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At least 19 recordsLinked to original sources
PubMed1982

The morphology of the bipolar cells, amacrine cells and ganglion cells in the retina of the turtle Pseudemys scripta elegans.

The morphology of the neurons that contribute to the inner plexiform layer of the retina of the turtle Pseudemys scripta elegans has been studied by light microscopy of whole-mount material stained by the method of Golgi. Cells have been distinguished on the basis of criteria that include dendritic branching patterns, dendritic morphology, dendritic tree sizes and stratification of processes in the inner plexiform layer. Many of the neurons have dendritic trees oriented parallel to and a few exhibit an orthogonal orientation with the linear visual streak present in the retina of this species. The neurons of the turtle retina have been compared, where possible, with the neurons of the lizard retina as described by Cajal. The findings are discussed in relation to other vertebrate retinas, and correlations are made with recent electrophysiological recordings of the turtle retina. Comments are made with regard to the significance of orientation of neurons relative to the linear visual streak.

Action Potentials↗
PubMed1980

Amacrine cells, displaced amacrine cells and interplexiform cells in the retina of the rat.

The amacrine cells in the retina of the rat are described in Golgi-stained whole-mounted retinae. Nine morphologically distinct types of cell were found: one type of diffuse cell, five types of unistratified cell, two types of bistratified cell, and one type of stratified diffuse cell. Measurements show that the largest unistratified cells have a dendritic field 2 mm across. One type of interplexiform cell is also described. Wide-field diffuse amacrine cells and unistratified amacrine cells were found with their somata located in either the inner nuclear layer or the ganglion cell layer. It is clear that there may be an amacrine cell system in the ganglion cell layer of the rat retina.

Age Factors↗
PubMed2002

Activation of mGluR5 modulates GABA(A) receptor function in retinal amacrine cells.

Amacrine cells in the vertebrate retina receive glutamatergic input from bipolar cells and make synapses onto bipolar cells, ganglion cells, and other amacrine cells. Recent studies indicate that amacrine cells express metabotropic glutamate receptors (mGluRs) and that signaling within the inner plexiform layer (IPL) of the retina might be modulated by mGluR activity. This study tests the hypothesis that activation of mGluR5 modulates GABA(A) receptor function in retinal amacrine cells. Whole cell voltage-clamp recordings were combined with pharmacology to establish the identity of the ionotropic GABA receptors expressed in primary cultures of chick amacrine cells and to determine how mGluR5 activity affected the behavior of those receptors. Application of GABA (20 microM) produced currents that reversed at -58.2 +/- 0.9 mV, near the predicted Cl(-) reversal potential of -59 mV. The GABA(A) receptor antagonist, bicuculline (50 microM), completely blocked the GABA-gated currents. cis-4-Aminocrotonic acid (CACA; 100 microM), a GABA(C) receptor agonist, produced small currents that were not blocked by the GABA(C) antagonist, (1,2,5,6-tetrahydropyridine-4-yl) methylphosphinic acid (TPMPA; 20 microM), but were completely blocked by bicuculline. These results indicate that cultured amacrine cells express GABA(A) receptors exclusively. Activating mGluR5 with (RS)-2-chloro-5-hydroxyphenylglycine (CHPG; 300 microM) enhanced GABA-gated currents by 10.0 +/- 1.5%. Buffering internal Ca(2+) with BAPTA (10 mM) blocked the CHPG-dependent enhancement. Activation of PKC with the cell-permeable PKC activators (-)-7-octylindolactam V, phorbol 12-myristate 13 acetate (PMA), or 1-oleoyl-2-acetyl-sn-glycerol (OAG) also enhanced GABA-gated currents in a dose-dependent manner. Preactivation of PKC occluded the mGluR5-dependent enhancement, and inhibition of Ca-dependent PKC isotypes with Gö6976 (35 nM) suppressed the effects of mGluR5 activation, suggesting that mGluR5 and PKC are part of the same pathway. To determine if mGluR5-dependent enhancement occurred at synaptic GABA(A) receptors, postsynaptic currents were recorded in the presence of CHPG. On average, the mean amplitudes of the quantal events were increased by about 18% when mGluR5 was activated. These results indicate that activation of mGluR5 enhances GABA-gated current in cultured amacrine cells in a manner that is both Ca(2+)- and PKC-dependent. These results support the possibility that glutamate released from bipolar cells can modulate the function of GABAergic amacrine cells and alter signaling in the inner plexiform layer.

Amacrine Cells↗
PubMed2003

[The effect of SP-8-CPT-cAMP on the tracer coupling between the retinal ganglion cells and amacrine cells].

PURPOSE: To study the effect of SP-8-CPT-cAMP on the tracer coupling between the retinal ganglion cells and amacrine cells in rabbits. METHODS: The retinas of rabbit were cultured and treated with SP-8-CPT-cAMP .4% neurobiotin was injected into retinal single OFF-alpha ganglion cell with micro-injection, following tissue fixation with 4% paraformaldehyde, Cells were visualized with 1:600 streptavidin-Cy3. The intensity of tracer diffusing through the gap junctions among the ganglion cells and amacrine cells was calculated with confocal microscope. RESULTS: In the dendritic field of injected ganglion cells and cross the field some other ganglion cells(G1) and amacrine cells locating in the inner nuclear layer were stained. Two types of amacrine cells: brighter one (A1) and dimmer one (A2) were found. The intensity of neurobiotin in coupled G1,A1,A2 after treated with SP-8-CPT-cAMP is much higher than that of the untreated retinas. CONCLUSION: The gap junctions exist among the OFF-alpha ganglion cells and between OFF-alpha ganglion cells and amacrine cells. SP-8-CPT-cAMP increases the permeability of gap junction in OFF-alpha ganglion cell network.

Amacrine Cells↗
PubMed1985

The coexistence of two neuroactive peptides in a subpopulation of retinal amacrine cells.

Amacrine cells are axonless interneurons of the vertebrate retina. Over the past few years many neuroactive peptides have been localized to these cells. We have previously demonstrated that a neuropeptide and a classical transmitter are colocalized in some amacrine cells. In this report, we show that two neuroactive peptides, which probably arise from different precursors, also coexist in some amacrine cells. Although some amacrine cells contain only enkephalin or neurotensin, others contain both of these neuroactive peptides.

Animals↗
PubMed2003

Differentiation of ganglion cells and amacrine cells in the rat retina: correlation with expression of HuC/D and GAP-43 proteins.

In order to understand the development of retinal cells, we have studied the temporal expression of HuC/D protein in embryonic, postnatal and adult rat retina. During development and in the adult retina, practically all cell somata in the ganglion cell layer and the vast majority of conventional amacrine cells in the inner nuclear layer displayed HuC/D immunoreactivity. Most but not all ganglion cells expressed HuC/D at embryonic day 15, suggesting a delay between final mitosis and the initiation of HuC/D expression. Immunoreactivity for HuC/D was also evident in developing but not mature horizontal cells. Combined immunohistochemical visualization of HuC/D protein and the growth-associated protein (GAP-43) showed a distinct localization of GAP-43 in a specific compartment close to the somato-dendritic region of developing HuC/D-positive cell somata. The localization of GAP-43 immunoreactivity to a specific soma compartment became less evident during maturation. Immunoreactivity for HuC/D and GAP-43 was also discernible in horizontal cells at postnatal day 14. In the adult retina, most GAP-43 immunoreactivity was seen in the inner plexiform layer. Detailed analysis showed that HuC/D and GAP-43 expression is restricted to subsets of retinal neurons during development and in the mature retina. Thus, GAP-43 appears to be correlated with initial steps of differentiation and outgrowth of dendritic processes in HuC/D-positive ganglion and amacrine cells.

Amacrine Cells↗
PubMed1980

The dendritic varicosity: a mechanism for electrically isolating the dendrites of cat retinal amacrine cells?

Amacrine dendritic varicosities from cat retina were reconstructed using serial electron micrographs. Each varicosity contained a synaptic input and a synaptic output, suggesting that they may function as isolated local circuits. A passive steady state electrical model demonstrated that for a given conductance change the varicose dendrite maximizes the local membrane potential and minimizes th distance membrane potential change as compared to other possible dendritic shapes. We, therefore, suggest that the function of the varicosities on amacrine cell dendrites might be to electrically isolate these local input-output circuits.

Animals↗
PubMed1999

Reciprocal synaptic interactions between rod bipolar cells and amacrine cells in the rat retina.

Reciprocal synaptic transmission between rod bipolar cells and presumed A17 amacrine cells was studied by whole cell voltage-clamp recording of rod bipolar cells in a rat retinal slice preparation. Depolarization of a rod bipolar cell evoked two identifiable types of Ca2+ current, a T-type current that activated at about -70 mV and a current with L-type pharmacology that activated at about -50 mV. Depolarization to greater than or equal to -50 mV also evoked an increase in the frequency of postsynaptic currents (PSCs). The PSCs reversed at approximately ECl (the chloride equilibrium potential), followed changes in ECl, and were blocked by gamma-aminobutyric acidA (GABAA) and GABAC receptor antagonists and thus were identified as GABAergic inhibitory PSCs (IPSCs). Bipolar cells with cut axons displayed the T-type current but lacked an L-type current and depolarization-evoked IPSCs. Thus L-type Ca2+ channels are placed strategically at the axon terminals to mediate transmitter release from rod bipolar cells. The IPSCs were blocked by the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, indicating that non-NMDA receptors mediate the feed-forward bipolar-to-amacrine excitation. The NMDA receptor antagonist 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid had no consistent effect on the depolarization-evoked IPSCs, indicating that activation of NMDA receptors is not essential for the feedforward excitation. Tetrodotoxin (a blocker of voltage-gated Na+ channels) reversibly suppressed the reciprocal response in some cells but not in others, indicating that graded potentials are sufficient for transmitter release from A17 amacrine cells, but suggesting that voltage-gated Na+ channels, under some conditions, can contribute to transmitter release.

Animals↗
PubMed1976

Synaptic organization and ionic basis of on and off channels in mudpuppy retina. I. Intracellular analysis of chloride-sensitive electrogenic properties of receptors, horizontal cells, bipolar cells, and amacrine cells.

Intracellular recordings from receptors, horizontal cells, bipolars, and amacrines have been carried out in the perfused mudpuppy eyecup. The introduction of a chloride-free (c-f) medium results in initial transient potential changes in many cells followed by a slow loss of light-evoked activity of the depolarizing bipolar, the horizontal cell, and the on depolarization of amacrine cells. The hyperpolarizing bipolar remains responsive to light stimulation in a c-f medium, but the antagonistic surround mechanism is abolished. These effects are reversible after returning to a normal ionic medium. The results of this study provide insight into the retinal connections which underlie ganglion cell receptive field organization. It is concluded that the depolarizing bipolar is excitatory to on ganglion cells and is also the pathway for on-excitation of on-off cells. The hyperpolarizing bipolar mediates the off discharge of off and on-off cells. Amacrine cells receive input from both depolarizing and hyperpolarizing bipolar cells. These findings raise the possibility that transmembrane movements of chloride ions are critical for the light responsiveness of horizontal and depolarizing bipolar cell activity.

Animals↗
PubMed2005

Retinal G-substrate, potential downstream component of NO/cGMP/PKG pathway, is located in subtype of retinal ganglion cells and amacrine cells with protein phosphatases.

The aim of this study was to determine the distribution and function of G-substrate, a specific substrate of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP)-cGMP-dependent protein kinase (PKG) signaling pathway, in normal rat retina and in G-substrate knockout mice. The retinas of adult wild-type rats and mice and G-substrate knockout mice were studied immunohistologically to characterize the upstream and downstream components of the NO-cGMP-PKG pathway. Immunoblot analysis showed that the molecular weight of retinal G-substrate was similar to that of cerebellar G-substrate. In adult rats and mice, retinal G-substrate was located in a subpopulation of amacrine cells and in C38-positive retinal ganglion cells (RGCs) but not in alpha RGCs. In addition, retinal G-substrate was co-expressed with other upstream and downstream signaling components of the NO-cGMP-PKG-G-substrate-phosphatase pathway in the adult retina. Electroretinographic (ERG) analysis demonstrated that there was no significant difference between the ERGs of wild-type and G-substrate knockout mice. These results suggest that retinal G-substrate plays a role as a downstream component of the NO-cGMP-PKG pathway. The co-localization of retinal G-substrate with protein Ser/Thr phosphatases suggests that it acts as an endogenous protein phosphatase inhibitor as in the cerebellum.

Amacrine Cells↗
PubMed2002

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

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

Ambystomatidae↗
PubMed1997

Brain-derived neurotrophic factor/neurotrophin-4 receptor TrkB is localized on ganglion cells and dopaminergic amacrine cells in the vertebrate retina.

The tyrosine kinase TrkB is a receptor for the neurotrophic factors brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT-4). Retinal ganglion cells are responsive to BDNF, and TrkB has been localized in ganglion cells as well as in a subpopulation of amacrine cells in the retina of the chicken and the rat. In the present paper, we analyzed the distribution of TrkB immunoreactivity in the retina of marmoset monkeys, ferrets, rabbits, rats, mice, chickens, pigeons, barn owls, Pseudemys turtles, Xenopus frogs, goldfishes, and carps. TrkB antibodies gave a positive reaction in all of these vertebrates. TrkB immunoreactivity was detected in the majority of retinal ganglion cells. Some amacrine cells also contained TrkB immunoreactivity; they were located mainly at the vitreal border of the inner nuclear layer, and their relative abundance varied in the different species. Until now, no information has been available concerning the neurochemical identity of the amacrine neurons containing TrkB. In some species (marmoset monkeys, rats, pigeons), we observed that the morphology and location of TrkB-immunoreactive amacrine cells was reminiscent of that of the well-described dopaminergic cells. To determine whether dopaminergic amacrine cells contained TrkB immunoreactivity, we therefore performed double-labelling immunohistochemistry by using tyrosine hydroxylase (TH) antibodies in combination with TrkB antibodies in marmoset monkeys, rats, pigeons, Pseudemys turtles, and goldfishes. The most novel finding of the present paper is that, in all of these species, the majority of dopaminergic neurons were found to contain TrkB immunoreactivity. Dopaminergic neurons, on the other hand, represented only a fraction of the TrkB+ amacrine cells. Our data suggest that BDNF and/or NT-4 might modulate expression of TH in the retina and may therefore influence the retinal dopaminergic system. Whatever the action of TrkB ligands on the retinal dopaminergic system, it was conserved during vertebrate evolution.

Animals↗
PubMed1988

Synapses from bipolar cells onto dopaminergic amacrine cells in cat and rabbit retinas.

Dopaminergic amacrine cells in the vertebrate retina have long been characterized as 'interamacrine' as they were only found to be pre- and postsynaptic to other amacrine cells. Immunohistochemistry with antibodies directed against tyrosine hydroxylase (TH) revealed synapses from bipolar cell axon terminals to TH-containing neuronal processes at ribbon synapses in the rhesus monkey retina. This finding challenged the notion of the dopaminergic amacrine cell phenotype as 'interamacrine'. In order to determine if the finding of synapses from bipolar cells to dopaminergic amacrine cells could be generalized to other species, we studied the synaptic organization of dopaminergic amacrine cells in the retinas of cats and rabbits with electron microscopy of TH immunoreactivity. In both species, TH-immunoreactive processes were found to be postsynaptic to bipolar axon terminals at ribbon synapses demonstrating that the original finding in the primate may be a significant feature in the retinas of many other vertebrates as well.

Animals↗
PubMed1987

Tyrosine hydroxylase immunoreactivity in the rhesus monkey retina reveals synapses from bipolar cells to dopaminergic amacrine cells.

The synaptic organization of dopamine-containing amacrine cells in the rhesus monkey retina was studied using immunohistochemistry of tyrosine hydroxylase (TH), the rate-limiting enzyme in the catecholamine synthetic pathway. Cell bodies of the TH-containing neurons were primarily in the innermost tier of the inner nuclear layer. Their synaptic processes, confined to the outermost stratum of the inner plexiform layer, contained mostly small, clear vesicles and were presynaptic to unlabeled amacrine cell processes and cell bodies at junctions that were symmetrical. Synapses onto the TH-immunoreactive neurons were from bipolar cell axon terminals, nonimmunoreactive amacrine cell processes, and other TH-containing amacrine cells in a decreasing order of predominance. The bipolar cells were presynaptic to the TH-containing neuronal processes at ribbon synapses. The size, structure, and position of the bipolar cell axon terminals, which, like the TH-reactive processes, were narrowly confined to the outermost stratum of the inner plexiform layer, indicate that they are recently described giant bistratified bipolar cells. The identification of this bipolar cell input now provides evidence for a pathway from the outer plexiform layer to dopaminergic amacrine cells in the inner plexiform layer via a type of cone bipolar cell.

Animals↗
PubMed1992

Dendritic co-stratification of ON and ON-OFF directionally selective ganglion cells with starburst amacrine cells in rabbit retina.

The morphology, dendritic branching patterns, and dendritic stratification of retinal ganglion cells have been studied in Golgi-impregnated, whole-mount preparations of rabbit retina. Among a large number of morphological types identified, two have been found that correspond to the morphology of ON and ON-OFF directionally selective (DS) ganglion cells identified in other studies. These cells have been characterized in the preceding paper in terms of their cell body size, dendritic field size, and branching pattern. In this paper, the two kinds of DS ganglion cell are compared in terms of their levels of dendritic stratification. They are compared with each other and also with examples of class III.1 cells, defined in the preceding paper with reference to our previous studies. Studies employing computer-aided, 3D reconstruction of dendritic trees, as well as analysis of a pair of ON DS and ON-OFF DS ganglion cells with overlapping dendritic trees show that the two types of DS ganglion cell partly co-stratify in the middle of sublamina b (stratum 4). The report that some ON DS ganglion cells extend a few dendrites into sublamina a is confirmed. The study of pairs of ON-OFF DS ganglion cells and starburst amacrine cells with overlapping dendritic trees reveals a precise co-stratification of these two cell types, and many points of close apposition of starburst boutons with ON-OFF DS ganglion cell dendrites in both sublaminae of the inner plexiform layer (IPL). This is confirmed by high-resolution light microscopy and by electron microscopy. It is possible to conclude, therefore, that ON DS are also partly co-stratified with type b starburst (cholinergic) amacrine cells, and are apparently also partly co-stratified with type a starburst amacrine cells, when occasional dendrites rise to that level. The co-stratification of the two kinds of DS ganglion cell is consistent with the sharing of some inputs in common, including some cone bipolar cell inputs. The co-stratification of both with starburst amacrine cells agrees with the physiological demonstration of the powerful pharmacological effects upon ON and ON-OFF DS ganglion cells reported for cholinergic agonists. The major difference in the dendritic stratification of bistratified ON-OFF DS ganglion cells and generally unistratified ON DS ganglion cells is consistent with the bisublaminar organization of ON and OFF pathways in the IPL. The problem of occasional branches of ON DS cells in sublamina a is discussed in terms of a threshold for OFF responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Cholinergic amacrine cells in the rabbit retina synapse onto other cholinergic amacrine cells.

Cholinergic amacrine cells in the rabbit retina have been detected by localizing choline acetyltransferase-like immunoreactivity. The characteristic array of normally placed and displaced amacrine cells was detected, as were two major synaptic plexuses in the inner plexiform layer. At the ultrastructural level, the most striking feature was the existence of contacts between the processes of cholinergic amacrine cells. Since this feature has also been detected in chicken and goldfish retina, it needs to be taken into account in any model which seeks to explain how the cholinergic amacrine cells are involved in generating directional selectivity at the ganglion cell level.

Animals↗
PubMed1992

Polyaxonal amacrine cells of rabbit retina: morphology and stratification of PA1 cells.

Polyaxonal amacrine cells are a new class of amacrine cell bearing one to six branching, axon-like processes, closely resembling the axons of Golgi type II cells found elsewhere in the central nervous system. Of the four types of polyaxonal amacrine cell that we have recognized in rabbit retina, three have been described previously in brief communications, and one is the subject of this paper. Type 1 polyaxonal (PA1) amacrine cells have larger cell bodies than most amacrine cells in Golgi preparations, averaging about 13 microns in diameter. These are typically positioned interstitially in the middle of the inner plexiform layer (IPL), although some are also found in the amacrine and ganglion cell layers. Axons and dendrites are broadly stratified in the middle of the IPL, in the vicinity of the a/b sublaminar border. Sparsely branching dendrites have a conventional appearance, branching at a narrow angle, and giving rise to smaller daughter branches, which taper gradually toward their termination. An unusual feature of the dendrites is the zig-zag course of some terminal branches. Clusters of small, pedunculated spines are common on proximal dendrites, and spines are virtually absent on axons. Axons emerge from proximal dendrites within 50 microns of the soma, and more rarely from the soma, in a tapering initial segment, commonly interrupted by one or two large swellings. Subsequent branching is at a wide angle, and the fine caliber is maintained in the transition from parent to daughter branches. The uniform thickness of the axonal branches is interrupted at intervals by boutons en passant. Although the extent of the dendritic tree is large, exceeding 500 microns in radial extent from the cell body, for cells a few millimeters distant from the visual streak, the axonal tree is much larger, and its radial extent is measured in millimeters. PA1 amacrine cells are believed to be polarized in their functional organization, with a primarily recipient dendritic tree and a primarily transmissive axonal tree. PA1 amacrine cells co-stratify with nab cone bipolar cells and with certain small tufted amacrine and ganglion cells at the a/b sublaminar border. The co-stratification of both axons and dendrites at the a/b sublaminar border of the IPL suggests that PA1 amacrine cells are important modulators of neural activity in the middle of the IPL, affecting both ON and OFF responses, and perhaps ON-OFF cells selectively.

Animals↗
PubMed2005

Structural and functional properties of homologous electrical synapses between retinal amacrine cells.

Retinal amacrine cells regulate activities of retinal ganglion cells, the output neurons to higher visual centers, through cellular mechanism of lateral inhibition in the inner plexiform layer (IPL). Electrical properties of gap junction networks between amacrine cells in the IPL were investigated using combined techniques of intracellular recordings, Lucifer yellow and Neurobiotin injection, dual patch-clamp recordings and high voltage electron microscopy in isolated retinas of cyprinid fish. Six types of gap-junctionally connected amacrine cells were classified after their light-evoked responses to light flashes were recorded. Among them, gap junction networks of three types of amacrine cells were studied with structure-function correlation analysis. Cellular morphology of intercellular connections between three homologous cell classes was characterized. The interconnections between laterally extending dendrites in the IPL were localized at dendritic tip terminals. Three types of cells presented the dendrodendritic connections of tip-contact manner in the homologous cell population. High voltage as well as conventional electron microscopy revealed gap junctions between the dendritic tips of Neurobiotin-coupled cells. Receptive field properties of these amacrine cells were examined, displacing a slit of light along the distance from recording sites in the dorsal intermediate region of the retina. Receptive field size, space length constant, response latency and conduction velocity were measured. Spatial and temporal properties of receptive fields were symmetric along horizontally expanding dendrites in the dorsal retina. Simultaneous dual patch-clamp recordings revealed that the lateral gap junction connections between homologous amacrine cells expressed bidirectional electrical synapses passing Na(+) spikes. These results demonstrate that bidirectional electrical transmission in gap junction networks of these amacrine cells is symmetric along the lateral gap junction connections between horizontally extending dendrites. Lateral inhibition regulated by amacrine cells in the IPL appears to be associated with the directional extension of the dendrites and the orientation of dendrodendritic gap junctions.

Action Potentials↗