Efferent dorsal unpaired median (DUM) neurons are pacemaker neurosecretory cells. A Ca²⁺ background current contributing to the pacemaker activity of cockroach DUM neurons is up-regulated by Neurohormone D (NHD), an octapeptide belonging to the adipokinetic hormone family. This modulation accelerates spiking and increases [Ca²⁺]_i. Using patch-clamp, calcium imaging and immunocytochemistry, we investigated the signalling pathway of NHD-induced current modulation. The membrane depolarization produced by NHD was related to the increase in membrane conductance for either Ca²⁺, Ba²⁺ or Sr²⁺. This increase was abolished by LOE-908, an inhibitor of noncapacitive Ca²⁺ entry (NCCE), and it was strongly attenuated by the PLC inhibitor U37122 and the DAG lipase inhibitor RHC80267. Arachidonic acid and ETYA mimicked the NHD effect on background current. This was abolished by L-NAME and ODQ, inhibitors of NO synthase and NO-sensitive guanylyl cyclase, respectively, but mimicked by the NO donor SNP and 8-bromo-cGMP. Immunocytochemistry using cGMP antibodies indicated that NHD and ETYA increase cGMP. Inhibition of PKG with KT5823 and Rp-8-pCPT-cGMPS had no effect while zaprinast, a cGMP-specific phosphodiesterase5,6,9 inhibitor, mimicked the NHD effect. Furthermore, inhibition of the cGMP-activated phosphodiesterase 2 (PDE2) by EHNA and trequinsin abolished the effect of NHD. We conclude that the final step of the NHD signal transduction is the PDE2-induced downregulation of the cAMP level. This removes a depression of NCCE directly attributed to cAMP since inhibition of PKA with KT5720, Rp-cAMPS and PKI14-22 amide did not mimick the NHD effect. We also demonstrate that any mechanism increasing the cGMP level can induce NCCE.