METHOD FOR LONG-TERM MEASUREMENTS OF SYMPATHETIC NERVE ACTIVITY IN FREELY MOVING RATS.

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The sympathetic nervous system is believed to play a major role in regulating cardiovascular function during exercise. However, only a few direct measurements of sympathetic nervous activity during whole body dynamic exercise have been attempted.In the present study, we have established methods for the measurements of the renal sympathetic nerve activity (RSNA) and cardiovascular function during treadmill exercise in rats. We trained Wistar rats to run on the treadmill over a week before the surgery. At least 2 days before the experiment, electrodes for the measurements of RSNA and electrocardiogramand electromyogram, catheters for the measurements of systemic arterial and central venous pressures were implanted under aseptic condition.The responses in RSNA to treadmill exercise and spontaneous movement was measured with a satisfactory signal to noise ratio for over a week. We observed no contamination by noise signals, which could have originated from the EMG and ECG or the experimental equipment, including the treadmill, on the RSNA recorded during the tread-mill exercise and voluntary movement. The ratio of RSNA signal to noise was enough to evaluate the response of sympathetic nerve activity to voluntary and involuntary movements in rats. This level of RSNA signal with satisfactory signal to noise ratio, lasted over a week after the surgery in approximately 70% of the animals of fifty rats. This experimental model allows us to study the neural mechanisms involved in the regulation of cardiovascular function during dynamic exercise in rats.