Developmental and regional-specific expression of FLRFamide peptides in the tobacco hornworm, Manduca sexta, suggests functions at ecdysis.

The developmental profile of a family of three FLRFamide (Phe-Leu-Arg-Phe-NH2) peptides in the tobacco hornworm, Manduca sexta, revealed regional-specific expression patterns within the segmental ganglia. Levels of the three peptides-F7G (GNSFLRF-amide), F7D (DPSFLRFamide), and F10 (pEDVVHS-FLRFamide)-were always higher in the thoracic than abdominal ganglia. The predominant peptide also differed regionally, with F7G being highest in the thoracic ganglia and F7G and F100 being equivalent in the abdominal ganglia. Furthermore, we found regional-specific transient declines in ganglion peptide levels temporally correlated to ecdysis. Thoracic ganglion peptide levels declined at each molt, while abdominal ganglion levels declined over a period of 2 days after ecdysis. The decline in central levels was accompanied by an increase in levels in peripheral neurohemal sites, the transverse nerves (TNs). These observations suggest peptides were released from neurosecretory cells (NSCs) at ecdysis. Distinct sets of thoracic and abdominal NSCs and their processes in peripheral neurohemal sites were immunoreactive, supporting the biochemical data. These results also suggest the regional differences may arise from cellular-specific expression patterns for this family of peptides. In addition, fine immunoreactive processes were observed traveling between TNs and skeletal muscles, suggestive of myotropic actions. We propose that the release of different M. sexta FLRFamides from regionally distinct NSCs leads to a coordinated modulation of skeletal and visceral muscles that facilitate ecdysis.