Hypothalamo‐Vagal Oxytocinergic Neurocircuits Modulate Gastric Emptying And Motility Following Stress

Abstract

Stress triggers and exacerbates the symptoms of functional gastrointestinal (GI) disorders, such as delayed gastric emptying and impaired gastric motility. The prototypical anti‐stress hormone, oxytocin (OXT), modulates GI tone and motility via vagal pathways. Following acute or chronic stress, the oxytocinergic neurocircuits from the hypothalamus to brainstem neurons of the dorsal vagal complex (DVC) undergo neuroplasticity. However, the physiological role of this neuroplasticity in modulating gastric functions following stress is yet unclear. In this study, we used chemogenetic technology to test the hypothesis that activation of hypothalamo‐vagal oxytocinergic neurocircuits plays a pivotal role in the modulation of gastric emptying and motility following stress.Male Sprague‐Dawley rats were used in all experiments. Six‐week‐old rats received bilaterally microinjections of AAV‐OXT‐Cre in the paraventricular nucleus of the hypothalamus (PVN), and retrogradely transported AAV that express Cre‐inducible hM3Dq (hM3Dq rats), hM4Di (hM4Di rats) or EGFP (EGFP rats, i.e. viral control) in the DVC. Four weeks after AAV injections, gastric emptying (GE) was assessed via the non‐invasive [13C]‐octanoic acid breath test technique. After 3 days of daily acclimation to the test chamber, two baseline of GE were taken 5 days apart. GE was then measured immediately following acute stress and after 5 days of either chronic homotypic (CHo, rats showed adaptation to stress) or heterotypic stress (CHe, rats did not adapt to stress). Our data showed that the baseline GE t1/2 was not different among hM3Dq, hM4Di and EGFP rats (70±3.5, 75±2.3, and 70±2.5 min, respectively; N=12–24, p>0.05, one‐way ANOVA). Acute stress (2hr restraint) delayed GE significantly in both EGFP and hM4Di rats that received either saline or CNO treatment. Delayed GE was also observed in hM3Dq rats that received saline; however, CNO administration to hM3Dq rats prevented the delay in GE. Following CHe, EGFP rats that received saline or CNO still showed delayed GE, whereas CNO administration to hM3Dq rats restored the delayed GE. Following CHo, GE of EGFP rats was restored to baseline, whereas CNO administration to hM4Di rats delayed GE.Another group of rats were anesthetized to monitor gastric motility via strain gauges sewn on the gastric wall. Application of CNO (20nmoles) on the floor of 4th ventricle of EGFP rats changed neither tone nor motility (−2.5±2 mg and 104±8% vs baseline, respectively). Conversely, CNO increased corpus tone (68±33mg) and antrum motility (158±21% vs baseline) when applied to hM3Dq rats following CHe, but decreased tone (−63±17mg) and motility (85±21% vs. baseline) when applied to hM4Di rats following CHo. Pretreatment of OXT receptor antagonist, atosiban, abolished the effects of CNO. Taken together, our data support the hypothesis that hypothalamo‐vagal oxytocinergic neurocircuits modulate gastric emptying and motility following stress.Support or Funding InformationNIDDK 120170 and TSF CURE funds GE (vs baseline) Acute stress CHe CHo Saline CNO Saline CNO Saline CNO EGFP (Control) 138±8% * (N=9) 135±13% * (N=12) 139±15% * (N=4) 134±16% * (N=6) 100±8% (N=4) 107±5% (N=6) hM3Dq 151±9% * (N=5) 81±12% (N=5) 134±13% * (N=5) 90±13% (N=5) hM4Di 118±7% * (N=6) 133±14% * (N=4) 119±7% (N=6) 141±9% * (N=4) *P<0.05, paired Student’s t‐test vs own baseline