Recruitment of GABAergic Inhibition and Synchronization of Inhibitory Interneurons in Rat Neocortex Larry S. Benardo. Departments of Neurology and Pharmacology, State University of New York Health Science Center, Brooklyn, NY 11203.
APStracts 4:0061N, 1997.
ABSTRACT
Intracellular recordings were obtained from pyramidal and interneuronal cells in rat neocortical slices to examine the recruitment of GABAergic inhibition and inhibitory interneurons. In the presence of the convulsant agent 4- aminopyridine (4-AP), after excitatory amino acid (EAA) ionotropic transmission was blocked, large amplitude triphasic IPSPs occurred rhythmically (every 10-40 s) and synchronously in pyramidal neurons. After exposure to the GABAA receptor antagonist picrotoxin, large amplitude monophasic slow IPSPs persisted in these cells. Interneurons in the presence of 4-AP and EAA blockers showed periodic spike firing. Although some spikes rode upon an underlying synaptic depolarization, much of the rhythmic firing consisted of spikes having highly variable amplitudes, arising abruptly from baseline, even during hyperpolarization. The spike firing and depolarizing synaptic potentials were completely suppressed by picrotoxin exposure, though monophasic slow IPSPs persisted in interneurons. This suggests that this subset of interneurons may participate in generating fast GABAA IPSPs, but not slow GABAB IPSPs. Cell morphology was confirmed by intracellular injection of Neurobiotin or the fluorescent dye Lucifer Yellow CH. Dye injection into interneurons often (>70%) resulted in the labelling of two to six cells (dye- coupling). These findings suggest that GABAAergic neurons may be synchronized via recurrent collaterals through the depolarizing action of synaptically activated GABAA receptors, and a mechanism involving electrotonic coupling. Though inhibitory neurons mediating GABAB IPSPs may be entrained by the excitatory GABAA mechanism, they appear to be a separate subset of GABAergic neurons capable of functioning independently with autonomous pacing. 

Received 13 September 1996; accepted in final form 4 February 1997.
APS Manuscript Number J736-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 20 February 1997