PURPOSE: The goal of this study was to investigate the effects of bicuculline(BIC) on the excitability of visual cortex, observe the induction of epileptiform activity and define the characteristics of spontaneous activity. METHODS: We divided 19 to 23-day-old Sprague-Dawley rats into 3 groups by the concentration of BIC:5(n=10), 20(n=12), and 40(n=10) microM. The slices from the rats were incubated in artificial CSF for 1 hour, and then extracellular recordings were performed. RESULTS: Spontaneous epileptiform activities were observed in all of the BIC groups. The latencies of 5, 20, and 40 microM BIC were 31.6+/-13.0, 34.0+/-11.9, and 6.3+/-3.2 min. The frequencies of 5, 20, and 40 microM BIC were 1.1+/-0.5, 2.7+/-1.8, and 19.1+/-23.3 min-1. The amplitudes of 5, 20, and 40 microM BIC were 5.4+/-1.4, 6.9+/-0.9, 11.1+/-1.3 mV. The durations of 5, 20, and 40 microM BIC were 444.6+/-169.1, 865.2+/-151.2, and 1,014.7+/-613.8 ms. CONCLUSION: BIC is associated with increased excitability in the visual cortex and induces spontaneous epileptiform activities. This induction was decreased by D-AP5 or CNQX.