Involvement of the serotonergic system in ethanol intake in the rat.

A two-bottle, free-choice paradigm was used to investigate the influence of the serotonergic (5-HT) system on ethanol intake in genetically heterogeneous Wistar rats. Systemic administration of the 5-HT1A agonist ipsapirone (1.25-5.0 mg/kg) caused a dose-dependent decrease in ethanol preference and intake, while the 5-HT2 antagonist ritanserin (1.25-5.0 mg/kg) and the 5-HT3 antagonists ondansetron (0.01-1.0 mg/kg) and granisetron (0.5-1.0 mg/kg) failed to alter ethanol consumption. The effect of ipsapirone treatment on ethanol intake was more pronounced in high-preferring animals than in low-preferring. A closer look at the microstructure of the rat's drinking behaviour by means of a microcomputer-controlled data acquisition system showed that ipsapirone treatment caused a significant decrease in the number of licks recorded at the ethanol-containing bottle and a decrease in the time spent at this bottle. Furthermore, ipsapirone treatment caused a significant increase in the number of breaks in licking behaviour recorded at this bottle. The drinking behaviour at the water-containing bottle was not affected by the ipsapirone treatment. Neither was the rat's eating behaviour altered by this treatment. These findings support the hypothesis that the 5-HT system is involved in the regulation of ethanol intake, with special emphasis on the involvement of the 5-HT1A receptor subtype, and may indicate that central reward-mediating mechanisms are influenced.