Synaptic organization and ionic basis of on and off channels in mudpuppy retina. III. A model of ganglion cell receptive field organization based on chloride-free experiments

A chloride-free environment produces selective changes in the retinal network which include a separation of on and off channels. The identification of chloride-sensitive and insensitivie neuronal activity permits identification of some of the connections and intervening polarities of synaptic interactions which are expressed in ganglion cell receptive field organization. These experiments support previous suggestions that surround antagonism is dependent on horizontal cell activity. In addition they suggest a model of the neuronal connections which subserve on-center, off-center, and on-off ganglion cells. Experimental tests of the on-off ganglion cell model favor the idea that this type of ganglion cell receives inhibitory input from amacrine cells and excitatory activation from depolarizing and hyperpolarizing bipolar cells.     

Synaptic organization and ionic basis of on and off channels in mudpuppy retina. II. Chloride-dependent ganglion cell mechanisms

Extracellular ganglion cell recordings in the perfused mudpuppy eyecup show that a chloride-free (c-f) perfusate abolishes the center and surround excitation of on-center cells, the surround excitation of off- center cells, and the on discharge of on-off cells. These changes in ganglion cell receptive field organization are anticipated in view of the effects of a c-f environment on the neurons which are presynaptic to the ganglion cells. However, chloride-dependent inhibitory postsynaptic (IPS) responses have been observed in on-off ganglion cells. These inhibitory postsynaptic potentials (IPSP's) are preceeded by (ESPS's) exitatory postsynaptic potentials and are apparently mediated by amacrine cells. The light-activated hyperpolarization of off cells is not the result of a chloride-dependent IPSP and probably results from disfacilitation.     

Synaptic inputs to the ganglion cells in the tiger salamander retina

The postsynaptic potentials (PSPs) that form the ganglion cell light response were isolated by polarizing the cell membrane with extrinsic currents while stimulating at either the center or surround of the cell's receptive field. The time-course and receptive field properties of the PSPs were correlated with those of the bipolar and amacrine cells. The tiger salamander retina contains four main types of ganglion cell: "on" center, "off" center, "on-off", and a "hybrid" cell that responds transiently to center, but sustainedly, to surround illumination. The results lead to these inferences. The on-ganglion cell receives excitatory synpatic input from the on bipolars and that synapse is "silent" in the dark. The off-ganglion cell receives excitatory synaptic input from the off bipolars with this synapse tonically active in the dark. The on-off and hybrid ganglion cells receive a transient excitatory input with narrow receptive field, not simply correlated with the activity of any presynaptic cell. All cell types receive a broad field transient inhibitory input, which apparently originates in the transient amacrine cells. Thus, most, but not all, ganglion cell responses can be explained in terms of synaptic inputs from bipolar and amacrine cells, integrated at the ganglion cell membrane.     

A model of anuran retina relating interneurons to ganglion cell responses

A model is presented which accounts for many characteristic response properties used to classify anuran ganglion cell types while being consistent with data concerning interneurons. In the model color is ignored and input stimuli are assumed to be only black and white at high contrast. We show that accurate ganglion cell responses are obtained even with simplified receptors and horizontal cells: Receptors are modeled as responding with a step change, while horizontal cells respond only to global changes in intensity brought about by full field illumination changes. A hyperpolarizing and depolarizing bipolar cell are generated y subtracting local receptor and horizontal potentials. Two transient amacrine cells (On and Off) are generated using a high-pass filter like mechanism with a thresholded output which responds to positive going changes in the corresponding bipolar cell potentials. The model shows how a selective combination of bipolar and amacrine channels can account for many of the response properties used to classify the anuran ganglion cell types (class-0 through 4) and makes several experimental predictions.     

Control of Retinal Sensitivity : III. Lateral Interactions at the Inner Plexiform Layer

Both the "on" and the "on-off" ganglion cells in the mudpuppy retina generate graded responses over a narrow range of log test intensities. Sustained full field or surround backgrounds change the range of center log test intensities that elicits the graded response for both cell types. The on-off, but not the on ganglion cells are further affected by moving or flashing surround backgrounds. These cells are hyperpolarized, threshold is elevated, and the entire graded range of response is elicited by a higher range of log center test intensities. Depolarizing activity is elicited in amacrine cells by moving backgrounds that affect the on-off ganglion cells, but bipolar activity is unaffected. These results suggest that the amacrine cells at the inner plexiform layer mediate a third stage of sensitivity control in the retina, increasing threshold for response to change specifically in the on-off ganglion cells.     

Analyses of bipolar cell responses elicited by polarization of horizontal cells

Simultaneous intracellular recordings were made from a bipolar cell and a horizontal cell in the carp retina. The properties of the bipolar cell were studied while injecting current into the horizontal cell. Hyperpolarization of horizontal cells, irrespective of their type, elicited a hyperpolarizing response in on-center bipolar cells and a depolarizing response in off-center bipolar cells. Analyses of the ionic mechanisms of bipolar cell responses revealed that depolarization of horizontal cells simulated and hyperpolarization opposed the effect of central illumination. The effect of polarization was exerted in such a manner that each type of horizontal cells modified the transmission from those photoreceptors from which they receive main inputs. In on- center bipolar cells, for example, the L-type horizontal cells receiving inputs mainly from red cones modified the cone-bipolar transmission accompanied by a conductance change of K+ and/or Cl- channels, and the intermediate horizontal cells receiving inputs from rods modified the rod-bipolar transmission accompanied by a conductance change of Na+ channels. In off-center bipolar cells, the effect of polarization of any type of horizontal cells was mediated mainly by conductance changes of Na+ channels. Feedback mechanisms from horizontal cells to photoreceptors could explain these results reasonably well.     

Photoreceptor Potentials of Opposite Polarity in the Eye of the Scallop, Pecten irradians

Intracellular recordings were obtained from single visual cells of the scallop, Pecten irradians. Two types of units are found. One type gives a graded, depolarizing response to light and the other a graded, hyperpolarizing response. The depolarizing cells are 2–3 log units more sensitive to light and have a longer latency than the hyperpolarizing type. At high light intensities the depolarizing cells are inactivated while the hyperpolarizing cells maintain their responses. When action potentials are seen they occur during illumination in depolarizing cells ("on" response) and after illumination in hyperpolarizing cells ("off" response). The evidence suggests that the depolarizing responses are from the microvilli-brearing proximal cells, and the hyperpolarizing responses from the ciliary-type distal cells of the retina, and that both responses are directly produced by light.     

Temporal tuning and nonlinearity of intraretinal pathways in turtle: Effects of temperature,stimulus intensity,and size

Flash responses, amplitude and phase transfer functions, and nonlinearities were measured in turtle retina for pathways with photoreceptor inputs and outputs from horizontal (HC), hyperpolarizing bipolar (HBC), sustained amacrine (AC), and on-off ganglion (GC) cells. Flash responses slowed and attenuated in all cells as temperature decreased. Whitenoise transfer properties of sustained-type cells (HC, HBC, AC) were of low- or bandpass type; highfrequency cut-off (f _c) and phase crossover frequency decreased with temperature. f _c increased as spot diameter was increased. Nonlinearity of these sustained-response pathways (distortion product frequencies in response to a sum-of-sinusoids input probe) increases with intensity and may depend on amplitude saturation limiting. On/off GC synaptic and spike activity increased as spot diameter decreased and intensity increased. Amplitude transfer functions had a low-frequency peak (PSP activity) and monotonically decreasing amplitude vs. frequency shape (spikes and transient PSP activity). Nonlinearity increased with stimulus intensity; it was maximal with 1 mm spot size, less with smaller (500 m) and larger (5 mm) spots. It may depend on the functional equivalent of full-wave rectification (on-off response).This work was supported by NEI grant R01 EY03383     

Influence of amacrine cells on receptive field organization of ganglion cells of the generalized vertebrate cone retina: Electronic simulation

Two classes of amacrine cells are simulated, small-field and large-field. Small-field amacrine cells are formed by input from a single bipolar cell, while large-field amacrine cell is formed by inputs from same 7 bipolar cells that form the ganglion cell. Only tonic amacrine cells are studied with both chromatic and luminosity types as well as double-and single-opponent receptive fields. Amacrine cells are used in both feedforward to ganglion cells and feedback to bipolar and horizontal cells. Feedback to bipolar cells or feedfoward to ganglion cells affected steady state levels in a predictable fashion. Negative feedback to bipolar cells and positive feedfoward to ganglion cells does not introduce transients to ganglion cells while negative feedback to horizontal cells and negative feedfoward does. Feedback to horizontal cells produces complex effects on bipolar, amacrine and ganglion cells dependent on such factors as center-surround field balance and negative feedback from luminosity type of horizontal cell to cones.     

Ionic mechanisms underlying the responses of off-center bipolar cells in the carp retina. II. Studies on responses evoked by transretinal current stimulation

Transretinal current pulses flowing from the receptor side to the vitreous side of the retina cause transient release of transmitter from the photoreceptor terminals, and in off-center bipolar cells they evoke transient depolarizations with a brief (less than 1 ms) synaptic delay. Since it is known that the presence of Na+ in the external medium is not essential for this type of transmitter release, we used this procedure to examine the role of [Na+]o in the generation of light- evoked responses (hyperpolarizing to spot illumination in the receptive field center and depolarizing to an annulus in the surround) of this type of bipolar cell. When the cell membrane was steadily depolarized by current injection through the recording microelectrode, the depolarizing response evoked by the transretinal current pulses decreased in amplitude and reversed its polarity at above +45 mV. Conversely, the response amplitude increased when the cell was steadily hyperpolarized. The reversal potential seems to be lowered in low [Na+]o (28 mM). Removal of Na+ from the superfusate hyperpolarized the cell and both the light-evoked and current-evoked responses disappeared. From these observations, it is hypothesized that the hyperpolarizing center response of the off-center bipolar cells is a result of removal of sustained depolarization produced by sodium permeability increase.     

A horizontal cell selectively contacts blue-sensitive cones in cyprinid fish retina: intracellular staining with horseradish peroxidase

A horizontal cell selectively contacting blue-sensitive cones has been intracellularly stained with horseradish peroxidase in the retina of a cyprinid fish, the roach. The light microscopical morphology of the cell belonged to the H3 category of horizontal cells found in cyprinid fish retinae. In response to spectral stimuli, the cell generated chromaticity-type S-potentials that were hyperpolarizing to blue and depolarizing to yellow-orange. A red-sensitive hyperpolarizing component was absent possibly because of suppression of the negative feedback pathway between luminosity-type (H1) horizontal cells and green-sensitive cones.     

Signal transmission through the dark-adapted retina of the toad (Bufo marinus). Gain, convergence, and signal/noise

Responses to light were recorded from rods, horizontal cells, and ganglion cells in dark-adapted toad eyecups. Sensitivity was defined as response amplitude per isomerization per rod for dim flashes covering the excitatory receptive field centers. Both sensitivity and spatial summation were found to increase by one order of magnitude between rods and horizontal cells, and by two orders of magnitude between rods and ganglion cells. Recordings from two hyperpolarizing bipolar cells showed a 20 times response increase between rods and bipolars. At absolute threshold for ganglion cells (Copenhagen, D.R., K. Donner, and T. Reuter. 1987. J. Physiol. 393:667-680) the dim flashes produce 10-50-microV responses in the rods. The cumulative gain exhibited at each subsequent synaptic transfer from the rods to the ganglion cells serves to boost these small amplitude signals to the level required for initiation of action potentials in the ganglion cells. The convergence of rod signals through increasing spatial summation serves to decrease the variation of responses to dim flashes, thereby increasing the signal-to-noise ratio. Thus, at absolute threshold for ganglion cells, the convergence typically increases the maximal signal-to-noise ratio from 0.6 in rods to 4.6 in ganglion cells.     

Two-photon imaging reveals somatodendritic chloride gradient in retinal ON-type bipolar cells expressing the biosensor Clomeleon

A somatodendritic gradient of Cl(-) concentration ([Cl(-)](i)) has been postulated to generate GABA-evoked responses of different polarity in retinal bipolar cells, hyperpolarizing in OFF cells with low dendritic [Cl(-)](i), and depolarizing in ON cells with high dendritic [Cl(-)](i). As glutamate released by the photoreceptors depolarizes OFF cells and hyperpolarizes ON cells, the bipolars' antagonistic receptive field (RF) could be computed by simply integrating glutamatergic inputs from the RF center and GABAergic inputs from horizontal cells in the RF surround. Using ratiometric two-photon imaging of Clomeleon, a Cl(-) indicator transgenically expressed in ON bipolar cells, we found that dendritic [Cl(-)](i) exceeds somatic [Cl(-)](i) by up to 20 mM and that GABA application can lead to Cl(-) efflux (depolarization) in these dendrites. Blockers of Cl(-) transporters reduced the somatodendritic [Cl(-)](i) gradient. Hence, our results support the idea that ON bipolar cells employ a somatodendritic [Cl(-)](i) gradient to invert GABAergic horizontal cell input.     

Spatio-temporal cross-correlation analysis of catfish retinal neurons

1. The receptive field properties of visual neurons in the retina of the catfish are studied by a white noise spatio-temporal stimulus. The spatial and temporal inputs of the stimulus are independent and lead to complete linear characterizations and local nonlinear characterizations of the neural response. 2. Horizontal cells, bipolar cells, and sustained or Type N amacrine cells all yield spatially coherent linear correlations. The horizontal cells have the shortest latency by these methods and exhibit a late depolarizing component that is wider in spatial extent than the initial hyperpolarizing component. Depolarizing Type N neurons have center-hyperpolarizing local nonlinearity. 3. Transient or Type C amacrine cells do not correlate well with the intensity of the stimulus, even though the Fast variety responds vigorously to the stimulus. 4. Ganglion cells are classified into Excitatory, Inhibitory and Biphasic classes based upon their linear correlations. Some ganglions exhibit responses dependent upon the orientation of stimulus. Although linear correlation of the Excitatory class is similar to that of the depolarizing Type N cell, the locally nonlinear character of these cell types is distinct. The receptive field of the Inhibitory ganglion cells has strong locally excitatory nonlinearity.     

Application of transretinal current stimulation for the study of bipolar-amacrine transmission

Transretinal current flowing from the receptor side to the vitreous side depolarizes the axon terminals of retinal cells and facilitates the release of transmitter. Such current elicited a depolarizing response in off-center bipolar cells and a hyperpolarizing response in on-center bipolar cells. It also elicited a response of relatively complex waveform in amacrine cells. The responses elicited in bipolar cells were suppressed in the presence of 5-10 mM glutamate in the perfusing Ringer solution, while the responses of amacrine cells persisted, although their waveform changed to a simple one that showed monotonic depolarization irrespective of the type of amacrine cell and were accompanied by a decrease in the membrane resistance. The results indicate excitatory synaptic transmission from bipolar cells to amacrine cells. Since the response elicited by current in ON-OFF cells was almost identical to those elicited in ON or OFF amacrine cells, the transient nature of their light response cannot be due to their membrane properties. ON-OFF cells responded to transretinal current flowing in the opposite direction with a small hyperpolarization accompanied by a resistance increase. The hyperpolarizing response was suppressed by the addition of GABA in glutamate Ringer solution. The results suggest an activation by the current of GABA-ergic feedback pathways from amacrine cells to bipolar cells.     

A new culturing strategy improves functional neuronal development of human neural progenitor cells

Cell replacement therapies that rely on in vitro differentiation of human neural progenitor cells are a promising strategy to compensate the progressive cell loss in neurodegenerative disorders like Parkinson's disease. We and others observed, that the functional differentiation of progenitors in standard differentiation medium remains limited. The aim of the present study was to optimize neuronal in vitro differentiation by mimicking the physiological shift from depolarizing to hyperpolarizing conditions that occurs during early brain development. Differentiation was initiated using a depolarizing high potassium- and low sodium-containing medium. Subsequently, the high potassium-containing medium was replaced by a hyperpolarizing medium containing low potassium and high sodium concentrations. This two-phase strategy significantly promoted the expression of neuronal markers, enhanced neurite growth, enlarged sodium inward currents, and increased action potential firing. Thus, depolarizing followed by hyperpolarizing culture conditions enable developing human neural progenitor cells to adopt more mature functional qualities.     

An elementary information processing component in the circuitry of the retina generating the on-responses

A pattern of neural connections that is a compulsory feature of photoreceptor terminals and is referred to as the synaptic ribbon complex was analyzed, and by combination of the structural information and information gained by intracellular recordings from photoreceptors, horizontal cells, and bipolar cells, it is possible to explain how the hyperpolarizing effect of light stimulating the photoreceptors is changed to a depolarization of depolarizing bipolar cells. The sign reversal is accomplished by the hyperpolarizing action of the horizontal cells on the photoreceptors, which blocks the transmission between the photoreceptors and the bipolar cells. This blocking action is controlled by the photoreceptor and it functions like a gate that is opened only when the photoreceptor is stimulated by light. The synaptic ribbon complex offers an example of an elementary information processing component with three input channels to the bipolar cells with each channel contributing a different piece of information and with the processing occurring presynaptically. Additional processing of information occurs within the dendritic tree through interactions of the responses of the individual dendritic endings to different types of input. This interaction can involve partial blocking of the conduction within the dendritic tree, making the interaction considerably more complex than simple summation. The responses recorded intracellularly from neurons reveal only the end result of the processing of information at the level of that neuron.     

A spatio-temporal model of cat's retinal cells

This paper presents a model of the spatiotemporal processes of simple ganglion cells of cat's retina. The model is based on the existence of two anatomical paths in the retina: a direct path, responsible for central excitatory effects, and a transversal path, responsible for peripherical inhibitory effects. Plausible spatial weighting functions and temporal transfer functions for photoreceptors, horizontal, bipolar and ganglion cell are introduced by prudent application of comparative neurophysiology.The response of the model to point light stimuli, moving light bars and sinusoidal gratings are obtained. They are in very good agreement with experimental data.     

Light-sensitive voltage responses in the neurons of the cerebral ganglion of Ciona savignyi (Chordata: Ascidiacea)

Light-responsive behaviors such as siphon contraction (1), phototropism (2), and gamete release (3, 4) have been described in several ascidian species. The pigmented spots around the siphon openers (5), the epithelial cells of the sperm duct (6, 7), and the cerebral ganglion (8) have been suggested to be the photoreceptor candidates underlying these behaviors. However, these arguments have not yet been settled because no direct electrophysiological recordings of light-induced receptor potentials have been reported. In this study, we focused on the cerebral ganglion and performed intracellular recordings from the neurons in the ventral side of the cerebral ganglion in an isolated in vitro preparation of the neural complex in Ciona savignyi. We found that 24% (n = 115) of the recorded neurons showed various types of voltage responses to light stimuli. Almost all (27/28) of the recorded voltage responses were "on" responses that included hyperpolarizing and depolarizing responses and could be categorized into five types, except for a complex response recorded in one cell; the remaining one (1/28) was a depolarizing "off" response. This is the first report of electrophysiological recordings of light-sensitive voltage responses from ascidian cerebral ganglion neurons.     

Characteristics of bipolar-bipolar coupling in the carp retina

ON and OFF bipolar cells were identified in the light-adapted carp retina by means of intracellular recording and Lucifer yellow dye injection. The receptive field centers, determined by measuring the response amplitudes obtained by centered spots of different diameters, were 0.3-1.0 mm for ON bipolar cells and 0.3-0.4 mm for OFF bipolar cells. These central receptive field values were much larger than the dendritic field diameters measured by histological methods. Simultaneous intracellular recordings were made from pairs of neighboring bipolar cells. Current of either polarity injected into one member of a bipolar cell pair elicited a sign-conserving, sustained potential change in the other bipolar cell. The coupling efficiency was nearly identical for both depolarizing and hyperpolarizing currents. The maximum separation of coupled bipolar cells was approximately 130 microns. This electrical coupling was reciprocal and summative, and it was observed in cell types of similar function and morphology. Dye coupling was observed in 4 out of 34 stained cells. These results strongly suggest that there is a spatial summation of signals at the level of bipolar cells, which makes their central receptive fields much larger than their dendritic fields.