Brain Tissues:Comparative Histological Studies Of Divergent Bats Regarding UV Vision, Language Gene Foxp2and Antioxidant Peroxiredoxins During Hibernation

Bats have a number of unique biological characteristics. This dissertation, on the topics of vision, echolocation and hibernation, details the comparative histological studies conducted on brain tissues of divergent bats to detect the cone-based UV vision, the relationship between language gene Foxp2and echolocation and an emerging class of peroxisome Peroxiredoxins in pre-and post-hibernation:1. We characterized Fos-like expression patterns in the primary visual cortex (VI) by binocular flicking stimulation with UV light to investigate cone-based UV vision in four bat species representing four lineages:Hipposideros armiger and Scotophilus kuhlii, insectivores using constant frequency (CF) or frequency modulation (FM) echolocation, respectively, and Rousettus leschenaultii and Cynopterus sphinx, cave-roosting and tree-roosting fruit bats, respectively. The optic centre processing the visual image, V1, appears more distinctly immunostaining in S. kuhlii and C. sphinx after1h of UV light stimuli while in H. armiger and R. leschenaultii, staining was no more distinct than in corresponding controls. Our immunohistochemical evidence supports differences in the distribution of cone-based UV vision in the order Chiroptera and supports our earlier postulate that due to possible sensory tradeoffs and roosting ecology, defects in the short wavelength opsin genes have resulted in loss of UV vision in CF but not in FM bats. In addition, fruit bats roosting in caves have lost UV vision but not those roosting in trees. Our results thus confirm that bats are a further mammalian taxon that has retained cone-based UV sensitivity in some species.2. Foxp2, a multi-functional transcription factor specially implicated in the development and neural control of vocalization, may have some relationship with the evolution and development of bats'echolocation. Here we employed in-situ hybridization to further investigate the divergent expressions of Foxp2in the anterior cingulate cortex (ACC) and olfactory tubercle (Tu), two representative brain areas of five species among four types of bats using or non-using different echolocation systems. Moreover, we compared these results from three insectivorous species with well-developed laryngeal echolocation (Rhinolophus ferrumequinum and Hipposideros armiger, bats emitting a long constant-frequency pulse, and Myotis ricketti, a species producing short frequency-modulated sonar pulses) with that from two species of Old World fruit bats lacking laryngeal echolocation(Rousettus leschenaultii, which uses a very rudimentary sonar system based on tongue-clicks, and Cynopterus sphinx, which lacks any echolocation). The most striking differences were seen in the ACC, which exhibited significant expression only in bats with laryngeal echolocation (Rhinolophus and Myotis), while in Tu, the signal labelling was more dense in Rousettus and Cynopterus, which commonly use mostly olfactory (and visual) cues instead of laryngeal echolocation to forage. No significant differences were observed between the species within each of the fruit bats and insectivorous bat groups. Therefore, this work not only confirmed our previous immunohistochemical results. We could also hypothesize that the expression of Foxp2in ACC may be related to laryngeal echolocation of insectivores, but in Tu may have some relationship with the food selection of fruit bats based on their olfactory neural system. Most importantly, our work could provide definitive morphofunctional locations for ensuing functional verification.3. Mammalian hibernation is characterized by prolonged bouts of torpor interspersed with brief periods of arousal. Adequate antioxidant defenses are needed to sustain the brain, an organ more susceptible to oxidative damage compared to most others in body because of its high oxygen utilization and the defense against high rates of oxyradical formation associated with massive oxygen-based thennogenesis during arousal. We characterized for the first time Prxâ…¢, DJ-1and Prxâ… , three peroxiredoxin immunohistochemical expression patterns in more than forty representative brain areas, to examine these protease distributions and the possible differentiation by comparison of the hibernating versus euthermic M ricketti. The results showed PrxIII, DJ-1and Prxâ…  were all expressed in both types of glia cells and neuron; moreover, we observed the whole distinct up-regulation of peroxiredoxins contributing to antioxidant defense during torpor. So this fully demonstrates that the family of peroxiredoxins most likely functions as the key brain antioxidant system of the hibernating mammals. Subsequently, through comparative analyses of the typical brain areas affected in ALS, AD and PD, such as primary motor cortex, hippocampus and substantia nigra between hibernators and non-hibernating model organisms, we further indicated the potential therapeutic value of the antioxidant neuroprotective mechanisms of hibernator. Lastly, considering the course of hibernation, we also hypothesized the remarkable antioxidant mechanism employed by hibernators is preconditioning, an endogenous neuroprotective mechanism in the brain based on peroxiredoxins and that this capacity may also have some relationship with the longevity of bats.