ABSTRACT
The behavioral responses induced by /?-endorphin and morphine in laboratory animals are different. In rats and golden hamsters, /?-endorphin given intraventricularly produces a strong catalepsy response, loss of righting reflect and profound hypothermia while morphine produces a mild catalepsy, an excitation and a mild hypothermia (Tseng et al, 1979). Unlike morphine, ^-endorphin given intracerebroventricularly (i.c.v.) does not produce running locomotor activity in mice (Wei et al, 1977). In cats, ^-endorphin produces analgesia without profound excitation and agitation which are typical behavioral signs produced by morphine (Meglio et al, 1977). These differential behavioral responses give support to the possibility of different modes of actions for ^-endorphin and morphine. This chapter describes the neural mechanism of ^-endorphin-induced antinociception. Morphine is used as a standard compound for comparison.
