Cumulative alterations in rat behavior during continuous administration of LSD or mescaline: absence of tolerance?

Male hooded rats were observed for 6 days following implantation with slow-release subcutaneous pellets containing LSD, mescaline, or control vehicle solution. In animals housed in isolation cages, continuous hallucinogen administration resulted in a gradual increase in head twitches and catatonic postures which peaked 3--4 days after pellet implantation and then declined. In animals housed in social colonies, there were also delayed increases in behavior following hallucinogen-pellet implantation, but these principally involved social behaviors such as fighting by mescaline-treated animals and social grooming by LSD-treated animals. This finding of gradual and cumulative effects of continuous hallucinogen administration contrasts with the usual finding of a rapid tolerance to hallucinogens following repeated injections.