Figure 2.

Clofibrate decreased nicotine self-administration in rats that had established a stable baseline of nicotine intake, but it did not alter food self-administration under a procedure in which baseline rates and patterns of responding were comparable to those of nicotine self-administration. Each dose of clofibrate was tested for three consecutive days. (a) Nicotine injection rates averaged across the 3 days of treatment and across the two preceding baseline days. (b) Nicotine injection rates on each day of testing, the two preceding baseline days, and the two sessions after treatment was discontinued (‘Post'). The two higher doses of clofibrate decreased nicotine intake during each day of testing. n=13, 8, 7, and 5, respectively, for the vehicle (‘Veh'), 100, 200, and 300 mg/kg conditions. (c) Nicotine injection rates averaged across the 3 days of treatment and across the two preceding baseline days for rats given two injections (a pretreatment injection of the PPARα antagonist MK886 (‘MK' 3 mg/kg) or vehicle and a treatment injection of clofibrate (100 mg/kg) or vehicle) before each test session. Clofibrate alone significantly decreased nicotine self-administration, but this effect was blocked by MK886; n=7, 11, 11, and 9, respectively, for the ‘Veh+Veh', ‘Veh+100', ‘MK+100', and ‘MK+Veh' conditions. (d) Rates of food self-administration averaged across the 3 days of treatment and across the two preceding baseline days. Rats received subcutaneous injections of nicotine (n=6) or saline (n=6) before every session. Clofibrate, nicotine, and their combination did not significantly alter food self-administration. In all panels, five responses were required for each nicotine injection or food pellet, and sessions lasted 2 h. ^*Significant difference from baseline. All data were presented as mean±SEM.