Effects of novelty and conditioned fear on small intestinal and colonic motility and behaviour in the rat

Abstract

Novelty and conditioned fear were used to investigate the effects of psychological stress on fasting small intestinal and colonic myoelectric activity and their relation with behaviour in freely moving rats fitted with bipolar electrodes on proximal jejunum and colon. Rats in both novelty and conditioned fear groups spent a 15 min session in a novel box, where only rats in the fear group received unescapable, repeated foot shock (10 × 6 s, 0.5 mA). Behaviour in groups reexposed to the box on day 1 or day 7 indicated a profound difference in emotional state. Conditioned fear rats remained largely immobile, while novelty rats displayed active exploratory behaviour. Behaviour during conditioned fear did not differ significantly between rats reexposed to the box either 1 or 7 days after foot shock, while novelty animals appeared more aroused on day 7. Conditioned fear on day 1 caused a significant increase in colonic spike burst frequency compared to basal values in the home cage. A smaller but significant increase was found in novelty rats. In groups tested after 7 days, both novelty and conditioned fear resulted in small increases in colonic burst frequency that did not differ significantly from each other. No effects were found on the incidence of the fasting jejunal Migrating Motility Complex. Defecation was see only in conditioned fear rats, but did not differ quantitatively between day 1 and day 7. We conclude that, in the rat, colonic myoelectric spike burst activity is highly responsive to psychological stress, while the fasting pattern of small intestinal activity is more resistant. The behavioural data indicate that the colonic response to stress is determined by the gross emotional impact of the stressor, but may show adaptation at longer intervals after shock conditioning.