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. The intensity-response functions of both the ERG waves fitted well to the Michaelis-Menten equation (V/Vmax = In/(In + sigma n). A sigma-value decrease and a Vmax and n increase were observed after picrotoxin treatment. The analysis of the intensity-response functions shows that, under a wide range of backgrounds, the GABAergic neurons influence the ON- and OFF-response in the distal retina in a similar way. They decrease the gain and the contrast gain of the b- and d-wave generating neuronal mechanisms and widen the intensity span of their responses under given background illumination. The GABAergic system is involved also in response 'scaling' in the ON- and OFF-channels in the distal retina. A very important effect in this respect seems to be the equalization of the range of the responses to increment stimuli under different backgrounds.
Kupenova
P
P
Department of Physiology, Medical Academy, Sofia, Bulgaria.
Vitanova
L
L
Mitova
L
L
Belcheva
S
S
D000222:Adaptation, Physiological / Q000187:drug effects*; D000818:Animals; D004596:Electroretinography; D007395:Interneurons / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000502:physiology; D010852:Picrotoxin / Q000494:pharmacology*; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D014426:Turtles / Q000502:physiology*; D005680:gamma-Aminobutyric Acid
D010852:Picrotoxin; D005680:gamma-Aminobutyric Acid