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M. Ikeda, H. Toyoda, A. Okabe, Y. Hotta, A. Fukuda; Differential Developmental Profiles of the Cation-Cl- Cotransporter Expression and Cl- Homeostasis in Rat Visual Cortex and Dorsal Lateral Geniculate Nucleus Contribute to Differential Ontogeny of GABAergic Actions . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4107.
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Purpose: A recent study suggested that gamma-aminobutylic acid (GABA) has differential roles in the activity dependent plasticity in the visual cortex (VC) and in the dorsal lateral geniculate nucleus (dLGN). In the present study, to investigate the GABAergic function of postnatal visual system development, we compared the differential development of [Cl-]i, cation-Cl- cotransporter expression and [Ca2+]i responses evoked by GABA in the VC and the dLGN during early stage of development. Methods: Using rat brain slices of postnatal day (P) 0-17, [Ca2+]i responses evoked by GABA and resting [Cl-]i were measured by calcium imaging and chloride imaging respectively. We also examined the expession changes of cation-Cl- cotransporters, e.g., outwardly-directed K+-Cl- cotransporter KCC2 and inwardly-directed Na+,K+-2Cl- cotransporter NKCC1, in VC and dLGN using in situ hybridization. Results: Excitatory effects of GABA is strong in VC but weak in dLGN as indicated by neuronal [Ca2+]i transients and resting [Cl-]i changes during neuronal development. In the P0 dLGN, the expression of KCC2 mRNA signals were significantly higher than that in VC. This suggests that extrusion of Cl- from neuron is stronger in dLGN than in VC, so that GABAergic excitatory effect was not observed in dLGN because of more negative equilibrium potential for Cl-. Conclusions: The present study indicates clear differences in molecular and physiological basis for the Cl- homeostasis and GABA actions during development of VC and dLGN. This could be related to the different roles of VC and dLGN in the visual system development.
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