Tetrahydro-beta-carbolines: effect on alcohol intake in rats

Some beta-carbolines, such as tetrahydro-beta-carboline (THBC) and 6-methoxy-THBC, occur normally in mammalian tissues, and 1-methyl-THBC has been found in human blood after alcohol intake. Continuous intraventricular (ICV) infusion of THBC and 1-methyl-THBC for 14 days was shown to increase voluntary alcohol intake in rats during the second week of infusion. In this study the experimental arrangement was slightly modified. Alcohol was offered for 7 days before the start of the 14 days of ICV infusion with Alzet minipumps and alcohol concentration (3-30% v/v) was increased every second day. The rats consumed less alcohol in the second day with the same concentration. Also, the dose of 47 nmoles/hr of 1-Me-THBC increased the voluntary alcohol intake over the controls, but only during the last 7 days. The same dose of 6-MeO-THBC, a serotonergic beta-carboline, was ineffective. Neither drug changed the total fluid intake. This study suggests that the increased voluntary alcohol intake by THBC's is not due to their serotonergic effect. A hypothesis concerning a possible involvement of opiate receptors is presented.