Analgesia and the cardiovascular changes evoked by stimulating neurones in the ventrolateral medulla in rats.

In rats anaesthetised with Saffan, selective excitation of neurones in the ventrolateral medulla in the region of nucleus paragigantocellularis lateralis (PGL) by microinjection of the synaptic excitant, D,L-homocysteic acid, produced an increase in the latency of the tail flick response to noxious heat usually accompanied by an increase in blood pressure and heart rate. These findings are discussed in relation to the role of neurones in PGL in generating both tonic descending inhibition in the dorsal horn and sympathetic vasomotor tone as well as their involvement in a descending pathway that mediates the hypoalgesia which is a feature of certain stress-induced hypertensive states.