Receptors for L-glutamate and GABA in the nervous system of an insect (Periplaneta americana)

The nervous system of the cockroach Periplaneta americana is well suited to studies of invertebrate amino acid receptors. Using a combination of radioligand binding and electrophysiological techniques, several distinct receptors have now been identified. These include an l-glutamate-gated chloride channel which has no known counterpart in the vertebrate nervous system, and a putative kainate/quisqualate receptor with pharmacological properties different from those of the existing categories of vertebrate excitatory amino acid receptors. GABA receptors have also been characterized in the cockroach nervous system. Bicuculline, benzodiazepines and steroids have revealed important differences between certain insect GABA-gated chloride channels and vertebrate GABA receptors. Identifiable neurones may facilitate the allocation of specific functions to amino acid receptor subtypes. In view of the existence of subtypes of amino acid receptors in insects, it is of interest to examine how this is reflected at the molecular level in terms of receptor subunit composition and amino acid sequence. Preliminary molecular cloning studies on insect GABA receptors are described.