Stress duration, gastric emptying, and ulcer development in three strains of rats

Psychological and physical stress induce differential effects on human colonic motility

OBJECTIVE

Stress modulates gut function, but whether the type of stressor influences colonic motor activity is unclear. The motor patterns and regional variations are also poorly understood. Our aim was to determine the effects of psychological and physical stress on colonic motility.

METHODS

Ambulatory colonic manometry was performed by placing a six-sensor probe up to the mid-transverse colon, without sedation, in 12 healthy subjects. Five hours later, a dichotomous listening test (psychological stress) was performed, which was preceded by listening to a narrative passage (control); recovery entailed listening to relaxing music (1 h each). Subsequently, intermittent hand immersion in cold (4 degrees C) water (physical stress) was performed, preceded by hand immersion in warm (37 degrees C) water (1/2-h each). Colonic pressure activity and cardiovascular responses were measured throughout the study.

RESULTS

When compared with the control period, both stressors induced a greater number of pressure waves (p < 0.05), and the area under the curve (p < 0.01), but only physical stress increased (p < 0.05) pulse rate and blood pressure. There were no regional differences in colonic motility. During recovery, the motor activity returned to baseline after physical stress, but remained high after psychological stress. Psychological stress induced more (p < 0.05) propagated contractions, whereas physical stress induced more (p < 0.05) simultaneous contractions.

CONCLUSIONS

Both stressors enhanced colonic motor activity, but psychological stress induced a prolonged response with propagated activity and without appreciable autonomic response. Thus, colonic motor responses may vary depending on the stressor.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.

Studies on the interaction between ICV effects of CRF and CNS noradrenaline depletion

The role of an intact locus coeruleus (LC) noradrenergic system for the central effects of corticotropin-releasing factor (CRF) was studied. Rats were treated with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4), a highly selective noradrenergic neurotoxin permanently affecting mainly the LC system. This procedure did not affect the activation of the sympathetic nervous system, as measured by plasma catecholamine levels, after either intracerebroventricular (ICV) or intraperitoneal (IP) administration of 8-micrograms CRF. Neither was the increased emotionality seen in an open field test after ICV injection of CRF altered. However, the ulceroprotective effect of 8-micrograms CRF ICV during a 2-hr water restraint stress was significantly antagonized by pretreatment with DSP-4, while CRF did exhibit an ulceroprotective effect after IP administration to DSP-4-treated animals. Our data indicate that the ulceroprotective effect of CRF under restraint stress is, at least partly, dependent on an intact locus coeruleus noradrenergic system.

Stress effects on gastrointestinal transit in the rat

Previous investigations of stress effects on gastric emptying, orocaecal, and colonic transit in rats have produced conflicting results. Here one type of stressor, a 'passive avoidance' situation, was used to investigate its effects on gastric emptying, orocaecal and colonic transit. After the rats had been trained to eat a standard amount of semisolid food, gastric emptying was determined (n = 12) by the food remaining in the stomach after various periods of rest, or stress exposure. Orocaecal transit (n = 14) was determined by breath hydrogen measurements after the food had been labelled with 1 g lactose. Colonic transit (n = 18) was measured as the arrival time of coloured faeces after infusion of a carmine red solution into the caecum through a chronically implanted catheter. The stressor had differential effects on transit through the stomach, small bowel and colon: gastric emptying was delayed (p less than 0.05) after stress (t1/2 = 2.66 h after stress, 1.97 h at rest). Orocaecal transit was accelerated (p less than 0.05) after stress; transit time decreased from 124.3 min at rest to 86.2 min after stress. Colonic transit was accelerated (p less than 0.01) under stress, from 15.5 h to 1.29 h. It is concluded that gastrointestinal transit in different parts of the gastrointestinal tract is differently affected by central nervous stimuli.

Restraint stress in biomedical research: a review

The use of restraint or immobilization for investigations of animal physiology, pathology and pharmacology has an extensive history. The major use of this technique has been as a "stressor" for the induction of stress response syndromes in animals. Many such syndromes have been characterized from the behavioral level to the neurochemical concomitants of stress. As a consequence of this particular use of the restraint procedure, much information concerning drug effects on stress response syndromes has been obtained. Indeed, many researchers in the area of gastrointestinal drugs routinely screen their new compounds in a restraint model of gastric stress ulcer. The purpose of this review is to present for researchers, a summary of the methods for, the parameters of, and known drug effects on, restraint-induced pathology. In our experience, this technique has proven to be a very useful one for the examination of both central and peripheral mechanisms of stress-related disorders, as well as for studying drug effects upon these disorders.

Regional rat brain noradrenaline turnover in response to restraint stress

Male Wistar rats were starved for 12 hr and then subjected to either 2 hr of wire mesh "envelope" restraint at room temperature; 2 hr of supine restraint in a specially constructed harness at room temperature or were not restrained. Eight brain regions were examined for NA level and the level of its major metabolite, MHPG-SO4. Plasma corticosterone and gastric ulcer incidence were also measured. All restrained rats displayed marked elevations in MHPG-SO4 levels in most brain regions. In addition, several brain regions in restrained animals showed a reduction in NA level. All restrained rats showed elevated plasma corticosterone levels and evidence of gastric lesions. In general, supine restraint produced greater alterations in regional brain NA turnover, greater evidence of ulcer disease, and higher plasma corticosterone levels than did wire mesh restraint. These data suggest that acute but intense stress in the form of restraint causes markedly altered brain NA activity--a possible neurochemical mechanism underlying the phenomenon of stress-induced disease.