| Abstract No.: | B-D2136 |
| Country: | Canada |
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| Title: | LAMINAR DISTRIBUTION OF CALCIUM BINDING PROTEIN IMMUNOPOSITIVE CELLS IN VISUAL AND AUDITORY CORTICES IN BLIND MICE |
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| Authors/Affiliations: | 1 Virginie Boucher*; 1 Marie-Eve Laramée; 1 Gilles Bronchti; 1 Denis Boire;
1 Université du Québec à Trois-Rivières, QC, Canada
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| Content: | Objectives: Early onset of blindness results in cross-modal activation of visual cortex by auditory stimuli. In addition blindfold experiments in normal human subject show similar cross-modal cortical activations. It has been suggested that these cross-modal cortical activations were made possible by a reduction of the activity of cortical inhibitory GABAergic circuits. Animal models of sensory deprivation have demonstrated a reduction of the expression of parvalbumin immunopositive GABAergic terminals (Jiao et al., 2006). This study investigates the role of afferent activity and of sensory modality on the expression of calcium binding proteins (CBPs): parvalbumin, calretinin and calbindin in cortical neurons in two models of early blindness mice. In the ZRDCT anophthalmic mouse auditory information can reach the visual cortex through a pathway between the inferior colliculus and the dorsal lateral geniculate nucleus. We previously demonstrated that auditory stimuli induce the expression of the immediate early gene c-fos in the primary visual cortex of the anophthalmic mice. In contrast neonatal enucleation in C57BL6 mice does not result neither in the ingrowth of axons form the inferior colliculus into the dLGN nor in c-fos expression in the primary visual cortex following the presentation with auditory stimuli. The goal of the present study is to investigate the role of the nature of afferent sensory information on the development of the laminar distribution of CBPs in the visual cortices and to compare this distribution with the auditory cortex.
Materials and Methods: The number of CBPs immunopositive neurons in each cortical layers were determined in the primary visual cortex, medial and lateral secondary visual cortices and in the auditory cortex in intact and neonatal enucleated C57BL6 mice and in ZRDCT anophthalmic mice. Size of these cortical areas and the total number of neurons therein were estimated using an unbiased stereological sampling design. Results: Our results show differences in the laminar distribution of the three calcium binding proteins between primary auditory and visual cortices in control mice. In enucleated mice, there is a reduction of the number of parvalbumin and calbindin immunopositive neurons in cortical layer V and of calretinin expressing neurons in layers II/III of the primary visual cortex compared to control mice. In anophthalmic mice, a reduction in the number of calbindin and parvalbumin immunopositive neurons in layer V of the primary visual cortex result in laminar distributions similar to that observed in the primary auditory cortex.
Conclusions: These results suggest that visual input contributes to the establishment of the normal number and laminar distribution of CBPs immunopositive neurons and that novel pathways conveying auditory information to the visual cortex alters the laminar distribution of these cells resulting in a visual cortex exhibiting features of the auditory cortex. |
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