The Role of Central Orexin‐A in Restraint Stress‐induced Gastric Dysmotility in Rats
Authors: Sinen Osman , Bülbül Mehmet 
Published: November 2023

Stress exposure stimulates the production of corticotropin‐releasing factor (CRF) in hypothalamic paraventricular nucleus (PVN) which in turn influences gastrointestinal (GI) motor functions by altering autonomic outflow in brain. In rodents, acute restraint stress (ARS) has been shown to delay gastric emptying (GE) by impairing the postprandial coordination of of antro‐pyloric contractions through a CRF‐dependent pathway. Besides its well‐defined orexigenic function, the hypothalamic neuropeptide orexin‐A (OXA) is also known to alter GI motor functions through central autonomic pathways. OXA‐producing cells reside mainly in lateral hypothalamic area (LHA), while its receptor OX1R is found in PVN. Accumulating evidence indicate that OXA‐containing neurons send intra‐hypothalamic projections to the CRF‐producing cells in PVN. Furthermore, central administration of OXA has been shown to enhance CRF‐induced neuroendocrine functions suggesting that central OXA may contribute to the CRF‐mediated impairment of GI motor functions under stressed conditions. The aim of the present study was to investigate the involvement of orexin‐A in CRF‐induced gastric motor dysfunction under stressed conditions. Central (icv) drug administrations were performed through an injection cannula stereotaxically placed into the lateral ventricle. Solid GE was measured following an overnight fasting in non‐stressed (NS) and ARS‐loaded rats following central pretreatment of CRF and OXA antagonists α‐helical‐CRF9,41 (10 nmol, 5 μl) and SB‐334867 (100 nmol, 5 μl), respectively. For recording of gastric motility, two miniature strain gages were implanted onto the serosal surface of antrum and pylorus. Postprandial antro‐pyloric contractions were monitored in conscious and freely‐moving rats simultaneously with microdialysis. To perform microdialysis, a probe with high molecular cut‐off membrane was placed into the PVN. The intra‐PVN microinjection of vehicle or selective SB‐334867 (10 nmol, 100 nL) was performed prior to the perfusion of the probe with artificial cerebro‐spinal fluid (aCSF) containing high KCl (100 mmol/L). CRF concentrations in microdialysis samples were quantified by enzyme immunoassay. Compared with NS rats, ARS significantly (p<0.01) delayed GE. The ARS‐induced delayed GE was partially attenuated both by pretreatment of SB‐334867 (p<0.05) and α‐helical‐CRF9,41 (p<0.05), whereas it was completely restored (p<0.01) when both antagonists were administered together. Perfusion with high KCl‐containing aCSF significantly increased the CRF level in microdialysates which was significantly attenuated by intra‐PVN microinjection of SB‐334867. Perfusion of KCl impaired the coordination of postprandial antro‐pyloric contractions. Compared with vehicle‐injected rats, KCL‐induced alterations were remarkably abolished by SB‐334867. These results suggest that central OXA plays a role in stress‐induced alterations in gastric motor functions through OX1R. Therefore, OX1R antagonism appears to be a candidate for the treatment of the stress‐related gastric motor dysfunctions.