GABAergic and glutamatergic neurons in the brain regulate phase II of migrating motor contractions in the Suncus murinus

Gastric contractions exhibit characteristic motor patterns in the fasted state, known as migrating motor contractions (MMC). MMC consist of three periodically repeated phases (phase I, II and III) and are known to be regulated by hormones and the autonomic and enteric nervous systems. However, the central regulation of gastric contractions in the fasted state is not completely understood. Here, we have examined the central effects of motilin, ghrelin, γ-aminobutyric acid (GABA) and L-glutamate signaling on gastric MMC by using suncus (Suncus murinus) as an animal model, because of their similar gastric motor patterns to those observed in humans and dogs. Intracerebroventricular (i.c.v.) administration of motilin and ghrelin had no effect on phase I and II contractions, respectively. Conversely, i.c.v. administration of GABA_A receptor antagonist, during phase I of the MMC, evoked phase II-like contractions and significantly increased the motility index (MI). This was compared with the i.c.v. administration of GABA which inhibited spontaneous phase II contractions with a significantly decreased MI. In addition, i.c.v. administration of L-glutamate during phase I also induced phase II-like irregular contractions with a significant increase in the MI. Taken together with previous findings, these results suggest that central GABAergic and glutamatergic signaling, with the coordination of both peripheral motilin and ghrelin, regulate phase II contractions of MMC in the fasted state.