The presence and distribution of crustacean cardioactive peptide in the central and peripheral nervous system of the stick insect, Baculum extradentatum

Crustacean cardioactive peptide (CCAP)-like immunoreactivity was localized and quantified in the central and peripheral nervous system of the Vietnamese stick insect, Baculum extradentatum, using immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). The brain, frontal ganglion, suboesophageal ganglion and ventral nerve cord displayed neurons and processes with CCAP-like immunoreactivity. The brain, in comparison to the other parts of the central nervous system, contained the greatest amount of CCAP (167 ± 18 fmol), and showed CCAP-like staining in neurons, neuropil regions and the central complex. There were also CCAP-like varicosities and processes associated with the corpus cardiacum. The alimentary canal of B. extradentatum contained CCAP with the largest amount localized in the midgut (1110 ± 274 fmol CCAP equivalents). The midgut contained numerous endocrine-like cells which stained positively for CCAP, whereas the foregut and hindgut revealed an extensive network of CCAP-like immunoreactive axons and varicosities. Based on physiological assays, the hindgut of the stick insect was found to be sensitive to CCAP, showing dose-dependent increases in contractions with threshold at 10−10 M CCAP and maximal response at 5 × 10−7 M CCAP. There were negligible quantities of CCAP in the oviducts and no CCAP-like immunoreactivity was associated with the oviducts. CCAP had no effect on spontaneous contractions of the oviducts. The presence of CCAP in the central nervous system, the stomatogastric nervous system, the corpus cardiacum and the alimentary canal, suggest broad ranging roles for CCAP in B. extradentatum.