Pharmacologically defined components of the normal porcine multifocal ERG.

Multifocal electroretinograms (mfERG) from isoflurane anesthetized pigs were recorded and sequential application of TTX, NMDA, APB and PDA were used to identify contributions to the mfERG from inner retinal neurons, ON-pathway, OFF-pathway and photoreceptors. The cellular origins of the first-order kernel (K1) and the first slice of the second-order kernel (K2.1) porcine mfERG are contributed from both inner and outer retina. For the K1 waveform, the n1 involved responses of cone photoreceptors and OFF-bipolar cells. The leading edge of p1 is dominated by ON-bipolar cell depolarization. The rear edge of p1, n2 and p2 are dominated by ON-bipolar activities and shaped by the activities of OFF-bipolar cells and retinal cells with NMDAr and voltage-gated sodium channels other than ganglion cells. The p3 is mainly inner retinal activities. For the K2.1 waveform, the p1 and n1 are the summation of activities of ON-, OFF-bipolar cells and retinal cells rich in NMDAr and voltage-gated sodium channels other than ganglion cells. The p2 seems to be related to the ganglion cells. Better understanding of the cellular origins of the normal porcine mfERG will be useful for comparing and defining the functional changes that may occur in diseased retinas.