N-Methyl-D-aspartate (NMDA), kainate and quisqualate receptors and the generation of fictive locomotion in the lamprey spinal cord.

The motor pattern underlying swimming can be elicited in an in vitro preparation of the lamprey spinal cord by applying excitatory amino acids in the bath activating N-methyl-D-aspartate (NMDA) receptors and kainate receptors, but not quisqualate receptors. L-DOPA exerts a weak rythmogenic effect due to an action on kainate receptors. The kainate-induced rhythm is unchanged when a NMDA receptor antagonist is applied (2APV) and the N-methyl-aspartate-induced fictive locomotion can occur when kainate receptors are blocked (PDA). The burst frequency of the NMA-induced activity (dose range 30-5000 microM) is wide and ranges from 0.05-0.1 Hz up to 2.5-4 Hz, while the kainate-induced activity (dose range 7-30 microM) ranges from 0.5-1 Hz up to 4-8 Hz. This frequency range overlaps largely with that of the intact swimming animal. The findings further consolidate that NMDA receptors are efficient and demonstrates that kainate can also be effective in inducing fictive locomotion, and also that activation of either receptor type is sufficient. It has previously been shown that fictive locomotion elicited via sensory stimuli is depressed by NMDA and kainate receptor antagonists. It is suggested that these effects, presumably via aspartate and/or glutamate actions, are exerted on the input stage of interneuronal network.