The effects of serotonin precursors (L-5-hydroxytryptophan and L-tryptophan, with or without MAO inhibitors) and of agonists (quipazine and 5-methoxy-N,N-dimethyltryptamine-MeO-DMT) were studied in 3 day REM-deprived or control rats, by recording the presence of the serotonin syndrome and the number of head shakes. The REM sleep-deprived rats showed a larger incidence of the serotonin syndrome...