RESEARCH
PROFILES
The
Mechanism of 4-AP Action
By
Anita Kaiser
Canadian Spinal Research Organization
Spinal cord
injury causes damage to the nerves in the spinal cord. Often the
myelin, the insulative coating surrounding the nerve axon, is damaged
or worn away. The myelin enables speedy transmission of electrical
signals across the nerves.
When a healthy
nerve cell transmits an 
electrical signal, it is excited causing
potassium ions to flow through it to bring the nerve back to a normal
state. A damaged nerve is no longer able to transmit signals. Injury
to the myelin allows the potassium ions to leak out preventing the
nerve from reaching an excited state to transmit a signal.
A drug 4-AP,
(4-aminopyridine) has been discovered that has the ability to counteract
the effects of demyelination. It is a nerve conduction enhancing
compound. The drug blocks the pore or channel that allows potassium
ions to flow through when the nerve cell is excited. This blocking
ability makes the cell more excitable. In other words, it amplifies
the impulse signal so that it can travel through the nerve past the
demyelinated area.
Up until now,
4-AP has provided temporary improvement in chronic, incomplete spinal
cord injury, since it has only been administered on a one-time basis.
It appears that the drug needs to be given daily in order to obtain
sustained improvement. Some effects include increased bowel and bladder
control, increased sexual function, increased sensation below the
level of injury, decreased stiffness or spasticity, and reduction
in pain. Currently, clinical trials are planned to examine the long
term usage of 4-AP.
