Protein kinase A signalling mediates Sema3A-induced growth cone collapse in nitrergic (NOS-positive) parasympathetic neurones. (A) The PKA inhibitor, KT-5720, prevented Sema3A-induced growth cone collapse in NOS-positive neurones. (B) Similar results were found with Rp-cAMPS. (C, D) In contrast, two separate inhibitors of PKG (C, KT-5823; D, Rp-8-Br-cGMPS) did not significantly affect Sema3A-collapse, but both caused growth cone collapse on their own. Tukey's test: *P < 0.05, **P < 0.01, ***P < 0.001 versus control; #P < 0.05, ###P < 0.001 versus Sema3A (n= 3–4 for all experiments). KT-5720, (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3′,2′,1′-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid, hexyl ester; KT-5823, (9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3′,2′,1′-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid, methyl ester; Rp-cAMPS, Rp-adenosine-3′,5′-cyclic monophosphorothioate; Rp-8-Br-cGMPS, Rp-8-bromoguanosine-3′,5′-cyclic monophosphorothioate; Sema3A, semaphorin 3A.