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 visual pigments in fully terrestrial vertebrates.

    27 November 2018

    As part of a broad study of the ocular and extraocular photoreceptors of reptiles, we have used high performance liquid chromatography (HPLC) to identify the retinoids present in whole eye extracts of the arboreal lizard Anolis carolinensis and the non-arboreal ruin lizard Podarcis sicula. Unexpectedly, only vitamin A2-derived chromophore was detected in Anolis, while a mixture of vitamin A1- and vitamin A2-derived chromophores was detected in Podarcis. These are the first examples of fully terrestrial vertebrates using vitamin A2-derived chromophore for visual pigment generation. Furthermore, microspectrophotometric (MSP) data for Anolis show a class of photoreceptor having a visual pigment with maximum absorbance at about 625 nm, some 40 nm further into the red than has been found in any terrestrial vertebrate examined to date.

  • Immunohistochemical demonstration of marked changes in the LHRH system of photosensitive and photorefractory European starlings (Sturnus vulgaris).

    27 November 2018

    Immunocytochemistry was used to determine the effects of photoperiod on the LHRH neurosecretory system in the brain of male European starlings. In this species, as in other birds, reproduction is triggered by long daylengths but continued exposure leads to photorefractoriness and to a complete shut-down of the reproductive system. These effects are thought to be mediated through changes in the secretion of LHRH. In starlings exposed to a photoperiod of 11 h light:13 h darkness (11L:13D) and with fully developed testes there was strong immunostaining of both LHRH perikarya (n = 522 +/- 43 S.E.M.) and fibres. Photosensitive short-day (8L:16D) starlings with undeveloped testes had an almost identical distribution of strongly immunoreactive perikarya (n = 523 +/- 62) but there were fewer fibres. In the median eminence, fibre number was reduced significantly (P less than 0.01) by some 30%. In long-day (18L:6D) photorefractory starlings with fully regressed testes there was an even more obvious change in the LHRH system. Perikarya were only weakly immunoreactive and there was a significant (P less than 0.01) reduction in mean diameter from 10 to 6.5 micron. In addition, there was a significant (P less than 0.05) reduction in cell number (312 +/- 62), although this may well result from the fact that some weakly stained cells fell below the limits of resolution and could not be counted. LHRH fibres disappeared almost entirely from the median eminence, and were not visible elsewhere in the brain. The higher neural pathways regulating photorefractoriness induced by long days are unknown but clearly both production of LHRH in the perikarya and release/storage of LHRH in the terminals is being profoundly modified.

  • Adaptive loss of ultraviolet-sensitive/violet-sensitive (UVS/VS) cone opsin in the blind mole rat (Spalax ehrenbergi).

    27 November 2018

    In previous studies, fully functional rod and long-wavelength-sensitive (LWS) cone photopigments have been isolated from the eye of the subterranean blind mole rat (Spalax ehrenbergi superspecies). Spalax possesses subcutaneous atrophied eyes and lacks any ability to respond to visual images. By contrast this animal retains the ability to entrain circadian rhythms of locomotor behaviour to environmental light cues. As this is the only known function of the eye, the rod and LWS photopigments are thought to mediate this response. Most mammals are dichromats possessing, in addition to a single rod photopigment, two classes of cone photopigment, LWS and ultraviolet-sensitive/violet-sensitive (UVS/VS) with differing spectral sensitivities which mediate colour vision. In this paper we explore whether Spalax is a dichromat and has the potential to use colour discrimination for photoentrainment. Using immunocytochemistry and molecular approaches we demonstrate that Spalax is a LWS monochromat. Spalax lacks a functional UVS/VS cone photopigment due to the accumulation of several deleterious mutational changes that have rendered the gene nonfunctional. Using phylogenetic analysis we show that the loss of this class of photoreceptor is likely to have arisen from the visual ecology of this species, and is not an artefact of having an ancestor which lacked a functional UVS/VS cone photopigment. We conclude that colour discrimination is not a prerequisite for photoentrainment in this species.

  • Entrainment of circadian programs.

    27 November 2018

    Of the three defining properties of circadian rhythmicity--persisting free-running rhythm, temperature compensation, and entrainment--the last is often poorly understood by many chronobiologists. This paper gives an overview of entrainment. Where have we been? Where are we now? Whence should we be going? Particular emphasis is given to a discussion of the Discrete vs. Continuous models for entrainment. We provide an integrated mechanism for entrainment from a limit-cycle perspective.

  • Extraretinal photoreceptors and their regulation of temporal physiology.

    27 November 2018

    The extraretinal photoreceptors of non-mammalian vertebrates play an important role in the regulation of temporal physiology. Both the regulation of circadian clocks and the photoperiodic response of many animals depend upon the photic information provided by these receptors. Since their discovery at the beginning of this century, and despite their importance, extraretinal photoreceptors have remained poorly understood. Until recently, their cellular location within the central nervous system, and the nature of the photopigments they use, remained a mystery. Antibodies directed against rod or cone photopigment proteins have been used in immunocytochemical procedures to localize extraretinal photoreceptors. However, findings have been confusing. The use of molecular approaches has led to the identification of several new photopigment gene families. Significantly, these genes are not expressed in the rods and cones of the retina, but in many sites within the central nervous system. Moreover, molecular approaches have proved useful in clarifying some of the earlier immunocytochemical results. Collectively, the recent findings show that non-mammalian vertebrates possess multiple extraocular photoreceptors that may express novel, rod or even cone photopigments. The future challenge is to link these photoreceptors with circadian and photoperiodic physiology.

  • Photopigments and circadian systems of vertebrates.

    27 November 2018

    In the retinal degeneration (rd) mouse the absence of rod cells and the progressive loss of cones does not result in a decrease in circadian phase shifting responses to light. By contrast, rd/rd mice are unable to perform simple visual tasks. In addition, rodless transgenic mice, and mice homozygous for the retinal degeneration slow (rds) mutation, show unattenuated circadian responses to light. Collectively these data suggest that cone cells lacking outer segments are sufficient to maintain normal circadian responses to light, or some unidentified photoreceptor within the retina. An action spectrum for circadian responses to light in rd/rd mice, and molecular analysis of retinally degenerate mice and blind mole rat eyes, suggests the involvement of a mid-to-long wavelength sensitive cone opsin in photoentrainment. Extraocular photoreceptors of non-mammalian vertebrates are currently being analyzed in order to identify functional and evolutionary similarities between visual and non-visual photoreceptor systems.

  • Photic entrainment of the circadian clock: from Drosophila to mammals.

    27 November 2018

    Entrainment is as fundamental to an organism's circadian timing as are the molecular mechanisms involved in the functioning of the intracellular clock oscillator. In nature, one of the principle, although not the only, circadian entraining stimulus (Zeitgeber) is provided by the daily light--dark cycles. In animals, the visual processing apparatus alone is inadequate to accomplish the task of transducing circadian photic signals to the clockwork machinery. In fact, it is ever more appreciated by circadian biologists that organisms as divergent as plants and mammals have evolved a wonderfully complex array of partly redundant specializations which can guarantee the precise alignment of biological and environmental time. Research in circadian biology is cruising at such a rate that attempts to review the state of the art can only hope, at best, to provide a snapshot of the speeding cruiser from its wake. This paper will hopefully provide a reasonably sharp portrayal of what is at hand.

  • Expression of developmentally defined retinal phenotypes in the histogenesis of retinoblastoma.

    27 November 2018

    Retinoblastoma, the most common intraocular tumor of childhood, is a malignant neoplasm that arises during retinal development. The embryonal cell target for neoplastic transformation is not yet clearly defined. To better understand the histogenetic potential of this tumor, the expression of photoreceptor and glial cell-associated proteins were examined in 22 primary retinoblastomas. Interphotoreceptor retinol-binding protein (IRBP), cone and rod opsins were selected as the photoreceptor specific proteins due to their different temporal patterns of expression during normal retinal development. Neoplastic Müller cell differentiation, and non-neoplastic reactive astrocytes were identified using cellular retinaldehyde binding-protein (CRAlBP), and glial fibrillary acidic protein (GFAP), respectively. Photoreceptor proteins were present in 16 cases and showed different cellular patterns of expression. IRBP and cone opsin were usually abundant. Although rod opsin was clearly identified in eight tumors, its expression was more restricted than either IRBP or cone opsin. This differential pattern of expression, opposite to the normal pattern of photoreceptor gene expression in the adult retina, corresponded to a marked decrease in mRNA for rod opsin. Cone opsin and IRBP colocalized in fleurettes demonstrating that neoplastic human cone cells are capable of IRBP synthesis. Müller cell differentiation was present in 12 of the 16 cases in which photoreceptor proteins were detected. In contrast, GFAP was only present in reactive, stromal astrocytes associated with blood vessels. Our data suggest that the retinoblastoma has the histogenetic potential of the immature neural retinal epithelium which can give rise to both photoreceptor and Müller cell lineages. The differential expression of cone and rod phenotypes in retinoblastoma is consistent with the "default" mechanism of cone cell differentiation.

  • A comparison of some photoreceptor characteristics in the pineal and retina. II. The Djungarian hamster (Phodopus sungorus).

    27 November 2018

    A rod-specific antiserum was used to immunolabel elements within the retina and pineal of the adult Djungarian hamster and Welsh Mountain sheep. In the retina immunostaining was localized to the outer segments and perikarya of photoreceptor cells, while in the pineal limited numbers of labelled pinealocytes were scattered throughout the gland. An enzyme-linked immunosorbent assay (ELISA) was then used to obtain a quantitative measure of rod opsin in total eye and pineal extracts from the Djungarian hamster. Total rod opsin (+/- SEM) in the eye was measured by absorbance spectroscopy (1.88 +/- 0.10 nmoles opsin/eye) and by using the ELISA (1.75 +/- 0.02 nmoles opsin/eye). The opsin content from a total of 56 pineals gave a mean value of 0.34 +/- 0.01 pmoles opsin/pineal. Since a functional photopigment should be coupled in a 1:1 ratio to a chromophore, we investigated whether we could identify 11-cis and/or all-trans retinaldehydes in the pineal extracts by quantitative extraction and HPLC analysis as the oximes. No evidence of 11-cis or all-trans retinaloxime could be found, the chromatograms were indistinguishable from those produced by extracts of cortical brain tissue. We conclude that the opsin present within the adult hamster pineal is not coupled to the common vertebrate retinaldehyde chromophore, and as a result, is unlikely to be part of a functional photopigment.

  • OxPPOPS Hernia

    15 January 2013

  • OxPPOPS Breast Cancer

    15 January 2013

  • SILENCE

    13 April 2016

    The Sleep in the Intensive Care Unit: Lowering Elements of Noise in the Critical Care Environment (SILENCE) research programme is funded by a feasibility study grant awarded by the NIHR Research for Patient Benefit scheme, and is sponsored by the University of Oxford. Final results are expected late 2018.

  • SILENCE

    13 April 2016

  • SILENCE

    13 April 2016

    The SILENCE programme is a series of linked research projects. Updates on progress will be posted here.

  • SILENCE

    13 April 2016

  • SILENCE

    21 April 2017

    Contact details for the SILENCE research programme

  • Non-contact vital signs monitoring

    20 September 2016

    The non-contact vital signs monitoring (NVSM) study was a joint collaboration between the Department of Engineering, the Nuffield Department of Clinical Neurosciences, and Oxehealth Ltd.

  • NVSM

    25 October 2016

    Significant project milestones will be displayed here

  • NVSM

    20 September 2016

    Contact details for the non-contact vital signs monitoring research team

  • Retinal Cell Biology and Degeneration

    15 January 2013

    NLO

    The discovery of a novel inner retinal photoreceptor cell, driving non-visual functions, has had a significant impact on the retinal neuroscience field. My research focuses on understanding the physiology and function of these photosensitive retinal ganglion cells.

  • Oxford Smart Specs Research Group

    13 June 2014

    DCN NLO

    We are developing a set of 'smart' electronic glasses (‘smart specs’) to enhance sight for the visually impaired.

  • Vision Group

    13 February 2014

    FMRIB NLO

    We use brain imaging techniques to investigate the human visual system, both in its normal state and in disease and disorder.

  • FMRIB P.A.I.N Group

    19 January 2015

    FMRIB NDA

    The Pain Analgesia/Anaesthesia Imaging Neuroscience group is a multidisciplinary team of scientists and clinicians. We research how the human central nervous system generates and modulates painful experiences in acute and chronic settings.

  • NeuroMetrology Lab

    13 April 2016

    DCN NDCN

    Our objective is to develop ways of accurately measuring neurological disorders such as Parkinson's disease.

  • Glioma Neurosurgery Research Group

    11 February 2016

    FMRIB NDCN

    Our research aims to understand the characteristics of individual brain tumours, combining cutting edge brain imaging, molecular neuropathology and neurosurgical techniques to develop personalized approaches for first-line cancer surgery.

  • Parkinson’s Neuropathology Group

    23 February 2016

    DCN

    We study why certain neuronal populations are vulnerable to neurodegeneration in Parkinson’s disease brain and whether pathological changes seen in the peripheral tissues mirror or precede what is ultimately seen in the brain, and how this can be used to develop biomarkers.

  • Neuro-Endocrinology Research Group

    11 February 2016

    DCN

    This cross-disciplinary research group links neuropathology, endocrinology and molecular genetics to explore how the genetics and epigenetics of pituitary tumours influences clinical characteristics and to identify targets for therapeutic intervention.

  • Large Artery Disease

    26 August 2016

    CPSD

    CPSD runs several research studies looking into the causes, investigation, and management of large artery atherosclerosis, carotid stenosis, vertebral artery disease and intracranial atherosclerosis.