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Nonimage-forming vision in mammals is mediated primarily by melanopsin (OPN4)-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs). In mouse M1-ipRGCs, melanopsin predominantly activates, via Gα

IntroductionMultimodal prehabilitation, an emerging field within the Perioperative Medicine specialty, requires close multidisciplinary team coordination. The goal is to optimise the patient’s health status in the 4–8 weeks before elective surgery to withstand surgical stress. Most patients are unfamiliar with the concept of prehabilitation but are interested in participating in such a programme after explanation. The objective of this randomised controlled trial is to evaluate the effect of prehabilitation (patient education video and multimodal prehabilitation) on the preoperative patient-centred coordinated care experience.Method and analysisOne hundred patients undergoing major elective surgery (cardiac, colorectal, hepatobiliary-pancreatic and urology) will be recruited into a two-group, parallel, superiority, single-blinded randomised controlled trial. Patients will be randomised to receive either preoperative patient education comprising of a video and prehabilitation programme with standard care (intervention) or standard care (control). The primary outcome measure will be the quality of preoperative patient care experience using the 11-item Chinese version of the Person-Centred Coordinated Care Experience Questionnaire (P3CEQ) before surgery. Secondary outcomes will include the change in Hospital Anxiety and Depression Scale (HADS) score from trial enrolment to before surgery, Quality of Recovery Score (QoR-15) on third day after surgery and Days Alive and At Home within 30 days after surgery (DAH30). Intention-to-treat and per-protocol analyses will be performed.Ethics and disseminationThe Joint CUHK-NTEC Clinical Research Ethics Committee approved the study protocol (CREC Ref. No. 2021.518-T). The findings will be presented at scientific meetings, in peer-reviewed journals and to study participants.Trial registration numberChiCTR2100053637.

G protein–coupled receptor (GPCR) signaling is ubiquitous. As an archetype of this signaling motif, rod phototransduction has provided many fundamental, quantitative details, including a dogma that one active GPCR molecule activates a substantial number of downstream G protein/enzyme effector complexes. However, rod phototransduction is light-activated, whereas GPCR pathways are predominantly ligand-activated. Here, we report a detailed study of the ligand-triggered GPCR pathway in mammalian olfactory transduction, finding that an odorant-receptor molecule when (one-time) complexed with its most effective odorants produces on average much less than one downstream effector. Further experiments gave a nominal success probability of tentatively ∼10 −4 (more conservatively, ∼10 −2 to ∼10 −5 ). This picture is potentially more generally representative of GPCR signaling than is rod phototransduction, constituting a paradigm shift.

From mouse to primate, there is a striking discontinuity in our current understanding of the neural coding of motion direction. In non-primate mammals, directionally selective cell types and circuits are a signature feature of the retina, situated at the earliest stage of the visual process1,2. In primates, by contrast, direction selectivity is a hallmark of motion processing areas in visual cortex3,4, but has not been found in the retina, despite significant effort5,6. Here we combined functional recordings of light-evoked responses and connectomic reconstruction to identify diverse direction-selective cell types in the macaque monkey retina with distinctive physiological properties and synaptic motifs. This circuitry includes an ON-OFF ganglion cell type, a spiking, ON-OFF poly-axonal amacrine cell and the starburst amacrine cell, all of which show direction selectivity. Moreover, we found unexpectedly that macaque starburst cells possess a strong, non-GABAergic, antagonistic surround mediated by input from excitatory bipolar cells that is critical for the generation of radial motion sensitivity in these cells. Our findings open a new door to investigation of a novel circuitry that computes motion direction in the primate visual system.

G protein-coupled receptor (GPCR) signaling is crucial for many physiological processes. A signature of such pathways is high amplification, a concept originating from retinal rod phototransduction, whereby one photoactivated rhodopsin molecule (Rho*) was long reported to activate several hundred transducins (G(T)*s), each then activating a cGMP-phosphodiesterase catalytic subunit (G(T)*·PDE*). This high gain at the Rho*-to-G(T)* step has been challenged more recently, but estimates remain dispersed and rely on some nonintact rod measurements. With two independent approaches, one with an extremely inefficient mutant rhodopsin and the other with WT bleached rhodopsin, which has exceedingly weak constitutive activity in darkness, we obtained an estimate for the electrical effect from a single G(T)*·PDE* molecular complex in intact mouse rods. Comparing the single-G(T)*·PDE* effect to the WT single-photon response, both in Gcaps(−/−) background, gives an effective gain of only ∼12–14 G(T)*·PDE*s produced per Rho*. Our findings have finally dispelled the entrenched concept of very high gain at the receptor-to-G protein/effector step in GPCR systems.

The pupil-aligned orientation of retinal photoreceptors is dynamically phototropic, but different between outer and inner segment., Almost a century ago, Stiles and Crawford reported that the human eye is more sensitive to light entering through the pupil center than through its periphery (Stiles-Crawford effect). This psychophysical phenomenon, later found to correlate with photoreceptor orientation toward the pupil, was dynamically phototropic, adjustable within days to an eccentrically displaced pupil. For decades, this phototropism has been speculated to involve coordinated movements of the rectilinear photoreceptor outer and inner segments. We report here that, unexpectedly, the murine photoreceptor outer segment has a seemingly light-independent orientation, but the inner segment’s orientation undergoes light-dependent movement, giving rise to nonrectilinear outer and inner segments in adult mice born and reared in darkness. Light during an early critical period (~P0 to P8), however, largely sets the correct photoreceptor orientation permanently afterward. Unexpectedly, abolishing rod and cone phototransductions did not mimic darkness in early life, suggesting photosignaling extrinsic to rods and cones is involved.

Numerous rhodopsin mutations have been implicated in night blindness and retinal degeneration, often with unclear etiology. D190N-rhodopsin (D190N-Rho) is a well-known inherited human mutation causing retinitis pigmentosa. Both higher-than-normal spontaneous-isomerization activity and misfolding/mistargeting of the mutant protein have been proposed as causes of the disease, but neither explanation has been thoroughly examined. We replaced wild-type rhodopsin (WT-Rho) in Rho(D190N/WT) mouse rods with a largely “functionally silenced” rhodopsin mutant to isolate electrical responses triggered by D190N-Rho activity, and found that D190N-Rho at the single-molecule level indeed isomerizes more frequently than WT-Rho by over an order of magnitude. Importantly, however, this higher molecular dark activity does not translate into an overall higher cellular dark noise, owing to diminished D190N-Rho content in the rod outer segment. Separately, we found that much of the degeneration and shortened outer-segment length of Rho(D190N/WT) mouse rods was not averted by ablating rod transducin in phototransduction—also consistent with D190N-Rho’s higher isomerization activity not being the primary cause of disease. Instead, the low pigment content, shortened outer-segment length, and a moderate unfolded protein response implicate protein misfolding as the major pathogenic problem. Finally, D190N-Rho also provided some insight into the mechanism of spontaneous pigment excitation.

In mammalian olfactory transduction, odorants activate a cAMP-mediated signaling pathway that leads to the opening of cyclic nucleotide-gated (CNG), nonselective cation channels and depolarization. The Ca2+ influx through open CNG channels triggers an inward current through Ca2+-activated Cl channels (ANO2), which is expected to produce signal amplification. However, a study on an Ano2-/- mouse line reported no elevation in the behavioral threshold of odorant detection compared with wild type (WT). Subsequent studies by others on the same Ano2-/- line, nonetheless, found subtle defects in olfactory behavior and some abnormal axonal projections from the olfactory receptor neurons (ORNs) to the olfactory bulb. As such, the question regarding signal amplification by the Cl current in WT mouse remains unsettled. Recently, with suction-pipette recording, we have successfully separated in frog ORNs the CNG and Cl currents during olfactory transduction and found the Cl current to predominate in the response down to the threshold of action-potential signaling to the brain. For better comparison with the mouse data by others, we have now carried out similar current-separation experiments on mouse ORNs. We found that the Cl current clearly also predominated in the mouse olfactory response at signaling threshold, accounting for ∼80% of the response. In the absence of the Cl current, we expect the threshold stimulus to increase by approximately sevenfold.

Background Physical prehabilitation (preparative rehabilitation) programs may have beneficial effects on enhancing physical strength and functional status before surgery, but their effects on postoperative recovery are unclear. Objectives This systematic review investigated the effectiveness of physical prehabilitation programs before cardiac surgery on postoperative recovery and other perioperative outcomes. Methods We searched for reports of randomised controlled trials of any prehabilitation programs that included physical activity or an exercise training component in adults undergoing elective cardiac surgery, published in any language, from six bibliographic databases (last search on June 20, 2019). We assessed trials for risk of bias, overall certainty of evidence and quality of intervention reporting using the Cochrane Risk of Bias Assessment Tool, GRADE system and the Template for Intervention Description and Replication checklist and guide, respectively. Results All 7 studies (726 participants) were at high risk of bias because of lack of blinding. The quality of prehabilitation reporting was moderate because program adherence was rarely assessed. The timing of prehabilitation ranged from 5 days to 16 weeks before surgery and from face-to-face exercise prescription to telephone counselling and monitoring. We found uncertain effects of prehabilitation on postoperative clinical outcomes (among the many outcomes assessed): perioperative mortality (Peto odds ratio 1.30, 95% confidence interval [CI] 0.28 to 5.95; I2 = 0%; low-certainty evidence) and postoperative atrial fibrillation (relative risk 0.75, 95% CI 0.38 to 1.46; I2 = 50%; very low-certainty evidence). However, prehabilitation may improve postoperative functional capacity and slightly shorten the hospital stay (mean difference −0.66 days, 95% CI −1.29 to −0.03; I2 = 45%; low-certainty evidence). Conclusion Despite the high heterogeneity among physical prehabilitation trials and the uncertainty regarding robust clinical outcomes, physical prehabilitation before cardiac surgery seems to enhance selected postoperative functional performance measures and slightly reduce the hospital length of stay after cardiac surgery.

Retinal rod and cone photoreceptors mediate vision in dim and bright light, respectively, by transducing absorbed photons into electrical signals. Their phototransduction mechanisms are essentially identical. However, one distinct difference between them is that, whereas a rod visual pigment remains stable in darkness, a cone pigment is liable to spontaneously dissociate into apo-opsin and retinal (the chromophore) without isomerization. This cone-pigment property has long been reported, but it has often been overlooked in the field. Importantly, because apo-opsin has constitutive activity, it triggers transduction signaling to produce electrical noise even in darkness. Currently, the precise apo-opsin content in dark-adapted cones is unknown, as is its associated dark activity. We report here a systematic study of red (L), green (M) and blue (S) cones, finding different percentages of apo-opsin across them in darkness. Surprisingly, we also found that apo-opsin signaling in L and M cones in darkness is actually much higher than the well-known holo-pigment thermal isomerization activity. As such, given the very low signal amplification at the pigment-to-transducin/phosphodiesterase step in cone transduction, apo-opsin noise may not be easily distinguishable from light-triggered responses and may affect cone vision near threshold.

In PNAS (1), we estimate ∼12–14 active transducin·phosphodiesterase complexes (GT\*·PDE\*s) produced per active rhodopsin (Rho*) in mouse rods. This is the effective gain—more informative by not including the empty gain from GT*s failing to activate PDE. Nearly all previous estimates were on the total number of GT* produced per Rho* merely because no one before us could measure the individual GT\*·PDE\*-triggered electrical event for direct comparison with the single-Rho* response. We do not state in our paper that previous measurements of the rate of GT* production per Rho* were all incorrect, but rather they spanned a wide range of values with no consensus … [↵][1]1To whom correspondence should be addressed. Email: kwyau{at}jhmi.edu. [1]: #xref-corresp-1-1

Olfactory transduction in vertebrate olfactory receptor neurons (ORNs) involves primarily a cAMP-signaling cascade that leads to the opening of cyclic-nucleotide–gated (CNG), nonselective cation channels. The consequent Ca2+ influx triggers adaptation but also signal amplification, the latter by opening a Ca2+-activated Cl channel (ANO2) to elicit, unusually, an inward Cl current. Hence the olfactory response has inward CNG and Cl components that are in rapid succession and not easily separable. We report here success in quantitatively separating these two currents with respect to amplitude and time course over a broad range of odorant strengths. Importantly, we found that the Cl current is the predominant component throughout the olfactory dose–response relation, down to the threshold of signaling to the brain. This observation is very surprising given a recent report by others that the olfactory-signal amplification effected by the Ca2+-activated Cl current does not influence the behavioral olfactory threshold in mice.

It is a deeply engrained notion that the visual pigment rhodopsin signals light as a monomer, even though many G protein-coupled receptors are now known to exist and function as dimers. Nonetheless, recent studies (albeit all in vitro) have suggested that rhodopsin and its chromophore-free apoprotein, R-opsin, may indeed exist as a homodimer in rod disk membranes. Given the overwhelmingly strong historical context, the crucial remaining question, therefore, is whether pigment dimerization truly exists naturally and what function this dimerization may serve. We addressed this question in vivo with a unique mouse line (S-opsin+Lrat−/−) expressing, transgenically, short-wavelength–sensitive cone opsin (S-opsin) in rods and also lacking chromophore to exploit the fact that cone opsins, but not R-opsin, require chromophore for proper folding and trafficking to the photoreceptor’s outer segment. In R-opsin’s absence, S-opsin in these transgenic rods without chromophore was mislocalized; in R-opsin’s presence, however, S-opsin trafficked normally to the rod outer segment and produced functional S-pigment upon subsequent chromophore restoration. Introducing a competing R-opsin transmembrane helix H1 or helix H8 peptide, but not helix H4 or helix H5 peptide, into these transgenic rods caused mislocalization of R-opsin and S-opsin to the perinuclear endoplasmic reticulum. Importantly, a similar peptide-competition effect was observed even in WT rods. Our work provides convincing evidence for visual pigment dimerization in vivo under physiological conditions and for its role in pigment maturation and targeting. Our work raises new questions regarding a potential mechanistic role of dimerization in rhodopsin signaling.

The long‐term goal of this research is to understand how retinal ganglion cells that express the photopigment melanopsin, also known as OPN4, contribute to vision in humans and other primates. Here we report the results of anatomical studies using our polyclonal antibody specifically against human melanopsin that confirm and extend previous descriptions of melanopsin cells in primates. In macaque and human retina, two distinct populations of melanopsin cells were identified based on dendritic stratification in either the inner or the outer portion of the inner plexiform layer (IPL). Variation in dendritic field size and cell density with eccentricity was confirmed, and dendritic spines, a new feature of melanopsin cells, were described. The spines were the sites of input from DB6 diffuse bipolar cell axon terminals to the inner stratifying type of melanopsin cells. The outer stratifying melanopsin type received inputs from DB6 bipolar cells via a sparse outer axonal arbor. Outer stratifying melanopsin cells also received inputs from axon terminals of dopaminergic amacrine cells. On the outer stratifying melanopsin cells, ribbon synapses from bipolar cells and conventional synapses from amacrine cells were identified in electron microscopic immunolabeling experiments. Both inner and outer stratifying melanopsin cell types were retrogradely labeled following tracer injection in the lateral geniculate nucleus (LGN). In addition, a method for targeting melanopsin cells for intracellular injection using their intrinsic fluorescence was developed. This technique was used to demonstrate that melanopsin cells were tracer coupled to amacrine cells and would be applicable to electrophysiological experiments in the future. J. Comp. Neurol. 524:2845–2872, 2016. © 2016 The Authors The Journal of Comparative Neurology Published by Wiley Periodicals, Inc.

Retinal rod and cone photoreceptors mediate vision in dim and bright light, respectively, by transducing absorbed photons into neural electrical signals. Their phototransduction mechanisms are essentially identical. However, one difference is that, whereas a rod visual pigment remains stable in darkness, a cone pigment has some tendency to dissociate spontaneously into apo-opsin and retinal (the chromophore) without isomerization. This cone-pigment property is long known but has mostly been overlooked. Importantly, because apo-opsin has weak constitutive activity, it triggers transduction to produce electrical noise even in darkness. Currently, the precise dark apo-opsin contents across cone subtypes are mostly unknown, as are their dark activities. We report here a study of goldfish red (L), green (M), and blue (S) cones, finding with microspectrophotometry widely different apo-opsin percentages in darkness, being ∼30% in L cones, ∼3% in M cones, and negligible in S cones. L and M cones also had higher dark apo-opsin noise than holo-pigment thermal isomerization activity. As such, given the most likely low signal amplification at the pigment-to-transducin/phosphodiesterase phototransduction step, especially in L cones, apo-opsin noise may not be easily distinguishable from light responses and thus may affect cone vision near threshold.

Odorants activate in mammalian olfactory receptor neurons (ORNs) an inward cyclic nucleotide-gated (CNG), nonselective cation current and, importantly, a follower inward Ca2+-activated Cl current serving to amplify the olfactory signal. This concept is nonetheless refuted by a report describing no increase in behavioral olfactory threshold for a mouse line engineered to harbor an ablated gene for the Cl current. Two other reports on the same mouse line, however, did observe some subtle olfactory defects. We take a different approach here by dissecting the normal mouse ORN receptor current into its CNG- and Cl-current components, and showing that, at signaling threshold to the brain, the Cl current indeed accounts for most of the olfactory response, and thus should contribute importantly to olfactory signaling.

Visual pigments can be spontaneously activated by internal thermal energy, generating noise that interferes with real-light detection. Recently, we developed a physicochemical theory that successfully predicts the rate of spontaneous activity of representative rod and cone pigments from their peak-absorption wavelength (λmax), with pigments having longer λmax being noisier. Interestingly, cone pigments may generally be ~25 fold noisier than rod pigments of the same λmax, possibly ascribed to an ‘open’ chromophore-binding pocket in cone pigments defined by the capability of chromophore-exchange in darkness. Here, we show in mice that the λmax-dependence of pigment noise could be extended even to a mutant pigment, E122Q-rhodopsin. Moreover, although E122Q-rhodopsin shows some cone-pigment-like characteristics, its noise remained quantitatively predictable by the ‘non-open’ nature of its chromophore-binding pocket as in wild-type rhodopsin. The openness/closedness of the chromophore-binding pocket is potentially a useful indicator of whether a pigment is intended for detecting dim or bright light. DOI: http://dx.doi.org/10.7554/eLife.18492.001, eLife digest At the back of our eyes is a thin layer of cells that contain light-absorbing pigment molecules. These cells convert light energy into electrical signals that the brain then interprets to allow us to see. In this cell layer, the so-called cone cells work in bright light and provide us with the sense of color, whereas rod cells are for vision in dim light. Each visual pigment consists of a protein with a pocket-like space that holds a compound called a chromophore. Light causes the chromophore to change shape inside the pocket, which in turn activates the pigment. However, the pigments can also become activated at random, even in darkness. These false signals, nicknamed “dark light”, are caused by heat instead of light and essentially create a kind of visual noise that can interfere with vision. In 2011, researchers found that pigments that are most sensitive to the longer wavelengths of light (that is, light redder in color) tend to be noisier. The researchers also found that cone pigments are noisier than rod pigments even if they are most sensitive to the same wavelengths of light. To understand what causes this difference between cone and rod pigments, Yue, Frederiksen et al. – who include many of the researchers involved in the 2011 study – made use of mice with a mutated pigment in their rod cells. The mutant pigment was more sensitive to light of shorter wavelengths and, importantly, it behaved like a cone pigment in some ways but kept the closed pocket that is found in rod pigments. Indeed,Yue, Frederiksen et al. showed that the noise level of this mutant pigment could be accurately predicted from the wavelength it was most sensitive to and how closed its pocket was (in other words, the pocket's “closedness”). Further analyses revealed that an open pocket seems to be common to cone pigments from different species. So, it appears that cone pigments are noisier because they have a more open pocket, and the extra space might allow the chromophore to move around and change shape more easily. Going forward, more visual pigments need to be tested to confirm the relationship between the openness of the chromophore-binding pocket and spontaneous activity. If confirmed, it might be possible to one day predict whether a pigment is intended for dim- or bright-light vision simply by knowing whether its chromophore-binding pocket is more open or closed. DOI: http://dx.doi.org/10.7554/eLife.18492.002

Summary The mammalian pupillary light reflex (PLR) involves a bilateral brain circuit whereby afferent light signals in the optic nerve ultimately drive iris-sphincter-muscle contraction via excitatory cholinergic parasympathetic innervation [1, 2]. Additionally, the PLR in nocturnal and crepuscular sub-primate mammals has a "local" component in the isolated sphincter muscle [3–5], as in amphibians, fish, and bird [6–10]. In mouse, this local PLR requires the pigment melanopsin [5], originally found in intrinsically photosensitive retinal ganglion cells (ipRGCs) [11–19]. However, melanopsin's presence and effector pathway locally in the iris remain uncertain. The sphincter muscle itself may express melanopsin [5], or its cholinergic parasympathetic innervation may be modulated by suggested intraocular axonal collaterals of ipRGCs traveling to the eye's ciliary body or even to the iris [20–22]. Here, we show that the muscarinic receptor antagonist, atropine, eliminated the effect of acetylcholine (ACh), but not of light, on isolated mouse sphincter muscle. Conversely, selective genetic deletion of melanopsin in smooth muscle mostly removed the light-induced, but not the ACh-triggered, increase in isolated sphincter muscle's tension and largely suppressed the local PLR in vivo. Thus, sphincter muscle cells are bona fide, albeit unconventional, photoreceptors. We found melanopsin expression in a small subset of mouse iris sphincter muscle cells, with the light-induced contractile signal apparently spreading through gap junctions into neighboring muscle cells. Light and ACh share a common signaling pathway in sphincter muscle. In summary, our experiments have provided details of a photosignaling process in the eye occurring entirely outside the retina.

In the mammalian retina, besides the conventional rod–cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment1–7. On ablation of the melanopsin gene, retinal ganglion cells that normally express melanopsin are no longer intrinsically photosensitive8. Furthermore, pupil reflex8, light-induced phase delays of the circadian clock9,10 and period lengthening of the circadian rhythm in constant light9,10 are all partially impaired. Here, we investigated whether additional photoreceptive systems participate in these responses. Using mice lacking rods and cones, we measured the action spectrum for phase-shifting the circadian rhythm of locomotor behaviour. This spectrum matches that for the pupillary light reflex in mice of the same genotype11, and that for the intrinsic photosensitivity of the melanopsin-expressing retinal ganglion cells7. We have also generated mice lacking melanopsin coupled with disabled rod and cone photo-transduction mechanisms. These animals have an intact retina but fail to show any significant pupil reflex, to entrain to light/dark cycles, and to show any masking response to light. Thus, the rod–cone and melanopsin systems together seem to provide all of the photic input for these accessory visual functions.

Summary Background: The visual system is now known to be composed of image-forming and non-image-forming pathways. Photoreception for the image-forming pathway begins at the rods and cones, whereas that for the non-image-forming pathway also involves intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin. In the mouse retina, the rod and cone photoreceptors become light responsive from postnatal day 10 (P10); however, the development of photosensitivity of the ipRGCs remains largely unexplored. Results: Here, we provide direct physiological evidence that the ipRGCs are light responsive from birth (P0) and that this photosensitivity requires melanopsin expression. Interestingly, the number of ipRGCs at P0 is over five times that in the adult retina, reflecting an initial overproduction of melanopsin-expressing cells during development. Even at P0, the ipRGCs form functional connections with the suprachiasmatic nucleus, as assessed by light-induced Fos expression. Conclusions: The findings suggest that the non-image-forming pathway is functional long before the mainstream image-forming pathway during development.

Non-image-forming vision in mammals is mediated primarily by melanopsin-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs). In mouse M1-ipRGCs, by far the best-studied subtype, melanopsin activates PLCβ4 (phospholipase C-β4) to open TRPC6,7 channels, mechanistically similar to phototransduction in fly rhabdomeric (microvillous) photoreceptors. We report here that, surprisingly, mouse M4-ipRGCs rely on a different and hitherto undescribed melanopsin-driven, ciliary phototransduction mechanism involving cyclic nucleotide as the second messenger and HCN channels rather than CNG channels as the ion channel for phototransduction. Even more surprisingly, within an individual mouse M2-ipRGC, this HCN-channel-dependent, ciliary phototransduction pathway operates in parallel with the TRPC6,7-dependent rhabdomeric pathway. These findings reveal a complex heterogeneity in phototransduction among ipRGCs and, more importantly, break a general dogma about segregation of the two phototransduction motifs, likely with strong evolutionary implications.