Extraretinal Photoreceptors Research Articles

The Blue-Light Photoreceptor CRYPTOCHROME Is Expressed in a Subset of Circadian Oscillator Neurons in the Drosophila CNS

In the fruit fly Drosophila melanogaster, CRYPTOCHROME (CRY) functions as a photoreceptor to entrain circadian oscillators to light-dark cycles and as a transcription factor to maintain circadian oscillator function in certain peripheral tissues. Given the importance of CRY to circadian clock function, we expected this protein to be expressed in all oscillator cells, yet CRY cellular distribution and subcellular localization has not been firmly established. Here we investigate CRY spatial expression in the brain using a newly developed CRY antibody and a novel set of cry deletion mutants. We find that CRY is expressed in s-LNvs, l-LNvs, and a subset of LNds and DN1s, but not DN2s and DN3s. CRY is present in both the nucleus and the cytoplasm of these neurons, and its subcellular localization does not change over the circadian cycle. Although CRY is absent in DN2s and DN3s, cry promoter activity and/or cry mRNA accumulation can be detected in these neurons, suggesting that CRY levels are regulated posttranscriptionally. Oscillators in DN2s and DN3s entrain to environmental light-dark cycles, which implies that they are entrained indirectly by retinal photoreceptors, extraretinal photoreceptors, or other CRY-expressing cells.

Inner retinal and extraretinal photoreceptor up-dates: Isolation and characterisation of VA opsin in Xenopus and the chicken

Inner retinal and extraretinal photoreceptor up-dates: Isolation and characterisation of VA opsin in Xenopus and the chicken

Non-visual photoreception by a variety of vertebrate opsins.

Extraretinal photoreceptors in animals are involved in a variety of physiological functions such as photo-entrainment of circadian rhythm, photoperiodicity and body colour change. We have identified pinopsin in the chicken pineal gland as a typical 'non-visual' photoreceptive molecule. Pinopsin with bound 11-cis-retinal shows a blue-light sensitivity (lambda max = 468 nm), and it may play a role in synchronizing the phase of the endogenous circadian oscillator with an environmental dark-light cycle. Pinopsin is not a unique pineal opsin in animals. In the zebrafish, we have detected expression of two rhodopsin genes, the nucleotide sequences of which are very similar but distinct from each other. One is canonical rhodopsin expressed in the retina, and the other is expressed in the pineal gland. The latter gene is widely distributed among teleosts, and we named it 'exo-rhodopsin' after extraocular rhodopsin. On the other hand, our effort to identify the 'deep brain opsin' responsible for the photoperiodic gonadal response resulted in the identification of two kinds of opsins; pinopsin in the toad anterior preoptic nucleus and rhodopsin in the pigeon lateral septum. Both of these opsins are localized in the cerebrospinal fluid-contacting neurons in the brain of the two animals. We also identified VAL opsin in zebrafish retinal horizontal cells, which have not been considered as photoreceptive cells. It has become evident that animals employ a wide variety of photoreceptive molecules for 'non-visual' purposes.

Hofbauer-Buchner Eyelet Affects Circadian Photosensitivity and Coordinates TIM and PER Expression in Drosophila Clock Neurons

Extraretinal photoreception is a common input route for light resetting signals into the circadian clock of animals. In Drosophila melanogaster, substantial circadian light inputs are mediated via the blue light photoreceptor CRYPTOCHROME (CRY) expressed in clock neurons within the brain. The current model predicts that, upon light activation, CRY interacts with the clock proteins TIMELESS (TIM) and PERIOD (PER), thereby inducing their degradation, which in turn leads to a resetting of the molecular oscillations within the circadian clock. Here the authors investigate the function of another putative extraretinal circadian photoreceptor, the Hofbauer-Buchner eyelet (H-B eyelet), located between the retina and the medulla in the fly optic lobes. Blocking synaptic transmission between the H-B eyelet and its potential target cells, the ventral circadian pacemaker neurons, impaired the flies' ability to resynchronize their behavior under jet-lag conditions in the context of nonfunctional retinal photoreception and a mutation in the CRY-encoding gene. The same manipulation also affected synchronized expression of the clock proteins TIM and PER in different subsets of the clock neurons. This shows that synaptic communication between the H-B eyelet and clock neurons contributes to synchronization of molecular and behavioral rhythms and confirms that the H-B eyelet functions as a circadian photoreceptor. Blockage of synaptic transmission from the H-B eyelet in the presence of functional compound eyes and the absence of CRY also results in increased numbers of flies that are unable to synchronize to extreme photoperiods, supplying independent proof for the role of the H-B eyelet as a circadian photoreceptor.

Veela defines a molecular link between Cryptochrome and Timeless in the light-input pathway to Drosophila 's circadian clock

Organisms use the daily cycles of light and darkness to synchronize their internal circadian clocks with the environment. Because they optimize physiological processes and behavior, properly synchronized circadian clocks are thought to be important for the overall fitness. In Drosophila melanogaster, the circadian clock is synchronized with the natural environment by light-dependent degradation of the clock protein Timeless, mediated by the blue-light photoreceptor Cryptochrome (Cry). Here we report identification of a genetic variant, Veela, which severely disrupts this process, because these genetically altered flies maintain behavioral and molecular rhythmicity under constant-light conditions that usually stop the clock. We show that the Veela strain carries a natural timeless allele (ls-tim), which encodes a less-light-sensitive form of Timeless in combination with a mutant variant of the F-box protein Jetlag. However, neither the ls-tim nor the jetlag genetic variant alone is sufficient to disrupt light input into the central pacemaker. We show a strong interaction between Veela and cryptochrome genetic variants, demonstrating that the Jetlag, Timeless, and Cry proteins function in the same pathway. Veela also reveals a function for the two natural variants of timeless, which differ in their sensitivity to light. In combination with the complex array of retinal and extraretinal photoreceptors known to signal light to the pacemaker, this previously undescribed molecular component of photic sensitivity mediated by the two Timeless proteins reveals that an unexpectedly rich complexity underlies modulation of this process.

Evolving visual pigments: Hints from the opsin-based proteins in a phylogenetically old “eyeless” invertebrate

Visual pigments are photosensitive receptor proteins that trigger the transduction process producing the visual excitation once they have absorbed photons. In spite of the molecular and morpho-functional complexity that has characterized the development of animal eyes and eyeless photoreceptive systems, opsin-based protein family appears ubiquous along metazoan visual systems. Moreover, in addition to classic rhodopsin photoreceptors, all Metazoa have supplementary non-visual photosensitive structures, mainly located in the central nervous system, that sense light without forming an image and that rather regulate the organism's temporal physiology. The investigation of novel non-visual photopigments exerting extraretinal photoreception is a challenging field in vision research. Here we propose the cnidarian Hydra as a useful tool of investigation for molecular and functional differences between these pigment families. Hydra is the first metazoan owning a nervous system and it is an eyeless invertebrate showing only an extraocular photoreception, as it has no recognized visual or photosensitive structures. In this paper we provide an overview of the molecular and functional features of the opsin-based protein subfamilies and preliminary evidences in a phylogenetically old species of both image-forming and non-visual opsins. Then we give new insights on the molecular biology of Hydra photoreception and on the evolutionary pathways of visual pigments.

Synaptic connections between eyelet photoreceptors and pigment dispersing factor‐immunoreactive neurons of the blowfly Protophormia terraenovae

Studies using various mutants of Drosophila melanogaster bearing defects in their visual system, including those of the retinal and extraretinal photoreceptor systems, have indicated that the extraretinal photoreceptor known as the Hofbauer-Buchner (H-B) eyelet plays an active, if subsidiary, role in the entrainment of circadian rhythms. In the present study, in the context of unraveling the function of extraretinal photoreception on circadian rhythms and photoperiodic responses, we searched for extraretinal photoreceptors in the blowfly, Protophormia terraenovae, and found that this fly has a homolog of the H-B eyelet. In addition, we show morphologically direct synaptic connections between the eyelet of P. terraenovae (called here Pt-eyelet, after the species' name) and pigment-dispersing factor (PDF)-immunoreactive neurons, which are putative circadian pacemaker neurons, by immunogold electron microscopy combined with intracellular dye injection. The Pt-eyelet was found to reside in the middle of the posterior surface of the optic lobe between the retina and the lamina, as does the H-B eyelet. This extraretinal photoreceptor was composed of at least four photoreceptor cells equipped with well-organized microvillar rhabdomeres. Rhodopsin 6-like immunoreactivity and also the response to light stimuli clearly showed the Pt-eyelet to be functional. The Pt-eyelet terminals in the accessory medulla exhibited synaptic bouton-like appearances and formed divergent multiple-contact output synapses. Synaptic contacts from the Pt-eyelet terminal to the PDF-immunoreactive neurons were identified by the presence of presynaptic ribbons and accumulated synaptic vesicles. Their possible function is discussed in relation to previous studies on circadian rhythm and photoperiodic response of P. terraenovae.

Genetic dissection of trophic interactions in the larval optic neuropil of Drosophila melanogaster

The larval visual system of Drosophila melanogaster consists of two bilateral clusters of 12 photoreceptors, which express Rhodopsin 5 and 6 (Rh5 and Rh6) in a non-overlapping manner. These neurons send their axons in a fascicle, the larval optic nerve (LON), which terminates in the larval optic neuropil. The LON is required for the development of a serotonergic arborization originating in the central brain and for the development of the dendritic tree of the circadian pacemakers, the small ventral lateral neurons (LNv) [Malpel, S., Klarsfeld, A., Rouyer, F., 2002. Larval optic nerve and adult extra-retinal photoreceptors sequentially associate with clock neurons during Drosophila brain development. Development 129, 1443–1453; Mukhopadhyay, M., Campos, A.R., 1995. The larval optic nerve is required for the development of an identified serotonergic arborization in Drosophila melanogaster. Dev. Biol., 169, 629–643]. Here, we show that both Rh5- and Rh6-expressing fibers overlap equally with the 5-HT arborization and that it, in turn, also contacts the dendritic tree of the LNv. The experiments described here aimed at determining whether Rh5- or Rh6-expressing fibers, as well as the LNv, influence the development of this serotonergic arborization. We conclude that Rh6-expressing fibers play a unique role in providing a signal required for the outgrowth and branching of the serotonergic arborization. Moreover, the innervation of the larval optic neuropil by the 5-HT arborization depends on intact Rac function. A possible role for these serotonergic processes in modulating the larval circadian rhythmicity and photoreceptor function is discussed.

Expression of UV-, blue-, long-wavelength-sensitive opsins and melatonin in extraretinal photoreceptors of the optic lobes of hawkmoths

Lepidopterans display biological rhythms associated with egg laying, eclosion and flight activity but the photoreceptors that mediate these behavioural patterns are largely unknown. To further our progress in identifying candidate light-input channels for the lepidopteran circadian system, we have developed polyclonal antibodies against ultraviolet (UV)-, blue- and extraretinal long-wavelength (LW)-sensitive opsins and examined opsin immunoreactivity in the adult optic lobes of four hawk moths, Manduca sexta, Acherontia atropos, Agrius convolvuli and Hippotion celerio. Outside the retina, UV and blue opsin protein expression is restricted to the adult stemmata, with no apparent expression elsewhere in the brain. Melatonin, which is known to have a seasonal influence on reproduction and behaviour, is expressed with opsins in adult stemmata together with visual arrestin and chaoptin. By contrast, the LW opsin protein is not expressed in the retina or stemmata but rather exhibits a distinct and widespread distribution in dorsal and ventral neurons of the optic lobes. The lamina, medulla, lobula and lobula plate, accessory medulla and adjacent neurons innervating this structure also exhibit strong LW opsin immunoreactivity. Together with the adult stemmata, these neurons appear to be functional photoreceptors, as visual arrestin, chaoptin and melatonin are also co-expressed with LW opsin. These findings are the first to suggest a role for three spectrally distinct classes of opsin in the extraretinal detection of changes in ambient light and to show melatonin-mediated neuroendocrine output in the entrainment of sphingid moth circadian and/or photoperiodic rhythms.

Photoperiodic Regulation of Seasonal Breeding in Birds

Day length-dependent breeding in birds commonly occurs in spring and summer, but may occur after exposure to complex changes in day length, as for example in transequatorial migrants. More rarely, some photoperiodic birds breed when day lengths are decreasing or are short. The flexibility of avian photoperiodic breeding strategies may reflect modifications to a common reproductive photoperiodic neuroendocrine system. This involves an extraretinal photoreceptor and a biological clock, which generates a circadian rhythm of photoinducibility to measure photoperiodic time. The pineal gland is not essential for the reproductive photoperiodic response. The current model of the avian photoperiodic response has been modified to accommodate short day breeders, by incorporating a role for seasonal changes in prolactin secretion in the termination of breeding. Analysis of the sites of expression of clock genes suggests that the biological clock for reproductive photoperiodic time measurement is in the medial basal hypothalamus. Photoperiodic signal transduction may involve a clock-dependent local conversion of thyroxine to triiodothyronine (T(3)) in the medial basal hypothalamus mediated by increased expression of the gene encoding type 2 iodothyronine deiodinase. This photoinduced increase in T(3) may stimulate the release of gonadotrophin-releasing hormone (GnRH) through thyroid hormone receptors in the median eminence. These may mediate retraction of glial cell end-feet ensheathing GnRH nerve terminals abutting onto the hypophysial portal vasculature, allowing GnRH to be released to stimulate gonadotrophin secretion.

Photic regulation of c-Fos expression in the protocerebrum of crayfish

In various species of crayfish it has been proposed that different extra-retinal photoreceptors and pacemakers could be involved in the photo entrainment mechanisms. The identity of the neural structures responsible for this phenomenon is not known. The objective of this work was to contribute to the knowledge of the neurophysiological mechanisms and structures underlying the biological clock of crayfish by studying c-fos induction in one of the neural structures proposed as a pacemaker, the brain. Using qualitative – quantitative immunohistochemical and image methods we identified light-induced c-Fos immunoreactivity in cells located in the median protocerebrum of the supraesophagic ganglion. The immunoreaction varied with circadian time. The protocerebrum showed a statistically significant c-Fos induction, especially in neurons of the dorsal anterior region and the protocerebral bridge. A statistically significant difference between the control and the experimental conditions indicated a differential sensitivity in the early subjective night. This is the first report on c-Fos expression in crayfish and indicates that this marker may be a useful tool for studying the circadian clock in this organism.

Identification of extraretinal photoreceptors in the teleost Phoxinus phoxinus.

The existence of cells capable of detecting changes of the photoperiod within the deep brain, the so-called deep brain photoreceptors, was proposed in the early years of the twentieth century. By using immunocytochemistry with antisera against phototransductory proteins on paraffin and vibratome sections, we have localized several positive areas in the brain of the teleost Phoxinus phoxinus. These areas were restricted to two encephalic regions: the epithalamus and the hypothalamus. Immunopositive (rod-opsin- and a-transducin-like) pinealocytes and parapinealocytes, as well as some sparse neurons in the habenula, were seen in the epithalamus. The immunoreaction of the hypothalamus was represented by a-transducin-like positive (magnocellular and parvicellular) neurons of the Nucleus Preopticus, as well as by a-transducin- and arrestin-like positive fibers corresponding to the hypothalamic-hypophyseal tract and a few fibers running towards the basal telencephalon. These findings corroborate the data published on other teleost fish and fully support the hypothesis of the presence of photosensitive cells in the encephalon of lower vertebrates. The labelling with antisera against different components of the phototransductory cascade also strengthens the idea that such cells employ a biochemical mechanism similar to that in the retinal visual photoreceptor cells, rods and cones. Although the function is still unclear, the detection of the photoperiod seems to be the most likely role for these extraretinal photoreceptors.

Mechanisms in the Photoperiodic Control of Reproduction in the Stickleback

In sticklebacks, sexual maturation is stimulated by long photoperiods but not by short photoperiods, even at high temperatures. Extra-retinal photoreception can mediate this response, and appears to be more important thanretinal photoreception. Although plasma melatonin levels are high at night and low during the day, experiments using melatonin administration via the water indicate that melatonin is of no or little importance for the photoperiodic response. Androgens can be aromatised to estrogens in the stickleback brain. Treatment with aromatase inhibitors stimulates maturation of males also under short photoperiod, suggesting that aromatase is involved in the suppressive actions of short photoperiod. Expression of both follicle stimulating hormone (FSH)-β and luteinizing hormone (LH)-β is higher under long than under short photoperiod. FSH-β is controlled by a negative steroid feedback on the brain-pituitary-gonad axis under short photoperiod and by a positive steroid feedback under long photoperiod. It is suggested that the former can suppress reproduction under short photoperiod and the latter can stimulate breeding under long photoperiod.

Circadian Rhythms in Infants

After completing this article, readers should be able to: 1. Describe how circadian rhythms are generated. 2. Describe how lighting influences the circadian system. 3. Delineate the period during which the origin of circadian rhythms develops. 4. Describe the relationship between maternal circadian rhythms and the development of circadian rhythms in infants. 5. Characterize the potential sequelae of impaired fetal and early neonatal circadian rhythms related to sleep patterns. 6. Describe beneficial lighting patterns for preterm infants in the neonatal intensive care nursery. Circadian rhythms are endogenously generated rhythms that have a period length of about 24 hours. Evidence gathered over the past decade indicates that the circadian timing system develops prenatally, with the suprachiasmatic nuclei (SCN) in the anterior hypothalamus, the site of a circadian clock, present by mid-gestation in primates. Recent evidence also shows that the circadian system of primate infants is responsive to light at very early stages (as early as 25 to 28 weeks’ gestation in humans) and that low-intensity lighting can regulate the developing clock. After birth, circadian system outputs mature progressively, with rhythms in sleep-wake cycles, body temperature, and hormone production generally developing between 1 and 3 months of age. The importance of light in regulation of circadian rhythm in infants is highlighted by the early establishment of rest-activity patterns that are in phase with the 24-hour light-dark cycle in preterm infants exposed to low-intensity cycled lighting. With the continued elucidation of circadian system development and influences on human physiology and illness, it is anticipated that consideration of circadian biology will become an increasingly important component of neonatal care. ### The Circadian Timing System Notable examples of circadian rhythms include the sleep-wake cycle and daily rhythms in body temperature and hormone production. Circadian rhythms are also involved in the pathogenesis of illnesses, such as reactive airway disease (eg, asthma) and myocardial infarction. The system responsible …

Circadian Locomotor Activity Rhythm in the Freshwater Crab Pseudothelphusa americana (De Saussure, 1857): Effect of Eyestalk Ablation

The circadian rhythm of locomotor activity in the freshwater crab, Pseudothelphusa americana, was studied in aquaria using infrared crossing sensors. Individuals with ablated eyestalks were compared with intact individuals in constant darkness (DD) and in light-dark cycles (LD). Our results showed that intact animals in DD displayed bimodal rhythms. In LD conditions the two peaks were associated with lights on and lights off, respectively. A significant difference in the free running periods before and after LD was observed in all intact animals. After eyestalk ablation (ES-X), the circadian rhythm of locomotor activity disappeared immediately, but reappeared several days later. Diurnal activity was seen in some ES-X animals when exposed to LD. Our results indicate that locomotor activity rhythm in P. americana is driven primarily by oscillators located outside the eyestalks, and that extraretinal photoreceptors mediate either entrainment or masking effects.

Low-dose Ultraviolet B Rays Alter the mRNA Expression of the Circadian Clock Genes in Cultured Human Keratinocytes

Current understanding of mammalian circadian rhythms suggests that they are regulated by light targeting signaling pathways in the hypothalamic suprachiasmatic nuclei. Recently, investigators have identified the existence of extraretinal photoreceptors and a potential role for the skin in this regulatory process has been implied. We demonstrated that mRNA of the circadian clock genes Per1, Clock, and bmal1/mop3 are expressed in normal human cultured keratinocytes. Low-dose ultraviolet B rays initially downregulate all circadian clock genes and then induce altered expression of the genes in keratinocyte cell cultures. Ultraviolet light targeting superficial layers of skin (keratinocytes) may therefore contribute to circadian rhythm modulation.

Photopigment gene expression and rhabdom formation in the crayfish (Procambarus clarkii).

This study examines the expression of the photopigment gene in the developing retina of the freshwater crayfish Procambarus clarkii(Crustacea, Malacostraca, Decapoda). Both sense and anti-sense RNA probes were used for in situ hybridization (ISH) of whole embryos collected at various stages during development. A characteristic of retinal development is the formation of screening pigment in the retinular cells of the retinal ommatidia. This pigmentation is seen as a band that begins at the lateral side of the retinal field and progresses medially. At hatching the retina is approximately 50% pigmented. ISH of whole embryos shows that expression of the photopigment gene by the retinular cells correlates with the extent of the screening pigment band in the retina and with the presence of rhabdoms within the ommatidia. Sections taken through embryos after being hybridized indicate that staining is localized in the cytoplasm of the retinular cells and in the axonal region below the basement membrane. No staining reaction was seen in the rhabdoms of older ommatidia. ISH staining was also seen at the anterior midline of the protocerebrum where extraretinal photoreceptors have been reported. The data presented here show a close correlation of opsin expression within the retinular cells of the ommatidia and the formation of the very early rhabdoms, similar to Drosophila. The results will be discussed in relation to recent studies in Drosophila that suggest rhodopsin plays a role in effecting the organization of the terminal web-like cytoskeleton at the base of the developing rhabdom microvilli.

Different structural organization of the encephalopsin gene in man and mouse

Encephalopsin, also called Panopsin, is a recently discovered extraretinal photoreceptor, which may play a role in non-visual photic processes such as the entrainment of circadian rhythm or the regulation of pineal melatonin production. Based on RT-PCR data and comparative genomic sequence analysis, we show that the human OPN3 gene consists of six exons and expresses various splice variants, while the murine homologue contains four exons and produces just one splice form. Furthermore, the human OPN3 gene overlaps with the neighboring KMO gene on a genomic as well as on an RNA level, whereas the corresponding genes in mouse lie close together but do not overlap. This finding is of particular interest, since differences in gene organization between man and mouse, that have been reported so far, occur within gene clusters, i.e. the number of genes within a certain cluster may differ between man and mouse. OPN3 provides an exception to this rule, since it is positionally uncoupled from other genes of the opsin family.

Larval optic nerve and adult extra-retinal photoreceptors sequentially associate with clock neurons during Drosophila brain development.

The visual system is one of the input pathways for light into the circadian clock of the Drosophila brain. In particular, extra-retinal visual structures have been proposed to play a role in both larval and adult circadian photoreception. We have analyzed the interactions between extra-retinal structures of the visual system and the clock neurons during brain development. We first show that the larval optic nerve, or Bolwig nerve, already contacts clock cells (the lateral neurons) in the embryonic brain. Analysis of visual system-defective genotypes showed that the absence of the afferent Bolwig nerve resulted in a severe reduction of the lateral neurons dendritic arborization, and that the inhibition of nerve activity induced alterations of the dendritic morphology. During wild-type development, the loss of a functional Bolwig nerve in the early pupa was also accompanied by remodeling of the arborization of the lateral neurons. Approximately 1.5 days later, visual fibers that came from the Hofbauer-Buchner eyelet, a putative photoreceptive organ for the adult circadian clock, were seen contacting the lateral neurons. Both types of extra-retinal photoreceptors expressed rhodopsins RH5 and RH6, as well as the norpA-encoded phospholipase C. These data strongly suggest a role for RH5 and RH6, as well as NORPA, signaling in both larval and adult extra-retinal circadian photoreception. The Hofbauer-Buchner eyelet therefore does not appear to account for the previously described norpA-independent light input to the adult clock. This supports the existence of yet uncharacterized photoreceptive structures in Drosophila.

Light augments FOS protein induction in brain of short-term enucleated hamsters

FOS protein is synthesized in neuronal nuclei in response to a variety of environmental stimuli and has been used as a marker of stimulus-specific brain function. The present studies were initiated to examine the effects of ultraviolet light on the induction of FOS protein immunoreactivity (FOS-IR) in several brain regions of adult male hamsters. Experiment 1 confirmed previous observations of FOS-IR induced in visual cortex in response to ultraviolet light. However, protein was also induced by ultraviolet or white light in a variety of other areas and induction occurred in both sighted and enucleated animals. Therefore, experiments were conducted to evaluate the effects of a 514 nm light on FOS-IR induction in blind or sighted animals. Experiments 2 and 3 were performed during the early subjective night and mid-subjective day, respectively, using animals about 4 days after bilateral enucleation or sham surgery. In Experiment 2, light and enucleation independently and interactively resulted in increased FOS-IR neuronal nuclei counts. In Experiment 3, there was a main effect of enucleation and an interaction between enucleation and light condition, but no main effect of light. In Experiment 4, conducted during the early subjective night using animals enucleated 60 days earlier, there were neither effects of light or enucleation. The results support the view that, under certain conditions related to subjective time of day and time since enucleation, light can act through unknown extraocular mechanisms to modify brain activity. Further, short term enucleation itself induces widespread alteration in brain function as indicated by increased FOS-IR expression. The results specifically do not support a role for extraretinal photoreception with respect to direct circadian rhythm regulation.