Identification of the cellular target for eclosion hormone in the abdominal transverse nerves of the tobacco hornworm, Manduca sexta

The isolated abdominal central nervous system of Manduca sexta undergoes an increase in cyclic GMP (cGMP) when exposed to the insect peptide eclosion hormone (EH) before pupal ecdysis. Previously, cGMP immunocytochemistry rev ealed that the EH-stimulated increase in cGMP was contained in numerous fil amentous processes within the transverse nerve associated with each abdomin al ganglion. These processes seemed to be the axons of neurosecretory cells projecting to this neurohemal organ. In the present paper, we now show tha t the EH-stimulated cGMP is not present in neurosecretory terminals. There is no colocalization of the EH-stimulated cGMP with immunoreactivity of two peptides, known to be present in axons in the transverse nerves. Furthermo re, there is no colocalization of EH-stimulated cGMP with the synaptic vesi cle protein, synaptotagmin. The neurosecretory axons are localized to a nar row band at the anterior margin of the transverse nerve, whereas the cellul ar elements showing an EH-stimulated cGMP increase are primarily present in the posterior region. There are two cell types in this region: a granular and a nongranular type. The cGMP immunoreactivity seems to be contained wit hin the nongranular type. During adult development, the cells of the poster ior compartment spread in a thin layer between the transverse and dorsal ne rves, become positive for myosin immunoreactivity between pupal stages 5 an d 8, and seem to form the adult ventral diaphragm muscles. We conclude that the EH-sensitive filaments in the transverse nerves of Manduca are most li kely to be intrinsic cells that subsequently develop into the ventral diaph ragm muscles of the adult. J. Comp. Neurol. 424:339-355, 2000. (C) 2000 Wil ey-Liss, Inc.