Effects of the conformationally restricted GABA analogues, cis- and trans-4-aminocrotonic acid, on GABA neurotransmission in primary neuronal cultures

The effects of the GABA analogues, cis- and trans-4-aminocrotonic acid (ACA) on GABA(A) receptor function and GABA uptake, together with the presence of rho-1 subunit mRNA and putative GABA(C) receptors, were studied in primary cultures of neocortical neurons and cerebellar granule cells. Both isomers induced a Cl- influx, which was inhibited by bicuculline, t-buthylbicyclophosphorothionate (TBPS), picrotoxinin (PTX), and gamma-hexachlorocyclohexane (gamma-HCH or lindane), [H-3]-flunitrazepam binding was also increased by both isomers and this increase was inhibited by bicuculline, In neocortical neurons, the transisomer completely inhibited the [H-3]GABA uptake, whereas the cis-isomer produced only a 25% inhibition at the highest concentration used. The possible presence of GABA(C) receptors was investigated only in neocortical cultures by using RT-PCR in order to detect the presence of the mRNA encoding the rho-1 subunit which assembles to form homooligomeric Cl- channels, The results presented here show that rho-1 subunits, and thus GABA(C) receptors, may represent a very minor population of GABA receptors in these neuronal preparations. We conclude that both GABA analogues may act as agonists at the GABA(A) receptors, although with very different potencies. (C) 1999 Wiley-Liss, Inc.