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Examining brain scans taken at various times of the year, scientists
have discovered that serotonin transporter activities, which help
regulate the neurotransmitter seratonin, vary according to the season.
According to the article, released on September 1, 2008 in Archives
of General Psychiatry, one of the
JAMA/Archives journals, this regular variance could potentially lead to
explanations of seasonal affective disorder and it's mood swings.
The authors explain seasonality as it relates to mood: "It is a
common experience in temperate zones that individuals feel happier and
more energetic on bright and sunny days and many experience a decline
in mood and energy during the dark winter season." It has been
suggested that this is related to serotonin levels in the brain, as
this neurotransmitter is integral to functions such as mating, feeding,
balance of energy, and sleep. The serotonin transporter binds to
serotonin, helping it exit the space between brain cells when the
communicate. This protein "is a key element in
regulating intensity and spread of the serotonin signal," according to
the authors.
To investigate this relationship, Nicole
Praschak-Rieder, M.D., and Matthaeus Willeit, M.D., of the Centre for
Addiction and Mental Health and the University of Toronto, Ontario,
Canada, and colleagues examined 88 healthy adults, with an average age
of 33 years, between 1999 and 2003. One positron emission
tomography (PET) scan was performed on each subject to assess the
potential binding of serotonin transporter using a measure of density
of the transporter. If this value is higher, serotonin circulates less
in the brain. the individual scans were grouped according to the season
taken, into either fall and winter or spring and summer.
In the fall and winter scans, the measured value was higher. The
authors summarize: "Serotonin
transporter binding potential values were significantly higher in all
investigated brain regions in individuals investigated in the fall and
winter compared with those investigated in the spring and summer."
Matching the scans to meteorological data, higher values generally
occurred when fewer hours of sunlight were available in the day.
The authors note that this correlation may have some bearing on mood:
"An
implication of greater serotonin transporter binding in winter is that
this may facilitate extracellular serotonin loss during winter, leading
to lower mood," they say. They continue, "Higher regional serotonin
transporter binding potential values in fall and winter may explain
hyposerotonergic [related to low serotonin levels] symptoms, such as
lack of energy, fatigue, overeating and increased duration of sleep
during the dark season."
In conclusion, they state, the implications of such results could be
very important for an understanding of Seasonal Affective Disorder and
other related diseases: "These findings have important
implications for understanding seasonal mood change in healthy
individuals, vulnerability to seasonal affective disorder and the
relationship of light exposure to mood… This offers a
possible explanation for the regular reoccurrence of depressive
episodes in fall and winter in some vulnerable individuals."
Seasonal Variation in Human Brain Serotonin Transporter Binding
Nicole Praschak-Rieder, MD; Matthaeus Willeit, MD; Alan A. Wilson, PhD;
Sylvain Houle, MD, PhD; Jeffrey H. Meyer, MD, PhD
Arch Gen Psychiatry. 2008;65(9):1072-1078.
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Written by Anna Sophia McKenney
Copyright: Medical News Today
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