Long-term dark rearing induces permanent reorganization in retinal circuitry

Retinal microvascular changes in unilateral functional amblyopia detected by oct-angiography and follow-up during treatment

OBJECTIVE

To evaluate the macular microvascular changes using optical coherence tomographic angiography (OCT-A) in children with unilateral amblyopia and their reversibility during treatment.

METHODS

Patients with unilateral strabismic or anisometropic amblyopia or residual amblyopia from early congenital cataract surgery, examined between October 2019 and March 2021, were included. Vessel density and perfusion density in the superficial capillary plexus and area, perimeter and circularity of the foveal avascular zone (FAZ) were analysed using OCT-A in amblyopic eyes, contralateral eyes and control group healthy eyes. Correlation analyses between the microvascular parameters and the visual acuity were performed. In a pilot study on a few patients from the amblyopic cohort, longitudinal follow-up during treatment was also performed.

RESULTS

A total of 128 eyes of 64 patients were included: 32 amblyopic eyes compared with 32 contralateral eyes and 64 control eyes. Vessel density and perfusion density in the superficial capillary plexus were significantly lower in amblyopic eyes compared to control eyes in 6 × 6 mm (p < 0.02) and 3 × 3 mm (p < 0.01) scans. Correlation analyses showed a linear decrease in vessel density and perfusion density with decreasing visual acuity. The microvascular changes observed were reversible with the occlusion treatment of amblyopia (p < 0.001).

CONCLUSIONS

The study found a decrease in vessel density and perfusion density in the macula of children with unilateral functional amblyopia. These microvascular changes were correlated with visual acuity and appeared to be reversible with treatment of amblyopia. On the whole, OCT-A appears to be a relevant complementary examination when it comes to diagnosing and monitoring functional amblyopia.

Congenital cataracts affect the retinal visual cycle and mitochondrial function: A multi-omics study of GJA8 knockout rabbits

Congenital cataracts are a threat to visual development in children, and the visual impairment persists after surgical treatment; however, the mechanisms involved remain unclear. Previous clinical studies have identified the effect of congenital cataracts on retinal morphology and function. To further understand the molecular mechanisms by which congenital cataracts affect retinal development, we analyzed retina samples from 7-week-old GJA8-knockout rabbits with congenital cataracts and controls by four-dimensional label-free quantification proteomics and untargeted metabolomics. Bioinformatics analysis of proteomic data showed that retinol metabolism, oxidative phosphorylation, and fatty acid degradation pathways were downregulated in the retinas of rabbits with congenital cataracts, indicating that their visual cycle and mitochondrial function were affected. Additional validation of differentially abundant proteins related to the visual cycle and mitochondrial function was performed using Parallel reaction monitoring and western blot experiments. Untargeted metabolome analysis showed significant upregulation of the antioxidant glutathione and ascorbic acid in the retinas of rabbits with congenital cataracts, indicating that their oxidative stress balance was not dysregulated. SIGNIFICANCE: Congenital cataracts in children can alter retinal structure and function, yet the mechanisms are uncertain. Here is the first study to use proteomics and metabolomics approaches to investigate the effects of congenital cataracts on retinal development in the early postnatal period. Our findings suggest that congenital cataracts have an impact on the retinal visual cycle and mitochondrial function. These findings give insight on the molecular pathways behind congenital cataract-induced visual function impairment in the early postnatal period.

Visual Deprivation Retards the Maturation of Dendritic Fields and Receptive Fields of Mouse Retinal Ganglion Cells

It was well documented that both the size of the dendritic field and receptive field of retinal ganglion cells (RGCs) are developmentally regulated in the mammalian retina, and visual stimulation is required for the maturation of the dendritic and receptive fields of mouse RGCs. However, it is not clear whether the developmental changes of the RGC receptive field correlate with the dendritic field and whether visual stimulation regulates the maturation of the dendritic field and receptive field of RGCs in a correlated manner. The present work demonstrated that both the dendritic and receptive fields of RGCs continuously develop after eye opening. However, the correlation between the developmental changes in the receptive field size and the dendritic field varies among different RGC types. These results suggest a continuous change of synaptic converging of RGC synaptic inputs in an RGC type-dependent manner. Besides, light deprivation impairs both the development of dendritic and receptive fields.

Effect of amblyopia treatment on macular microvasculature in children with anisometropic amblyopia using optical coherence tomographic angiography

To measure the retinal microvascular density in patients with anisometropic amblyopia using optical coherence tomographic angiography (OCTA) and to evaluate the effects of successful amblyopia treatment on microvasculature in retina. 59 children (5–12 years old) including 22 newly diagnosed unilateral anisometropic amblyopia, 16 recovered unilateral anisometropic amblyopia, and 21 control children were imaged with OCTA using 6 × 6-mm macular scan pattern. Vessel densities of the superficial capillary plexus (SCP), the deep capillary plexus (DCP), and the overall macular thickness were acquired and compared among the three groups. After adjustment for axial length, the amblyopia group showed lower macular vessel density in the SCP (P = 0.005) and in the DCP (P = 0.004) compared with that of the control group. However, for the recovered amblyopia group, no difference of vessel density was found when compared with the control group in both the SCP (P = 0.548) and the DCP (P = 0.124). No difference of the mean macular thickness was found among three groups (P ≥ 0.15). Children with anisometropic amblyopia have reduced macular vessel density in OCTA, while no difference of macular vessel density was found between the recovered amblyopic and control eyes. Macular thickness showed no difference in anisometropic amblyopia and remained unchanged after amblyopic treatment.

Sensory Experience Modulates Atrx-mediated Neuronal Integrity in the Mouse Retina

Mutation of the α-thalassemia/mental retardation syndrome X-linked protein, ATRX, causes intellectual disability and is associated with pleiotropic defects including ophthalmological abnormalities. We have previously demonstrated that Atrx deficiency in the mouse retina leads to the selective loss of inhibitory interneurons and inner retinal dysfunction. Onset of the amacrine cell neurodegenerative phenotype in Atrx-deficient retinas occurs postnatally after neuronal specification, and coincides with eye opening. Given this timing, we sought to interrogate the influence of light-dependent visual signaling on Atrx-mediated neuronal survival and function in the mouse retina. Retina-specific Atrx conditional knockout (cKO) mice were subjected to light deprivation using two different paradigms: (1) a dark-rearing regime, and (2) genetic deficiency of metabotropic glutamate receptor 6 (mGluR6) to block the ON retinal signaling pathway. Scotopic electroretinography was performed for adult dark-reared Atrx cKO mice and controls to measure retinal neuron function in vivo. Retinal immunohistochemistry and enumeration of amacrine cells were performed for both light deprivation paradigms. We observed milder normalized a-wave, b-wave and oscillatory potential (OP) deficits in electroretinograms of dark-reared Atrx cKO mice compared to light-exposed counterparts. In addition, amacrine cell loss was partially limited by genetic restriction of retinal signaling through the ON pathway. Our results suggest that the temporal features of the Atrx cKO phenotype are likely due to a combined effect of light exposure upon eye opening and coincident developmental processes impacting the retinal circuitry. In addition, this study reveals a novel activity-dependent role for Atrx in mediating post-replicative neuronal integrity in the CNS.

Daily visual stimulation in the critical period enhances multiple aspects of vision through BDNF-mediated pathways in the mouse retina

Visual experience during the critical period modulates visual development such that deprivation causes visual impairments while stimulation induces enhancements. This study aimed to determine whether visual stimulation in the form of daily optomotor response (OMR) testing during the mouse critical period (1) improves aspects of visual function, (2) involves retinal mechanisms and (3) is mediated by brain derived neurotrophic factor (BDNF) and dopamine (DA) signaling pathways. We tested spatial frequency thresholds in C57BL/6J mice daily from postnatal days 16 to 23 (P16 to P23) using OMR testing. Daily OMR-treated mice were compared to littermate controls that were placed in the OMR chamber without moving gratings. Contrast sensitivity thresholds, electroretinograms (ERGs), visual evoked potentials, and pattern ERGs were acquired at P21. To determine the role of BDNF signaling, a TrkB receptor antagonist (ANA-12) was systemically injected 2 hours prior to OMR testing in another cohort of mice. BDNF immunohistochemistry was performed on retina and brain sections. Retinal DA levels were measured using high-performance liquid chromatography. Daily OMR testing enhanced spatial frequency thresholds and contrast sensitivity compared to controls. OMR-treated mice also had improved rod-driven ERG oscillatory potential response times, greater BDNF immunoreactivity in the retinal ganglion cell layer, and increased retinal DA content compared to controls. VEPs and pattern ERGs were unchanged. Systemic delivery of ANA-12 attenuated OMR-induced visual enhancements. Daily OMR testing during the critical period leads to general visual function improvements accompanied by increased DA and BDNF in the retina, with this process being requisitely mediated by TrkB activation. These results suggest that novel combination therapies involving visual stimulation and using both behavioral and molecular approaches may benefit degenerative retinal diseases or amblyopia.

Rearing Light Intensity Affects Inner Retinal Pathology in a Mouse Model of X-Linked Retinoschisis but Does Not Alter Gene Therapy Outcome

Purpose

To test the effects of rearing light intensity on retinal function and morphology in the retinoschisis knockout (Rs1-KO) mouse model of X-linked retinoschisis, and whether it affects functional outcome of RS1 gene replacement.

Methods

Seventy-six Rs1-KO mice were reared in either cyclic low light (LL, 20 lux) or moderate light (ML, 300 lux) and analyzed at 1 and 4 months. Retinal function was assessed by electroretinogram and cavity size by optical coherence tomography. Expression of inward-rectifier K⁺ channel (Kir4.1), water channel aquaporin-4 (AQP4), and glial fibrillary acidic protein (GFAP) were analyzed by Western blotting. In a separate study, Rs1-KO mice reared in LL (n = 29) or ML (n = 27) received a unilateral intravitreal injection of scAAV8-hRs-IRBP at 21 days, and functional outcome was evaluated at 4 months by electroretinogram.

Results

At 1 month, no functional or structural differences were found between LL- or ML-reared Rs1-KO mice. At 4 months, ML-reared Rs1-KO mice showed significant reduction of b-wave amplitude and b-/a-wave ratio with no changes in a-wave, and a significant increase in cavity size, compared to LL-reared animals. Moderate light rearing increased Kir4.1 expression in Rs1-KO mice by 4 months, but not AQP4 and GFAP levels. Administration of scAAV8-hRS1-IRBP to Rs1-KO mice showed similar improvement of inner retinal ERG function independent of LL or ML rearing.

Conclusions

Rearing light conditions affect the development of retinal cavities and post-photoreceptor function in Rs1-KO mice. However, the effect of rearing light intensity does not interact with the efficacy of RS1 gene replacement in Rs1-KO mice.

Early light deprivation effects on human cone-driven retinal function

PURPOSE

To assess whether the early light deprivation induced by congenital cataract may influence the cone-driven retinal function in humans.

METHODS

Forty-one patients affected by congenital cataract (CC) who had undergone uncomplicated cataract extraction surgery and intraocular lens implant, and 14 healthy subjects (HS) were enrolled. All patients underwent complete ophthalmological and orthoptic evaluations and best-corrected visual acuity (BCVA) measurement; light-adapted full-field electroretinograms (ERG) and photopic negative responses (PhNR) were recorded to obtain a reliable measurement of the outer/inner retinal function and of the retinal ganglion cells' function respectively.

RESULTS

Mean values of light-adapted ERG a- and b-wave and PhNR amplitude of CC eyes were significantly reduced and photopic ERG b-wave implicit time mean values were significantly delayed when compared to HS ones. When studying photopic ERG mean amplitudes at 5 ms, significant differences were found when comparing CC and control eyes. In CC eyes, statistically significant correlations were found between a- and b- wave amplitudes and PhNR amplitudes. No significant correlations were found between ERG parameters and BCVA, as well as between the age of CC patients at surgery and the time elapsed from lens extraction. No significant differences were found when functional parameters of bilateral and unilateral congenital cataract (uCC) eyes were compared, however uCC eyes showed significant differences when compared with contralateral healthy eyes.

CONCLUSION

We found a significant impairment of cone-driven retinal responses in patients with a history of congenital cataract. These changes might result from the long-lasting effects of early light deprivation on the cone retinal pathways. Our findings support the relevance of retinal involvement in deficits induced by early light deprivation.

Sensory experience shapes the development of the visual system's first synapse

Specific connectivity patterns among neurons create the basic architecture underlying parallel processing in our nervous system. Here we focus on the visual system's first synapse to examine the structural and functional consequences of sensory deprivation on the establishment of parallel circuits. Dark rearing reduces synaptic strength between cones and cone bipolar cells, a previously unappreciated effect of sensory deprivation. In contrast, rod bipolar cells, which utilize the same glutamate receptor to contact rods, are unaffected by dark rearing. Underlying the physiological changes, we find the localization of metabotropic glutamate receptors within cone bipolar, but not rod bipolar, cell dendrites is a light-dependent process. Furthermore, although cone bipolar cells share common cone partners, each bipolar cell type that we examined depends differentially on sensory input to achieve mature connectivity. Thus, visual experience differentially affects maturation of rod versus cone pathways and of cell types within the cone pathway.

Dark rearing alters the normal development of spatiotemporal response properties but not of contrast detection threshold in mouse retinal ganglion cells

The mouse visual system is immature when the eyes open two weeks after birth. As in other mammals, some of the maturation that occurs in the subsequent weeks is known to depend on visual experience. Development of the retina, which as the first stage of vision provides the visual information to the brain, also depends on light-driven activity for proper development but has been less well studied than visual cortical development. The critical properties for retinal encoding of images include detection of contrast and responsiveness to the broad range of temporal stimulus frequencies present in natural stimuli. Here we show that contrast detection threshold and temporal frequency response characteristics of ON and OFF retinal ganglion cells (RGCs), which are poor at eye opening, subsequently undergo maturation, improving RGC performance. Further, we find that depriving mice of visual experience from before birth by rearing them in the dark causes ON and OFF RGCs to have smaller receptive field centers but does not affect their contrast detection threshold development. The modest developmental increase in temporal frequency responsiveness of RGCs in mice reared on a normal light cycle was inhibited by dark rearing only in ON but not OFF RGCs. Thus, these RGC response characteristics are in many ways unaffected by the experience-dependent changes to synaptic and spontaneous activity known to occur in the mouse retina in the two weeks after eye opening, but specific differences are apparent in the ON vs. OFF RGC populations.

Dopamine D1 receptors regulate the light dependent development of retinal synaptic responses

Retinal synaptic connections and function are developmentally regulated. Retinal synaptic activity plays critical roles in the development of retinal synaptic circuitry. Dopamine receptors have been thought to play important roles in the activity-dependent synaptic plasticity in central nervous system. The primary goal of this study is to determine whether dopamine D1 receptor regulates the activity-dependent development of retinal light responsiveness. Accordingly, we recorded electroretinogram from wild type mice and mice with genetic deletion of D1 dopamine receptor (D1-/- mice) raised under cyclic light conditions and constant darkness. Our results demonstrated that D1-/- mice have reduced amplitudes of all three major components of electroretinogram in adulthood. When the relative strength of the responses is considered, the D1-/- mice have selective reduction of the amplitudes of a-wave and oscillatory potentials evoked by low-intermediate intensities of lights. During postnatal development, D1-/- mice have increased amplitude of b-wave at the time of eye-opening but reduced developmental increase of the amplitude of b-wave after eye opening. Light deprivation from birth significantly reduced the amplitudes of b-wave and oscillatory potentials, increased the outer retinal light response gain and altered the light response kinetics of both a- and b-waves of wild type mice. In D1-/- mice, the effect of dark rearing on the amplitude of oscillatory potentials was diminished and dark rearing induced effects on the response gain of outer retina and the kinetics of a-wave were reversed. These results demonstrated roles of dopamine D1 receptor in the activity-dependent functional development of mouse retina.

Experience-dependent and independent binocular correspondence of receptive field subregions in mouse visual cortex

The convergence of eye-specific thalamic inputs to visual cortical neurons forms the basis of binocular vision. Inputs from the same eye that signal light increment (On) and decrement (Off) are spatially segregated into subregions, giving rise to cortical receptive fields (RFs) that are selective for stimulus orientation. Here we map RFs of binocular neurons in the mouse primary visual cortex using spike-triggered average. We find that subregions of the same sign (On-On and Off-Off) preferentially overlap between the 2 monocular RFs, leading to binocularly matched orientation tuning. We further demonstrate that such subregion correspondence and the consequent matching of RF orientation are disrupted in mice reared in darkness during development. Surprisingly, despite the lack of all postnatal visual experience, a substantial degree of subregion correspondence still remains. In addition, dark-reared mice show normal monocular RF structures and binocular overlap. These results thus reveal the specific roles of experience-dependent and -independent processes in binocular convergence and refinement of On and Off inputs onto single cortical neurons.

Lack of early pattern stimulation prevents normal development of the alpha (Y) retinal ganglion cell population in the cat

Binocular deprivation of pattern vision (BD) early in life permanently impairs global motion perception. With the SMI-32 antibody against neurofilament protein (NFP) as a marker of the motion-sensitive Y-cell pathway (Van der Gucht et al. [2001] Cereb. Cortex 17:2805-2819), we analyzed the impact of early BD on the retinal circuitry in adult, perceptually characterized cats (Burnat et al. [2005] Neuroreport 16:751-754). In controls, large retinal ganglion cells exhibited a strong NFP signal in the soma and in the proximal parts of the dendritic arbors. The NFP-immunoreactive dendrites typically branched into sublamina a of the inner plexiform layer (IPL), i.e., the OFF inner plexiform sublamina. In the retina of adult BD cats, however, most of the NFP-immunoreactive ganglion cell dendrites branched throughout the entire IPL. The NFP-immunoreactive cell bodies were less regularly distributed, often appeared in pairs, and had a significantly larger diameter compared with NFP-expressing cells in control retinas. These remarkable differences in the immunoreactivity pattern were typically observed in temporal retina. In conclusion, we show that the anatomical organization typical of premature Y-type retinal ganglion cells persists into adulthood even if normal visual experience follows for years upon an initial 6-month period of BD. Binocular pattern deprivation possibly induces a lifelong OFF functional domination, normally apparent only during development, putting early high-quality vision forward as a premise for proper ON-OFF pathway segregation. These new observations for pattern-deprived animals provide an anatomical basis for the well-described motion perception deficits in congenital cataract patients.

Developmental mechanisms that regulate retinal ganglion cell dendritic morphology

One of the fundamental features of retinal ganglion cells (RGCs) is that dendrites of individual RGCs are confined to one or a few narrow strata within the inner plexiform layer (IPL), and each RGC synapses only with a small group of presynaptic bipolar and amacrine cells with axons/dendrites ramified in the same strata to process distinct visual features. The underlying mechanisms which control the development of this laminar-restricted distribution pattern of RGC dendrites have been extensively studied, and it is still an open question whether the dendritic pattern of RGCs is determined by molecular cues or by activity-dependent refinement. Accumulating evidence suggests that both molecular cues and activity-dependent refinement might regulate RGC dendrites in a cell subtype-specific manner. However, identification of morphological subtypes of RGCs before they have achieved their mature dendritic pattern is a major challenge in the study of RGC dendritic development. This problem is now being circumvented through the use of molecular markers in genetically engineered mouse lines to identify RGC subsets early during development. Another unanswered fundamental question in the study of activity-dependent refinement of RGC dendrites is how changes in synaptic activity lead to the changes in dendritic morphology. Recent studies have started to shed light on the molecular basis of activity-dependent dendritic refinement of RGCs by showing that some molecular cascades control the cytoskeleton reorganization of RGCs.

Effects of light deprivation on visual evoked potentials in migraine without aura

Background

The mechanisms underlying the interictal habituation deficit of cortical visual evoked potentials (VEP) in migraine are not well understood. Abnormal long-term functional plasticity of the visual cortex may play a role and it can be assessed experimentally by light deprivation (LD).

Methods

We have compared the effects of LD on VEP in migraine patients without aura between attacks (MO, n = 17) and in healthy volunteers (HV, n = 17). Six sequential blocks of 100 averaged VEP at 3.1 Hz were recorded before and after 1 hour of LD. We measured VEP P100 amplitude of the 1^st block of 100 sweeps and its change over 5 sequential blocks of 100 responses.

Results

In HV, the consequence of LD was a reduction of 1^st block VEP amplitude and of the normal habituation pattern. By contrast, in MO patients, the interictal habituation deficit was not significantly modified, although 1^st block VEP amplitude, already lower than in HV before LD, further decreased after LD.

Conclusions

Light deprivation is thought to decrease both excitatory and subsequent inhibitory processes in visual cortex, which is in line with our findings in healthy volunteers. The VEP results in migraine patients suggest that early excitation was adequately suppressed, but not the inhibitory mechanisms occurring during long term stimulation and habituation. Accordingly, deficient intracortical inhibition is unlikely to be a primary factor in migraine pathophysiology and the habituation deficit.

Activity-dependent disruption of intersublaminar spaces and ABAKAN expression does not impact functional on and off organization in the ferret retinogeniculate system

In the adult visual system, functionally distinct retinal ganglion cells (RGCs) within each eye project to discrete targets in the brain. In the ferret, RGCs encoding light increments or decrements project to independent On and Off sublaminae within each eye-specific layer of the dorsal lateral geniculate nucleus (dLGN). Here we report a manipulation of retinal circuitry that alters RGC action potential firing patterns during development and eliminates the anatomical markers of segregated On and Off sublaminae in the LGN, including the intersublaminar spaces and the expression of a glial-associated inhibitory molecule, ABAKAN, normally separating On and Off leaflets. Despite the absence of anatomically defined On and Off sublaminae, electrophysiological recordings in the dLGN reveal that On and Off dLGN cells are segregated normally. These data demonstrate a dissociation between normal anatomical sublamination and segregation of function in the dLGN and call into question a purported role for ABAKAN boundaries in the developing visual system.

Light-evoked synaptic activity of retinal ganglion and amacrine cells is regulated in developing mouse retina

Recent studies have shown a continued maturation of visual responsiveness and synaptic activity of retina after eye opening, including the size of receptive fields of retinal ganglion cells (RGCs), light-evoked synaptic output of RGCs, bipolar cell spontaneous synaptic inputs to RGCs, and the synaptic connections between RGCs and ON and OFF bipolar cells. Light deprivation retarded some of these age-dependent changes. However, many other functional and morphological features of RGCs are not sensitive to visual experience. To determine whether light-evoked synaptic responses of RGCs undergo developmental change, we directly examined the light-evoked synaptic inputs from ON and OFF synaptic pathways to RGCs in developing retinas, and found that both light-evoked excitatory and inhibitory synaptic currents decreased, but not increased, with age. We also examined the light-evoked synaptic inputs from ON and OFF synaptic pathways to amacrine cells in developing retinas and found that the light-evoked synaptic input of amacrine cells is also downregulated in developing mouse retina. Different from the developmental changes of RGC spontaneous synaptic activity, dark rearing has little effect on the developmental changes of light-evoked synaptic activity of both RGCs and amacrine cells. Therefore, we concluded that the synaptic mechanisms mediating spontaneous and light-evoked synaptic activity of RGCs and amacrine cells are likely to be different.

Permanent functional reorganization of retinal circuits induced by early long-term visual deprivation

Early sensory experience shapes the functional and anatomical connectivity of neuronal networks. Light deprivation alters synaptic transmission and modifies light response properties in the visual system, from retinal circuits to higher visual centers. These effects are more pronounced during a critical period in juvenile life and are mostly reversed by restoring normal light conditions. Here we show that complete light deprivation, from birth to periods beyond the critical period, permanently modifies the receptive field properties of retinal ganglion cells. Visual deprivation reduced both the strength of light responses in ganglion cells and their receptive field size. Light deprivation produced an imbalance in the ratio of inhibitory to excitatory inputs, with a shift toward larger inhibitory conductances. Ganglion cell receptive fields in visually deprived animals showed a spatial mismatch of inhibitory and excitatory inputs and inhibitory inputs were highly scattered over the receptive field. These results indicate that visual experience early in life is critical for the refinement of retinal circuits and for appropriate signaling of the spatiotemporal properties of visual stimuli, thus influencing the response properties of neurons in higher visual centers and their processing of visual information.

Hardwiring of fine synaptic layers in the zebrafish visual pathway

Background

Neuronal connections are often arranged in layers, which are divided into sublaminae harboring synapses with similar response properties. It is still debated how fine-grained synaptic layering is established during development. Here we investigated two stratified areas of the zebrafish visual pathway, the inner plexiform layer (IPL) of the retina and the neuropil of the optic tectum, and determined if activity is required for their organization.

Results

The IPL of 5-day-old zebrafish larvae is composed of at least nine sublaminae, comprising the connections between different types of amacrine, bipolar, and ganglion cells (ACs, BCs, GCs). These sublaminae were distinguished by their expression of cell type-specific transgenic fluorescent reporters and immunohistochemical markers, including protein kinase Cβ (PKC), parvalbumin (Parv), zrf3, and choline acetyltransferase (ChAT). In the tectum, four retinal input layers abut a laminated array of neurites of tectal cells, which differentially express PKC and Parv. We investigated whether these patterns were affected by experimental disruptions of retinal activity in developing fish. Neither elimination of light inputs by dark rearing, nor a D, L-amino-phosphono-butyrate-induced reduction in the retinal response to light onset (but not offset) altered IPL or tectal lamination. Moreover, thorough elimination of chemical synaptic transmission with Botulinum toxin B left laminar synaptic arrays intact.

Conclusion

Our results call into question a role for activity-dependent mechanisms – instructive light signals, balanced on and off BC activity, Hebbian plasticity, or a permissive role for synaptic transmission – in the synaptic stratification we examined. We propose that genetically encoded cues are sufficient to target groups of neurites to synaptic layers in this vertebrate visual system.

Effect of visual experience on the maturation of ON-OFF direction selective ganglion cells in the rabbit retina

Activity-dependent neural plasticity is well known in the development of the visual cortical circuitry. However, the role of neural plasticity in the developing retina is less well understood. In the light of recent findings that light deprivation alters the development of synaptic pathway in the mouse and turtle retinas, we studied whether visual experience is required for the maturation of the ON-OFF direction selective ganglion cells (DSGCs) in the rabbit retina. The DSGCs of rabbits raised under a normal light-dark cycle and in the constant darkness were recorded extracellularly at various postnatal stages. Receptive field properties, such as direction selectivity, velocity tuning, classical center-surround interaction and motion-induced surround inhibition were examined. Recorded cells were subsequently injected with Neurobiotin in order to characterize their morphological features and tracer coupling patterns. Our results revealed that visual experience is not critical for the maturation of the classical receptive field properties of the DSGCs, such as direction selectivity and velocity tuning. However, the dark-reared rabbits showed altered surround inhibition, which is mediated by the amacrine cells of the inner retina. In addition, the DSGCs of both normal- and dark-reared rabbits showed similar dendritic features and tracer coupling patterns. Taken together, this study indicates that visual experience plays a less significant role on the DS circuitry maturation in the retina than in the cortex.