Summer is ending, the days are getting shorter, and the mood is changing: a phenomenon that is certainly not accidental, but that happens because the brain is able to sense the change of season , thanks to a circuit of neurons that modifies the signal molecules (neurotransmitters) in response to changes in daylight.

This is indicated by a study on mice conducted at the University of California in San Diego , and signed by the two Cagliari researchers Alessandra Porcu and Davide Dulcis .

The results , published in the journal Science Advances, may have important implications for light therapy against mood disorders , such as depression.

THE RESEARCH - The study focused on a small brain structure, the suprachiasmatic nucleus , which is hidden in the hypothalamus and is made up of about 20,000 neurons . It is a sort of "clock" that regulates the body's circadian rhythms, that is, the physical, mental and behavioral changes that follow the 24-hour cycle, affecting every aspect, from body temperature to hormone production.

This natural clock works on the basis of inputs from specialized cells in the retina that communicate changes in the intensity and duration of daylight.

The researchers found, in particular, that the neurons of the suprachiasmatic nucleus coordinate with each other to adapt to variations in light : they do this by changing the types and quantities of neurotransmitters which, in turn, affect the activity of the brain and the behaviors.

Seasonal changes have also been found in the number of neurons that produce neurotransmitters in the paraventricular nucleus, a region of the brain that controls stress, metabolism, and other autonomic functions.

"The most important discovery in this study is that we figured out how in the suprachiasmatic nucleus by inducing the expression of dopamine in the paraventricular nucleus," emphasizes , who, like , .