Altitude, temperature, circadian rhythms and exercise
Adam P. Sharples, James P. Morton, Henning Wackerhage in Molecular Exercise Physiology, 2022
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.
The Pineal Gland Energy Transducer
Len Wisneski in The Scientific Basis of Integrative Health, 2017
One possibility is cryptochrome, the vitamin B-based, light-absorbing protein pigment in the eye and SCN, which is sensitive to blue light (Ivanchenko et al., 2001). It is found both in the retinal ganglion and the inner retina (Sancar, 2000). Cryptochrome was discovered in plants and identified as the protein that allows plants to bend toward light. Other possible photoreceptors are the nonrod, noncone vitamin A-based opsin photopigments, such as melanopsin (Provencio et al., 1998). The retinal distribution of melanopsin cells bears a striking resemblance to the retinal cells known to connect to the SCN in rodents. The inner retina seems to be the only mammalian site at which melanopsin is expressed, suggesting a role in nonvisual photoreceptive tasks (Provencio et al., 2000). So, in the end, melanopsin and cryptochrome are viable, but unconfirmed, photoreceptor candidates of the mammalian clock.
Lifestyle factors
Jane Hanley, Mark Williams in 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
By the wearing of negative lenses, the image focus behind the retina. The compensatory axial growth of the eye caused then, and LIM was constructed eventually. Previously, it has been reported that myopia caused by long-wavelength 530 nm green light is because of the movement of the eyeball to the back of the retina induced by aberration,25 which is consistent with the nature of myopia induced by negative lenses. In our work, we found that melanopsin protein expression decreased in the guinea pig retina after LIM. This is consistent with the 530 nm green light-induced myopia which was reported in the guinea pig previously.27 The characteristic absorption spectrum of melanopsin is 480 nm,28 and the peak of blue light-induced circadian rhythm is also 480 nm. Previous studies had reported that short-wavelength 480 nm blue light could inhibit the occurrence and development of myopia and protect myopia.29 Melanopsin is a retinal visual opsin that is sensitive to blue light and insensitive to long wavelength (>540nm) light. Therefore, we speculated that the decrease in melanopsin expression induced by the negative lens in our study might lead to the decrease in blue light absorption by the retina.
Dysregulated light/dark cycle impairs sleep and delays the recovery of patients in intensive care units: A call for action for COVID-19 treatment
Published in Chronobiology International, 2022
Diego Golombek, Seithikurippu Pandi-Perumal, Ruth E. Rosenstein, Per Olof Lundmark, David Warren Spence, Daniel P. Cardinali, Russel J. Reiter, Gregory M. Brown
The importance of optimal circadian rhythms for preserving good overall health is well established (Cable et al. 2021). These rhythms, with a period length of ~24 h, are embedded in every regulatory function of the body and have profound implications for health maintenance and treatment. Timing of exposure to environmental light has clear effects on pineal melatonin synthesis and secretion and, in turn, on circadian regulation. The rhythm of the master circadian rhythm pacemaker (the suprachiasmatic nuclei [SCN]) is entrained by environmental light, which is mediated by the photopigment melanopsin, located in a tiny group of light-sensitive retinal ganglion cells, the axons of which project to the SCN as well as to areas regulating sleep and pupillary responses (Hastings et al. 2019). Actions on the SCN ultimately have broad physiological consequences.
Tasimelteon for treating non-24-h sleep-wake rhythm disorder
Published in Expert Opinion on Pharmacotherapy, 2019
Shohei Nishimon, Mari Nishimon, Seiji Nishino
Circadian rhythms are behavioral, physiological, and biochemical processes that occur close to a 24-h period [1]. Individuals who have normal oscillations can maintain sleep-wake cycle, performance pattern, and hormone secretions [2]. Such rhythms are synchronized by the master biological clock in the suprachiasmatic nucleus (SCN) [3,4]. Interestingly, although the circadian period of the SCN is slightly over 24 h in humans [5], light information can entrain circadian rhythms through the intrinsically photosensitive retinal ganglion cells (ipRGCs), which are distinguished from the retinal rod and cone cells in visual perception [6,7]. In particular, melanopsin, which belongs to the opsin family of G-protein coupled receptors (GPCRs), regulates the circadian clock and pupil diameters, and it plays a crucial role as a photopigment [8]. Anatomically, light information that is input to the SCN via the retinohypothalamic tract (RHT) is relayed to the pineal gland by the multisynaptic pathway, including the paraventricular nucleus, intermediolateral cell column, and superior cervical ganglion (SCG) [9].
Related Knowledge Centers
- Cone Cell
- Opsin
- Photopigment
- Retina
- Retinal
- Rhodopsin
- Rod Cell
- Suprachiasmatic Nucleus
- Vertebrate Visual Opsin
- Intrinsically Photosensitive Retinal Ganglion Cell