Surgeons in Japan have severed and then reconnected the spinal cords
of neonatal rats, the first time this has been consistently achieved in
mammals. The reconnections were permanent, and left the rats’ spinal cords
‘hardly distinguishable from normal’, the researchers say.
In 32 newborn rats, the spinal cord was severed and a piece of embryonic
spinal cord grafted in its place. In the 22 rats which survived, the grafts
were either completely absorbed into the spinal cord, or joined so successfully
that they made a seamless spinal cord. The animals were soon able to run
and jump as normal, say the researchers.
A control group of 28 rats also had their spinal cords severed, but
were given either no grafts, grafts of different material, or grafts of
spinal cord material inserted back to front. The animals did not function
‘We didn’t use drugs such as neuro-trophic factor in this surgery,’
says Yasushi Iwashita of Kyoto University. ‘It was purely surgical technique.’
He says that similar experiments have been unsuccessful in the past because
the scientists did not match the grafted portion with the severed section
of the spine. The Kyoto team took care to make the match in terms of physiology
and orientation. Iwashita believes the axons in the central nervous system
need positional ‘cues’ if they are to regrow properly – hence the need to
position the grafted segment accurately.
But Iwashita warns that the experiments were only successful in very
young rats, which seem to have the characteristics of much lower vertebrates,
such as chickens. ‘Neonate mammals have a greater plasticity than adult
mammals, so this kind of experiment cannot be applied to adults directly.
There are many difficult problems in applying the results to human spinal
cord injuries directly,’ he says.