Responses of spinal neurones to a substance P analogue, noxious pinch and bradykinin.

It is likely that substance P is a neurotransmitter at the first afferent synapse. These synapses may mediate pain sensations from thermal, mechanical or chemical (bradykinin) stimulation of nociceptors. Correlation of the responsiveness of dorsal horn neurones to iontophoretic application of a substance P analogue and mechanical or chemical stimulation of the hind limb suggested that sensitivity to substance P was shown by cells responding to chemical but not mechanical noxious stimulation.