The role of hypothalamic Orexin-A in stress-induced gastric dysmotility: An agonistic interplay with corticotropin releasing factor.

Background: Central Orexin-A (OXA) modulates gastrointestinal (GI) functions and stress response. This study aimed to investigate whether OXA and CRF interact at hypothalamic level.

Methods: Solid gastric emptying (GE), fecal output (FO), plasma corticosterone (CORT), and postprandial antro-pyloric motility were assessed in rats that underwent acute restraint stress (ARS) and pretreated with central OX1R and/or CRF receptor antagonists SB-334867 and alpha-helical CRF . Microdialysis was performed to assess ARS-induced release of OXA and CRF in PVN and LHA, respectively. Immunofluorescence labeling was performed to detect the stress-induced changes in OXA and to assess the hypothalamic distribution of OX1R and CRF1/2 receptors. ARS-induced c-Fos immunoreactivity was evaluated in PVN and LHA of rats received OX1R and CRF receptor antagonists.

Key Results: ARS delayed GE by disturbing the coordination of antro-pyloric contractions while stimulating FO and CORT secretion. ARS-induced alterations in GE, FO, plasma CORT, and antro-pyloric motility were attenuated by OX1R and/or CRF receptor antagonists, however, these changes were completely restored in rats received both antagonists. ARS stimulated release of OXA and CRF which were significantly attenuated by α-CRF and SB-334867, respectively. The OX1R was detected in CRF-immunoreactive cells, whereas dense expression of CRF2 receptor but not CRF1 was observed in LHA. ARS remarkably increased OXA immunoreactivity in LHA. ARS-induced c-Fos expression in LHA and PVN was abolished by α-CRF and SB-334867, respectively.

Conclusions & Inferences: Our findings suggest a reciprocal contribution of OXA and CRF which seems to be involved in the mediation of stress-induced alterations in neuroendocrine and GI motor functions.