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J Neyton

Publications and source records attributed to J Neyton.

28 records · Page 2Linked to original sources
PubMed1984

Decrease of gap junction permeability induced by dopamine and cyclic adenosine 3':5'-monophosphate in horizontal cells of turtle retina.

The axon terminals of the H1 horizontal cells of the turtle retina are electrically coupled by extensive gap junctions. Dopamine (10 nM to 10 microM) induces a narrowing of the receptive field profile of the H1 horizontal cell axon terminals, increases the coupling resistance between them, and decreases the diffusion of the dye Lucifer Yellow in the network formed by the coupled axon terminals. These actions of dopamine involve the activation of D1 receptors located on the membrane of the H1 horizontal cell axon terminals proper. Increases of the intracellular cyclic AMP concentration induced by either stimulating the adenylate cyclase activity with forskolin or inhibiting the phosphodiesterase activity with isobutylmethylxanthine, theophylline, aminophylline, or compound RO 20-1724 elicit effects similar to those of dopamine on the receptive field profile of the H1 horizontal cell axon terminals, on their coupling resistance, and on the diffusion of Lucifer Yellow in the axon terminal network. It is concluded that dopamine decreases the permeability of the gap junctions between the axon terminals of the H1 horizontal cells of the turtle retina and that this action probably involves cyclic AMP as a second messenger.

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PubMed1982

gamma-Aminobutyric acid antagonists decrease junctional communication between L-horizontal cells of the retina.

The antagonists of gamma-aminobutyric acid, bicuculline and picrotoxin, were found to narrow the receptive field profile of the large field horizontal cell (L1HC) in the turtle retina when added to the perfusion medium in micromolar concentrations. The coupling resistance between neighboring L1HCs was increased by bicuculline or picrotoxin. Under control conditions, the dye Lucifer yellow injected into one L1HC diffused into a large number of neighboring L1HCs; bicuculline or picrotoxin greatly restricted dye passage between these same cells. We conclude that antagonists of gamma-aminobutyric acid decrease the conductance of gap junctions between L1HCs.

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PubMed1981

Involvement of small-field horizontal cells in feedback effects on green cones of turtle retina.

Light stimuli depolarize green cones of turtle retina through a circuit involving a feedback connection from luminosity horizontal cells (L-HC) to green cones. In turtle retina two types of L-HC have been distinguished: large-field L-HC and small-field L-HC. The spatial properties of the feedback depolarizations of green cones were compared with those of both large- and small-field L-HC. Green cones were found to be more effectively depolarized by relatively small spots of red light than by large red annuli. Moreover, red light stimulation of the periphery of the receptive field could reduce the depolarizing influence of central red stimuli. These spatial properties greatly differ from those of the large-field L-HC, whereas they strongly resemble those of the small-field L-HC. These results suggest that the small-field L-HC mediate the feedback action on green cones.

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PubMed1981

Center-surround antagonistic organization in small-field luminosity horizontal cells of turtle retina.

1. The spatial properties of the small-field luminosity horizontal cell (L2-HC) were investigated in the retina of the turtle by using circular or annular light stimuli of varying dimensions. 2. The amplitude of the hyperpolarizing response induced by dim light spots decreased when the diameter of the spot was increased beyond about 1,000 micrometer. 3. With bright-light stimuli the peak amplitude of the light responses increased monotonically when increasing the illuminated area, but a delayed antagonistic effect appeared with spots of more than 1,000-micrometer diameter. 4. Depolarizing responses were observed if the periphery of the receptive field was stimulated with annuli of light in the presence of central background illumination. 5. The interaction of the inputs converging on the L2-HC from the peripheral and central regions of the receptive field was found to be nonlinear. The same peripheral stimulation could result either in an enhancement or in a depression of the central response according to the intensity of the central illumination. 6. By comparing the receptive-field properties of the L2-HC and the red cones a model is proposed that explains the antagonistic surround mechanism of the L2-HC on the basis of the antagonistic peripheral mechanism in cones. '

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PubMed1980

Feed-back modulation of cone synapses by L-horizontal cells of turtle retina.

Light stimulation of the periphery of the receptive field of turtle cones can evoke both transient and sustained increases of the cone Ca2+ conductance, which may become regenerative. Such increase in the cone Ca2+ conductance evoked by peripheral illumination results from the activation of a polysynaptic pathway involving a feed-back connexion from the L-horizontal cells (L-HC) to the cones. Thus the hyperpolarization of a L-HC by inward current injection can evoke a Ca2+ conductance increase in neighbouring cones. The cone Ca2+ channels thus activated are likely located at its synaptic endings and probably intervene in the cone transmitter release. Therefore the feed-back connexion between L-HC and cones by modifying the Ca2+ conductance of cones could actually modulate the transmitter release from cone synapses. Such feed-back modulation of cone synapses plays a role in the organization of the colour-coded responses of the chromaticity type-horizontal cells and probably of other second order neurones, post-synaptic to the cones. The mechanisms operating the feed-back connexion from L-HC to cones are discussed.

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PubMedDate not supplied

Single-channel currents of an intercellular junction.

We have used a double whole-cell patch-clamp system to make the first quantitative recordings of the single-channel current from an intercellular junction, presumably a gap junction. The junctional channel has various conductance states and discriminates poorly between cations and anions. It seems to change slowly from one conductance state to another.

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PubMedDate not supplied

Horizontal cells of turtle retina: a neurotransmitter control of electrical junctions?

Recent experiments suggest that GABA and dopamine can modulate the permeability of the electrical junctions between horizontal cells of the turtle retina. The possible significance and functional advantages of a chemical control of the electrical junctions are briefly discussed. A similar mechanism could combine in a network of interacting elements the low energy cost and low intrinsic noise typical of the electrical synapses with the great functional plasticity typical of the chemical transmission.

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