3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Adult neurogenesis in the brain of chiroptera(2016) Chawana, RichardThe 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.Item A neuroanatomical evaluation of cholinergic,catecholaminergic, serotonergic and orexinergic neural systems in mammals pertaining to the phylogenetic affinities of the Chiroptera(2015) Calvey, TanyaOne of the few remaining mysteries in mammalian phylogeny is the issue of Chiropteran phylogeny. In order to further investigate the diphyletic hypothesis that states that Megachiroptera evolved from primate-like gliders and that Microchiroptera evolved from insectivores, the cholinergic, catecholaminergic, serotonergic and orexinergic systems were analyzed in, not only five insectivores (Crocidura cyanea, Crocidura olivieri, Sylvisorex ollula, Paraechinus aethiopicus and Atelerix frontalis) and three prosimian primates (Galagoides demidoff, Perodicticus potto and Lemur catta), but in species from other orders of interest including the Afrotheria (Potamogale velox, Amblysomus hottentotus and Petrodromus tetradactylus), Lagomorpha (Lepus capensis) and Scandentia (Tupaia belangeri). Brains of the mammals were coronally sectioned and immunohistochemically stained with antibodies against cholineacetyltransferase, tyrosine hydroxylase, serotonin and orexin-A. The presence or absence of 93 nuclei within these neuromodulatory systems was entered into modern cladistics software for analysis of the 13 studied species, as well as an additional 40 previously studied mammals. The majority of nuclei revealed in the current study were similar among the species investigated and to mammals generally, but certain differences in the nuclear complement highlighted potential phylogenetic interrelationships. The Afrotherian, A. hottentotus, presented unusual cholinergic interneurons in the cerebral cortex, hippocampus, olfactory bulb and amygdala, and exhibited an unusual foreshortening of the brain, such that a major mesencephalic flexure in the brainstem was evident. The Afrotherian, P. tetradactylus, lacked the catecholaminergic A15d nucleus as in a previously studied member of Macroscelididae. The three Insectivoran shrews lacked the cholinergic parabigeminal and Edinger-Westphal nuclei, had a mediodorsal arch of the cholinergic laterodorsal tegmental nucleus, lacked the catecholaminergic A4 and A15d nuclei and presented an incipient ventral division of the substantia nigra which is identical to previously studied Microchiroptera. All three prosimians presented a central compact division of catecholaminergic locus coeruleus (A6c) surrounded by a shell of less densely packed (A6d) tyrosine hydroxylase immunopositive neurons. This combination of compact and diffuse divisions of the locus coeruleus complex is only found in primates and Megachiropterans of all the mammalian species studied to date. T. belangeri of the Scandentia contained ChAT+ neurons within the nucleus of the trapezoid body as well as the superior olivary nuclear complex, which has not been described in any mammal studied to date. L. capensis of the Lagomorpha presented vi the rodent specific rostral dorsal midline medullary nucleus (C3), while T. belangeri was lacking both the ventral and dorsal divisions of the anterior hypothalamic group (A15v and A15d), and both species were lacking the primate/Megachiropteran specific compact portion of the locus coeruleus. Our neuroanatomical analysis suggests a phylogenetic relationship between the Soricidae (shrews) and the Microchiropterans, supports the phylogenetic grouping of primates with Megachiropterans, confirms previous molecular evidence of the relationship between lagomorphs and rodents within the super-order Glires, and suggests that primates are phylogenetically closer to Megachiroptera than to any members of the Euarchontoglires. The cladistic analysis confirmed the neuroanatomical analysis with the most parsimonious tree placing Megachiroptera into the Euarchontoglires as a sister group to primates and the Microchiroptera next to Soricidae within the Laurasiatheria.Item An assessment of phylogenetic origin in Chiroptera using the neuromodulatory system(2008-03-11T06:48:32Z) Maseko, Busisiwe ConstanceABSTRACT The current study documents the findings from immunohistochemical examination of the brains of microbats and megabats (Chiroptera) using antibodies for cholineacetyltransferase (cholinergic neurons), tyrosine hydroxylase (dopaminergic, adrenergic and noradrenergic neurons), and serotonin (serotonergic neurons). The objective of the study was firstly to describe the anatomical organization and morphology of the neuromodulatory systems (nuclear complement) in both microbats and megabats, as there is no literature on these systems in the brains of chiropterans. Secondly, we aimed to investigate whether or not there are differences in these systems between the two suborders of chiroptera in hopes to shed some light on the phylogeny of the two, which is a controversial subject. The two groups were found to possess clear differences in their respective neuromodulatory nuclear complements. The differences observed between the two groups include a dorsal division of the locus coeruleus (A6d), which was absent in microbats but present in megabats, also the absence of an A4 in microbats but clear presence in megabats, and the parabigeminal (PBg) nucleus that was absent in microbats but clearly visible in megabats. The microbats were found to possess a complement that appeared similar to that of insectivores; whereas megabats had a complement resembling that of primates, carnivores and rodents. The differences found between the two groups suggest a diphyletic origin for the two groups.