Neuronal Organization of Deep Brain Opsin Photoreceptors in Adult Teleosts

Abstract

Biological impacts of light beyond vision, i.e., non-visual functions of light, signify the need to better understand light detection (or photoreception) systems in vertebrates. Photopigments, which comprise light-absorbing chromophores bound to a variety of G-protein coupled receptor opsins, are responsible for visual and non-visual photoreception. Non-visual opsin photopigments in the retina of mammals and extra-retinal tissues of non-mammals play an important role in non-image-forming functions of light, e.g., biological rhythms and seasonal reproduction. This review highlights the role of opsin photoreceptors in the deep brain, which could involve conserved neurochemical systems that control different time- and light-dependent physiologies in in non-mammalian vertebrates including teleost fish.

Keywords: evolution; extra-retinal; light-sensitive; neurochemical; non-image-forming.

FIGURE 1

Opsin localization and photosensitivity in the brain of adult teleost fish. (A) An illustration mapping the neuronal groups that express deep brain photopigments, VA-opsin, VAL-opsin, Opsin4, and TMT-opsin (indicated by color dots). (B) An illustration mapping the diurnal rhythmicity (of clock-related gene expression; green dots) and light-sensitivity (of c-fos expression; orange dots), based on a previous work by Moore and Whitmore (2014). Red dotted lines in (A,B) divide the rostral and caudal regions of the adult brain, based on a previous work by Hang et al. (2015). Anatomical nomenclature used in this review are according to a brain atlas of adult zebrafish (Wullimann et al., 1996). Abbreviation (for A): Cb, cerebellum; Di, diencephalon; HB, hindbrain; MB, midbrain; OB, olfactory bulb; ON, optic nerve; Tel, telencephalon; TeO, optic tectum; (for B): A, anterior thalamic nucleus; ATN, anterior tuberal nucleus; CCe, corpus cerebellum; CM, corpus mamillare; CP, central posterior thalamic nucleus; Dc, central zone of dorsal telencephalic area; Dd, dorsal zone of dorsal telencephalic area; DIL, diffuse nucleus of the inferior lobe; Dl, lateral zone of dorsal telencephalic area; DP, dorsal posterior thalamic nucleus; DTN, dorsal tegmental nucleus; ECL, external cellular layer of olfactory bulb; Ha, habenula; Hc, caudal zone of periventricular hypothalamus; Hd, dorsal zone of periventricular hypothalamus; Hv, ventral zone of periventricular hypothalamus; ICL, inner cellular layer of olfactory bulb; LCa, caudal lobe of the cerebellum; LH, lateral hypothalamus; LX, vagal lobe; NLV, nucleus of lateral lemniscus; PGZ, periventricular gray zone; PP, periventricular pretectal nucleus; PPa, parvocellular preoptic nucleus, anterior part; PPp, parvocellular preoptic nucleus, posterior part; PTN, posterior tuberal nucleus; SOC, supraoptic/chiasmatic nucleus; TeO, optic tectum; TL, longitudinal torus; TPp, periventricular nucleus of posterior tuberculum; Val, lateral division of valvula cerebelli; Vam, medial division of valvula cerebelli; VL, ventrolateral thalamic nucleus; VM, ventromedial thalamic nucleus; Vp, posterior nucleus of ventral telencephalic area; Vs, supracommissural nucleus of ventral telencephalic area; Vv, ventral nucleus of ventral telencephalic area; ZL, zone limitans.