Differentiation of excitatory amino acid receptors in the rat caudal trigeminal nucleus: a microiontophoretic study.

The excitatory amino acid antagonist, D-alpha-aminoadipate, was found to be a potent antagonist of responses to N-methyl-D-aspartate and L-aspartate, but less potent against L-glutamate responses of neurones in the rat caudal trigeminal nucleus. The responses to quisqualate and kainate were relatively unaffected by D-alpha-aminoadipate, but were antagonized by the two antagonists cis-2,3-piperidine dicarboxylate and gamma-D-glutamylglycine. These two antagonists had effectively similar spectra of activity. It is concluded that there is a distinct N-methyl-D-aspartate receptor in the trigeminal nucleus caudalis, and that kainate and quisqualate may act on a different, but common, receptor. Exogenously applied L-glutamate appears to act at both of these receptors, but exogenously applied L-aspartate appears to act almost exclusively on a D-alpha-aminoadipate sensitive site that may be the N-methyl-D-aspartate receptor. The kainate/quisqualate receptor is thought to be involved in the synaptic excitation of neurones in the caudal trigeminal nucleus by non-noxious mechanical stimuli.