Fig. 2

Pentylenetetrazole and picrotoxin treatments induce expression of the synaptic-activity-regulated gene fos in 2-day-old zebrafish embryos, and this expression is suppressed by the anticonvulsant drug VPA. (A) Treatment of 50 hpf embryos with the GABA_A receptor inhibitors PTZ (20 mM) or picrotoxin (300 μM) caused rapid induction of fos expression in the forebrain within 30 minutes of addition of drug, which was increased at 60 and 90 minutes after initial addition. Treatment of 50 hpf embryos with PTZ (20 mM) also induced strong fos expression in the trunk muscle after 30, 60 and 90 minutes of treatment, whereas treatment with picrotoxin (300 μM) only induced detectable fos expression after 90 minutes of treatment. (B) PTZ-induced expression of fos in the developing CNS is greatest in the ventral telencephalon (subpallium; arrows) and ventral diencephalon (arrowheads) within the forebrain of 50 hpf embryos. In the ventral diencephalon, the fos expression domain induced by PTZ encompasses the preoptic area, posterior tuberculum and hypothalamus. (C) Treatment of embryos with the anticonvulsant VPA suppresses PTZ- and picrotoxin-induced expression of fos in the ventral telencephalon and ventral diencephalon. 50 hpf embryos were incubated for 60 minutes in E3 medium containing 1 mM VPA or E3 medium only (no VPA), after which either 20 mM PTZ (+PTZ) or 300 μM picrotoxin (+Picrotoxin) was added and embryos were incubated for a further 90 minutes. Embryos were then fixed and analysed for expression of fos transcripts.