Nat Med. 2008 Jan;14(1):69-74.

Recovery of supraspinal control of stepping via indirect propriospinal relay connections after spinal cord injury.

Courtine G, Song B, Roy RR, Zhong H, Herrmann JE, Ao Y, Qi J, Edgerton VR, Sofroniew MV.

Department of Physiological Sciences, University of California, Los Angeles, California 90095-1763, USA.

Spinal cord injuries (SCIs) in humans and experimental animals are often associated with varying degrees of spontaneous functional recovery during the first months after injury. Such recovery is widely attributed to axons spared from injury that descend from the brain and bypass incomplete lesions, but its mechanisms are uncertain. To investigate the neural basis of spontaneous recovery, we used kinematic, physiological and anatomical analyses to evaluate mice with various combinations of spatially and temporally separated lateral hemisections with or without the excitotoxic ablation of intrinsic spinal cord neurons. We show that propriospinal relay connections that bypass one or more injury sites are able to mediate spontaneous functional recovery and supraspinal control of stepping, even when there has been essentially total and irreversible interruption of long descending supraspinal pathways in mice. Our findings show that pronounced functional recovery can occur after severe SCI without the maintenance or regeneration of direct projections from the brain past the lesion and can be mediated by the reorganization of descending and propriospinal connections. Targeting interventions toward augmenting the remodeling of relay connections may provide new therapeutic strategies to bypass lesions and restore function after SCI and in other conditions such as stroke and multiple sclerosis.

Relevance

This research proves that there are other ways to achieve functional recovery without regrowing the damaged long axons in the spinal cord. The central nervous system can reorganize to use smaller nerves to complete the motor pathway. By adding exercise to the equation we believe that we can assist this reorganization and enhance functional recovery.

Brain. 2007 Nov;130(Pt 11):2993-3003.

Reaching training in rats with spinal cord injury promotes plasticity and task specific recovery.

Girgis J, Merrett D, Kirkland S, Metz GA, Verge V, Fouad K.

McGill University, Centre for Neuronal survival, Montreal, Canada.

In the current study we examined the effects of training in adult rats with a cervical spinal cord injury (SCI). One group of rats received 6 weeks of training in a single pellet reaching task immediately after injury, while a second group did not receive training. Following this period changes in cortical levels of BDNF and GAP-43 were analysed in trained and untrained animals and in a group with training but no injury. In another group of rats, functional recovery was analysed in the reaching task and when walking on a horizontal ladder. Thereupon, the cortical forelimb area was electrophysiologically examined using micro-stimulation followed by tracing of the lesioned corticospinal tract (CST). We found that trained rats improved substantially in the reaching task, when compared to their untrained counterparts. Trained rats however, performed significantly worse with their injured forelimb when walking on a horizontal ladder. In parallel to the improved recovery in the trained task, we found that the cortical area where wrist movements could be evoked by micro-stimulation expanded in trained rats in comparison to both untrained and uninjured rats. Furthermore, collateral sprouting of lesioned CST fibres rostral to the injury was increased in trained rats. Post-injury training was also found to increase cortical levels of GAP-43 but not BDNF. In conclusion we show that training of a reaching task promotes recovery of the trained task following partial SCI by enhancing plasticity at various levels of the central nervous system (CNS), but may come at the cost of an untrained task.

Relevance

From our point of view, the most important point here is the conclusion that the task trained is the task learned, and that training a specific task may come at the cost of an untrained task.. If you only train a specific task (such as body weight supported walking) you may not be able to stand or be able to walk without body weight support. Therefore, it is vitally important to train in as many tasks as possible in order to gain proficiency in all of them.

These studies complement each other because training more tasks will increase the stimulus to the nervous system, this increase in stimulus may assist in forming new propriospinal connections leading to greater functional recovery.