APStracts 2:0162N, 1995.

Preferential suppression of the ON pathway by GABAC receptors in the amphibian retina. Zhang, Jian, and Malcolm M. Slaughter. Departments of Physiology, Biophysical Sciences, and Ophthalmology, School of Medicine, State University of New York, 120 Cary Hall, Buffalo, New York 14214.

APStracts 2:0162N, 1995.

SUMMARY AND CONCLUSIONS
1) Electrophysiological recordings were obtained from neurons in the amphibian intact retina and retinal slice preparations. The effects of GABA were evaluated in the presence of bicuculline or SR95531, which block the GABA A receptor, and baclofen, which saturates the GABA B receptor. 2) Under these conditions, GABA preferentially reduced ON light responses in amacrine and ganglion cells, apparently through a presynaptic mechanism that reduced bipolar cell input. GABA also produced a small hyperpolarization in the resting membrane potential of ganglion cells. 3) Picrotoxin blocked these effects of GABA. The action of GABA was duplicated by muscimol and by trans- aminocrotonic acid. Cis-aminocrotonic acid was neither a potent nor selective agonist. This pharmacology is indicative of the GABA C receptor. 4) In voltage clamp recordings of ganglion cells in the slice preparation, GABA produced a large chloride conductance that was blocked by bicuculline or SR95531, and a smaller chloride conductance that was not blocked by these GABA A receptor antagonists, but was blocked by picrotoxin. This indicates that ganglion cells possess both GABA A and GABA C receptors. 5) The GABA C receptor current was relatively non-desensitized. Consequently, while the peak GABA A receptor current was more than five fold larger than the GABA C receptor current, after desensitization the latter current was larger . Both currents reversed near the chloride equilibrium potential.

Received 13 February 1995; accepted in final form 22 May 1995.
APS Manuscript Number J99-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.