Responses of neurons of the nucleus raphe obscurus to noxious stimuli.

Extracellular recordings were made from neurons located in the nucleus raphe obscurus (NRO), raphe magnus (NRM), and raphe pallidus (NRP) of urethane-anesthetized rats. Noxious cutaneous stimuli had excitatory, inhibitory or no effect on neurons of the raphe nuclei. Most of the neurons were excited by noxious stimuli. The distribution of responses of noxiously activated units in the NRO is similar to that observed in the NRM. It is suggested that the NRO is also a component of the endogenous pain suppression system that originates in the NRM.