Mammalian cerebral cortical tissue responds to low-intensity visible light.

Low levels of visible light directed onto slices of rat cerebral cortical tissue enhanced net potassium-induced release of the neurotransmitter gamma-aminobutyric acid (GABA) from these brain slices. At higher light intensity, net potassium-induced release was suppressed. These effects were apparently not from increased temperature. The amount of light enhancing this neurotransmitter release is approximately equal to the amount of light that can penetrate the head and reach the brain at the intensities of sunlight; this was determined by measuring the light entering the rat head through fur, scalp, skull, and dura mater and considering several natural lighting conditions. These results suggest that ambient light may be sufficient to alter the release of transmitters from mammalian cerebral cortex in vivo.