The influence of ondansetron and m-chlorophenylpiperazine on scopolamine-induced cognitive, behavioral, and physiological responses in young healthy controls

Background: There is evidence from animal and human experiments that leading and memory come under the separate influence of both cholinergic and serotonergic pathways. We were interested in learning whether serotonergic drugs could attenuate or exacerbate the memory-impairing effects of anticholinergic blockade in humans. Methods: The selective serotonin 5-HT₃ receptor antagonist ondansetron (0.15 mg/kg IV) and the serotonergic agent m- chlorophenylpiperazine (m-CPP; 0.08 mg/kg IV) were administered in combination with the anticholinergic agent scopolamine (0.4 mg PO) and compared to scopolamine alone in 10 young, healthy volunteers. Testing occurred on three separate days. Results: As expected, IV administration of scopolamine induced significant impairments in episodic memory and processing speed; however, these scopolamine-induced cognitive deficits were not attenuated by pretreatment with IV ondansetron (0.15 mg/kg), nor were they exacerbated by administration of IV m-CPP (0.8 mg/kg) in addition to scopolamine; however, administration of IV m-CPP was followed by a significant increase of self-rated functional impairment, altered self- reality, and dysphoria ratings, and scopolamine's effect on pupil size was potentiated. Conclusions: Together, these results suggest that in young, healthy volunteers scopolamine-induced changes of cognitive performance are only minimally modulated by the serotonergic effects on ondansetron and m- CPP. Further studies with older controls are needed to test whether these findings may be influenced by age.