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Melanopsin for precise optogenetic activation of astrocyte-neuron networks
摘要： Optogenetics has been widely expanded to enhance or suppress neuronal activity and it has been recently applied to glial cells. Here, we have used a new approach based on selective expression of melanopsin, a G-protein-coupled photopigment, in astrocytes to trigger Ca2+ signaling. Using the genetically encoded Ca2+ indicator GCaMP6f and two-photon imaging, we show that melanopsin is both competent to stimulate robust IP3-dependent Ca2+ signals in astrocyte fine processes, and to evoke an ATP/Adenosine-dependent transient boost of hippocampal excitatory synaptic transmission. Additionally, under low-frequency light stimulation conditions, melanopsin-transfected astrocytes can trigger long-term synaptic changes. In vivo, melanopsin-astrocyte activation enhances episodic-like memory, suggesting melanopsin as an optical tool that could recapitulate the wide range of regulatory actions of astrocytes on neuronal networks in behaving animals. These results describe a novel approach using melanopsin as a precise trigger for astrocytes that mimics their endogenous G-protein signaling pathways, and present melanopsin as a valuable optical tool for neuron–glia studies.
关键词： neuron–glia interactions,synaptic plasticity,optogenetics,astrocytes,melanopsin
更新于2025-09-23 15:23:52
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Yellow filter effect on melatonin secretion in the eye: Role in IOP regulation
摘要： Purpose: Melatonin is a neurohormone mainly synthesized in the pineal gland; however, it is also present in the aqueous humor. One of melatonins’ functions in the eye is the regulation of intraocular pressure. Melatonin is known to be sensitive to light. Recently, the photopigment which controls melatonin synthesis, melanopsin, was found in the crystalline lens. Therefore, light conditions is an interesting possible way of regulating melatonin levels in the aqueous humor. The current study used yellow-filters, since melanopsin is activated by short-wavelength (blue light). methods: New Zealand white rabbits were used, divided in two groups, one under controlled 12h-light/dark cycles, while the rest had their cages encased with a yellow filter (λ 465-480). IOP measurements were taken every week at the same time before they were anesthetized for aqueous humour extraction. Results: Keeping the rabbits under the yellow filter resulted in a decrease in IOP up to 43.8 ± 7.8% after 3 weeks. This effect was reversed after the topical application of selective and non-selective melatonin receptors antgonists, 4PPDOT and luzindole. Also, blocking melanopsin by its antagonist AA92593 under white light condition decreased IOP. Finally, melatonin levels were found significantly higher in the aqueous humor of rabbits developed under yellow filter compared to controls (37.4 ± 4.2 ng/ml and 15.3 ± 3.1 ng/ml, respectively). Conclusion: Yellow filters modulate melatonin levels in the aqueous humour due to deactivating melanopsin activity. This effect leaded to a decrease in IOP mediated by melatonin receptors.
关键词： Melatonin,Intraocular pressure,Melanopsin.,Yellow filter
更新于2025-09-23 15:22:29
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Melatonin suppression is exquisitely sensitive to light and primarily driven by melanopsin in humans
摘要： Introduction: Light elicits a range of non-visual responses in humans. Driven predominantly by intrinsically photosensitive retinal ganglion cells (ipRGCs), but also by rods and/or cones, these responses include melatonin suppression. A sigmoidal relationship has been established between melatonin suppression and light intensity, however photoreceptoral involvement remains unclear. Methods and Results: In this study, we first modelled the relationships between alpha-opic illuminances and melatonin suppression using an extensive dataset by Brainard and colleagues. Our results show that 1) melatonin suppression is better predicted by melanopic illuminance compared to other alpha-opic illuminances, 2) melatonin suppression is predicted to occur at levels as low as ~1.5 melanopic lux (melanopsin-weighted irradiance 0.2 μW/cm2), 3) saturation occurs at 305 melanopic lux (melanopsin-weighted irradiance 36.6 μW/cm2). We then tested this melanopsin-weighted illuminance response model derived from Brainard and colleagues’ data and show that it predicts equally well melatonin suppression data from our laboratory, although obtained using different intensities and exposure duration. Discussion: Together, our findings suggest that melatonin suppression by monochromatic lights is predominantly driven by melanopsin, and that it can be initiated at extremely low melanopic lux levels in experimental conditions. This emphasizes the concern of the non-visual impacts of low light intensities in lighting design and light-emitting devices.
关键词： melatonin,light,mathematical model,dose-response relationship,humans,circadian,melanopsin
更新于2025-09-19 17:15:36
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Using Flickering Light to Enhance Nonimage-Forming Visual Stimulation in Humans
摘要： PURPOSE. Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate nonimage-forming visual functions such as pupillary constriction and circadian photoentrainment. Optimizing daytime nonimage-forming photostimulation has health benefits. We aimed to enhance ipRGC excitation using flickering instead of steady light. METHODS. Human subjects were tested with a three-dimensional matrix of flickering 463-nm stimuli: three photon counts (13.7, 14.7 and 15.7 log photons cm?2), three duty cycles (12%, 47%, and 93%) and seven flicker frequencies (0.1, 0.25, 0.5, 1, 2, 4, and 7 Hz). Steady-state pupil constrictions were measured. RESULTS. Among stimuli containing 13.7 log photons cm?2, the one flickering at 2 Hz with a 12% duty cycle evoked the greatest pupil constriction of 48% ± 4%, 71% greater than that evoked by an equal-intensity (12.3 log photons cm?2 s?1) continuous light. This frequency and duty cycle were also best for 14.7 log photons cm?2 stimuli, inducing a 58% ± 4% constriction which was 38% more than that caused by an equal-intensity (13.3 log photons cm?2 s?1) constant light. For 15.7 log photons cm?2 stimuli, the 1-Hz, 47% duty cycle flicker was optimal although it evoked the same constriction as the best 14.7 log photons cm?2 flicker. CONCLUSIONS. Pupillary constriction depends on flicker frequency and duty cycle besides intensity. Among the stimuli tested, the one with the lowest photon count inducing a maximal response is 13.3 log photons cm?2 s?1 flickering at 2 Hz with 12% duty cycle. Our data could guide the design of healthier architectural lighting and better phototherapy devices for treating seasonal affective disorder and jet lag.
关键词： pupillary light reflex,melanopsin,phototherapy,nonimage-forming vision
更新于2025-09-19 17:15:36
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Synaptic Specializations of Melanopsin-Retinal Ganglion Cells in Multiple Brain Regions Revealed by Genetic Label for Light and Electron Microscopy
摘要： Kim et al. express a genetically encoded electron microscopy (EM) tag in mRGCs of the mouse retina and use serial block-face electron microscopy to analyze the optic nerve and synaptic neuropil in five different brain regions. They find that mRGC synaptic terminals show target-specific specializations corresponding to differences in responses to light.
关键词： melanopsin,brain regions,synaptic specializations,electron microscopy,retinal ganglion cells
更新于2025-09-19 17:13:59
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nGnG Amacrine Cells and Brn3b-negative M1 ipRGCs are Specifically Labeled in the ChAT-ChR2-EYFP Mouse
摘要： PURPOSE. Experimental access to specific cell subtypes is essential for deciphering the complexity of retinal networks. Here, we characterized the selective labeling, caused by ectopic transgene expression, of two atypical retinal neurons in the ChAT-Channelrhodopsin-2 (ChR2)-EYFP mouse. METHODS. Retinal sections and flat-mounts were prepared for double-staining immunohistochemistry with antibodies against EYFP and various neuronal markers. Sagittal/coronal brain slices were made to visualize EYFP signals in central nuclei. Whole-cell recordings were conducted to test the functionality of ChR2. RESULTS. Two populations of EYFP-positive retinal cells were observed. The inner nuclear layer (INL)-located one (type I cell) distributed regularly throughout the entire retina, whereas the ganglion cell layer (GCL)-residing one (type II cell) was restricted ventrally. None of them was cholinergic, as evidenced by the complete absence of ChAT immunoreactivity. Type I cells were immunolabeled by the amacrine marker syntaxin. However, the vast majority of them were neither positive to GABA/GAD65, nor to GlyT1/glycine, suggesting that they were non-GABAergic non-glycinergic amacrine cells (nGnG ACs), which was confirmed by double-labeling with the nGnG AC marker PPP1R17. Type II cells were immunopositive to melanopsin, but not to Brn3a or Brn3b. They possessed dendrites stratifying in the outermost inner plexiform layer (IPL) and axons projecting to the suprachiasmatic nucleus (SCN) rather than the olivary pretectal nucleus (OPN), suggesting that they belonged to a Brn3b-negative subset of M1-type intrinsically photosensitive retinal ganglion cells (ipRGCs). Glutamatergic transmission-independent photocurrents were elicited in EYFP-positive cells, indicating the functional expression of ChR2. CONCLUSIONS. The ChAT-ChR2-EYFP retina exhibits ectopic, but functional, transgene expression in nGnG ACs and SCN-innervating M1 ipRGCs, thus providing an ideal tool to achieve efficient labeling and optogenetic manipulation of these cells.
关键词： melanopsin,transgenic mouse,ipRGC,retina,nGnG amacrine cell
更新于2025-09-19 17:13:59
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Photoreceptive retinal ganglion cells control the information rate of the optic nerve
摘要： Information transfer in the brain relies upon energetically expensive spiking activity of neurons. Rates of information flow should therefore be carefully optimized, but mechanisms to control this parameter are poorly understood. We address this deficit in the visual system, where ambient light (irradiance) is predictive of the amount of information reaching the eye and ask whether a neural measure of irradiance can therefore be used to proactively control information flow along the optic nerve. We first show that firing rates for the retina’s output neurons [retinal ganglion cells (RGCs)] scale with irradiance and are positively correlated with rates of information and the gain of visual responses. Irradiance modulates firing in the absence of any other visual signal confirming that this is a genuine response to changing ambient light. Irradiance-driven changes in firing are observed across the population of RGCs (including in both ON and OFF units) but are disrupted in mice lacking melanopsin [the photopigment of irradiance-coding intrinsically photosensitive RGCs (ipRGCs)] and can be induced under steady light exposure by chemogenetic activation of ipRGCs. Artificially elevating firing by chemogenetic excitation of ipRGCs is sufficient to increase information flow by increasing the gain of visual responses, indicating that enhanced firing is a cause of increased information transfer at higher irradiance. Our results establish a retinal circuitry driving changes in RGC firing as an active response to alterations in ambient light to adjust the amount of visual information transmitted to the brain.
关键词： neural coding,ipRGC,retina,melanopsin,information
更新于2025-09-10 09:29:36
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Orexin-A Suppresses Signal Transmission to Dopaminergic Amacrine Cells From Outer and Inner Retinal Photoreceptors
摘要： The neuropeptides orexin-A and orexin-B are widely expressed in the vertebrate retina; however, their role in visual function is unclear. This study investigates whether and how orexins modulate signal transmission to dopaminergic amacrine cells (DACs) from both outer retinal photoreceptors (rods and cones) and inner retinal photoreceptors (melanopsin-expressing intrinsically photosensitive retinal ganglion cells [ipRGCs]). A whole-cell voltage-clamp technique was used to record light-induced responses from genetically labeled DACs in ?at-mount mouse retinas. Rod and cone signaling to DACs was con?rmed pharmacologically (in wild-type retinas), whereas retrograde melanopsin signaling to DACs was isolated either pharmacologically (in wild-type retinas) or by genetic deletion of rod and cone function (in transgenic mice). Orexin-A attenuated rod/cone-mediated light responses in the majority of DACs and inhibited all DACs that exhibited melanopsin-based light responses, suggesting that exogenous orexin suppresses signal transmission from rods, cones, and ipRGCs to DACs. In addition, orexin receptor 1 antagonist SB334867 and orexin receptor 2 antagonist TCS OX229 enhanced melanopsin-based DAC responses, indicating that endogenous orexins inhibit signal transmission from ipRGCs to DACs. We further found that orexin-A inhibits melanopsin-based DAC responses via orexin receptors on DACs, whereas orexin-A may modulate signal transmission from rods and cones to DACs through activation of orexin receptors on DACs and their upstream neurons. Our results suggest that orexins could in?uence visual function via the dopaminergic system in the mammalian retina.
关键词： orexin,dopamine,ipRGC,melanopsin,amacrine cell,retina
更新于2025-09-09 09:28:46
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The Post-Illumination Pupil Response (PIPR)
摘要： The post-illumination pupil response (PIPR) has been quantified using four metrics, but the spectral sensitivity of only one is known; here we determine the other three. To optimize the human PIPR measurement, we determine the protocol producing the largest PIPR, the duration of the PIPR, and the metric(s) with the lowest coefficient of variation. METHODS. The consensual pupil light reflex (PLR) was measured with a Maxwellian view pupillometer. Experiment 1: Spectral sensitivity of four PIPR metrics (plateau, 6 seconds, area under curve early and late recovery) was determined from a criterion PIPR to a 1-second pulse and fitted with vitamin A1 nomogram (kmax ? 482 nm). Experiment 2: The PLR was measured as a function of three stimulus durations (1 second, 10 seconds, 30 seconds), five irradiances spanning low to high melanopsin excitation levels (retinal irradiance: 9.8–14.8 log quanta.cm(cid:2)2.s(cid:2)1), and two wavelengths, one with high (465 nm) and one with low (637 nm) melanopsin excitation. Intra- and interindividual coefficients of variation (CV) were calculated. RESULTS. The melanopsin (opn4) photopigment nomogram adequately describes the spectral sensitivity of all four PIPR metrics. The PIPR amplitude was largest with 1-second short-wavelength pulses (?12.8 log quanta.cm(cid:2)2.s(cid:2)1). The plateau and 6-second PIPR showed the least intra- and interindividual CV ((cid:3)0.2). The maximum duration of the sustained PIPR was 83.0 6 48.0 seconds (mean 6 SD) for 1-second pulses and 180.1 6 106.2 seconds for 30-second pulses (465 nm; 14.8 log quanta.cm(cid:2)2.s(cid:2)1). CONCLUSIONS. All current PIPR metrics provide a direct measure of the intrinsic melanopsin photoresponse. To measure progressive changes in melanopsin function in disease, we recommend that the PIPR be measured using short-duration pulses (e.g., (cid:3)1 second) with high melanopsin excitation and analyzed with plateau and/or 6-second metrics. Our PIPR interstimulus intervals between duration data provide a baseline for the selection of consecutive pupil testing sequences.
关键词： pupil light reflex,intrinsically photosensitive retinal ganglion cells (ipRGCs),melanopsin,post-illumination pupil response
更新于2025-09-09 09:28:46
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Melanopsin-Mediated Post-Illumination Pupil Response in Early Age-Related Macular Degeneration
摘要： PURPOSE. To determine whether melanopsin-expressing intrinsically photosensitive retinal ganglion cell (ipRGC) inputs to the pupil light re?ex (PLR) are affected in early age-related macular degeneration (AMD). METHODS. The PLR was measured in 40 participants (20 early AMD and 20 age-matched controls) using a custom-built Maxwellian view pupillometer. Sinusoidal stimuli (0.5 Hz, 11.9 seconds duration, 35.68 diameter) were presented to the study eye and the consensual pupil response was measured to lights with high melanopsin excitation (464 nm [blue]) and with low melanopsin excitation (638 nm [red]) that biased activation to the outer retina. Two melanopsin PLR metrics were quanti?ed: the phase amplitude percentage (PAP) during the sinusoidal stimulus presentation and the post-illumination pupil response (PIPR). The PLR during stimulus presentation was analyzed using latency to constriction, the transient pupil response and maximum pupil constriction metrics. Diagnostic accuracy was evaluated using receiver operating characteristic (ROC) curves. RESULTS. The blue PIPR was signi?cantly less sustained in the early AMD group (P < 0.001). The red PIPR was not signi?cantly different between groups (P > 0.05). The PAP and blue stimulus constriction amplitude were signi?cantly lower in the early AMD group (P < 0.05). There was no signi?cant difference between groups in the latency or transient amplitude for both stimuli (P > 0.05). ROC analysis showed excellent diagnostic accuracy for the blue PIPR metrics (area under the curve > 0.9). CONCLUSIONS. This is the initial report that the melanopsin-controlled PIPR is dysfunctional in early AMD. The noninvasive, objective measurement of the ipRGC controlled PIPR has excellent diagnostic accuracy for early AMD.
关键词： illumination pupil response,pupil light re?ex,intrinsically photosensitive retinal ganglion cells,post-illumination pupil response,ipRGCs,melanopsin
更新于2025-09-09 09:28:46