Single sensory neurons activate excitatory amino acid receptors in the lamprey spinal cord

The effects of excitatory amino acid (EAA) antagonists were tested on sensory afferent excitation in the lamprey spinal cord. Paired intracellular recordings were made from mechanosensory neurons (dorsal cells) and second order sensory neurons (giant interneurons). Stimulation of individual dorsal cells evoked mono- and/or polysynaptic excitatory postsynaptic potentials (EPSPs) in giant interneurons. These EPSPs were depressed by the EAA antagonists cis-2,3-piperidine dicarboxylate and kynurenic acid. Small components of the synaptic potentials were due to electrical coupling since they were not depressed by EAA antagonists or by calcium-free solution. The N-methyl-D-aspartate antagonist 2-amino-5-phosphonovalerate did not depress short-latency EPSPs. Thus, mechanosensory neurons in the lamprey spinal cord activate EAA receptors (kainate/quisqualate receptors) on interneurons, via mixed chemical and electrical synapses.