LSD acts synergistically with serotonin depletion: evidence from behavioral studies in cats.

Administration of LSD (100 mug/kg, IP) or the serotonin depleting drug p-chlorophenylalanine (150 mg/kg/day for 5 days) both induce dramatic behavioral changes which include the common stereotyped responses of rapid flicking movements of the limbs and abortive attempts at grooming. The combined action of LSD and p=chlorophenylalanine results in a marked increase in the occurrence of these behaviors, suggesting that LSD acts synergistically with serotonin depletion. These data therefore support the hypothesis that the behavioral effects of LSD may be attributable to its well known electrophysiological effect of depressing the activity of serotonin containing neurons. In addition, limb flicking and abortive grooming may serve as a useful behavioral model for studying the actions of LSD, since these behaviors are quantifiable, easily scored, and occur with an extremely low frequency in normal cats.