Cytotoxic action of lindane in neocortical GABAergic neurons is primarily mediated by interaction with flunitrazepam‐sensitive GABA A receptors

The cytotoxic action of the γ‐isomer of hexachlorocyclohexane (γ‐HCH; lindane) was studied in cultured mouse neocortical neurons by measurements of the reduction in mitochondrial function using the MTT (3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyltetrazolium bromide) test. The cells were exposed to 30‐300 μM lindane in the culture medium for different periods of time and lindane cytotoxicity was found to be time‐ and concentration‐dependent. Lindane cytotoxicity could be ameliorated by addition of gamma aminobutyric acid (GABA) in a concentration‐dependent manner but this effect of GABA was not blocked by bicuculline or picrotoxinin (PTX). Lindane induced cytotoxicity was also reduced by the GABA A receptor agonists muscimol and THIP (4,5,6,7‐tetrahydroisoxazolo[5,4‐c]pyridin‐3‐ol). This effect was enhanced by the simultaneous presence of flunitrazepam but only at the highest lindane concentrations studied (200 and 300 μM). Flunitrazepam by itself had no effect on lindane‐induced cytotoxicity. The protective effect of GABA plus flunitrazepam was blocked by the benzodiazepine receptor antagonist flumazenil and by the GABA A antagonist bicuculline, suggesting the involvement of central benzodiazepine receptors allosterically coupled to the GABA recognition site at the GABA A receptor. When 100 μM PTX was used to suppress the protective effect of GABA and flunitrazepam, a significant effect of PTX was observed only at 300 μM lindane. The GABA B receptor agonist, baclophen, only marginally reduced the cytotoxic effect induced by the highest lindane concentrations. It is concluded that the cytotoxic action of lindane in neocortical neurons in culture is mediated primarily through an interaction with allosterically coupled GABA‐benzodiazepine recognition sites at the GABA A receptor. J. Neurosci. Res. 52:276–285, 1998. © 1998 Wiley‐Liss, Inc.