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Journal of Ophthalmology
Volume 2013 (2013), Article ID 352917, 13 pages
http://dx.doi.org/10.1155/2013/352917
Research Article

Sustained and Transient Contributions to the Rat Dark-Adapted Electroretinogram b-Wave

Department of Optometry and Vision Sciences, University of Melbourne, 4th Floor, 162 Alice Hoy Building, Monash Road, Parkville, VIC 3010, Australia

Received 31 October 2012; Accepted 31 January 2013

Academic Editor: Andrew G. Lee

Copyright © 2013 Trung M. Dang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The most dominant feature of the electroretinogram, the b-wave, is thought to reflect ON-bipolar cell responses. However, a number of studies suggest that the b-wave is made up of several components. We consider the composition of the rat b-wave by subtracting corneal negative components obtained using intravitreal application of pharmacological agents to remove postreceptoral responses. By analyzing the intensity-response characteristic of the PII across a range of fixed times during and after a light step, we find that the rat isolated PII has 2 components. The first has fast rise and decay characteristics with a low sensitivity to light. GABAc-mediated inhibitory pathways enhance this transient-ON component to manifest increased and deceased sensitivity to light at shorter (<160 ms) and longer times, respectively. The second component has slower temporal characteristics but is more sensitive to light. GABAc-mediated inhibition enhances this sustained-ON component but has little effect on its sensitivity to light. After stimulus offset, both transient and sustained components return to baseline, and a long latency sustained positive component becomes apparent. The light sensitivities of transient-ON and sustained-OFF components are consistent with activity arising from cone ON- and OFF-bipolar cells, whereas the sustained-ON component is likely to arise from rod bipolar cells.