Responses of substantia nigra neurones to noxious stimulation.

Experiments were performed to determine whether substantia nigra neurones respond to noxious stimulation. Some nigral neurones were found to respond to both noxious radiant heat and intra-arterially administered bradykinin. Most nociceptive neurones were excited by noxious stimulation although some exhibited a reduction in firing rate. Following the injection of bradykinin, responses to noxious heat were reduced in magnitude for periods of up to an hour. These results show that some nigral neurones are nociceptive and provide further support for the suggestion that dopamine is involved in nociceptive mechanisms. In addition it is suggested that bradykinin may represent a rather gross of non-specific form of noxious stimulation.