Physiology labs at the beginning of the semester started off on the boring side of interesting because many of them were conducted with computer simulation software (we had SimNeuron, SimMuscle, … you get the gist) that generated the data for us. Some time in the last few weeks, though, the labs have gotten interactive and fun! It started off when we measured the effects of certain vasodilators and vasoconstrictors on a biopsied rat aorta. We’ve also done ECGs one one another, taken blood pressure in various physical states, and listened to heart sounds to complement our cardiovascular unit. Today’s lab was probably the pinnacle of the semester: each lab group operated on a live, anesthetized rat to study the effect of vagus stimulation! Even our professor had been looking forward to it for a while. At the last class, he reminded us enthusiastically that it was “VAGUS, BABY!” coming up 🙂
Lest the word “operate” gives the wrong impression I will preface by saying that each rat was sacrificed after the experiment with a high dose of KCl injected into the heart, while still under anesthesia. I think and hope it did not suffer at all.
Our standard white lab rat came to us fully sedated by the lab technician. We picked it up and laid it out on a glass stretcher. The first task was to cut open the chest and find the trachea for intubation. Strictly speaking, this was not necessary for the vagus investigation, but it was a good experience for us to have. This required “atraumatically” tearing through some layers of muscle and making a “T”-shaped incision in the trachea through which a cannula was inserted, all of which Rina did expertly!
Then, we located the carotid artery, which is relatively large and easy to identify because of its pulsation. The vagus nerve, in contrast, is a minuscule strip on the underside of the artery. Priyanka and a Hungarian student joining us for the day separated the nerve, and placed an electrical insulator under it. For the next part of the experiment, we inserted subcutaneous ECG leads, placed an electrode on the nerve, and measured the heart rate. (Because of the nerve’ parasympathetic function, stimulation of the nerve led to a reduction in heart rate. Administering atropine, a parasympathetic antagonist, reversed the effect.)
Afterwards, the official experiment was over, but we dissected the rest of the rat to see its internal organs, all so similar to humans’ viscera. The set-up looked something like by then: this [warning! not for the squeamish]. We also cut into the head and removed the brain. Although some found this extra dissection a bit gruesome, I felt better knowing that we got the most out of the sacrificed life.
Initially, I was actually bit skeptical that the lab experiment was worth the life. Couldn’t this be one of the simulated ones? In retrospect, though, it was about more than the physiology of the vagus nerve. It was the first time I had ever cut into something living, and also the first time I killed a mammal (not that I kill other classes of animals on the regular or anything, but I have no mercy when it comes to bugs!). It’s a different facet of medicine from all the theory stuffed into our heads these years, and one necessitating a prepared emotional response. This was “just a lab rat”, but soon, it won’t be!