NATURE OF POTENTIALS ASSOCIATED WITH SYNAPTIC TRANSMISSION IN LATERAL GENICULATE OF CAT

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Abstract
The potentials associated with synaptic transmission in the lateral geniculate body of the cat were studied by means of steel micro-electrodes inserted into the nucleus with a stereotaxically directed micromanipulator. Only the responses to electrical stimulation of the group of fibers of larger diameter in both the homo lateral and contralateral optic nerves were studied. The effectiveness of the geniculate synapses is indicated by the fact that the amplitude of the post-synaptic spike is nearly linearly related to the amplitude of the pre-synaptic spike. The synaptic potential was studied by means of synaptic blocking with asphyxia, deep sodium pentobarbital anaesthesia and repetitive stimulation. The asphyxial block could not be controlled and the pentobarbital block only with some difficulty due to the efficiency of the synaptic relay. Repetitive stimulation provided an easy and readily reversible method for revealing the synaptic potential. The spatial distribution of the synaptic potential was investigated using histological procedures. It was shown that the flows of current associated with the synaptic potential are derived from the initial portion of the optic radiation axons (positive synaptic potential) and flow into the dendrites and cell bodies in the geniculate (negative synaptic potential). The level at which the synaptic potential reverses from positive to negative in the one geniculate is related to the cell layers and depends upon which optic nerve is related to the cell layers and depends upon which optic nerve is stimulated.

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