Effects of baclofen on operant performance for food pellets and vegetable shortening after a history of binge-type behavior in non-food deprived rats

Abstract

Operant performance of non-food deprived rats (n=8) was assessed under progressive ratio (PR) and concurrent PR-fixed ratio schedules of food pellet and/or vegetable shortening reinforcement. Post operant baselines, rats were matched and divided into 2 groups based upon the schedule of shortening availability: High restriction binge group (H, 1-hr home cage shortening access each week on Monday, Wednesday, and Friday) and Low restriction (L, 1-hr shortening access daily). Chow and water were continuously available; only access to the shortening was restricted. After 8 weeks, operant performance was reassessed. Lever pressing for shortening increased in the H rats for all schedules, but was either unaffected or decreased in the L rats. Pellet responding under the concurrent schedules increased for both groups. The effects of four dosages of (R)-baclofen (0.3-1.8 mg/kg, i.p.) on operant performance were also assessed. For both groups, 1.0 mg/kg baclofen significantly reduced shortening responding relative to saline for all schedules except one, but had no or minimal effect on pellet responding. This suggests a specific effect of baclofen on responding maintained by fat. These results indicate that intermittent episodes of bingeing on fat can increase the reinforcing efficacy of fat and that GABAB receptor activation can attenuate this effect.

Baclofen, raclopride, and naltrexone differentially reduce solid fat emulsion intake under limited access conditions

“…In that same study, the D 1 antagonist SCH23390 had no effect on consumption of the high-fat chow. Finally, recent work using our limited access binge protocol indicates that SCH23390 only reduces intake of 100% shortening at dosages that also suppress intake of chow (Corwin and Wojnicki, 2006). This indicates that the intake reductions were due to nonspecific motor impairment.…”

“…This indicates that the intake reductions were due to nonspecific motor impairment. In contrast, raclopride had more fat-specific effects (Corwin and Wojnicki, 2006). Taken together, the available evidence indicates that fat intake can be modulated by peripheral injections of D 2 , but not D 1 , receptor antagonists, and that these effects are not explained by generalized motor disruption.…”

“…Rats on the Intermittent schedule of access were provided 1-hr of availability to their assigned solid fat emulsion on Mondays, Wednesdays, and Fridays only (I-18%, I-32%, and I-56%, N=10 each). These schedules were chosen based upon studies in which intermittent access induced binge-type consumption of 100% solid vegetable shortening (Corwin, 2004;Corwin, et al, 1998;Dimitriou, et al, 2000;Thomas, et al, 2002;Wojnicki et al, 2006). Rats were then placed on their assigned access schedules for a period of five weeks to establish a baseline before drug dose-effect curves were determined.…”

“…In addition, another study showed that baclofen reduced fat-maintained lever pressing at a lower dosage than was necessary for reductions in chow-maintained lever pressing (Wojnicki et al, 2006). Previous research, therefore, suggests that GABA B receptor activation can selectively reduce intake of and responding for fat under limited access conditions.…”

“…The food intake reducing effects of baclofen appear to be specific to fat, as baclofen had no effect on sucrose intake under limited access conditions (Corwin and Wojnicki, 2006). In addition, another study showed that baclofen reduced fat-maintained lever pressing at a lower dosage than was necessary for reductions in chow-maintained lever pressing (Wojnicki et al, 2006).…”