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Subject: search.filters.subject.Neurogenesis

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Now showing 1 - 4 of 4
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    Synaptogenesis and spinogenesis of adult hippocampal neurogenesis in laboratory long-evans rat exposed to enriched environment
    (2017) Uzokwe, Chioma Blessing
    This research studied adult hippocampal neurogenesis in the dentate gyrus of the hippocampus of the Long-Evans rat. Eighteen male Long-Evans rats were exposed to complex enriched environment, the running wheel environment for exercise as single influencing factor and the standard laboratory environment for 28 days. Thereafter the rats were transcardially perfused with 0.9 normal saline followed by 4% paraformaldehyde. The brains were removed and frozen sagittal sections cut at 50 μm. Brain sections were stained with Cresyl violet for cytoarchitecture. Immunohistochemistry and immunofluorescence techniques were employed for the immature neurons with defined processes using the marker doublecortin (DCX), neuronal proliferation marker Ki-67, the synapse marker, synaptophysin and the dendritic spine marker, synaptobrevin. Giemsa staining was used to identify pyknotic neurons followed by counts for DCX, Ki-67, pyknotic positive cells, and volume density of the dentate gyrus. Results indicated a statistically significant increase in brain weight (p=0.5) for the complex enriched group when compared to the running group and control. The typical cytoarchitecture of the hippocampus in rodents was observed with more densely packed granule cell layer in the dorsal limb of the dentate gyrus compared to the ventral limb especially in the enriched group. The Ki-67 immunopositive cell number between groups showed a variable difference with a three-fold increase each between the standard control and exercise, and between the exercise and enriched but a six-fold increase between the standard control and the complex enriched groups. Comparing the DCX immunopositive results, we observed also that the neuronal numbers, structure, dendritic patterns as well as the neuronal arrangement on the dorsal and ventral limbs of the dentate gyrus varied significantly among groups. The apoptotic cell numberusing pyknotic cells, showed the standard control group to have the highest number of cells compared to the exercise versus the enriched group; noting a five-fold difference between the standard control and exercise, a twenty seven-fold difference between the standard control versus enriched and a twenty one-fold difference between 6 the exercise and complex enriched group. The volumetric analysis showed a 15-fold difference between the standard control and exercise groups, a five-fold difference between the exercise and complex enriched and a nineteen-fold difference between the standard control and complex enriched groups. However, no statistical significant difference was found in the volumetric analysis of the dentate gyrus between the groups.
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    Adult neurogenesis in the brain of chiroptera
    (2016) Chawana, Richard
    The current thesis, studying adult neurogenesis in the brains of Chiroptera (bats), is a collection of four related studies investigating the occurrence of neurogenesis in the two suborders of adult bats, megachiroptera (megabats) and microchiroptera (microbats), from different environments, including the wild and captive habitats. The studies were carried out in order to understand the dynamics associated with adult neurogenesis in mammals living in their natural habitat given that much of the current understanding is based on experiments done on laboratory bred or captive raised animals. The investigation of megachiropterans and microchiropterans was stimulated by the findings of a previous study which failed to show adult neurogenesis in some microchiropteran species, which is in contrast to the almost universal occurrence of the phenomenon in nearly all mammals. In addition, the use of chiropterans was appealing given their behavioural attributes, which have been previously associated with the occurrence of neurogenesis. These include such behaviours as good spatial abilities, high sociality and complex behaviours such as fusion-fission sociality. In addition, the highly debatable evolutionary history of chiropterans provided a framework in which to evaluate specific neural characters in terms of phylogenetic relationships. Using immunohistochemical methods, the presence and characteristics of proliferating and newly generated neurons in the brain of eight wild-caught adult megachiropteran species was examined. For the neurogenic patterns observed, direct homologies were evident in other mammalian species. Numerous proliferating cells and immature neurons were identified in the subventricular zone (SVZ) and the dentate gyrus. From the SVZ, these cells migrated to the olfactory bulb through a typically mammalian rostral migratory stream (RMS). Some newlygenerated cells were observed emerging from the RMS to the neocortex. Similar to primates, proliferating cells and immature neurons were identified in the SVZ of the temporal horn of the lateral ventricle of the megachiropterans and were observed to migrate to the rostral and caudal piriform cortex through a primate-like temporal migratory stream. A similar study using three microchiropteran species revealed almost similar findings. However, distinct differences to the megachiropterans were noted, especially so in the migratory pathway to the piriform cortex, where cells appeared to migrate from the RMS through an insectivore-like ventral migratory stream to populate the entire piriform cortex. In addition microchiropterans had immature axons in the anterior commissure, something which was not observed in megachiropterans but was previously reported in insectivores. Using immunohistochemical and stereological methods, the effect of animal capture and handling on the occurrence of adult neurogenesis in 10 microchiropterans species was investigated. These animals were euthanized and perfusion fixed at specific time points following capture to investigate the effect of stress as a possible explanation for the negative findings regarding adult hippocampal neurogenesis in microchiropterans reported in a previous study. This investigation revealed that when euthanized and perfused within 15 minutes of capture, abundant putative adult hippocampal neurogenesis could be detected using doublecortin immunohistochemistry, but the ability to readily observe these cells rapidly diminishes if the microchiropterans have not been euthanased within 15 minutes of capture. Also using immunohistochemical and stereological methods, proliferative and immature cells within the dentate gyrus of adult Egyptian fruit bats from three distinct environments (fifth generation captive bred, wild-caught from the primary rainforest of central Africa and wildcaught from the South African woodlands) was quantified and compared. Four previously reported methods to assess the effect of the environment on proliferative and immature cells were used. These include: (1) the comparison of raw totals of proliferative and immature cells; and these totals standardized to (2) brain mass, (3) the volume of the granular cell layer (GCL), and (4) the total number of granule cells in the dentate gyrus. For all methods, the numbers of proliferative cells did not differ statistically amongst the three groups. For the immature cells standardizations to brain mass and GCL volume revealed no difference between the three groups studied; however, the raw numbers and standardization to total granule cell numbers indicated that the two groups of wild-caught bats had significantly higher numbers of immature neurons than the captive-bred bats. In conclusion, the observation of the ventral migratory stream in the microchiropterans and insectivores, in contrast to the temporal migratory stream in megachiropterans and primates adds another neural characteristic supporting the diphyletic origin of Chiroptera, and aligns microchiropterans with insectivores and megachiropterans with primates. In microchiropterans, the presence of doublecortin, revealing adult neurogenesis, in the hippocampus is highly sensitive to capture and handling. Lastly, the interpretation of the effect of the environment on the numbers of immature neurons appears method dependent. It is possible that current methods are not sensitive enough to reveal the effect of different environments on proliferative and immature cells.
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    The presence and pattern of adult neurogenesis in the brains of three prosimian primates
    (2015) Fasemore, Thandi Mamorapelo D
    This study investigated the presence and pattern of adult neurogenesis in the Subventricular zone (SVZ) of the lateral ventricle, the dentate gyrus (DG) of hippocampus and potential neurogenic sites in three prosimian primates. While two nocturnal species, the Galagoides demidoff phasma (Galago) and the Perodictus potto (Potto) were caught in the wild, the Lemur catta (Lemur) was a zoo kept diurnal animal. Two brain specimens from each species, perfusion-fixed with 4% paraformaldehyde were cut at 50 μm thick frozen sections in sagittal and coronal planes. Using doublecortin (DCX) and Ki-67 antibodies, immature neurons and proliferating cells were identified respectively in the SVZ and DG and in potential sites such as the striatum, corpus callosum, amygdala, and piriform cortex in all the three species. DCX positive cells were observed in the cerebellum of the Lemur and the Galago but not in the Potto. There were no Ki-67 proliferating cells observed in the cerebellum and the neocortex of all the three species. Interspecies analysis indicated that the estimated rate of Ki-67 proliferating cells in Potto was 1.9 times higher than that of the Lemur and 4.8 times higher than that of the Galago. There was no statistical significant variation in the number of estimated Ki-67 cells within the three species but a significant difference (P ≤ 0.05) when comparing Potto with the Lemur and Galago. There was no significant difference (P ≥ 0.05) in the number of Ki-67 cells between the Lemur and the Galago. Variations do exist in the cell proliferation pattern among these three prosimian primates.
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    Neurogenesis in the central nervous system of the Nile crocodile (Crocodylus niloticus) throughout ontogenesis
    (2015) Ngwenya, Ayanda
    The body and central nervous system of the Nile crocodile (Crocodylus niloticus) is known to grow continuously, even past sexual maturity. Previous studies on crocodilians show a gradual decrease in the rate of growth of the brain as individuals mature; however, the data on brain growth are limited and there are no data on growth rates of the spinal cord and retina. The current thesis provides a description of the growth rates of the brain, spinal cord and eye (ocular volume) of 70 juvenile and sub-adult Nile crocodiles ranging between 92 g and 90 kg in mass. Body growth in the crocodiles is accompanied by growth of all central nervous system structures (brain, spinal cord and eye), although growth occurs at different rates, with the spinal cord being the fastest growing structure, followed by the eye and the brain. The neurogenic regions (areas to which new neurons are continuously added) of the brain were revealed using doublecortin immunohistochemistry. Labelled cells were observed in all the regions of the telencephalon (including the cortical mantle, dorsal ventricular ridge, striatum, septal nuclei and the olfactory bulbs) as well as the molecular and granular layers of the cerebellar cortex, but not in the diencephalon or brainstem.