Dopamine Signaling Stimulates the Hedgehog Pathway by Attenuating cAMP/PKA Activity (A) Pergolide increases patched2 (ptch2) expression in in situ hybridization on spinal cross-sections, retaining the ventrodorsal expression gradient (exposure 24–33 hpf). (B) PCR indicates a dose-dependent increase in patched2 expression after pergolide exposure (Kruskal-Wallis, p = 0.0102 with Dunn’s multiple comparison, p < 0.05). (C) Gli2b morpholino inhibits development of islet1:GFP+ motor neurons. This is not rescued by pergolide (56 hpf), capable of promoting motor neuron development in siblings (51 hpf) (p < 0.01, p < 0.0001). (D) NPA partially rescues impaired development of HB9 immunolabeled motor neurons in the smoothened (smu) mutant at 33 hpf (p < 0.0001; lateral trunk views are shown). (E) The phosphodiesterase inhibitor rolipram abolishes the promoting effect of pergolide on development of islet-1:GFP+ motor neurons. (F) The adenylate cyclase inhibitor SQ22536 mimics the action of pergolide by promoting islet-1:GFP+ motor neuron development, and rolipram inhibits development of islet-1:GFP+ motor neurons (p < 0.0001). (G) Model for dopamine action. By inhibiting adenylate cyclase (AC), dopamine (DA), acting through the D4a receptor, reduces the inhibitory influence of cAMP-dependent PKA on the hedgehog pathway, which is normally activated by hedgehog (Hh) acting through the Smoothened receptor (Smo). Upward and downward arrows indicate positive or negative influences, respectively, of D4a activity. Error bars represent SEM. Scale bars, 50 μm (A and D).
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