H L Alderson1, T W Robbins, B J Everitt. 1. Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3 EB, UK.
Abstract
RATIONALE: Second-order schedules of drug-self-administration provide a method of examining drug-seeking behaviour, which is maintained in part by the presentation of a discrete, drug-associated light CS. Previous results have found that lesions of the basolateral amygdala (BLA) impair the acquisition of i.v. cocaine self-administration under this type of schedule. OBJECTIVES: The present experiments examined the effects of excitotoxic lesions of the BLA on the acquisition of i.v. heroin self-administration under both continuous reinforcement and second-order schedules, in order to investigate possible commonalties in the neural basis of heroin- and cocaine-seeking behaviour. METHODS: Rats received quinolinic acid or sham vehicle lesions of the BLA prior to i.v. self-administration training. Initially, heroin self-administration under a continuous reinforcement schedule was acquired. Each active lever-press resulted in a 0.04 mg i.v. heroin infusion, paired with presentation of a 20-s light conditioned stimulus. Following acquisition of responding under this schedule, the response requirement was gradually increased to a second-order schedule of FI15(FR5:S). RESULTS: There was no effect of lesions of the BLA on the acquisition of heroin self-administration under a continuous reinforcement schedule. The acquisition of heroin-seeking behaviour under a second-order schedule of self-administration was not affected by lesions of the BLA, but lesioned rats showed a significantly higher baseline level of responding. CONCLUSIONS: These results indicate that the rewarding effects of heroin do not depend on the integrity of the BLA. The BLA is also not critically involved in mediating heroin-seeking behaviour under a second-order schedule of reinforcement, and this stands in marked contrast to the effects of BLA lesions on the acquisition of cocaine-seeking behaviour. These findings suggest that discrete heroin cues were not critical in maintaining heroin-seeking behaviour under the second-order schedule used here and that other learning systems are engaged in the control of this behaviour.
RATIONALE: Second-order schedules of drug-self-administration provide a method of examining drug-seeking behaviour, which is maintained in part by the presentation of a discrete, drug-associated light CS. Previous results have found that lesions of the basolateral amygdala (BLA) impair the acquisition of i.v. cocaine self-administration under this type of schedule. OBJECTIVES: The present experiments examined the effects of excitotoxic lesions of the BLA on the acquisition of i.v. heroin self-administration under both continuous reinforcement and second-order schedules, in order to investigate possible commonalties in the neural basis of heroin- and cocaine-seeking behaviour. METHODS: Rats received quinolinic acid or sham vehicle lesions of the BLA prior to i.v. self-administration training. Initially, heroin self-administration under a continuous reinforcement schedule was acquired. Each active lever-press resulted in a 0.04 mg i.v. heroin infusion, paired with presentation of a 20-s light conditioned stimulus. Following acquisition of responding under this schedule, the response requirement was gradually increased to a second-order schedule of FI15(FR5:S). RESULTS: There was no effect of lesions of the BLA on the acquisition of heroin self-administration under a continuous reinforcement schedule. The acquisition of heroin-seeking behaviour under a second-order schedule of self-administration was not affected by lesions of the BLA, but lesioned rats showed a significantly higher baseline level of responding. CONCLUSIONS: These results indicate that the rewarding effects of heroin do not depend on the integrity of the BLA. The BLA is also not critically involved in mediating heroin-seeking behaviour under a second-order schedule of reinforcement, and this stands in marked contrast to the effects of BLA lesions on the acquisition of cocaine-seeking behaviour. These findings suggest that discrete heroin cues were not critical in maintaining heroin-seeking behaviour under the second-order schedule used here and that other learning systems are engaged in the control of this behaviour.
Authors: Christian A Heidbreder; Eliot L Gardner; Zheng-Xiong Xi; Panayotis K Thanos; Manolo Mugnaini; Jim J Hagan; Charles R Ashby Journal: Brain Res Brain Res Rev Date: 2005-07