I’m not impressed with this recent exercise in microsurgical technique to allow researchers to transplant the head of one rat to another rat’s body. In all honesty, I don’t see the point.
I’m going to put the discussion of this paper below the fold because it seems more an exercise in animal cruelty than anything else; I’ve included one figure illustrating the surgery, but it will be at thumbnail size and you’ll have to click on it to see it in all its gory vulgarity.
First, let’s get the justification out of the way. It’s a techniques paper to improve on methods for CSA. “CSA”, if you were curious, is short for “cephalosomatic anastomosis”, because obviously we’ve got to distance ourselves from what is being done with sciencey language, rather than just saying “head transplant”.
We thus developed several animal CSA models, including a full head transplant in mice, with the goal of testing both neuroprotective techniques (e.g., hypothermia) and antirejection immunological protocols. Here, we improve on the bicephalic preparations employed by past pioneers (see above).
This is not new. Of course you’ve got to concern yourself with rejection in any organ transplant; these concerns have already been worked on, and the head transplant is no different nor does this procedure add significantly to our body of knowledge. Another concern is ischemia and shock. If the switching of circulatory systems isn’t free of trauma or major disruptions in blood flow, you can cause serious organ damage. The brain is especially sensitive to this kind of problem, but again, these transitions and solutions are not new to surgeons — every time open heart surgery is performed, these changes are addressed.
So I’m at a loss. None of this is novel or necessary. It’s impressively delicate surgery, because I sure couldn’t stitch one teeny-tiny rat carotid to another rat’s, but the end result seems so futile and irrelevant.
Here’s what they did. Take one very small rat, the head donor, and one very large rat — 6 times larger than the donor — and anesthetize them. Open up the recipient rat’s neck and expose the jugular vein and carotid artery; tie them off (basically killing the recipient rat’s brain), and insert silicone tubes that travel through a peristaltic pump to help maintain a steady pressure, and then passes through a water bath that cools the blood to 31.5°C (hypothermia also helps protect the brain), and connect those to the axillary artery and vein of the donor rat.
Now the fun begins. Since oxygenated blood is now flowing from the host rat to the donor’s head, open up the donor’s chest, tie off the donor heart and lungs, and you can throw away the back half of the donor.
You can then stitch the donor rat’s head to the back of the neck of the host rat. Voila!
You may have noticed a bit of a cheat there. You use a host 6 times larger than the donor so, apparently, you have excess circulatory capacity and you can divert part of it to keep both animals “alive”. And it worked! For 6 hours, anyway.
In our experiment, the donor head was first connected to a rat’s blood supply, by peristaltic pumps, and only thereafter separated donor head from the donor body. In this state, the donor head was maintained for up to 6 hours, with no obvious abnormalities in the donor’s EEG or corneal reflexes. Following nociceptive stimuli, the donor head exhibited substantial movement.
Again, that last sentence is using a sciencey word to remove us all a bit from what they were doing. What it means is that when they did something painful to the donor head, it twitched and squirmed.
These are not surprising results. It’s exactly what I would expect would happen: maintain the blood supply to the head and you can do anything you want to the rest of the body, and the brain will still function. It doesn’t solve any of the major problems with head transplants. There is no restoration of nervous system connectivity. All they’ve shown is that you’ll be able to keep a disembodied head alive for a few hours if you dedicate the circulatory and respiratory systems of an entire decapitated corpse to pumping blood through it.
Not particularly useful. Unpleasant and grisly. A waste of rats for an irrelevant purpose.
If you must, here’s an illustration of the procedure.
Li PW, Zhao X, Zhao YL, Wang BJ, Song Y, Shen ZL, Jiang HJ, Jin H, Canavero S, Ren XP (2017) A cross-circulated bicephalic model of head transplantation. CNS Neurosci Ther. 2017 Apr 21. doi: 10.1111/cns.12700. [Epub ahead of print]