And in humans, that combination of achievements has eluded researchers. Nevertheless, says Young, recent experiments with adult rats show that some axon regeneration and recovery after severe spinal cord injury might be possible. Although the experiments leave some questions unanswered and it will be important for other groups of researchers to repeat the study, they have generated enormous interest. In their experiments, Henrich Cheng, the surgeon in Olson's group, cut through the spinal cords of adult rats, removed a short segment from each, and grafted into the gap a 'bridge' of 18 tiny pieces of nerve taken from the muscle tissue between the animal's ribs. Newspapers and TV stations reported the new findings with great excitement.
Gage agrees that the severed spinal cord axons regrew in the rats.
But he is not convinced that those newly formed fibers actually caused the animals' partial recovery of their ability to walk, an issue that he believes can be resolved by more experiments. Such differences of opinion are not unusual among scientists. In fact, studies of spinal cord regeneration have a long history and embrace many different research strategies. Other scientists ask why the CNS of a very young mammal can repair itself automatically but the CNS of an adult mammal cannot. As scientists learn the answers to these and other questions about the development and function of the central nervous system, they can design strategies for repairing damage to the spinal cord and brain.