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Biomedical subjects

N Wioland

Publications and source records attributed to N Wioland.

At least 37 records · Page 2Linked to original sources
PubMed1987

[Contribution of internal layers of the retina to the genesis of the light peak in the electrooculogram in the chicken].

We report that in the Chicken retina, Na aspartate which selectively blocks signal transmission between the photoreceptors and second order neurons also largely modifies the EOG. In treated eyes, the standing potential is reduced and the LP which is very transient in the Chicken eye is substituted for by a reactivity to light with much slower rise and delayed culmination time. The data are discussed in terms of interaction between pigment epithelium and neuroretina in the pharmacological determinism of the LP.

Animals↗
PubMed1986

Anisotropic inhibition in the receptive field surround of the frog retinal ganglion cells, evidenced by bicuculline and SR 95103, a new GABA antagonist.

When GABA antagonists (picrotoxin, bicuculline methiodide and SR 95103) were intravitreally injected in the frog, they increased the number of spikes of transient retinal ganglion cells, as well as the duration of the response. Thus, the transient pattern of the response became more sustained. GABA antagonists also provoked a marked increase in the size of the receptive field, which might be due to the abolition of the inhibition exerted by the surround upon the centre of the field. In fact, a stimulus applied to the surround of the field simultaneously with one applied to the centre no longer provoked the reduction of the field area nor that of the number of spikes. These are effects which were always observed before drug injection. After picrotoxin injection, the enlarged field was concentric with the initial one, both angular diameters doubled, whereas after bicuculline or SR 95103, the enlarged field was not concentric with the initial one and only one diameter increased. Thus, GABA inhibition appears to be distributed according to an anisotropic spatial pattern. Whether this anisotropy might be an input for direction selectivity in the frog visual system is a topic of discussion. With respect to SR 95103, this compound proved to act like a selective GABA antagonist with long lasting effects.

Animals↗
PubMed1985

On GABAergic mechanisms in the optokinetic nystagmus of the frog: effects of bicuculline, allylglycine and SR 95103, a new GABA antagonist.

In a monocular situation, an intravitreal injection of the GABA antagonists, bicuculline or SR 95103 provoked both the suppression of the optokinetic nystagmus (OKN) related to the injected eye and the appearance of a Nasal-Temporal (N-T) component in the OKN triggered by the contralateral non-injected eye (this N-T component being absent in control OKN). These two effects were added in a binocular condition. Similar results were obtained with L-C allylglycine which reduces the endogenous GABA level, but these effects were delayed when compared to those of GABA antagonists. All these data are roughly analogous to those previously obtained with picrotoxin (a non-competitive GABA antagonist) and thus confirm that GABA mechanisms are involved in the control of the frog OKN. Furthermore, SR 95103 acted in this model as a potent selective GABA antagonist, as has been demonstrated in another system.

Allylglycine↗
PubMed1985

Stereospecific effects of the alpha-aminoadipic acid on the retina: a morphological and electrophysiological study.

In both frog and chicken an intravitreal injection of the dextrorotatory (D)-isomer of alpha-aminoadipic acid (alpha-aaa) leads to a progressive disappearance of the ERG b-wave without affecting a and c components. Tectal evoked potentials (TEP) are no longer recorded. These physiological effects are concomitant with a specific glial cell damage, without any apparent damage to neurons. The levorotatory (L)-isomer at low concentrations is more gliotoxic than the D-isomer, the ERG b-wave is suppressed, while the amplitude of both a and c components is increased. TEPs are always recorded, i.e., a visual message is still generated in the retina and transmitted to the optic tectum when the Müller cells have been damaged and the b-wave is abolished. At higher concentrations the L-isomer suppresses TEPs and damages both glial and neuronal cells. Thus alpha-aaa appears to be a good tool for analyzing ERG components, especially subcomponents of the c-wave.

2-Aminoadipic Acid↗
PubMed1985

Enhanced sensory convergence to the visual cortex in the rodless (rd/rd) mouse.

The rd/rd mutation provokes a specific degeneration of the photoreceptive cells in the mouse retina, without affecting other neuronal elements. This degeneration starts 8 to 10 days after birth. Discriminative learning experiments have shown the degenerated retina to remain light-sensitive, the sensitivity being reduced to 10(-5) of normal with a peak still at 500 nm. An ontogenetic study showed a progressive vanishing of visual potentials (electroretinogram and visual evoked potentials) during the third week of life. Potentials of auditory origin, which can be recorded from the visual cortex in normal mice, were found to be clearly facilitated by the absence of the visual input either because of retinal degeneration in rd mouse or provoked by enucleation at birth.

Animals↗
PubMed1985

A cone-triggered c-wave in the chicken ERG time integration characteristics.

The c-waves recorded from the cone-dominant retina of the chicken proved to be cone-triggered. The time course and time integration properties of this retinal potential were compared with those of the rod-triggered c-wave recorded in the frog under scotopic conditions. The results clearly demonstrate that there is no evidence for time integration in cone-triggered c-waves but that rod-triggered c-waves follow the Bunsen-Roscoe law over more than 2 log units. We propose that these time-related differences may be used in other species as a differentiation criterion between cone-triggered and rod-triggered c-waves.

Animals↗
PubMed1985

Photopic c-wave in the chicken ERG: sensitivity to sodium azide, epinephrine, sodium iodate, barbiturates, and other general anesthetics.

The c-wave recorded in the chicken electroretinogram proved to be a cone-triggered component. The questions arose whether its reactivity to various specific drugs (sodium iodate, sodium azide, epinephrine, or barbiturates) were similar to those described for classic rod-triggered c-waves. We also tested the sensitivity of the chicken c-wave to various general anesthetics. Urethane was found to be the drug that best preserves the c-wave in electrophysiological recordings.

Anesthetics↗
PubMed1984

Evidence for both photopic and scotopic characteristics in the c-wave of chicken and frog ERG.

The electroretinographic c-wave was studied in two species with duplex retinas, the frog (rod-dominant) and the chicken (highly cone-dominant). In both species a cone driven c-wave was recorded in addition to the classical rod-driven c-wave. An attempt was made to specify the differential characteristics with respect to time-course, time integration, adaptational changes and spectral sensitivity of cone-driven vs rod-driven c-waves. These data confirm the generality of the c-wave generation by both rod and cone systems.

Adaptation, Ocular↗
PubMed1984

[Pharmacological sensitivity of the photopic c-wave in the electroretinogram of the chicken. I. Effects of sodium azide, adrenaline, and a barbiturate].

The c-wave recorded in the chicken electroretinogram proved to be cone-triggered. The effect of various drugs active on pigment epithelium and on c-waves in scotopic retinas were tested in order to determine whether a similar mechanism may underlie both rod- and cone-triggered c-waves. Our results indeed point to such a similar reactivity of both types of c-waves. Pentothal, a short-acting barbiturate induced--as it does in the sheep--a transient disappearance of the c-wave. Sodium azide and adrenaline produced very similar effects: when injected i.v., these drugs produced a transient increase in the resting potential of the eye (the "azide potential"). When injected im or i.p., both drugs provoked--as they do in rabbit or in rat retinas--an increase in the voltage of the c-wave, but this increase was preceded in the chicken by a partial or total suppression of this component.

Animals↗
PubMed1984

[Pharmacologic sensitivity of the photopic c wave in the electroretinogram of the chicken. II. Effects of sodium iodate and general anesthesia].

Iodate poisoning is known to induce both a retinal degeneration which is restricted in a first stage to the pigment epithelium and a selective suppression of the c-wave ([5] to [10]). In the chicken we did not obtain such electrophysiological or morphological effects. In both acute (i.v. or i.m. injections, up 50 mg/kg) and chronic experiments (4 X 45 mg/kg daily) the photopic c-wave of the chicken appeared to be fairly insensitive to sodium iodate, except at high concentrations (greater than 100 mg/kg in a single injection) which proved to be highly cardiotoxic. The ultrastructure of the retinal pigment epithelium and of the photoreceptors appeared quite normal in retinas treated with the highest concentration of the drug. Sodium pentobarbital (Nembutal), ketamine (Ketalar) and ethyl-carbamate (Urethane) were used as general anesthetics. The c-wave appeared to be differentially sensitive to these drugs. The suppressant effect was strongest with Nembutal and lowest with Urethane. The selective sensitivity of the c-wave to general anesthetics may explain why it was repeatedly stated in the literature that c-waves did not exist in a number of cone dominated retinas.

Anesthesia, General↗
PubMed1983

Involvement of GABAergic mechanisms in the optokinetic nystagmus of the frog.

Frog optokinetic nystagmus (OKN) was studied before and after an intravitreal injection of picrotoxin, a specific non-competitive GABA antagonist. In monocular vision, the OKN displayed a directional asymmetry favouring the Temporal-Nasal (T-N) stimulation. In that case, the nystagmus extinction frequency (NEF) is low, about 2 frames/s. In binocular vision, the OKN is symmetrical with a facilitation of performances compared to monocular vision (NEF = 3 frames/s). In monocular as in binocular vision, an intravitreal injection of picrotoxin (between 1 X 10(-4) and 5 X 10(-3) M) provoked the disappearance of the injected eye OKN and a spectacular facilitation in the performances of the intact eye, with the appearance of a N-T component and the increase of the NEF value reaching 7 or 11.5 frames/s according to the experimental conditions. This contralateral facilitation was no longer observed after the optic nerve of the injected eye had been cut, indicating that such a facilitation can only be explained by alterations of a central process triggered by the visual input. It is concluded that GABAergic mechanisms might be responsible for the inhibition of the N-T component in the frog OKN and might be involved in the control of the power of temporal resolution in this animal.

Animals↗
PubMed1983

[Stereospecificity of the action of alpha-aminoadipic acid on the retina: a morphological and electrophysiological study].

An intravitreal injection of the D isomer of the alpha-amino adipic acid (alpha-aa) entails the progressive disappearance of the ERG b wave as well as that of tectal evoked potentials (TEP). These physiological effects are concomitant with a specific glial cell damage in frog and chicken retinas. At low concentrations, the L isomer is more gliotoxic than the D isomer; the ERG b wave is suppressed while TEP are always recorded. At higher concentrations, the L isomer suppresses TEP and damages both glial and neuronal cells.

2-Aminoadipic Acid↗
PubMed1981

Effects of DL-alpha-amino adipic acid on Müller cells in frog and chicken retinae in vivo: relation to ERG b wave, ganglion cell discharge and tectal evoked potentials.

In both frog and chicken, an intravitreal injection of DL-alpha-amino-adipic acid, (DL-alpha aaa) provoked a progressive depression and eventually the disappearance of the ERG b wave that was concomitant with severe damage to the Müller cells without any apparent damage to retinal neurons. Ganglion cell discharges as well as tectal evoked potentials were still recorded, i.e. a visual message was still generated in the retina and transmitted to the optic tectum, when the Müller cells had been damaged to as to provoke an abolition of the ERG b-wave. The whole of the drug-induced effects proved to be reversible.

2-Aminoadipic Acid↗
PubMed1980

Effects of some amino acids (GABA, glycine, taurine) and of their antagonists (picrotoxin, strychnine) on spatial and temporal features of frog retinal ganglion cell responses.

When intravitreally injected in the frog, GABA reduced the receptive field area of transient retinal ganglion cells, and it decreased the response duration and the number of spikes both at ON and at OFF. Conversely, its antagonist picrotoxin provoked an increase in the duration of both ON and OFF discharges as well as a marked increase in the number of spikes. Furthermore, picrotoxin provoked a marked increase in the size of the receptive field of both sustained and ON-OFF cells by abolishing the inhibition exerted by the surround upon the centre of the field. Glycine and taurine did not affect the size of the receptive field of these ganglion cells. They had no effect on the responses of sustained ganglion cells, while they totally suppressed OFF discharges of transient ganglion cells, without modifying their ON discharges. Conversely, their antagonist strychnine totally suppressed the ON dishcarges while the OFF discharges were still recorded, though with a reduced number of spikes and an increased latency, An histoautoradiographic study, carried out in parallel, showed that GABA is taken up by both horizontal cells and amacrine cells, while glycine and taurine are taken up by the amacrine cells only.

Amino Acids↗