Blood pressure, heart rate, and behavioral responses to psychological "novelty" stress in freely moving rats

We developed a new model of psychological "open-field" stress in freely mov ing rats. Blood pressure and heart rate of. the rats were measured by radio telemetry and behavior analyzed by video tracking software. Open-field expo sure induced marked increases in blood pressure and heart rate. Repeated da ily exposure induced pressor responses that were slightly higher on Day 4 w hen compared to Day 1. Pretreatment with the beta1-adrenoceptor antagonist atenolol inhibited the tachycardia whereas the ganglion blocker pentolinium inhibited the presser response, indicating involvement of the sympathetic nervous system. Pretreatment with diazepam prevented the novelty stress-ind uced presser response and reduced the tachycardia. These results show that the psychological stress of exposing rats to an open field induces marked c ardiovascular effects that are mediated by sympathetic hyperactivity. This model is unique in that it focuses on psychological stress and allows conco mitant measurement of blood pressure. heart rate, and behavior in freely mo ving rats.