Perinatal High Fat Diet Decreases Oxytocinergic Innervation to the Brainstem
Authors: Alvarez Jared , Carson Kaitlin E. , Browning Kirsteen 
Published: May 2022

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 Kidney Diseases or the National Institutes of Health.