Our previous report showed that the pars intercerebralis (PI)-ablated cockroach, Periplaneta americana (PIX), exhibited
hypertrophy and a significant increase in α-
amylase and
protease activities in the midgut under constant darkness (DD). Bath-applied
crustacean cardioactive peptide (CCAP) and
allatostatin (AST) stimulated α-
amylase and
protease activities in the dissected midgut cultured in medium. However, the functional relationship and regulatory mechanism between the brain, particularly the pars intercerebralis and the midgut digestive activity remain to be investigated. Here, we investigated the immunohistochemical reactivities (IHCr) against CCAP and AST in the midgut of cockroach subjected to the above operation (PIX-DD). Three types of IHCr cells were observed in both the muscle layer and the epithelium: (1) CCAP-ir only, (2) AST-ir only and (3) both reactivities are colocalized. The number of all three types increased intensively after PIX under DD compared with that of
sham operated control that was kept under constant condition (CNT-DD), indicating that the PI suppresses the expression of CCAP and AST in the midgut epithelium. We also showed that co-administration of CCAP and AST to the midgut caused increases of 1.5-fold and 1.4-fold for α-
amylase and
protease activities, respectively, compared with application of either
peptide above. On the other hand, CCAP-ir in the muscle layer was more strongly expressed but AST-ir was suppressed in PIX-DD. While these
peptides showed opposite effects on spontaneous contraction, when epithelially released, these
peptides both activated the digestive
enzyme system. Overall, up-regulated AST-6 and down-regulated CCAP in the stomatogastric nerve in the muscle layer produce the same end result, that is, stimulation of digestive activity (
hypertrophy) via both enzyme activation and the retarded peristalsis that leads to increased throughput time.