Central and peripheral components of the inhibitory actions of 5-HTP on ethanol consumption in the rat.

When administered under a backward conditioning paradigm, 5-HTP administration resulted in a decrease in ethanol intake followed by a persistently decreased ethanol consumption. A central component to this inhibitory effect was suggested by the inability of xylamidine to significantly reduce the initial inhibitory effect of 5-HTP. The persistent rejection was prevented by xylamidine. Methysergide reduced the initial as well as the persistent effects of 5-HTP. In studies utilizing a forward conditioning paradigm, 5-HTP and lithium were each effective in developing CTAs to ethanol and saccharin. Only the ethanol-5-HTP pairing showed a persistent aversion. A peripheral component to the actions of 5-HTP was suggested by xylamidine blocking the CTAs induced by 5-HTP. Xylamidine also prevented the persistent ethanol avoidance induced by 5-HTP, but was ineffective in antagonizing lithium-induced CTAs. These results suggest central as well as peripheral components associated with the inhibitory effects of 5-HTP on ethanol consumption. Central actions appear to mediate the initial inhibitory effects while peripheral actions appear to be associated with persistent avoidance of ethanol following 5-HTP treatment.