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Postnatal light sensing in mice linked to later learning

By ZHU LIXIN in Hefei | China Daily | Updated: 2022-08-15 09:30

Chinese scientists have discovered that mice that are stimulated by sensing light in the first few days of life are better able to learn later in life than those that are not.

The stimulation of a specific type of retinal cells in mice during early postnatal life functionally contributes to learning in adulthood, revealing a previously unknown function of the cells.

The discovery was made by scientists at the University of Science and Technology of China based in Hefei, Anhui province, and was published in the international science journal Cell.

The cells targeted are known as intrinsically photosensitive retinal ganglion cells, or ipRGCs, one of three types of photoreceptors in the retina, which sense light and also contribute to the vision.

The other two types of retinal photoreceptors are rods and cones, which mainly work to create visual images, while ipRGCs mainly help mediate non-image brain functions such as the circadian rhythm and mood regulation.

As mice are born blind, their ipRGCs respond to light much earlier than their rods and cones and mediate the earliest light sensation in mammals, according to the article.

The scientists discovered that light sensation by ipRGCs in newborn mice activates neurons in the brain that release oxytocin, a substance that controls several bodily processes and also helps neurons form connections with each other.

The oxytocin-releasing neurons help form synapses, the points of contact in the brain where information is transmitted between neurons.

Researchers deprived newborn mice of light sensation both by genetically altering their cells to be unable to sense light, and by keeping genetically normal mice in the dark. Both methods ensured the target mice were unable to perceive light.

It was observed that both groups of mice raised without this initial sensation of light developed reduced spine densities in pyramidal cells in multiple brain areas. These mice were significantly less sensitive to auditory stimulation once grown, apparently demonstrating that their ability to learn had been impaired.

The researchers came to the conclusion that light sensation by ipRGCs in early life is key to the adult learning ability of mice.

The USTC scientists said the discovery is an important reminder to public health researchers to pay attention to the light environment to which infants are subjected, and to further explore how the light environment may influence infant brain development.

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