Research progress of visual perception training on postoperative reconstruction of binocular vision in patients with intermittent exotropia / 国际眼科杂志(Guoji Yanke Zazhi)

Intermittent exotropia(IXT)is a common ophthalmic disease with high incidence, variable deviation, and varying degrees of impaired binocular visual function. The defect of binocular visual function is related to the changes of visual cortex. IXT involves the functional changes of many brain regions, including the cortical areas related to binocular fusion. After correcting the eye position, the abnormal changes of cerebral cortex still exist in some patients with IXT, and the recovery of binocular vision is still difficult. In order to solve these problems, visual perception training is gradually applied to the postoperative reconstruction of binocular visual function in patients with IXT. Visual perception training repairs the visual cortex from the brain level, improving the ability of the visual cortex to process information by constantly stimulating the visual center, thus repairing the visual central function, so that patients can obtain good binocular visual function, stabilize the eye position and reduce recurrence. This article reviews the mechanism of binocular visual impairment and the role of visual perception training in the treatment of IXT. It is hoped to provide more evidence for visual perception training to reconstruct postoperative binocular visual function and reduce the recurrence rate in patients with IXT.

Methcathinone Increases Visually-evoked Neuronal Activity and Enhances Sensory Processing Efficiency in Mice / 神经科学通报·英文版

Methcathinone (MCAT) belongs to the designer drugs called synthetic cathinones, which are abused worldwide for recreational purposes. It has strong stimulant effects, including enhanced euphoria, sensation, alertness, and empathy. However, little is known about how MCAT modulates neuronal activity in vivo. Here, we evaluated the effect of MCAT on neuronal activity with a series of functional approaches. C-Fos immunostaining showed that MCAT increased the number of activated neurons by 6-fold, especially in sensory and motor cortices, striatum, and midbrain motor nuclei. In vivo single-unit recording and two-photon Ca2+ imaging revealed that a large proportion of neurons increased spiking activity upon MCAT administration. Notably, MCAT induced a strong de-correlation of population activity and increased trial-to-trial reliability, specifically during a natural movie stimulus. It improved the information-processing efficiency by enhancing the single-neuron coding capacity, suggesting a cortical network mechanism of the enhanced perception produced by psychoactive stimulants.

A Comprehensive Overview of the Role of Visual Cortex Malfunction in Depressive Disorders: Opportunities and Challenges / 神经科学通报·英文版

Major depressive disorder (MDD) is a highly heterogeneous mental disorder, and its complex etiology and unclear mechanism are great obstacles to the diagnosis and treatment of the disease. Studies have shown that abnormal functions of the visual cortex have been reported in MDD patients, and the actions of several antidepressants coincide with improvements in the structure and synaptic functions of the visual cortex. In this review, we critically evaluate current evidence showing the involvement of the malfunctioning visual cortex in the pathophysiology and therapeutic process of depression. In addition, we discuss the molecular mechanisms of visual cortex dysfunction that may underlie the pathogenesis of MDD. Although the precise roles of visual cortex abnormalities in MDD remain uncertain, this undervalued brain region may become a novel area for the treatment of depressed patients.

Contextual Fear Learning and Extinction in the Primary Visual Cortex of Mice / 神经科学通报·英文版

Fear memory contextualization is critical for selecting adaptive behavior to survive. Contextual fear conditioning (CFC) is a classical model for elucidating related underlying neuronal circuits. The primary visual cortex (V1) is the primary cortical region for contextual visual inputs, but its role in CFC is poorly understood. Here, our experiments demonstrated that bilateral inactivation of V1 in mice impaired CFC retrieval, and both CFC learning and extinction increased the turnover rate of axonal boutons in V1. The frequency of neuronal Ca2+ activity decreased after CFC learning, while CFC extinction reversed the decrease and raised it to the naïve level. Contrary to control mice, the frequency of neuronal Ca2+ activity increased after CFC learning in microglia-depleted mice and was maintained after CFC extinction, indicating that microglial depletion alters CFC learning and the frequency response pattern of extinction-induced Ca2+ activity. These findings reveal a critical role of microglia in neocortical information processing in V1, and suggest potential approaches for cellular-based manipulation of acquired fear memory.

Research progress on the structural plasticity of neurons in the visual cortex / 中华实验眼科杂志

During the development of visual cortex, the structure of neurons will adaptively change and adjust according to the changes of external environment, which shows structural plasticity.The experience-dependent plasticity of visual cortex is based on the structural changes of neurons, which mainly include change of synaptic connections, disappearance or increase of dendritic spines, turnover of dendritic spines, changes in the size of dendritic spines, changes in postsynaptic density and alterations of perineuronal nets.The structural changes of neurons have significant influence on the plasticity of visual cortex function and structure, and are highly associated with some molecules or non-neuronal components such as paired immunoglobulin-like receptor B, Ly-6/neurotoxin-like protein 1, Nogo, microglia and extracellular matrix and so on.In addition, external intervention factors such as abnormal visual experience and environmental enrichment can have significant impact on the regulation of the structural changes of neurons, and finally influence the development of visual function and the recovery from visual impairment.In comparison with the functional studies, studies on the structural plasticity of visual cortical neurons depend on the state-of-the-art imaging techniques at cellular or sub-cellular level with more visualizable and convincing results.The constant exploration of the structural plasticity of visual cortex will enhance our understanding of visual development-related diseases, such as amblyopia, and lay the foundation for related basic research and innovative treatments.Advances in the structural plasticity of visual cortex were reviewed in this article.

Modulation of Spike Count Correlations Between Macaque Primary Visual Cortex Neurons by Difficulty of Attentional Task / 神经科学通报·英文版

Studies have shown that spatial attention remarkably affects the trial-to-trial response variability shared between neurons. Difficulty in the attentional task adjusts how much concentration we maintain on what is currently important and what is filtered as irrelevant sensory information. However, how task difficulty mediates the interactions between neurons with separated receptive fields (RFs) that are attended to or attended away is still not clear. We examined spike count correlations between single-unit activities recorded simultaneously in the primary visual cortex (V1) while monkeys performed a spatial attention task with two levels of difficulty. Moreover, the RFs of the two neurons recorded were non-overlapping to allow us to study fluctuations in the correlated responses between competing visual inputs when the focus of attention was allocated to the RF of one neuron. While increasing difficulty in the spatial attention task, spike count correlations were either decreased to become negative between neuronal pairs, implying competition among them, with one neuron (or none) exhibiting attentional enhancement of firing rate, or increased to become positive, suggesting inter-neuronal cooperation, with one of the pair showing attentional suppression of spiking responses. Besides, the modulation of spike count correlations by task difficulty was independent of the attended locations. These findings provide evidence that task difficulty affects the functional interactions between different neuronal pools in V1 when selective attention resolves the spatial competition.

Research progress on the interaction between myopia and visual cortex / 中华眼底病杂志

Myopia is a major problem of public health in China, and even in the world, and slowing down the progress of myopia has become a hot issue of concern. However, the effects of the current therapeutic and interventional modalities to myopia, including optical lenses, chemical drugs, and laser surgery, the effect of treatment and intervention is not very satisfactory, and these modalities may incur some side effects. This situation suggests that the pathogenic and regulatory mechanisms of myopia remain elusive, and the myopia treatments lack the accurate and effective targets to the etiology. A complete visual experience depends on the entire visual pathway from the retina to the visual cortex, in which any structural and functional defect can lead to visual abnormalities. In recent years, with the advances in the infrared spectroscopy and the magnetic resonance imaging technology, more and more evidence has shown that the progression of myopia is related to the visual cortex. Improving the functional connectivity and blood prefusion between different regions of the visual cortex may impede myopia profession. In-depth understanding of the interaction between myopia and the visual cortex is helpful to search for accurate and effective myopia treatment targets and novel intervention strategies.

Restoration of FMRP expression in adult V1 neurons rescues visual deficits in a mouse model of fragile X syndrome

Many people affected by fragile X syndrome (FXS) and autism spectrum disorders have sensory processing deficits, such as hypersensitivity to auditory, tactile, and visual stimuli. Like FXS in humans, loss of Fmr1 in rodents also cause sensory, behavioral, and cognitive deficits. However, the neural mechanisms underlying sensory impairment, especially vision impairment, remain unclear. It remains elusive whether the visual processing deficits originate from corrupted inputs, impaired perception in the primary sensory cortex, or altered integration in the higher cortex, and there is no effective treatment. In this study, we used a genetic knockout mouse model (Fmr1KO), in vivo imaging, and behavioral measurements to show that the loss of Fmr1 impaired signal processing in the primary visual cortex (V1). Specifically, Fmr1KO mice showed enhanced responses to low-intensity stimuli but normal responses to high-intensity stimuli. This abnormality was accompanied by enhancements in local network connectivity in V1 microcircuits and increased dendritic complexity of V1 neurons. These effects were ameliorated by the acute application of GABAA receptor activators, which enhanced the activity of inhibitory neurons, or by reintroducing Fmr1 gene expression in knockout V1 neurons in both juvenile and young-adult mice. Overall, V1 plays an important role in the visual abnormalities of Fmr1KO mice and it could be possible to rescue the sensory disturbances in developed FXS and autism patients.

Study on the cortical synaptic density and visual function in monocular form deprivation rats with amblyopia / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To study the effect of monocular form deprivation(MD)on the synaptic density in the visual cortex of the amblyopic rats during the critical period of visual development, the visual cortical synaptophysin(SYN)expression and significance of its expression, as well as the relationship between the synaptic density and the visual function. This research will provide mechanisms underlying the pathogenesis and clinical treatment of amblyopia.<p>METHODS: Normal newborn Long Evans rats were randomly divided into normal control group and amblyopia model group, each with 16 rats. Both groups of rats were raised in the same environment. The normal control group did not receive any treatment. On the 13d after birth, the amblyopic model group received monocular suture to establish a classic monocular form deprived amblyopic model. Both groups of rats were received Visual evoked potential(F-VEP)detection on the 51d. Samples were taken immediately after the detection. The transmission electron microscope and Image J image analysis software were used to observe and analyse the synaptic density in the V1M of the primary visual cortex of the two groups of rats. Frozen sections of visual cortex were stained by immunofluorescence histochemical staining by bleaching method and the expression of SYN positive neurons was observed and quantitatively analyzed. <p>RESULTS: F-VEP examination showed that compared with the normal control group, the P2 latency of the deprived eyes in the amblyopic group was significantly long, and the amplitude of P2 wave was significantly lower than that of normal eyes(<i>P</i><0.05); Transmission electron microscopy results showed that the synaptic density of the bilateral visual cortex of the amblyopic model group was significantly reduced compared with the normal control group(<i>P</i><0.05), the contralateral visual cortex of the amblyopic eye decreased more significantly(<i>P</i><0.05); immunofluorescence staining results showed that the brain slices in the visual cortex of the two groups were intact and the tissue structure was clear under the microscope. Compared with the normal control group, the expression intensity of SYN positive neurons in the amblyopic group was significantly reduced(<i>P</i><0.01).<p>CONCLUSION: There is structural synaptic plasticity during the critical period of visual development. Monocular form deprivation can reduce the synaptic density, SYN expression and the visual function in the primary visual cortex of the amblyopic rats.

Research progress on the abnormal brain structure and function of patients with strabismus / 国际眼科杂志(Guoji Yanke Zazhi)

@#Strabismus is a common type of eye movement disorders, which is characterized by ocular misalignment and binocular visual dysfunction. Alignment relies on the normal structure and function of the visual and oculomotor systems. Any abnormalities of these regions may lead to strabismus. With the application of neurophysiological techniques and radioautography in the early years, the impairment of primary visual cortex was found, including decreased number of binocular neurons and metabolic changes of ocular dominant column. In recent years, the progress of functional magnetic resonance imaging has promoted to find more functional changes in human strabismic brains, especially in extrastriate cortex. In addition to the structural impairment of cerebral cortex and intercortical connections, functional remodeling of cerebral cortex was also observed in patients with strabismus. Besides, studies based on voxel-based morphometry and diffusion tensor imaging provided more precise anatomical evidence for human brain abnormalities. To provide reference for further studies, we review the current literature on functional and morphological deficits within brain regions in strabismus.

In Vivo Two-photon Calcium Imaging in Dendrites of Rabies Virus-labeled V1 Corticothalamic Neurons / 神经科学通报·英文版

Monitoring neuronal activity in vivo is critical to understanding the physiological or pathological functions of the brain. Two-photon Ca imaging in vivo using a cranial window and specific neuronal labeling enables real-time, in situ, and long-term imaging of the living brain. Here, we constructed a recombinant rabies virus containing the Ca indicator GCaMP6s along with the fluorescent protein DsRed2 as a baseline reference to ensure GCaMP6s signal reliability. This functional tracer was applied to retrogradely label specific V1-thalamus circuits and detect spontaneous Ca activity in the dendrites of V1 corticothalamic neurons by in vivo two-photon Ca imaging. Notably, we were able to record single-spine spontaneous Ca activity in specific circuits. Distinct spontaneous Ca dynamics in dendrites of V1 corticothalamic neurons were found for different V1-thalamus circuits. Our method can be applied to monitor Ca dynamics in specific input circuits in vivo, and contribute to functional studies of defined neural circuits and the dissection of functional circuit connections.

Orexin B Enhances the Synaptic Transmission from LGN to Orexin-sensitive Neurons in L6b of Visual Cortex / 中山大学学报(医学科学版)

@#【Objective】To unmask the effect of Orexin B on the synaptic transmission between feed-forward projection from the lateral geniculate nucleus（LGN）to orexin-sensitive neurons in layer 6b（L6b）of visual cortex（VC）.【Methods】C57 mice at P25-P30 were used for micro-injection of CTB555 and ChR2-EGFP into LGN to label the neurons feedback projection to LGN from L6b and the feed-forward projection from LGN to the neurons in L6b of VC respectively. The EPSC in L6b cells was intracellularly recorded from the neurons labeled by CTB555.【Results】The neurons feedback projection to LGN in L6b are mainly pyramidal neurons, and the most of these cells are activated by orexin B，called orexin- sensitive neurons. Orexin B enhanced the NMDAR-mediated postsynaptic current in orexin-sensitive neurons in L6b by electrical or optical stimulation on the LGN projection to VC［electrical stimulation：（125.1 ± 3.7）%，optical stimulation：（123.8 ±3.8）%. In the case of OX2R′s blocker，the effect of Orexin B on EPSC amplitude disappeared with significant statistical significance，P < 0.05］，thus，strengthening the synaptic transmission between LGN and orexin-sensitive neurons in L6b.【Conclusions】Orexin B enhances the synaptic transmission between LGN to pyramidal neurons in L6b of VC.

Research on the formation mechanism and measurement method of stereoscopic vision / 国际眼科杂志(Guoji Yanke Zazhi)

@#Stereopsis is to perceive vision depth through the subtle three-dimensional differences between two eyes, and it is closely related to human working and living. There are different visual cortices in the cerebral cortex, which are involved in the formation of stereo vision, and process different visual information received. Clinical evaluation of stereo vision is needed to guide clinical decision-making. Traditional assessment is mainly based on static stereoscopic acuity, while binocular disparity appears dynamically with time in daily life. Nowadays 3D technology has been used to evaluate stereo vision. This paper mainly reviews the development mechanism and measurement methods of stereoscopic vision.

Effects of IGF-1 mediated enrichment environment on visual cortex plasticity in adult amblyopic mice / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To investigate the effect and possible mechanism of enriched environment on regulating the plasticity of visual cortex in adult monocular deprivation amblyopia mice.<p>METHODS: In this experimental study, a total of 72 Kunming mice were randomly divided into control group(Nor), monocular deprivation+ standard environment group(MD+SE), monocular deprivation + enriched environment group(MD+EE)and monocular deprivation+ fluoxetine group(MD+FLX). MD model of mice were established at postpartum 21d, and then fed the mice under SE or EE for 4wk. For the mice in MD+FLX group, they were fed by water with fluoxetine. The visual acuity and flash visual evoked potential of mice in each group were detected. Ultrastructral modifications of synaptic junctions in each group were detected using the electronic microscope. We also applied the molecular biology to study the role of enriched environment in visual cortex of adult amblyopic mice whether through regulating the expression of IGF-1, IGF-1R and IGFBP5.<p>RESULTS: 1)Visual acuity examination: the successful rate of forepaw-reaching reflex in MD+SE group mice is lower than that in Nor group(<i>P</i><0.001). Compared to MD+SE group, the successful rate of forepaw-reaching reflex improved in MD+EE group(<i>P</i><0.001)and MD+FLX group(<i>P</i><0.001). The difference is not significant between the MD+EE group and MD+FLX group(<i>P</i>=0.816); 2)Flash-visual evoked potential examination: compare to the Nor group, the P2 latency was prolonged(<i>P</i><0.01), and the P2 amplitude was decreased(<i>P</i><0.01)of flash-visual evoked potential(F-VEP)in the deprived eye in MD+SE group mice; After raring in enriched environment, the P2 latency was shortened(<i>P</i>=0.003)and P2 amplitude was increased(<i>P</i>=0.000)in the deprivated eye detected with F-VEP, which is not significant in P2 latency and amplitude when compare to MD+FLX group(<i>P</i>>0.05); 3)The structural modifications of synaptic junctions examined by electromicrographs: Compare to the Nor group, the synaptic clefts increased(<i>P</i><0.01), the synaptic active zone shortened(<i>P</i><0.01), and the thickness of PSD decreased(<i>P</i><0.01)in MD+SE group mice. After raring in enriched environment, the synaptic clefts decreased(<i>P</i>=0.0035), the synaptic active zone prolonged(<i>P</i>=0.000)and the thickness of PSD increased(<i>P</i>=0.000)in the visual cortex contralateral to the deprived eye, which is not significant in all of the structural parameters of the synaptic junction in visual cortex when compare to MD+FLX group(<i>P</i>>0.05); 4)IGF-1, IGF-1R and IGFBP5 expression detected by Western-blot: Compare to the Nor group, the IGF-1 and IGF-1R expression in visual cortex contralateral to deprivated eye are both down-regulated in MD+SE group(<i>P</i><0.01; <i>P</i><0.01). After raring in enriched environment, the expression of IGF-1 and IGF-1R in MD+EE group was significantly higher than that in MD+SE group(<i>P</i>=0.016; <i>P</i>=0.041), but still lower than that in Nor group(<i>P</i>=0.001; <i>P</i>=0.001). The different expression of IGFBP5 in each group is not significant(<i>P</i>>0.05). <p>CONCLUSION: Environmental enrichment can improve the visual function through reactivating the plasticity of monocular deprivation amblyopia mice. The mechanism is presumed to be related to the expression of IGF-1 and IGF-1R.

Roles of two-photon calcium imaging technology for visual cortex Ⅱ/Ⅲ layer neurons in model animals / 国际眼科杂志(Guoji Yanke Zazhi)

@#Calcium is an important messenger in the mammalian nerve cells which mediates a variety of intracellular signal transduction pathways and plays critical roles in regulating the neuronal functions. Calcium signaling exerts its highly specific function in a defined sub-region of the cell, especially in the visual cortex of the brain. Detection of calcium signals in neurons is particularly important for the studying of neuronal function. The two-photon microscope has a unique advantage in the detection of calcium signal in the superficial cortex. In this paper, the application of two-photon in the <i>in vivo</i> detection of the visual cortical Ⅱ/Ⅲ layer of model animals are reviewed.

Expression of collapsin response mediator protein 2 in visual cortex of form deprivation amblyopic rats / 中华实验眼科杂志

Objective To study the expression of collapsin response mediator protein 2 (CRMP-2) in the visual cortex of monocular form deprivation amblyopia rats.Methods Sixty-four 14-day-old rats were randomly divided into monocular deprivation amblyopia group and normal control group by random number table method.Right eyelid margin suture was performed at 14 days after birth in the monocular deprivation amblyopia group.Eight rats in the monocular deprivation amblyopia group and the normal control group were observed at 14,21,45 and 120 days after birth,respectively.Flash visual evoked potential (F-VEP) was used to dectect the latency and amplitude of P1 wave.The expression of CRMP-2 in visual cortex was observed by immunohistochemical method.The use and care of the animals complied with Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission.This study protocol was approved by Ethic Committee of the University of South China (No.20140228).Results F-VEP results showed that the amplitudes of P1 were decreased and latent periods of P1 were prolonged in the monocular deprivation amblyopia group compared with the normal control group (t=16.760,P =0.000;t =-22.919,P =0.000).CRMP-2 expression levels in the visual cortex of monocular deprivation amblyopia groups and normal control groups were compared at different time points after birth,and the differences were statistically significant (Fgroup =8.855,P =0.010;Ftime =63.091,P =0.000).Compared with normal control groups,the expressions of CRMP-2 at the postnatal 21,45 and 120 days were obviously decreased in the monocular deprivation amblyopia groups,the differences were statistically significant (all at P＜0.05).Conclusions CRMP-2 may be involved in the occurrence and development of amblyopia.

Influence of enriched environment on visual function and synaptic plasticity in adult amblyopic mice / 中华实验眼科杂志

Objective To examine role and possible mechanism of enriched environment (EE) on regulating recovery of visual function in adult monocular deprivation amblyopia mice.Methods A total of 72 healthyKunming mice were divided into normal control group,monocular deprivation (MD) group,MD+EE group and M D+ fluoxetine group by random number table.Except for the normal control group,the mice in the other groups were sutured on the right eyelid 21 days after birth to establish MD amblyopia model.the mice were fed in standard environment or EE for 4 weeks according to the group.Visual acuity and flash visual evoked potential (F-VEP) of mice in each group were detected.The distribution of microtubule associated protein 2 (MAP2) in visual cortex of adult amblyopic mice were detected by immunohistochemistry.The expression of MAP2,synaptophysin (SYP) and postsynaptic density protein-95 (PSD-95) protein in visual cortex of adult amblyopic mice were detected by western blot.The experimental protocol was approved by the Animal Care and Use Committee of Hunan Children's Hospital and conformed to the National Institutes of Health Guide for the Care and Use of Laboratory Animals.Results There was a significant difference in the visual acuity of deprived eye among each group (F=114.632,P＜0.001).The visual acuity in MD group is lower than that in normal control group,with a significant difference (t =15.480,P＜0.001).Compared with MD group,visual acuity was restored in MD+ EE group and MD +fluoxetine group,with significant differences (t =15.071,P ＜ 0.001;t =14.841,P ＜ 0.001).There was a significant difference in the P2 latency and amplitude of F-VEP in deprived eye among each group (F=36.510,P=0.000;F=34.140,P=0.000).Compare with normal control group,P2 latency was prolonged and P2 amplitude of F-VEP was decreased in deprived eye in MD group,with significant differences (t =10.220,P =0.000;t =10.09,P =0.000).Western blot assay showed that there was a significant difference in the expression of MAP2 in visual cortex contralateral deprived eye among each group (F=18.142,P=0.000).The expression of MAP2 in MD group was significantly lower than that in normal contral group (t=3.056,P＜0.01);Compared with MD group,MAP2 expression was increased in MD+EE group and MD+fluoxetine group (t =2.541,P =0.031;t =2.157,P =0.017).There were significant differences in the expression of SYP and PSD-95 in visual cortex contralateral to deprived eye among each group (F =12.871,P =0.000;F =25.060,P =0.000).Compared with normal contral group,SYP and PSD-95 expression in visual cortex were down-regulated in MD group,with significant differences (t =6.054,P =0.000;t =8.631,P =0.000).The expression of SYP and PSD-95 protein in MD+EE group and MD+fluoxetine group were significantly higher than those in MD group (all at P＜0.05).Conclusions EE can recover visual function through up-regulating the expression of MAP2,which can modulate the dendritic branch trim and neural plasticity of visual cortex in adult MD mice.

Effects of enriched environment on the subunits N-mehyl-D-aspartate receptors at the 17th area of the visual cortex in adult amblyopia rats / 中华实验眼科杂志

Objective To explore the effect of enriched environment on the level of NR2A and NR2B subunits of N-mehyl-D-aspartate (NMDA) receptors which belong to glutamate receptors with excitability at the 17th area of the visual cortex in amblyopia rats after the critical period,and to understand the possible mechanism of synaptic plasticity of the visual cortex in adult amblyopia rats.Methods Eighty Wistar rats were divided into normal group and experimental group by random number table.Right eyelids of all rats were sutured through the whole critical period in order to establish monocular deprivation (MD) amblyopia model.The rats in experimental group were divided into the amblyopia group,standard environment (SE) group and environmental enrichment (EE) group on P45 in random.The sutured right eyelids were opened on P46 in the SE group and EE group.All rats were sacrificed to get the 17th area of the left visual cortex on P60,P75 and P105.Three rats were used at different time points from each group.The Ⅰ-Ⅵ layers of the visual cortex area 17 were observed by using hematoxylin-eosin staining.The expression of NMDA-NR2A and NMDA-NR2B was detected by immunohistochemistry.Integrated optical density of NMDA-NR2A and NMDA-NR2B was detected by using special image analysis software (Image-Pro Plus 6.0).The use of animals complied with Regulation on the Managenment Experimental Ainimals from Shandong Eye Institute and Association for Research in Vision and Ophthalmology (ARVO).Results The positive expression of NMDA-NR2A and NMDA-NR2B were observed in the visual cortex.The positive cells were mostly round or elliptical and mainly expressed in cell membrane.The expression of NMDA-NR2A in P60,P75 and P105 from four groups had statistical differences (all at P＜0.05).There were less positive cells in amblyopia group and EE group than normal control group on P60,P75 and P105,while there were more positive cells in EE group than amblyopia group.Amblyopia can lead to reduced NMDA-NR2A expression in the visual cortex.The expression of NMDA-NR2A was stronger than that in the amblyopia group by intervention 15 days,30 days,and 60 days with the rich environments,but did not reach the normal level (all at P＜0.05).The expression of NMDA-NR2B in P60,P75 and P105 from four groups also had statistical difference (all at P＜0.05).There were more positive cells in amblyopia group than those in normal control group on P60,P75 and P105.There were more positive cells in EE group than normal control group on P60,while there were equal positive cells in EE group and normal control group on P75 and P105.Amblyopia can lead to increase NMDA-NR2B expression in the visual cortex.The expression of NMDA-NR2B was weaker than that in the amblyopia group by intervention 15 days with the rich environments,but did not reach the normal level (all at P＜ 0.05).The expression of NMDA-NR2B after intervention 30 days and 60 days reached the normal levels (all at P＞ 0.05).Conclusions The plasticity of visual cortex exists not only in the critical period but also after the critical period of visual development.EE,as a non-invasion method,can improve and recover the synaptic plasticity in visual cortex of adult rats by the expression of NMDA-NR2A and NMDA-NR2B.

Can Anodal Transcranial Direct Current Stimulation Increase Steady-State Visual Evoked Potential Responses?

BACKGROUND: It has been frequently reported that non-negligible numbers of individuals have steady-state visual evoked potential (SSVEP) responses of low signal-to-noise-ratio (SNR) to specific stimulation frequencies, which makes detection of the SSVEP difficult especially in brain–computer interface applications. We investigated whether SSVEP can be modulated by anodal transcranial direct-current stimulation (tDCS) of the visual cortex. METHODS: Each participant participated in two 20-min experiments—an actual tDCS experiment and a sham tDCS experiment—that were conducted on different days. Two representative electroencephalogram (EEG) features used for the SSVEP detection, SNR and amplitude, were tested for pre- and post-tDCS conditions to observe the effect of the anodal tDCS. RESULTS: The EEG features were significantly enhanced by the anodal tDCS for the electrodes with low pre-tDCS SNR values, whereas the effect was not significant for electrodes with relatively higher SNR values. CONCLUSION: Anodal tDCS of the visual cortex may be effective in enhancing the SNR and amplitude of the SSVEP response especially for individuals with low-SNR SSVEP.

Layer-specific cholinergic modulation of synaptic transmission in layer 2/3 pyramidal neurons of rat visual cortex

It is known that top-down associative inputs terminate on distal apical dendrites in layer 1 while bottom-up sensory inputs terminate on perisomatic dendrites of layer 2/3 pyramidal neurons (L2/3 PyNs) in primary sensory cortex. Since studies on synaptic transmission in layer 1 are sparse, we investigated the basic properties and cholinergic modulation of synaptic transmission in layer 1 and compared them to those in perisomatic dendrites of L2/3 PyNs of rat primary visual cortex. Using extracellular stimulations of layer 1 and layer 4, we evoked excitatory postsynaptic current/potential in synapses in distal apical dendrites (L1-EPSC/L1-EPSP) and those in perisomatic dendrites (L4-EPSC/L4-EPSP), respectively. Kinetics of L1-EPSC was slower than that of L4-EPSC. L1-EPSC showed presynaptic depression while L4-EPSC was facilitating. In contrast, inhibitory postsynaptic currents showed similar paired-pulse ratio between layer 1 and layer 4 stimulations with depression only at 100 Hz. Cholinergic stimulation induced presynaptic depression by activating muscarinic receptors in excitatory and inhibitory synapses to similar extents in both inputs. However, nicotinic stimulation enhanced excitatory synaptic transmission by ~20% in L4-EPSC. Rectification index of AMPA receptors and AMPA/NMDA ratio were similar between synapses in distal apical and perisomatic dendrites. These results provide basic properties and cholinergic modulation of synaptic transmission between distal apical and perisomatic dendrites in L2/3 PyNs of the visual cortex, which might be important for controlling information processing balance depending on attentional state.