An appraisal of the strengths and weaknesses of newborn and juvenile rat models for researching gastrointestinal development

Abstract

SummaryResearch on the impact of bioactive compounds on the development and functional maturation of the gastrointestinal (GI) tract using newborn and juvenile rats has greatly contributed to the knowledge of GI physiology and to the improved clinical management of both premature and full-term newborns. Of the animal models available, two types have been described for use with young rats -maintenance models and substitution models. Maintenance models are those in which the young are reared with the dam and therefore benefit from continuation of natural nutrition and maternal care. Substitution models are those in which the young are reared in the absence of the dam using artificially formulated milk delivered by various means into specific GI sites. In this review, we describe these models and their operation, and discuss the strengths and weaknesses of each. Attention is also given to questions of scientific validity and some animal welfare issues raised by the use of these models.

The newborn rat gastric emptying rate is volume and not developmentally dependent

“…The newborn rat is a suitable animal model to study gastric emptying regulation early in life for two important reasons. Firstly, at birth, the rat gastrointestinal tract maturation is said to be comparable to the 32 weeks gestation human infant . Secondly, the newborn rodent, while with the mother, maintains a full stomach content volume that progressively empties following maternal separation‐induced fasting.…”

“…Firstly, at birth, the rat gastrointestinal tract maturation is said to be comparable to the 32 weeks gestation human infant. 38,39 Secondly, the newborn rodent, while with the mother, maintains a full stomach content volume 12 that F I G U R E 4 Panel A: Gastric fundic muscle strips from 1-week old rats (N = 16) stimulated with KCl (65 mmol/L) at incremental resting tensions (wall strain) in the absence and presence of the ROCK-2 inhibitor Y27632 (5 × 10 −6 mol/L for 30 min). Panel B: ROCK-2 activity (pMYPT1/MYPT1) for 1 week old rats' snap-frozen fundic tissue obtained at basal (0 mN), low (4 mN) and high (10 mN) resting tensions without and following KCl (65 mmol/L) stimulation.…”

Maternal separation and gastrointestinal transit time in neonate rats

“…3 This present study compares the influence of maternal separation (substitution model) versus maternal presence (maintenance model) on Gltt in young rats for future experimental design. 4…”

“…3 This present study compares the influence of maternal separation (substitution model) versus maternal presence (maintenance model) on GItt in young rats for future experimental design. 4 GItt is the time required for ingested material to transit and be excreted from the GI tract. There is considerable interest in understanding the transit time of experimental animals for nutritional research, design of inflammatory bowel disease animal models 5 and pharmacokinetic studies.…”

Electroencephalographic responses to tail clamping in anaesthetized rat pups

“…2,3 This timing is important for the humane management of newborns, especially in experimental settings (e.g. Henare et al 4 ). The rat pup is the focus of the present paper as it has been used in previous work exploring the ontogeny of peripheral pain mechanisms.…”