Effects of fluvoxamine on a multiple schedule of ethanol- and food-maintained behavior in two rat strains

Rationale: Previous studies show that selective serotonin reuptake inhibitors (SSRIs), including fluvoxamine, have a greater effect on ethanol-maintained responding compared with an alternative reinforcer. However, none of these studies matched baseline responding for reinforcers. Because behavioral effects of many drugs depend on the baseline response rate, the preferential effects of SSRIs may be due to different baseline response rates. Objectives: Fluvoxamine effects on ethanol- and food-maintained responding were compared using a multiple schedule of behavior, providing matched baseline responding and allowing within-subject analysis in two strains of rats. Methods: The multiple schedule consisted of three consecutive 5-min, fixed-ratio five components (Food1, Ethanol, Food2). Fluvoxamine ( 3 - 30 mg/kg, i. p.) was administered 30 min presession. In Lewis rats, fluvoxamine effects were determined at several available ethanol concentrations [ 8, 16, 32, and 8% (w/v) redetermination]. In Sprague - Dawley rats, fluvoxamine effects were determined when the available ethanol concentration was 8% (w/v). Results: Baseline responding was stable and well matched under all conditions except 32% ethanol, when responding for ethanol was lower than for food. After the administration of 17.8 mg/kg fluvoxamine, ethanol- maintained responding was 15 - 33% lower than food-maintained responding in four of the five conditions tested. Breath ethanol assessments indicated that rats had blood ethanol levels of 33 mg/dl following responding for 8% ethanol. Conclusions: These results are in agreement with previous findings that SSRIs preferentially reduce ethanol-maintained responding and suggest this is not likely due to different baseline levels of responding between the comparison conditions. Further, these results support the hypothesis that alteration of synaptic serotonin can modulate ethanol reinforcement.