osmotic pressure than the tissues due to the contribution of the oncotic pressure). This higher pressure may be due to an actual increase (e.g., salt retention due to kidney failure) or it may be a relative increase (e.g., edema due to low serum protein in the blood due to nutritional deficiency). Obstruction to venous blood flow also results in edema due to the mechanically caused increase in blood pressure in upstream capillaries. Capillary damage due to infection, bacterial toxins, or other trauma will also allow fluids to move from the blood into tissues, and the exudation of fluid into extracellular spaces is part of the general process of inflammation.

Common conditions causing or characterized by edema are congestive heart failure, some renal problems, varicose veins, cirrhosis, malnutrition and allergic conditions such as angioneurotic edema.

AMYLOIDOSIS

Amyloidosis is a group of diseases that result from the abnormal deposition of a particular protein, called amyloid, in various tissues of the body. Amyloid protein can be deposited in a localized area and may not be harmful or only affect a single tissue of the body. This form of amyloidosis is called localized amyloidosis. Amyloidosis that affects tissues throughout the body is referred to as systemic amyloidosis. Systemic amyloidosis can cause serious changes in virtually any organ of the body.

Amyloidosis can occur as its own entity or "secondarily" as a result of another illness, including multiple myeloma, chronic infections (such as tuberculosis or osteomyelitis), or chronic inflammatory diseases (such as rheumatoid arthritis and ankylosing spondylitis). Amyloidosis can also be localized to a specific body area from aging. This localized form of amyloidosis does not have systemic implications for the rest of the body. The protein that deposits in the brain of patients with Alzheimer's disease is a form of amyloid.

Systemic amyloidosis has been classified into three major types that are very different from each other. These are distinguished by a two-letter code that begins with an A (for amyloid). The second letter of the code stands for the protein that accumulates in the tissues in that particular type of amyloidosis. The types of systemic amyloidosis are currently categorized as primary (AL), secondary (AA), and hereditary (ATTR).

In addition, other forms of amyloidosis include beta-2 microglobulin amyloidosis and localized amyloidoses.

BLOOD PLASMA

Blood plasma is the yellow liquid component of blood, in which the blood cells in whole blood would normally be suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid. It is mostly water (90% by volume) and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide (plasma being the main medium for excretory product transportation). Blood plasma is prepared by spinning a tube of fresh blood containing an anti-coagulant in a centrifuge until the blood cells fall to the bottom of the tube. The blood plasma is then poured or drawn off. Blood plasma has a density of approximately 1025 kg/m3, or 1.025 kg/l. 

Blood serum is blood plasma without fibrinogen or the other clotting factors (i.e., whole blood minus both the cells and the clotting factors). 

Plasmapheresis is a medical therapy that involves blood plasma extraction, treatment, and reintegration.

FRESH FROZEN PLASMA AND OTHER TRANSFUSED PLASMAS

"Fresh frozen plasma" (FFP) is prepared from a single unit of blood or by apheresis, drawn from a single person. It is frozen to −40 °C (−40.0 °F) after collection and can be stored for ten years from date of collection. The term "FFP" is sometimes used informally to mean any frozen transfusable plasma product, including products which do not meet the standards for FFP. FFP contains all of the coagulation factors and proteins present in the original unit of blood. It is used to treat coagulopathies from warfarin overdose, liver disease, or dilutional coagulopathy. Other transfusable plasma is identical except that the coagulation factors are no longer considered completely viable. This is particularly important for Factor VIII and hemophilia, but these have been mostly replaced by more specific Factor VIII concentrates in the developed world and true FFP is rarely used for that indication.

Plasma used as a source of Cryoprecipitate (Plasma, Cryoprecipitate Reduced) cannot be used for treatment of some coagulation problems but is still acceptable for many uses.

DRIED PLASMA

"Dried plasma" was developed and first used in WWII. Prior to the United States' involvement in the war, liquid plasma and whole blood were used. The "Blood for Britain" program during the early 1940s was quite successful (and popular in the United States) based on Dr. Charles Drew's contribution. A large project was begun in August of the year 1940 to collect blood in New York City hospitals for the export of plasma toBritain. Dr. Drew was appointed medical supervisor of the "Plasma for Britain" project. His notable contribution at this time was to transform the test tube methods of many blood researchers, including himself, into the first successful mass productiontechniques.

Nonetheless, the decision was made to develop a dried plasma package for the armed forces as it would reduce breakage and make the transportation, packaging, and storage much simpler. 

The resulting Army-Navy dried plasma package came in two tin cans containing 400 ccbottles. One bottle contained enough distilled water to completely reconstitute the dried plasma contained within the other bottle. In about three minutes, the plasma would be ready to use and could stay fresh for around four hours. 

Following the "Plasma for Britain" invention, Dr. Drew was named director of the Red Cross blood bank and assistant director of the National Research Council, in charge of blood collection for the United States Army and Navy. Dr. Drew argued against the armed forces directive that blood/plasma was to be separated by the race of the donor. Dr. Drew argued that there was no racial difference in human blood and that the policywould lead to needless deaths as soldiers and sailors were required to wait for "same race" blood. 

By the end of the war the American Red Cross had provided enough blood for over six million plasma packages. Most of the surplus plasma was returned to the United States for civilian use. Serum albumin replaced dried plasma for combat use during theKorean War.

PLASMA SHIFT

Blood plasma volume may be expanded by or drained to extravascular fluid when there are changes in Starling forces across capillary walls. For example, when blood pressure drops in circulatory shock, Starling forces drive fluid into the blood vessels, causing autotransfusion.

Also prolonged still standing causes an increase in transcapillary hydrostatic pressure. As a result, approximately 12% of blood plasma volume crosses into the extravascular compartment. This causes and increase in hematocrit, serum total protein, blood viscosity and, as a result of increased concentration of coagulation factors, it causes orthostatic hypercoagulability. 

CHRONIC NASAL DISCHARGE IN THE CAT

Chronic upper respiratory tract (URT) disease is a relatively common problem in cats, and can have many causes. The most common form is termed chronic post viral or idiopathic rhinitis. In this condition viral infection (e.g. cat ‘flu - caused by feline herpesvirus or feline calicivirus) causes the initial mucosal damage; but the chronic signs relate to secondary bacterial infection of the damaged nasal passages. This may then lead on to chronic osteomyelitis of the turbinate bones (bacterial infection of the fine bones within the nose).  More unusual causes include:

•  Fungal infections which are very uncommon in the UK .

•  Inflammation which can result in polyps of inflammatory tissue.

•  Neoplasia (cancer) which can be localised within the nose, or be part of more widespread disease.

•  Physical damage which can result from foreign objects getting stuck up the nose, facial trauma (e.g. from cat bites or car accidents), or be associated with severe dental disease.

WHAT ARE THE CLINICAL SIGNS OF CHRONIC URT DISEASE ?

The main signs are nasal discharge and difficulty in breathing, ie chronic “snuffles”. The exact nature of the discharge, whether both sides of the nose are affected, and the presence of other clinical signs are dependent on the exact nature of the disease process occurring within the nose, and on the presence of any other illness the cat may have.

In order to determine the extent and nature of the disease it is important that the cat be given a thorough physical examination by a veterinary surgeon. Particular points that the vet will look for include:

•  The presence of nasal discharge, and whether it is bilateral (affecting both sides of the nose) or unilateral (affecting only one side of the nose). Some diseases tend to show unilateral signs (e.g. foreign bodies or cancer), while others more often cause bilateral signs (e.g. chronic post viral rhinitis). The type of discharge can also be important; whether it is clear, purulent (pus), or blood stained. Although the presence of a discharge can be helpful in making a diagnosis, it can on occasion be misleading.

•  Facial swelling may indicate a more serious underlying problem such as cancer or fungal infections arising within the nasal chambers. Although facial pain is seen rarely, resentment of facial examination is common among cats with URT obstruction, especially those with intranasal foreign bodies, or polyps.

•  Sneezing, difficulty in breathing, noisy breathing and mouth breathing may all be seen, but their presence is usually of little diagnostic value.

•  Examination of the eyes may reveal ocular discharge ‘runny eyes', usually resulting from tear duct damage associated with previous URT viral disease, but occasionally associated with cancer within the nose. Another legacy of URT viral infection can be the development of chronic inflammation of the cornea (the clear front part of the eye).

•  Evidence of painful or infected ears may be associated with inflammatory polyps. Cats with polyps may have problems eating if the polyps are large enough to cause obstruction at the back of the throat.

•  Cat's with URT obstruction often have a poor appetite and so experience a degree of weight loss. Marked weight loss is more suggestive of cancer, fungal disease or severe systemic disease.

•  The size and shape of the kidneys may be altered if certain cancers are present.

• Mild to moderate enlargement of the lymph nodes (glands) at the angle of the jaw is common, resulting from a local inflammatory response. If the lymph nodes become very large, or if lymph nodes elsewhere in the body are also affected, cancer or fungal infections are most likely to be the cause.

Over-interpretation of clinical signs can be very misleading since different diseases can give rise to similar signs. However, a few general rules do apply, e.g. facial deformity (changes in face shape) with associated pain, especially if accompanied by a unilateral nose bleed or marked lymph node swelling is suggestive of more serious underlying problems such as nasal cancer or fungal disease. Lack of these clinical signs does not rule out these diagnoses as some cases of nasal lymphosarcoma (a common type of cancer) can cause bilateral nasal obstruction and little nasal discharge of any kind. Although post viral rhinitis usually presents as chronic bilateral purulent discharge, it can also result in unilateral discharge, sometimes blood tinged and occasionally with severe nose bleeds.

 

HISTORY IS IMPORTANT TO HELP WITH DIAGNOSIS      

It is very important to know the answers to a number of questions relating to the cat's previous experiences, e.g.

•  Did the cat have an acute URT infection (cat ‘flu) as a kitten? This is the most common initiating cause of chronic rhinitis.

•  Is there any history of facial trauma, dental disease or ear infections?

•  At what age did the cat first develop the clinical signs? The age of onset and speed of onset of clinical signs can often be misleading, but can occasionally be of help in the diagnosis.

•  Has the nasal discharge always been of the same type, consistency and colour, and has it always been unilateral or bilateral? Are the signs progressing, is the cat systemically ill, and has the cat responded to any previous treatments? The answers to these questions may help determine the underlying cause of the problems.

 

My cat had ‘flu as a kitten and has had 'snuffles' ever since, although he is well in himself.  Should I ask the vet to find out what is wrong with him?

 

Arrange for your vet to examine your cat but if chronic post viral rhinitis is believed to be the most likely cause of the patient's clinical signs, and the cat is not too distressed by the nasal discharge, it is probably best not to put it through further examinations (except perhaps an FeLV test). Further investigations are generally best left for cats with severe or progressive clinical signs, or those with evidence of generalised disease.

When considering treating cats with severe chronic URT disease it is helpful, where possible, to differentiate between the possible underlying causes. This allows the correct treatment to be given and the probable outcome to be discussed. However, since most cases of URT disease will result from chronic post viral damage, it is important to remember that tests may give negative results and the likelihood for full recovery, even with treatment, may be poor.

TESTS TO FIND THE CAUSE   

•  Non-invasive tests, such as haematology, biochemistry and tests for FeLV and FIV may help to determine the extent of systemic disease.

 

•  Nose and throat swabs may be taken to look for the presence of bacteria, viruses or fungi.

 

•  For the best hope of finding a diagnosis it is necessary to give the cat a general anaesthetic in order to perform more extensive investigations. These include taking radiographs (X-rays) and examining the nose and mouth. Detailed examination includes looking up the cat's nose, and examining behind its soft palate (the flap of skin at the back of the throat). While examining the nose it is possible to take samples to look for bacteria, fungi, evidence of inflammation or cancer cells. These methods do not allow very good access to the nasal chambers, so it is possible that underlying disease may sometimes be missed.

 

•  If the less invasive methods of investigation are not successful in gaining a diagnosis it may be necessary to perform an exploratory rhinotomy under general anaesthesia. This involves surgically opening the nasal chambers via the front of the cat's face. This allows for the close inspection of the nasal chambers, the collection of material for biopsy, and the removal of diseased tissue. The procedure is not to be undertaken lightly since although it can be beneficial in some cases, for example where a foreign body, fungal infection or cancer is present, the procedure is traumatic for the cat, and should be reserved for patients with severe clinical signs or those which are already suspected of having nasal cancer or fungal disease. Surgical intervention is rarely curative in cases of chronic post viral rhinitis.

CAN CHRONIC URT DISEASE BE TREATED ?   

Yes, but in most cases treatment is unlikely to give a long term cure. In most cases the clinical signs can merely be controlled, since the chronically damaged bones cannot be repaired.

Antibiotics can be given to reduce secondary bacterial infection. It is usually necessary to give them for a long period or as repeated courses in order to control the clinical signs. Since extended courses of antibiotics are generally not advisable for the overall health of the cat, they are usually given only when the cat is severely affected. It is generally hoped that with time the cat, and its owners, will learn to live with the cat's disease, without the need for repeated courses of antibiotics.

Steam inhalation can help. Make a small room, such as the bathroom, steamy or construct a box or tent structure in which a bowl of boiling water can make the atmosphere steamy. Avoid any human proprietary decongestants as many of these are toxic to cats. If the cat is severely affected by ‘snuffles' and is undergoing further investigation, it is possible to therapeutically flush the pus from the nasal passages while the cat is under general anaesthetic. Although this procedure can occasionally give some degree of short term relief, the clinical signs usually return. The most essential aspect of treatment is good nursing care, keeping the cat's face clean and clear of discharge, and encouraging it to eat by feeding warmed up food that is strong smelling. Specific treatments can be given where specific causes have been found, e.g. polyps can be surgically removed, some cancers can be controlled with chemotherapy, and fungal disease can be treated with anti-fungal drugs.

DRUGS THAT DISRUPT MICROTUBULES

Colchicine, colcemid, and nocadazol inhibit polymerization by binding to tubulin and preventing its addition to the plus ends. The figure to the right shows this inhibition by colchicine (red). Vinblastine and vincristine aggregate tubulin and lead to microtubule depolymerization. Taxol stabilizes microtubules by binding to a polymer. 

MICROTUBULE MOTILITY: EXPERIMENTS IN VITRO

One can label beads with kinesin or dyneins and watch the direction of movement in a cell at the light microscopic level. What would happen if the beads were simply labeled with "cytoplasmic extract"? This cartoon shows the motility process in vitro. The tubule is moving along a negatively charged glass surface and the vesicle moves along the tubule. 

This electron micrograph shows microtubules in cross section with the MAP bridge. The arrows point to bridges between microtubules. The star points to a MAP bridge to the vesicle. In summary, MAPs accelerate polymerization, serve as "motors" for vesicles and granules, and essentially control cell compartmentation.

MICROTUBULE ASSOCIATED PROTEINS (MAPS) FUNCTION

Microtubule associated proteins (MAPs) are tissue and cell type specific. They are high molecular weight proteins (200-300 K) or the tau (20-60 k) proteins. One domain binds to tubulin polymers or unpolymerized tubulin. This speeds up polymerization, facilitates assembly and stabilizes the microtubules. The other end will bind to vesicles or granules. MAPs vary with the cell type. The best examples are found in neurons. 

Furthermore, it is believed that some of these MAPs may bind to special sites on the alpha tubulin that form after it is in the microtubule. These are sites where a specific molecule is acetylated or the tyrosine residue is removed from the carboxy terminal. These sites are important marker sites for stabilized microtubules, because they disappear when microtubules are depolymerized. 

This figure shows a 3-D view of a neuron with its processes containing microtubules. At higher magnifications, the vesicles are seen attached to MAPs and moving along the microtubule conveyer belt. The MAPs include kinesins and dynein which "walk" along the microtubules in opposite directions.The kinesins move the vesicle along towards the plus end and dynein walks towards the minus end. In neurons, as the microtubules grow from the cell body through the processes, the plus end is more peripheral. These proteins have head regions that bind to microtubules and also bind ATP. The head domains are thus ATPase motors. The tail domain binds to the organelle to be moved. It is not known how the energy from ATP breakdown is converted into vectorial transport. 

MICROTUBULE FORMATION

The first stage of formation is called "nucleation". The process requires tubulin, Mg++ and GTP and also proceeds at 37 C. This stage is relatively slow until the microtubule is initially formed. Then the second phase, called "elongation" proceeds much more rapidly. 

During "nucleation", an alpha and a beta tubulin molecule join to form a heterodimer. Then these attach to other dimers to form oligomers which elongate to form protofilaments. Each dimer carries two GTP molecules. However the GTP that appears to function binds to the beta tubulin molecules. When a tubulin molecule adds to the microtubule, the GTP is hydrolyzed to GDP. Eventually the oligomers will join to form the ringed microtubule. The hydrolysis of GTP of course is facilitated at a temperature of 37 C and stopped at temperatures of 4 C. 

This figure shows that, as the oligomers assemble, they form a series of rings, 25 nm in diameter. In cross section, each ring consists of 13 beads. The rows of beads in longitudinal section are called protofilaments.

In the cell itself, microtubules are formed in an area near the nucleus called the "aster". Microtubules are polar with a plus end (fast growing) and a minus end (slow growing). Usually the minus end is the anchor point. In this figure, the plus end is shown to the left by the numerous tubulin dimers. This is the end that carries the GTP molecules which may be hydrolyzed to GDP. Hydrolysis is not necessary, however (see p 810 in text and discussion below). 

Tests have shown that microtubules will form normally with nonhydrolyzable GTP analog molecules attached. However, they will not be able to depolymerize (see below). Thus, the normal role of GTP hydrolysis may be to promote the constant growth of microtubules as they are needed by a cell. 

DYNAMIC INSTABILITY

Microtubules may vary in their rate of assembly and disassembly. Tubulin half life is nearly a full day, however, the half life of a given microtubule may be only 10 minutes. Thus, they are in a continued state of flux. This is believed to respond to the needs of the cell and is called "dynamic instability". Furthermore, there are regulatory processes that appear to control this in a cell. Microtubule growth would be promoted in a dividing or moving cell. However, microtubule growth would be more controlled in a stable, polarized cell. 

As described in your text, the cell can provide a GTP cap on the growing end of a microtubule to regulate further growth. This happens when the tubulin molecules are added faster than the GTP can be hydrolyzed. Thus, the microtubule becomes stable and does not depolymerize. It may also be encouraged to continue growing. Once the GTP is hydrolyzed, it begins to shrink, however. Another way of capping a microtubule is to put a structure at its end, such as a cell membrane.