Maternal High Fat Diet Alters Expression of Myenteric Ganglia and Glia Prior to the Development of Obesity
Authors: McMenamin Caitlin Alannah , Browning Kirsteen 
Published: June 2021

Diet‐induced obesity is known to disrupt gastrointestinal (GI) functions possibly due to a loss of myenteric neurons. Few studies, however, have assessed the effects of diet either prior to obesity or on the development of myenteric ganglia. The aim of the present study was to assess the effects of a high fat diet (HFD) on the development of myenteric neurons and glial cells in rats.Sprague‐Dawley rats were fed either a control or HFD (14% of 60% kcal from fat, respectively) from embryonic day 13; the fundus, corpus and duodenum were removed subsequently and fixed at postnatal ages 2, 4, 6 and 12 weeks. Tissues were processed for immunohistochemical detection of total myenteric neurons (protein gene product 9.5; PGP9.5) as well as cholinergic‐immunoreactive (choline acetyltransferase; ChAT‐IR) neurons, nitrergic (nitric oxide synthase; NOS‐IR) neurons, RNA‐binding protein (HuC/D), and glial cells (glial fibrillary acid protein; GFAP‐IR). Confocal microscope images were taken at a magnification of 40× and 60× and analyzed using Image J software.HFD rats were significantly heavier than control rats by 8 weeks of age (282±4g vs 226±6g, P<0.05) and were regarded as obese by 12 weeks of age (292±12g vs 380±12g P<0.05). While there was no difference in size of myenteric ganglia throughout the study (12 weeks: fundus 15,969±1,191 mm2 vs 12,966±946; corpus 15,586±606 vs 15,440±527; duodenum 9,532±715 vs 8,685±651; P>0.05), there was a decrease in number of myenteric neurons per ganglia by 4 weeks of age in the fundus (29 ± 3.6 vs. 38 ± 2.6 neurons/ganglia; n=5; P<0.05) and corpus (34.6 ± 0.8 vs. 44.3 ± 1.2 neurons/ganglia; n=5; P<0.05), and by 6 weeks of age in the duodenum (26 ± 1.5 vs. 34.6 ± 2.9 neurons/ganglia; n=5; P<0.05). A selective loss of nitrergic neurons was observed by 12 weeks of age in the fundus (13.5 ± 0.9% vs 20 ± 0.9% of total neurons; P<0.05), corpus (10.7 ± 0.7% vs 19 ± 3.1% of total neurons; P<0.05), and duodenum (8.5 ± 2.5% vs 16.5 ± 2.0% of total neurons; P<0.05). HFD exposure increased myenteric glial cell density by at 4 weeks of age in the fundus (69.9±2.6 vs 62.32±3.1 pixels/cm2; P<0.05), corpus (87.0±7.5 vs 62.9±4.9 pixels/cm2; P<0.05) and duodenum (96.1±5.9 vs 56.9±4.0 pixels/cm2; P<0.05) compared to controls, suggesting a possible diet‐induced inflammation of the gastrointestinal tract. Nuclear aggregation of HuC/D, suggesting compromised neuronal health, was observed in myenteric neurons at 12 weeks of age in the fundus (68.6 ± 8.5% vs 41.6 ± 6.6% nuclear localization; P<0.05), corpus (55.0 ± 5.4% vs 23.5 ± 3.4%; P<0.05) and duodenum (52.4 ± 5.5% vs 34.7 ± 1.0%; P<0.05).The present study suggests that exposure to a HFD induces loss of inhibitory nitrergic neurons accompanied by glial proliferation can be observed in the rat myenteric plexus even prior to the onset of obesity, suggesting that diet may alter gastrointestinal functions independently of increased adiposity.Support or Funding InformationFunded by NIH 078364 and NSF IOS1148978