Cytoarchitectonic and retinal projections characterization of the primary visual nuclei in bat (Artibeus palnirostris)
Visual system, Nissl; CTb; relative optical density; stereology; bats.
In many vertebrates, most of the brain is devoted to the processing of vision, more than any other sensory modality. This is probably due to the extremely complex task required from vision: classifying and translating the wide range of visual stimuli that animals face in the physical environment. The retina modifies and processes light trigged signals in photoreceptors which are sent to higher centers by ganglion cells. These cells axons form the optic nerves which deliver visual information to brain structures with diverse functions such as the dorsal lateral geniculate nucleus (DGL), from which the visual information rises to the cerebral cortex; the superior colliculus (SC), responsible for mediating visuomotor funtions; and the pretectal complex (CPT), involved in the pupillary light reflex and optokinetic nystagmus. In order to describe the citoarchitecture and the pattern of retinal projection in these structures in Artibeus planirostris bat, CTb intraocular injections were performed and coronal sections of the brain stained with Nissl method and sections subjected to immunohistochemistry for CTb were analyzed. Regarding to the cytoarchiteture, DGL was homogeneous and without evident lamination. However, the retinal projection revealed two layers with significantly different marking intensity, and massive contralateral input. The SC was identified as a laminar structure composed by seven layers, where retinal input was observed only on the contralateral side, targeting the superficial layers I and II. Medial pretectal nucleus, pretectal olivary nucleus, anterior pretectal nucleus, posterior pretectal nucleus and nucleus of optic tract were identified composing the CPT. Only the anterior pretectal nucleus lack retinal input, which is predominantly contralateral in all other nuclei. In sumary, the results show morphometrical and stereological features in a bat specie for the first time.