Abnormalities in rod photoreceptors, amacrine cells, and horizontal cells in human retinas with retinitis pigmentosa

PURPOSE: To evaluate changes in the rods and amacrine cells and horizontal cells in human retinas with retinitis pigmentosa. METHODS: Seven retinas from patient donors with retinitis pigmentosa and 14 age- and postmortem-matched normal human retinas were processed for immunocytochemistry and confocal microscopy. The following cell-specific antibodies were used: anti-rhodopsin (rods), anti-gamma-aminobutyric acid (amacrine cells), anticalbindin (cones and horizontal cells), anti-glial fibrillary acidic protein (astrocytes and reactive Müller cells), and anti-synaptophysin and anti-SV2 (synaptic vesicles). RESULTS: In retinal regions with significant photoreceptor loss, the rods, gamma-aminobutyric acid-positive amacrine cells, and calbindin-positive horizontal cells had undergone neurite sprouting. The rod, amacrine and horizontal cell neurites were associated with the surfaces of glial fibrillary acidic protein-immunoreactive Müller cells. Most rod neurites that projected into the inner retina contacted the somata of gamma-aminobutyric acid-positive amacrine cells. CONCLUSIONS: Rods, amacrine and horizontal cells undergo neurite sprouting in human retinas with retinitis pigmentosa. These changes in the retinal neurons may contribute to the electroretinographic abnormalities and progressive decline in vision noted by patients with retinitis pigmentosa. These alterations may also complicate strategies for treatment of retinitis pigmentosa.     

Expression of brain-derived neurotrophic factor in cholinergic and dopaminergic amacrine cells in the rat retina and the effects of constant light rearing

Brain-derived neurotrophic factor (BDNF) regulates many aspects of neuronal development, including survival, axonal and dendritic growth and synapse formation. Despite recent advances in our understanding of the functional significance of BDNF in retinal development, the retinal cell types expressing BDNF remains poorly defined. The goal of the present study was to determine the localization of BDNF in the mammalian retina, with special focus on the subtypes of amacrine cells, and to characterize, at the cellular level, the effects of constant light exposure during early postnatal period on retinal expression of BDNF. Retinas from 3-week-old rats reared in a normal light cycle or constant light were subjected to double immunofluorescence staining using antibodies to BDNF and retinal cell markers. BDNF immunoreactivity was localized to ganglion cells, cholinergic amacrine cells and dopaminergic amacrine cells, but not to AII amacrine cells regardless of rearing conditions. Approximately 75% of BDNF-positive cells in the inner nuclear layer were cholinergic amacrine cells in animals reared in a normal lighting condition. While BDNF immunoreactivity in ganglion cells and cholinergic amacrine cells was significantly increased by constant light rearing, which in dopaminergic amacrine cells was apparently unaltered. The overall structure of the retina and the density of ganglion cells, cholinergic amacrine cells and AII amacrine cells were unaffected by rearing conditions, whereas the density of dopaminergic amacrine cells was significantly increased by constant light rearing. The present results indicate that cholinergic amacrine cells are the primary source of BDNF in the inner nuclear layer of the rat retina and provide the first evidence that cholinergic amacrine cells may be involved in the visual activity-dependent regulation of retinal development through the production of BDNF. The present data also suggest that the production or survival of dopaminergic amacrine cells is regulated by early visual experience.     

Intrinsic properties and functional circuitry of the AII amacrine cell

Amacrine cells represent the most diverse class of retinal neuron, comprising dozens of distinct cell types. Each type exhibits a unique morphology and generates specific visual computations through its synapses with a subset of excitatory interneurons (bipolar cells), other amacrine cells, and output neurons (ganglion cells). Here, we review the intrinsic and network properties that underlie the function of the most common amacrine cell in the mammalian retina, the AII amacrine cell. The AII connects rod and cone photoreceptor pathways, forming an essential link in the circuit for rod-mediated (scotopic) vision. As such, the AII has become known as the rod-amacrine cell. We, however, now understand that AII function extends to cone-mediated (photopic) vision, and AII function in scotopic and photopic conditions utilizes the same underlying circuit: AIIs are electrically coupled to each other and to the terminals of some types of ON cone bipolar cells. The direction of signal flow, however, varies with illumination. Under photopic conditions, the AII network constitutes a crossover inhibition pathway that allows ON signals to inhibit OFF ganglion cells and contributes to motion sensitivity in certain ganglion cell types. We discuss how the AII's combination of intrinsic and network properties accounts for its unique role in visual processing.     

Physiology of Normal and Abnormal Colour Vision

The physiology of colour vision is reviewed in the light of recent neurophysiological and anatomical studies in vertebrate retinas. The physiological correlate of trichromasy is the existence of three classes of cone cells, each possessing exclusively one of three photopigments with maximum spectral sensitivity at either 440 nm, 540 nm or 570 nm. The electrical responses of single cells of the various types within the retina and lateral geniculate nucleus exhibit both spatial and chromatic coding which is opponent in character. The horizontal and amacrine cells show sophisticated responses which demonstrate their important roles in the processing of information about colour vision. Human abnormal colour vision is reviewed in the light of recent psychophysical studies. Red-green dichromasy is due to the absence of one of the two photopigments normally active in the red-green range of the spectrum. In the red-green anomalous trichromasies one of the photopigments active in that range is replaced by an abnormal photopigment although the spectral loci of the peak sensitivity of these photopigments and the shape of their absorption curves have not yet been accurately identified. The traditional association of mono-chromasy with a rod-only retina has been challenged by the finding of cone cells in histological preparation of eyes of achromats, and the psychophysical evidence that more than one receptor type participates in visual function. One of these receptor types is the normal rod but the other may be a normal blue-sensitive cone or a cone filled with rhodopsin, the rod photopigment.     

The rod circuit in the rabbit retina

Mammalian retinae have a well-defined neuronal pathway that serves rod vision. In rabbit retina, the different populations of interneurons in the rod pathway can be selectively labeled, either separately or in combination. The rod bipolar cells show protein kinase C immunoreactivity; the rod (AII) amacrine cells can be distinguished in nuclear-yellow labeled retina; the rod reciprocal (S1 & S2) amacrine cells accumulate serotonin; and the dopaminergic amacrine cells show tyrosine-hydroxylase immunoreactivity. Furthermore, intracellular dye injection of the microscopically identified interneurons enables whole-population and single-cell studies to be combined in the same tissue. Using this approach, we have been able to analyze systematically the neuronal architecture of the rod circuit across the rabbit retina and compare its organization with that of the rod circuit in central cat retina. In rabbit retina, the rod interneurons are not organized in a uniform neuronal module that is simply scaled up from central to peripheral retina. Moreover, peripheral fields in superior and inferior retina that have equivalent densities of each neuronal type show markedly different rod bipolar to AII amacrine convergence ratios, with the result that many more rod photoreceptors converge on an AII amacrine cell in superior retina. In rabbit retina, much of the convergence in the rod circuit occurs in the outer retina whereas, in central cat retina, it is more evenly distributed between the inner and outer retina.     

Substance P immunoreactivity in normal human retina and in retinoblastoma

Substance P (SP) immunoreactivity was demonstrated using the indirect immunofluorescence technique in one normal and one retinoblastomatous human retina. In the normal retina SP immunoreaction was located in nerve fibres but not in the neurons in the inner plexiform layer. A similar location was observed in the histologically normal areas of the retinoblastoma sample. SP immunoreactive neurons, probably amacrine cells, were, however, observed in the transitional area between the normal retina and the tumour. The tumour mass, although mainly SP negative, contained clusters of pleomorphic cells with an intense SP immunoreaction. The general distribution of SP immunoreaction in human retina resembles that of other mammals. The positive SP immunoreaction in retinoblastoma cells suggests that the tumour either may have its origin in the amacrine cells or that the retinoblasts are capable of redifferentiating in the direction of the amacrine cell population. The general problems concerning the origin and pathogenesis of retinoblastoma are discussed.     

Cellular positioning and dendritic field size of cholinergic amacrine cells are impervious to early ablation of neighboring cells in the mouse retina

We have examined the role of neighbor relationships between cholinergic amacrine cells upon their positioning and dendritic field size by producing partial ablations of this population of cells during early development. We first determined the effectiveness of L-glutamate as an excitotoxin for ablating cholinergic amacrine cells in the developing mouse retina. Subcutaneous injections (4 mg/g) made on P-3 and thereafter were found to produce a near-complete elimination, while injections at P-2 were ineffective. Lower doses on P-3 produced only partial reductions, and were subsequently used to examine the effect of partial ablation upon mosaic organization and dendritic growth of the remaining cells. Four different Voronoi-based measures of mosaic geometry were examined in L-glutamate-treated and normal (saline-treated) retinas. Partial depletions of around 40% produced cholinergic mosaics that, when scaled for density, approximated the mosaic geometry of the normal retina. Separate comparisons simulating a 40% random deletion of the normal retina produced mosaics that were no different from those experimentally depleted retinas. Consequently, no evidence was found for positional regulation in the absence of normal neighbor relationships. Single cells in the ganglion cell layer were intracellularly filled with Lucifer Yellow to examine the morphology and dendritic field extent following partial ablation of the cholinergic amacrine cells. No discernable effect was found on their starburst morphology, and total dendritic field area, number of primary dendrites, and branch frequency were not significantly different. Cholinergic amacrine cells normally increase their dendritic field area after P-3 in excess of retinal expansion; despite this, the present results show that this growth is not controlled by the density of neighboring processes.     

Primary Cilia in Amacrine Cells in Retinal Development

PurposePrimary cilia are conserved organelles found in polarized cells within the eye that regulate cell growth, migration, and differentiation. Although the role of cilia in photoreceptors is well-studied, the formation of cilia in other retinal cell types has received little attention. In this study, we examined the ciliary profile focused on the inner nuclear layer of retinas in mice and rhesus macaque primates.MethodsRetinal sections or flatmounts from Arl13b-Cetn2 tg transgenic mice were immunostained for cell markers (Pax6, Sox9, Chx10, Calbindin, Calretinin, ChaT, GAD67, Prox1, TH, and vGluT3) and analyzed by confocal microscopy. Primate retinal sections were immunostained for ciliary and cell markers (Pax6 and Arl13b). Optical coherence tomography (OCT) and ERGs were used to assess visual function of Vift88 mice.ResultsDuring different stages of mouse postnatal eye development, we found that cilia are present in Pax6-positive amacrine cells, which were also observed in primate retinas. The cilia of subtypes of amacrine cells in mice were shown by immunostaining and electron microscopy. We also removed primary cilia from vGluT3 amacrine cells in mouse and found no significant vision defects. In addition, cilia were present in the outer limiting membrane, suggesting that a population of Müller glial cells forms cilia.ConclusionsWe report that several subpopulations of amacrine cells in inner nuclear layers of the retina form cilia during early retinal development in mice and primates.     

Morphology of quisqualate-induced neurotoxicity in the chicken retina

In this study, the acute neurotoxic effects of quisqualic acid on the chick retina were examined 2 hr or 2 days following intravitreal injections of either 100 or 200 nmol quisqualic acid (QUIS). Both doses resulted in marked nuclear pyknosis and cytoplasmic swelling of a large population of cells located in the inner aspect of the inner nuclear layer, consistent with amacrine cells. The associated swelling of the inner plexiform layer was primarily due to swollen processes of amacrine cells. Also affected was a row of cells located in the outer margin of the inner nuclear layer, consistent with horizontal cells. Ganglion cells developed hyperchromic, vacuolated cytoplasm. Bipolar cells appeared to be spared from damage at these doses. Electron microscopy of photoreceptor synapses revealed that QUIS was associated with a decrease in the relative frequency of long synaptic ribbons and an increase in the frequency of short ribbons, granular ribbons, "synaptic stalks," and paranuclear granules. After 2 days survival, most ganglion cells and some amacrine cells appeared normal, while degeneration was observed in a small number of photoreceptors. Remaining photoreceptor terminals appeared normal. QUIS may provide a useful tool in understanding the dynamics of normal photoreceptor ribbon turnover. The results are also discussed in relation to other known classes of excitatory amino acids.     

Colchicine causes excessive ocular growth and myopia in chicks.

Colchicine has been reported to destroy ganglion cells (GCs) in the retina of hatchling chicks. We tested whether colchicine influences normal ocular growth and form-deprivation myopia, and whether it affects cells other than GCs. Colchicine greatly increased axial length, equatorial diameter, eye weight, and myopic refractive error, while reducing corneal curvature. Colchicine caused DNA fragmentation in many GCs and some amacrine cells and photoreceptors, ultimately leading to the destruction of most GCs and particular sub-sets of amacrine cells. Colchicine-induced ocular growth may result from the destruction of amacrine cells that normally suppress ocular growth, and corneal flattening may result from the destruction of GCs whose central pathway normally plays a role in shaping the cornea.     

Localization of classical neurotransmitters in interneurons of the larval tiger salamander retina

Autoradiography was used to visualize the neurons in the tiger salamander retina that exhibit high-affinity uptake of 3H-dopamine, [3H]-serotonin, [3H]-glycine, and [3H]-GABA. Both [3H]-dopamine and [3H]-serotonin were accumulated by amacrine cells and by displaced amacrine cells. [3H]-glycine was taken up by amacrine cells, displaced amacrine cells, bipolar cells, and displaced bipolar cells. [3H]-GABA was accumulated by amacrine cells and by cells in the ganglion cell layer that may be displaced amacrine or ganglion cells. [3H]-GABA was also taken up by horizontal cells, bipolar cells, and displaced bipolar cells.     

Organization of the inner retina following early elimination of the retinal ganglion cell population: effects on cell numbers and stratification patterns.

The present study has examined the effects of early ganglion cell elimination upon the organization of the inner retina in the ferret. The population of retinal ganglion cells was removed by optic nerve transection on the second postnatal day, and retinas were subsequently studied in adulthood. Numbers of amacrine and bipolar cells were compared in the nerve-transected and nerve-intact retinas of operated ferrets, while stratification patterns within the inner plexiform layer were compared in these and in normal ferret retinas. Early ganglion cell elimination was found to produce a 25% reduction in the population of glycine transporter-immunoreactive amacrine cells, and 18 and 15% reductions in the populations of parvalbumin and calbindin-immunoreactive amacrine cells, respectively. GABAergic amacrine cells were also reduced by 34%. The number of calbindin-immunoreactive displaced amacrine cells, by contrast, had increased in the ganglion cell-depleted retina, being three times their normal number. Other amacrine and bipolar cell types were unaffected. Despite these changes, the stratification patterns associated with these cell types remained largely intact within the inner plexiform layer. The present results demonstrate a class-specific dependency of inner retinal neurons upon the ganglion cell population in early postnatal life, but the ganglion cells do not appear to provide any critical signals for stratification within the inner plexiform layer, at least not after birth. Since they themselves do not produce stratified dendritic arbors until well after birth, the signals for stratification of the bipolar and amacrine cell processes should arise from other sources.     

Synaptic organization of GABAergic amacrine cells in the salamander retina

The synaptic organization of GABA-immunoreactive (GABA-IR) amacrine cells in the inner plexiform layer (IPL) of salamander retina was studied with the use of postembedding immuno-electron microscopy. A total of 457 GABA-IR amacrine synapses, with identified postsynaptic elements, were analyzed on photomontages of electron micrographs covering 3,618 microm2 of the IPL. GABA-IR amacrine synapses were distributed throughout the IPL, with a small peak at the proximal margin of sublamina a. The majority of the output targets (81%) were GABA(-) neurons. Most of the contacts were simple synapses with one postsynaptic element identified as a process of an amacrine cell (55%), bipolar cell (19%) or ganglion cell (26%), and serial synapses were very rare. Of the 89 postsynaptic bipolar terminals, 63% participated in a reciprocal feedback synapse with the same presynaptic GABA-IR amacrine profile. There appeared to be no preference between GABA-IR amacrine contacts with rod- or cone-dominated bipolar cells (9.1% vs. 8.9%) or in the total number of amacrine synapses in sublaminas a and b (52% vs. 47%). The preponderance of amacrine cell input to bipolar cells in the OFF layer was derived from GABA-IR cells. These findings provide ultrastructural support to the existing physiological studies regarding the functional roles of the GABAergic amacrine cells in this species. Our results have added to the data base demonstrating that, in contrast to mammals, GABA-IR amacrine cells in amphibians and other nonmammals contact other amacrine cells more frequently, suggesting greater involvement of GABAergic amacrine cells in modulating lateral inhibitory pathways.     

Coupling pattern of S1 and S2 amacrine cells in the rabbit retina

Previous studies have shown that indoleamine-accumulating cells (IACs) in the rabbit retina consist of two main cell types: S1 and S2 amacrine cells (Vaney, 1986; Sandell & Masland, 1986). Both cell types are wide-field GABA amacrine cells that make reciprocal synaptic contacts with rod bipolar cell terminals (Ehinger & Holmgren, 1979; Strettoi et al., 1990). We have examined the coupling pattern of S1 and S2 amacrine cells after the intracellular injection of Neurobiotin. Our results may be summarized as follows: (1) S1 amacrine cells were extensively coupled and their dendrites formed a network similar to but less dense than the matrix stained with an antibody to serotonin. (2) Morphological observations and cluster analysis, based on a scattergram, showed that the vast majority of coupled cells were S1 amacrine cells, accounting for approximately half of the total IACs. The rest of the uncoupled IACs were S2 amacrine cells. (3) Sometimes, two adjacent varicosities, one from an injected S1 and one from a coupled S1, contacted a single rod bipolar terminal. (4) S2 amacrine cells were also coupled but much less than the S1s. (5) Rarely, crossover coupling between S1 and S2 amacrine cells was observed. These results suggest that the extensive coupling between S1 amacrine cells, combined with a larger dendritic field, may contribute a wide-field component to the inhibitory surround of the rod pathway. By comparison, the smaller, weakly coupled S2 amacrine cells may provide a local component.     

Synaptic organization of two types of amacrine cells with CRF-like immunoreactivity in the turtle retina

The ultrastructural features and synaptic contacts of two amacrine cell types with corticotropin-releasing factor-like immunoreactivity in the turtle retina were examined using electron immunocytochemistry. Type A cells were found only in the visual streak and had elongated dendritic arborizations that ran parallel to the visual streak. These cells arborized primarily in stratum 1 and near the border of strata 2 and 3 of the inner plexiform layer, with some processes extending into stratum 5. Type B cells were found only ventral to the visual streak and arborized primarily in a wide band in strata 4 and 5, with sparse dendritic arborizations in stratum 1. There was a diffuse cytoplasmic reaction product within each cell type; however, large labeled vesicles were rarely observed. Type A amacrine cells received many conventional synaptic contacts from amacrine cells in stratum 1 and at the border of strata 2 and 3, but only a small number of contacts in stratum 5. Bipolar synaptic contacts onto type A amacrine cells were observed in strata 1 and at the border of strata 2 and 3. The only positively identified synaptic outputs of type A cells were conventional synapses onto amacrine cells in strata 1 and at the border of 2 and 3. Type B amacrine cells received synaptic contacts from amacrine cells in strata 1 and 5, and bipolar cell synaptic input in stratum 5. They made conventional synapses onto amacrine cells in strata 1 and 5, and onto bipolar cells in stratum 5. We also found conventional synaptic contacts between unlabeled amacrine cells and type B amacrine cells outside of the primary layers of stratification. In addition, there were specialized junctions observed between type A cell profiles in stratum 1 and between type B cell profiles in stratum 5. The unique regional distributions of the type A and B cells, as well as their differences in synaptic connectivity, suggested that these amacrine cells play distinct physiological roles although they contain the same neuropeptide.     

AMPA receptor kinetics limit retinal amacrine cell excitatory synaptic responses

Amacrine cells that respond transiently to maintained illumination are thought to mediate transient inhibitory input to ganglion cells. The excitation of these transient amacrine cells is thought to be limited by inhibitory feedback to bipolar cells. We investigated the possibility that desensitizing AMPA and/or kainate (KA) receptors on amacrine cells might also limit the duration of amacrine cell excitation. To determine how these receptors might affect amacrine cell input and output, we made whole-cell recordings from amacrine and ganglion cells in the salamander retinal slice. The specific AMPA receptor antagonist GYKI-53655 blocked non-NMDA receptor-mediated amacrine cell excitatory postsynaptic currents (EPSCs) and kainate puff-elicited currents, indicating that AMPA, and not KA, receptors mediated the responses. Cyclothiazide, an agent that reduces AMPA receptor desensitization, increased the amplitude and duration of amacrine cell EPSCs. To measure the output of transient amacrine cells, we recorded glycinergic inhibitory postsynaptic currents (IPSCs) from ganglion cells, and found that these were also enhanced by cyclothiazide. Thus, prolongation of amacrine cell AMPA receptor activation enhanced amacrine cell output. Current responses elicited by puffing glycine onto ganglion cell dendrites were not affected by cyclothiazide, indicating that the enhancement of glycinergic IPSCs was not due to a direct effect on glycine receptors. These data suggest that rapid AMPA receptor desensitization and/or deactivation limits glycinergic amacrine cell excitation and the resulting inhibitory synaptic output.     

Loss of cholinergic and dopaminergic amacrine cells in streptozotocin-diabetic rat and Ins2Akita-diabetic mouse retinas

PURPOSE: To identify amacrine cells that are vulnerable to degeneration during the early stages of diabetes. METHODS: Whole retinas from streptozotocin (STZ)-diabetic rats and Ins2(Akita) mice were fixed in paraformaldehyde. Apoptotic cells in the retina were quantified using terminal dUTP nick-end labeling (TUNEL) and active caspase-3 (CM-1) immunohistochemistry. Immunohistochemical markers for choline acetyltransferase (ChAT) and tyrosine hyroxylase (TH) were also used to quantify populations of amacrine cells in the Ins2Akita mouse retinas. RESULTS: The number of TUNEL-positive nuclei increased from 29+/-4 in controls to 72+/-9 in the STZ-diabetic rat retinas after only 2 weeks of diabetes. In rats, CM-1-immunoreactive (IR) cells were found primarily in the inner nuclear and ganglion cell layers after 2, 8, and 16 weeks of diabetes. At each end point, the number of CM-1-IR cells in the retina was elevated by diabetes. Approximately 2% to 6% of the CM-1-IR cells in the inner nuclear layer (INL) were double-labeled for TH immunoreactivity. After 6 months of diabetes in the Ins2Akita mouse, the morphology of the labeled ChAT-IR and TH-IR amacrine cell somas and dendrites appeared normal. A quantitative analysis revealed a 20% decrease in the number of cholinergic and a 16% decrease in dopaminergic amacrine cells in the diabetic mouse retinas, compared with the nondiabetic control. CONCLUSIONS: Dopaminergic and cholinergic amacrine cells are lost during the early stages of retinal neuropathy in diabetes. Loss of these neurons may play a critical role in the development of visual deficits in diabetes.     

Light and electron microscopical analysis of nitric oxide synthase-like immunoreactive neurons in the rat retina.

We have investigated the morphology of the NOS-like immunoreactive neurons and their synaptic connectivity in the rat retina by immunocytochemistry using antisera against nitric oxide synthase (NOS). In the present study, several types of amacrine cells were labeled with anti-NOS antisera. Type 1 cells had large somata located in the inner nuclear layer (INL) with long and sparsely branched processes ramifying mainly in stratum 3 of the inner plexiform layer (IPL). Somata of type 2 cells with smaller diameters were also located in the INL. Their fine processes branched mostly in stratum 3 of the IPL. A third population showing NOS-like immunoreactivity was a class of displaced amacrine cells in the ganglion cell layer (GCL). Their soma size was similar to that of the type 1 cells; however, their processes stratified mainly in strata 4 and 5 of the IPL. Labeled neurons were evenly distributed throughout the retina, and the mean densities were 57.0 +/- 9.7 cells/mm2 for the type 1 cells, 239.3 +/- 43.4 cells/mm2 for the type 2 cells and 121.2 +/- 27.5 cells/mm2 cells for the displaced amacrine cells. The synaptic connectivity of NOS-like immunoreactive amacrine cells was identified in the IPL by electron microscopy. NOS-labeled amacrine cell processes received synaptic input from other amacrine cell processes and bipolar cell axon terminals in all strata of the IPL. The most frequent postsynaptic targets of NOS-immunoreactive amacrine cells were other amacrine cell processes. Ganglion cell dendrites were also postsynaptic to NOS-like immunoreactive neurons in both sublaminae of the IPL. Synaptic outputs onto bipolar cells were observed in sublamina b of the IPL. In addition, a few synaptic contacts between labeled cell processes were observed. Our results suggest that NOS immunoreactive cells may be modulated by other amacrine cells and ON cone bipolar cells, and act preferentially on other amacrine cells.     

Morphological and physiological properties of the A17 amacrine cell of the rat retina

In addition to the well-studied AII amacrine cell, there is another amacrine cell type participating in the rod pathway of the mammalian retina. In cat, this cell is called the A17 amacrine cell, and in rabbits, it is called the indoleamine-accumulating amacrine cell (S1 and S2); however, the presence of the corresponding cell type has not yet been described in detail for the rat retina. To this end, we injected amacrine cells with Neurobiotin in vertical retinal slices. After histological processing, we were able to reconstruct the morphology of a wide-field amacrine cell which showed characteristics of A17 and S1/S2 amacrine cells. The rat wide-field amacrine cells exhibited the same stratification pattern, their dendrites bore varicosities and ramified in sublamina 5 of the inner plexiform layer (IPL), and they were dye-coupled to other amacrine cells. To determine whether those amacrine cells shared electrophysiological characteristics as well, we performed whole-cell patch-clamp recordings and examined their voltage-activated currents and neurotransmitter-induced currents. We never observed voltage-gated Na+ currents and spike-like potentials upon depolarization by current injection in these cells. We identified GABA- and glycine-sensitive Cl- currents that could be blocked by bicuculline and strychnine, respectively. We also observed kainate- and AMPA-activated currents, which could be inhibited by the application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Finally, a 400-ms full-field light stimulus was used to characterize the light responses of A17 amacrine cells. The light ON-induced inward current could be suppressed by the application of 2,3-Dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulphonamide (NBQX), while the majority of the light OFF-induced current was inhibited by bicuculline and reduced to a smaller extent by NBQX. CPP, an NMDA blocker, had no effect on the light response of rat A17 amacrine cells.