RELEASE OF ENDOGENOUS GLUTAMATE FROM THE FROG SPINAL CORD FOLLOWING DORSAL ROOT STIMULATION

Abstract

The effects of dorsal root stimulation on the release of endogenous glutamate and aspartate from the hemisected or intra-arterially perfused frog spinal cord were studied. The release of amino acids was measured using a gas chromatograph-mass spectrometer. Repetitive stimulation applied to the dorsal roots produced ventral root potentials and caused a significant increase in the glutamate releases above the resting efflux. In low Ca solution, the ventral root potential was abolished and the glutamate efflux following dorsal root stimulation was significantly decreased. In these experiments, the stimulus strength was adjusted just maximal for the fast ventral root potential. The resting efflux and the evoked release of aspartate caused by dorsal root stimulation was much smaller than the glutamate release. It is suggested that glutamate is an excitatory transmitter in primary afferents that mediates the fast synaptic transmission in the frog spinal cord.