Gastric ulceration in rats is exacerbated by allowing a so-called recovery period after exposure to an ulcerogenic stressor. One hypothesis, which has support from pharmacological studies, argues that this effect is brought about by a rebound of parasympathetic activation. We tested this parasympathetic rebound hypothesis by presenting animals with a fear-inducing (sympathetic-activating) conditioned stimulus (CS) after 2 hr of water-restraint stress. Contrary to the hypothesis, presentation of such a CS increased severity of ulceration compared with those animals that did not receive the CS after restraint stress and control animals. These ulceration data favor instead a sustained activation hypothesis for ulceration, whereby presentation of the CS effectively prolonged the length of time during which animals were under stress, thus enhancing the degree of ulceration. Measurement of plasma corticosterone however indicated a negative correlation between adrenocortical activity and degree of gastric ulceration, contrary to that expected by a sustained activation hypothesis. It is suggested that this inconsistency may be because of the activating of a pituitary-endorphinogenic mediated stress analgesia.
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