A "melanopic" spectral efficiency function predicts the sensitivity of melanopsin photoreceptors to polychromatic lights

Photoreception in the mammalian retina is not restricted to rods and cones but extends to a small number of intrinsically photosensitive retinal ganglion cells expressing the photopigment melanopsin. These mRGCs are especially important contributors to circadian entrainment, the pupil light reflex, and other so-called nonimage-forming (NIF) responses. The spectral sensitivity of melanopsin phototransduction has been addressed in several species by comparing responses to a range of monochromatic stimuli. The resultant action spectra match the predicted profile of an opsin:vitamin A-based photopigment (nomogram) with a peak sensitivity (λ(max)) around 480 nm. It would be most useful to be able to use this spectral sensitivity function to predict melanopsin's sensitivity to broad-spectrum, including "white," lights. However, evidence that melanopsin is a bistable pigment with an intrinsic light-dependent bleach recovery mechanism raises the possibility of a more complex relationship between spectral quality and photoreceptor response. Here, we set out to empirically determine whether simply weighting optical power at each wavelength according to the 480-nm nomogram and integrating across the spectrum could predict melanopsin sensitivity to a variety of polychromatic stimuli. We show that pupillomotor and circadian responses of mice relying solely on melanopsin for their photosensitivity (rd/rd cl) can indeed be accurately predicted using this methodology. Our data therefore suggest that the 480-nm nomogram may be employed as the basis for a new photometric measure of light intensity (which we term "melanopic") relevant for melanopsin photoreception. They further show that measuring light in these terms predicts the melanopsin response to light of divergent spectral composition much more reliably than other methods for quantifying irradiance or illuminance currently in widespread use.     

Short-wavelength light sensitivity of circadian, pupillary, and visual awareness in humans lacking an outer retina

As the ear has dual functions for audition and balance, the eye has a dual role in detecting light for a wide range of behavioral and physiological functions separate from sight. These responses are driven primarily by stimulation of photosensitive retinal ganglion cells (pRGCs) that are most sensitive to short-wavelength ( approximately 480 nm) blue light and remain functional in the absence of rods and cones. We examined the spectral sensitivity of non-image-forming responses in two profoundly blind subjects lacking functional rods and cones (one male, 56 yr old; one female, 87 yr old). In the male subject, we found that short-wavelength light preferentially suppressed melatonin, reset the circadian pacemaker, and directly enhanced alertness compared to 555 nm exposure, which is the peak sensitivity of the photopic visual system. In an action spectrum for pupillary constriction, the female subject exhibited a peak spectral sensitivity (lambda(max)) of 480 nm, matching that of the pRGCs but not that of the rods and cones. This subject was also able to correctly report a threshold short-wavelength stimulus ( approximately 480 nm) but not other wavelengths. Collectively these data show that pRGCs contribute to both circadian physiology and rudimentary visual awareness in humans and challenge the assumption that rod- and cone-based photoreception mediate all "visual" responses to light.     

Spectral sensitivity of vision and bioluminescence in the midwater shrimp Sergestes similis

In the oceanic midwater environment, many fish, squid, and shrimp use luminescent countershading to remain cryptic to silhouette-scanning predators. The mid-water penaeid shrimp, Sergestes similis Hansen, responds to downward-directed light with a dim bioluminescence that dynamically matches the spectral radiance of oceanic down-welling light at depth. Although the sensory basis of luminescent countershading behavior is visual, the relationship between visual and behavioral sensitivity is poorly understood. In this study, visual spectral sensitivity, based on microspectrophotometry and electrophysiological measurements of photoreceptor response, is directly compared to the behavioral spectral efficiency of luminescent countershading. Microspectrophotometric measurements on single photoreceptors revealed only a single visual pigment with peak absorbance at 495 nm in the blue-green region of the spectrum. The peak electrophysiological spectral sensitivity of dark-adapted eyes was centered at about 500 nm. The spectral efficiency of luminescent countershading showed a broad peak from 480 to 520 nm. Both electrophysiological and behavioral data closely matched the normalized spectral absorptance curve of a rhodopsin with lambda(max) = 495 nm, when rhabdom length and photopigment specific absorbance were considered. The close coupling between visual spectral sensitivity and the spectral efficiency of luminescent countershading attests to the importance of bioluminescence as a camouflage strategy in this species.     

Melanopsin forms a functional short-wavelength photopigment

Recently, melanopsin has emerged as the leading candidate for the elusive photopigment of the mammalian circadian system. This novel opsin-like protein is expressed in retinal ganglion cells that form the retinohypothalamic tract, a neuronal connection between the retina and the suprachiasmatic nucleus. These hypothalamic structures contain the circadian pacemaker, which generates daily rhythms in physiology and behavior. In mammals, proper synchronization of these rhythms to the environmental light-dark cycle requires retinal input. Surprisingly, rod and cone photoreceptors are not required. Instead, the melanopsin-containing ganglion cells are intrinsically sensitive to light, perhaps responding via a melanopsin-based signaling pathway. To test this hypothesis, we have characterized melanopsin following heterologous expression in COS cells. We found that melanopsin absorbed maximally at 424 nm after reconstitution with 11-cis-retinal. Furthermore, melanopsin activated the photoreceptor G-protein, transducin, in a light-dependent manner. In agreement with the measured absorbance spectrum, melanopsin was most efficiently excited by blue light (420-440 nm). In contrast, published action spectra suggest that the photopigment underlying the intrinsic light sensitivity of SCN-projecting RGCs has an absorption maximum near 484 nm. In summary, our experiments constitute the first direct demonstration that melanopsin forms a photopigment capable of activating a G-protein, but its spectral properties are not consistent with the action spectrum for circadian entrainment.     

The primary visual pathway in humans is regulated according to long-term light exposure through the action of a nonclassical photopigment

BACKGROUND: The mammalian eye shows marked adaptations to time of day. Some of these modifications are not acute responses to short-term light exposure but rely upon assessments of the photic environment made over several hours. In the past, all attempts at a mechanistic understanding have assumed that these adaptations originate with light detection by one or other of the classical photoreceptor cells (rods or cones). However, previous work has demonstrated that the mammalian eye contains non-rod, non-cone photoreceptors. This study aimed to determine whether such photoreceptors contribute to retinal adaptation. RESULTS: In the human retina, second-order processing of signals originating in cones takes significantly longer at night than during the day. Long-term light exposure at night is capable of reversing this effect. Here, we employed the cone ERG as a tool to examine the properties of the irradiance measurement pathway driving this reversal. Our findings indicate that this pathway (1) integrates irradiance measures over time periods ranging from at least 15 to 120 min; (2) responds to relatively bright light, having a dynamic range almost entirely outside the sensitivity of rods; (3) acts on the cone pathway primarily through a local retinal mechanism; and (4) detects light via an opsin:vitamin A photopigment (lambda(max) approximately 483 nm). CONCLUSIONS: A photopigment with a spectral sensitivity profile quite different from those of the classical rod and cone opsins but matching the standard profile of an opsin:vitamin A-based pigment drives adaptations of the human primary cone visual pathway according to time of day.     

Spectral sensitivity of melanophores of a freshwater teleost, Zacco temmincki

1. The melanophores of a freshwater teleost, Zacco temmincki, responded to changes in illumination: in darkness the melanophores induced a melanosome aggregation and when subjected to light they caused a melanosome dispersion. 2. Using monochromatic light, the spectral sensitivity of the melanophores was examined. 3. The melanophores showed a different sensitivity to light between 400 and 600 nm with a maximum at about 525 nm. 4. The action spectrum closely resembled a porphyropsin absorbance curve, suggesting a porphyropsin or similar photopigment is active in the melanophore light response of Zacco temmincki.     

Gene duplication is an evolutionary mechanism for expanding spectral diversity in the long-wavelength photopigments of butterflies

Butterfly long-wavelength (L) photopigments are interesting for comparative studies of adaptive evolution because of the tremendous phenotypic variation that exists in their wavelength of peak absorbance (lambda(max) value). Here we present a comprehensive survey of L photopigment variation by measuring lambda(max) in 12 nymphalid and 1 riodinid species using epi-microspectrophotometry. Together with previous data, we find that L photopigment lambda(max) varies from 510-565 nm in 22 nymphalids, with an even broader 505- to 600-nm range in riodinids. We then surveyed the L opsin genes for which lambda(max) values are available as well as from related taxa and found 2 instances of L opsin gene duplication within nymphalids, in Hermeuptychia hermes and Amathusia phidippus, and 1 instance within riodinids, in the metalmark butterfly Apodemia mormo. Using maximum parsimony and maximum likelihood ancestral state reconstructions to map the evolution of spectral shifts within the L photopigments of nymphalids, we estimate the ancestral pigment had a lambda(max) = 540 nm +/- 10 nm standard error and that blueshifts in wavelength have occurred at least 4 times within the family. We used ancestral state reconstructions to investigate the importance of several amino acid substitutions (Ile17Met, Ala64Ser, Asn70Ser, and Ser137Ala) previously shown to have evolved under positive selection that are correlated with blue spectral shifts. These reconstructions suggest that the Ala64Ser substitution has indeed occurred along the newly identified blueshifted L photopigment lineages. Substitutions at the other 3 sites may also be involved in the functional diversification of L photopigments. Our data strongly suggest that there are limits to the evolution of L photopigment spectral shifts among species with only one L opsin gene and that opsin gene duplication broadens the potential range of lambda(max) values.     

Photoendocrine Transduction in Cultured Chick Pineal Cells: IV. What Do Vitamin A Depletion and Retinaldehyde Addition Do to the Effects of Light on the Melatonin Rhythm?

Abstract: Light has at least two distinguishable effects on the circadian rhythm of melatonin output displayed by dispersed chick pineal cells in static culture: acute suppression of melatonin output and entrainment (phase shifts) of the underlying pacemaker. Previous results indicated that these two effects of light are mediated by different mechanistic pathways. The pathways for the acute and phase-shifting effects of light either branch from the same, single photopigment or differ from the outset, starting from separate photopigments. If a single rhodopsin-like photopigment mediates both effects of light, then vitamin A depletion and retinoid addition should affect both responses in parallel, although not proportionately. We therefore compared the effects of vitamin A depletion and retinoid addition on the acute and phase-shifting effects of light under several experimental conditions. When chick pineal cells were depleted of vitamin A, acute responses to light were markedly reduced. Addition of 11-cis-retinaldehyde specifically restored (and enhanced) the acute response. When allowed to free run in constant red light, depleted cells displayed a rhythm of melatonin output with the same period as that of control cells. In contrast to the acute effects, phase shifts in response to 2- or 4-h light pulses did not differ between depleted and control cells. Addition of retinaldehyde to depleted cells did not, by itself, reduce melatonin output or induce phase shifts. Retinaldehyde did increase the acute response to 4-h light pulses but not the ensuing phase shifts. Responses increased with duration of the light pulse: Both the acute effect and the phase shifts induced by 4-h light pulses were considerably larger than those induced by 2-h (or 1-h) light pulses. Addition of retinaldehyde to depleted cells increased the acute effect of 2-h (or 1-h) light pulses to at least that seen with 4-h light pulses but did not Increase the size of the ensuing phase shifts. These results strongly confirm previous dissociations of the mechanistic pathways mediating the acute and phase-shifting effects of light on chick pineal cells. They also support a role for rhodopsin-like photopigment in the acute, but not phase-shifting, response. They favor, but do not prove, the conclusion that separate photopigments mediate the acute and entraining effects of light.     

Exquisite Light Sensitivity of Drosophila melanogaster Cryptochrome

Drosophila melanogaster shows exquisite light sensitivity for modulation of circadian functions in vivo, yet the activities of the Drosophila circadian photopigment cryptochrome (CRY) have only been observed at high light levels. We studied intensity/duration parameters for light pulse induced circadian phase shifts under dim light conditions in vivo. Flies show far greater light sensitivity than previously appreciated, and show a surprising sensitivity increase with pulse duration, implying a process of photic integration active up to at least 6 hours. The CRY target timeless (TIM) shows dim light dependent degradation in circadian pacemaker neurons that parallels phase shift amplitude, indicating that integration occurs at this step, with the strongest effect in a single identified pacemaker neuron. Our findings indicate that CRY compensates for limited light sensitivity in vivo by photon integration over extraordinarily long times, and point to select circadian pacemaker neurons as having important roles.     

Vertebrate ancient opsin photopigment spectra and the avian photoperiodic response

In mammals, photoreception is restricted to cones, rods and a subset of retinal ganglion cells. By contrast, non-mammalian vertebrates possess many extraocular photoreceptors but in many cases the role of these photoreceptors and their underlying photopigments is unknown. In birds, deep brain photoreceptors have been shown to sense photic changes in daylength (photoperiod) and mediate seasonal reproduction. Nonetheless, the specific identity of the opsin photopigment 'sensor' involved has remained elusive. Previously, we showed that vertebrate ancient (VA) opsin is expressed in avian hypothalamic neurons and forms a photosensitive molecule. However, a direct functional link between VA opsin and the regulation of seasonal biology was absent. Here, we report the in vivo and in vitro absorption spectra (λ(max) = ~490 nm) for chicken VA photopigments. Furthermore, the spectral sensitivity of these photopigments match the peak absorbance of the avian photoperiodic response (λ(max) = 492 nm) and permits maximum photon capture within the restricted light environment of the hypothalamus. Such a correspondence argues strongly that VA opsin plays a key role in regulating seasonal reproduction in birds.     

Eye function of Mysidacea (Crustacea) in the northern Baltic Sea

Eye spectral sensitivity, [S(lambda)], was measured in seven northern Baltic mysid species using an electroretinogram technique. Their S(lambda) curves were compared with the spectral distribution of underwater light at their normal habitats. In the littoral species Neomysis integer, Praunus flexuosus and Praunus inermis, the S(lambda) maxima, [S(lambda)(max)], were in the wavelength-bands of 525-535, 505-515 and 520-530 nm respectively. The neoimmigrant species Hemimysis anomala had a S(lambda)(max) around 500 nm and high sensitivity at 393 nm, possibly indicating UV-sensitivity. S(lambda) of the pelagic species Mysis mixta and Mysis relicta sp. II was at about 505-520 nm. M. relicta sp. I from Pojoviken Bay and fresh water humic Lake P??j?rvi had S(lambda)(max) at approximately 550 nm and 570 nm respectively. This is in accordance with a similar long-wavelength shift in light transmittance of the respective waters. The eyes of the latter population were also damaged by strong light. The pontocaspian neoimmigrant H. anomala is clearly adapted to waters transmitting more blue light.     

The Effects of Lithium on a Neuronal in Vitro Orcadian Pacemaker

Previous studies have suggested a causal connection between abnormalities of the circadian system and affective disorders. The effectiveness of lithium or rubidium as a treatment for affective disorders and the ability of lithium or rubidium to influence circadian pacemakers has stimulated research into the mechanism of lithium's action on circadian systems. In this study we used a neuronal in vitro circadian pacemaker preparation, the eye of the mollusc Bulla, to examine the cellular effects of lithium and rubidium. Continuous extracellular LiCl application lengthens the period of the circadian rhythm of the Bulla pacemaker in a concentration-dependent manner. Rubidium was found to be more effective than lithium in period lengthening. Stable phase delays were generated by 2-h pulses of 395 mM LiCl applied extracellularly from zeitgeber time (ZT) 5-7 (mid subjective day). Concomitant continuous application of 16 mM LiCl and light (a depolarizing agent) generated period lengthening substantially greater than the arithmetic sum of the modest period lengthening of each treatment alone. Furthermore, LiCl pulses, applied together with depolarizing extracellular KC1 concentrations, yielded an increasing magnitude of phase delays with increasing KC1 concentration. These data suggest that LiCl acts intracellularly on the circadian pacemaker cells by entering through a voltage-dependent channel, most likely a sodium channel.     

Chronic ethanol intake alters circadian period-responses to brief light pulses in rats

Although chronic alcohol intake is associated with widespread disruptions of sleep-wake cycles and other daily biological rhythms in both human alcoholics and experimental animals, the extent to which the chronobiological effects of alcohol are mediated by effects on the underlying circadian pacemaker remains unknown. Nevertheless, recent studies indicate that both adult and perinatal ethanol treatments may alter the free-running period and photic responsiveness of the circadian pacemaker. The present experiment was designed to further characterize the effects of chronic ethanol intake on the response of the rat circadian pacemaker to brief light pulses. Ethanol-treated and control animals were exposed to 15-min light pulses during either early or late subjective night on the first day of constant darkness following entrainment to a 12:12 light-dark cycle. Relative to pulses delivered during early subjective night and to “no-pulse” conditions, light pulses delivered during late subjective night resulted in period-shortening after-effects under constant darkness, but only in control animals, not in ethanol-treated animals. These results indicate that chronic ethanol intake reduces the responsiveness of the circadian pacemaker to acute photic stimulation, and suggest that the chronobiological disruptions seen in human alcoholics are due in part to alterations in circadian pacemaker function.     

Spectral correspondence between visual spectral sensitivity and bioluminescence emission spectra in the click beetle Pyrophorus punctatissimus (Coleoptera: Elateridae)

The presence of two spectral mechanisms, near-ultraviolet and green (lambda(max)=545nm), is strongly suggested by electroretinographic visual spectral sensitivity curves obtained under dark and red chromatic adaptation conditions in the compound eyes of the click beetle Pyrophorus punctatissimus. The bioluminescence emission of the dorsal prothoracic lanterns is deep green (lambda(max)=543nm) and that of the ventral abdominal lantern is lime green (lambda(max)=556nm) in colour in P. punctatissimus. A broad green visual receptor would detect both deep green and lime green bioluminescent optical signals.     

Light-induced melatonin suppression in humans with polychromatic and monochromatic light

The relative contribution of rods, cones, and melanopsin to non-image-forming (NIF) responses under light conditions differing in irradiance, duration, and spectral composition remains to be determined in humans. NIF responses to a polychromatic light source may be very different to that predicted from the published human action spectra data, which have utilized narrow band monochromatic light and demonstrated short wavelength sensitivity. To test the hypothesis that only melanopsin is driving NIF responses in humans, monochromatic blue light (lambda(max) 479 nm) was matched with polychromatic white light for total melanopsin-stimulating photons at three light intensities. The ability of these light conditions to suppress nocturnal melatonin production was assessed. A within-subject crossover design was used to investigate the suppressive effect of nocturnal light on melatonin production in a group of diurnally active young male subjects aged 18-35 yrs (24.9+/-3.8 yrs; mean+/-SD; n=11). A 30 min light pulse, individually timed to occur on the rising phase of the melatonin rhythm, was administered between 23:30 and 01:30 h. Regularly timed blood samples were taken for measurement of plasma melatonin. Repeated measures two-way ANOVA, with irradiance and light condition as factors, was used for statistical analysis (n=9 analyzed). There was a significant effect of both light intensity (p<0.001) and light condition (p<0.01). Polychromatic light was more effective at suppressing nocturnal melatonin than monochromatic blue light matched for melanopsin stimulation, implying that the melatonin suppression response is not solely driven by melanopsin. The findings suggest a stimulatory effect of the additional wavelengths of light present in the polychromatic light, which could be mediated via the stimulation of cone photopigments and/or melanopsin regeneration. The results of this study may be relevant to designing the spectral composition of polychromatic lights for use in the home and workplace, as well as in the treatment of circadian rhythm disorders.     

Adaptation of a deep-sea cephalopod to the photic environment. Evidence for three visual pigments

Watasenia scintillans, a bioluminescent deep-sea squid, has a specially developed eye with a large open pupil and three visual pigments. Photoreceptor cells (outer segment: 476 micron; inner segment: 99 micron) were long in the small area of the ventral retina receiving downwelling light, whereas they were short (outer segment: 207 micron; inner segment: 44 micron) in the other regions of the retina. The short photoreceptor cells contained the visual pigment with retinal (lambda max approximately 484 nm), probably for the purpose of adapting to their environmental light. The outer segment of the long photoreceptor cells consisted of two strata, a pinkish proximal area and a yellow distal area. The visual pigment with 3-dehydroretinal (lambda max approximately 500 nm) was located in the pinkish proximal area, giving high sensitivity at longer wavelengths. A newly found pigment (lambda max approximately 471 nm) was in the yellow distal area. The small area of the ventral retina containing two visual pigments is thought to have a high and broad spectral sensitivity, which is useful for distinguishing the bioluminescence of squids of the same species in their environmental downwelling light. These findings were obtained by partial bleaching of the extracted pigment from various areas of the retina and by high-performance liquid chromatographic analysis of the chromophore, complemented by microscopic observations.     

Circadian effects of light no brighter than moonlight

In mammals, light entrains endogenous circadian pacemakers by inducing daily phase shifts via a photoreceptor mechanism recently discovered in retinal ganglion cells. Light that is comparable in intensity to moonlight is generally ineffective at inducing phase shifts or suppressing melatonin secretion, which has prompted the view that circadian photic sensitivity has been titrated so that the central pacemaker is unaffected by natural nighttime illumination. However, the authors have shown in several different entrainment paradigms that completely dark nights are not functionally equivalent to dimly lit nights, even when nighttime illumination is below putative thresholds for the circadian visual system. The present studies extend these findings. Dim illumination is shown here to be neither a strong zeitgeber, consistent with published fluence response curves, nor a potentiator of other zeitgebers. Nevertheless, dim light markedly alters the behavior of the free-running circadian pacemaker. Syrian hamsters were released from entrained conditions into constant darkness or dim narrowband green illumination (~0.01 lx, 1.3 x 10(-9) W/cm(2), peak lambda = 560 nm). Relative to complete darkness, constant dim light lengthened the period by ~0.3 h and altered the waveform of circadian rhythmicity. Among animals transferred from long day lengths (14 L:10 D) into constant conditions, dim illumination increased the duration of the active phase (alpha) by ~3 h relative to complete darkness. Short day entrainment (8 L:16 D) produced initially long alpha that increased further under constant dim light but decreased under complete darkness. In contrast, dim light pulses 2 h or longer produced effects on circadian phase and melatonin secretion that were small in magnitude. Furthermore, the amplitude of phase resetting to bright light and nonphotic stimuli was similar against dimly lit and dark backgrounds, indicating that the former does not directly amplify circadian inputs. Dim illumination markedly alters circadian waveform through effects on alpha, suggesting that dim light influences the coupling between oscillators theorized to program the beginning and end of subjective night. Physiological mechanisms responsible for conveying dim light stimuli to the pacemaker and implications for chronotherapeutics warrant further study.     

TheBulla ocular circadian pacemaker

In an effort to understand the cellular basis of entrainment of circadian oscillators we have studied the role of membrane potential changes in the neurons which comprise the ocular circadian pacemaker of Bulla gouldiana in mediating phase shifts of the ocular circadian rhythm. We report that: 1. Intracellular recording was used to measure directly the effects of the phase shifting agents light, serotonin, and 8-bromo-cAMP on the membrane potential of the basal retinal neurons. We found that light pulses evoke a transient depolarization followed by a smaller sustained depolarization. Application of serotonin produced a biphasic response; a transient depolarization followed by a sustained hyperpolarization. Application of a membrane permeable analog of the intracellular second messenger cAMP, 8-bromo-cAMP, elicited sustained hyperpolarization, and occasionally a weak phasic depolarization. 2. Changing the membrane potential of the basal retinal neurons directly and selectively with intracellularly injected current phase shifts the ocular circadian rhythm. Both depolarizing and hyperpolarizing current can shift the phase of the circadian oscillator. Depolarizing current mimics the phase shifting action of light, while hyperpolarizing current produces phase shifts which are transposed approximately 180 degrees in circadian time to depolarization. 3. Altering BRN membrane potential with ionic treatments, depolarizing with elevated K+ seawater or hyperpolarizing with lowered Na+ seawater, produces phase shifts similar to current injection. 4. The light-induced depolarization of the basal retinal neurons is necessary for phase shifts by light. Suppressing the light-induced depolarization with injected current inhibits light-induced phase shifts. 5. The ability of membrane potential changes to shift oscillator phase is dependent on extracellular calcium. Reducing extracellular free Ca++ from 10 mM to 1.3 X 10(-7) M inhibits light-induced phase shifts without blocking the photic response of the BRNs. The results indicate that changes in the membrane potential of the pacemaker neurons play a critical role in phase shifting the circadian rhythm, and imply that a voltage-dependent and calcium-dependent process, possibly Ca++ influx, shifts oscillator phase in response to light.     

Predicting human nocturnal nonvisual responses to monochromatic and polychromatic light with a melanopsin photosensitivity function

The short-wavelength (blue) light sensitivity of human circadian, neurobehavioral, neuroendocrine, and neurophysiological responses is attributed to melanopsin. Whether melanopsin is the sole factor in determining the efficacy of a polychromatic light source in driving nonvisual responses, however, remains to be established. Monochromatic (λ(max) 437, 479, and 532 nm administered singly and in combination with 479 nm light) and polychromatic (color temperature: 4000 K and 17000 K) light stimuli were photon matched for their predicted ability to stimulate melanopsin, and their capacity to affect nocturnal melatonin levels, auditory reaction time, and subjective alertness and mood was assessed. Young, healthy male participants aged 18-35 yrs (23.6?±?3.6 yrs [mean?±?SD]; n=12) participated in 12 overnight sessions that included an individually timed 30-min nocturnal light stimulus on the rising limb of the melatonin profile. At regular intervals before, during, and after the light stimulus, subjective mood and alertness were verbally assessed, blood samples were taken for analysis of plasma melatonin levels, and an auditory reaction time task (psychomotor vigilance task; PVT) was performed. Proc GLM (general linear model) repeated-measures ANOVA (analysis of variance) revealed significantly lower melatonin suppression with the polychromatic light conditions (4000 and 17000 K) compared to the "melanopsin photon-matched" monochromatic light conditions (p相似文献   

Phase-shifting the fruit fly clock without cryptochrome

The blue light photopigment cryptochrome (CRY) is thought to be the main circadian photoreceptor of Drosophila melanogaster. Nevertheless, entrainment to light-dark cycles is possible without functional CRY. Here, we monitored phase response curves of cry(01) mutants and control flies to 1-hour 1000-lux light pulses. We found that cry(01) mutants phase-shift their activity rhythm in the subjective early morning and late evening, although with reduced magnitude. This phase-shifting capability is sufficient for the slowed entrainment of the mutants, indicating that the eyes contribute to the clock's light sensitivity around dawn and dusk. With longer light pulses (3 hours and 6 hours), wild-type flies show greatly enhanced magnitude of phase shift, but CRY-less flies seem impaired in the ability to integrate duration of the light pulse in a wild-type manner: Only 6-hour light pulses at circadian time 21 significantly increased the magnitude of phase advances in cry(01) mutants. At circadian time 15, the mutants exhibited phase advances instead of the expected delays. These complex results are discussed.