Researchers at UC Berkeley found that mice can detect light before full retina development, according to a recently published study.
Led by UC Berkeley graduate student Franklin Caval-Holme and campus neurobiology professor Marla Feller, the researchers examined how mouse pups are able to detect light, despite not having fully developed retinas, which are critical to sight. According to Feller, most of her earlier work was done under the assumption that mouse pups were completely blind, but a UCSF study showed that was not the case.
“Roughly 10 years ago, a lab at UCSF showed that mice that were one week old, and we thought blind, would turn away from bright lights,” Feller said in an email. “They went on to show that this behavior — called ‘photo aversion’ — was not mediated by rods and cones but by a different light sensitive pathway of the retina.”
After conducting a series of experiments, Caval-Holme and Feller found that the pathway was mediated by a type of cell called intrinsically photosensitive retinal ganglion cells, or ipRGCs. Their research found that these cells were connected in a way that amplified the organism’s ability to detect light.
These types of connections, known as electrical synapses, were present in the one week-old mice, but not in adults, according to Feller. She added that the absence of these synapses in adults were indicators that neurons in an immature nervous system are not always arranged as those in adult systems.
“In other words, the developing nervous system isn’t just wiring up to be an adult brain but might take some excursions along the way to mediate something important for the animal at that time,” Feller said in the email.
While the study was focused on light detection in mice, Feller and Caval-Holme said the conclusions could be applied to organisms with similar light-sensing cell types, including human fetuses. If these types of cells were present in fetal human retina, according to Caval-Holme, then a fetus would have the ability to respond to changes in light while in the womb.
While human retinas mature at 26 weeks, Feller said in the email that her research focused on mice in stages before the period where the retina becomes fully developed. According to Feller, it is possible that intense light can be detected by fetuses in the womb before the late second trimester.
Feller added that the detection of light in fetuses is not the same as what people typically consider to be sight.
“There is some evidence that the brightest sunlight can get through the womb and activate these ipRGCs,” Feller said in the email. “There is some evidence that light activation of them might be important for the normal maturation of the blood vessels of the eye.”