Interactions between CNS regulation and serotonergic modulation of crayfish hindgut motility

Motility is a critical function of the gastrointestinal (GI) system governed by neurogenic and myogenic processes. Due to its major role in maintaining homeostasis, overlapping mechanisms have evolved for its adaptive operation including modulation by the central nervous system (CNS), enteric nervous system (ENS) and intrinsic pacemaker cells. Our understanding of the modulatory mechanisms that underlie intestinal motility remains incomplete. Crayfish provide a tractable ex vivo model to study the interplay between CNS and neurochemical regulation of GI motor patterns. Our study investigated the effects of CNS denervation and exogenously applied serotonin (5-HT) on crayfish hindgut motility. Multiscale spatial measurements showed stable motility parameters throughout 90 min of control conditions. Denervation, i.e. separating the gut from the CNS, resulted in a significant decrease in the magnitude and synchrony of hindgut contractions, while preserving the underlying frequency and directional bias of the waves. Subsequent application of 5-HT to the denervated preparation enhanced motility but disrupted spatiotemporal coordination. Treatment with TTX (a sodium channel blocker) had minor impacts on motility metrics, indicating a prominent role of myogenic mechanisms. Our model provides a multiscale analysis framework to dissect CNS and interrelated neurochemistry contributions to GI motor dynamics.