Christine Byrd - US grants

DESCRIPTION: The purpose of this investigation is to determine if there is a population of cells in the adult zebrafish that retain the capacity to differentiate into neurons. In Experiment 1, immunohistochemistry (BrdU antib is designed to label newly divided cells in the adult olfactory bulb, and thes cells will be examined for double labeling with neuron-specific antibodies (including Hu, neuron-specific endolase and TUJ1) or glial-specific antibodies (including GFAP). It is hypothesized that at least a subset of newly formed c in the olfactory bulb will be identified as neurons. Experiment 2 is designed determine if the newly generated cells originate in the olfactory bulb itself if they migrate from the telencephalic ventricular zone. The vital dye diI wi be injected into the telencephalic ventricle to label precursor ventricular ce and examination of the distribution of their progeny will be performed after various survival times. It is hypothesized that diI-labeled progeny will appe in the olfactory bulb following an undetermined migration period. The final experiment will attempt to identify the markers for the migratory route from t ventricular zone to the olfactory bulb using immunohistochemical techniques. Antibodies will include PSA-NCAM, GFAP, vimentin and microtubule-associated proteins. It is hypothesized that one or more of these molecules may be invol in forming the route for cell migration.

DESCRIPTION (From the Applicant's Abstract): The major goal of this proposal is to examine the importance of olfactory afferent innervation on the maintenance of the olfactory bulb in adult zebrafish. Plasticity in the adult central nervous system is an important element in recovery from brain injury and disease as well as in learning and memory. An examination of lesion-induced changes after permanent olfactory deafferentation should lead to a better understanding of the normal information that the olfactory bulb receives from the olfactory organ. Olfactory axons have been shown in mammals to influence a variety of features in the olfactory bulb, including expression of proteins. How olfactory axons influence the stabilization of their target in the adult brain is unknown, however. Changes in input to the olfactory bulb, caused by removal of the olfactory afferent axons, will likely result in numerous changes in the brain. This proposal attempts to begin analyzing the mechanisms underlying the interactions between these two structures, with the long-term goal of elucidating cellular and molecular factors involved in stabilization of adult brain organization. Removal of the olfactory organ results in a significant decrease in olfactory bulb volume. This proposal attempts to explain the reason for this reduction, by determining whether there are fewer cells, smaller cells, or higher packing density of cells in the experimentally manipulated bulb.

DESCRIPTION (provided by applicant): The overall aim of this proposal is to examine degeneration and regeneration of an adult brain structure, with the goal of better understanding the mature brain's ability to heal after damage. We have developed a model for synaptic plasticity in the olfactory bulb in zebrafish: one that produces temporary, partial deafferentation and allows potential regeneration of the adult brain to be observed. Repeated intranasal irrigation with Triton X-100 in this animal results in long-term, partial deafferentation of the olfactory bulb with a resulting deficit in bulb volume. Cessation of the detergent treatment allows the olfactory epithelium to recover and reinnervate the olfactory bulb, reversing the deafferentation-induced decrease in bulb volume. This proposal examines the mechanisms by which bulb volume is reduced and restored in this model. The hypothesis of this R15 proposal is that repeated chemical ablation of the olfactory epithelium produces deafferentation-related changes in cell genesis and cell survival in the olfactory bulb, and these effects are reversed with reinnervation by regenerated olfactory axons. Bromodeoxyuridine immunocytochemistry and TUNEL methods will be used to label newly formed cells and apoptotic cells, respectively. The first specific aim is to determine specific alterations in cell genesis and cell survival induced by repeated ablation of the olfactory epithelium with detergent. The hypothesis of this aim is that repeated assault on the olfactory epithelium by intranasal irrigation with detergent reduces the size of the olfactory bulb and this decrease in bulb size is possibly due to increased cell death and/or decreased cell genesis. Specific alterations in the patterns of cell genesis and cell survival will be analyzed to determine the effects of decreased afferent input on cell formation and cell fate. The second specific aim is to determine the effect of reinnervation on cell genesis and cell survival in the deafferented olfactory bulb. The hypothesis of this aim is that reinnervation will cause a reversal of the deafferentation-induced reduction in bulb size through decreased cell death and/or increased cell genesis. Zebrafish is used because it is an important model organism with similar basic cytoarchitecture as other vertebrates, including human, and the potential for future work on molecular mechanisms involved in brain plasticity. These studies permit investigation into the adult brain's potential for recovery from physical or functional deafferentation due to injury or disease. PUBLIC HEALTH RELEVANCE: This project examines the ability of the adult brain to recover from damage due to injury or disease. Cell genesis and cell death will be examined with a novel, reversible deafferentation method using repeated intranasal irrigation with detergent in zebrafish. This work will lead to a better understanding of the plasticity of the adult brain and the cellular interactions that are important in maintenance of adult brain structures.