Immunohistochemical reactivity against short neuropeptide F (sNPF) was observed in the brain-corpus cardiacum and midgut paraneurons of the American cockroach, Periplaneta americana. Four weeks of starvation increased the number of sNPF-ir cells in the midgut epithelium but the refeeding decreased the number in 3h. Dramatic rises in sNPF contents in the midgut epithelium and hemolymph of roaches starved for 4 weeks were confirmed by ELISA. Starvation for 4 weeks reduced α-amylase, protease and lipase activities in the midgut of P. americana but refeeding restored these to high levels. Co-incubation of dissected midgut with sNPF at physiological concentrations inhibited α-amylase, protease and lipase activities. sNPF injection into the hemocoel led to a decrease in α-amylase, protease and lipase activities, whereas PBS injection had no effects. The injection of d-(+)-trehalose and l-proline into the hemocoel of decapitated adult male cockroaches that had been starved for 4 weeks had no effect on these digestive enzymes. However, injection into the hemocoel of head-intact starved cockroaches stimulated digestive activity. Injection of d-(+)-trehalose and l-proline into the lumen of decapitated cockroaches that had been starved for 4 weeks increased enzymes activities and suppressed sNPF in the midgut. Our data indicate that sNPF from the midgut paraneurons suppresses α-amylase, protease and lipase activities during starvation. Injection of d-(+)-trehalose/l-proline into the hemocoel of head-intact starved cockroach decreased the hemolymph sNPF content, which suggests that sNPF could be one of the brain factors, demonstrating brain-midgut interplay in the regulation of digestive activities and possibly nutrition-associated behavioral modifications.
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