Calcitonin gene-related peptide (CGRP), a neuropeptide synthesized by motor neurons, stimulates the expression of AChR and AChE at the vertebrate neuromuscular junctions. The signaling mechanism of CGRP-induced AChE expression in muscle was determined bothin vitroandin vivo. In cultured chick myotubes, the intracellular cAMP-dependent protein kinase (PKA) activity increased to ∼2-fold after the application of CGRP or PKA activators; the induction was blocked by PKA inhibitors.in vivotransfection analysis on chick gastrocnemius muscles showed that the transfection of cDNA encoding constitutively active mutant Gαsincreased the expression of AChE mRNA and protein to ∼2-fold, while the constitutively active mutant GαicDNA transfection showed an opposite effect. The induced catalytic subunit of AChE at ∼105 kDa was determined by specific antibody. These findings indicate that the CGRP-induced AChE expression in chick muscle is mediated by a PKA-dependent pathway.