Background Enteric nervous system (ENS) abnormalities have been implicated in delayed gastric emptying but studies exploring potential treatment options are limited by the lack of an experimental animal model. We examined the ENS abnormalities in the mouse stomach associated with aging, developed a novel model of gastroparesis, and established a new approach to measure gastric emptying. Methods A modified gastric emptying assay was developed, validated in nNOS −/− mice, and tested in mice at multiple ages. Age‐related changes in ENS structure were analyzed by immunohistochemistry. Gastric aganglionosis was generated in Wnt1‐iDTR mice using focal administration of diphtheria toxin (DT) into the anterior antral wall. Key Results Older mice (>5 months) exhibit hypoganglionosis in the gastric antrum and a decreased proportion of nNOS neurons as compared to younger mice (age 5‐7 weeks). This was associated with a significant age‐dependent decrease in liquid and solid gastric emptying. A novel model of gastric antrum hypoganglionosis was established using neural crest‐specific expression of diphtheria toxin receptor. In this model, a significant reduction in liquid and solid gastric emptying is observed. Conclusions & Inferences Older mice exhibit delayed gastric emptying associated with hypoganglionosis and a reduction in nNOS‐expressing neurons in the antrum. The causal relationship between antral hypoganglionosis and delayed gastric emptying was verified using a novel experimental model of ENS ablation. This study provides new information regarding the pathogenesis of delayed gastric emptying and provides a robust model system to study this disease and develop novel treatments.

Background Tamoxifen is widely used for Cre‐estrogen receptor‐mediated genomic recombination in transgenic mouse models to mark cells for lineage tracing and to study gene function. However, recent studies have highlighted off‐target effects of tamoxifen in various tissues and cell types when used for induction of Cre recombination. Despite the widespread use of these transgenic Cre models to assess gastrointestinal (GI) function, the effect of tamoxifen exposure on GI motility has not been described. Methods We examined the effects of tamoxifen on GI motility by measuring total GI transit, gastric emptying, small intestinal transit, and colonic contractility in wild‐type adult mice. Key Results We observed a significant delay in total GI transit in tamoxifen‐treated mice, with unaltered gastric emptying, accelerated small intestinal transit, and abnormal colonic motility. Conclusion Our findings highlight the importance of considering GI motility alterations induced by tamoxifen when designing protocols that utilize tamoxifen as a Cre‐driver for studying GI function.

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