Inhibitory mechanisms in the cerebral cortex.

A LINC-8 computer facilitated quantitative analysis of the magnitude and duration of conduction and potential changes during recurrent pyramidal and surface evoked IPSPs in pyramidal tract neurones of barbiturate anaesthetized cats. Potentiation of recurrent pyramidal IPSPs by surface evoked IPSPs and a similar IPSP reversal potential for both, coupled with evidence of occlusion following simultaneous activation of various inhibitory pathways suggested a common inhibitory pathway to corticospinal neurones. Exploration of the cortex with closely spaced multibarreled micropipettes revealed that glutamate evoked firing of some nonpyramidal neurones was associated with a decreased firing frequency of neighbouring pyramidal and other nonpyramidal neurones, an inhibitory pattern in joint scatter diagrams and unidirectional negative cross-correlations at latencies sufficiently short to suggest a monosynaptic connection. Further studies on these putative inhibitory neurones evaluated their spontaneous activity patterns, responses to stimulation of inhibitory pathways and to iontophoretic applications of acetylcholine