GABA B receptors presynaptically modulate excitatory synaptic transmission in the rat supraoptic nucleus in vitro. Kombian, Samuel B., Jeffrey A. Zidichouski and Quentin J. Pittman. Neuroscience Research Group, University of Calgary & 2 Ciba-Geigy Canada Ltd.
APStracts 3:0051N, 1996.
SUMMARY AND CONCLUSIONS
1. The effect of GABA B receptor activation on excitatory synaptic transmission in the rat supraoptic nucleus (SON) was examined using the nystatin perforated-patch whole-cell recording technique in coronal hypothalamic slices. 2. Stimulation of the hypothalamic region dorso-medial to the SON elicited glutamate and GABA A receptor-mediated synaptic responses in electrophysiologically-identified magnocellular neurosecretory cells. 3. Bath application of the GABA B receptor agonist, [+/-]-baclofen reversibly reduced pharmacologically-isolated, glutamate-mediated excitatory postsynaptic currents (EPSCs) in a concentration-dependent manner. At the concentrations used, baclofen altered neither the postsynaptic conductances of these cells nor their response to bath applied AMPA. 4. The baclofen-induced synaptic depression was accompanied by an increase in paired pulse facilitation (PPF). This increase in PPF, as well as the synaptic depression, was blocked by the GABA B receptor antagonists CGP36742 and saclofen. 5. In addition to blocking the actions of baclofen in this nucleus, CGP36742 caused an increase in the evoked EPSC amplitude without altering postsynaptic cell conductances or responses induced by bath applied AMPA. Contrary to the action of CGP36742, saclofen caused a baclofen-like depression of the evoked EPSC suggesting that it may act as a partial GABA B receptor agonist. 6. These results indicate that the activation of presynaptic GABA B receptors reduces fast excitatory synaptic transmission in the SON. They further suggest that presynaptic GABA B receptors may be tonically activated in vitro . Thus, GABA B receptors may influence the level of activity and excitation of SON neurons and hence modulate the secretion of the regulatory neuropeptides vasopressin and oxytocin.

Received 30 November 1995; accepted in final form 4 March 1996.
APS Manuscript Number J809-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96