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At least 1,351 records · Page 75Linked to original sources
PubMed1984

Nucleoside triphosphates and hydrolysis-resistant analogues: effects on PIII responses in the isolated skate retina.

Responses to test flashes were recorded extracellularly from the aspartate-treated, isolated retina of the skate, before and after topical application to the retina of solutions containing GTP, ATP, or certain hydrolysis-resistant analogues. When applied to strongly light-adapted retinas (greater than or equal to 87% bleached), the analogues p(CH2)ppG, p(NH)ppG and p(CH2)ppA induced sustained decreases in threshold of the PIII response. Similar treatment of light-adapted retinas with GTP or ATP also promoted decreases in threshold, but these changes appeared relatively transient. All of the test substances lacked significant activity when applied to dark-adapted (unbleached) retinas. The results are discussed in relation to other studies examining the effects of light on GTP- and ATP-dependent processes within the photoreceptors.

Adaptation, Ocular↗
PubMed1984

Dark-adaptation of the human rod system.

Following substantial bleaching, dark-adaptation thresholds of a complete rod monochromat and of a subject with normal colour vision were measured using a Wright colorimeter. When precautions were taken to ensure that the fixation point fell on the same retinal area during the threshold measurements as during the bleaching period, the dark-adaptation threshold curves of the rod monochromat followed exactly the same course as those of the normal subject subsequent to the cone-rod break of the long-term, normal dark-adaptation curve; irrespective of the intensity and the duration of the bleaching and the wavelength of the test stimulation. In contrast to the normal subject, however, the dark-adaptation curves of the rod monochromat showed no evidence of any cone function at photopic intensities. Furthermore, as opposed to previous measurements which show a simple linear relationship between fraction of bleached rhodopsin and log threshold, the present results show that there is a close linearity between log fraction of bleached rhodopsin and log threshold. This linear relationship is obtained despite varying extents of bleaching and subsequent dark-adaptation periods.

Adaptation, Ocular↗
PubMed1984

Light adaptation in luminosity horizontal cells in the turtle retina. Role of cellular coupling.

Intracellular recordings were made from L-type horizontal cells in the retina of the turtle Clemmys caspica. The test flashes covered a retinal area smaller than the receptive field of the impaled cells. Increment responses were compared between two states of light adaptation that were equal in intensity but differed in spatial pattern. The peak amplitude of the response to a dim test flash was larger when measured during large-field background compared to the one obtained during small-field one. It is suggested that this phenomenon of surround enhancement is due to the cellular coupling between neighboring horizontal cells.

Adaptation, Ocular↗
PubMed1995

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. The results indicate that the action of APB on ERG OFF-response does not depend significantly on GABAergic and glycinergic neurotransmission in frog retina.

Adaptation, Ocular↗
PubMed2004

Localization of dopamine D1-receptor to A-type horizontal cells in the rabbit retina by single cell RT-PCR.

Dopamine is an important neurotransmitter regulating light-dark adaptation in the retina. The effect of dopamine is widespread and dependent on the localization of its receptors. We performed single cell RT-PCR on A-type horizontal cells visually selected from dissociated rabbit retinal neurons. Dopamine D1-receptor mRNA was positively identified. Subsequent sequencing of the fragment showed 82% homology with rat D1 receptor and 87% homology with human D1 receptor. This study supported previous observations that dopamine regulated A-type horizontal cell coupling via D1 receptors at the level of transcription.

Adaptation, Ocular↗
PubMed2005

Photoreceptor adaptation in intrinsically photosensitive retinal ganglion cells.

A rare type of mammalian retinal ganglion cell (RGC) expresses the photopigment melanopsin and is a photoreceptor. These intrinsically photosensitive RGCs (ipRGCs) drive circadian-clock resetting, pupillary constriction, and other non-image-forming photic responses. Both the light responses of ipRGCs and the behaviors they drive are remarkably sustained, raising the possibility that, unlike rods and cones, ipRGCs do not adjust their sensitivity according to lighting conditions ("adaptation"). We found, to the contrary, that ipRGC sensitivity is plastic, strongly influenced by lighting history. When exposed to a constant, bright background, the background-evoked response decayed, and responses to superimposed flashes grew in amplitude, indicating light adaptation. After extinction of a light-adapting background, sensitivity recovered progressively in darkness, indicating dark adaptation. Because these adjustments in sensitivity persisted when synapses were blocked, they constitute "photoreceptor adaptation" rather than "network adaptation." Implications for the mechanisms generating various non-image-forming visual responses are discussed.

Action Potentials↗
PubMed1995

Oxygen consumption in the isolated toad retina.

Retinal O2 utilization was studied to identify the O2 consuming processes in the retina and the spatial distribution of those processes. Neural retina, retinal pigment epithelium and choroid were dissected from the toad eye and superfused with an oxygenated Ringer's solution. Double-barreled microelectrodes were used to measure O2 and local voltage simultaneously within the retina in both light and dark adaptation. The profile of PO2 was measured during a withdrawal of the electrode tip across the retinal pigment epithelium and through the neural retina. The PO2 decreased through the distal retina, reaching a minimum in the inner segment or outer nuclear layer, and then increased steadily through the proximal retina. From fitting PO2 profiles measured in the dark-adapted retina to a three-layer diffusion model, O2 consumption was found to be 1.0 +/- 0.4 and 0.4 +/- 0.3 ml O2 (100 g min)-1 in the outer and inner halves of the retina, respectively. Light decreased consumption in both halves of the retina. In steady illumination (500 nm) that saturated the ERG b- and c-waves, O2 utilization decreased significantly to 48% and 68% of the dark values in the outer and inner retina, respectively. When Na+ was removed from the superfusate to inhibit the photoreceptor Na+/K+ pump, O2 consumption in the outer retina decreased by about the same amount as in light, but O2 consumption in the inner retina was not significantly affected.

Adaptation, Ocular↗