Olfactory bulb glial cell transplant preserves muscles in paraplegic rats

Spinal chord injuries represent a serious and irreversible handicap that is sadly frequent in our society. Because of the permanent break in the nervous connections between the brain and the organs and muscles, such injuries impair their movement inducing atrophy and deterioration while they disturb organic functions.

The pioneering studies carried out by Santiago Ramón y Cajal established that while nerve cells from the peripheral nervous system (PNS) have the capacity to repair themselves, the same does not apply to adult brain cells and spinal cord cells from the central nervous system (CNS). The difference is not in the nerve cells themselves but in the cellular enviroment that gives them support – the glial cells. These cells are involved in the transmision of nerve impulses and produce myelin. Schwann cells (a variety of glial cell) in the peripheral nervous system (PNS) provide factors that contribute to the regeneration of the axons whereas the glia of the CNS do not have such a nurturing role. For this reason, one of the strategic experimental approaches for the regeneration of spinal chord neurons consists in altering their cellular enviroment by introducing cells that create a supportive environment for axon regeneration in the damaged area. The glial cells that surround the axons in the olfactory bulb (OBG) are a promising example because they promote axon regeneration in the CNS.

In an experiment using paraplegic rats, it was found that 8 months after a transplant treatment in a transected spinal chord using OBS, axon regeneration was taking place and sensorial and motor recovery was perceived in behavioural tests. The investigation recently published in the Journal of Physiology (London) [J Physiol 586.10 (2008) pp 2593–2610], with the collaboration of scientists from the “Centro de Biología Molecular Severo Ochoa” (CSIC-UAM), Córdoba University, and the “Instituto de Biomedicina de Valencia” (CSIC), has analysed for the first time the muscular characteristics of paraplegic animals treated with an OBG transplant and compared them with those of untreated paraplegic animals and healthy control animals.

The study exhibits a high correlation between the functional capability shown by the animals in behavioural tests and some biochemical parameters. The parameters measured differentiate the muscular characteristics of paraplegic and healthy animals and they established that animals treated with the transplant had more similar characteristics to the healthy animals than the untreated paraplegic animals. In spite of the global effect of OBG transplants, only 3 of the 9 treated animals (and none of the untreated) showed near normal muscle characteristics. This could imply that maintaining the muscular phenotype might rely on the interaction between the transplanted cells and other factors.

One the possible factors that affect the result could be the physical exercise to which the animals were subjected. This could be significant since it is well known that rehabilitation treatment aids regenerative therapies. Both voluntary and assisted exercise stimulates synaptic plasticity and the regenerative capabilities of neurons of the CNS as well as re-establishes adequate trophic factors. The role of the OBG in establishing a nurturing cellular environment for axon regeneration could induce adaptation in the local spinal circuits that favours the conservation of muscular properties and automatic contractions even while the damaged neural pathways are not fully recovered.