title: Post-receptoral contributions to the rat scotopic electroretinogram a-wave.
abstract: The electroretinogram is a widely used objective measure of visual function. The best characterised feature of the full-field dark-adapted flash ERG, is the earliest corneal negativity, the a-wave, which primarily reflects photoreceptoral responses. However, recent studies in humans and primates show that there are post-receptoral contributions to the a-wave. It is not clear if such contributions exist in the rat a-wave. We consider this issue in the rat a-wave, using intravitreal application of pharmacological agents that isolate post-receptoral ON-pathways and OFF-pathways. In anaesthetised adult long Evans rats, we show that the ON-pathway (2-amino-4-phosphonobutyric acid, APB sensitive) makes negligible contribution to the a-wave. In contrast, CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) or PDA (cis-piperidine-2,3-dicarboxylic acid) sensitive mechanisms modify the a-wave in two ways. First, for bright luminous energies, OFF-pathway inhibition (CNQX or PDA) results in a 22% reduction to the early phase of the leading edge of the a-wave up to 14 ms. Second, OFF-pathway inhibition removed a corneal negativity that resides between the a-wave trough and the b-wave onset.
authors.affiliation: Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Australia.
authors.forename: Trung M
authors.initials: TM
authors.lastname: Dang
authors.forename: Tina I
authors.initials: TI
authors.lastname: Tsai
authors.forename: Algis J
authors.initials: AJ
authors.lastname: Vingrys
authors.forename: Bang V
authors.initials: BV
authors.lastname: Bui
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000008:administration & dosage; D000613:Aminobutyrates / Q000008:administration & dosage; D000818:Animals; D003623:Dark Adaptation / Q000502:physiology; D004596:Electroretinography / Q000379:methods*; D058449:Intravitreal Injections; D055254:Night Vision / Q000187:drug effects / Q000502:physiology*; D010875:Pipecolic Acids / Q000008:administration & dosage; D051381:Rats; D020318:Rats, Long-Evans; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*
chemical_list: D000613:Aminobutyrates; D010875:Pipecolic Acids; C029262:2,3-piperidinedicarboxylic acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; C012729:2-amino-4-phosphonobutyric acid