Growth hormone response to baclofen in patients with seasonal affective disorder: effects of light therapy.

There is evidence for gamma-aminobutyric acid (GABA) dysfunction in the pathophysiology and treatment response of patients with major depression, but this has not been studied in seasonal affective disorder (SAD). Growth hormone (GH) response to a challenge with a GABAB receptor agonist, baclofen, is considered an in vivo index of hypothalamic GABAB receptor function in humans. To explore the role of GABAB receptor function in SAD, we compared the GH response to baclofen challenge in 15 patients with SAD and 20 matched healthy controls. Of the 15 patients with SAD, 14 had repeat baclofen challenge following 2-week treatment with light therapy. The results showed that baclofen administration led to a significant increase in GH release both in patients with SAD and normal controls. There was no significant difference in the GH response to baclofen between the two groups. Furthermore, 2-week treatment with light therapy did not significantly alter the baclofen-induced GH response in patients with SAD, in spite of a clear therapeutic effect. The results of this study suggest that hypothalamic GABAB receptor function, as measured by baclofen induced GH release, is not altered in patients with SAD or by light therapy.