Activation of oxytocin receptors in mouse GABAergic amacrine cells modulates retinal dopaminergic signaling.

BACKGROUND: Oxytocin, secreted by oxytocin neurons in the hypothalamus, is an endogenous neuropeptide involved in modulating multiple sensory information processing pathways, and its roles in the brain have been associated with prosocial, maternal, and feeding-related behaviors. Visual information is necessary for initiating these behaviors, with the retina consisting of the first stage in the visual system mediating external stimulus perception. Oxytocin has been detected in the mammalian retina; however, the expression and possible function of oxytocin receptors (OxtR) in the retina remain unknown. Here, we explore the role of oxytocin in regulating visual information processing in the retina. RESULTS: We observed that OxtR mRNA and protein are expressed in the mouse retina. With Oxtr-Cre transgenic mice, immunostaining, and fluorescence in situ hybridization, we found that OxtRs are mainly expressed in GABAergic amacrine cells (ACs) in both the inner nuclear layer (INL) and ganglion cell layer (GCL). Further immunoreactivity studies showed that GABAergic OxtR+ neurons are mainly cholinergic and dopaminergic neurons in the INL and are cholinergic and corticotrophin-releasing hormone neurons in the GCL. Surprisingly, a high level of Oxtr mRNAs was detected in retinal dopaminergic neurons, and exogenous oxytocin application activated dopaminergic neurons to elevate the retinal dopamine level. Relying on in vivo electroretinographic recording, we found that activating retinal OxtRs reduced the activity of bipolar cells via OxtRs and dopamine receptors. CONCLUSIONS: These data indicate the functional expression of OxtRs in retinal GABAergic ACs, especially dopaminergic ACs, and expand the interactions between oxytocinergic and dopaminergic systems. This study suggests that visual perception, from the first stage of information processing in the retina, is modulated by hypothalamic oxytocin signaling.

Orexin-A Intensifies Mouse Pupillary Light Response by Modulating Intrinsically Photosensitive Retinal Ganglion Cells.

We show for the first time that the neuropeptide orexin modulates pupillary light response, a non-image-forming visual function, in mice of either sex. Intravitreal injection of the orexin receptor (OXR) antagonist TCS1102 and orexin-A reduced and enhanced pupillary constriction in response to light, respectively. Orexin-A activated OX1Rs on M2-type intrinsically photosensitive retinal ganglion cells (M2 cells), and caused membrane depolarization of these cells by modulating inward rectifier potassium channels and nonselective cation channels, thus resulting in an increase in intrinsic excitability. The increased intrinsic excitability could account for the orexin-A-evoked increase in spontaneous discharges and light-induced spiking rates of M2 cells, leading to an intensification of pupillary constriction. Orexin-A did not alter the light response of M1 cells, which could be because of no or weak expression of OX1Rs on them, as revealed by RNAscope in situ hybridization. In sum, orexin-A is likely to decrease the pupil size of mice by influencing M2 cells, thereby improving visual performance in awake mice via enhancing the focal depth of the eye's refractive system.SIGNIFICANCE STATEMENT This study reveals the role of the neuropeptide orexin in mouse pupillary light response, a non-image-forming visual function. Intravitreal orexin-A administration intensifies light-induced pupillary constriction via increasing the excitability of M2 intrinsically photosensitive retinal ganglion cells by activating the orexin receptor subtype OX1R. Modulation of inward rectifier potassium channels and nonselective cation channels were both involved in the ionic mechanisms underlying such intensification. Orexin could improve visual performance in awake mice by reducing the pupil size and thereby enhancing the focal depth of the eye's refractive system.

Effects of blue light-exposed retinal pigment epithelial cells on the process of ametropia.

Ametropia is one of the most common ocular disorders worldwide, to which almost half of visual impairments are attributed. Growing evidence has linked the development of ametropia with ambient light, including blue light, which is ubiquitous in our surroundings and has the highest photonic energy among the visible spectrum. However, the underlying mechanism of blue light-mediated ametropia remains controversial and unclear. In the present study, our data demonstrated that exposure of the retinal pigment epithelium (RPE) to blue light elevated the levels of the vital ametropia-related factor type Ⅰ collagen (COL1) via ß-catenin inhibition in scleral fibroblasts, leading to axial ametropia (hyperopic shift). Herein, our study provides evidence for the vital role of blue light-induced RPE dysfunction in the process of blue light-mediated ametropia, providing intriguing insights into ametropic aetiology and pathology by proposing a link among blue light, RPE dysfunction and ametropia.

Aerobic exercise delays retinal ganglion cell death after optic nerve injury.

Aerobic exercise has been shown to play a crucial role in preventing neurological diseases and improving cognitive function. In the present study, we investigated the effect of treadmill training on retinal ganglion cells (RGCs) following optic nerve transection in adult rats. We exercised the rats on a treadmill for 5 d/week (30 min/d at a rate of 9 m/min) or placed control rats on static treadmills. After 3 weeks of exercise, the left optic nerve of each rat was transected. After the surgery, the rat was exercised for another week. The percentages of surviving RGCs in the axotomized eyes of inactive rats were 67% and 39% at 5 and 7 days postaxotomy, respectively. However, exercised rats had significant more RGCs at 5 (74% survival) and 7 days (48% survival) after axotomy. Moreover, retinal brain-derived neurotrophic factor (BDNF) protein levels were significantly upregulated in response to exercise compared with those in the axotomized eyes of inactive rats. Blocking BNDF signaling during exercise by intraperitoneal injections of ANA-12, a BDNF tropomyosin receptor kinase (TrkB) receptor antagonist, reduced the number of RGCs in exercised rats to the level of RGCs in the inactive rats, effectively abolishing the protection of RGCs afforded by exercise. The results suggest that treadmill training effectively rescues RGCs from neurodegeneration following optic nerve transection by upregulating the expression of BDNF.

Morphological alterations of intrinsically photosensitive retinal ganglion cells after ablation of mouse photoreceptors with selective photocoagulation.

In this work, we investigated changes in the morphology of intrinsically photosensitive retinal ganglion cells (ipRGCs), M1 subtype, and pupillary light reflex following local and selective ablation of photoreceptors in mice. Laser photocoagulation was used to selectively destroy four patches of photoreceptors per eye at around 4 papillary diameters from the optic disc and at the 3, 6, 9, and 12 o'clock positions between the retinal vessels in the adult mouse retina, leaving cells in the inner retina intact. Morphological parameters of individual M1 cells specifically labeled by the antibody against melanopsin (PA1-780), including dendritic field size, total dendritic length, and dendritic branch number, were examined 1, 2, 4, and 8 weeks after photocoagulation with Neurolucida software. A considerable reduction in these parameters in M1 cells in the "lesioned areas" was found at all the four time points after photocoagulation, as compared with those in the "unlesioned areas". Although M1 cells in the lesioned areas showed significant changes as early as 1 week after laser treatment and the changes gradually increased, reaching a peak value at 2 weeks, morphological restoration was clearly seen in these cells over time. However, no difference in the morphological parameters of M1 cells was observed between the unlesioned areas of laser-treated mice and the corresponding areas of age-matched normal mice without laser lesions. Fluorescence intensity of the somata of melanopsin-positive M1 cells located inside the lesioned areas was significantly decreased at all the four time points after photocoagulation, whereas no changes in pupillary light reflex were detected at different light irradiations, indicating that photocoagulation-induced local photoreceptor loss and alterations of ipRGCs may be insufficient to cause abnormalities in non-image-forming (NIF) visual functions. The results suggest that intact photoreceptors could be crucial for maintaining the expression levels of melanopsin and normal morphology of M1 cells.

[Refractive development and form-deprivation induced myopic refractive error in CBA/CaJ mice].

Due to the advantages in genetic manipulation, mice have become one of the most commonly used mammalian models for the study of mechanisms underlying myopia development. However, the vast majority of laboratory mouse strains are incapable of synthesizing melatonin, a neurohormone that may play an important role in myopia generation in humans. The present study investigated refractive development profiles in the CBA/CaJ mouse, a strain proficient in melatonin, and determined whether and how its refractive development could be affected by form-deprivation. Eccentric infrared photoretinoscopy revealed that this animal could be stably refracted, and the refractive error underwent developmental changes, which increased with age in the hyperopic direction and eventually got stable approximately 9 weeks after birth. The absolute values of refractive error in CBA/CaJ mice were larger than those of age-matched C57BL/6 mice, whereas the time points when refractive error reached steady state were similar between the two strains. Five weeks of form-deprivation applied to 3-week-old CBA/CaJ mice by translucent occluder wear caused a significant myopic shift in refractive error, indicating that this strain could be adequately used as a myopia model.

A non-image-forming visual circuit mediates the innate fear of heights in male mice.

The neural basis of fear of heights remains largely unknown. In this study, we investigated the fear response to heights in male mice and observed characteristic aversive behaviors resembling human height vertigo. We identified visual input as a critical factor in mouse reactions to heights, while peripheral vestibular input was found to be nonessential for fear of heights. Unexpectedly, we found that fear of heights in naïve mice does not rely on image-forming visual processing by the primary visual cortex. Instead, a subset of neurons in the ventral lateral geniculate nucleus (vLGN), which connects to the lateral/ventrolateral periaqueductal gray (l/vlPAG), drives the expression of fear associated with heights. Additionally, we observed that a subcortical visual pathway linking the superior colliculus to the lateral posterior thalamic nucleus inhibits the defensive response to height threats. These findings highlight a rapid fear response to height threats through a subcortical visual and defensive pathway from the vLGN to the l/vlPAG.

Topical administration of GLP-1 eyedrops improves retinal ganglion cell function by facilitating presynaptic GABA release in early experimental diabetes.

ABSTRACT: Diabetic retinopathy is a prominent cause of blindness in adults, with early retinal ganglion cell (RGC) loss contributing to visual dysfunction or blindness. In the brain, defects in y-aminobutyric acid (GABA) synaptic transmission are associated with pathophysiological and neurodegenerative disorders, whereas glucagon-like peptide-1 (GLP-1) has demonstrated neuroprotective effects. However, it is not yet clear whether diabetes causes alterations in inhibitory input to RGCs and whether and how GLP-1 protects against neurodegeneration in the diabetic retina through regulating inhibitory synaptic transmission to RGCs. In the present study, we used the patch-clamp technique to record GABA subtype A receptor-mediated miniature inhibitory postsynaptic currents (mIPSCs) in RGCs from streptozotocin-induced diabetes model rats. We found that early diabetes (4 weeks of hyperglycemia) decreased the frequency of GABAergic mIPSCs in RGCs without altering their amplitude, suggesting a reduction in the spontaneous release of GABA to RGCs. Topical administration of GLP-1 eyedrops over a period of 2 weeks effectively countered the hyperglycemia-induced downregulation of GABAergic mIPSC frequency, subsequently enhancing the survival of RGCs. Concurrently, the protective effects of GLP-1 on RGCs in diabetic rats were eliminated by topical administration of exendin-9-39, a specific GLP-1 receptor antagonist, or SR95531, a specific antagonist of the GABA subtype A receptor. Furthermore, extracellular perfusion of GLP-1 was found to elevate the frequencies of GABAergic mIPSCs in both ON- and OFF-type RGCs. This elevation was shown to be mediated by activation of the phosphatidylinositol-phospholipase C/inositol 1,4,5-trisphosphate receptor/Ca2+/protein kinase C signaling pathway downstream of GLP-1 receptor activation. Moreover, multielectrode array recordings revealed that GLP-1 functionally augmented the photoresponses of ON-type RGCs. Optomotor response tests demonstrated that diabetic rats exhibited reductions in visual acuity and contrast sensitivity that were significantly ameliorated by topical administration of GLP-1. These results suggest that GLP-1 facilitates the release of GABA onto RGCs through the activation of GLP-1 receptor, leading to the de-excitation of RGC circuits and the inhibition of excitotoxic processes associated with diabetic retinopathy. Collectively, our findings indicate that the GABA system has potential as a therapeutic target for mitigating early-stage diabetic retinopathy. Furthermore, the topical administration of GLP-1 eyedrops represents a non-invasive and effective treatment approach for managing early-stage diabetic retinopathy.

Form and function of the M4 cell, an intrinsically photosensitive retinal ganglion cell type contributing to geniculocortical vision.

The photopigment melanopsin confers photosensitivity upon a minority of retinal output neurons. These intrinsically photosensitive retinal ganglion cells (ipRGCs) are more diverse than once believed, comprising five morphologically distinct types, M1 through M5. Here, in mouse retina, we provide the first in-depth characterization of M4 cells, including their structure, function, and central projections. M4 cells apparently correspond to ON α cells of earlier reports, and are easily distinguished from other ipRGCs by their very large somata. Their dendritic arbors are more radiate and highly branched than those of M1, M2, or M3 cells. The melanopsin-based intrinsic photocurrents of M4 cells are smaller than those of M1 and M2 cells, presumably because melanopsin is more weakly expressed; we can detect it immunohistochemically only with strong amplification. Like M2 cells, M4 cells exhibit robust, sustained, synaptically driven ON responses and dendritic stratification in the ON sublamina of the inner plexiform layer. However, their stratification patterns are subtly different, with M4 dendrites positioned just distal to those of M2 cells and just proximal to the ON cholinergic band. M4 receptive fields are large, with an ON center, antagonistic OFF surround and nonlinear spatial summation. Their synaptically driven photoresponses lack direction selectivity and show higher ultraviolet sensitivity in the ventral retina than in the dorsal retina, echoing the topographic gradient in S- and M-cone opsin expression. M4 cells are readily labeled by retrograde transport from the dorsal lateral geniculate nucleus and thus likely contribute to the pattern vision that persists in mice lacking functional rods and cones.

Cross-modal modulation gates nociceptive inputs in Drosophila.

Animals' response to a stimulus in one sensory modality is usually influenced by other modalities.1 One important type of multisensory integration is the cross-modal modulation, in which one sensory modality modulates (typically inhibits) another. Identification of the mechanisms underlying cross-modal modulations is crucial for understanding how sensory inputs shape animals' perception and for understanding sensory processing disorders.2,3,4 However, the synaptic and circuit mechanisms that underlie cross-modal modulation are poorly understood. This is due to the difficulty of separating cross-modal modulation from multisensory integrations in neurons that receive excitatory inputs from two or more sensory modalities5-in which case it is unclear what the modulating or modulated modality is. In this study, we report a unique system for studying cross-modal modulation by taking advantage of the genetic resources in Drosophila. We show that gentle mechanical stimuli inhibit nociceptive responses in Drosophila larvae. Low-threshold mechanosensory neurons inhibit a key second-order neuron in the nociceptive pathway through metabotropic GABA receptors on nociceptor synaptic terminals. Strikingly, this cross-modal inhibition is only effective when nociceptor inputs are weak, thus serving as a gating mechanism for filtering out weak nociceptive inputs. Our findings unveil a novel cross-modal gating mechanism for sensory pathways.

Exendin-4 promotes retinal ganglion cell survival and function by inhibiting calcium channels in experimental diabetes.

Progressive damage of retinal ganglion cells (RGCs) is observed in early diabetic retinopathy. Intracellular Ca2+ overload mediated by Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) is involved in neurodegeneration, whereas glucagon-like peptide-1 (GLP-1) provides neuroprotection. However, whether GLP-1 plays a neuroprotective role in diabetic retinas by modulating VGCCs remains unknown. We found that eye drops of exendin-4, a long-acting GLP-1 receptor (GLP-1R) agonist, prevented the increase of L-type Ca2+ current (ILCa) densities of RGCs induced by 4-week hyperglycemia and promoted RGC survival by suppressing L-type VGCC (L-VGCC) activity in streptozotocin-induced diabetic rats. Moreover, exendin-4-induced suppression of ILCa in RGCs may be mediated by a GLP-1R/Gs/cAMP-PKA/ryanodine/Ca2+/calmodulin/calcineurin/PP1 signaling pathway. Furthermore, exendin-4 functionally improved the light-evoked spiking ability of diabetic RGCs. These results suggest that GLP-1R activation enhances cAMP to PP1 signaling and that PP1 inactivates L-VGCCs by dephosphorylating them, thereby reducing Ca2+ influx, which could protect RGCs against excitotoxic Ca2+ overload.

Short-term acute bright light exposure induces a prolonged anxiogenic effect in mice via a retinal ipRGC-CeA circuit.

Light modulates mood through various retina-brain pathways. We showed that mice treated with short-term acute bright light exposure displayed anxiety-related phenotypes in a prolonged manner even after the termination of the exposure. Such a postexposure anxiogenic effect depended upon melanopsin-based intrinsically photosensitive retinal ganglion cell (ipRGC) activities rather than rod/cone photoreceptor inputs. Chemogenetic manipulation of specific central nuclei demonstrated that the ipRGC-central amygdala (CeA) visual circuit played a key role in this effect. The corticosterone system was likely to be involved in this effect, as evidenced by enhanced expression of the glucocorticoid receptor (GR) protein in the CeA and the bed nucleus of the stria terminalis and by the absence of this effect in animals treated with the GR antagonist. Together, our findings reveal a non-image forming visual circuit specifically designed for "the delayed" extinction of anxiety against potential threats, thus conferring a survival advantage.

Potential Choroidal Mechanisms Underlying Atropine's Antimyopic and Rebound Effects: A Mediation Analysis in a Randomized Clinical Trial.

Purpose: To investigate whether choroidal vascularity participates in high-dose atropine's antimyopia and rebound mechanisms. Methods: A mediation analysis was embedded within a randomized controlled trial. In total, 207 myopic children were assigned randomly to group A/B. Participants in group A received 1% atropine weekly (phase 1) and 0.01% atropine daily (phase 2) for 6 months each. Those in group B received 0.01% atropine daily for 1 year. Four plausible intervention mediators were assessed: total choroidal area (TCA), luminal area (LA), stromal area (SA), and choroidal vascularity index (CVI). Results: In group A, LA, SA, and TCA increased significantly after receiving 1% atropine for 6 months. The increment diminished after tapering to 0.01% atropine. In group B, those parameters remained stable. TCA mediated approximately one-third of 1% atropine's effect on spherical equivalent progression in both phases. In phase 1, the mediation effect of TCA was shared by LA and SA, while only that of LA remained significant in phase 2. No mediation effect of CVI was found. Conclusions: One percent atropine induced choroidal thickening by increasing both LA and SA, while 0.01% atropine had little choroidal response. The choroidal changes following 1% atropine treatment diminished after switching to 0.01% atropine. TCA, but not CVI, partially explains atropine's antimyopic and myopic-rebound mechanisms. SA may serve as a potential biomarker to predict the postrebound treatment efficacy of high-dose atropine. (ClinicalTrials.gov number, NCT03949101.).

Assessment of visual function in blind mice and monkeys with subretinally implanted nanowire arrays as artificial photoreceptors.

Retinal prostheses could restore image-forming vision in conditions of photoreceptor degeneration. However, contrast sensitivity and visual acuity are often insufficient. Here we report the performance, in mice and monkeys with induced photoreceptor degeneration, of subretinally implanted gold-nanoparticle-coated titania nanowire arrays providing a spatial resolution of 77.5 µm and a temporal resolution of 3.92 Hz in ex vivo retinas (as determined by patch-clamp recording of retinal ganglion cells). In blind mice, the arrays allowed for the detection of drifting gratings and flashing objects at light-intensity thresholds of 15.70-18.09 µW mm-2, and offered visual acuities of 0.3-0.4 cycles per degree, as determined by recordings of visually evoked potentials and optomotor-response tests. In monkeys, the arrays were stable for 54 weeks, allowed for the detection of a 10-µW mm-2 beam of light (0.5° in beam angle) in visually guided saccade experiments, and induced plastic changes in the primary visual cortex, as indicated by long-term in vivo calcium imaging. Nanomaterials as artificial photoreceptors may ameliorate visual deficits in patients with photoreceptor degeneration.

Signaling Mechanism for Modulation by GLP-1 and Exendin-4 of GABA Receptors on Rat Retinal Ganglion Cells.

Glucagon-like peptide-1 (GLP-1) is expressed in retinal neurons, but its role in the retina is largely unknown. Here, we demonstrated that GLP-1 or the GLP-1 receptor (GLP-1R; a G protein-coupled receptor) agonist exendin-4 suppressed γ-aminobutyric acid receptor (GABAR)-mediated currents through GLP-1Rs in isolated rat retinal ganglion cells (GCs). Pre-incubation with the stimulatory G protein (Gs) inhibitor NF 449 abolished the exendin-4 effect. The exendin-4-induced suppression was mimicked by perfusion with 8-Br-cAMP (a cAMP analog), but was eliminated by the protein kinase A (PKA) inhibitor Rp-cAMP/KT-5720. The exendin-4 effect was accompanied by an increase in [Ca2+]i of GCs through the IP3-sensitive pathway and was blocked in Ca2+-free solution. Furthermore, when the activity of calmodulin (CaM) and CaM-dependent protein kinase II (CaMKII) was inhibited, the exendin-4 effect was eliminated. Consistent with this, exendin-4 suppressed GABAR-mediated light-evoked inhibitory postsynaptic currents in GCs in rat retinal slices. These results suggest that exendin-4-induced suppression may be mediated by a distinct Gs/cAMP-PKA/IP3/Ca2+/CaM/CaMKII signaling pathway, following the activation of GLP-1Rs.

Green light analgesia in mice is mediated by visual activation of enkephalinergic neurons in the ventrolateral geniculate nucleus.

Green light exposure has been shown to reduce pain in animal models. Here, we report a vision-associated enkephalinergic neural circuit responsible for green light-mediated analgesia. Full-field green light exposure at an intensity of 10 lux produced analgesic effects in healthy mice and in a model of arthrosis. Ablation of cone photoreceptors completely inhibited the analgesic effect, whereas rod ablation only partially reduced pain relief. The analgesic effect was not modulated by the ablation of intrinsically photosensitive retinal ganglion cells (ipRGCs), which are atypical photoreceptors that control various nonvisual effects of light. Inhibition of the retino-ventrolateral geniculate nucleus (vLGN) pathway completely abolished the analgesic effects. Activation of this pathway reduced nociceptive behavioral responses; such activation was blocked by the inhibition of proenkephalin (Penk)-positive neurons in the vLGN (vLGNPenk). Moreover, green light analgesia was prevented by knockdown of Penk in the vLGN or by ablation of vLGNPenk neurons. In addition, activation of the projections from vLGNPenk neurons to the dorsal raphe nucleus (DRN) was sufficient to suppress nociceptive behaviors, whereas its inhibition abolished the green light analgesia. Our findings indicate that cone-dominated retinal inputs mediated green light analgesia through the vLGNPenk-DRN pathway and suggest that this signaling pathway could be exploited for reducing pain.

The role of ipRGCs in ocular growth and myopia development.

The increasing global prevalence of myopia calls for elaboration of the pathogenesis of this disease. Here, we show that selective ablation and activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) in developing mice induced myopic and hyperopic refractive shifts by modulating the corneal radius of curvature (CRC) and axial length (AL) in an opposite way. Melanopsin- and rod/cone-driven signals of ipRGCs were found to influence refractive development by affecting the AL and CRC, respectively. The role of ipRGCs in myopia progression is evidenced by attenuated form-deprivation myopia magnitudes in ipRGC-ablated and melanopsin-deficient animals and by enhanced melanopsin expression/photoresponses in form-deprived eyes. Cell subtype-specific ablation showed that M1 subtype cells, and probably M2/M3 subtype cells, are involved in ocular development. Thus, ipRGCs contribute substantially to mouse eye growth and myopia development, which may inspire novel strategies for myopia intervention.

Altered Retinal Dopamine Levels in a Melatonin-proficient Mouse Model of Form-deprivation Myopia.

Reduced levels of retinal dopamine, a key regulator of eye development, are associated with experimental myopia in various species, but are not seen in the myopic eyes of C57BL/6 mice, which are deficient in melatonin, a neurohormone having extensive interactions with dopamine. Here, we examined the relationship between form-deprivation myopia (FDM) and retinal dopamine levels in melatonin-proficient CBA/CaJ mice. We found that these mice exhibited a myopic refractive shift in form-deprived eyes, which was accompanied by altered retinal dopamine levels. When melatonin receptors were pharmacologically blocked, FDM could still be induced, but its magnitude was reduced, and retinal dopamine levels were no longer altered in FDM animals, indicating that melatonin-related changes in retinal dopamine levels contribute to FDM. Thus, FDM is mediated by both dopamine level-independent and melatonin-related dopamine level-dependent mechanisms in CBA/CaJ mice. The previously reported unaltered retinal dopamine levels in myopic C57BL/6 mice may be attributed to melatonin deficiency.

Visual cortex encodes timing information in humans and mice.

Despite the importance of timing in our daily lives, our understanding of how the human brain mediates second-scale time perception is limited. Here, we combined intracranial stereoelectroencephalography (SEEG) recordings in epileptic patients and circuit dissection in mice to show that visual cortex (VC) encodes timing information. We first asked human participants to perform an interval-timing task and found VC to be a key timing brain area. We then conducted optogenetic experiments in mice and showed that VC plays an important role in the interval-timing behavior. We further found that VC neurons fired in a time-keeping sequential manner and exhibited increased excitability in a timed manner. Finally, we used a computational model to illustrate a self-correcting learning process that generates interval-timed activities with scalar-timing property. Our work reveals how localized oscillations in VC occurring in the seconds to deca-seconds range relate timing information from the external world to guide behavior.

Orexin-A differentially modulates inhibitory and excitatory synaptic transmission in rat inner retina.

In this work, modulation by orexin-A of the release of glutamate and GABA from bipolar and amacrine cells respectively was studied by examining the effects of the neuropeptide on miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) of rat retinal ganglion cells (GCs). Using RNAscope in situ hybridization in combination with immunohistochemistry, we showed positive signals for orexin receptor-1 (OX1R) mRNA in the bipolar cell terminals and those for orexin receptor-2 (OX2R) mRNA in the amacrine cell terminals. With whole-cell patch-clamp recordings in rat retinal slices, we demonstrated that application of orexin-A reduced the interevent interval of mEPSCs of GCs through OX1R. However, it increased the interevent interval of mIPSCs, mediated by GABAA receptors, through OX2R. Furthermore, orexin-A-induced reduction of mEPSC interevent interval was abolished by the application of PI-PLC inhibitors or PKC inhibitors. In contrast, orexin-A-induced increase of GABAergic mIPSC interevent interval was mimicked by 8-Br-cAMP or an adenylyl cyclase activator, but was eliminated by PKA antagonists. Finally, application of nimodipine, an L-type Ca2+ channel blocker, increased both mEPSC and mIPSC interevent interval, and co-application of orexin-A no longer changed the mEPSCs and mIPSCs. We conclude that orexin-A increases presynaptic glutamate release onto GCs by activating L-type Ca2+ channels in bipolar cells, a process that is mediated by an OX1R/PI-PLC/PKC signaling pathway. However, orexin-A decreases presynaptic GABA release onto GCs by inhibiting L-type Ca2+ channels in amacrine cells, a process that is mediated by an OX2R/cAMP-PKA signaling pathway.