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Results for “Retinal Bipolar Cells”

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PubMed1994

Glutamate in some retinal neurons is derived solely from glia.

Glutamate is the most abundant excitatory neurotransmitter in the vertebrate central nervous system. It is widely assumed that neurons using this transmitter derive it from several sources: (i) synthesizing it themselves from alpha-ketoglutarate or aspartate, (ii) synthesize it from glial-derived glutamine, or (iii) take up glutamate from the extracellular space. By use of immunocytochemistry we show that glutamate is abundant in the retinal ganglion and bipolar cells of the rabbit, but that immunoreactivity for glutamate in these neurons is reduced below immunocytochemical detection limits after the specific inhibition of glutamine synthesis in glial cells by D,L-methionine D,L-sulphoximine. GABA immunoreactivity in retinal amacrine cells was also reduced after inhibition of glutamine synthetase but the patterns and densities of immunoreactivity for taurine and glycine were unaffected. Therefore, this experimental paradigm does not induce generalized metabolic changes in neurons or glia. This study demonstrates that some glutamatergic neurons are dependent on the synthetic processes in glia for their neurotransmitter content.

Animals↗

PubMed2002

High-resolution imaging of living retina through optic adaptive retinal imaging system.

PURPOSE: To evaluate the possibility as well as the usage of adaptive optics in high-resolution retinal imaging. METHODS: From March to November 2001, the fundus of 25 adults were checked by using Optic Adaptive Retinal Imaging System (OAS). The age of the subjects varied from 18 - 48 years. All had normal visual acuity from 0.9 to 1.0. No abnormality was found in the ocular examination, and their medical as well as ocular history was unremarkable. RESULTS: High-resolution images of the retinal cells, photoreceptor and bipolar cell, were analysed. In these images, the cells are clearly resolved. The density of the photoreceptor at area 1.5 degree from the foveloa is around 40 000 - 50 000/mm2. At area 3 degree, it drops to less than 30 000/mm2. CONCLUSION: Optic Adaptive Retinal Imaging System (AOS) is able to get high-resolution image of retinal cells in living human eyes. It may be widely used in ophthalmology experimentally and clinically.

Adolescent↗

PubMed2007

Retinal organization in the retinal degeneration 10 (rd10) mutant mouse: a morphological and ERG study.

Retinal degeneration 10 (rd10) mice are a model of autosomal recessive retinitis pigmentosa (RP), identified by Chang et al. in 2002 (Vision Res. 42:517-525). These mice carry a spontaneous mutation of the rod-phosphodiesterase (PDE) gene, leading to a rod degeneration that starts around P18. Later, cones are also lost. Because photoreceptor degeneration does not overlap with retinal development, and light responses can be recorded for about a month after birth, rd10 mice mimic typical human RP more closely than the well-known rd1 mutants. The aim of this study is to provide a comprehensive analysis of the morphology and function of the rd10 mouse retina during the period of maximum photoreceptor degeneration, thus contributing useful data for exploiting this novel model to study RP. We analyzed the morphology and survival of retinal cells in rd10 mice of various ages with quantitative immunocytochemistry and confocal microscopy; we also studied retinal function with the electroretinogram (ERG), recorded between P18 and P30. We found that photoreceptor death (peaking around P25) is accompanied and followed by dendritic retraction in bipolar and horizontal cells, which eventually undergo secondary degeneration. ERG reveals alterations in the physiology of the inner retina as early as P18 (before any obvious morphological change of inner neurons) and yet consistently with a reduced band amplification by bipolar cells. Thus, changes in the rd10 retina are very similar to what was previously found in rd1 mutants. However, an overall slower decay of retinal structure and function predicts that rd10 mice might become excellent models for rescue approaches.

Animals↗

PubMed1994

A novel GABA receptor on bipolar cell terminals in the tiger salamander retina.

We studied the pharmacology of the GABA receptors on bipolar cell terminals in the retinal slice preparation. Whole-cell patch-clamp recordings were made from the somas of bipolar cells and GABA was puffed near their terminals, after synaptic transmission was blocked. GABA puffs evoked a large chloride current that was reduced by picrotoxin, but in many cells this current was insensitive to blockade by the competitive GABAA receptor antagonists bicuculline and SR95531. Pentobarbital, an enhancer of GABAA receptor-mediated responses, did not significantly increase the magnitude of the current responses to GABA puffed at the bipolar cell terminals. To confirm the effectiveness of GABAA antagonists and pentobarbital in the slice preparation, we measured GABA currents in ganglion cells. In contrast to bipolar cells, the ganglion cell GABA responses were strongly reduced by both bicuculline and SR95531. In addition, pentobarbital strongly enhanced the action of GABA at the ganglion cells. The isomeric GABA agonists cis- and transaminocrotonic acid (CACA and TACA), elicited picrotoxin-sensitive currents in both bipolar and ganglion cells. TACA was more effective than CACA at both cell types. In bipolar cells, TACA and CACA currents were relatively resistant to bicuculline blockade, but in ganglion cells both currents were reduced by bicuculline. GABA receptors on bipolar terminals appear to be pharmacologically different from the GABA receptors found on ganglion cell dendrites. The bipolar cell terminal GABA receptor pharmacology is similar to the pharmacology reported for the rho 1 GABA receptor subunit that was isolated from retina and expressed in Xenopus oocytes (Cutting et al., 1991; Polenzani et al., 1991; Shimada et al., 1992). This receptor, which is both bicuculline and pentobarbital insensitive, has been called the GABAC receptor (Johnston, 1986; Shimada et al., 1992). However, some bipolar cells were somewhat sensitive to blockade by bicuculline, suggesting that these cells had both GABAA and GABAC receptors on their bipolar terminals.

Animals↗

PubMed2026

Long-term functional synaptic integration of genome-edited retinal organoids in a primate model of macular degeneration.

Retinal organoids represent a promising regenerative strategy for restoring vision in retinal degenerative diseases, but the capacity of host cone bipolar cells in the primate macula to rewire with transplanted photoreceptors has not been established. In this study, we transplanted genome-edited ISL1-/- human retinal organoids lacking ON-bipolar cells into an acute laser-induced macular photoreceptor ablation non-human primate model. Using immunohistochemistry, ultrastructural imaging, and focal macular electroretinography, we demonstrate that host rod and cone bipolar cells actively extend dendrites toward grafted photoreceptors and form synaptic contacts, with evidence of functional signal transmission in a subset of transplanted eyes. Longitudinal, per-eye analyses revealed that host ON-bipolar responses improved in two of four eyes with ISL1-/- graft by up to 21.6% and remained stable for up to 2 years post transplantation. Moreover, OFF-pathway connectivity showed potential progressive maturation, with delayed increase in d-wave after 13 months in one of those eyes. These findings provide the first demonstration of long-term anatomical host-graft synaptic integration in the primate macula, establishing that central cone bipolar circuits retain the capacity for durable rewiring with human stem-cell-derived grafts. Our results highlight ISL1-/- retinal organoids as a promising approach for central vision restoration in macular degeneration.

Animals↗

PubMed2000

Expression of GABA(C) receptor rho1 and rho2 subunits during development of the mouse retina.

Retinal gamma-aminobutyric acid type C (GABA(C)) receptors consist of rho subunits. Here we report our results from a competitive PCR and patch-clamp electrophysiology study quantifying rho subunit message and characterizing GABA(C) receptor-mediated currents at different stages of mouse retinal development. Mouse rho1 message is first detected at postnatal day 6 (P6), increases significantly until P9 and remains at this level through adulthood, whereas mouse rho2 message does not appear until P9, peaks at P15 and remains at this level through adulthood. There is an approximate twofold excess of rho1 compared to rho2 message at most stages of development, which persists in adulthood. Functional GABA(C) receptors are detected in acutely dissociated bipolar cells of P9 or older mouse retina. Early in development (P9-10), GABA(C) receptors are composed solely of rho1 subunits, but subsequently contain rho1 and/or rho2 subunits (by P11 and later). These findings are intriguing because the onset and rapid increase in rho subunit transcription and functional expression match the initiation and active period of bipolar cell differentiation in retinal development as well as the stage of eye opening and initial visual experience in the rodent. The investigation of mouse rho subunits here forms a basis for future studies on the role of GABA(C) receptors in retinal development.

Age Factors↗

PubMed1997

Localization of dystrophin and beta-dystroglycan in bovine retinal photoreceptor processes extending into the postsynaptic dendritic complex.

Dystrophin is an actin-binding protein of the membrane cytoskeleton that binds to dystroglycan, an integral membrane protein of the plasma membrane that is posttranslationally cleaved into a transmembrane dystrophin-binding beta-moiety and an extracellular laminin- and agrin-binding alpha-moiety. Mutations of dystrophin may not only cause Duchenne muscular dystrophy but may also be associated with abnormal electroretinograms assumed to result from disturbed neurotransmission between retinal photoreceptors and bipolar cells. Here we show by confocal laser microscopy and immunogold electron microscopy that dystrophin and beta-dystroglycan are colocalized in bovine rod photoreceptor synaptic complexes distal from the ribbon-containing active synaptic zones. Both proteins are restricted to a microdomain of the photoreceptor plasma membrane that forms the lateral wall of the synaptic cavity and projects with finger-like extensions into the postsynaptic dendritic complex. Within the cavity these processes eventually come into close contact with bipolar cell dendritic endings. We speculate that the dystrophin-dystroglycan complex of the cavital plasma membrane stabilizes the elaborate synaptic morphology or plays a role in the immobilization of still unknown transporters and receptors involved in certain aspects of neurotransmission to bipolar cells. A further outcome of this study is that dystrophin and dystroglycan are located along the vitread membrane surface of Müller cell endfeet where this protein complex may be important for the attachment of the retina to the basal lamina and the vitreous.

Animals↗

PubMed2006

In vivo electrical stimulation of rabbit retina: effect of stimulus duration and electrical field orientation.

Information that defines the depth of activation of retinal neurons is useful in considering strategies for stimulation with a retinal prosthesis, or interpreting the results from human studies that have previously been performed. The purpose of this study was to test the assertion that electrical pulse durations >0.5 msec preferentially stimulate retinal neurons deep to the ganglion cell layer. Thirteen Dutch-belted rabbits (1.2-2.0 kg) were used in this study. A Goldmann-like dome was used to deliver photic stimuli to the retina to measure the electroretinogram (ERG) and the light-induced cortical potential (VECP). Then, a micromanipulator was used to position a 500 microm inner diameter bipolar electrode near the visual streak on the epi-retinal surface. Symmetric biphasic pulses (7-1600 microA; 0.25 msec and 2.0 msec pulses per phase; biphasic pulses delivered at 2 Hz) were delivered to the retina with a current source. Extra-dural electrodes were used to record electrical evoked cortical potentials (EECPs) over the occipital cortex by performing 50 consecutive computer-averaged stimulations. The effect on the EECP of sequential epi-retinal (i.e. return electrode on epi-retinal surface) vs. trans-retinal (i.e. return electrode behind sclera) stimulation was compared. The effect upon the ERG, VECP and EECP was then assessed after 2,3,dihydroxy-6-nitro-7-sulfamoyl-benzo-f-quinoxaline (NBQX) at 112 microM concentration, d-2-amino-7-phosphonoheptanoic acid (D-AP7) at 1200 microM concentration, and l-amino-4-phosphonobutyrate (APB) at 300 microM concentration were delivered into the vitreous cavity to selectively block neuronal input to the retinal ganglion cells. Median values were reported. The amplitudes of the light-induced ERG and VECP were markedly reduced by instillation of the intra-vitreal synaptic blocking drugs. By comparison, pharmacological blockade of input to the retinal ganglion cells did not significantly alter the threshold charge or amplitude of the electrically-induced cortical responses (P>0.05). For the electrical stimuli, there was no significant difference in threshold charge for the EECP for epi-retinal vs. trans-retinal stimulation (P>0.05). The amplitude of the EECP increased linearly with increasing charge using both 0.25 msec and 2.0 msec pulses, even after synaptic blockade of input to the ganglion cells. The lack of obvious degradation of cortical amplitudes after drug instillation indicates that neurons of the middle retina are not being preferentially driven with epi-retinal stimulation, at least not with stimulus pulses up to 2.0 msec in duration. This conclusion is in contrast to prior evidence that 2.0 msec pulses would preferentially stimulate deeper retinal neurons, specifically the bipolar cells. Based upon our own observations in other studies, we believe that preferential stimulation of the middle retina in fact can be achieved by epi-retinal stimulation, by using pulse durations at least 5 times longer than those used in this study.

2-Amino-5-phosphonovalerate↗

PubMed1993

Membrane currents evoked by excitatory amino acid agonists in ON bipolar cells of the mudpuppy retina.

1. Whole-cell patch-clamp recordings were obtained from ON bipolar cells in a retinal slice preparation of the mudpuppy, Necturus maculosus. The effects of excitatory amino acid (EAA) agonists applied in the presence of cobalt (2-5 mM) were examined. 2. At the holding potential of -50 mV, L-2-amino-4-phosphonobutanoic acid (L-AP4, 5-10 microM) evoked an outward current accompanied by a conductance decrease. The zero current potential of the L-AP4-evoked current was near 0 mV independent of whether the intracellular Ringer solution contained CsCl or CsCH3SO4. The currents evoked by light were also accompanied by a conductance decrease and reversed near 0 mV. Replacing external sodium with choline or N-methyl-D-glucamine generated an outward current and suppressed the response to L-AP4. The response to L-AP4 was enhanced by removing extracellular calcium and suppressed by increasing extracellular calcium. These results indicate that L-AP4 closes nonspecific cation channels that are blocked by extracellular calcium. 3. In 2 mM cobalt, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA, 50-100 microM) evoked membrane currents that were accompanied by a conductance increase. AMPA-evoked currents exhibited a significant chloride dependence and were suppressed by gamma-aminobutyric acid-A (GABAA) antagonists bicuculline and picrotoxin; a GABA uptake blocker, nipecotic acid; and a glycine antagonist, strychnine. AMPA-induced currents were virtually absent in the presence of 5 mM cobalt and nominally 0 mM extracellular calcium. These results indicate that the conductance increase induced by AMPA in the presence of 2 mM cobalt is largely the result of calcium-dependent synaptic inputs onto GABAA and glycine receptors of ON bipolar cells. 4. N-methyl-D-aspartic acid (250 microM) was ineffective when applied in the presence of 100 microM cadmium or 2 mM cobalt. 5. 1S,3R/1R,3S-1-aminocyclopentane-1,3-dicarboxylic acid (100-200 microM) evoked an outward current accompanied by a conductance decrease and appears to be an agonist at the L-AP4 receptor. 6. The findings of this study suggest that the only type of EAA receptor in mudpuppy ON bipolar cells is the L-AP4 receptor and that L-AP4 receptor activation results in the closing of nonspecific cation channels that are blocked by extracellular calcium.

Amino Acids↗

PubMed2004

Inwardly rectifying potassium channels in rat retinal ganglion cells.

Inwardly rectifying potassium channels (Kir channels) are important for neuronal signalling and membrane excitability. In the present work we characterized, for the first time, Kir channels in rat retinal ganglion cells (RGCs), the output neurons in the retina, using immunocytochemical and patch-clamp techniques. Various subunits of Kir channels (Kir1.1, 2.1, 2.3, 3.1, 3.2 and 3.3) were expressed in RGCs, but with distinct subcellular localization. Kir1.1 was mainly expressed in axons of RGCs. Kir2.1 and Kir2.3 were both present in somata of RGCs. Whereas staining for Kir3.1 was profoundly present in an endoplasmic reticulum-like structure and Kir3.2 was strongly expressed in the cytoplasm and the cytomembrane of somata, dendrites and axons of RGCs, faint, sparse labelling for Kir3.3 was seen in the cytomembrane. Immunoreactivity for Kir4.1 and Kir4.2 was not detectable in RGCs. Whole-cell currents mediated by Kir channels were recorded in isolated RGCs and they differed from hyperpolarization-activated currents (I(h)) by showing full activation in < 10 ms, no inactivation, and being significantly suppressed by 300 microM Ba2+. Unlike in retinal horizontal cells and bipolar cells, these currents were mainly mediated by G-protein-coupled Kir3 (GIRK) channels, as demonstrated by the fact that GDP(beta)S and GTP(gamma)S included in the pipette solution markedly decreased and increased the currents, respectively. Furthermore, the GIRK channels were probably coupled to GABA(B) receptors, because baclofen considerably increased the Kir currents and the increased currents were suppressed by Ba2+. These characteristics of the Kir currents provide more versatility for signalling of RGCs.

Animals↗

PubMed2004

Distribution of metabotropic P2Y receptors in the rat retina: a single-cell RT-PCR study.

P2Y receptors are metabotropic G-protein linked purinergic receptors, which are especially widespread in the central nervous system. The purpose of the present study was to determine the distribution patterns of P2Y receptors in distinct retinal cell types in the adult retina. Retinal ganglion cells (RGC), bipolar cells (BPC) and Muller cells (MC) of adult pigmented rats were analyzed for their expression of P2Y-receptor subtypes P2Y1, P2Y2, P2Y4, and P2Y6 by single-cell reverse transcription polymerase chain reaction (SC-RT-PCR). SC-RT-PCR resulted in a positive amplification signal for all P2Y-receptor subtype mRNAs in all cell types examined. However, subtype distribution differed among the different cell types. The percentage of cells expressing a distinct P2Y subtype was: (a) for RGCs: 80% with P2Y1, 100% with P2Y2, 30% with P2Y4 and 50% with P2Y6, (b) for BPCs: 60% with P2Y1, 40% with P2Y2, 20% with P2Y4 and 80% with P2Y6, and (c) for MCs: 60% with P2Y1, 80% with P2Y2, 60% with P2Y4 and 100% with P2Y6. Our data show that different subtypes of P2Y receptors (P2Y1, P2Y2, P2Y4 and P2Y6) are expressed in various retinal cells and indicate that extracellular purines and pyrimidines act on RGCs, BPCs and MCs via different P2Y receptors.

Animals↗

PubMed1997

Excitatory amino acid transporter 5, a retinal glutamate transporter coupled to a chloride conductance.

Although a glutamate-gated chloride conductance with the properties of a sodium-dependent glutamate transporter has been described in vertebrate retinal photoreceptors and bipolar cells, the molecular species underlying this conductance has not yet been identified. We now report the cloning and functional characterization of a human excitatory amino acid transporter, EAAT5, expressed primarily in retina. Although EAAT5 shares the structural homologies of the EAAT gene family, one novel feature of the EAAT5 sequence is a carboxy-terminal motif identified previously in N-methyl-D-aspartate receptors and potassium channels and shown to confer interactions with a family of synaptic proteins that promote ion channel clustering. Functional properties of EAAT5 were examined in the Xenopus oocyte expression system by measuring radiolabeled glutamate flux and two-electrode voltage clamp recording. EAAT5-mediated L-glutamate uptake is sodium- and voltage-dependent and chloride-independent. Transporter currents elicited by glutamate are also sodium- and voltage-dependent, but ion substitution experiments suggest that this current is largely carried by chloride ions. These properties of EAAT5 are similar to the glutamate-elicited chloride conductances previously described in retinal neurons, suggesting that the EAAT5-associated chloride conductance may participate in visual processing.

Amino Acid Sequence↗

PubMedDate not supplied

Photoreceptor calcium channels: insight from night blindness.

The genetic locus for incomplete congenital stationary night blindness (CSNB2) has been identified as the CACNA1f gene, encoding the alpha 1F calcium channel subunit, a member of the L-type family of calcium channels. The electroretinogram associated with CSNB2 implicates alpha 1F in synaptic transmission between retinal photoreceptors and bipolar cells. Using a recently developed monoclonal antibody to alpha 1F, we localize the channel to ribbon active zones in rod photoreceptor terminals of the mouse retina, supporting a role for alpha 1F in mediating glutamate release from rods. Detergent extraction experiments indicate that alpha 1F is part of a detergent-resistant active zone complex, which also includes the synaptic ribbons. Comparison of native mouse rod calcium currents with recombinant alpha 1F currents reveals that the current-voltage relationship for the native current is shifted approximately 30 mV to more hyperpolarized potentials than for the recombinant alpha 1F current, suggesting modulation of the native channel by intracellular factors. Lastly, we present evidence for L-type alpha 1D calcium channel subunits in cone terminals of the mouse retina. The presence of alpha 1D channels in cones may explain the residual visual abilities of individuals with CSNB2.

Alcohol Oxidoreductases↗

PubMed1994

An array of early differentiating cones precedes the emergence of the photoreceptor mosaic in the fetal monkey retina.

We previously have demonstrated that approximately 10% of cones in the fetal monkey retina precociously express the red/green opsin. These data suggested the possibility that a subset of cones differentiates prior to their nascent cone neighbors. To further assess this early cone differentiation in the fetal monkey retina, we used monoclonal antibodies proven to be important developmental markers of photoreceptor phenotypes and synaptogenesis (XAP-1, specific to photoreceptor membranes; SV2, specific to synaptic vesicle protein). Although these two antibodies recognize functionally distinct antigens, our analyses revealed that both identify a subset of precociously immunoreactive cones. Further, XAP-1- and SV2-positive cones are distributed in the same pattern as precocious red/green-sensitive cones in immature regions of the fetal monkey retina. These results support the hypothesis that the primate retina possesses a spatially organized protomap that may induce the emergence of the photoreceptor mosaic and trigger the formation of color-specific pathways that include horizontal, bipolar, and retinal ganglion cells.

Animals↗

PubMed1999

Glutamate receptors differ in rod- and cone-dominated off-center bipolar cells.

The axon morphology of off-center bipolar cells in salamander retinal slices was correlated with light responses and dendritic glutamate responses of these cells under voltage clamp. Cells with telodendria ramifying exclusively in the distal one-quarter of the inner plexiform layer were rod dominated, whereas cells with more centrally ramifying telodendria were cone dominated. The glutamate responses of the centrally ramifying cells displayed more apparent desensitization and a smaller underlying single channel conductance (1.2+/-0.3 pS) than did the distally ramifying cells (2.8+/-0.4 pS), although the responses for both classes of cells were strongly enhanced by cyclothiazide. These results suggest that different subtypes of AMPA receptors are present on rod- and cone-dominated cells, and that these may differ with respect to desensitization kinetics.

Ambystoma↗

PubMed1972

Synapses onto different morphological types of retinal ganglion cells.

The percentage of bipolar and amacrine synapses onto ganglion cell dendrites of the ground squirrel has been determined by electron microscopy of cells impregnated by the Golgi method. One group of ganglion cells has mainly amacrine input (approximately 97 percent); the other group has an approximately equal bipolar and amacrine input. Morphologically distinct types of ganglion cells usually have a consistent synaptic input, but exceptions may exist.

Animals↗

PubMed1990

Localization of immunoreactive cholecystokinin precursor to amacrine cells and bipolar cells of the macaque monkey retina.

We used antisera that recognized precursors of the neuropeptide cholecystokinin extended at the carboxyl terminus in an immunocytochemical study of the macaque retina. A subpopulation of bipolar cells with long, obliquely oriented dendrites was labeled. Their axons terminated exclusively in the fifth stratum of the inner plexiform layer, where they contacted processes of amacrine and ganglion cells. Based on their morphology, these cells appeared to be the type that contacts short-wavelength cones selectively. Two types of amacrine cells were also labeled, and processes from both types formed dense plexuses in the second and fourth strata of the inner plexiform layer. The majority of their synaptic connections were with other amacrine cells, but they had more contacts with bipolar cell axons and retinal ganglion cell dendrites than any other peptidergic cells in the macaque retina. We studied extracts of macaque retina with gel-filtration chromatography and radioimmunoassays to confirm our immunohistochemical results. We found cholecystokinin octapeptide and other immunoreactive forms that were amidated at their carboxyl termini and were therefore likely to be biologically active. Unlike most other regions of the CNS, however, the retina had relatively low concentrations of amidated forms, and forms with extended carboxyl termini that are presumably their precursors were far more abundant. These findings suggest that the rate of cholecystokinin synthesis in the retina is quite high, as we would expect if the peptide were found in tonically active neurons.

Amino Acid Sequence↗

PubMed2004

The population of bipolar cells in the rabbit retina.

The population of bipolar cells in the rabbit retina was studied using Golgi impregnation and photocatalyzed filling of single cells with dihydrorhodamine, a quantitative sampling technique. The Golgi method revealed the morphology and stratification of cells in detail. The photofilling method allowed us to estimate the frequency of the cell types. From a sample of 243 Golgi-impregnated bipolar cells and 107 photofilled cells, we identified 1 type of rod bipolar cell and 12 types of cone bipolar cells. An analysis based on retinal coverage indicates that this number of types could be contained within the number of bipolar cells known to exist. The dendrites of most cone bipolars contacted all the cones within the individual cone bipolar cell's dendritic field. Types of bipolar cell were encountered at roughly similar frequency, without any one type predominating. The rabbit retina thus contains about a dozen parallel and roughly equipotent through-pathways.

Animals↗