J Physiol Volume 586, Number 22, 5419-5436, November 15, 2008 DOI: 10.1113/jphysiol.2008.160028
Dark adaptation recovery of human rod bipolar cell response kinetics estimated from scotopic b-wave measurements
A. M. Cameron1,
L. Miao1,
R. Ruseckaite1,
M. J. Pianta2 and
T. D. Lamb1
1 Division of Neuroscience, John Curtin School of Medical Research and ARC Centre of Excellence in Vision Science, Australian National University, Canberra, ACT 0200, Australia
2
Department of Optometry and Vision Sciences, University of Melbourne, Carlton, Victoria 3053, Australia
We recorded ganzfeld scotopic ERGs to examine the responses of human rod bipolar cells in vivo, during dark adaptation recovery following bleaching exposures, as well as during adaptation to steady background lights. In order to be able to record responses at relatively early times in recovery, we utilized a ‘criterion response amplitude’ protocol in which the test flash strength was adjusted to elicit responses of nearly constant amplitude. In order to provide accurate and unbiased measures of response kinetics, we utilized a curve-fitting procedure to fit a smooth function to the measured responses in the vicinity of the peak, thereby extracting both the time-to-peak and the amplitude of the responses. Following bleaching exposures, the responses exhibited both desensitization and accelerated kinetics. During early post-bleach recovery, the flash sensitivity and time-to-peak varied according to a power-law expression (with an exponent of 6), as found in the presence of steady background light. This light-like phenomenon, however, appeared to be set against the backdrop of a second, more slowly recovering ‘pure’ desensitization, most clearly evident at late post-bleach times. The post-bleach ‘equivalent background intensity’ derived from measurements of flash sensitivity faded initially with an S2 slope of 
0.24 decades min–1, and later as a gentle S3 tail. When calculated from kinetics, the results displayed only the S2 slope. While the recovery of rod bipolar cell response kinetics can be described accurately by a declining level of opsin in the rods, the sensitivity of these cells is reduced further than expected by this mechanism alone.
(Received 18 July 2008;
accepted after revision 16 September 2008;
first published online 18 September 2008)
Corresponding author A. M. Cameron and T. D. Lamb: Division of Neuroscience, John Curtin School of Medical Research and ARC Centre of Excellence in Vision Science, Australian National University, Canberra, ACT 0200, Australia. Email: allison.cameron{at}anu.edu.au and trevor.lamb{at}anu.edu.au
Copyright © 2008 The Physiological Society.
