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Tara A. LeGates, Cara M. Altimus, Sunggu Yang, Alfredo Kirkwood, Edward T. Weber, Samer Hattar; Melanopsin-expressing Retinal Ganglion Cells Mediate Light Modulation Of Cognitive Functions And Mood Related Behaviors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3465.
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The evolution of life on earth has been profoundly affected by light. Light influences the behavior of many organisms, behaviors as simple as phototropism or as complex as image formation and object tracking. In humans, light has impacts on physiological functions including sleep, mood, and cognitive functions that are important for the quality of life. It is well documented that changes in light input can result in mood and cognitive dysfunction as observed in a seasonal form of depression known as seasonal affective disorder (SAD), "jet-lag", and shift work. Despite the importance of light, very little is known regarding the retinal and neuronal pathways through which light affects these physiological functions.
To gain a better understanding of how light information influences cognitive functions and mood related behaviors, we housed mice in a light paradigm that provided exposure to light pulses at all phases of the circadian cycle without inducing circadian arrhythmicity or sleep deprivation. We then assessed learning and mood related behaviors in mice housed under this light cycle and mice housed under 12 hour light: 12 hour dark.In mammals, light is transduced by photoreceptors in the retina into an electrical signal that can be interpreted by the brain. To determine the retinal cells responsible for conveying the disruptive light information to the brain to influence learning and mood, we used a mouse line lacking melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). These ipRGCs have been shown to convey light information to modulate circadian rhythms and sleep but have not been linked to light-influenced mood and cognitive related functions.
We show that animals exposed to the light paradigm described above show learning deficits as well as increased depression-related behaviors. Interestingly, this disruptive light paradigm does not cause any learning deficits or increases in depression-related behaviors in mice lacking ipRGCs. Furthermore, mice lacking ipRGCs elicit decreased anxiety- and depression-related behaviors even when housed in a 12:12 light/dark cycle.
These findings establish the influence of light on cognitive functions and mood related behaviors directly without causing circadian arrhythmicity or inducing sleep deprivation. This presents a new role for ipRGCs in modulating higher order functions.
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