Purinergic modulation of frog electroretinographic responses: The role of the ionotropic receptor P2X7.

The contribution of the purinergic receptors P2X7 (P2X7Rs) to the electroretinographic (ERG) responses was studied by testing the effects of the selective P2X7R antagonist A438079 and the selective P2X7R agonist Bz-ATP on the electroretinograms obtained in perfused frog (Rana ridibunda) eyecup preparations under a variety of stimulation conditions. The P2X7R blockade by 200 µM A438079 diminished the amplitude of the photoreceptor components: the a-wave and the pharmacologically isolated mass receptor potential. In the pure rod-driven and pure cone-driven responses, the amplitude of the postreceptoral ON (b-wave) and OFF (d-wave) components was also diminished.

Ionotropic purinergic receptors P2X in frog and turtle retina: glial and neuronal localization.

Purinergic signaling is represented in both the peripheral and central nervous system (CNS), and in particular in the retina, which may be regarded as a part of the CNS. While purigenic signaling is relatively well studied in mammalian retinas, little is known about it in retinas of lower vertebrates. The aim of present study was to investigate, using immunocytochemistry, the distribution of purinoreceptors P2X in retinas of frog and turtle, which are appropriate models of the brain neuron-to-glia interactions.

NR2C and NR2D subunits of NMDA receptors in frog and turtle retina.

Glutamate NMDA (N-methyl-D-aspartate) receptors are widely distributed in the central nervous system where they are involved in cognitive processes, motor control and many other functions. They are also well studied in the retina, which may be regarded as a biological model of the nervous system. However, little is known about NR2C and NR2D subunits of NMDA receptors, which have some specific features as compared to other subunits.

Immunocytochemical study of NR1, NR2A and NR2B subunits of NMDA receptor in frog retina (Rana ridibunda).

The NMDA receptors are ionotropic glutamate receptors that are involved in a variety of functions in the nervous system and in particular in the retina. They are composed of NR1 and NR2 subunits. The NMDA receptors have been fairly well studied in the retina of mammals, however, there is only limited information concerning these receptors in the retinas of lower vertebrates.

GABAa and GABAc receptor-mediated modulation of responses to color stimuli: electroretinographic study in the turtle Emys orbicularis.

GABAergic transmission is involved in color coding in the retina. The specific contribution of different GABA receptors to spectral sensitivity of the retinal responses is not well characterized. We studied GABAa and GABAc receptor-mediated effects on the intensity-response functions of the electroretinographic ON (b-wave) and OFF (d-wave) responses to color stimuli.

GABAa and GABAc receptor mediated influences on the intensity-response functions of the b- and d-wave in the frog ERG.

We assessed the contribution of GABAa and GABAc receptors to GABAergic effects on b- and d-wave in frog ERG in a wide range of light stimulation conditions. The amplitude of both b- and d-wave was increased during GABAa receptor blockade by bicuculline as well as during additional GABAc receptor blockade by picrotoxin. The effects of GABAa receptor blockade were more pronounced in light adaptation conditions.

AMPA and kainate receptors in turtle retina: an immunocytochemical study.

1. Glutamate is one of the main neurotransmitters in the retina. Its effects are mediated by a large number of ionotropic and metabotropic receptors.

Non-NMDA receptors in frog retina: an immunocytochemical study.

Glutamate is one of the main neurotransmitters in the retina. Its effects are mediated by a large number of ionotropic and metabotropic membrane receptors. The distribution of ionotropic AMPA receptor subunits GluR1-4, kainate receptor subunits GluR5-7 and KA2, delta receptors 1-2, as well as the metabotropic receptor mGluR6 were studied in the frog retina.

Immunocytochemical study of glycine receptors in the retina of the frog Xenopus laevis.

The expression of glycine receptors in the retina of clawed frog, Xenopus laevis was studied immunocytochemically. Glycine receptors (GlyRs), as revealed by means of several different antibodies, were mainly distributed in the inner (IPL) and the outer plexiform layers. Their composition was determined to include alpha2 and alpha3 subunits.

Immunocytochemical localization of glycine and glycine receptors in the retina of the frog Rana ridibunda.

Glycine and glycine receptors (GlyRs) were analyzed immunocytochemically in the retina of the frog Rana ridibunda. Glycine was localized to somata of glycinergic amacrine and interplexiform cells. Approximately 50% of the cells in the amacrine cell layer were found to be glycinergic.

Participation of the GABAergic system in the action of 2-amino-4-phosphonobutyrate on the OFF responses of frog retinal ganglion cells.

Perfusion of dark adapted frog eyecups with the ON pathway blocker 2-amino-4-phosphonobutyrate (APB) not only abolished the ganglion cells (GCs)' ON responses and the ERG b-wave, but it markedly potentiated the OFF responses of all ON-OFF and phasic OFF GCs and the d-wave amplitude of a simultaneously recorded ERG as well. The blockade of GABA(A) and GABA(C) receptors by picrotoxin eliminated this potentiating effect in 24 out of 41 GCs, although in the rest of the cells it did not produce any change in the APB effect. On the other hand, the d-wave potentiation was preserved during the GABAergic blockade in all experiments.

Effect of GABAergic blockade on light responses of frog retinal ganglion cells.

The effect of GABAergic blockade by picrotoxin on ganglion cells (GC) activity was investigated in perfused dark adapted eyecups of frog (Rana ridibunda). PT had diverse effects on the light responses of GC in contrast to its uniform potentiating effect on the amplitude of the ERG b- and d-wave. In some (n=32) of PT-sensitive ON-OFF GC the ON and OFF responses were changed in a similar manner (both responses were potentiated or both were inhibited), but in the other (n=10) the both responses were changed in a different manner.

Immunocytochemical and electrophysiological characterization of GABA receptors in the frog and turtle retina.

The expression of GABA receptors (GABARs) was studied in frog and turtle retinae. Using immunocytochemical methods, GABA(A)Rs and GABA(C)Rs were preferentially localized to the inner plexiform layer (IPL). Label in the IPL was punctate indicating a synaptic clustering of GABARs.

Effect of 2-amino-4-phosphonobutyrate on the OFF responses of frog retinal ganglion cells and local ERG after glycinergic blockade.

Perfusion with the ON channel blocker 2-amino-4-phosphonobutyrate (APB) of dark adapted frog eyecups not only abolished the ganglion cells' (GC) ON responses and the ERG b-wave, but markedly potentiated the OFF responses of ON-OFF and phasic OFF-GCs and the d-wave amplitude of simultaneously recorded local ERG. Glycinergic blockade by strychnine prevented this potentiating effect in 31 out of 69 GCs, but did not change it at all in the other cells. At the same time the d-wave potentiation was preserved during the glycinergic blockade in all eyecups.

Influence of picrotoxin and strychnine on the spectral sensitivity of the turtle ERG b- and d-waves: II. Light adaptation.

The aim of the present work was to investigate the role of GABA and glycine, the two main inhibitory neurotransmitters in the retina, in the spectral sensitivity coding under conditions of light adaptation. To study this question, spectral sensitivity curves, based on the turtle ERG responses to stimuli of different wavelengths, were constructed. The spectral sensitivity curves.

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

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.

The application of in vitro isolation, cryopreservation and patch-clamp microelectrode recording methods to adult rat thymic nurse cells.

Characterisation of the ionic mechanisms possessed by immune cells has begun to reveal a range of transmembrane ion channel properties which may have immunological significance. Since thymic epithelial cells appear to influence selection of the T cell repertoire, understanding their membrane physiology may be of importance. A method is therefore outlined for the targeting of patch-clamp electrophysiological measurements to acutely isolated, fresh and cryopreserved adult rat thymic nurse cells.

Effect of 2-amino-4-phosphonobutyrate on ERG OFF-response after glycinergic and GABAergic blockade.

Superfusion with 200 microM 2-amino-4-phosphonobutyrate (APB) of dark and chromatically adapted frog eyecups caused marked potentiation of the ERG OFF-response (d-wave). Blockade of the glycinergic synapses by strychnine did not change this effect at all. Blockade of the GABAergic synapses by picrotoxin slightly diminished the effect of APB in chromatically-adapted eyes with isolated cones' activity, and did not change it in dark-adapted eyes.

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

The intensity-response (V/log I) function of ERG OFF response (d-wave) in dark and light adapted superfused frog eyecups was investigated before and after blockade of the retinal ON channel by 2-amino-4-phosphonobutyrate (APB). The V/log I function of the dark adapted d-wave had two distinct components, each of them consisting of an ascendent and descendent part. In eyes adapted to mesopic or photopic background the V/log I function had only one component.

Comparative investigation of retinal responses to brief light stimuli: 2-amino-4-phosphonobutyrate studies--II. Turtle retina (Emys orbicularis).

1. Electroretinogram (ERG) and responses of single ganglion cells to 75 microseconds light flashes, presented on two different backgrounds, were studied. Additionally, stimulation with long lasting stimuli (ordinarily 5 sec ON-, 15 sec OFF-) was used.

Comparative investigation of retinal responses to brief light stimuli: 2-amino-4-phosphonobutyrate studies--I. Frog retina, Rana ridibunda.

1. Electroretinogram (ERG) and responses of single ganglion cells to 75 microseconds light flashes, applied at two different backgrounds, were studied. Additionally, a stimulation with long-lasting stimuli (ordinarily 5 sec ON-, 5 sec OFF-) was used.

Participation of the GABAergic system of the turtle retina in the light adaptation process.

A comparative study was made of the ERG b- and d-wave intensity-response functions before and after GABAergic blockade by means of 0.4 mmol l-1 picrotoxin. A wide range of background intensities, including part of the high photopic range, were used.

Comparative studies on the effects of some enkephalin agonists on the ERG of frog and turtle.

1. Effects of mu-agonist morphine in a concentration of 1.10(-5)-1.

Participation of GABA in the sensitivity control of the OFF-response in the turtle ERG.

The intensity-response--V/log I, function of the d-wave in the turtle ERG was investigated before and after blockade of the GABAergic transmission by 0.4 mmol/l picrotoxin (PT) under conditions of two adapting background illuminations--0.01 and 10 lx.