Researchers Confirm Serotonin’s Involvement in SAD

In a study recently published in the journal Current Biology, a team of biologists took a major step toward identifying the underlying neurobiological mechanism responsible for seasonal affective disorders (SAD), a type of depression that occurs during winter months. Researchers propose that the neurotransmitters serotonin and melatonin may be involved in the disorder because high concentrations of serotonin are linked to feelings of well-being and happiness, and low levels are linked to depression — playing a major role in regulating an individual’s mood. During the study, researchers reported that they localized the seasonal light-cycle effects that cause SAD to a specific region in the mid-brain called the dorsal raphe nucleus in mouse-model experiments. The dorsal raphe nucleus is linked to the brain’s master biological clock and also responds to melatonin, a key hormone involved in the regulation of sleep, blood pressure and seasonal reproduction. To test the effect of seasonal light cycles, researchers divided mice into three groups. One group was born and raised in an environment with a summer-like light-cycle, the second with spring and fall, and the third with a winter-like light-cycle. After administering several tests, researchers found that the mice raised in a summer cycle exhibited lower levels of depression-like behavior compared to their spring, fall and winter counterparts. They also found that serotonergic neurons fired faster in the summer-light-cycle mice and they had elevated levels of serotonin and the neurotransmitter norepinephrine, which is known to excite serotonergic neurons. To read more about this study, click here.