Background. During recent years hypotheses about the pathophysiology of seasonal affective disorder/winter type (SAD) have focused monoaminergic mechanisms. There is substantial evidence that serotonergic systems play an important role. The potential role of catecholaminergic pathways has not been fully explored.

Methods. Eleven drug-free, symptomatic depressed patients with SAD and 11 healthy age- and gender-matched healthy controls were invited to participate in a 123Iβ-CIT single photon emission computed tomography (SPECT) study to assess striatal density of dopamine transporters (DATs). The cerebellum was used as reference region. Ratios were calculated between mean counts in left and right striatum and cerebellum. These ratios minus 1 represent specific/non-displaceable binding and are assumed to be directly related to DAT availability at the time of binding equilibrium.

Results. Displaceable 123Iβ-CIT binding in the area corresponding to the left striatum was significantly reduced in SAD patients compared to healthy controls (10·49±0·91 v. 11·95±1·54, respectively; 2-tailed P = 0·017, Mann–Whitney U test).

Conclusions. These data suggest reductions in the availability of striatal DAT binding sites in untreated symptomatic depressed SAD patients. It remains unclear whether these reductions represent a primary defect or an attempt to overcome a state of possible lowered dopamine availability in the synaptic cleft during a depressive episode of SAD. However, these findings provide evidence that brain dopaminergic systems may be involved in the pathophysiology of SAD.