delta 1-Tetrahydrocannabinol-induced circling behavior in rats: a possible measure of psychotomimetic activity?

Relatively high dosages of delta 1-tetrahydrocannabinol (delta 1-THC) markedly suppressed almost all normally occurring behavioral elements in rats as observed in both a small and a large open field. This effect persisted following repeated treatment and testing for 3 consecutive days. The psychotropically inert but related compound cannabidiol (CBD) did not suppress behavior, but in contrast had a mild activating effect. Both compounds decreased defecation during the test procedure. In addition, delta 1-THC, but not CBD, induced a bizarre circling and turning response, that was evident over all 3 test days and occurred even when the rats were deeply sedated. It is suggested that an analysis of this phenomenon may be useful in measuring the psychotomimetic action of delta 1-THC and similar compounds in rats.