Altered brain stem responsivity to duodenal pain after a single stressful experience

A single session of foot shock stress produces stable and long lasting sensitization of behavioral, hormonal and intestinal motility responses to novel stressful stimuli in laboratory rats. This is reflected in increased expression of the activity marker protein Fos in brain areas involved, following an external stressor. We present data from awake, freely moving rats in which a silicone balloon was surgically implanted in the duodenum. Firstly, cardiovascular reflexes to distentions were studied using telemetry with surgically implanted transmitters, 2 weeks after a single, 15-min session of foot shocks. The distentions caused characteristic, bi-phasic responses in both mean arterial blood pressure and heart rate that were not different between preshocked and control animals. Secondly, the numbers of Fos immunopositive cells were quantified in selected brain areas, 1 h after repeated distention of the duodenum. We found an increase in distention-induced Fos in preshocked rats in the nucleus tractus solitarius and a weaker effect in the central nucleus of the amygdala. This could be a first indication that altered visceral afferent processing in previously stressed rats, found earlier for the colon, may be a general and not an organ-specific phenomenon.