Central serotonin-like activity of 6-chloro-2-[1-piperazinyl]-pyrazine (CPP; MK-212).

CPP, administered systemically, elicited four distinct responses characteristic of serotonin-receptor activation in the central nervous system. The crossed extensor reflex in the acutely spinalized rat was enhanced by treatment with CPP, 1-16 mg/kg. CPP, 1.11-10 mg/kg, elicited a dose-related increase in head twitches in mice. A complex motor syndrome in rats similar to that produced by pargyline plus tryptophan (or other treatments effecting increased activation of central serotonin receptors) was produced by 1.25-5 mg/kg of CPP. An increase in twitch frequency of the mylohyoideus muscle in the urethane anesthetized rat occured after CPP at 0.1 mg/kg or less. Complete abolition of all four effects of CPP was achieved by pretreatment with the centrally acting indoleamine antagonist methergoline. The peripherally acting serotonin antagonist xylamidine was ineffective or only weakly active, depending upon the test procedure, in preventing the serotonin-like actions of CPP. These findings indicate that CPP has a serotoninmimetic action in the central nervous system.