Sunlight Reaches Deep into Brain to Play Key Role in Metabolism

Published September 2020 | Nature

A multi-institutional team of scientists led by Richard Lang, PhD, from Cincinnati Children’s has located, in mice, certain neurons inside the brain that express the protein Opsin 5, which can detect a specific wavelength of violet light from the sun. Those neurons, in turn, send signals that influence a number of body functions—including metabolism.

This discovery of another way that sunlight affects health has wide-ranging implications that could change treatment for people with metabolic disorders, recommendations for pregnant women, or how preterm infants are cared for in hospitals.

What does this mean for human health? Since the advent of the Industrial Age and now the Digital Age, many more people are spending most of their time inside, exposed to various types of indoor lighting that nearly always lack the violet wavelengths found in outdoor sunlight.

“With the modernization of society, many of us are now exposed to artificial lighting that is neither appropriate in timing nor spectral composition. This is not how we evolved.” says first author Kevin Zhang.

To further explore the questions raised by these findings, Cincinnati Children’s has installed a custom-designed, programmable, full-spectrum lighting system as part of the new neonatal intensive care unit in its new Critical Care Building, which opened to patients in November 2021.

“We have a great deal more to learn about how light affects human development and influences energy metabolism and disease susceptibility,” Lang says. “This may be the dawn of a new understanding of how people can live healthier lives in the modern world.”

This color-enhanced confocal microscope image shows the location of sunlight-sensing neurons in the mouse brain. The bright pink dots indicate light-sensing neurons within the hypothalamus. The blue label identifies neurons in adjacent regions of the brain. The red strands at the bottom show axons from retinal ganglion cells.

This coronal view of a mouse brain shows the location of light-sensing cells relative to the rest of the brain. Uppermost in blue are the two cortical hemispheres. The light sensing cells (bright pink) are located in the Eiffel Tower shaped patch in the hypothalamus at the base of the brain.