Showing papers by "Mark D. Rollag published in 2000"

A Novel Human Opsin in the Inner Retina

Abstract: Here we report the identification of a novel human opsin, melanopsin, that is expressed in cells of the mammalian inner retina. The human melanopsin gene consists of 10 exons and is mapped to chromosome 10q22. This chromosomal localization and gene structure differs significantly from that of other human opsins that typically have four to seven exons. A survey of 26 anatomical sites indicates that, in humans, melanopsin is expressed only in the eye. In situ hybridization histochemistry shows that melanopsin expression is restricted to cells within the ganglion and amacrine cell layers of the primate and murine retinas. Notably, expression is not observed in retinal photoreceptor cells, the opsin-containing cells of the outer retina that initiate vision. The unique inner retinal localization of melanopsin suggests that it is not involved in image formation but rather may mediate nonvisual photoreceptive tasks, such as the regulation of circadian rhythms and the acute suppression of pineal melatonin. The anatomical distribution of melanopsin-positive retinal cells is similar to the pattern of cells known to project from the retina to the suprachiasmatic nuclei of the hypothalamus, a primary circadian pacemaker.

Cultured amphibian melanophores: a model system to study melanopsin photobiology.

Abstract: Publisher Summary Melanopsin is expressed by scattered perikarya among the amacrine and ganglion cells of the primate retina. In amphibians, melanopsin is expressed in the retina, hypothalamus, iridial myocytes, and melanophores. Amphibian melanophore responses to light protect vital organs against ultraviolet irradiation and produce rapid color changes needed for camouflage responses and animal survival. From a technical standpoint, it is important to understand the regulation and expression of melanopsin to avoid misinterpreting the actions of other agents on amphibian melanophores studied in lighted environments. This chapter describes the Xenopus melanophore model system. It also describes methods for monitoring the effects of melanopsin gene overexpression on the photobiological response of cultured transgenic melanophores. As computerized image analysis techniques for easy and reliable automated measurement of pigment dispersion are developed, it is anticipated that assay technologies in the melanophore model system will become more sophisticated. Future transgenic studies are likely to use Xenopus tropicalis instead of Xenopus laevis as a melanophore source to avoid the complications of pseudotetraploidy.

The effect of polarized versus nonpolarized light on melatonin regulation in humans.

Abstract: The aim of this study was to compare the effects of polarized light versus nonpolarized light on melatonin secretion in healthy, humans (mean age, 25 years; N = 6). On separate evenings, each subject was exposed to four different light intensities (20, 40, 80 and 3200 lx) of both polarized and nonpolarized light, as well as to a control, dark exposure. Each evening experiment consisted of a 120 min dark exposure (0000–0200 h) followed by a 90 min light exposure (0200–0330 h). Subjects' pupils were dilated prior to exposures. Blood samples were drawn at the start and end of each light-exposure period and later assayed for melatonin by radioimmunoassay. When compared to control exposures, both polarized and nonpolarized light elicited significant suppression of plasma melatonin at each illuminance (P < 0.03 to P < 0.0001), There were no significant differences between the effects of polarized light and nonpolarized light at any illuminance. The two light stimuli modalities demonstrated very similar...