Regulation of Heart Function in the Rat

Photographic Illustrations

To provide students with better preparation for this laboratory exercise, the teaching staff put together the following visual documentation of the procedures. Not every procedure is shown, but the photos should help students visualize the anatomical structures and be better prepared for this lab.

Click on each photo to see an enlarged image.

	Initial incision. Note use of forceps to lift skin so scissors can stay clear of underlying structures. Note: All photos below are taken from the same angle (looking at rat's left side, with nose to the right in photo) unless indicated.
	A glass probe is used to pull the trachea ventrally to allow room for the suture threads.
	Suture threads have been inserted under the trachea, one rostral (to the right in photo) and one caudal to the intended cannulation site.
	A small scissors is used to cut a hole between rings of cartilage in the trachea. Try to make the smallest hole possible using these scissors; you can always enlarge it later if needed. If the hole is too large it will cause problems.
	A cannula (plastic tube) is inserted into the hole. Slide the cannula about 1 cm down into the trachea. The appropriate distance depends on the position of the hole in the trachea; the important thing is to insert the cannula far enough to seal off air leakage and hold it in place, while not pushing the tip down as far as the bronchi.
	Threads have been tied. Note that one thread (to the left in photo) tightens the seal of the trachea around the cannula, while the other one helps prevent the cannula from being accidentally yanked out.
	Cutting the wall of the upper abdomen, in preparation for opening the chest cavity. The dark organ is the spleen.
	As soon as the diaphragm has been cut, the ventilator is attached.
	Cutting through the ribs to expose the chest cavity. The ventilator is briefly turned off while making these cuts.
	The large dark organ (at left in photo) is the liver. The pinkish organ (near bottom of photo) is the left lung. The ventilator should be turned off for a few seconds while cutting through the ribs, so the lungs will deflate (as seen here), making it easier to avoid cutting them.
	Removing the sternum (and attached portions of ribs). Note the hemostats (in this case two were needed to clamp off both internal thoracic arteries).
	Hook inserted through apex of heart. This step requires patience, because the hook should pierce enough of the heart wall to hold tight but not go deep enough to penetrate the chambers of the heart.
	After hooking the heart, attach the other end of the thread to the force transducer. It is better to use a shorter thread than seen in this photo. (If the Chart signal is poor, move the transducer down and retie the thread at a shorter distance.)
	(View from tail end.) Note placement of hook in heart. Also note the two hemostats used to close off both internal thoracic arteries. Note protruding ribs at rat's right side (to the left in photo); it might have been better to cut them a little shorter so the heart wouldn't bump into them when it beats. The large dark organ in foreground is the liver; you can also see a triangular remnant of the diaphragm above and to the rat's right of the liver (left side of photo).
	Experiment in progress. A measured amount of drug (e.g. epinephrine) is dripped directly onto the heart surface, and the resulting changes are observed in Chart.
	(View from rat's right side; nose to the left in photo.) In preparation for finding one of the vagus nerves, a plastic dropper was used to siphon off some of the blood that is obscuring the structures in the neck. Alternatively, a piece of absorbent gauze can be used. A glass probe (at right in photo) is being used to probe for the right vagus nerve.
	(View from rat's right side; nose to the left in photo.) Isolated right vagus nerve. Note how close to the trachea the vagus is. The right sternomastoid muscle is being held away laterally by the glass probe on the right. Glass probes were used to tease the muscles apart from one another and to separate the vagus from its sheath of connective tissue.