BACKGROUND This study examined whether prazosin reduces alcohol drinking over the course of prolonged treatment and whether it blocks initiation of alcohol drinking in rats with a genetic predisposition toward high alcohol drinking, i.e, alcohol-preferring (P) rats. METHODS In study one, alcohol-experienced P rats that had been drinking alcohol 2 hrs/day for several months were treated daily with prazosin (0, 0.5, 1.0 or 2.0 mg/kg BW) for 7 weeks. In study two, alcohol-naïve P rats were treated daily with prazosin (0, 1.0 or 2.0 mg/kg BW) for two weeks prior to, or concomitantly with, initiation of alcohol access and throughout 3 weeks of alcohol availability. Prazosin treatment and alcohol access were then discontinued for 2 weeks followed by reinstatement of alcohol access without prazosin treatment for 4 weeks, followed by resumption of daily prazosin treatment (2.0 mg/kg BW) for 3 weeks. RESULTS Prazosin reduced alcohol drinking throughout 7 weeks of treatment in P rats accustomed to drinking alcohol. Following termination of prazosin treatment, alcohol drinking slowly returned to pretreatment baseline. Reduced alcohol intake was accompanied by increased water intake. In alcohol-naïve P rats, prazosin administration prior to the first opportunity to drink alcohol and throughout 3 weeks of alcohol access retarded acquisition of alcohol drinking and reduced the amount of alcohol consumed. When prazosin was administered concomitantly with the first opportunity to drink alcohol, it abolished acquisition of alcohol drinking. Discontinuation of prazosin treatment allowed expression of a genetic predisposition toward high alcohol drinking to gradually emerge. Prazosin retained the ability to reduce alcohol intake with repeated treatments. CONCLUSIONS Prazosin decreased alcohol drinking during prolonged treatment and may be useful for treating alcoholism and alcohol use disorders. Prazosin may also be useful for deterring initiation of drinking in individuals with a family history of alcoholism.

Evidence suggests that noradrenergic signaling may play a role in mediating alcohol-drinking behavior in both rodents and humans. We have investigated this possibility by administering clonidine to alcohol-drinking rats selectively bred for alcohol preference (P line). Clonidine is an α2-adrenergic receptor agonist which, at low doses, inhibits noradrenergic signaling by decreasing norepinephrine release from presynaptic noradrenergic neurons. Adult male P rats were given 24-h access to food and water and scheduled access to a 15% (v/v) alcohol solution for 2 h daily. Rats received intraperitoneal (IP) injections with clonidine (0, 10, 20, 40, or 80 µg/kg body weight [BW], 10–11 rats/treatment group) once/day at 30 min prior to onset of the daily 2-h alcohol access period for 2 consecutive days. Clonidine, in doses of 40 or 80 µg/kg BW, significantly reduced alcohol intake on both days of treatment (p < 0.001). Two weeks later, rats were treated with clonidine for 5 consecutive days and clonidine, in doses of 40 or 80 µg/kg BW, reduced alcohol intake on all 5 treatment days (p < 0.001). Clonidine did not alter water consumption during the daily 2-h free-choice between alcohol and water. In a separate group of male P rats, clonidine (40 µg/kg BW) suppressed intake of a saccharin solution (0.04 g/L). These results are consistent with and complement our previous findings that the α1-adrenergic receptor antagonist, prazosin, decreases voluntary alcohol drinking in alcohol-preferring rats, but suggests that effects of clonidine may not be specific for alcohol. The results suggest that although activation of the noradrenergic system plays an important role in mediating voluntary alcohol drinking, care is needed in selecting which drugs to use to suppress central noradrenergic signaling in order to maximize the selectivity of the drugs for treating alcohol-use disorders.