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S. Hattar, M. Kumar, J. Tung, A. Park, P. Tong, D.M. Berson, K.–W. Yau; Diverse Brain Targets of Melanopsin–Expressing Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2004;45(13):660.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A rare type of mammalian retinal ganglion cell is intrinsically photosensitive and expresses melanopsin, an opsin–like protein. These cells innervate the suprachiasmatic nucleus (SCN, the brains circadian pacemaker), the intergeniculate leaflet (IGL, also implicated in circadian modulation), and the olivary pretectal nucleus, (OPN, which mediates the pupillary light reflex) (Berson et al., Science 295, 2002; Hattar et al., Science 295, 2002; Gooley et al., J. Neurosci 23, 2003). We sought to identify other brain targets of these cells which might indicate novel functional roles for this system.Methods: In mice with the melanopsin gene replaced by the tau–lacZ marker gene (Hattar et al., 2002, ibid), we traced axons of melanopsin ganglion cells with X–gal staining or anti–ß–galactosidase immunohistochemistry, in some cases after unilateral enucleation. Results: In the hypothalamus, targets besides the SCN included the preoptic region (including the ventrolateral preoptic nucleus, which is implicated in sleep regulation), supraoptic nucleus, ventral subparaventricular zone (implicated in masking behavior), and lateral hypothalamus. Labeling of the lateral geniculate complex included, besides the IGL, the ventral division (LGNv, implicated in visuomotor functions) and a thin stratum where the dorsal LGN abuts the lateral posterior nucleus (suggesting a possible role in cortical perceptual mechanisms). Labeled fibers arborized sparsely throughout the superficial layers of the superior colliculus, a gaze control center. The lateral habenula was densely labeled at its lateral margin, where it abuts the lateral dorsal and central lateral thalamic nuclei. Unilateral enucleation reduced labeling far more on the contralateral than on the ipsilateral side in all nuclei except the SCN. Conclusions: Photosensitive ganglion cells distribute their irradiance–encoding signals to a variety of circuits involved in functions other than synchronization of circadian rhythms and pupillary control.
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