Oxytocin mediates the inhibitory action of acute lithium on the morphine dependence in rats

The role of central oxytocin in inhibitory action of lithium on the develop ment of morphine dependence was behavioral investigated in rats. Acute lith ium could enhance the morphine-induced analgesia in rats with or without ch ronic morphine treatment; this effect could be inhibited by intraventricula r injection of oxytocin antagonist d (CH2)(5)-Tyr (Me)-[Orn(8)]-Vasotocin ( OVT). Lithium could attenuate naloxone-precipitated withdrawal signs in mor phine dependent rats. The reduction of the expression of naloxone-precipita ted withdrawal signs by lithium was reversed by ICV of OVT. The lithium sig nificantly inhibited the conditioned place preference (CPP) induced by morp hine, which inhibitory action of lithium could also reverse by ICV injectio n of OVT. These results suggested that lithium might inhibit the physical d ependence on morphine as well as psychological dependence in rats, and that this inhibitory effect of lithium on the development of morphine dependenc e might be associated with oxytocin systems in the central nervous system. (C) 2001 Elsevier Science Ireland Ltd and the Japan Neuroscience Society. A ll rights reserved.