8-OHDPAT effects upon cocaine unconditioned and conditioned behaviors - A role for drug stimulus effects

The effects of the 5-HT1A agonist (+/-)-8-hydroxy-dipropylaminotetralin (8-OHDPAT) upon the unconditioned and conditioned behavior induced by cocaine were assessed in rats, Separate groups (n = 7) received saline, cocaine (10 mg/kg) 8-OHDPAT (0.2 mg/kg), or 8-OHDPAT (0.2 mg/kg) plus cocaine (10 mg/kg) for eight treatment sessions (two per week) in which the rats were tested for 20 min in an open-field. On the eight treatment session, cocaine enhanced locomotion and rearing but decreased grooming. 8-OHDPAT also decreased grooming and, when given in combination with cocaine, enhanced locomotion but attenuated cocaine-induced rearing. The two 8-OHDPAT groups differed substantially from each other and from the cocaine group in terms of locomotion during the drug treatment phase. Subsequently, all groups received a series of conditioning tests in which they received saline, 0.1, 0.2, or 0.4 mg/kg 8-OHDPAT prior to the testing, Groups which had received either 8-OHDPAT or cocaine prior to the conditioning tests exhibited equivalent conditioned effects on the saline conditioning test. When conditioning test were conducted with 8-OHDPAT, however, only the group which had previously received the combined 0.2 mg/kg 8-OHDPAT plus cocaine treatment exhibited a conditioned response and this effect only occurred at the 0.2 8-OHDPAT dose level. These observations indicate the important influence of the stimulus properties of drugs for the study of drug conditioning and for understanding drug interactions with cocaine. Published by Elsevier Science Inc.