Microelectrode depth study of electroretinographic b- and d-waves in frog retina

The depth profiles of the b- and d-waves of the electroretinogram were studied in the isolated frog retina placed with its receptor side up. The electrode was introduced into the retina from the receptor side and the reference electrode was placed on the vitreal side. The b-wave was maximum in amplitude in the receptor layer, and decreased as the electrode was advanced proximally from the outer plexiform layer until it disappeared at the inner limiting membrane. The b-wave in the inner plexiform layer was different from that in the distal portion of the inner nuclear layer in form and peak latency. The results suggested that the b-wave is generated in the layers between the inner limiting membrane and the outer plexiform layer, and that at least two processes are involved in the generation of the b-wave. The depth profile of the d-wave resembled that of the b-wave except in the receptor layer; it was recorded in the whole retinal layers as was the b-wave, and decreased as the electrode was advanced proximally until it disappeared at the inner limiting membrane. The peak latency of the d-wave was longer in the inner plexiform layer than in the distal portion of the inner nuclear layer. The results indicated that the d-wave consists of the off-response of the late receptor potential and the postsynaptic components, the latter being generated by a similar mechanism as the b-wave.