Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.
  • Vitamin A2-based photopigments within the pineal gland of a fully terrestrial vertebrate.

    27 November 2018

    Fully terrestrial vertebrates were previously thought to exclusively employ vitamin A1 to generate visual pigments. However, recent studies on the visual system of the lizard Anolis carolinensis have shown that its visual pigments are vitamin A2-based. This unexpected result prompted an investigation of the pineal photopigments in this species [13]. HPLC analysis has shown that this extraretinal photoreceptor also exclusively utilizes a vitamin A2-derived chromophore. The adaptive significance of this chromophore within the pineal is unclear. The extended long wavelength sensitivity characteristic of vitamin A2-based visual pigment systems may enhance important visual tasks such as prey detection or mate selection [13]. A similar argument cannot be made for the pineal, whose role is not image formation, but rather detection of the irradiance changes associated with dawn and dusk. We suggest that the pineal may passively utilize whatever retinoids have been adaptively selected by the visual system.

  • Sleep differences in the UK between 1974 and 2015: Insights from detailed time diaries.

    27 November 2018

    It is often stated that sleep deprivation is on the rise, with work suggested as a main cause. However, the evidence for increasing sleep deprivation comes from surveys using habitual sleep questions. An alternative source of information regarding sleep behaviour is time-use studies. This paper investigates changes in sleep time in the UK using the two British time-use studies that allow measuring "time in bed not asleep" separately from "actual sleep time". Based upon the studies presented here, people in the UK sleep today 43 min more than they did in the 1970s because they go to bed earlier (~30 min) and they wake up later (~15 min). The change in sleep duration is driven by night sleep and it is homogeneously distributed across the week. The former results apply to men and women alike, and to individuals of all ages and employment status, including employed individuals, the presumed major victims of the sleep deprivation epidemic and the 24/7 society. In fact, employed individuals have experienced a reduction in short sleeping of almost 4 percentage points, from 14.9% to 11.0%. There has also been a reduction of 15 percentage points in the amount of conflict between workers work time and their sleep time, as measured by the proportion of workers that do some work within their "ideal sleep window" (as defined by their own chronotype).

  • Teleost multiple tissue (tmt) opsin: a candidate photopigment regulating the peripheral clocks of zebrafish?

    27 November 2018

    Isolated organs and cell lines from zebrafish exhibit circadian oscillations in clock gene expression that can be entrained to a 24-h light/dark cycle. The mechanism underlying this cellular photosensitivity is unknown. We report the identification of a novel opsin family, tmt-opsin, that has a genomic structure characteristic of vertebrate photopigments, an amino acid identity equivalent to the known photopigment opsins, and the essential residues required for photopigment function. Significantly, tmt-opsin is expressed in a wide variety of neural and non-neural tissues, including a zebrafish embryonic cell line that exhibits a light entrainable clock. Collectively the data suggest that tmt-opsin is a strong candidate for the photic regulation of zebrafish peripheral clocks.

  • Diminished pupillary light reflex at high irradiances in melanopsin-knockout mice.

    27 November 2018

    In the mammalian retina, a small subset of retinal ganglion cells (RGCs) are intrinsically photosensitive, express the opsin-like protein melanopsin, and project to brain nuclei involved in non-image-forming visual functions such as pupillary light reflex and circadian photoentrainment. We report that in mice with the melanopsin gene ablated, RGCs retrograde-labeled from the suprachiasmatic nuclei were no longer intrinsically photosensitive, although their number, morphology, and projections were unchanged. These animals showed a pupillary light reflex indistinguishable from that of the wild type at low irradiances, but at high irradiances the reflex was incomplete, a pattern that suggests that the melanopsin-associated system and the classical rod/cone system are complementary in function.

  • Photic regulation of Fos-like immunoreactivity in the suprachiasmatic nucleus of the mouse.

    27 November 2018

    In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus functions as the primary pacemaker of the circadian system. Light has been shown to induce Fos-like immunoreactivity (Fos-LI) in the SCN of rats and hamsters. The purpose of the present study was to evaluate extensively the effect of light on Fos-LI in the mouse SCN. Brief pulses of light administered to animals otherwise in constant darkness were found to induce Fos-LI. This photic induction was unaffected by the rd mutation, which causes the profound loss of photoreceptors but fails to affect circadian responses to light. Light regulation of Fos-LI was dependent upon the phase of the circadian cycle in which the light pulse was administered. Phases at which light causes phase shifts of the circadian system were permissive for Fos-LI induction (CT 16 and 24), while phases in which light does not cause phase shifts were not permissive (CT 6 and 9). The time course of the induction at CT 16 was also described. In a light/dark cycle, Fos-LI was found to be rhythmically expressed with Fos-LI elevated soon after the lights came on but remaining low throughout the rest of the cycle. However, this rhythm is a direct consequence of the light because in constant darkness Fos-LI was always low. These results have implications regarding the possible functional roles of Fos in the circadian system and add to our understanding of light regulation of circadian physiology in the mouse.

  • Circadian oscillation of photopigment transcript levels in the mouse retina.

    27 November 2018

    The mammalian retina contains an autonomous circadian oscillator that can sustain rhythms in outer segment disc shedding and melatonin synthesis even in the absence of cues from the central oscillator in the suprachiasmatic nucleus (SCN). The present investigation aimed to ascertain whether the steady-state levels of rod and cone opsin mRNA exhibited a circadian oscillation in the mouse, and if so, to characterise this oscillation with regard to phase. Retinas were collected from mice free-running in constant darkness at circadian times (CT) 0, 4, 12, 16, and 20. RNA was extracted for the production of Northern blots, which were sequentially hybridised with probes for alpha-tubulin (control), ultraviolet opsin, and rhodopsin. Whereas no significant oscillation was detected in the levels of alpha-tubulin, the levels of both ultraviolet opsin and rhodopsin transcripts oscillated with an amplitude of at least 3-fold. The highest levels were found at around CT12 (which corresponds to the subjective evening, the time of activity onset in the mouse). These results show that the levels of rod and cone photopigment mRNA are under circadian control. The significance of the rhythms and their phasing is discussed. These findings have potential clinical implications both with regard to nocturnal light treatment of phase asynchrony, and in the timing of chemo- and radiotherapy.

  • Circadian clocks: A cry in the dark?

    27 November 2018

    Cryptochrome proteins are key components of the circadian systems of both Drosophila and mammals. In Drosophila, they appear to be responsible for the entrainment of the circadian clock by the light-dark cycle, while in mammals they perform an important role in rhythm generation itself.

  • Photopigments and photoentrainment in the Syrian golden hamster.

    27 November 2018

    The Syrian golden hamster (Mesocricetus auratus) is an important model in the study of circadian rhythms. However, as in other mammals, little is known about the photoreceptors that mediate circadian entrainment. Using immunocytochemistry and RNA blot hybridization, we found no evidence for the presence of blue-/UV-sensitive opsin. In contrast, green-sensitive cone opsin was demonstrated in the retina both by immunocytochemistry and reverse-transcription PCR. When used as a probe in RNA blot hybridization, this PCR fragment labelled one transcript (5.8 kb) in hamster retinal RNA. These findings are in accordance with preliminary data from other investigators using electroretinography, which showed one cone-mediated photoreceptive mechanism with a maximum sensitivity of 501 nm, but none at shorter wavelengths. However, we found that non-saturating pulses of ultraviolet radiation (357 nm) caused phase shifts in locomotor behaviour. These results corroborate earlier reports that UV radiation can regulate the photoperiodic response in this animal. Having confirmed these apparently contradictory earlier reports, we discuss the mechanisms that might create a UV-triggered non-visual response in a green cone monochromat. Finally, we propose the use of the Syrian golden hamster as a model for photoreceptor development and function in the absence of S/UV cones.

  • Rhodopsin-like sensitivity of extra-retinal photoreceptors mediating the photoperiodic response in quail.

    27 November 2018

    It has been known for some 50 years that birds use photoreceptors in or near the hypothalamus to mediate the photoperiodic responses that control seasonal breeding. So far, however, attempts to identify the photopigment by determining an action spectrum have failed. The problems stem from the selective filtering of light by the tissues surrounding the photoreceptors and the need to deliver defined amounts of light over the days or weeks required to induce a quantitative measure of photostimulation. Here we have developed a technique which produces a quantitative action spectrum for the photoperiodic response in the Japanese quail; the results indicate the presence of a rhodopsin photopigment with a peak sensitivity of approximately 492 nm. The photoreceptors exhibit a level of sensitivity comparable with that of vertebrate visual pigments. We conclude that the brain photoreceptors of birds are based on a rhodopsin/rhodopsin-like photopigment.