Document Type

Honors Thesis

Publication Date

Spring 2019

Abstract

Intrinsically photosensitive retinal ganglion cells (ipRGCs) comprise a small subset of photoreceptors found in the eye containing the newly discovered photopigment, melanopsin. ipRGCs project directly to the hypothalamic suprachiasmatic nucleus (SCN), the central “pacemaker” underlying the generation and entrainment of circadian rhythms. Photic stimuli detected by ipRGCs are transmitted to the SCN via the retinohypothalamic tract (RHT), mediating the entrainment of the SCN pacemaker. In addition to circadian entrainment, these pathways may also contribute to seasonal changes seen in both animals and humans, such as seasonal breeding cycles in animals and seasonal affective disorder in humans. Our lab has recently found that changes in the laboratory lighting environment can alter voluntary alcohol intake in mice, which may be related to the seasonal variation in alcohol use seen in humans. In this study, we examined the possible role of melanopsin signaling in mediating the effects of photoperiod on alcohol intake. Male and female melanopsin knockout (Opn4 -/-) and wild-type control mice of the same genetic background were housed individually in running-wheel cages and initially kept on a 12:12 light-dark (LD) cycle for 3 weeks, followed by constant light (LL) or constant darkness (DD) for 3 weeks, then returned to LD 12:12 for the final 3 weeks. Animals had continuous access to running wheels, plain water, and 10% ethanol solution throughout the experiment. Wheel turns were monitored by a computer interface and ethanol and water intake were recorded manually at weekly intervals. While Opn4-/- mice showed the expected reductions in circadian light sensitivity from controls, the two genotypes displayed identical reductions in ethanol intake under LL and DD. Thus, melanopsin-based photoreception is not necessary for light-induced changes in alcohol preference drinking in mice.

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