Effect of kainic acid and NMDA on the pattern electroretinogram, the scotopic threshold response, the oscillatory potentials and the electroretinogram in the urethane anaesthetized cat

Abstract

Kainic acid (KA, 12.5–100 nmol) or N-methyl- d-aspartate (NMDA 25–250 nmol) was injected into the vitreous of one eye of urethane anaesthetized 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 oscillatory potentials (OPs), PERG and focal ERG (FERG). At 50 nmol KA, the b-wave and scoptic threshold response (STR) were normal. At 100 nmol KA, the STR was absent and the b-wave reduced by over 50%. OPs and STRs were 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 dendrites of ganglion cells. NMDA damage was slight with <200 nmol. These data show that the cat PERG has a proximal component which is very sensitive to low doses of KA; the PERG and FERG are very similar; the STR 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.