Shift-effect in the rabbit retinal ganglion cells

Synchronized amplification of local information transmission by peripheral retinal input

Sensory stimuli have varying statistics influenced by both the environment and by active sensing behaviors that rapidly and globally change the sensory input. Consequently, sensory systems often adjust their neural code to the expected statistics of their sensory input to transmit novel sensory information. Here, we show that sudden peripheral motion amplifies and accelerates information transmission in salamander ganglion cells in a 50 ms time window. Underlying this gating of information is a transient increase in adaptation to contrast, enhancing sensitivity to a broader range of stimuli. Using a model and natural images, we show that this effect coincides with an expected increase in information in bipolar cells after a global image shift. Our findings reveal the dynamic allocation of energy resources to increase neural activity at times of expected high information content, a principle of adaptation that balances the competing requirements of conserving spikes and transmitting information.

A polyaxonal amacrine cell population in the primate retina

Amacrine cells are the most diverse and least understood cell class in the retina. Polyaxonal amacrine cells (PACs) are a unique subset identified by multiple long axonal processes. To explore their functional properties, populations of PACs were identified by their distinctive radially propagating spikes in large-scale high-density multielectrode recordings of isolated macaque retina. One group of PACs exhibited stereotyped functional properties and receptive field mosaic organization similar to that of parasol ganglion cells. These PACs had receptive fields coincident with their dendritic fields, but much larger axonal fields, and slow radial spike propagation. They also exhibited ON-OFF light responses, transient response kinetics, sparse and coordinated firing during image transitions, receptive fields with antagonistic surrounds and fine spatial structure, nonlinear spatial summation, and strong homotypic neighbor electrical coupling. These findings reveal the functional organization and collective visual signaling by a distinctive, high-density amacrine cell population.

Bipolar cells contribute to nonlinear spatial summation in the brisk-transient (Y) ganglion cell in mammalian retina

The receptive field of the Y-ganglion cell comprises two excitatory mechanisms: one integrates linearly over a narrow field, and the other integrates nonlinearly over a wide field. The linear mechanism has been attributed to input from bipolar cells, and the nonlinear mechanism has been attributed to input from a class of amacrine cells whose nonlinear "subunits" extend across the linear receptive field and beyond. However, the central component of the nonlinear mechanism could in theory be driven by bipolar input if that input were rectified. Recording intracellularly from the Y-cell in guinea pig retina, we blocked the peripheral component of the nonlinear mechanism with tetrodotoxin and found the remaining nonlinear receptive field to be precisely co-spatial with the central component of the linear receptive field. Both linear and nonlinear mechanisms were caused by an excitatory postsynaptic potential that reversed near 0 mV. The nonlinear mechanism depended neither on acetylcholine nor on feedback involving GABA or glycine. Thus the central components of the ganglion cell's linear and nonlinear mechanisms are apparently driven by synapses from the same rectifying bipolar cell.

Effects of remote stimulation on the mean firing rate of cat retinal ganglion cells

Visual stimulation outside the classical receptive field can have pronounced effects on cat retinal ganglion cells. We characterized the effects of such stimulation by varying the contrast, spatial frequency, temporal frequency, and spatial extent of remote drifting sinusoidal gratings. We found that the mean firing rate of some X-cells and most Y-cells increased to remote gratings of low spatial frequency and high temporal frequency and decreased to ones of high spatial frequency and low temporal frequency. At least 10-20% contrast was required to see either effect, which quickly saturated at higher contrasts. Both effects were substantial, raising or lowering the mean rate of some cells by over 40 impulses/sec. Classical receptive field mechanisms were not involved because the remote gratings caused little or no response modulation. We conclude that, in addition to a mean-increasing mechanism known from previous work, a mean-decreasing one operates in the cat retina. This mechanism prefers slower motion and resolves finer patterns than the mean-increasing one. We incorporate these findings into a model consisting of pools of small and large rectifying subunits of opposite polarity. Model estimates of subunit radius were primarily independent of eccentricity and averaged approximately 0.15 and approximately 0.60 degrees for the mean-decreasing and mean-increasing mechanisms, respectively. This makes the subunits approximately the center size of central X- and Y-cells. Because smooth movements of the eyes, head, or body should engage these mechanisms under natural conditions, we propose that the mean rate changes that would ensue are functionally relevant to cat vision.

Functional circuitry of the retinal ganglion cell's nonlinear receptive field

A retinal ganglion cell commonly expresses two spatially overlapping receptive field mechanisms. One is the familiar "center/surround," which sums excitation and inhibition across a region somewhat broader than the ganglion cell's dendritic field. This mechanism responds to a drifting grating by modulating firing at the drift frequency (linear response). Less familiar is the "nonlinear" mechanism, which sums the rectified output of many small subunits that extend for millimeters beyond the dendritic field. This mechanism responds to a contrast-reversing grating by modulating firing at twice the reversal frequency (nonlinear response). We investigated this nonlinear mechanism by presenting visual stimuli to the intact guinea pig retina in vitro while recording intracellularly from large brisk and sluggish ganglion cells. A contrast-reversing grating modulated the membrane potential (in addition to the firing rate) at twice the reversal frequency. This response was initially hyperpolarizing for some cells (either ON or OFF center) and initially depolarizing for others. Experiments in which responses to bars were summed in-phase or out-of-phase suggested that the single class of bipolar cells (either ON or OFF) that drives the center/surround response also drives the nonlinear response. Consistent with this, nonlinear responses persisted in OFF ganglion cells when ON bipolar cell responses were blocked by L-AP-4. Nonlinear responses evoked from millimeters beyond the ganglion cell were eliminated by tetrodotoxin. Thus, to relay the response from distant regions of the receptive field requires a spiking interneuron. Nonlinear responses from different regions of the receptive field added linearly.

Neurofibrillar long-range amacrine cells in mammalian retinae

A distinct population of wide-field, unistratified amacrine cells are shown to be selectively stained by using neurofibrillar methods in rabbit and cat retinae. Their cell bodies may be located in the inner nuclear, inner plexiform or ganglion cell layers and they branch predominantly in stratum 2 of the inner plexiform layer. Characteristically, each cell has two or more long-range distal processes which extend for 2-3 mm beyond a more symmetrical, proximal dendritic field of 0.6-0.8 mm diameter. Although the neurofibrillar long-range amacrines account for less than 1 amacrine in 500, they achieve effective coverage of the retina by both the proximal and distal dendrites.

Somatostatin-like immunoreactive material in associational ganglion cells of human retina

The retinal ganglion cell is classically viewed as the output cell of the retina, sending a single axon via the optic nerve to synapse in visual relay nuclei of the brain. However, some ganglion cells, termed associational ganglion cells, have axons which do not leave the retina and presumably serve intraretinal communication. Using high-affinity and specific monoclonal antibodies to somatostatin-14 and the avidin-biotin-peroxidase immunohistochemical procedure, somatostatin-immunoreactive associational ganglion cells are specifically stained in human retinas obtained at necropsy. These cells are more numerous in the inferior than the superior retina; they have dendrites which ramify in the inner plexiform layer; and they have sparsely branching axons, many of which can be traced over 1 cm. These axons do not enter the optic nerve. They follow remarkably straight courses at the border of the inner plexiform layer and ganglion cell layer and thereby form a gridwork of fibers covering the entire retinal area. These observations verify the existence of associational ganglion cells in the human and establish somatostatin as a neurotransmitter or neuromodulator candidate for these neurons. The morphology of these cells suggests that they are involved in long-distance interactions within the retina.

The periphery effect in cat retinal ganglion cells: variation with functional class and eccentricity

We have studied the responses of ganglion cells of the cat retina to visual stimulation remote from the center of their receptive field. Following previous work, this response is termed the periphery effect (PE). Cells were identified as Y-, X- or W-class from the latency of their response to optic chiasm stimulation and from their receptive field properties. The strength of the PE elicited by a rotating windmill or counterphased grating stimulus was measured for ganglion cells of all major classes. The PE was consistently stronger in Y- than in X-cells, and the strength of the effect in both X- and Y-cells increased significantly with retinal eccentricity. A PE was elicited from about 47% of W-cells studied. In some (36%) the effect was excitatory, as for X- and Y-cells; in others (11%) it was inhibitory. Despite this heterogeneity, the PE in W-cells increased significantly with eccentricity. These variations of the PE with eccentricity and cell class have implications for the circuitry of the inner plexiform layer.

Wide-spreading terminal axons in the inner plexiform layer of the cat's retina: evidence for intrinsic axon collaterals of ganglion cells

Extracellular, iontophoretic injections of horseradish peroxidase (HRP) were made directly into the cat's retina. The retinas were processed with the cobalt-enhanced diaminobenzidine method and prepared as whole-mounts. These retinas reveal HRP-filled axons that extend widely and terminate within the inner plexiform layer. The axons are morphologically distinct from ganglion and amacrine cell dendritic trees that were retrogradely labelled from the same injection sites. The axons are long and straight, approximately 1 micron in diameter, and in some cases can be traced for several millimeters in the inner plexiform layer. Each axon gives rise to many short, terminal branches that extend, on average, 100 microns from the parent axon and bear clusters of boutons. The terminal branches are widely spaced so that the bouton clusters are distributed in small, isolated patches along the length of the axon. Bouton clusters vary in size and contain from two to over 100 loosely arranged boutons. Single boutons are frequently large, up to 3 microns in diameter. In one case a terminal axon was traced to its origin from the parent axon of an HRP-filled ganglion cell. It is suggested, therefore, that these axons are intrinsic to the retina and originate as primary collaterals of ganglion cells.

A comparison of the shift response of X- and Y-cells in the cat's retina

The shift response (McIlwain or peripheral effect) was elicited by either flashing or shifting a grating while the receptive field (RF) was covered by a 30 degree mask in the cat. The responses elicited by shifting the grating was comparable to that elicited by flashing the grating. In 10% of the units, the on- and off-responses elicited by flashing the grating were unequal in amplitude. The larger response corresponded with the light phase which leads to excitation of the surround mechanism of the RF. The maximum firing rates of the shift response did not differ in the different types of units, but the amplitude of the shift response (maximum - maintained firing rates) was significantly larger in Y-cells. For all types of cells, the amplitude of the shift response increased with greater eccentricity of the RF. A strong inhibitory period was found in on-center Y-cells but not in the other types of cells. The latency of the shift response was significantly shorter in Y-cells. The differences in the responses of X- and Y-cells suggest that the lateral pathways used are different for the X- and Y-cells.