OFF Retinal Ganglion Cells Research Articles

Genetic Control of Circuit Function:Vsx1andIrx5Transcription Factors Regulate Contrast Adaptation in the Mouse Retina

Transcriptional programs guide the specification of neural cell types in the developing nervous system. However, it is unclear whether such programs also control specific aspects of neural circuit function at maturity. In the mammalian retina, Vsx1 and Irx5 transcription factors are present in a subset of bipolar interneurons that convey signals from photoreceptors to ganglion cells. The biased expression of Vsx1 and Irx5 in hyperpolarizing OFF compared with depolarizing ON bipolar cells suggests that these transcription factors may selectively regulate signal processing in OFF circuits. To test this hypothesis, we generated mice lacking both Vsx1 and Irx5. Bipolar cells in these mice were morphologically normal, but the expression of cell-specific markers in some OFF but not ON bipolar cells was reduced or absent. To assess visual function in Vsx1(-/-)Irx5(-/-) retinas, we recorded light responses from ensembles of retinal ganglion cells (RGCs). We first identified functional RGC types in control mice and describe their response properties and adaptation to temporal contrast using a simple linear-nonlinear model. We found that space-time receptive fields of RGCs are unchanged in Vsx1(-/-)Irx5(-/-) mice compared with control retinas. In contrast, response threshold, gain, and range were lowered in a cell-type-specific manner in OFF but not ON RGCs in Vsx1(-/-)Irx5(-/-) retinas. Finally, we discovered that the ability to adapt to temporal contrast is greatly reduced in OFF RGCs in the double mutant, suggesting that Vsx1 and Irx5 control specific aspects of visual function in circuits of the mammalian retina.

Molecular identification of a retinal cell type that responds to upward motion

The retina contains complex circuits of neurons that extract salient information from visual inputs. Signals from photoreceptors are processed by retinal interneurons, integrated by retinal ganglion cells (RGCs) and sent to the brain by RGC axons. Distinct types of RGC respond to different visual features, such as increases or decreases in light intensity (ON and OFF cells, respectively), colour or moving objects. Thus, RGCs comprise a set of parallel pathways from the eye to the brain. The identification of molecular markers for RGC subsets will facilitate attempts to correlate their structure with their function, assess their synaptic inputs and targets, and study their diversification. Here we show, by means of a transgenic marking method, that junctional adhesion molecule B (JAM-B) marks a previously unrecognized class of OFF RGCs in mice. These cells have asymmetric dendritic arbors aligned in a dorsal-to-ventral direction across the retina. Their receptive fields are also asymmetric and respond selectively to stimuli moving in a soma-to-dendrite direction; because the lens reverses the image of the world on the retina, these cells detect upward motion in the visual field. Thus, JAM-B identifies a unique population of RGCs in which structure corresponds remarkably to function.

Survival and axonal regeneration of off-center retinal ganglion cells of adult cats are promoted with an anti-glaucoma drug, nipradilol, but not BDNF and CNTF

OFF-center retinal ganglion cells (RGCs) occupy a smaller proportion than ON RGCs when RGCs regenerate axons into a transplanted peripheral nerve. We examined whether the regeneration ability of OFF RGCs in adult cats was promoted when the numbers of regenerating RGCs were increased with brain-derived neurotrophic factor (BDNF)+ciliary neurotrophic factor (CNTF)+forskolin (BCF) or 3,4-dihydro-8-(2-hydroxy-3-isopropylamino)-propoxy-3-nitroxy-2H-1-benzopyran (nipradilol), an anti-glaucoma drug. ON or OFF RGCs were morphologically determined on the basis of their dendritic ramification in the inner plexiform layer using computational analysis. In the normal intact retina the ratio of ON and OFF RGCs (ON/OFF ratio) was 1.25 (55%/44%); whereas, it was 2.61 in regenerating RGCs with saline injection (control) 6 weeks after peripheral nerve transplantation. Estimated numbers of regenerating ON and OFF RGCs were 2149 and 895, respectively. An injection of BCF increased only numbers of ON RGCs into 5766 (2.7-fold to control) but not that of OFF RGCs, n=858. Nipradilol increased both estimated numbers of ON (11,518, 5.4-fold to control) and OFF RGCs (7330, 8.2-fold to control). In the retinas with optic nerve (OpN) transection and intravitreal saline-, BCF- or nipradilol-injection, numbers of ON and OFF RGCs surviving axotomy showed similar trend to that in regenerating RGCs. Thus, nipradilol promoted the survival and regeneration abilities of both of ON and OFF RGCs whereas BCF only did the abilities of ON RGCs. The distribution of tropo-myosin-related kinase B, BDNF receptor, was sparser in the outer two thirds of inner plexiform layer. The lower surviving ability of OFF-RGCs may be attributed in part to the distribution.

Different Mechanisms Generate Maintained Activity in ON and OFF Retinal Ganglion Cells

Neuronal discharge is driven by either synaptic input or cell-autonomous intrinsic pacemaker activity. It is commonly assumed that the resting spike activity of retinal ganglion cells (RGCs), the output cells of the retina, is driven synaptically, because retinal photoreceptors and second-order cells tonically release neurotransmitter. Here we show that ON and OFF RGCs generate maintained activity through different mechanisms: ON cells depend on tonic excitatory input to drive resting activity, whereas OFF cells continue to fire in the absence of synaptic input. In addition to spontaneous activity, OFF cells exhibit other properties of pacemaker neurons, including subthreshold oscillations, burst firing, and rebound excitation. Thus, variable weighting of synaptic mechanisms and intrinsic properties underlies differences in the generation of maintained activity in these parallel retinal pathways.

Network Variability Limits Stimulus-Evoked Spike Timing Precision in Retinal Ganglion Cells

Visual, auditory, somatosensory, and olfactory stimuli generate temporally precise patterns of action potentials (spikes). It is unclear, however, how the precision of spike generation relates to the pattern and variability of synaptic input elicited by physiological stimuli. We determined how synaptic conductances evoked by light stimuli that activate the rod bipolar pathway control spike generation in three identified types of mouse retinal ganglion cells (RGCs). The relative amplitude, timing, and impact of excitatory and inhibitory input differed dramatically between On and Off RGCs. Spikes evoked by repeated somatic injection of identical light-evoked synaptic conductances were more temporally precise than those evoked by light. However, the precision of spikes evoked by conductances that varied from trial to trial was similar to that of light-evoked spikes. Thus, the rod bipolar pathway modulates different RGCs via unique combinations of synaptic input, and RGC temporal variability reflects variability in the input this circuit provides.

Responses of rabbit retinal ganglion cells to electrical stimulation with an epiretinal electrode

Rational selection of electrical stimulus parameters for an electronic retinal prosthesis requires knowledge of the electrophysiological responses of retinal neurons to electrical stimuli. In this study, we examined the effects of cathodal and anodal current pulses on the extracellularly recorded responses of OFF and ON rabbit retinal ganglion cells (RGCs) in an in vitro preparation. Current pulses (1 msec duration), delivered by a 125 µm electrode placed on the inner retinal surface within the receptive field of a RGC, produced both short-latency (⩽5 msec) and long-latency (8–60 msec) responses. The long-latency responses, but not the short-latency responses, were abolished upon application of the glutamate receptor antagonists CNQX and NBQX, thus indicating that the long-latency responses of RGCs are due to activation of presynaptic neurons in the retina. The latency of the long-latency response depended upon the polarity of the stimulus. For OFF RGCs, the average latency was 11 msec for a cathodal stimulus and 24 msec for an anodal stimulus. For ON RGCs, the average latency was 25 msec for a cathodal stimulus and 16 msec for an anodal stimulus. The threshold current also depended upon the polarity of the stimulus, at least for OFF RGCs. The average threshold current for evoking a long-latency response in OFF RGCs was 10 µA for a cathodal stimulus and 21 µA for an anodal stimulus. In ON RGCs, the average threshold current was 13 µA for a cathodal stimulus and 15 µA for an anodal stimulus.

Visual Stimulation Is Required for Refinement of ON and OFF Pathways in Postnatal Retina

ON and OFF pathways separately relay increment and decrement luminance signals from retinal bipolar cells to cortex. ON-OFF retinal ganglion cells (RGCs) are activated via synaptic inputs onto bistratified dendrites localized in the ON and OFF regions of the inner plexiform layer. Postnatal maturational processes convert bistratifying ON-OFF RGCs to monostratifying ON and OFF RGCs. Although visual deprivation influences refinement of higher visual centers, no previous studies suggest that light regulates either the development of the visual-evoked signaling in retinal ON and OFF pathways, nor pruning of bistratified RGC dendrites. We find that dark rearing blocks both the maturational loss of ON-OFF responsive RGCs and the pruning of dendrites. Thus, in retina, there is a previously unrecognized, pathway-specific maturation that is profoundly affected by visual deprivation.

Mechanisms Underlying Developmental Changes in the Firing Patterns of ON and OFF Retinal Ganglion Cells during Refinement of their Central Projections

Patterned neuronal activity is implicated in the refinement of connectivity during development. Calcium-imaging studies of the immature ferret visual system demonstrated previously that functionally separate ON and OFF retinal ganglion cells (RGCs) develop distinct temporal patterns of spontaneous activity as their axonal projections undergo refinement. OFF RGCs become spontaneously more active compared with ON cells, resulting in a decrease in synchronous activity between these cell types. This change in ON and OFF activity patterns is suitable for driving the activity-dependent refinement of their axonal projections. Here, we used whole-cell and perforated-patch recording techniques to elucidate the mechanisms that underlie the developmental alteration in the ON and OFF RGC activity patterns. First, we show that before the refinement period, ON and OFF RGCs have similar spike patterns; however, during the period of segregation, OFF RGCs demonstrate significantly higher spike rates relative to ON cells. With increasing age, OFF cells require less depolarization to reach their action potential threshold and fire more spikes in response to current injection compared with ON cells. In addition, spontaneous postsynaptic currents and potentials are greater in magnitude in OFF cells than ON cells. In contrast, before axonal refinement, there are no differences in the intrinsic excitability or synaptic drive onto ON and OFF cells. Together, our results show that developmental changes in ON and OFF RGC excitability and in the strength of their synaptic drives act together to reshape the spike patterns of these cells in a manner appropriate for the refinement of their connectivity.

Relative contributions of bipolar cell and amacrine cell inputs to light responses of ON, OFF and ON–OFF retinal ganglion cells

Light-evoked postsynaptic currents (lePSCs) were recorded from ON, OFF and ON–OFF ganglion cells in dark-adapted salamander retinal slices under voltage clamp conditions, and the cell morphology was examined using Lucifer yellow fluorescence with confocal microscopy. The current–voltage relations of the lePSCs in all three types of ganglion cells are approximately linear within the cells' physiological range. The average chloride/cation conductance ratio ( Δg Cl(NR)/ Δg C(NR)) of the lePSCs is near 3, suggesting that ganglion cell light responses are associated with a greater postsynaptic conductance change at the amacrine-ganglion cell inhibitory synapses than at the bipolar-ganglion cell excitatory synapses. By comparing the charge transfer of lePSCs in normal Ringer's and in picrotoxin+strychnine+Imidazole-4-acidic acid, we found that the GABAergic and glycinergic amacrine–bipolar cell feedback synapses decreased the light-induced glutamatergic vesicle release from bipolar cells to all ganglion cells, and the degree of release reduction varied widely from ganglion cell to ganglion cell, with a range of 3–28 fold.

ON–OFF retinal ganglion cells temporally encode OFF/ON sequence

While the functions of ON and OFF retinal ganglion cells have been intensively investigated, that of ON–OFF cells has not. In the present study, the temporal properties of spike trains emitted from ON-OFF cells in response to randomly flickering or multiphase ramp stimuli were examined in the Japanese quail. The results indicate that the firing of ON-spikes was influenced by the recent firing of OFF-spikes, and vice versa. As a result of this interaction, OFF/ON sequence of light intensity change was encoded with a spike pair with an interval of 20 ms, indicating that temporal coding is utilized in the vertebrate visual system as early as the retina. Thus, the present results suggest that retinal neuronal circuits may detect specific sequential features of stimuli.

Processing of scotopic increments and decrements.

Rod and cone photoreceptors send their signals to ON- and OFF-retinal ganglion cells through different pathways in the primate retina. We hypothesized that increments and decrements of light may be processed differently by the rod-bipolar pathway because of the funneling of the rod signal through the rod bipolar cell. We tested this hypothesis using a psychophysical adaptation paradigm, which has provided evidence that photopic increments and decrements of light are processed by ON- and OFF-pathways in the human visual system. We had observers adapt to either a rapid-on or rapid-off sawtooth waveform, under both photopic and scotopic conditions. We then measured detection thresholds for one cycle of a rapid-on or rapid-off sawtooth stimulus. For photopic stimuli, sawtooth adaptation asymmetrically raised thresholds for test stimuli in a manner that depended on the polarity of the adaptation stimulus. For scotopic stimuli, thresholds were raised, but no significant selective adaptation effect was found. By repeating the photopic condition with sawtooth stimuli which had been filtered using an impulse response function derived for the rod system, we demonstrated that the lack of selective adaptation was not a consequence of the sluggish temporal response of the rod-bipolar pathway. We conclude instead that the reduced effectiveness of sawtooth adaptation is due to channeling of rod photoreceptor signals through the rod bipolar cell before reaching ON- and OFF-ganglion cells.

Development and Organization of the Retina: From Molecules to Function

Development of Vision and the Pre-Visual System S.S. Easter, Jr., et al. Cellular and Molecular Aspects of Photoreceptor Differentiation R. Adler. Embryonic Patterning of Cone Subtypes in the Mammalian Retina K.C. Wikler, D.L. Stull. Development of Cone Distribution Patterns in Mammals A. Szel, et al. Genesis of Topographic and Cellular Diversity in the Primate Retina P. Rakic. Development of ON and OFF Retinal Ganglion Cell Mosaics L.M. Chalupa, et al. Getting to Grips with Neuronal Diversity: What is a Neuronal Type? J.E. Cook. Glio-Neuronal Interactions in Retinal Development A. Reichenbach. Comparative Anatomy and Function of Mammalian Horizontal Cells L. Peichl, et al. Parallel Pathways of Primate Vision: Sampling of Information in the Fourier Space by M and P Cells L. Peichl, et al. Parallel Pathways of Primate Vision: Sampling of Information in the Fourier Space by M and P Cells L.C.L. Silveira, H.D. De Mello, Jr. Transient and Persistent Na+, Ca2+, and Mixed-Cation Currents in Retinal Ganglion Cells A.T. Ishida. Synaptic Transmission Between Retinal Neurons M. Wilson. Scaling the Retina, Micro and Macro B.L. Finlay, R.L. Snow. Retinal Ganglion Cell Axonal Transport: Moving Down the Road to Functional Connections K.L. Moya. 5 Additional Articles. Index.

The development of retinal ganglion cell dendritic stratification in ferrets.

A signature feature of mature ferret retinal ganglion cells (RGCs) is the stratification of their dendrites within either ON or OFF sublayers of the retinal inner plexiform layer (IPL). Dendritic stratification is achieved through the gradual restriction of RGC dendrites which initially ramify throughout the IPL. We examined the time course of stratification by retrogradely labeling ferret retinas with DiI at various postnatal ages. Stratification of beta and alpha RGC dendrites into either the ON or OFF sublayers of the IPL begins around postnatal day 5, when class-specific morphologies begin to emerge, and is largely completed by eye opening, at the end of the first postnatal month. Our results imply that dendritic stratification of ferret ON and OFF RGCs, as in other mammals, occurs independently of visually driven activity.

Stratification of ON and OFF ganglion cell dendrites depends on glutamate-mediated afferent activity in the developing retina.

A fundamental attribute of the vertebrate visual system is the segregation of ON and OFF pathways signalling increments and decrements of light. In the mature retina, dendrites of ON- and OFF-centre retinal ganglion cells (RGCs) stratify in different sublaminae of the inner plexiform layer (IPL), and are differentially innervated by two types of bipolar cells which depolarize and hyperpolarize on exposure to light. This stratification of ON and OFF RGCs is achieved by the gradual restriction of their dendrites which ramify throughout the IPL early in development. The factors underlying this regressive event are unknown. Dendritic stratification occurs around the time that bipolar cells form synapses in the IPL, which raises the possibility that synaptic activity is involved in this process. Here we test this hypothesis by treating the developing cat retina with the glutamate analogue 2-amino-4-phosphonobutyric acid (APB), which hyperpolarizes ON cone bipolar and rod bipolar cells, thereby preventing their release of glutamate. We report that intraocular injection of APB during the period when dendritic stratification normally occurs prevents the formation of structurally segregated ON and OFF retinal pathways. These results provide evidence that glutamate-mediated afferent activity regulates the remodelling of RGC dendrites during development.

Benzodiazepines and the mammalian retina. III. Postnatal development

Iontophoretic effects of the benzodiazepine receptor agonist, flurazepam, and antagonist, flumazepil (RO-15-1788) on the retinal ganglion cells of kittens (7–9 weeks of age) have been compared with those of adult cats (18–22 weeks of age). In the adult retina, flurazepam decreased and flumazepil increased the visually evoked and spontaneous firing of ON-, but produced no effects on the response of OFF-retinal ganglion cells. However, in the kittens retina, in which ON-cells' selectivity to GABA is not fully developed 3, both the visually evoked and spontaneous activities of ON- and OFF-cells were inhibited by flurazepam and enhanced by flumazepil. This suggests that postnatal development of benzodiazepine action parallels that of GABA action at the retinal ganglion cells in the cat retina.