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Altitude, temperature, circadian rhythms and exercise
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Henning Wackerhage, Kenneth A. Dyar, Martin Schönfelder
How is the master pacemaker in the brain synchronised to the environmental day-night cycle? The cryptochrome-encoding genes CRY1/2 are key candidates for linking the master clock to ambient light as cryptochromes are blue light-sensing proteins. However, Cry1/2 knockout mice still increase the expression of Per1 and Per2 in response to light (72), suggesting CRY1 and CRY2 proteins are not needed to synchronise the master clock with the day/night cycle. So where are the light sensors that help to entrain the master clock in the suprachiasmic nucleus? Researchers found that if they knocked out a protein in mice called melanopsin, containing intrinsically photosensitive retinal ganglion cells of the eye, the animals demonstrated normal pattern vision, yet struggled to link their circadian rhythms to the day-night cycle (73). As melanopsin responds mostly to blue light, this wavelength of visible light keeps melanopsin more active during the day and less active at night.
Endocrine Functions of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The retinal cells and pigment epithelium have circadian oscillators that are integrated through neural synapses, electrical coupling (gap junctions), and released neurochemicals. Ganglion cells produce the photopigment melanopsin, which plays a non-image-forming role in the setting of the circadian rhythms. Fibers from the ganglion cells form the retino-hypothalamic tract that innervates the SCN. These fibers contain two substances, pituitary adenylate cyclase activating polypeptide (PACAP) and glutamate, both of which regulate, through their respective receptors, the circadian rhythms of the SCN.
Lifestyle factors
Published in Jane Hanley, Mark Williams, Fathers and Perinatal Mental Health, 2019
Problems occur when the process of sleep and preparation for sleep are disturbed, and the full circadian cycle cannot be completed. Photoreceptors within the eye are used to detect light and the exposure to natural sunlight, which has blue light, is detected by the retina. Melanopsin, a light-sensitive retinal protein, is expressed by photoreceptors, which respond most strongly to blue light. This signals the hypothalamus to produce cortisol and warm up the body. When darkness approaches the hypothalamus signals the production of the hormone melatonin, which is responsible for sleep and the body temperature drops. This sensitivity allows the circadian rhythm to be synchronised with the twenty-four-hour solar day.
Changes of Melanopsin Expression in the Retina of Guinea Pig during Experimental Myopia and Recovery Period
Published in Current Eye Research, 2023
Hongping Xu, Yan Dong, Fen He, Bo Qin
Melanopsin is the photosensitive pigment produced by the intrinsically photosensitive retinal ganglion cells (ipRGCs).10 The melanopsin-contained retinal ganglion cells can not only absorb light, but also have complex synaptic connections with a variety of neurons in the retina, such as amacrine cells and bipolar cells. The ipRGCs are critical for the regulation of circadian rhythm and the functions of other non-imaging visual system.11,12 Some researchers believed that the melanopsin-contained ganglion cells might exert a protective effect in the development of myopia.13 And the inhibitory effect of retinal melanopsin on the development of defocus myopia was also observed.14 Combined with these, we speculated that, in the development of myopia, melanopsin might be involved in the transmission and regulation of visual information. However, the expression and role of melanopsin in FDM and LIM, as well as their recovery stages, are not explored before, which motivated this study. Here, we used Immunofluorescence and western blotting methods to detect the expression of the melanopsin protein in the retina of the guinea pig in the FDM and LIM models. Also, during FDM and LIM recovery periods, the melanopsin expression was examined.
Potential mechanisms of retinal ganglion cell type‐specific vulnerability in glaucoma
Published in Clinical and Experimental Optometry, 2020
Anna Ym Wang, Pei Ying Lee, Bang V Bui, Andrew I Jobling, Ursula Greferath, Alice Brandli, Michael A Dixon, Quan Findlay, Erica L Fletcher, Kirstan A Vessey
In understanding intrinsic mechanisms of RGC vulnerability it is also helpful to examine mechanisms that make RGCs more resilient to damage. In metabolic diseases of patients and mouse models of Leber's hereditary optic neuropathy and dominant optic atrophy, intrinsically light‐sensitive melanopsin RGCs were preserved.2015 Melanopsin RGCs are large RGCs that express the light‐sensitive protein melanopsin, and project to the hypothalamic suprachiasmatic nucleus which is involved in control of circadian rhythms. In optic nerve transection or crush injury, melanopsin RGCs were more resistant than other RGCs to cell death and constituted the majority of the remaining RGC population.2015 Melanopsin RGCs were also resistant to cell death during IOP injury,2006 despite having shown reduced dendritic branching.2015
Effect of pinealectomy on the circadian clock of the chick retina under different monochromatic lights
Published in Chronobiology International, 2019
Jiang Bian, Zixu Wang, Yulan Dong, Jing Cao, Yaoxing Chen
Avian retina possess a self-sustained molecular clock (Bailey et al. 2004; Chaurasia et al. 2006; Chong et al. 2003; Singh et al. 2013; Toller et al. 2006). As the key regulatory enzyme in the melatonin biosynthetic pathway, the AANAT contains an E-box enhancer element (Chong et al. 2000), which can be activated by CLOCK/BMAL1 heterodimer and may provide a link from the circadian clock to AANAT transcription. In comprehensive analysis of the phases (Figure 4), the acrophase of melanopsin was in advance of positive-regulating clock gene cBmal1, the cBmal1 showed a phase advance of approximately 6–8 h relative to cAanat and retina melatonin, meanwhile, the acrophases of negative clock genes followed cAanat and melatonin. These results seem to indicate a regulatory relationship of melanopsin, clock genes and melatonin.