Fig. 7.

Detection of secondary motoneurons by simultaneous GFP imaging and zn5 immunohistochemistry. A photomicrograph of the rostral spinal cord from a 66 hpf transgenic islet-1-GFP embryo that was exposed to 33 μm nicotine from 22 to 66 hpf is shown. Red fluorescence indicates zn5-positive cells; the green fluorescence is from the GFP expression. Secondary motoneurons (zn5) are abundant at this developmental point; however, they do not express GFP. The few dorsal GFP-positive cells are likely to be interneurons. This rules against the idea that nicotine is inducing apoptosis in spinal secondary motoneurons of zebrafish embryos. The secondary motoneurons are indeed present; they just fail to express GFP. Scale bar, 20 μm.