Unique behavioral effects of β endorphin and their relationship to thermoregulation and hypothalamic function

Intraventricular (ivt) injections of sub-cataleptic doses of β endorphin in rats were observed to result in wet-dog shakes. Subsequent to the wet-dog shakes, copious salivation accompanied by a clonic, seizure-like state was occasionally observed to occur. This sialogogic effect of β endorphin was blocked by naloxone and diminished by injections of thyrotropin releasing hormone. None of these behaviors were observed following ivt injection of morphine in equi-antinociceptive doses. Furthermore, hypophysectomy was observed to attenuate or block these behaviors. Both the wet-dog shakes and "sialogogic seizures" were demonstrated to be dependent upon dose as well as ambient temperature. It appears possible that the occurrence of initial wet-dog shakes may result in the elevated body temperature which then precipitates excess salivation. Since both β endorphin induced wet-dog shakes and salivation were shown to be correlated with alterations in temperature, it is possible that these effects of β endorphin indicate a physiological role for that peptide in thermoregulation.