DISRUPTION OF GABA-DEPENDENT CHLORIDE FLUX BY CYCLODIENES AND HEXACHLOROCYCLOHEXANES IN PRIMARY CULTURES OF CORTICAL-NEURONS

The effect of convulsant and nonconvulsant hexachlorocyclohexane (HCH) isomers and cyclodienes on GABA-induced Cl- flux was studied in prima ry cultures of neocortical neurons by measuring the GABA-stimulated Cl -36(-) uptake. GABA induced a dose-dependent chloride uptake. The conv ulsant agents gamma-HCH and cyclodienes alpha-endosulfan, dieldrin and aldrin blocked this Cl-36(-) uptake. A total or partial inhibition of GABA-induced Cl-36(-) uptake was produced by the noncompetitive GABA( A) antagonists picrotoxinin (PTX) and pentylenetetrazol, respectively. The inhibitory potencies of Cl-36(-) uptake by the organochlorine com pounds (alpha-endosulfan > dieldrin > gamma-HCH > aldrin) were well co rrelated with their inhibitory potencies of [S-35]TBPS binding. Positi ve modulators of GABAergic function (flunitrazepam and phenobarbital) prevented the blocking of GABA-induced chloride uptake by PTX but not that induced by alpha-endosulfan. The depressant beta- and delta-HCH i somers produced a biphasic response, increasing or decreasing the GABA -stimulated chloride uptake, depending on the HCH isomer and GABA conc entrations used. The present results support the idea of cyclodienes a nd gamma-HCH action at the GABA(A) receptor by interacting with the TB PS binding site. A different interaction of PTX and alpha-endosulfan i n the same recognition site is also suggested. An increase of GABA-ind uced Cl-36(-) flux by beta- and delta-HCH can account for the depressa nt activity of these compounds. This work also demonstrates the useful ness of primary neuronal cultures to perform functional studies of the GABA(A) receptor, taking into account allosteric interactions between the different recognition sites of the GABA(A) receptor.