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Fig. 4 Identification of known neuroactive compounds with anticonvulsant activity in the zebrafish embryo. Known inhibitors of neural activity were identified within the Microsource Spectrum Collection on the basis of their concentration-dependent suppression of PTZ-induced fos expression and inhibition of PTZ-induced locomotor activity. Compounds were administered to 50 hpf embryos for 90 minutes in 96-well plates, at a final concentration of 0.9, 2.7, 8.2, 24.7 or 74.1 μM (as indicated), then 20 mM PTZ was added and embryos were incubated for a further 60 minutes, before being fixed and analysed for expression of fos. In parallel, 4-day-old zebrafish larvae were exposed to the same range of compound concentrations in 48-well plates for 90 minutes, then PTZ was added and larvae were incubated for a further 10 minutes. 48-well plates were then transferred to the Viewpoint Zebrabox for live tracking of locomotor activity over a 10 minute period. Black, green and red traces indicate swimming speeds of 0–1.5, 1.5–6 and >6 mm/second, respectively. (A) Ethinylestradiol; (B) allopregnanolone; (C) nimodipine; (D) nitrendipine; (E) methiothepin; (F) pimozide. (G) The anticonvulsant activity of the positive control compound VPA is shown, for comparison.