NATURE OF DENDRITIC POTENTIALS AND SYNAPTIC MECHANISMS IN CEREBRAL CORTEX OF CAT

Abstract

Combined use of electrophysiological and pharmacological methods discloses that the 10-12 msec. surface negative response of the apical dendrites of cerebral or cerebellar cortex produced by any mode of stimulation is a postsynaptic potential (psp). When the dendritic electrogenesis is blocked by d-tubocurarine, the response cannot be evoked by electrical stimuli. Like electro-genic membrane of other synapses, that of the apical dendrites is not electrically excitable. The implications of these findings for the interpretation of cortical potentials and of the organization of cortical synapses are explored. Evidence is presented for the existence of hyperpolarizing (inhibitory) psp''s as well as the depolarizing (excitatory) variety. The electrogenesis of the former appears to be considerable, as much as 80% of the surface negative depolarizing response being masked by simultaneous occurrence of hyperpolarizing psp''s. Analysis of pharmacological effects on central synapses is made possible by the data and viewpoint of the paper. For example, it is shown that d-tubocurarine potentiates convulsant action of strychnine in the spinal cord. The former drug therefore acts like the latter to block inhibitory synaptic activity in the spinal cord. Metrazol exerts its cortical convulsant action by activating excitatory synapses, whereas strychnine causes convulsive activity in the cortex as well as in the spinal cord by blockading inhibitory synapses.