Figure 2.

Effects of the 5-HT_1B receptor agonist CP 94,253 on cocaine self-administration under a fixed ratio (FR) 5 schedule of reinforcement following 21 days of forced abstinence. Data are expressed as the number of cocaine reinforcers obtained (±SEM) at doses previously found to be on the ascending (0.075 mg/kg/0.1 mL, i.v.) and descending (0.75 mg/kg/0.1 mL, i.v.) limbs of the cocaine dose–effect function (see Figure 1). Prior to testing, there were no differences between vehicle and CP 94,253 groups in the number of cocaine reinforcers (0.75 mg/kg/0.1 mL, i.v.) obtained during cocaine self-administration training (data not shown). Rats (n = 7–9/group) were pretreated with vehicle (1 mL/kg, s.c.; open squares) or CP 94,253 (5.6 mg/kg, s.c.; closed triangles) 15 min before FR5 testing. There was a cocaine dose by CP 94,253 pretreatment interaction [F(1, 29) = 4.56, p < 0.05], with subsequent analysis indicating that CP 94,253 attenuated cocaine intake on both the ascending [t (13) = 2.77, p < 0.05] and descending [t (16) = 2.62, p < 0.05] limbs of the cocaine dose–effect function compared to vehicle treated rats. Asterisk (*) represents a difference from vehicle, independent sample t tests.