Melanopsin: a novel photopigment involved in the photoentrainment of the brain's biological clock?

Melanopsin may be the key photopigment that helps regulate the brain's biological clock.

• The suprachiasmatic nucleus (SCN) generates circadian rhythms of approximately 24 hours.
• Daily adjustments to the SCN's clock are primarily influenced by the light/dark cycle through a process called photoentrainment.
• Melanopsin is expressed exclusively in retinal ganglion cells that project to the SCN via the retinohypothalamic tract.
• These retinal ganglion cells are intrinsically photosensitive, suggesting their role in light information processing.
• While evidence supports melanopsin as a candidate for the circadian photopigment, further functional experiments are necessary to confirm its role.

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