Transient expression of GABAA receptor subunit mRNAs in the cellular processes of cultured cortical neurons and glia

In this study, we have studied by in situ hybridisation histochemistry the expression and intracellular distribution of the GABA(A) receptor subunit mRNAs in cultured neurons obtained from postnatal day 1-3 rats in order to determine how neurotransmitter receptor expression may be regulated during development of the nervous system. In postnatal cortical cells, we found that GABA(A) receptor subunit mRNAs coding for alpha 2, alpha 5, beta 2, beta 3 and gamma 2 subunits were transiently expressed in the cellular processes and growth cones after 1-3 days in culture. These observations indicate that GABA(A) receptor subunit mRNAs are transported (or trafficked) into the cellular processes of early postnatal cortical cells. These selective localisations were rarely observed after 5 days in culture and only in cells which had not made cell-to-cell contact. The localisation of subunit mRNAs in the processes was more effectively maintained up to 5 days or even longer if cell-to-cell contact was avoided by culturing the cells at low density or by inhibiting neurite sprouting pharmacologically with the GABA receptor channel antagonist TBPS. Finally, immunocytochemistry revealed the expression of GABA(A) receptors in the growth cones of pyramidal neurons in culture. Thus, the expression of mRNA correlates to the expression of protein. These results suggest that the selective trafficking of GABA(A) receptor subunit mRNAs during synaptogenesis may be regulated by synapse formation and/or glial-neural communication. (C) 1999 Published by Elsevier Science B.V. All rights reserved.