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|Title:||SIZE OF THE PRIMARY SENSORY CORTICES IN BLIND AND IN SIGHTED MICE. |
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|Authors/Affiliations:||1 Sonia Guillemette*; 1 Robin Tremblay; 1 Karyne Arsenault; 1 Nicole Chabot; 1 Boire Denis; 1 Gilles Bronchti; |
1 Universite du Quebec a Trois-Rivieres, QC, Canada
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|Content:||Objectives: Following sensory deprivation there is a reorganization of both spared and deprived cortices. We want here to determine the effect of early visual deprivation on the areal extent of the primary sensory cortices. We surmise a smaller primary visual cortex (V1) in the blind compared to the sighted, but are auditory (AC) and somatosensory (S1) cortices correspondingly enlarged? In our laboratory, we used the ZRDCT/An anophthalmic mouse, in which neither retina nor optic nerves develop, and ZRDCT/RAX/Chumd.j or C57Bl/6 mice as controls. Materials and methods/results 1: Since the entire cortical volume is larger in the sighted than in the blind, all volume and surface values were reported to the volume or surface of the entire cortex. In adults, the relative size of V1 and of V2 delimited on Nissl-stained coronal serial sections were surprisingly similar in blind and controls, and so was AC. |
Material and methods/results 2: The areal extent of the cortical barrelfield, measured on flat mounted cytochrome oxydase stained sections, was not different between the two strains. Therefore the relative size devoted to S1 is larger in the blind. Do these differences reflect the dependence of the blind mice on this non-visual modality or are they present in the early postnatal period? Materials and methods 3: Using serotonin transporter immunochemistry which delineates precisely the primary sensory areas during the first 2 weeks of life, we measured the volume of the auditory, visual and barrel cortices in mutant and control pups at the end of the first postnatal (P) week.
Results 3: As in adults, blind mice had a smaller overall cortical volume than sighted mice. But, in contrast with what we found in adults, at P9 the relative size of V1 was significantly smaller (0.026±0.001 vs 0.033±0.003, p<0.05) in anophthalmic mutant mice than in controls and AC and S1 were considerably enlarged (0.023±0.001 vs 0.019±0.001, p<0.01; and 0.05±0.004 vs 0.038±0.003, p<0.05, respectively) in the young blind pups.
Conclusion: At this young age, the absence of spontaneous activity in the visual system seems to affect the development of V1. We suggest that the relatively “normal” size of V1 at adulthood reflects its later activation by auditory and somatosensory inputs.
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