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 prima ry cultures of neocortical neurons and cerebellar granule cells. Both isome rs induced a Cl- influx, which was inhibited by bicuculline, t-buthylbicycl ophosphorothionate (TBPS), picrotoxinin (PTX), and gamma-hexachlorocyclohex ane (gamma-HCH or lindane), [H-3]-flunitrazepam binding was also increased by both isomers and this increase was inhibited by bicuculline, In neocorti cal neurons, the transisomer completely inhibited the [H-3]GABA uptake, whe reas the cis-isomer produced only a 25% inhibition at the highest concentra tion 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 thu s GABA(C) receptors, may represent a very minor population of GABA receptor s in these neuronal preparations. We conclude that both GABA analogues may act as agonists at the GABA(A) receptors, although with very different pote ncies. (C) 1999 Wiley-Liss, Inc.