Original Research Article

Documenta Ophthalmologica

, 122:149

First online:

Post-receptoral contributions to the rat scotopic electroretinogram a-wave

  • Trung M. DangAffiliated withDepartment of Optometry and Vision Sciences, University of Melbourne
  • , Tina I. TsaiAffiliated withDepartment of Optometry and Vision Sciences, University of Melbourne
  • , Algis J. VingrysAffiliated withDepartment of Optometry and Vision Sciences, University of Melbourne
  • , Bang V. BuiAffiliated withDepartment of Optometry and Vision Sciences, University of Melbourne Email author 

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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.

Keywords

Electroretinogram A-wave Rat Photoreceptoral Post-receptoral