Changes in [Ca2+]0, [K+]0 and neuronal activity during oenanthotoxin-induced epilepsy in cat sensorimotor cortex.

Effects of the convulsant drug oenanthotoxin on field potentials, neuronal discharges and extracellular free Ca2+ and K+ concentrations were studied in the sensorimotor cortex of cats. Fifteen to 20 min after topical OETX application spike activity developed (surface negative, deeper layers positive) with a frequency of 0.5-1/sec. With the maturation of the focus spikes became multipeaked and the reversal point of field potential polarity shifted deeper into the cortex. Spontaneous seizures developed when the spike activity had become negative in polarity in recording depths of 1300 micron below the cortical surface. Spontaneous seizures were associated with large rises in [K+]0 and reductions in [Ca2+]0 (delta [K+]0, delta [Ca]0). The latter were often larger than maximum changes in normal cortex. The decay in [Ca2+]0 associated with spontaneous seizures tended to precede the onset of ictal activity. The findings suggest that OETX, like other epileptogenic drugs, uses Ca2+-dependent mechanisms for the initiation of epileptiform activity.