Light‐evoked FOS induction within the suprachiasmatic nuclei (SCN) of melanopsin knockout (Opn4^−/−) mice: A developmental study

Abstract

The aims of this study were to address three related questions: (1) Do the photosensitive ganglion cells of the mouse convey light information to the suprachiasmatic nuclei (SCN) at P0? (2) Do the differentiating rods and cones contribute to light-evoked FOS induction within the murine SCN at P4? (3) How does light-evoked FOS induction within the SCN of melanopsin knockout (Opn4-/-) mice differ at P4 and P14? Our approaches took advantage of the published descriptions of murine ocular development, melanopsin knockout (Opn4-/-) mouse, and light-induced expression of FOS (the phosphoprotein product of immediate early gene c-fos) within the SCN as a marker of retinohypothalamic tract competence. Collectively, our results show that photosensitive melanopsin-dependent retinal ganglion cells provide light information to the murine SCN on the day of birth, and possibly beforehand, and that developing rods and cones fail to provide light information to the SCN during early postnatal life. On the basis of previous publications and data presented here, we suggest that at ages around P14 the rods and cones might be capable of fully compensating for the loss of melanopsin-photosensitive ganglion cells if exposure to light is of sufficiently long duration. These results are related to the broader context of recent findings and the potential role(s) of a neonatal photoreceptor.

Intrinsically Photosensitive Retinal Ganglion Cells

“…13 A ) (178, 205). Furthermore, these neonatal ipRGCs appear to be functionally connected to the SCN, as light increases the expression of c- fos in this nucleus (74, 119, 178, 222). …”

Melanopsin and inner retinal photoreception

“…Melanopsin expression is first detected in the mouse retina at embryonic day (E)10.5 [120], following the appearance of retinal ganglion cells at E9. The rodent RHT is present at postnatal day (P)0 [121,122], and ipRGCs are functional and capable of inducing c-fos within the SCN at least as early as that [115,121,123]. By contrast, rod opsin expression is not detectable until P5 [124] and rod/cone responses until P10-12 [125][126][127].…”

Perinatal light imprinting of circadian clocks and systems (PLICCS): A signature of photoperiod around birth on circadian system stability and association with cancer

“…Siberian hamster neonates (P0-P21) exposed to different photoperiods and temperatures elicited sex differences in basal plasma cortisol levels, cortisol stress response, and bone length symmetry in later life (Benderlioglu et al, 2007). With regard to circadian clocks and systems development, it is interesting to note that light is detectable at the suprachiasmatic nuclei (SCN) level at P0 in wild type but not in melanopsin k/o mice as determined by FOS expression (Lupi et al, 2006). Neonatal (P6-P9) mice demonstrated melanopsin-dependent negative phototaxis and intrinsically photosensitive retinal ganglion cell (ipRGC) firing before opening their eyes (Johnson et al, 2010).…”