Behavioral, physiological and neuroendocrine responses in healthy volunteers to m-chlorophenylpiperazine (m-CPP) with and without ondansetron pretreatment.

Several serotonin3 (5-HT3) antagonists have been shown to attenuate the anxiogenic effects of the serotonergic agent, m-chlorophenylpiperazine (m-CPP), in animal models, but little data regarding possible effects of 5-HT3 antagonists on responses to m-CPP are available from studies in humans. Therefore, we studied the behavioral, physiological and neuroendocrine responses of 12 healthy volunteers to i.v. administered placebo and m-CPP (0.08 mg/kg), with and without i.v. pretreatment with the selective 5-HT3 antagonist, ondansetron (0.15 mg/kg). Compared to placebo, m-CPP given alone significantly increased ratings of anxiety and several other behavioral measures. m-CPP also produced statistically significant increases in temperature, systolic and diastolic blood pressure, heart rate, and in plasma concentrations of adrenocorticotropic hormone, cortisol, prolactin and norepinephrine. Responses to ondansetron given alone were no different from those of placebo. Pretreatment with ondansetron did not affect peak behavioral responses to m-CPP, but was associated with a significantly earlier return to baseline levels of ratings of anxiety and functional deficit as well as a summary measure of overall behavioral effects. Following ondansetron pretreatment, the increases produced by m-CPP in systolic and diastolic blood pressure and heart rate were no longer significantly different from placebo. Ondansetron pretreatment significantly reduced their plasma cortisol response to m-CPP without affecting the other plasma hormone responses. Plasma concentrations of m-CPP were unaffected by ondansetron pretreatment. These findings suggest that in normal human subjects some behavioral, cardiovascular and neuroendocrine effects of m-CPP may be partially modulated by 5-HT3 receptor-mediated mechanisms.

Biological and behavioral responses to D-amphetamine, alone and in combination with the serotonin3 receptor antagonist ondansetron, in healthy volunteers.

Evidence that serotonin3 (5-hydroxytryptamine3, 5-HT3) antagonists attenuate behavioral responses to D-amphetamine and cocaine suggests that 5-HT3 receptors modulate brain dopamine in animals. This study examined the potential interactions of the 5-HT3 antagonist ondansetron and D-amphetamine in 10 healthy human volunteers. After the subjects were pretreated with placebo or ondansetron (0.15 mg/kg, i.v.), 5-h challenge tests with oral D-amphetamine (0.5 mg/kg) were performed. As animal studies and early clinical studies with ondansetron have suggested nonlinear dose-response relationships, three subjects also underwent pilot studies with three doses of ondansetron (0.15, 0.05, and 0.015 mg/kg) before they received D-amphetamine. Administration of D-amphetamine increased plasma levels of cortisol, prolactin, growth hormone; elevated blood pressure, pulse, and temperature; and tended to increase self-ratings of activation/euphoria and anxiety. Amphetamine-induced increases in plasma prolactin were significantly reduced by ondansetron pretreatment, but the other neuroendocrine responses were unchanged. Diastolic blood pressure elevations were also significantly attenuated after administration of the lower ondansetron doses, but the other physiologic responses were unchanged. In subjects with minimal or moderate activation/euphoria responses, ondansetron pretreatment only minimally affected these effects of D-amphetamine. Preliminary data, however, indicate that those subjects with robust activation-euphoria responses to D-amphetamine had attenuated responses after ondansetron pretreatment. Taken together, these results suggest that some but not most of D-amphetamine's biological and behavioral effects may be modified by a 5-HT3 antagonist in healthy human volunteers.