A simple preparation for obtaining a reliable heart rate record in freely moving rats

A technique for recording heart rate (HR) from freely moving rats using a specially developed harness and subdermal electrodes is described. Electrodes are implanted via a hypodermic needle. Animals prepared in this way are unrestricted in their behavior and show no signs of distress. EKG signals are of high fidelity and are relatively free of electromyographic interference. These characteristics enable reliable phasic HR responses to be recorded during periods of high skeletal muscle activity such as those exhibited during aversive conditioning. Since the procedure is relatively untraumatic, electrodes may be removed and reimplanted at a later date.