(A) The expression of mRNA encoding mammal-like melanopsin (OPN4m) was detected in the infundibular nucleus (IN) within the mediobasal hypothalamus (MBH) (arrowheads in the lower row); however, OPN4m was not detected in the septal region. Faint expression of Xenopus-like melanopsin (OPN4x) mRNA was detected in the septal region (arrowheads in the upper raw) but was not detected in the MBH. (B) Expression analysis of both melanopsins based on high-sensitivity in situ hybridization revealed the expression of OPN4m in the IN (arrowheads in a high-magnification image). (C) The JTK_CYCLE algorithm revealed a pattern of OPN4m expression in the IN that lacked a distinctive periodicity (adjusted p-value: 1.0, Benjamini–Hochberg q-value: 1.0, period: 20, Phase 12). Each point represents the mean ± SEM (n = 3). CO: optic chiasm, IN: infundibular nucleus, LS: lateral septum, LV: lateral ventricle, ME: median eminence, PVO: paraventricular organ, 3V: third ventricle.