Medicine

Surgeons Conduct Head Transplants on Rats, Say Humans Are Next

After 14 head transplants on rats, a pair of surgeons say they will attempt a human head transplant in the next 10 months in China.

Chinese scientists have transplanted the head of a donor rat onto the back of a host body, creating an equally garish and impressive two-headed rat that may offer insights into the viability of an eventual human head transplant.

The process, which was done by way of a rat triad, which included a donor, recipient, and blood supply rat, provided a continuous blood supply to the donor brain throughout the transplant, avoiding brain tissue hypothermia — a condition where the brain suffers in absence of a blood supply. The problem has long been one of the major barriers to carrying out a successful head transplant in animal specimens.

At the end of the experiment, discussed in a paper published in CNS Neuroscience and Therapeutics, lead author Li Peng-Wei and colleagues reported that the donor head had “no obvious abnormalities” and “exhibited substantial movement.” While critics of the plan abound, the study lays clear the authors’ belief that “this model will facilitate current efforts toward the first human head transplant.”

Scientists have been trying to perfect the head transplant for decades, though attempts have overwhelmingly been met with problems of hypothermia and immune rejection — the recipient body and new head refusing to work together to ensure one another’s survival. In the 1950s, a Soviet researcher famously made 19 attempts to create a two-headed dog, while a neurosurgeon in Cleveland transplanted a monkey head onto its beheaded peer in the 1970s, keeping the brain alive for seven days.

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While these techniques tested techniques for keeping the brain alive in the absence of a blood supply, authors of the study said their goal, in contrast to that of Chinese researchers, was not the long-term viability of the specimen. In this study, scientists believe to have surmounted these issues, though they recognize that long-term immune rejection continues to be a primary risk and will require further study.

Like the Soviet study from the 1950, Chinese researchers cut the donating specimen at the chest, not the neck, in a technique that may offer an alternative to head detachment for a successful head transplant. They employed the use of rat triads, which enabled them to maintain a permanent blood supply to the donor brain until its blood vessels were connected to those of the recipients.   

The study involved 60 rats of varying weights, though the donor and recipient rat maintained a weight ratio of 1-to-6 in order to avoid circulatory overload in the eventual two-headed rat.

After all rats were anesthetized, researchers opened the chest of the donor rat, connecting two of its major veins — the thoracic aorta and superior vena — to the recipient rat by way of two silicon blood vessels. The blood supply rat was connected to the donor brain and an external pump kept blood circulating to the donor brain throughout the transplant, avoiding brain tissue hypothermia. Scientists also used a temperature change device to keep the blood of the donor rat warm.

In the meantime, researchers made an incision on the back of the recipient rat’s neck and cut the vessels that would attach to the new head. The donor head was placed above the cut, its blood vessels then inserted and grafted on to those of the recipient. Researchers then closed the incision with stitches, reporting full cross-circulation between donor and recipient and that neither donor nor recipient had their circulation interrupted in the process.

The silicon blood vessels were removed and, in the end, 14 triads survived for an average of 36 hours. During this time, researchers reported that oxygen levels in the blood remained normal. After the operation, rats exhibited normal pain and corneal reflexes. Aside from accidentally losing one triad during anesthesia, the researchers reported no other anomalies in donors or recipients.

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Authors of the paper are optimistic that they have demonstrated a successful head transplant technique that assumes substantially fewer risks than those attempted in the past. “We speculate that the method used in this experiment can provide a new idea for the short-term preservation of central nervous system transplantation,” they wrote. The team is blazing a controversial trail towards the first human head transplant, which may come sooner than expected.

Two of the authors on the paper are Chinese neurosurgeon Xiao-Ping Ren and Italian neurosurgeon Sergio Canavero, who has received criticism in response to his ambitious plans to carry out the first human head transplant later this year. In an interview offered by his public relations agency, OOOM, Canavero said that “the first human head transplantation will already be conducted within the next 10 months in China.”

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