The way that the spinal cord sprouts new nerve fibers after a spinal cord injury was further illuminated today by new research conducted in Rhesus monkeys.
We spoke with Ephron Rosenzweig, a researcher at the University of California, San Diego, who performed this work, which provides insight into why patients with mild spinal cord injuries can sometimes experience substantial recovery, and may aid in future research therapies for severe spinal cord injuries.
Rosenzweig answered our questions about the ethics of such work.
Q: Where do you get the monkeys from?
A: They are born and raised in very large enclosures at a dedicated primate facility. They grow up in normal family groups, form strong bonds with peers, and live normal lives.
Q: What is done to ensure the monkeys are treated humanely?
A: Every precaution is taken to ensure that the monkeys do not suffer in any way. During surgery, there is a dedicated anesthesiologist, just as there would be for a human, to make sure that the monkey is deeply anesthetized and not feeling any pain. The lesion itself is very small and precise and spares autonomic function and locomotion [involuntary movement] — the main result is a weakness of the right hand. After surgery, the monkeys are given analgesics to eliminate pain during the healing process, and are constantly monitored for signs of discomfort. Any discomfort is alleviated immediately.
Q: How is research on monkeys regulated? What kind of approval is needed for a study like this?
A: All work must be performed in accordance with the guidelines of the American Association for the Accreditation of Laboratory Animal Care, which reviews each institution’s compliance regularly. In addition, every procedure must be approved by the Institutional Animal Care and Use Committee before it is used on an animal. These procedures are subject to regular reviews and renewals to ensure the welfare of the animals.
Q: Why is this kind of work on monkeys necessary? Why can't you just use mice?
A: The nervous system of primates (both monkeys and humans) is very different from the nervous system of rodents. The most obvious external difference — size — can actually be a critical limiting factor in some treatments. Moreover, differences in immune function can have drastic effects on the efficacy and safety of treatments. Finally, as this work clearly demonstrates, differences in the organization and function of neural subsystems can hide or reveal crucial information regarding spinal cord injury. Rodent models are still the mainstay of [spinal cord injury] research, but it is of the utmost importance that we also have primate models to allow careful evaluation of treatments before translating those treatments to humans.
Q: Are there alternatives to using monkeys in research and testing?
A: There are alternatives at some steps of the process. In vitro work (on isolated cells in dishes ) is useful for testing large numbers of potential treatment compounds. Rodent work is useful for further assessing the functions of possible treatments. But many scientists agree that there is no substitute for research in monkeys to ensure the safety and efficacy of a treatment before beginning clinical trials in humans.
Q: What advances has this research brought us? Has it given us knowledge that we wouldn't otherwise have?
A: This research has revealed an unsuspected capability of the nervous system (in particular, the corticospinal tract) to generate new, compensatory growth after an injury. Such extensive growth was not evident in previous studies of rodents. We can now study the mechanisms behind this growth, then attempt to elicit and enhance new growth in the spinal cord of humans living with severe [spinal cord injury.]