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

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.

Ionotropic GABA Receptors and Distal Retinal ON and OFF Responses

“…Dong and Hare [ 232 ] argue that one of the most important functions of the GABA C input to rod bipolar cells is to make the scotopic b-waves more transient, especially those elicited by dim stimuli. However, results of many other authors indicate that the GABA C receptor blockade significantly diminishes the amplitude of the scotopic b-wave in addition to slowing down its kinetics ( rodents : [ 153 , 223 , 224 , 226 , 227 ]; rabbit : [ 233 ]) ( Table 3 ). The sensitivity and operational range of the scotopic b-wave are also reduced in GABA C receptor knockout mice and in wild type mice with pharmacologically blocked GABA C receptors [ 153 ].…”