Science: Refresh awareness! Reveals non-classical pathways in which visual information is passed into the brain.

Learn about the latest progress in neuroscience The retina is a thin layer of cells at the back of the eye, which can convert light signals into electrical signals. After these information are sent to more than 40 brain regions of the brain, they can form conscious imaging vision, help organisms perceive the shape, color and movement of external objects, such as the cars running on the street, the beautiful night scene under neon lights, and the subconscious non consciousness Imaging vision enables organisms to perceive light and dark (such as pupil reflection to light), day and night, and affects a variety of physiological functions of organisms.these functions are mainly realized by retinal ganglion cells (RGC), which are the only neurons in the retina that connect the brain and transmit retinal information from the eyes to the brain. Currently, 40 subtypes of RGC have been found in transcriptomics.the traditional view is that RGC achieves the above functions mainly by releasing excitatory neurotransmitter glutamate.it has been found that RGC can release the inhibitory neurotransmitter gamma aminobutyric acid (GABA) in some mammals. Whether these inhibitory neurotransmitters also participate in the above-mentioned functions is unclear.on May 1, 2020, the team of Tiffany M. Schmidt, Department of neurobiology, Northwestern University, published an article in science, revealing the non classical loop of visual information transmission: RGC can also transmit visual information to the large brain by releasing inhibitory neurotransmitter gamma aminobutyric acid.the researchers injected the DIO carrying AAV virus into the subretina of GAD2 CRE mice. The results showed that the retina mainly projected to the non imaging related suprachiasmatic nucleus (SCN), geniculate lobule (IGL) and ventrolateral geniculate nucleus (vlgn), but rarely to the imaging related areas of the anterior olivary tectal nucleus.however, the excitatory axons of RGC projected to the lateral geniculate dorsal nucleus, which is the key area of imaging function.at the same time, intrinsic photosensitive retinal ganglion cells (iprgcs) are the main cell type of RGCs. Immunofluorescence assay showed that about 12% of iprgcs co expressed with gad2, and the most expression was in temporal dorsal side of retina.further, fluorescence in situ hybridization (FISH) showed that gad2 mRNA was also co labeled with iprgcs, which indicated that iprgcs might release inhibitory neurotransmitters.then does iprgcs release inhibitory neurotransmitters in physiological state? The researchers selected the suprachiasmatic nucleus (SCN), which mainly receives input from the retina, and recorded the synaptic currents of 79 neurons after light activation of iprgcs in the suprachiasmatic nucleus. It was found that 32 neurons could be induced by light stimulation, including 3 neurons with inhibitory postsynaptic currents and 11 neurons with excitatory processes There were also inhibitory postsynaptic currents.in addition, NMDA receptor blockers can block excitatory postsynaptic currents.these electrophysiological results demonstrate that iprgcs can release functional inhibitory neurotransmitters.after specifically knockout the gad2 of iprgcs in transgenic mice (hereinafter referred to as iprgcs-gad2 knockout mice), pupillary light reflex was performed in dark, dark and bright environment respectively. The results showed that iprgcs-gad2 knockout mice performed normally in bright environment, but showed stronger pupil contraction response in dark environment.to further confirm the above conclusion, the researchers designed an interesting experiment: mice were put into the light dark cycle (LD cycle, Under 100 lux (incandescent lamp can emit 12.56 lux light per watt), iprgcs-gad2 knockout mice showed normal performance, but in low brightness light, the circadian rhythm amplitude of iprgcs-gad2 knockout mice was significantly increased, and the free activity under light was also obvious.these results suggest that the sensitivity of the non imaging visual system is reduced after the low light level decreases the release of inhibitory neurotransmitters of iprgcs.in general, this paper reveals that there is another circuit from RGCs to transmit visual information to the brain, and there is an inhibitory RGCs neural circuit to control non imaging visual function.also filled in the blank: the role of inhibitory neurotransmitters in "eye to brain" information integration.