INTRODUCTION: Systemic sepsis occurs in 20-50 % of patients admitted to non-cardiac intensive care units and despite management, continues to be a serious clinical challenge. Development of novel therapeutic strategies is hampered by lack of an animal model which accurately and reproducibly mimics the clinical condition. AIMS: To refine a rat model of caecal ligation and puncture (CLP) induced sepsis; to investigate the effect of CLP on the structure of selected regions of the central and peripheral nervous system; to investigate the effect of CLP on structure and function of the gastrointestinal tract. METHODS: Under anaesthesia, the caecum was either ligated below the ileocaecal valve and punctured or only mobilised and the animals were allowed to recover for 18- 20 hours, during which time the following parameters were investigated: bacteraemia; locomotor activity; food and water intake; body weight; core temperature; serum lactate and glucose; white blood cell and platelet cell counts. The spinal cord, sciatic nerves and gut tissues were taken for quantitative and qualitative analysis using light microscopy. The above parameters were also investigated in a group of un-operated rats. In vitro studies were performed to compare the spontaneous and evoked contractile activity of the stomach, duodenum, colon and hepatic portal vein from either CLP or sham CLP animals. RESULTS: CLP but not sham CLP induced bacteraemia, lethargy (depressed nocturnal locomotor activity), anorexia, gastric retention, weight loss, pyrexia (within 4-5 hours) followed by hypothermia (from 17 hours), leucopaenia, thrombocytopaenia and hypoglycaemia after 18-20 hours. CLP also induced injury to the spinal cord and sciatic nerve characterised by peri-vascular oedema and myelin sheath swelling. There was massive mucosal sloughing, mucosal haemorrhage and vascular congestion in the gut tissue, indicative of gastrointestinal dysfunction in CLP but not in sham CLP rats. No significant differences were found between un-operated and sham CLP animals. Although CLP inflicted severe damage to the gut mucosa and inflammatory cell infiltration of the muscle layers, gastric, duodenal, colonic and hepatic portal vein tissue exhibited spontaneous contractile activity, although generally at a frequency lower than in sham CLP animals and with an elevated baseline tone. In addition, tissues were still capable of responding to a range of pharmacological agonists including acetylcholine, 5- hydroxytryptamine, phenylephrine and thrombin although the responses were modified in CLP animals. CONCLUSION: The spectrum of functional and histopathological changes described in the current study following CLP in the rat are consistent with the development of multi-organ dysfunction syndrome observed in patients with sepsis and argue that the refined model described is more clinically relevant for investigation of novel therapies than other models (e.g. LPS infusion). The results allow a reduction in the number of animals used by obviating the need for an un-operated group and permit the reduction of the post-CLP observation time required to obtain valid pathological results compared to previous investigations. The pathological changes observed in the spinal cord and sciatic nerve following CLP could explain the acute myelopathy and critical illness polyneuropathy that frequently occur following sepsis. The in vitro gut studies provide an insight into the mechanism(s) underlying gut dysfunction observed in patients with sepsis and show that despite severe damage the gut is likely to retain its capacity to respond to prokinetic drugs which could be used to treat motor disorders. These findings raise the possibility of identifying therapeutic interventions to restore neural and gastrointestinal tract function to normal and promote patients recovery