Possible
mediation of seasonal affective disorder
by hypothalamus neuronal signals
Melatonin
is secreted by neurons in the suprachiasmatic
nucleus of the hypothalamus. A study compared 55
patients with seasonal affective disorder (SAD)
and 55 matched healthy control subjects. Plasma
levels of melatonin in each subject were
measured every 30 minutes for 24 hours, once in
the winter and once in the summer. During the
periods of measurement the light condition was
maintained at < 1 lux. In patients with SAD
active melatonin secretion lasted significantly
longer in winter than in summer (9.0 versus 8.4
hours, p = 0.001) while in healthy subjects,
there was no difference. It is however worth
noting that the difference in the duration of
melatonin secretion between winter and summer
was reported for men but not women, which is
surprising since SAD is more common with women
than with men. Another concern is the small
effect size of the change in duration of the
melatonin offset. In fact many subjects went
against the group trend, although they all
became depressed in winter and remitted in
summer. Thus the researchers concluded that
while the melatonin offset is of interest it is
unlikely to be a strong pathogenic factor. Arch
Gen Psychiatry 58: 1108-1116,
2001