title: Effects of picrotoxin on light adapted frog electroretinogram are not due entirely to its action in proximal retina.
abstract: In order to evaluate the site of action of picrotoxin (antagonist of ionotropic GABA receptors) on the electroretinographic (ERG) b- and d-waves, in this study we compared its effects on the intensity-response function of the ERG waves in intact light adapted frog eyecup preparations with its effects in eyecups, where the activity of proximal neurons was blocked by 1 mMN-methyl-d-aspartate (MNDA). Picrotoxin markedly enhanced the b- and d-wave amplitude and slowed the time course of the responses at all stimulus intensities in the intact eyecups. Perfusion with NMDA alone caused significant enhancement of the b-wave amplitude and diminution of the d-wave amplitude without altering their time course in the entire intensity range. When picrotoxin was applied in combination with NMDA, an enhancement of the b-wave amplitude and slowing of its time course were observed at all stimulus intensities. The increase of the b-wave amplitude was significantly higher than that seen in NMDA group. Combined application of picrotoxin and NMDA caused an enhancement of the d-wave amplitude at the lower stimulus intensities and its diminution at the higher ones, while the d-wave time course was delayed over the entire intensity range. The results obtained indicate that a part of picrotoxin effects on the amplitude and time course of the photopic ERG b- and d-waves are due to its action in the distal frog retina.
authors.affiliation: Department of Physiology, Medical Faculty, Medical University, 1431 Sofia, Bulgaria. Electronic address: epopova@abv.bg.
authors.forename: E
authors.initials: E
authors.lastname: Popova
mesh_terms: D000221:Adaptation, Ocular / Q000187:drug effects*; D000704:Analysis of Variance; D000818:Animals; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003623:Dark Adaptation / Q000187:drug effects / Q000502:physiology; D004596:Electroretinography / Q000187:drug effects*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology*; D016202:N-Methylaspartate / Q000494:pharmacology; D010775:Photic Stimulation / Q000379:methods; D010852:Picrotoxin / Q000494:pharmacology*; D011895:Rana ridibunda / Q000502:physiology*; D012160:Retina / Q000187:drug effects / Q000502:physiology*
chemical_list: D000697:Central Nervous System Stimulants; D018690:Excitatory Amino Acid Agonists; D018756:GABA Antagonists; D016202:N-Methylaspartate; D010852:Picrotoxin
keywords: Distal retina; Electroretinogram; Frog; GABA; Picrotoxin; Proximal retina