A characteristic effect of hallucinogens on investigatory responding in rats.

The disruption of the temporal distribution of investigatory responses by rats in a novel hole-board following lysergic acid diethylamide-25 (LSD), as described in a companion paper (Geyer and Light, 1979), was found to be a characteristic effect of a variety of hallucinogens. Similar effects were produced by indoleamine hallucinogens, such as LSD, N,N-dimethyltryptamine, and psilocin, and by phenylethylamine hallucinogens, such as mescaline or 2,5-dimethoxy-4-methylamphetamine (DOM). Congeners of DOM that are inactive in humans had no significant effects. Furthermore, of a variety of other psychoactive drugs tested, only apomorphine produced an effect similar to that of the hallucinogens. These results suggest that a simple behavioral measure of exploration in a hole-board may provide a useful animal model with which to examine the common effects of hallucinogens.