Encouraging regeneration in the central nervous system: is there a role for olfactory ensheathing cells?

The olfactory system holds a privileged position within the adult mammalian central nervous system; olfactory neurons undergo continual replacement and regeneration of synaptic contacts following injury, a feature shared by only a select few neuronal systems. The olfactory ensheathing cell, a glial cell found only in this system, is thought to play a central role in this regenerative process and has hence been the focus of numerous studies into promoting CNS regeneration following injury, in particular of the spinal cord. In trials, olfactory ensheathing cells have achieved some of the most promising results yet in promoting CNS regeneration, including a degree of functional recovery in humans following CNS injury. Comparatively, numerous other strategies, both those involving cellular transplantation and those examining neutralisation of inhibitory factors of the CNS, have achieved limited success. A combinational strategy, with olfactory ensheathing cells at its centre, is arguably the best way forward in encouraging effective recovery following CNS injury. This review examines the inhibitory environment of the CNS and the research to date on overcoming its effects on the regrowth of injured axons. The efficacy of therapies involving olfactory ensheathing cells, and the place of these therapies among the many other strategies being developed is examined.