How changes in day length change the brain and subsequent behavior – Neuroscience News

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Summary: Neurons in the suprachiasmatic nucleus coordinate to adapt to different lengths of daylight, changing at the cellular and network level. Neurons changed in the mix and expression of dopamine, altering brain activity and, subsequently, daily routine behaviors.

Source: UCSD

Seasonal changes in light (longer days in summer, shorter days in winter) have long been associated with human behaviors, affecting everything from sleep and eating patterns to ‘brain and hormonal activity.

Seasonal affective disorder (SAD) is a good example: a type of depression related to decreased exposure to natural sunlight, which typically occurs during the winter months and more often at higher latitudes when daylight hours days are shorter.

Bright light therapy has been shown to be an effective remedy for treating SAD, as well as conditions such as nonseasonal major depression, postpartum depression, and bipolar disorder, but such as seasonal changes in day length and exposure to light affects and alters the brain at a cellular and circuit level. kept scientists largely in the dark.

In a new study, published on September 2, 2022, a Advances in Scienceresearchers at the University of California San Diego School of Medicine used a mouse model to illuminate a process in which affected neurons change neurotransmitter expression in response to day-length stimuli, leading to related behavioral changes .

The work was led by lead study author Davide Dulcis, Ph.D., an associate professor in the Department of Psychiatry at the UC San Diego School of Medicine and a member of the UC San Diego Center for Circadian Biology .

Within the hypothalamus of the human brain is a small structure called the suprachiasmatic nucleus (SCN), which consists of approximately 20,000 neurons. (The average human brain contains approximately 86 billion neurons and another 85 billion non-neuronal cells.)

The SCN is the body’s timekeeper, regulating most circadian rhythms—physical, mental, and behavioral changes that follow a 24-hour cycle and affect everything from metabolism and body temperature to when hormones are released.

The SCN works from input from specialized photosensitive cells in the retina, which communicate changes in light and day length to our body.

In the new study, Dulcis and colleagues describe how SCN neurons coordinate with each other to adapt to different lengths of daylight, changing at the cellular and network level. Specifically, they found that in mice, whose brains function similarly to humans, neurons changed in the mix and expression of key neurotransmitters, which in turn altered brain activity and behaviors later newspapers

In this scheme, sunlight signals neural signals to the suprachiasmatic nucleus, the brain’s master clock, which in turn coordinates the biological clocks that regulate body-wide functions and consequent behaviors. Credit: National Institute of General Medical Sciences

Seasonal changes in light exposure have also been shown to alter the number of neurotransmitter-expressing neurons in the paraventricular nucleus (PVN), a brain region that plays an essential role in controlling stress, metabolism , growth, reproduction, immune functions and other autonomic functions. .

“The most impressive new finding of this study is that we discovered how to artificially manipulate the activity of specific SCN neurons and successfully induce dopamine expression within the hypothalamic PVN network,” said Dulcis.

“We have revealed novel molecular adaptations of the SCN-PVN network in response to day length to adjust hypothalamic function and daily behavior,” added first author Alexandra Porca, Ph.D., a member of the Dulcis lab.

“The multisynaptic neurotransmitter change we showed in this study could provide the anatomical/functional link mediating seasonal changes in mood and the effects of light therapy.”

The authors suggest that their findings provide a new mechanism that explains how the brain adapts to seasonal changes in light exposure. And because the adaptation occurs within neurons located exclusively in the SCN, the latter represents a promising target for new treatments for disorders associated with seasonal changes in light exposure.

About this neuroscience research news

Author: Scott La Fee
Source: UCSD
Contact: Scott La Fee – UCSD
Image: Image is credited to the National Institute of General Medical Sciences

See also

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Original Research: Open access
“Seasonal changes in day length induce the change of multisynaptic neurotransmitters to regulate hypothalamic network activity and behavior” by Alessandra Porcu et al. Advances in Science


Summary

Seasonal changes in day length induce multisynaptic neurotransmitter switching to regulate hypothalamic network activity and behavior.

Seasonal changes in day length (photoperiod) affect numerous physiological functions. The suprachiasmatic nucleus (SCN)-paraventricular nucleus (PVN) axis plays a key role in the processing of photoperiod-related information.

Seasonal variations in SCN and PVN neurotransmitter expression have been observed in humans and animal models. However, the molecular mechanisms by which the SCN-PVN network responds to altered photoperiod are unknown.

Here, we show in mice that neuromedin S (NMS) and vasoactive intestinal polypeptide (VIP) neurons in the SCN show photoperiod-induced neurotransmitter plasticity.

In vivo recording of calcium dynamics revealed that NMS neurons alter PVN network activity in response to winter-like photoperiod. Chronic manipulation of NMS neurons is sufficient to induce neurotransmitter switching in PVN neurons and affects locomotor activity.

Our findings reveal previously unidentified molecular adaptations of the SCN-PVN network in response to seasonality and the role of NMS neurons in adjusting hypothalamic function to day length through a coordinated multisynaptic neurotransmitter switch that affects the behaviour.

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