Two types of identified ascending interneurons with distinct GABA receptors in the crayfish terminal abdominal ganglion. Miyata, Hiroki, Toshiki Nagayama and Masakazu Takahata. Animal Behaviour and Intelligence, Division of Biological Sciences, Graduate School of Science, Hokkaido University, 060 Sapporo, Japan.
APStracts 3:0247N, 1996.
More than half of identified ascending interneurons originating terminal abdominal ganglion of the crayfish received inhibitory sensory inputs from hair afferents innervating tailfan on the side contralateral to their main branches. Biochemical aspects of this transverse lateral inhibition of ascending interneurons were examined by using neurophysiological and pharmacological techniques. Local application of GABA and its agonist, muscimol into the neuropil induced membrane hyperpolarization of identified ascending interneurons with an increase in the membrane conductance. Since the reversal potential of IPSPs in ascending interneurons elicited by the sensory stimulation and GABA injection was similar, and the sensory-stimulated IPSPs of the interneurons were blocked by GABA and muscimol application, this study strongly suggested GABAergic nature of transverse lateral inhibition of ascending interneurons. According to the response to GABA A antagonists, bicuculline and picrotoxin, ascending interneurons were classified into two types, picrotoxin-sensitive and picrotoxin-insensitive interneurons. Identified ascending interneurons, VE-1 and RO-4 showed a pharmacological profile similar to classical GABA A receptor of the vertebrates. Bath application of both bicuculline and picrotoxin reversibly reduced the amplitudes of IPSPs. Another identified ascending interneurons, CA-1, RO-1 and RO-2 were not affected significantly by the bath application of GABA A and GABA B antagonists, though bath application of low chloride saline reversed the sensory-stimulated IPSPs. IPSPs of the picrotoxin-sensitive interneurons had rather faster time course and shorter duration in comparison with that of the picrotoxin-insensitive interneurons.

Received 30 July 1996; accepted in final form 12 November 1996.
APS Manuscript Number J604-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996