Behavioural studies of faecal continence in the rat

Abstract

A behavioural animal model of faecal continence and/or incontinence would be of value in experimental studies of the mechanisms by which sacral neuromodulation can effect continence mechanisms in humans. The aim of this behavioural study was to establish whether the rat, an obligate coprophagic species, exhibits patterns of faecal continence. Standard rat cages were modified to consist of a food and drink area, a nesting area and an empty latrine area. Three floor pressure pads were connected to hour meters to record the time spent in each area over the course of 4 days. The door to the latrine was open for 2 days and closed for another 2 days to create a physical barrier that could only be surmounted by climbing over a partition. In the first 2 days, most faecal pellets (74 ± 20 %; p < 0.0001) were deposited in the latrine and this was not changed by door closure (81 ± 13 %). Door closure had no effect per se on pellet output (p = 0.99), nor did it alter the place preference for defaecation (p = 0.17, two factor ANOVA). Rats spent less time in the latrine area accounting for 23 and 13 % of total time before and after the door was closed, respectively. Normal and infrared videography showed that the place preference for pellets was not due to pellet collection for coprophagic purposes. The rat demonstrates place preference for defaecation and may drop pellets to mark remote boundaries. This simple method may prove useful in future animal studies of neuropathic faecal incontinence and refinement of neuromodulation interventions that lack placebo effects.