ERG OFF response in frog retina: light adaptation and effect of 2‐amino‐4‐phosphonobutyrate

2000

Acta Physiol Scand

Self Cite

The effect of glycinergic blockade by strychnine and GABAergic blockade by picrotoxin on the intensity-response function and time course of ERG b- and d-wave was investigated in dark and light adapted frog eyecups as well as in chromatically adapted eyecups, in which the responses were predominantly mediated by one photoreceptor type. Both of the blockers markedly increased the maximal response amplitude and thus increased the contrast gain of the mechanisms generating ERG waves. Strychnine but not picrotoxin narrowed the dynamic range of the b-wave in all eyecups. The glycine and GABAergic control on retinal sensitivity however, depended on photoreceptor input. The b-wave sensitivity was increased to the greatest extent when green rods mediated the response; it was slightly increased when the response was mediated by red cones and was not changed at all when red rods mediated the b-wave. On the other hand the d-wave sensitivity was enhanced regardless of photoreceptor input so that it became equal (dark) or even greater (light adapted eyes) than that of the b-wave. Strychnine shortened but picrotoxin increased the implicit time of the b-wave and both the blockers markedly slowed the d-wave time course. Thus the blockers considerably diminished or fully eliminated the initial difference in time course between the ON and OFF response. The glycine- and GABAergic blockade did not principally alter the light adaptation process expressed in decreasing retinal sensitivity, narrowing the dynamic range and speeding the time course of the responses with increasing background illumination.

Section: Experiments With 430 Nm Test Stimuli On 550 Nm Background Stsupporting

confidence: 85%

Section: Discussionsupporting

confidence: 72%

Section: Strychnine Effects Control Seriessupporting

confidence: 63%

Section: Experiments With 430 Nm Test Stimuli On 550 Nm Background Stmentioning

confidence: 99%

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Glycinergic and GABAergic control of intensity-response function of frog ERG waves under different conditions of light stimulation

2000

Acta Physiol Scand

Self Cite

“…This enabled using the results from the first stimulus session in the test experiments as an autocontrol. The V\log I curves of the ERG ON-and OFF-responses to chromatic stimuli (Figs 1, 2, open symbols) were similar to those obtained with white stimuli (see Vitanova et al 1987, Kupenova et al 1991, Popova et al 1995. When the intensity-response curves of the ON-and OFFresponses were obtained in wide range of stimulus intensities, they could not be approximated to one and the same function.…”

Section: Control Experimentssupporting

confidence: 71%

Influence of picrotoxin and strychnine on the spectral sensitivity of the turtle ERG b‐ and d‐wave: I. Dark adaptation

Kupenova

Vitanova

Acta Physiologica Scandinavica

et al. 1997

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The ERG ON- (b-wave) and OFF-response (d-wave) to differently coloured stimuli was studied using a wide range of stimulus intensities in dark adapted turtle retina. The intensity-response curve of the b-wave showed saturation but that of the d-wave, decline in the high-intensity stimulus range. The curves of the relative spectral sensitivity of the ERG ON- and OFF-response were similar and showed a maximum in the longwave part of the spectrum. GABAergic blockade by 50 mumol L-1 picrotoxin caused an increase of the sensitivity, contrast sensitivity and the amplitude range of both ON- and OFF-responses without narrowing of the response dynamic range. In the range of lower stimulus intensities the ON-responses to blue stimuli and the OFF-responses to red stimuli were affected to a greater extent. An increased ERG b- and d-wave sensitivity was also observed during glycinergic blockade by 50 mumol L-1 strychnine. In the low intensity stimulus range the effect was maximal on the ON-response to blue stimuli and on the OFF-responses to 570 nm stimuli. It was concluded that the GABA- and glycinergic systems in the retina equalize rather than make different the relative spectral sensitivities of the ON- and OFF-responses.

Effects of dopamine receptor blockade on the intensity-response function of electroretinographic b- and d-waves in light-adapted eyes

2013

J Neural Transm

The effects of dopamine receptor blockade by sulpiride (D2-class antagonist) and sulpiride plus SCH 23390 (D1-class antagonist) on the V - log I function of the electroretinographic (ERG) b- and d-waves were investigated in light-adapted frog eyes. Sulpiride significantly decreased the absolute sensitivity of the b- and d-waves. The amplitude of the both waves was diminished over the whole intensity range studied. A similar effect on the b-, but not d-wave amplitude was seen during the perfusion with sulpiride plus SCH 23390. The effect on the d-wave amplitude depended on stimulus intensity. The threshold of the d-wave was not significantly altered. The suprathreshold d-wave amplitude was enhanced at the lower stimulus intensities and remained unchanged at the higher ones. The results obtained indicate that the action of endogenous dopamine on the photopic ERG shows clear ON-OFF asymmetry. Participation of different classes of dopamine receptors is probably responsible for this difference.