THE LATE POSITIVE RETINAL POTENTIAL IN DOGS

The late positive potential of the mammalian electroretinogram has bee n called the 'PI' or the 'c-wave' potential. It is unusual among retin al potentials because its peak implicit time increases in response to increasing stimulus intensity and because it cannot be demonstrated co nsistently in small samples of normal humans or normal dogs. We record ed wideband (DC-1 kHz) responses from 34 normal Beagles or dogs of sim ilar size. Of the 34, 11 produced a late positive potential set that s atisfied the criteria for c-waves. Multiple aspartate injections alway s increased c-wave amplitude and stimulus-response linearity in all 'p roducers'. Non-producers were never converted to producer status by as partate blocking of the inner retina. Interaction of late positive and negative potentials and the possible influence of normal individual v ariations in the trans-epithelial potential are discussed. Individual mammal c-wave production is controlled by outer retinal phenomena whic h vary between individuals.