CHANGES IN PLASMA-GLUCOSE LEVEL AFFECT ROD-ERG BUT NOT CONE-ERG IN THE ANESTHETIZED CAT

1. Changes in plasma glucose have been shown previously to affect rod- driven electroretinogram (ERG) and optic nerve response, as well as th e scotopic threshold response (STR) in the arterially perfused cat eye . 2. This study addressed the question of whether well controlled chan ges in plasma glucose affect the rod- vs cone-driven ERG of the anesth etized cat. The rod ERG was recorded at intensities of up to 1.5 log u nits above b-wave threshold, and the cone ERG in the presence of a whi te full-field background of 320 mW/m2. 3. Transient infusions of gluco se during somatostatin infusion (to block hormone secretion of the pan creas) were used to increase plasma glucose, while infusions of insuli n were used to decrease plasma glucose. 4. We found that the rod-drive n b-wave and the STR are sensitive to small changes in plasma glucose whereas the cone-driven b-wave is not. 5. Fast and slow PIII, isolated by intravitreal aspartate and elicited by longer pulses of light, wer e not affected by large changes in plasma glucose. 6. These results ob tained in vivo confirm and extend previous observations in vitro in th e perfused cat eye, revealing another disparity in the neurophysiology and metabolism of the rod and cone systems. 7. The dark-adapted cat r etina appears to be, considering its needs, only marginally supplied w ith glucose, as shown by the glucose sensitivity of the rod-driven b-w ave and STR.