Gap junctions between AII amacrine cells and calbindin-positive 
bipolar cells in the rabbit retina

Electrical synapses or gap junctions occur between many retinal neurons. However, in most cases, the gap junctions have not been visualized directly. Instead, their presence has been inferred from tracer spread throughout the network of cells. Thus, tracer coupling is taken as a marker for the presence of gap junctions between coupled cells. AII amacrine cells are critical interneurons in the rod pathway of the mammalian retina. Rod bipolar cell output passes to AII amacrine cells, which in turn make conventional synapses with OFF cone bipolar cells and gap junctions with ON cone bipolar cells. Injections of biotinylated tracers into AII amacrine cells reveals coupling between the AII amacrine cell network and heterologous coupling with a variety of ON cone bipolar cells, including the calbindin-positive cone bipolar cell. To directly visualize gap junctions in this network, we prepared material for electron microscopy that was double labeled with antibodies to calretinin and calbindin to label AII amacrine cells and calbindin-positive cone bipolar cells, respectively. AII amacrine cells were postsynaptic to large vesicle-laden rod bipolar terminals, as previously reported. Gap junctions were identified between AII amacrine cells and calbindin-positive cone bipolar cell terminals identified by the presence of immunostaining and ribbon synapses. This represents direct confirmation of gap junctions between two different yet positively identified cells, which are tracer coupled, and provides additional evidence that tracer coupling with Neurobiotin indicates the presence of gap junctions. These results also definitively establish the presence of gap junctions between AII amacrine cells and calbindin bipolar cells which can therefore carry rod signals to the ON alpha ganglion cell.

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Light-induced modulation of coupling between AII amacrine cells in the rabbit retina

Visual Neuroscience ◽

10.1017/s0952523800012220 ◽

1997 ◽

Vol 14 (3) ◽

pp. 565-576 ◽

Cited By ~ 107

Author(s):

Stewart A. Bloomfield ◽

Daiyan Xin ◽

Tristan Osborne

Keyword(s):

Receptive Field ◽

Gap Junctions ◽

Electrical Coupling ◽

Amacrine Cells ◽

Bipolar Cells ◽

Field Size ◽

Background Illumination ◽

Aii Amacrine Cells ◽

Aii Amacrine ◽

Cone Bipolar Cells

AbstractThe rod-driven, AII amacrine cells in the mammalian retina maintain homologous gap junctions with one another as well as heterologous gap junctions with on-cone bipolar cells. We used background illumination to study whether changes in the adaptational state of the retina affected the permeabilities of these two sets of gap junctions. To access changes in permeability, we injected single AII amacrine cells with the biotinylated tracer, Neurobiotin, and measured the extent of tracer coupling to neighboring AII cells and neighboring cone bipolar cells. We also measured the center-receptive field size of All cells to assess concomitant changes in electrical coupling. Our results indicate that in well dark-adapted retinas, AII cells form relatively small networks averaging 20 amacrine cells and covering about 75 μm. The size of these networks matched closely to the size of AII cell on-center receptive fields. However, over most of their operating range, AII cells formed dramatically larger networks, averaging 326 amacrine cells, which corresponded to an increased receptive-field size. As the retina was light adapted beyond the operating range of the AII cells, they uncoupled to form networks comparable in size to those seen in well dark-adapted retinas. Our results, then, indicate that the adaptational state of the retina has a profound effect on the extent of electrical coupling between AII amacrine cells. Although we observed light-induced changes in the number of tracer-coupled cone bipolar cells, these appeared to be an epiphenomenon of changes in homologous coupling between AII amacrine cells. Therefore, in contrast to the robust changes in AII–AII coupling produced by background illumination, our data provided no evidence of a light-induced modulation of coupling between AII cells and on-cone bipolar cells.

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Meclofenamic Acid Blocks Electrical Synapses of Retinal AII Amacrine and on-Cone Bipolar Cells

Journal of Neurophysiology ◽

10.1152/jn.00112.2009 ◽

2009 ◽

Vol 101 (5) ◽

pp. 2339-2347 ◽

Cited By ~ 41

Author(s):

Margaret Lin Veruki ◽

Espen Hartveit

Keyword(s):

Amacrine Cells ◽

Bipolar Cells ◽

Electrical Synapse ◽

Dependent Manner ◽

Electrical Synapses ◽

Meclofenamic Acid ◽

Aii Amacrine Cells ◽

Rod Pathway ◽

Aii Amacrine ◽

Cone Bipolar Cells

Gap junction channels constitute specialized intercellular contacts that can serve as electrical synapses. In the rod pathway of the retina, electrical synapses between AII amacrine cells express connexin 36 (Cx36) and electrical synapses between AII amacrines and on-cone bipolar cells express Cx36 on the amacrine side and Cx36 or Cx45 on the bipolar side. For physiological investigations of the properties and functions of these electrical synapses, it is highly desirable to have access to potent pharmacological blockers with selective and reversible action. Here we use dual whole cell voltage-clamp recordings of pairs of AII amacrine cells and pairs of AII amacrine and on-cone bipolar cells in rat retinal slices to directly measure the junctional conductance ( Gj) between electrically coupled cells and to study the effect of the drug meclofenamic acid (MFA) on Gj. Consistent with previous tracer coupling studies, we found that MFA reversibly blocked the electrical synapse currents in a concentration-dependent manner, with complete block at 100 μM. Whereas MFA evoked a detectable decrease in Gj within minutes of application, the time to complete block of Gj was considerably longer, typically 20–40 min. After washout, Gj recovered to 20–90% of the control level, but the time to maximum recovery was typically >1 h. These results suggest that MFA can be a useful drug to investigate the physiological functions of electrical synapses in the rod pathway, but that the slow kinetics of block and reversal might compromise interpretation of the results and that explicit monitoring of Gj is desirable.

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Dark-adapted response threshold of OFF ganglion cells is not set by OFF bipolar cells in the mouse retina

Journal of Neurophysiology ◽

10.1152/jn.01202.2011 ◽

2012 ◽

Vol 107 (10) ◽

pp. 2649-2659 ◽

Cited By ~ 27

Author(s):

A. Cyrus Arman ◽

Alapakkam P. Sampath

Keyword(s):

Ganglion Cells ◽

Amacrine Cells ◽

Bipolar Cells ◽

Response Threshold ◽

Mouse Retina ◽

Signal Flow ◽

Visual Threshold ◽

Aii Amacrine Cells ◽

Aii Amacrine ◽

Cone Bipolar Cells

The nervous system frequently integrates parallel streams of information to encode a broad range of stimulus strengths. In mammalian retina it is generally believed that signals generated by rod and cone photoreceptors converge onto cone bipolar cells prior to reaching the retinal output, the ganglion cells. Near absolute visual threshold a specialized mammalian retinal circuit, the rod bipolar pathway, pools signals from many rods and converges on depolarizing (AII) amacrine cells. However, whether subsequent signal flow to OFF ganglion cells requires OFF cone bipolar cells near visual threshold remains unclear. Glycinergic synapses between AII amacrine cells and OFF cone bipolar cells are believed to relay subsequently rod-driven signals to OFF ganglion cells. However, AII amacrine cells also make glycinergic synapses directly with OFF ganglion cells. To determine the route for signal flow near visual threshold, we measured the effect of the glycine receptor antagonist strychnine on response threshold in fully dark-adapted retinal cells. As shown previously, we found that response threshold for OFF ganglion cells was elevated by strychnine. Surprisingly, strychnine did not elevate response threshold in any subclass of OFF cone bipolar cell. Instead, in every OFF cone bipolar subclass strychnine suppressed tonic glycinergic inhibition without altering response threshold. Consistent with this lack of influence of strychnine, we found that the dominant input to OFF cone bipolar cells in darkness was excitatory and the response threshold of the excitatory input varied by subclass. Thus, in the dark-adapted mouse retina, the high absolute sensitivity of OFF ganglion cells cannot be explained by signal transmission through OFF cone bipolar cells.

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Gap junctional regulatory mechanisms in the AII amacrine cell of the rabbit retina

Visual Neuroscience ◽

10.1017/s0952523804215127 ◽

2004 ◽

Vol 21 (5) ◽

pp. 791-805 ◽

Cited By ~ 38

Author(s):

XIAO-BO XIA ◽

STEPHEN L. MILLS

Keyword(s):

Nitric Oxide ◽

Gap Junctions ◽

Bipolar Cell ◽

Light Adaptation ◽

Amacrine Cells ◽

Adenosine Monophosphate ◽

Morphological Type ◽

Rabbit Retina ◽

Aii Amacrine Cells ◽

Aii Amacrine

Gap junctions are commonplace in retina, often between cells of the same morphological type, but sometimes linking different cell types. The strength of coupling between cells derives from the properties of the connexins, but also is regulated by the intracellular environment of each cell. We measured the relative coupling of two different gap junctions made by AII amacrine cells of the rabbit retina. Permeability to the tracer Neurobiotin was measured at different concentrations of the neuromodulators dopamine, nitric oxide, or cyclic adenosine monophosphate (cAMP) analogs. Diffusion coefficients were calculated separately for the gap junctions between pairs of AII amacrine cells and for those connecting AII amacrine cells with ON cone bipolar cells. Increased dopamine caused diffusion rates to decline more rapidly across the AII–AII gap junctions than across the AII–bipolar cell gap junctions. The rate of decline at these sites was well fit by a model proposing that dopamine modulates two independent gates in AII–AII channels, but only a single gate on the AII side of the AII–bipolar channel. However, a membrane-permeant cAMP agonist modulated both types of channel equally. Therefore, the major regulator of channel closure in this network is the local cAMP concentration within each cell, as regulated by dopamine, rather than different cAMP sensitivity of their respective gates. In contrast, nitric oxide preferentially reduced AII–bipolar cell permeabilities. Coupling from AII amacrine cells to the different bipolar cell subtypes was differentially affected by dopamine, indicating that light adaptation actingviadopamine release alters network coupling properties in multiple ways.

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Coupling from AII amacrine cells to ON cone bipolar cells is bidirectional

The Journal of Comparative Neurology ◽

10.1002/cne.1292 ◽

2001 ◽

Vol 437 (4) ◽

pp. 408-422 ◽

Cited By ~ 50

Author(s):

E. Brady Trexler ◽

Wei Li ◽

Stephen L. Mills ◽

Stephen C. Massey

Keyword(s):

Amacrine Cells ◽

Bipolar Cells ◽

Aii Amacrine Cells ◽

Aii Amacrine ◽

Cone Bipolar Cells

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Rod signals are routed through specific Off cone bipolar cells in primate retina

10.1101/2020.05.17.100982 ◽

2020 ◽

Author(s):

Amanda J. McLaughlin ◽

Kumiko A. Percival ◽

Jacqueline Gayet-Primo ◽

Teresa Puthussery

Keyword(s):

Bipolar Cell ◽

Amacrine Cell ◽

Amacrine Cells ◽

Cell Types ◽

Bipolar Cells ◽

Visual Signals ◽

Night Time ◽

Pass Through ◽

Aii Amacrine ◽

Cone Bipolar Cells

AbstractAdapting between scotopic and photopic illumination involves switching the routing of retinal signals between rod and cone-dominated circuits. In the daytime, cone signals pass through parallel On and Off cone bipolar cells, that are sensitive to increments and decrements in luminance, respectively. At night, rod signals are routed into these cone-pathways via a key glycinergic interneuron, the AII amacrine cell (AII-AC). In primates, it is not known whether AII-ACs contact all Off-bipolar cell types indiscriminately, or whether their outputs are biased towards specific Off-bipolar cell types. Here, we show that the rod-driven glycinergic output of AII-ACs is strongly biased towards a subset of macaque Off-cone bipolar cells. The Off-bipolar types that receive this glycinergic input have sustained physiological properties and include the Off-midget bipolar cells, which provide excitatory input to the Off-midget ganglion cells (parvocellular pathway). The kinetics of the glycinergic events are consistent with the involvement of the α1 glycine receptor subunit. Taken together with results in mouse retina, our findings point towards a conserved motif whereby rod signals are preferentially routed into sustained Off signaling pathways.Significance StatementVisual signals pass through different retinal neurons depending on the prevailing level of illumination. Under night-time light levels, signals from rods pass through the AII amacrine cell, an inhibitory interneuron that routes rod signals into On and Off bipolar cells to detect increments and decrements in light intensity, respectively. Here, we show in primate retina that the output of AII amacrine cells is strongly biased towards specific Off bipolar cell types, which suggests that rod signals reach the brain via specific neural channels. Our results further our understanding of how visual signals are routed through visual circuits during night-time vision.

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Functional Organization of Cone Bipolar Cells in the Rat Retina

Journal of Neurophysiology ◽

10.1152/jn.1997.77.4.1716 ◽

1997 ◽

Vol 77 (4) ◽

pp. 1716-1730 ◽

Cited By ~ 91

Author(s):

Espen Hartveit

Keyword(s):

Receptor Antagonist ◽

Functional Organization ◽

Amacrine Cells ◽

Bipolar Cells ◽

Short Latency ◽

Rat Retina ◽

Long Latency ◽

Aii Amacrine Cells ◽

Aii Amacrine ◽

Cone Bipolar Cells

Hartveit, Espen. Functional organization of cone bipolar cells in the rat retina. J. Neurophysiol. 77: 1716–1730, 1997. The responses of cone bipolar cells in slices of rat retina to ionotropic glutamate receptor agonists were recorded with the whole cell voltage-clamp technique in the presence of 5 mM Co2+ and nominally 0 mM Ca2+ extracellularly. Application of the non- N-methyl-d-aspartate (non-NMDA) receptor agonists kainate and (S)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate had a series of effects on cone bipolar cells (types 1–9), and the different cell types could be classified as on- or off-type cells according to which type(s) of responses they displayed. First, direct responses were observed in cell types 1–4 as short-latency inward currents at −70 mV with reversal potentials ( E revs) close to 0 mV, characteristic of nonselective cation channels. Second, some cells, among types 5–9, did not display short-latency inward currents to kainate at −70 mV. Other type 5–8 cells displayed short-latency kainate responses, but the currents could not be reversed ( E rev of +40 mV or greater). I suggest that these responses are conveyed to the cone bipolar cells through gap junctions, most likely with AII amacrine cells. The lack of reversal is likely due to a substantial voltage drop across the gap junctions resulting in an inadequate voltage control of AII amacrine cells when the recording pipette is on the cone bipolar cell. Kainate responses recorded directly from AII amacrine cells had E rev ∼ 0 mV. Third, long-latency indirect responses selective for chloride ions ( E rev ∼ chloride equilibrium potential) were observed in many cone bipolar cells during longer-lasting application of kainate. The long-latency response component was suppressed by coapplication of the γ-aminobutyric acid-A (GABAA) receptor antagonist picrotoxin and the GABAC receptor antagonist 3-aminopropyl(methyl)phosphinic acid. This long-latency component was absent in axotomized bipolar cells, suggesting that it was due to external Ca2+-independent release of GABA onto the axon terminals of the cone bipolar cells. All kainate-evoked response components were blocked by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. Application of NMDA evoked no response in cone bipolar cells. These results suggest that cone bipolar cells types 1–4 are off cone bipolar cells, whereas cone bipolar cells types 5–9 are on cone bipolar cells.

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