A picrotoxin-resistant GABA-gated chloride channel receptor subtype in the cockroach central nervous system

Abstract

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the cockroach central nervous system (CNS). Electrophysiological assays performed at cercal-afferent giant-interneuron (GI) synapses demonstrated that a biphasic (transient and stable phases) increase in membrane conductance, in response to long-lasting (30-s) neuropilar pressure microapplication of GABA, could be explained by the presence of two GABA-operated chloride channel receptor subtypes in the postsynaptic membrane. The low stable membrane conductance increase, representing less than 30% of the maximum response, reached during the early transient phase, was not desensitized quickly. It was reproduced by neuropilar pressure microapplication of cis-4-aminocrotonic acid (CACA) and was not, as the fast phase, antagonized by bath application of 10μM picrotoxin (PTX). Imidazole-4-acetic acid (I-4AA) and Zn2+ did not modulate GABA and CACA-induced responses. Furthermore, a presynaptic target site for CACA, that modulates Ach release, was identified. Arch. Insect Biochem. Physiol. 37:231–238, 1998. © 1998 Wiley-Liss, Inc.