Analgesic effects of cyclazocine and morphine microinjected into the rat dorsomedial hypothalamus demonstrated by the bradykinin-induced flexor reflex test

The analgesic effect of cyclazocine microinjected into the diencephalon of rats was studied by using the bradykinin-induced flexor reflex test. The dorsal portion of the medial hypothalamic area was sensitive to cyclazocine with respect to the production of analgesia (ED 50 2.6 μg/rat). Microinjections of morphine into the same portion also produced a dose-dependent analgesic effect (ED 50 2.5 μg/rat). As naloxone (0.9 mg/kg s.c.) antagonized both these analgesic effects, the findings suggest that the dorsal portion of the medial hypothalamic area of the rat is one of the primary target sites of analgesix drugs.