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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 retina contains three types of photoreceptors: rods, cones and intrinsically photosensitive retinal ganglion cells (ipRGCs). Rods are responsible for vision at low light levels (scotopic vision). Cones are active at higher light levels (photopic vision), are capable of color vision, and are responsible for high spatial acuity. Ganglion cells collect electrical messages of the visual signals from the two layers of neurons and serve as the final neuronal output of the retina [5]. The mammalian retina is not only a light-sensing tissue that conveys photic information to the brain, but it also has an intrinsic circadian system.
Air Pollution
Published in William J. Rea, Kalpana D. Patel, Air Pollution and the Electromagnetic Phenomena as Incitants, 2018
William J. Rea, Kalpana D. Patel
According to Rea, M.S. and M.G Figueiro,13 photoreceptors in the mammalian retina convert light into neural signals sent via the retinohypothalamic tract (RHT) to the master clock in the SCN. The well-known visual photoreceptors, rods (operating at low, scotopic light levels) and cones (operating at high, photopic light levels) and a recently discovered intrinsically photosensitive retinal ganglion cell (ipRGC)19 all participate in the conversion of retinal light exposures into neural signals for the SCN, a phenomenon called circadian phototransduction.20
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.
Exploring the effects of large-area dorsal skin irradiation on locomotor activity and plasm melatonin level in C3H/He mice
Published in Chronobiology International, 2021
Xuewei Fan, Zeqing Chen, Wenqi Li, Haokuan Qin, Shijie Huang, Zhicheng Lu, Yinghua Li, Muqing Liu
In addition to image-forming function, light can also regulate mammalian growth, reproduction, migration and circadian rhythm in nonvisual ways. In terms of circadian clock system, light is mainly received by intrinsically photosensitive retinal ganglion cells (ipRGC) in the retina and transmit to suprachiasmatic nucleus (SCN) (Claustrat et al. 2005a). The master circadian pacemaker within the SCN relays the temporal information to whole body through nerves, fluids, temperature and food intake signals, so that peripheral clock oscillation can be synchronized to the central clock (Brown and Azzi 2013; Mohawk et al. 2012). For a long time, this hierarchical control structure was considered to be dominated only by SCN. But now this view is gradually challenged. In the absence of rods, cones, and melanopsin, the retina could be directly synchronized by environmental light (Buhr and Van Gelder 2014; Buhr et al. 2015; Tosini and Menaker 1996). Recently, studies have further confirmed that skin of mammals had direct photosensitivity (Haltaufderhyde et al. 2015; Kusumoto et al. 2020; Suh et al. 2020; Tsutsumi et al. 2009), and could even be entrained directly by light both in vitro and in vivo (Buhr et al. 2019). These indicated that peripheral circadian clock of some directly exposed tissues, such as skin, retina and cornea, was probably controlled by both the SCN and external light cues.
Should “Retro-ocular Pain, Photophobia and Visual Acuity Loss” Be Recognised as a Distinct Entity? The ROPPVAL Syndrome
Published in Neuro-Ophthalmology, 2021
Francesco Pellegrini, Erika Mandarà, Daniele Brocca
Photophobia is defined as a painful sensation to light exposure. Recently, a novel population of retinal neurons, intrinsically photosensitive retinal ganglion cells (IPRGCs), have been identified as photophobia transducers in the eye.13 Notably, these IPRGCs project onto trigeminal neurons14 and pain nuclei in the thalamus,15,16 which are also involved in migraine pathogenesis. We believe that “stimuli”, like those involved in migraine, may trigger the trigeminal nerve fibres which collect painful light sensations from the eye when activated by IPRGCs. We believe that the ciliary ganglia located in orbital-fat behind the globe may play a major role in determining this stereotyped syndrome, because of the relief of symptoms when amitriptyline or cyclopentolate drops are administered. We can speculate that activated trigeminal pain-sensing fibres and light-activated fibres may affect parasympathetic neurons and/or vice versa. Cyclopentolate is an anticholinergic drug, thus paralyses the iris sphincter constrictor and ciliary body muscles. Cycloplegia is commonly used in ophthalmology to reduce inflammation and pain due to different ocular conditions such as iritis where the ciliary body over-contraction is the main cause of pain.