In order to examine the involvement of brain angiotensin Ⅱ (All)in the development of tolerance to morphine anal-gesia in rats,antibodies against AⅡ (AⅡ IgG)or saralasin,the antagonist of AⅡ,was administered intracerebroventricularly (icv)to prevent the endogenously released AⅡ from activating AⅡ receptors,and the dynamic course of the development of morphine tolerance was monitored.Acute morphine tolerance was induced by 6 successive injections of morphine (6mg/kg,sc)at 2 h intervals; this tolerance could ...