Is the release of glutamate from photoreceptors increased or decreased in the presence of light?

In the presence of light, the release of glutamate from photoreceptors is decreased. Photoreceptors, which include rods and cones, respond to light through a process known as phototransduction. When light hits the photopigments within these cells, it causes a series of biochemical reactions that ultimately lead to the hyperpolarization of the photoreceptor membrane.

As the photoreceptor hyperpolarizes in response to light, the amount of calcium ions entering the cell decreases. This reduction in calcium concentration is crucial because calcium ions are involved in the fusion of vesicles containing glutamate with the presynaptic membrane for release into the synaptic cleft. With less calcium available, the release of glutamate is inhibited, leading to a decrease in glutamate levels being released into the surrounding synapses.

This change in neurotransmitter release is fundamental to the visual processing pathway, as decreased glutamate levels will signal downstream bipolar cells and other retinal neurons that light is present, ultimately influencing the signals sent to the brain for vision processing. Thus, the correct answer reflects the physiological response of photoreceptors to light exposure, emphasizing the complex nature of visual signal transduction.