The s-wave of the multifocal electroretinogram in cats.
PURPOSE: To characterize the s-wave of the multifocal electroretinogram (mfERG) in cats, and to determine the contribution of the inner retina to the s-wave by examining the effects of tetrodotoxin (TTX) and N-methyl D: -aspartate (NMDA) injected into the vitreous cavity. METHODS: mfERGs were recorded from 15 eyes of 15 male cats under general anesthesia. The stimulus consisted of 37 elements, and the luminance of the bright and the black elements were 200 and 4 cd/m2, respectively. The stimuli were presented in a pseudorandom binary m-sequence at six different base periods (bpds) from 13.3 to 426.7 ms. Fifty microliters of 7.0 microM TTX followed by 50 microl of 4.0 mM NMDA were injected into the vitreous cavity. RESULTS: The shape of the mfERGs in the cats resembled that in humans. The s-wave appeared on the descending limb of P1, as seen in human mfERGs, in 11 eyes, and the s-wave amplitude increased significantly as the bpd was increased. TTX and NMDA resulted in the disappearance of the s-wave at all bpds, while the amplitude of P1 remained unchanged. CONCLUSIONS: The s-wave is present in the mfERG in the cat, and its loss following injections of TTX and NMDA supports the view that the s-wave reflects the function of the ganglion cells and their axons.