Abolition of the morphine effect on body temperature in midbrain raphe lesioned rats

The hyperthermia and the hypothermia elicited by 5 mg/kg, i.p. or 30 mg/kg i.p. of morphine in rats are abolished by a previous lesion of the midbrain raphe resulting in a lowering of forebrain 5-HT and 5-hydroxyindolacetic acid. Lesions lateral to the midbrain raphe which do not modify brain 5-HT are without effect on body temperature changes induced by morphine. Animals lesioned in the midbrain raphe are still able to respond with a hyperthermia or with a hypothermia when they are treated respectively with 2,4-dinitrophenol or phentolamine.