EFFECT OF KAINIC ACID AND NMDA ON THE PATTERN ELECTRORETINOGRAM, THE SCOTOPIC THRESHOLD RESPONSE, THE OSCILLATORY POTENTIALS AND THE ELECTRORETINOGRAM IN THE URETHANE-ANESTHETIZED CAT

Kainic acid (KA, 12.5-100 nmol) or N-methyl-D-aspartate (NMDA 25-250 n mol) was injected into the vitreous of one eye of urethane anaesthetiz ed cats, Pattern electroretinograms (PERGs) were recorded to transient contrast reversing bars. Scotopic luminance electroretinograms (ERGs) were recorded to blue flashes. All doses of KA reduced the oscillator y potentials (OPs), PERG and focal ERG (FERG). At 50 nmol KA, the b-wa ve and sceptic threshold response (STR) were normal. At 100 nmol KA, t he STR was absent and the b-wave reduced by over 50%. OPs and STRs wer e reduced in all NMDA injected eyes. NMDA at 25 nmol enhanced the FERG , PERG, and b-wave and high doses (above 150 nmol) reduced them. Light microscopic examination of retinas showed 25 nmol KA only damaged den drites of ganglion cells. NMDA damage was slight with < 200 nmol. Thes e data show that the cat PERG has a proximal component which is very s ensitive to low doses of KA; the PERG and FERG are very similar; the S TR and PERG are generated by different structures and that the OPs and the FERG and PERG are all generated close to the ganglion cell layer, proximal to the STR.