SEROTONERGIC RECEPTORS MODIFY THE VOLUNTARY INTAKE OF ALCOHOL AND MORPHINE BUT NOT OF COCAINE AND NICOTINE BY RATS

Effects of fluvoxamine, a relatively selective 5-HT uptake inhibitor, and ipsapirone, a relatively selective 5-HT1A agonist, were studied on the initiation and/or maintenance of the voluntary intake of alcohol, morphine, cocaine, and/or nicotine in rats using the two-bottle free- choice method. Fluvoxamine (30 mg/kg/day in the drinking fluid) when g iven during existing morphine consumption increased the intake of this drug (1 +/- 1 vs. 3 +/- 1 mg/kg/day) but had no effect on alcohol (2 +/- 2 vs. 2 +/- 2 g/kg/day) or cocaine (10 +/- 10 vs. 13 +/- 10 mg/kg/ day) intake. Ipsapirone (10 mg/kg/day in the drinking fluid) when give n during existing alcohol or morphine consumption decreased the intake of the first (2 +/- 2 vs. 1 +/- 1 g/kg/day) and increased the intake of the second drug (2 +/- 1 vs. 4 +/- 1 mg/kg/day), but had no effect on nicotine (1 +/- 1 vs. 1 +/- 1 mg/kg/day) or cocaine (7 +/- 8 vs. 7 +/- 6 mg/kg/day) intake. Ipsapirone when given before exposure to the above drugs reduced subsequent alcohol (2 +/- 1 vs. 1 +/- 1 g/kg/day) and increased subsequent morphine intake (2 +/- 2 vs. 4 +/- 1 mg/kg/da y), but had no effect on the voluntary consumption of cocaine (8 +/- 7 vs. 10 +/- 6 mg/kg/day) and nicotine (1 +/- 1 vs. 1 +/- 1 mg/kg/day). These results suggest: (1) selective stimulation of 5-HT1A receptors reduces alcohol preference, (2) stimulation of all 5-HT receptors has no effect on alcohol intake, indicating the presence of inhibitory rec eptors, (3) stimulation of the serotonergic system in general stimulat es morphine preference, (4) the serotonin system does not affect nicot ine or cocaine preference and (5) the serotonergic system is not invol ved in the voluntary consumption of all, but only of some drugs/chemic als of abuse. Recognition of these drug/chemical-specific sites in the brain might lead to a better understanding of differences in drug abu se patterns among humans and help in the development of specific drugs for the treatment of selective drug addictions.