Rats were trained to lever press according to variable interval 10 s schedules during daily experimental sessions composed of six 3 min food reinforcement periods and were treated twice daily for 6 days with either vehicle or escalating regimens of Δ9-tetrahydrocannabinol. On days 7 and 8, the rats were challenged with vehicle and cumulative doses of SR141716A (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4,-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxyamide hydrochloride), a cannabinoid CB1receptor antagonist, up to 3 and 9 mg/kg, respectively. Response rates increased during Δ9-tetrahydrocannabinol withdrawal and towards those of the vehicle treatment group suggesting a waning of the direct effects of Δ9-tetrahydrocannabinol. SR141716A reduced response rates but only in rats pre-treated with Δ9-tetrahydrocannabinol. These data suggest that dependence upon Δ9-tetrahydrocannabinol was induced and SR141716A precipitated withdrawal. Copyright (C) 2000 Elsevier Science B.V.
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