Influence of pertussis toxin on thermic responses to morphine and neurotensin in rats.

The influence of pertussis toxin (PTX) on thermic responses elicited by morphine and neurotensin was evaluated in unrestrained rats kept at 22 degrees C. High doses of morphine (9-36 micrograms/rat i.c.v.) lowered body temperature and low doses (1.25, 2.5 micrograms/rat i.c.v.) produced hyperthermia. The hyperthermic effect was more resistant than the hypothermic effect to naloxone antagonism. Neurotensin (50, 100 micrograms/rat i.c.v.) induced marked hypothermia followed by hyperthermia. I.c.v. injection of PTX (1 microgram), six days before morphine (18 micrograms/rat i.c.v.), replaced the opiate hypothermia by consistent hyperthermia and reduced by 60% the hyperthermia elicited by morphine (2.5 micrograms/rat i.c.v.). The toxin also affected the thermic responses induced by neurotensin (50 micrograms/rat i.c.v.) administered six days after PTX (1 microgram/rat i.c.v.). The initial hypothermia was enhanced by 173% and the late hyperthermia was fully antagonized. It thus appears that PTX-sensitive G-proteins play different roles in the molecular events underlying the thermoregulatory responses to morphine and neurotensin.