Biomedical subjects

N Wioland

Publications and source records attributed to N Wioland.

At least 19 recordsLinked to original sources

PubMed1994

[Event-related potentials and language processing].

The contribution of cognitive event-related potentials (ERPs) and particularly of the N400 component to the study of language processing is considered. After a general presentation of the various components of cognitive evoked potentials which are differentiated from early potentials (sensitive to perceptive parameters), the neurophysiological and psychological correlates of ERPs are discussed. Before the presentation of the main studies concerned with the correlation between specific late components and linguistic processes, it is proposed an introduction to some theoretical models of language processing which serve as conceptual framework supporting most of the experimental approaches in this field. The results of EPs studies devoted to functional asymetries in language processing are briefly mentioned. Then a number of studies are analysed, these demonstrate the sensitivity of event-related potential measures to linguistic manipulations. Finally, the studies concerned with the N400 are reviewed, this potential appears to be the more specifically language-related ERP component, even if its connection with specific linguistic processes or its differentiation from N200 are still under debate. Nevertheless language-related electrophysiological investigations may become in the near future a useful complementary approach to our understanding of language processing and language disorders.

Brain↗

PubMed1993

Acute blockade of dopamine receptors with haloperidol: a retinal model to study impairments of dopaminergic transmission.

A pulse of dopamine produces a transient dose-correlated increase in the transepithelial potential (TEP) of the chicken eye, mimicking the light-induced response, the light peak (LP). Acute blockade of retinal dopaminergic transmission with haloperidol, a mixed antagonist, produced a dose-correlated TEP voltage decrease which was rapidly reversed by intravitreal injection of dopamine. The LP recorded thereafter was strongly reduced. These data confirm the hypothesis that dopamine released by light from amacrine cells triggers light-induced changes in the TEP of the intact chicken eye, and that these potentials could well provide an electrophysiological tool to evaluate retinal dopaminergic deficiency.

Animals↗

PubMed1992

Dopamine and melatonin interactions in the intact chicken eye. Electrooculographic and biochemical study.

Electrophysiological and biochemical techniques were used to investigate the interactions between dopamine (DA) and melatonin (MEL) in the intact chicken eye. Endogenous DA depletion induced by intraocular administration of alpha-methyl-para-tyrosine (alpha-MPT), a selective tyrosine hydroxylase inhibitor, decreases the transepithelial potential (TEP) of the retinal pigment epithelium and reduces the light peak (LP) recorded by an indirect electro-oculographic (EOG) method. An intraocular injection of MEL also reduces the TEP but does not reduce the LP. Retinal MEL is increased after endogenous DA depletion and a tight inverse correlation between DA and MEL contents was found. The present data, together with other findings support the hypothesis (1) that in the intact chicken eye, DA and MEL play respectively a role of light and dark signals on the TEP, and (2) that a balance between these two neurohormones may be responsible for the regulation of RPE events which are dependent on light-dark conditions.

Animals↗

PubMed1991

Light and dark induced variations of the c-wave voltage of the chicken eye after treatment with sodium aspartate.

Light and dark-induced variations of the ERG c-wave voltage were recorded in control chickens and after intravitreal injection of Na aspartate, a treatment whose main effect is to functionally disconnect the pigment epithelium-photoreceptor complex from second order neurons. After aspartate, the fast light rise which characterizes this preparation is no longer observed; it is substituted for by a potential variation of much slower time course and of lower magnitude. The data totally confirm previous findings obtained through an indirect EOG technique and suggest the participation of inner retinal layers in the generation of the light peak in the chicken eye.

Animals↗

PubMed1991

Is dopamine involved in the generation of the light peak in the intact chicken eye?

The implication for dopamine (DA) in the modulation of the standing potential (SP) and the light peak (LP) was tested in intact chickens using an indirect EOG method. After an intravenous or intravitreal injection of DA, a transient, dose-dependent increase in the SP was observed. The LP, recorded after an intravenous injection, was preserved. But after an intravitreal injection, the LP was strongly reduced or even abolished depending on the dose of DA, whereas the photoreceptor response was unchanged. The data supports the hypothesis that the light peak, which is generated by a neural retina-pigment epithelium interaction, could be triggered by dopamine released at light onset from the inner retinal layers.

Animals↗

PubMed1990

EOG and ERG modifications induced in the chicken eye after blockade of catecholamine and 5-hydroxytryptamine biosynthesis.

The involvement of catecholaminergic and indoleaminergic systems in the modulation of the standing potential of the eye was tested in chickens by means of an indirect electrooculography method and direct current electroretinogram recordings. D,L alpha-monofluoromethyl dopa (MFMD), 50 and 100 nmol), a highly specific inactivator of aromatic L-amino acid decarboxylase, was injected intravitreally. This treatment is known to induce a selective and irreversible blockade of dopamine and 5-hydroxytryptamine biosynthesis. Five hours after drug injection an important increase in the standing potential appeared. The light peak was delayed by about 5 min but its amplitude was unchanged. The return of the standing potential to basal value during maintained illumination was delayed by 5-10 min. The time course of the dark trough was not modified. The intensity-voltage functions were also studied for the various electroretinogram components, 5 hr after MFMD. The voltage of the b-wave was reduced (by 65% with the highest intensity), while the other components were little affected. Substantial reduction in dopamine and 5-hydroxytryptamine concentrations were found in treated retinas. These data, together with previous results, suggest that the standing potential of the chicken eye may be modulated by a balance between catecholamine and indoleamine systems.

Animals↗

PubMed1990

Electrooculographic and electroretinographic study in the chicken after dopamine and haloperidol.

The implication of dopamine in the modulation of the standing potential of the eye was tested in the chicken through an indirect electrooculographic method and direct current electroretinogram (ERG) recording after haloperidol, a mixed D1-D2 antagonist. The standing potential of the eye was reduced within 15 min after intravitreal injection of the antagonist (150 micrograms). This effect is rapidly reversed by an application of dopamine. The fast oscillation was preserved but the light peak was either strongly reduced or abolished. The dark trough showed an apparently normal time course. The intensity-voltage function was studied for the various ERG components. After haloperidol the b-wave and the c-wave were strongly reduced, whereas the a-wave was little affected. Together with previous data obtained with intraocular injections of dopamine, our data suggest the involvement of dopamine in the modulation of the standing potential. They also support the hypothesis that the light peak, which is generated by a photoreceptor-pigment epithelium interaction, is influenced by dopamine or by a related substance. The modulatory effect could also be due to a balance between several neurotransmitter systems.

Animals↗

PubMed1990

Effects of intravitreal and intravenous administrations of dopamine on the standing potential and the light peak in the intact chicken eye.

We studied the modifications of the standing potential (SP) of the eye and of the light peak (LP) after exposure to dopamine, a neurotransmitter released at light by the inner retina and known to affect electrical properties of the retinal pigment epithelium. Intravenous or intravitreal injections of dopamine (DA) were performed on intact chickens. "Choroidal" application (through an intravenous injection) induced a transient increase of the SP and the LP was preserved. On the other hand, "apical" applications of DA (through an intraocular injection) also increased the SP but considerably depressed the LP. These results are in agreement with the hypothesis that the light-induced release of dopamine from the neuroretina may be responsible for the LP generation in the intact chicken eye.

Animals↗

PubMed1989

Neurotransmission in the frog retina: possible physiological and histological correlations.

In the frog retina, extracellular recordings of transient ganglion cells have shown that the inhibitory surround of the receptive field of these cells was mediated by gamma-aminobutyric acid and acetylcholine (through the nicotinic receptors). Histoautoradiographic and immunocytochemical studies for the two respectively have shown that these neurotransmitters can act through horizontal and amacrine cells. The separation of the ON and OFF channels mediated by glutamate at the bipolar cell level may also be obtained by glycine and/or acetylcholine (through muscarinic receptors). Respective histoautoradiographic and immunocytochemical studies indicate that these neurotransmitters act at the amacrine cell level. These data are consistent with the functional separation of spatial and temporal organization of retinal information, with horizontal cells especially responsible for the spatial organization of the ganglion cell responses and amacrine cells involved in both spatial and temporal organization of the responses.

Acetylcholine↗

PubMed1989

Electrooculographic study in the chicken after treatment with neurotoxin 6-hydroxydopamine.

The implication of dopamine in the modulation of the standing potential of the eye was tested in the chicken by an indirect electrooculogram (EOG) method. After a single rapid systemic injection of dopamine, a transient dose-dependent increase in the EOG voltage was observed. EOG recordings during light and dark adaptation were performed after retinal dopamine depletion was induced by intraocular injections of the neurotoxin 6-hydroxydopamine (6-OHDA). The eyes were injected on two successive days with a mixture of 6-OHDA (50 micrograms), pargyline (a monoamine oxidase inhibitor), and ascorbate added as an antioxidant. Following this treatment EOG recordings were performed 1, 4, and 8 days after the second injection. The electrophysiological changes appeared most spectacular on the fourth day: an important increase in the EOG basal values as well as of the amplitude of the light peak and of the dark trough were observed. Substantial reduction in retinal concentration of dopamine was found in treated retinas. These unexpected electrophysiological data offer additional evidence for the involvement of a catecholamine in the generation of the light peak and the dark trough of the EOG.

Animals↗

PubMed1988

On cholinergic mechanisms in the optokinetic nystagmus of the frog: antagonistic effects of muscarinic and nicotinic systems.

In a monocular situation, an intravitreal injection of acetylcholine (ACh) agonists (especially muscarinic agonists like muscarine or oxotremorine) 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. These two effects were added in a binocular condition. Similar results were obtained with ACh nicotinic antagonists (D-tubocurarine, alpha-bungarotoxin, hexamethonium and gallamine). ACh muscarinic antagonists (atropine, scopolamine) had only moderate effects and failed to provoke an N-T component in the contralateral OKN. These data show that ACh mechanisms are involved in the control of the frog OKN, especially in directional asymmetry, nicotinic and muscarinic systems acting in an antagonistic way.

Animals↗

PubMed1987

Physiological effects of muscarinic vs nicotinic ACh antagonists upon ganglion cell activity in the frog retina.

The intravitreal administration of ACh agonists (eserine, carbachol, oxotremorine) or that of ACh muscarinic antagonists (scopolamine, atropine) provoked a reduction of the On-Off ganglion cell discharges. The agonists depressed the Off discharges more than the On discharges, while the ACh muscarinic antagonists depressed the On- more than the Off discharges. These drugs did not modify the ganglion cell receptive field area; thus, the muscarinic cholinergic system seems not to be involved in the spatial organization of the On-Off ganglion cells, but rather seems to play an important part in the separation of On and Off information channels. ACh nicotinic antagonists [hexamethonium, D-tubocurarine (D-TC), alpha-bungarotoxin (alpha-BGTX)] provoked an increase of the receptive field area of On-Off ganglion cells, this enlargement being due to the suppression of the inhibition normally exerted by the surround upon the centre of the field. Moreover D-TC and alpha-BGTX, but but hexamethonium, increased the number of ganglion cell discharges. These data are analogous to those obtained after administration of GABA antagonists and show that through nicotinic receptors, ACh seems to be involved in the spatial organization of the On-Off ganglion cell.

Acetylcholine↗

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↗