Perinatal high fat diet (pHFD) exposure is known to affect the development of vagal neurocircuits that control gastrointestinal (GI) motility and reduce stress resiliency in offspring. Descending oxytocin (OXT; prototypical, anti-stress peptide) and corticotropin releasing factor (CRF; prototypical, stress peptide) inputs from the paraventricular nucleus (PVN) of the hypothalamus to the dorsal motor nucleus of the vagus (DMV) modulate the GI stress response. However, how these descending inputs, and their associated changes to GI motility and stress responses, are altered following pHFD exposure are unknown. The present study usedin vivorecordings of gastric tone and motility,in vivoassays of gastric emptying rates,in vitroelectrophysiological recordings from brainstem slice preparations, and retrograde neuronal tracing experiments to investigate the hypothesis that pHFD alters descending PVN-DMV inputs, dysregulating DMV neuronal responses and subsequent gastric motility. Basal gastric emptying rates were found to be significantly delayed in pHFD rats, which also demonstrating an inability to mount an appropriate response to acute stress with a further delay in gastric emptying. Neuronal tracing experiments suggested that pHFD reduced PVNOXTneurons that project to the DMV but increased PVNCRFprojections. Whole cell patch clamp recordings of DMV neurons demonstrated that, following pHFD, PVNCRFprojections are tonically active, altering GABAergic inputs to DMV neurons. Lastly, blocking DMV CRF receptors in pHFD rats restored the appropriate gastric response to brainstem oxytocin application. Taken together, these results indicate that pHFD exposure leads to an upregulating of CRF inputs to the DMV, resulting in tonic CRF activation on the system and altering gastric motility. These results suggest that pHFD exposure leads gastric dysmotility, leading to a maladaptive gastric stress response and reduced stress resiliency.

Perinatal high fat diet (pHFD) exposure alters the development of vagal neurocircuits that control gastrointestinal (GI) motility and reduce stress resiliency in offspring. Stress causes a delay in gastric emptying that is, at least in part, vagally dependent. Descending oxytocin (OXT; prototypical, anti-stress peptide) and corticotropin releasing factor (CRF; prototypical, stress peptide) inputs from the paraventricular nucleus (PVN) of the hypothalamus to the dorsal motor nucleus of the vagus (DMV) modulate the gastric response to stress, but how these descending inputs are altered following pHFD exposure is unknown. The present study used in vivo recordings of gastric tone and motility, in vivo assays of gastric emptying rates, in vitro electrophysiological recordings from DMV neurons in brainstem slices, and retrograde tracing experiments to investigate the hypothesis that pHFD alters descending PVN-DMV inputs, dysregulating vagal efferent control of gastric functions.Basal gastric emptying rates were significantly delayed in pHFD rats (76.87±22.07min vs. 57.63±6.94min for control, p=0.0338; via two-tailed unpaired t-test), which were also unable to respond to acute stress (2hr restraint) with a further delay in gastric emptying (66.81±9.30 minutes) unlike control rats (66.07±10.79 minutes). Neuronal tracing experiments showed that pHFD reduced PVNOXT-DMV projections (10.5±6.6 control vs. 3.3±2.7 pHFD cells/section, p=0.0032; via two-tailed unpaired t-test) but increased PVNCRF-DMV projections (9.83±5.184 control vs. 19.85±12.89 pHFD cells/section, p=0.0158; via two-tailed unpaired t-test). In vitro whole cell patch clamp recordings demonstrated that OXT (100nM) application decreased the frequency of miniature inhibitory currents (mIPSCs) in pHFD but not control DMV neurons (65.18%±27.30 vs 97.89%±15.36 respectively, p=0.0101; via two-tailed unpaired t-test). Moreover, the CRF antagonist, astressin (1μM) increased mIPSC frequency in pHFD but not control DMV neurons (129.9±42.95% vs. 82.87±5.35% respectively, p=0.0411 via unpaired two-tailed t-test) suggesting pHFD PVNCRF-DMV inputs are tonically active. In vivo recordings of gastric tone showed that DMV microinjection of OXT (150pmols/60nl) decreased gastric tone in control rats, but increased tone in pHFD rats (control: -134.2±79.06 mg vs. pHFD: +142.2±244.5 mg, p=0.0070; via two-tailed unpaired t-test). Lastly, in pHFD rats, 4th ventricular astressin (10μg/2μl) application restored the appropriate gastroinhibitory response to OXT (baseline: +142.2±244.5 mg vs astressin: -75.67±271.67 mg, p=0.0015; via two-tailed paired t-test).Collectively, these results indicate that pHFD exposure upregulates, and tonically activates, PVNCRF-DMV inputs. Together with the reduced PVNOXT-DMV innervation, this leads to gastric dysmotility, maladaptive gastric stress responses and reduced stress resiliency in pHFD offspring. NIH DK111667 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Introduction Perinatal high fat diet (pHFD) exposure is known to increase anxiety in offspring, and reduce stress resilience, however the mechanism that causes this functional change is unknown. Oxytocin is the prototypical anti‐stress peptide, and the paraventricular nucleus of the hypothalamus (PVN) provides descending inputs to the dorsal vagal complex (DVC) within the brainstem. The DVC provides parasympathetic extrinsic control over the gastrointestinal tract. The present study was designed to investigate the hypothesis that changes in oxytocin hypothalamic‐brainstem innervation may be partially responsible for the lack of stress resilience observed following a pHFD. Methods Rats were fed control or high fat diet (14 or 60% kcal from fat, respectively) from embryonic day 13, and weaned onto the same diet at postnatal day 21. At 6‐8 weeks of age, 7 rats were anesthetized, perfused transcardially and brains removed for immunohistochemical processing. In another set of experiments 8 rats (N=4 control, 4 pHFD) the retrograde tracer cholera toxin B (CTB; 0.5%) was injected into the DVC (5 injections of 120nl throughout the rostro‐caudal extent of the DVC). After recovery for 10 days, rats were perfused transcardially and brains removed as above. Coronal slices (50um) were processed for immunohistochemical detection of oxytocin in the brainstem, as well as and oxytocin, CTB, and oxytocin/CTB co‐localization in the hypothalamus. Results were compared using an unpaired t‐test. Results In naïve rats, total oxytocin fluorescence in the DMV was 5.754 arbitrary units/area (AU) in control rats vs. 1.547 AU/area in pHFD rats (p=0.0272). Within the hypothalamus, it was found that there were significantly fewer (p=0.0006) oxytocinergic cells innervating the DVC in pHFD rats (2.250 cells/mid‐PVN coronal slice) compared to control (11.17 cells/mid‐PVN coronal slice). There was also a significant reduction in CTB‐positive neurons in pHFD (71.60 cells/mid‐PVN coronal slice) rats compared to control (185.5 cells/mid‐PVN coronal slice) rats (p < 0.001). In contrast, no significant differences were found in the number of PVN oxytocin‐positive cells when comparing control versus pHFD rats (126.5 cells vs. 88.87 cells, respectively; p=0.0904). Conclusions These data suggest that pHFD decreases oxytocin innervation to the DVC. Previous studies have shown that oxytocin is important in regulating the gastrointestinal response to stress; given the decrease in oxytocin immunoreactivity observed following pHFD this may provide a potential mechanism to explain the increased anxiety and decreased stress resilience under these conditions. Following this study, it will be important to correlate the results with their functional significance through electrophysiology and behavioral assays. Acknowledgements The project described was supported by NIH 1R25DK113652 and DK111667. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Diabetes and Digestive and Kidne...

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