GABA(A) RECEPTOR SUBUNIT MESSENGER-RNAS SHOW DIFFERENTIAL EXPRESSION DURING CORTICAL DEVELOPMENT IN THE RAT-BRAIN

Developmental changes of the expression of various GABA(A) receptor subunits (alpha1, alpha3, alpha4, beta1-3, and gamma2) were examined in the fetal rat cerebral cortex using in situ hybridization histochemistry. The subunits showed three main patterns of development. The alpha1 subunit showed the first pattern, in which no expression was observed during embryonic development. The alpha4, and beta1 subunits showed the second pattern, in which expression was observed in both the undifferentiated neuroepithelium and the developing cortical layers. The alpha3, beta2, beta3, and gamma2 subunits showed the third pattern, in which expression was only seen in the developing cortical layers. These findings strongly suggest the following: (i) the alpha1 subunit is involved in GABAergic transmission in the mature cerebral cortex; (ii) the alpha4 and beta1 subunits are involved in both the differentiation of the neuroepithelium and the development of the cortical plate, and (iii) the alpha3, beta2, beta3, and gamma2 subunits are involved in the development of the cortical plate. Subunits already expressed on embryonic day 13 (beta1, beta3, and gamma2) appear especially likely to have a special role in neuronal development.