Assessment of a Neonatal Rat Model of Necrotizing Enterocolitis

Introduction: A neonatal rat model of necrotizing enterocolitis (NEC) is useful to investigate this devastating and obscure disease. The aim of this study was to assess a neonatal rat model of NEC to evaluate whether the histological appearance of the damaged intestine could be predicted by the clinical behaviour of the animals and the macroscopic appearance of the gut. Materials and Methods: Neonatal rats were delivered at term and assigned either to a control group consisting of breastfeeding and no stress factors, or to a NEC group in which NEC was induced by gavage feeding + hypoxia + oral lipopolysaccharide (4 mg/kg/day once daily for the first 2 days of life). Clinical status was assessed on day 4 using a clinical sickness score (general appearance, response to touch, natural activity, body Colour; 0-3 for each variable). Neonatal rats were sacrificed at 4 different time points: day 1, day 2, day 3, and day 4. At sacrifice, a macroscopic assessment of the gut was performed using a new scoring system based on: colour (0-2), consistency (0-2) and degree of dilatation (0-2). The resected gut was stained with haematoxylin/eosin, and evaluated microscopically by 2 independent blinded scorers, including a consultant histopathologist. The histology results were used to validate the macroscopic gut assessment. Results were compared by ANOVA and linear regression analysis. Ethics Committee and Home Office approvals were obtained. Results: In the control group NEC was not present either macroscopically or histologically. The clinical sickness score was higher in the NEC group (median=4.5; range=2-6) compared to controls (median=0; range=0-1; p < 0.0001). In the NEC group the macroscopic appearance (from day 2) and histological score (from day 1) increased significantly (p < 0.0001) and were strongly correlated (r(2)=0.74, p < 0.0001). Conclusions: The clinical behaviour and macroscopic appearance of the intestine are valid tools to assess gut damage in our neonatal rat model of NEC. This allows future studies that are not exclusively based on histology.