The present study investigated the circadian variation in the behavioral response to the selective 5-HT2A/2C receptor agonist (+/-)-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI). Rats were subcutaneously injected with DOI at 0000, 0400, 0800, 1200, 1600, or 2000 hours. The wet-dog shake (WDS) response was counted following administration of DOI. A circadian rhythm that peaked...