Therapeutic drug approach to stimulate clinical recovery after brain injury.

The identification of strategies by which the central nervous system (CNS) can transform itself in response to injury has incited the systematic exploration of methods to enhance neurological recovery after CNS injury. Several pharmaceuticals have been shown to promote such recovery; however, more rigorous clinical trials are necessary to establish their clinical relevance. The major impediment for these strategies in the clinical arena is the astounding heterogeneity surrounding neuroplasticity and regeneration. Tolerance to injury and varied rates of recovery are likely governed by genetic and environmental factors that remain largely elusive. The extraordinary complexity of the neural networks in the CNS impedes the assessment of 'plain' pharmacological interventions in therapeutic trials. 'Proof-of-principle' studies of pharmacological interventions enhancing neuroplasticity or regeneration may therefore at first focus on surrogate markers, such as functional MRI, magnetoencephalography and diffusion tensor imaging, or investigate seemingly more uniform systems, such as spinal cord injuries. The discovery that experimental adult CNS lesions can essentially regenerate has rejected the conviction that adult axon injury is always permanent and spurred research into determining whether the circumstances under which such regeneration occurs can be created in human CNS injury. The hostility of the microenvironment preventing axonal regrowth has been linked to key molecular targets involving myelin-associated factors and glial scar components. While the mechanisms involved are better understood now and potential therapeutic targets are identified, the crucial question whether manipulating the molecular regulation of axonal repair is feasible and will benefit patients remains uncertain. While factual repair of brain tissue may still be years away, research into the mechanisms of adaptation after brain injury offers more tangible return on the short run.