Most of us are familiar with the “winter blues,” the depression-like
symptoms known as “seasonal affective disorder,” or SAD, that occurs when the
shorter days of winter limit our exposure to natural light and make us more
lethargic, irritable and anxious. But for rats it’s just the opposite.
Biologists at UC San Diego have found that rats experience
more anxiety and depression when the days grow longer. More importantly, they
discovered that the rat’s brain cells adopt a new chemical code when subjected
to large changes in the day and night cycle, flipping a switch to allow an
entirely different neurotransmitter to stimulate the same part of the brain.