Serotonergic mechanisms in levodopa-induced "on-off" and sleep disorders in Parkinson's disease.

Serotonergic mechanisms have been implicated in levodopa-induced psychiatric toxicity reactions in Parkinson's disease (PD). Although CNS serotonin levels are reduced in Parkinsonian patients, the contribution of this abnormality to the pathophysiology of the motor symptoms of the disease are largely unknown. The following report concerns a 62-year-old female Parkinsonian patient with levodopa-induced "On-Off", depression and sleep disturbances, the severity of which was dramatically reduced by administration of low dosage amitriptyline (a serotonergic agent). The report suggests that impaired central serotonergic functions may be implicated in the pathophysiology of the levodopa-induced "On-Off" and that pharmacologic manipulations of serotonergic functions may be useful in the management of this motor side effect of chronic levodopa therapy.