Effect of MPTP on zebrafish embryos. ETvmat2:GFP embryos untreated (A–D) or treated with 20 μg/ml (E–H) or 40 μg/ml (I–L) MPTP from 24 hpf to 5 dpf were examined at the last day. Photos were taken under a fluorescence microscope in ventral views (A, B, E, F, I, J), and whole-mount embryos after th in situ hybridization are in dorsal (C, G, K) and lateral (D, H, L) views, with rostral to the left. The neural clusters of ventral diencephalon and hypothalamus at a deep focal plane reduced significantly after MPTP exposure (E, I), while neural clusters located more dorsally and appeared at a shallow focal plane were almost unaffected (F, J). Similar reduction of ventral diencephalic and pretectal catecholaminergic clusters after MPTP treatment was observed with TH staining (G, H, K, L). Note that TH population 1 and 6 (G) and the pretectal cluster (G, H) were already eliminated after exposure to 20 μg/ml MPTP. (M) A schematic diagram representing the MPTP-sensitivity of different monoaminergic neuronal groups. 1, 2, 4, 5, 6: ventral diencephalic TH populations; DC: diencephalic catecholaminergic cluster; Hc: caudal hypothalamus neural cluster; Hi: intermediate hypothalamus neural cluster; HyV: hypothalamic vmat2-expression cluster; LC: locus coeruleus; Pa: neural cluster of paraventricular organ; Pt: pretectal neural cluster; PtC: pretectal catecholaminergic cluster; PtV: pretectal vmat2-expression cluster; PTa: anterior group of the posterior tubercular neurons; PTp: posterior group of the posterior tubercular neurons; Ra: raphe nuclei; Te: telencephalic neurons. Hi, highly MPTP-sensitive; Mo, moderately MPTP-sensitive; Re, MPTP-resistant.