Ethanol effects on multiple fixed-interval, fixed-ratio responding in mice with deletions of the serotonin transporter gene.

Serotonin transporter (SERT) knock out (KO) mice self-administer less ethanol than either heterozygous (HET) or wild type (WT) mice; however the mechanistic basis for this difference remains unclear. Here we examine the possibility that ethanol more readily decreases responding in KO mice, thereby limiting ethanol self-administration. To examine whether KO mice were more sensitive to the response-decreasing effects of ethanol, we administered ethanol (0.2 to 3.2 g/kg) to mice responding under a multiple fixed-ratio (FR) 30-response, fixed-interval (FI) 300-sec schedule of milk presentation. Ethanol decreased responding similarly in all three genotypes. FR responding tended to be decreased at lower doses than FI responding. The decreased level of ethanol self-administration in SERT KO mice is not explained by an increased sensitivity to the response-decreasing effects of ethanol in KO mice, as sensitivity to the response decreasing effects of ethanol was similar in the KO, HET and WT mice.