We developed a new model of psychological “open-field”
stress in freely moving rats. Blood pressure and heart
rate of the rats were measured by radiotelemetry and behavior
analyzed by video tracking software. Open-field exposure
induced marked increases in blood pressure and heart rate.
Repeated daily exposure induced pressor responses that
were slightly higher on Day 4 when compared to Day 1. Pretreatment
with the β1-adrenoceptor antagonist atenolol
inhibited the tachycardia whereas the ganglion blocker
pentolinium inhibited the pressor response, indicating
involvement of the sympathetic nervous system. Pretreatment
with diazepam prevented the novelty stress-induced pressor
response and reduced the tachycardia. These results show
that the psychological stress of exposing rats to an open
field induces marked cardiovascular effects that are mediated
by sympathetic hyperactivity. This model is unique in that
it focuses on psychological stress and allows concomitant
measurement of blood pressure, heart rate, and behavior
in freely moving rats.