Lght Evoked Potentials In a Carp Visual Center During Retinal Bicuculline Application

Abstract

Abstract: : Purpose: To investigate visual center light response changes provoked by bloking retinal GABAa receptor in the rod– or cone–dominated conditions. Methods: Evoked potentials (EP) in a carp optic tectum and electroretinograms (ERG) in response to light stimuli were simultaneously registered under the dark– or light–adapted conditions. Monochromatic green (λ = 528 nm) or red (λ = 658 nm) light were used for light stimulation (stimulus duration 1 ms) and for adaptive lights (quantum output for both light stimuli was 4.5x10⁹photons/mm²x sec , for both light backgrounds – 4.5x10⁸photons/mm²x sec ). Retinal GABAa receptor inhibition was achieved by the retinal surface superfusion with bicuculline solution (10^–5 M). Results: In the dark bicuculline application did not change tectal EP to green and red light ON–set, but decreased rod–driven ERG b–wave amplitudes to both light stimuli (to 65±21% and to 72±20% of control level ). In conditions of red light adaptation bicuculline increased cone–dominated EP to red light ON–set more effectively (152±21%) than the EP to the green light ON–set (122±10%). Under these conditions ERG to red light did not change, but ERG b–wave amplitude evoked by the green light significantly decreased. When the retina was adapted to the green light, bicuculline also increased both tectal EP amplitudes to light ON–set (for green light–197±50% and for red light –190±40%), and the ERG b–wave amplitude after green (133±21%) and red light (143±20%) stimuli. Bicuculline also either greatly (up to 150–200% of the control level) enhanced tectal EP to the light OFF–set or provoked its appearance independently of the adaptation conditions and wavelength of the light stimuli. Conclusions: Blocking retinal GABAa receptors with bicuculline increases tectal EP to light OFF–set, cone–driven ERG b–wave and tectal EP to the light ON–set. The same dose of bicuculine also decreased rod–driven ERG b–wave, but did not significantly affect rod–driven tectal EP in response to the light ON–set .

Keywords: electrophysiology: non–clinical • retina • superior colliculus/optic tectum