Serotonin transporter binding is reduced in seasonal affective disorder following light therapy.

OBJECTIVE: To investigate the effects of light therapy on serotonin transporter binding (5-HTT BPND ), an index of 5-HTT levels, in the anterior cingulate and prefrontal cortices (ACC and PFC) during winter in seasonal affective disorder (SAD). 5-HTT BPND fluctuates seasonally to a greater extent in SAD relative to health. We hypothesized that in SAD, 5-HTT BPND would be reduced in the ACC and PFC following light therapy. METHODS: Eleven SAD participants underwent [11 C] DASB positron emission tomography (PET) scans to measure 5-HTT BPND before and after 2 weeks of daily morning light therapy. RESULTS: The primary finding was a main effect of treatment on 5-HTT BPND in the ACC and PFC (repeated-measures manova, F(2,9) = 6.82, P = 0.016). This effect was significant in the ACC (F(1,10) = 15.11 and P = 0.003, magnitude of decrease, 11.94%) and PFC (F(1,10) = 8.33, P = 0.016, magnitude of decrease, 9.13%). 5-HTT BPND also decreased in other regions assayed following light therapy (repeated-measures manova, F(4,7) = 8.54, P = 0.028) including the hippocampus, ventral striatum, dorsal putamen, thalamus and midbrain (F(1,10) = 8.02-36.94, P < 0.0001-0.018; magnitude -8.83% to -16.74%). CONCLUSIONS: These results demonstrate that light therapy reaches an important therapeutic target in the treatment of SAD and provide a basis for improvement of this treatment via application of [11 C]DASB PET.

Light therapy and serotonin transporter binding in the anterior cingulate and prefrontal cortex.

OBJECTIVE: To investigate the effects of light therapy on serotonin transporter binding (5-HTT BPND ), an index of 5-HTT levels, in the anterior cingulate and prefrontal cortices (ACC and PFC) of healthy individuals during the fall and winter. Twenty-five per cent of healthy individuals experience seasonal mood changes that affect functioning. 5-HTT BPND has been found to be higher across multiple brain regions in the fall and winter relative to spring and summer, and elevated 5-HTT BPND may lead to extracellular serotonin loss and low mood. We hypothesized that, during the fall and winter, light therapy would reduce 5-HTT BPND in the ACC and PFC, which sample brain regions involved in mood regulation. METHOD: In a single-blind, placebo-controlled, counterbalanced, crossover design, [(11) C]DASB positron emission tomography was used measure 5-HTT BPND following light therapy and placebo conditions during fall and winter. RESULTS: In winter, light therapy significantly decreased 5-HTT BPND by 12% in the ACC relative to placebo (F1,9 = 18.04, P = 0.002). In the fall, no significant change in 5-HTT BPND was found in any region across conditions. CONCLUSION: These results identify, for the first time, a central biomarker associated with the intervention of light therapy in humans which may be applied to further develop this treatment for prevention of seasonal depression.