Sustained and transient contributions to the rat dark-adapted electroretinogram b-wave

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. © 2013 trung m. dang et al.