Isolation of the carotid sinus baroreceptor in the conscious rat model

We developed a chronic technique by which we can completely isolate the carotid sinus baroreceptor region in the rat and study the carotid baroreceptor reflex control of heart rate and arterial pressure in conscious rats. Using sterile techniques, the left and right carotid sinus regions were exposed through a midline neck incision. Overlying muscles were retracted and the omohyoideus muscle was cut to expose the region. The right and left sympathetic trunks and aortic nerves were cut leaving only the vagus nerves intact. The left carotid sinus was destroyed by scraping the surface of the sinus bulb and then crushing the carotid sinus nerve. A fine hair was placed around the root of the bifurcation of the right common carotid artery with a fine needle threader and tied in place. Two stainless steel bail bearings, 1/32nd in. O.D., were placed inside the common carotid artery followed by a special flexible catheter. Arterial pressure was monitored via a catheter placed in the femoral artery. Both catheters were externalized at the back. The two catheters were conjoined externally to allow for closed loop function of the reflex system during recovery. After two days open loop carotid sinus function was assessed by changing the carotid sinus pressure and monitoring arterial pressure changes. When carotid sinus pressure is changed between 50 and 175 mmHg the arterial pressure decrease averaged nearly 50 mmHg and the heart rate changes were from 450 to 350 beats/min. This technique is highly reliable for isolating the rat carotid sinus in the conscious rat model. Supported by NIH-H37-HL-19039.