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Some species mon discount arava on line treatment 7 february, yet flocks of these birds are established only in exist today only in captivity trusted 20 mg arava symptoms 3 days dpo. There are many questions regarding captive breed- Research on White-naped Crane eggs has shown that ing buy arava line treatment nail fungus. Are the progeny of these birds releasable in their the microclimate surrounding these large eggs is native habitat or non-native habitats? Incubated netic changes that result from captive breeding that eggs do not have any temperature gradient. Is this might affect the ability of captive-bred birds to sur- microclimate essential for successful hatching of vive in the wild? What are the risks of introducing diseases to native populations or altering the ecology of the habitat with the introduction of captive-bred birds? As a consequence of domestication, there are behavioral and anatomic changes which become evident within the first few generations. The behavioral changes include three major charac- teristics: docility, curiosity and a disrespect of species barriers. Does this thermal gradient have a spe- an endeavor face difficult economic and scientific cific function? Over a century ago, Darwin and Wallace proposed conflicting views about the origin and function of Harvesting prominent male secondary sexual features and their effects on the female’s choice of a mate. Research and Avian veterinarians will need to play a significant debate on this subject is still very intense today. How are genetics, resistance to disease and reproduc- Ranching differs from captive breeding in that the tive strength of avian species being altered when breeder flock is not removed from its native habitat. How large a flock is The number of offspring “harvested” is based on the needed to allow mate selection and adequately pro- local site biological data. Parrots appear to have considerable potential as a Should this practice be discouraged in order to pre- sustainable harvest. Both large Aviculturists who intend to provide birds for reintro- and small landowners can participate, and there is duction programs will need to establish specific considerable potential to increase harvests through flocks for this purpose that are separate from birds existing management techniques. These birds must be maintained and managed differently from compan- Because habitat protection is an integral part of suc- ion birds to minimize the effects of domestication. Some of the problems associated with harvesting To prevent losses, the flock must be divided into include the social and political structures needed to viable groups, managers must be attentive to hus- allow for the lawful export of the harvest, protection bandry and sanitation and movements must be re- of the birds from poaching and over-exploitation, stricted between populations. Avian veterinarians fluctuations in demand for birds, ensuring that im- will be important members of the management portation of these birds does not increase the level of teams. With a decrease in available habitat, all the factors for disease transmission among free-ranging birds Avian veterinarians may play an important role in (eg, nutrition, increased proximity, stress) become the prevention of disease on the ranch and during the more significant. Psittacines have the potential for reintroduction once appropriate criteria have been met. Factors that con- tributed to the decline of the native population must Captive Breeding and Reintroduction be modified sufficiently in order for the newly re- When faced with imminent extinction, captive breed- leased birds to survive. Habitat protection, predator ing with the goal of reintroduction remains the only control, harvest of free-ranging birds and reduction alternative for preservation of a species. The conser- of human activity, both recreational and commercial, vation community is not in full agreement about must also be considered. Until we have a greater captive breeding of endangered and threatened spe- understanding of how these and other factors affect cies because of the many scientific, economic and populations, release of captive-bred psittacine birds political considerations involved. However, before a captive breeding program for a Under some circumstances it may be preferable to species can be established, several questions need to establish new populations in previously non-native be asked. How many founding members are needed tions needs to be thoroughly evaluated to minimize to ensure an adequate gene pool? If not based in a Trade in neotropical parrots has played a significant public institution, does sufficient cooperation and role in the decline of these species, affecting perhaps accountability exist among private breeders to en- as many as 17% of the endangered neotropical par- sure a successful breeding program? Trade and habitat destruction affects an addi- issue of ownership of progeny been resolved? These changes have the help ensure protection for wildlife in foreign coun- potential to significantly improve the situation for tries equal to the protection we provide for our own these endangered and threatened species. Until 1992, all United States legislation effecting No single act will have as much influence on the trade in wild-caught birds was at the state level. This ground-breaking law sought to effect on diseases of pet birds as a result of their establish importation restrictions that would be en- increasing domestication? How will the pet bird dif- forceable, not result in an increased rate of smug- fer from the wild bird? With a shrinking habitat and gling or diseased birds and allow for the growth of the increasing human population, almost all species are avicultural industry. One of the major impacts of this feeling the presence of humans, both directly and type of legislation was to increase the public’s aware- indirectly. These observa- ists and the pet industry realized it was in the inter- tions can be of extreme importance to the conserva- est of all parties’ to ensure the continued survival of tion of many species. After several years of discussions and negotiations, the Wild Bird Conservation Act of In summary, conservation is both a science and a 1992 was enacted. Only when avian veterinarians have de- lation affecting the importation into the United fined their own conservation ethic, can they help States of wild-caught birds. Avian veterinarians con- companion bird clients and aviculturists better un- tributed to the passage of this act. Avian act require certification of foreign breeding facilities veterinarians can work together with conservation- by the U. Input by avian ists, aviculturists and biologists to continue to im- veterinarians will continue to be needed in this area. Golden, Fulcrum Publish- tional Council for Bird Preservation and People Sharing the World. Ritchie I eterinary medical decisions are often made by comparing the similarities and differ- C H A P T E R ences that occur between individual pa- V tients and an established animal model. This comparison concept is functional because of the relative similarity between a collie and a poodle, or a Persian and a Siamese, or a holstein and an angus. Any respective difference in anatomy or physiology or in an animal’s response to a drug or infectious 1 agent is easy to qualify when compared to a generic species model. In a single day, an avian practitioner may be presented with patients that belong to five different orders. The avian clinician can be most effective by disposing of the philosophical handicap of basing medical deci- sions on a generic companion bird. Instead, the vet- erinarian must look for the natural differences that exist in patients from such diverse geographic loca- Ross A. There is not a wealth of scientifically derived infor- mation available, particularly with respect to vari- ances in avian dietary adaptations, behavioral char- acteristics and response to drug preparations and infectious agents. The clinician must compensate by applying a broad medical checks-and-balances sys- tem based on the use of numerous diagnostic and therapeutic tools. Medical management decisions for a particular genera within an order must be based on the interpretation of several changes that indicate that an abnormality is truly an abnormality.
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Neurons in the nervous system reside in a nondividing state and therefore potential virus vectors for gene therapy must be capable of infecting postmitotic cells order 10 mg arava mastercard treatment 7. Lentiviruses (from the Latin word lentus meaning slow) cause slow chronic and progressive degenerative diseases of the nervous order discount arava line medications osteoporosis, hematopoietic cheap arava 20 mg amex treatment 0f osteoporosis, musculoskeletal, and immune systems. These viruses are the only retroviruses able to integrate into the chromo- somes of cells that are not mitotically active. The efficiency of gene transfer is high and reports indicate that lentiviral vectors injected into the adult rat brain stably transduce terminally differentiated cells in vivo, without a decrease in transgene expression or toxicity for at least 6 months in vivo. These genes and their products show homology throughout the animal kingdom from the nematode to the primates. The products of the Bcl-2 family of protooncogenes have been extensively characterized as proteins that regulate cell death. A possible ther- apeutic approach to preventing neuronal degeneration may be via the modula- tion of apoptosis by members of the Bcl-2 family, including bcl-xl and bax. In Alzheimer’s, levels of Bcl-2 protein are significantly higher than aged-matched adult brain, and this protein is predominantly localized to activated astrocytes rather than neurons. Thus, overex- pression of Bcl-2 may prevent the degeneration of motor neurons by inhibiting free radical mediated damage. Poor survival of grafted neurons has been a major issue in neural transplanta- tion. Attempts to increase the survival of grafted neurons have been made by expressing the Bcl-2 gene in cells before transplantation. This concept has been tested with a cell line generated from the substantia nigra. In the rodent fimbria-fornix lesion model of cholinergic neuron degeneration, neuroprotective effects have been demonstrated by the Bcl-xL gene. Expression of Bcl-xL by lentiviral vectors in this model significantly increases cholinergic neuron survival in the septal region subsequent to axotomy of the pathway. Studies of this nature provide evidence that overexpression of antiapototic factors via gene trans- fer in vivo is sufficient to rescue neuronal populations after axotomy. Within a span of approximately 20 years, the transplantation of cells into the brain evolved from the laboratory setting to clinical trials for severe Parkinson’s. Throughout the 1980s and 1990s, tissues were grafted into the brain to study aspects of neural cell development and to identify the function of different brain areas. Now, we are in a new era of establishing the most appropriate cell grafting technologies for application in the clinic. Unfortunately, the dramatic restorative functional changes seen in certain animal models of neurological disease were not seen with the transfer of the grafting techniques to the human situation. Case in point—transplants of fetal substantia nigra neurons stereotaxically injected into the striatum of Parkinson’s patients. The results from the initial clinical trials were partly encouraging in that there were no major side effects from this type of operation. Some of the transplanted cells in the human striatum show extended survival for years, and for some pa- tients there was a therapeutically significant reduction in the motor symptoms (rigidity and bradykinesia). The modest to moderate improvement seen in some patients does, however, gradually disappear. To date we cannot predict with certainty that Parkinson’s patients who are ideal candidates for a transplant will benefit from this grafting procedure. One of the primary problems with transplanting neurons into the lab animal and human brain has been the issue of poor graft survival. In humans only about 5% of the fetal dopamine neurons survive using the current transplantation protocols. This raises the issue of just how representative are the animal models of human neurological disorders. Although fetal neurons have shown the greatest potential in terms of graft survival and clinical efficacy for Parkinson’s, there are serious concerns associated with the use of human fetal neurons, namely tissue availability, quality control, and ethics. To circumvent some aspects of these problems, research has examined neural xenografts for Parkinson’s and the use of stem or neuronal cells grown in culture. It is now possible to isolate subpopulations of stem or neuronal progenitor cells from the developing or adult nervous system, expand the cells in culture, and then use the cells for transplanta- tion or as vehicles for gene delivery to selected sites of the nervous system. These cells survive in vitro in media enriched with growth factors and with passage express a neuronal phenotype. A major advantage of using progenitor cells for transplan- tation is that they have not been transformed or immortalized and exist naturally in the brain. Continued collaborative efforts between the basic and the clinical research sectors using stem or progenitor cells for ex vivo transgene delivery will be critical to the progression of effective therapy for Parkinson’s and other neu- rodegenerative conditions. As previously described, a variety of non-neuronal primary cells and cell lines have been used largely as a way to deliver an active substance that promotes survival or growth of neurons. Research centered on cell replacement strategies now focus predominantly on the use of neural stem cells. Stem Cells in the Adult Brain Until just a few years ago, it was generally assumed and believed that the adult brain was incapable of generating new neurons. Research on a number of fronts has estab- lished that the adult mammalian brain contains stem cells that can give rise to the full spectrum of neurons and glial cells. In particular, the subventricular zone, an important layer that forms during development and persists into adulthood retains the capacity to generate both neurons and glial cells (Fig. Stem cells by strict definition over the lifetime of the animal must be able to proliferate, show self-renewal, produce progeny with multilineage characteristics, and divide when injured. Progenitor cells refer to cells with a more restricted potential than stem cells, and precursor cells refer to cells within a given developmental pathway. The presence of neural stem cells in the adult brain has established the possibility for using the mature brain as a source of precursor cells for transplantation and helps to establish new therapy directions for neurological injury and disease. In fact, as our understanding of stem cell neurobiology grows, it may be possible to control the proliferation and migration of such cells into areas of the nervous system affected by the diseases discussed in this chapter. The notion of self-repair in the brain is now visible at the basic research level. The potential growth factors governing the commitment and differentiation of the neuronal lineage are indicated. More- over, these newly generated neurons had also made connections to their appropri- ate target. Multipotent stem cell proliferation and differentiation can be regulated by neu- rotrophic factors. When growth factors are added in sequence to neural stem cells, they regulate whether the cells will acquire neuronal or glial characteristics. One sector of gene therapy research focuses on a neural-stem-cell-based strat- egy. With the capability of differentiating along multiple cell lineages, stem cells may be very effective for the delivery of therapeutic gene prod- ucts throughout the brain or spinal cord. The enzyme deficiency in this mouse model causes lysosomal accumulations of undegraded glycosominoglycans in the brain and other tissues that results in fatal degenerative changes. Similar therapeutic paradigms are also being evaluated for other inherited neurogenetic diseases that are characterized by an absence of discrete gene products.
