International Journal of Comparative Psychology

Experiments are described in which Sprague Dawley rats were deliberately subjected to a daily 15- min white noise regime (90 dB) for 3 or 6 weeks, to determine its effects on the cardiovascular system and intestinal mucosa. In one set of experiments cardiovascular responses were monitored by radiotelemetry. Exposure to noise increased heart rate and mean arterial pressure and reduced stimulation of the parasympathetic nervous system. In the second set of experiments, one group of rats was exposed to the noise protocol for 3 weeks and a second group was not. All the rats were then anaesthetized and the small intestines of half the animals were fixed for microscopy. The remaining rats had their mesenteric microvasculature perfused for one minute with fluorescent albumin before fixing for microscopy. The rats exposed to noise showed significantly more eosinophils and degranulated mast cells in the intestinal villi than the quiet rats. In addition, the villi were swollen and the epithelial cells had widened junctions. The noise group also showed significantly more leakage of fluorescent albumin from the mesenteric microvessels. These experiments demonstrate that 90 dB white noise reduces stimulation the parasympathetic nervous system and also induces an inflammatory response in the intestinal mucosa, resulting in structural damage. These results are consistent with a stress response.