Melanopsin Regulates Both Sleep-Promoting and Arousal-Promoting Responses to Light
(A) Plasma corticosterone levels were assessed from terminal blood following a 30 min light pulse at ZT14. All three wavelengths produced significant rise in plasma corticosterone levels. However, blue light evoked significantly higher corticosterone secretion compared to violet, green, and dark conditions (one-way ANOVA for wavelength, F(3.30) = 39.80, p ≤ 0.001. Posthoc Tukey dark versus violet p ≤ 0.001, dark versus blue p ≤ 0.001, dark versus green p = 0.002, violet versus blue p ≤ 0.001, and blue versus green p ≤ 0.001). Responses to green light were significantly lower compared to either violet or blue light. (B) Opn4-/- mice (open bars) show not only an overall elevation of plasma corticosterone levels in response to light (two-way ANOVA for wavelength and genotype, wavelength effect F(2.36) = 42.135 p ≤ 0.001, posthoc Tukey Opn4-/- dark versus blue p = 0.001, Opn4-/- dark versus green p = 0.013) but also showed different responses to wildtype mice (open bars, wavelength x genotype interaction F(2.36) = 13.809 p ≤ 0.001). Responses to blue light were significantly attenuated (wildtype versus Opn4-/- blue p = 0.004) whereas responses to green light were elevated (p = 0.029). As such, there was no significant difference in corticosterone response between blue and green light in Opn4-/- mice. Baseline levels of corticosterone at ZT14 were significantly elevated in Opn4-/- mice compared to wildtype controls (p = 0.017). Histograms reflect mean ± SEM, n = 5–10/group. Significant differences indicated by *** p ≤ 0.001, ** p ≤ 0.01, * p ≤ 0.05, NS = not significant. The data used to make this figure can be found in S5 Data.