Influence
of sunlight on serotonin production in the
brain
The
concept that serotonin is involved in seasonal
mood disorders is based on indirect measures of
serotonin activity, such as the response to
serotonin reuptake inhibitors or tryptophan
depletion. However, the cerebrospinal fluid
(CSF) concentrations of serotonin and other
neurotransmitters, such as dopamine and
noradrenaline, are normal in of patients
suffering from seasonal affective disorder. CSF
levels are, however, imprecise indicators of
serotonin release by the brain, which has
prompted the measurement of serotonin
concentrations from blood vessels draining the
brain as a more accurate assessment of brain
serotonin.
Vascular catheters were placed high in an
internal jugular vein in 101 healthy men to
directly sample venous blood from the brain.
Then blood was analysed for levels of serotonin
and metabolites, and the association between
these levels and the season and weather
conditions was determined.
Turnover of serotonin by the brain was lower in
winter than in summer or spring and the rate of
serotonin production was directly associated
with the prevailing duration of bright
sunlight.
The results obtained with this new technique
provide further evidence that sunlight and
season factors are responsible for alterations
in brain serotonin turnover which underlie
seasonal mood disorders. It remains to be
determined whether patients predisposed to
affective disorders are influenced environmental
factors in the same way as healthy
volunteers. Lancet
360: 1840-1842, 2002