Behavioral responses to intravenous meta-chlorophenylpiperazine in patients with seasonal affective disorder and control subjects before and after phototherapy.

A comparison of the baseline and post-infusion effects of the serotonin agonist meta-chlorophenylpiperazine (m-CPP) in 10 patients with seasonal affective disorder (SAD) and 11 healthy control subjects revealed significantly different subjective response profiles between the groups. Several baseline and m-CPP-stimulated responses in symptoms putatively related to serotonergic function changed significantly after a week's exposure to phototherapy in the SAD patients but not the control subjects. Before phototherapy, depressed patients with SAD reported activation-euphoria responses to m-CPP and significant decreases in carbohydrate hunger, but insignificant changes in feeling slowed or sleepy, while control subjects reported no mood or appetite changes but significant increases in feeling slowed down following m-CPP. After phototherapy, which led to a significant reduction in baseline depressive symptom rating to near-euthymic levels in the SAD patients, almost all of the patients' responses to m-CPP were normalized and no longer differed from the control subjects' responses. These results provide evidence of a possible dysregulation in serotonergic neurotransmission in depressed SAD patients that normalizes following treatment with phototherapy.