Sites of action of morphine involved in the development of physical dependence in rats. I. Comparison of precipitated morphine withdrawal after intraperitoneal and intraventricular injection of morphine antagonists.

In rats made dependent on morphine by implantation of morphine pellets, withdrawal, as precipitated by intraventricular injection of morphine antagonists, was compared to withdrawal as precipitated by systemic antagonist application. The results, most clearly those obtained with a hydrophilic compound, diallyl-nor-morphinium-bromide, point to periventricularly located sites of action for the release of most withdrawal signs by antagonists. Jumping, reaching only low levels after i.ventr. injection of levallorphan and nalorphine, was very pronounced when the benzomorphane derivative SH 254, was used. In the case of writhing and diarrhea, the situation is more complicated. Possibly, central as well as peripheral mechanisms are involved in the expression of these signs.