Excitatory transmitters, ventral root potentials and [K+]o in the isolated frog leg-spinal cord preparation.

Motoneuron depolarizations and changes in [K+]o were studied in the isolated frog spinal cord in response to non-nociceptive (touch/pressure) and nociceptive (acetic acid, heat, pinch) stimulation of the skin of the leg. Kynurenate, APV (D(-)-2-amino-5-phosphonovalerate), and 1.0 mM Mg2+ blocked or substantially reduced responses produced by all types of stimuli. Spantide was minimally effective in reducing nociceptive responses and had insignificant effects on responses to innocuous stimuli. These observations are consistent with the notion that excitatory amino acids activating both N-methyl-D-aspartate (NMDA) and non-NMDA receptors participate in the reflex responses to cutaneous stimuli in the frog spinal cord.