Selective modulation of the cardiovascular response but not the antinociception evoked from the dorsal PAG, by 5-HT in the ventrolateral medulla.

In lightly ananesthetised rats, electrical stimulation in the dorsal part of the periaqueductal grey matter (dPAG) produced an increase in the latency of the tail flick response accompanied by an increase in blood pressure and heart rate. Microinjection of 40-50nmol 5-HT bilaterally into the rostral part of nucleus paragigantocellularis lateralis (PGL) at the level of the facial nucleus attenuated the cardiovascular response to stimulation of the dPAG but had no effect on the analgesia. It is suggested that cardiovascular control neurones, but not the pain control neurones in the rostral part of PGL are subject to inhibitory serotonergic modulation.