THE PHOTORECEPTORS AND NEUROTRANSMITTERS DRIVING SUBCONCOIUS RESPONSES TO LIGHT
Keenan, William T
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Our sensory systems allow us to detect and successfully navigate the environment. The visual system translates environmental light into our conscious perception of sight, as well as subconscious physiological responses such as circadian photoentrainment, the pupillary light reflex, and mood modulation among others. The first step in these processes is photon detection by photoreceptors in the neural retina of the eye. In mammals, 3 general classes of photoreceptors exist: rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs). ipRGCs, in addition to being photoreceptors, are the critical relay for light information from rods and cones to brain areas responsible for the subconscious responses to light. In order for this light information to get to the brain, ipRGCs are known to employ 2 distinct neurotransmitters: glutamate and PACAP. However, the contribution of each photoreceptor and neurotransmitter to subconscious behaviors remains unclear. In this thesis, I demonstrate the role each photoreceptor plays in responding to the multitude of potential environmental light conditions. I show, similar to the photoreceptors, the neurotransmitters relay distinct and necessary aspects of the information detected by the photoreceptors. In addition, I identify novel neurotransmitters within subsets of ipRGCs which may be responsible for relaying their own unique aspect of the light environment to the brain.