Chemogenetic activation of hypothalamo‐vagal oxytocinergic neurocircuits restores delayed gastric emptying following stress

Abstract

Stress maladaptation plays a significant role in the development and/or exacerbation of functional gastrointestinal (GI) disorders, including impaired gastric emptying and decreased gastric motility. The prototypical anti‐stress hormone, oxytocin (OXT), modulates GI tone and motility via vagal pathways. We have shown recently that gastric‐projecting hypothalamo‐vagal oxytocinergic neurocircuits undergo neuroplasticity as a consequence of either acute or chronic stress. To study the role of oxytocinergic inputs from the paraventricular nucleus of the hypothalamus (PVN) to the brainstem dorsal vagal complex (DVC) in stress‐induced gastric dysfunction, we utilized designer receptor exclusively activated by designer drugs (DREADD) technology as a tool to test the hypothesis that chemogenetic activation of oxytocinergic neurons within hypothalamo‐vagal neurocircuits prevents the delayed gastric emptying following stress.To express the DREADD receptor hM3Dq in OXT‐expressing neurons projecting from the PVN to the DVC, AAV‐OXT‐Cre was microinjected bilaterally (30nl) into the PVN of 6‐wk‐old male Sprague‐Dawley rats. The Cre‐dependent retrogradely transported DREADD vector, AAVrg‐hSyn‐DIO‐hM3DGq‐mCherry, was microinjected bilaterally (50nl) into the DVC (DREADD rats). Another group of age‐matched rats received AAV‐OXT‐Cre microinjection in the PVN and a control vector, AAVrg‐hSyn‐DIO‐EGFP, microinjection into the DVC (control rats). The expression and functionality of hM3Dq in the OXT neurons in the PVN was confirmed by observing co‐localization of OXT in immunoreactivity with mCherry or EGFP expression, and that mCherry+ PVN preautonomic neurons responded to CNO application (10uM) with an increase in action potential firing rate.After confirming the expression of hM3Dq in oxytocin neurons, gastric emptying (GE) was assessed via the non‐invasive [13C]‐octanoic acid breath test technique. After 7 days of daily acclimation to the testing chamber, 2 baseline measurement of GE were taken 5 days apart. GE was also measured immediately following stress loading on day 1 (acute stress) and after 5 days of chronic variable stress. Our preliminary data indicated that baseline GE half time was not different between control, DREADD or naïve (no vector injected) rats (control: 63.1±7.76 min, DREADD: 69.9±5.1 min, naïve: 62.3±3.5 min, N=6–12 for each group, p>0.05). Acute stress (2hr restraint) delayed GE significantly in control rats that received either saline (0.3ml) or CNO (3mg/kg, 0.3ml), and in DREADD rats that received saline (138±9% vs baseline; N=7). Conversely, CNO administration to DREADD rats prevented delayed GE (72.4±4% vs baseline; N=3) in response to acute stress. Following chronic variable stress, control rats that received saline or CNO still showed delayed GE (132±7% vs baseline; N=3), whereas CNO administration to DREADD rats also restored the delayed GE (99±22% vs baseline; N=3). Taken together, our data support the hypothesis that chemogenetic activation of oxytocinergic PVN‐DVC neurocircuitry prevented the delayed GE observed following both acute and chronic stress.Support or Funding InformationNIH DK55530This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.