State-Dependent Effects of β-Endorphin on Core Temperature in Stressed and Non-Stressed Rats

Abstract

β-Endorphin, γ-endorphin, δ-endorphin and morphine injected i.c.v. caused hyperthermia in non stressed rats; however, the same dose of β-endorphin and morphine caused hypothermia in stressed animals. These effects of β-endorphin were antagonized by naloxone. The results suggest that effects of β-endorphin are different depending on the animal's state and that these effects are mediated via opioid receptors.