Eye-specific retinogeniculate segregation proceeds normally following disruption of patterned spontaneous retinal activity

Background: Spontaneous retinal activity (SRA) is important during eye-specific segregation within the dorsal lateral geniculate nucleus (dLGN), but the feature(s) of activity critical for retinogeniculate refinement are controversial. Pharmacologically or genetically manipulating cholinergic signaling during SRA perturbs correlated retinal ganglion cell (RGC) spiking and disrupts eye-specific retinofugal refinement in vivo, consistent with an instructive role for SRA during visual system development. Paradoxically, ablating the starburst amacrine cells (SACs) that generate cholinergic spontaneous activity disrupts correlated RGC firing without impacting retinal activity levels or eye-specific segregation in the dLGN. Such experiments suggest that patterned SRA during retinal waves is not critical for eye-specific refinement and instead, normal activity levels are permissive for retinogeniculate development. Here we revisit the effects of ablating the cholinergic network during eye-specific segregation and show that SAC ablation disrupts, but does not eliminate, retinal waves with no concomitant impact on normal eye-specific segregation in the dLGN. Results: We induced SAC ablation in postnatal ferret pups beginning at birth by intraocular injection of a novel immunotoxin selective for the ferret vesicular acetylcholine transporter (Ferret VAChT-Sap). Through dual-patch whole-cell and multi-electrode array recording we found that SAC ablation altered SRA patterns and led to significantly smaller retinal waves compared with controls. Despite these defects, eye-specific segregation was normal. Further, interocular competition for target territory in the dLGN proceeded in cases where SAC ablation was asymmetric in the two eyes. Conclusions: Our data demonstrate normal eye-specific retinogeniculate development despite significant abnormalities in patterned SRA. Comparing our current results with earlier studies suggests that defects in retinal wave size, absolute levels of SRA, correlations between RGC pairs, RGC burst frequency, high frequency RGC firing during bursts, and the number of spikes per RGC burst are each uncorrelated with abnormalities in eye-specific segregation in the dLGN. An increase in the fraction of asynchronous spikes occurring outside of bursts and waves correlates with eye-specific segregation defects in studies reported to date. These findings highlight the relative importance of different features of SRA while providing additional constraints for computational models of Hebbian plasticity mechanisms in the developing visual system. Electronic supplementary material The online version of this article (doi:10.1186/1749-8104-9-25) contains supplementary material, which is available to authorized users

Effects of Early Postnatal Exposure to Ethanol on Retinal Ganglion Cell Morphology and Numbers of Neurons in the Dorsolateral Geniculate in Mice

Background: The adverse effects of fetal and early postnatal ethanol intoxication on peripheral organs and the central nervous system are well documented. Ocular defects have also been reported in about 90% of children with fetal alcohol syndrome, including microphthalmia, loss of neurons in the retinal ganglion cell (RGC) layer, optic nerve hypoplasia, and dysmyelination. However, little is known about perinatal ethanol effects on retinal cell morphology. Examination of the potential toxic effects of alcohol on the neuron architecture is important because the changes in dendritic geometry and synapse distribution directly affect the organization and functions of neural circuits. Thus, in the present study, estimations of the numbers of neurons in the ganglion cell layer and dorsolateral geniculate nucleus (dLGN), and a detailed analysis of RGC morphology were carried out in transgenic mice exposed to ethanol during the early postnatal period

The metabotropic glutamate agonist 2-amino-4-phosphonobutyric acid (APB) does not activate currents in postnatal retinal ganglion cells

WHEREAS in the mature retina the glutamate agonist 2-amino-4-phosphonobutyric acid (APB) selectively activates currents in rod bipolar and ON-cone bipolar cells, recent molecular studies have suggested the possibility of a transient appearance of the APB-sensitive receptor in developing retinal ganglion cells. In the present study the whole-cell and perforated variations of the patch-clamp method were employed to assess the responsivity of postnatal cat retinal ganglion cells to APB. Recently, APB treatment has been shown in our laboratory to block the normal stratification of retinal ganglion cell dendrites into ON and OFF sublaminae of the inner plexiform layer. Although application of this glutamate agonist elicited inward sustained currents, amino acid analysis revealed that the APB product (RBI) was contaminated by 8% glycine. In subsequent experiments applications of uncontaminated APB (Cal Biochem) never yielded responses in postnatal retinal ganglion cells which displayed normal currents to other glutamate agonists. The findings do not support the notion of transient expression of APB receptors in retinal ganglion cells during the development period studied

Cellular reorganization in the human retina during normal aging

PURPOSE. To characterize the nature and extent of neuronal reorganization in the human retina during normal aging. METHODS. Retinas of young (18-34 years old) and aged (68-77 years old) human donors were examined. Immunocytochemical methods and antibodies directed against Go-alpha, protein kinase C, parvalbumin, calbindin, calretinin, and choline acetyltransferase were used to stain different retinal cell types. Confocal images of retinal sections from the optic disc to the peripheral edge were taken at three eccentricities, and the density and length of cellular processes were quantified with neuroanatomical analysis software. RESULTS. Dendritic fibers of rod and On-cone bipolar cells were found to extend well beyond the normal boundary of the outer plexiform layer (OPL) into the outer nuclear layer (ONL) in aged retinas. Length and density of these elongated fibers were significantly greater in aged than in young retinas. This phenomenon demonstrated a clear spatial gradient that was most prevalent in the periphery and was infrequent in the central region of the retina. Horizontal cells, which normally make triad synaptic connections with photoreceptors and bipolar cells, also had dendrites that extended into the ONL in aged retinas, and these were spatially juxtaposed with the elongated dendrites of bipolar cells. CONCLUSIONS. Rod and On-cone bipolar cells, as well as horizontal cells of the human retina, undergo extensive dendritic reorganization during normal aging. Although literature on aging has tended to emphasize degenerative and regressive changes, the present findings provide evidence for a remarkable degree of cellular plasticity in the aged human retina. Copyright © Association for Research in Vision and Ophthalmology

Nitric oxide differentially modulates ON and OFF responses of retinal ganglion cells

Several lines of evidence suggest that nitric oxide (NO) can regulate diverse retinal functions, but whether this gas is capable of modulating the visual responses of retinal output neurons has not been established. In the present study the effects of NO on rod-driven responses of retinal ganglion cells were tested by making whole cell patch-clamp recordings from morphologically identified ganglion cells in the isolated ferret retina. Bath application of L-arginine, the substrate of nitric oxide synthase, and S-nitroso-N-acetylpenicillamine, the NO donor, was found to differentially affect ON and OFF discharge patterns. The introduction of these drugs significantly decreased visual responses of retinal ganglion cells, but the effects were more pronounced on OFF than on ON discharges. The peak discharge rates of ON responses were usually reduced by about 40%, but not completely blocked. In contrast, OFF responses were completely blocked in most cells. These differential effects were observed in ON-OFF cells as well as in cells that yielded just ON or OFF discharges. The OFF responses that were blocked by NO were also blocked by DL-2-amino-phosphonobutyric acid (APB) and strychnine, suggesting the involvement of the APB-sensitive rod pathway

Spontaneous activity of morphologically identified ganglion cells in the developing ferret retina

Whole-cell patch-clamp recordings were made from morphologically identified ganglion cells in the intact retina of developing ferrets. As early as 3 d after birth, all ganglion cells exhibited bursts of spontaneous activity, with the interval between bursts gradually decreasing with maturity. By 2 weeks after birth, ganglion cells could be morphologically differentiated into three major classes (α, β, and γ), and at this time each cell class was characterized by a distinct pattern of spontaneous activity. Dual patch-clamp recordings from pairs of neighboring cells revealed that cells of all morphological classes burst in a coordinated manner, regardless of cell type. These observations suggest that a common mechanism underlies the bursting patterns exhibited by all ganglion cell classes, and that class-specific firing patterns emerge coincident with retinal ganglion cell morphological differentiation

Eye-specific retinogenicu late segregation independent of normal neuronal activity

The segregation of initially intermingled left and right eye inputs to the dorsal lateral geniculate nucleus (DLGN) during development is thought to be in response to precise spatial and temporal patterns of spontaneous ganglion cell activity. To test this hypothesis, we disrupted the correlated activity of neighboring ganglion cells in the developing ferret retina through immunotoxin depletion of starburst amacrine cells. Despite the absence of this type of correlated activity, left and right eye inputs segregated normally in the DLGN. By contrast, when all spontaneous activity was blocked, the projections from the two eyes remained intermingled. Thus, certain features of normal neural activity patterns are not required for the formation of eye-specific projections to the DLGN