Effects of morphine on plasma B-endorphin and cortisol levels and on body temperature in guinea-pigs pretreated with 6-hydroxydopamine

1. i.c.v. morphine administration (50 μg/10 μl) to sham-lesioned guinea-pigs produces a decrease of body temperature 90 min after injection. 2. This effect was blocked in animals that received i.c.v. 6-OHDA injections 20 days before. 3. On the other hand, morphine injection to sham-lesioned guinea-pigs resulted 30 and 90 min later in suppressed plasma B-END and cortisol concentration. 4. This suppressive effect was increased 20 days after 6-OHDA injections. 5. These results indicate that in the guinea-pig the effects of morphine on both body temperature and plasma levels of B-END and cortisol are altered by hypothalamic DA lesions, and suggest that hypothalamic DA neurons would be one of the sites participating in morphine-induced delayed decreased in plasma B-END and cortisol.