TASK-1 and TASK-3 show high levels of mRNA accumulation in the locus ceruleus; TWIK-1 is highly expressed by adjacent mesencephalic trigeminal neurons. Panels show dark-field images of coronal sections through the dorsolateral pons corresponding to autoradiograms in Figure 1D. Arrowheads in each panel mark the approximate boundary of the locus ceruleus, which had high levels of labeling for TASK-1 (A) and was even more densely labeled for TASK-3 (B). Large mesencephalic trigeminal neurons are located lateral to the locus ceruleus; these neurons showed high levels of TWIK-1 (arrow in C). Scale bar, 300 μm.