Spontaneous locomotor recovery in spinal cord injured rats is accompanied by anatomical plasticity of reticulospinal fibers

Abstract

Although injured axons in mammalian spinal cords do not regenerate, some recovery of locomotor function following incomplete injury can be observed in patients and animal models. Following a lateral hemisection injury of the thoracic spinal cord, rats spontaneously recover weight-bearing stepping in the hind limb ipsilateral to the injury. The mechanisms behind this recovery are not completely understood. Plasticity in the reticulospinal tract (RtST), the tract responsible for the initiation of walking, has not been studied. In this study, rats received lateral thoracic hemisection of the spinal cord, and RtST projections were compared in two groups of rats, one early in recovery (7 days) and the other at a time point when weight-bearing stepping was fully regained (42 days). We found that this recovery occurs in parallel with increased numbers of collaterals of spared RtST fibers entering the intermediate lamina below the injury at L2. Sprouting of injured RtST fibers above the lesion was not found. In conclusion, our study suggests that sprouting of spared RtST fibers might be involved in the recovery of locomotion following incomplete spinal cord injury.

Plasticity After Spinal Cord Injury: Relevance to Recovery and Approaches to Facilitate It

“…Moreover, plantar stepping that returned to a mouse hind-limb ipsilateral to a thoracic spinal cord hemisection was abolished by delayed, contralateral hemisection [18]. These results indicate that the spinal cord is able to adapt after incomplete injury by mechanisms involving functional redundancy [19], locomotor networks preserved after a second complete lesion [17], spared long-tract axon collateral sprouting [20], sprouting of spinal interneurons even capable of bridging a staggered hemisection [18], and/or adaptations of motoneurons [21] in the thoracolumbar spinal cord caudal to the SCI.…”

Progesterone Reduces Secondary Damage, Preserves White Matter, and Improves Locomotor Outcome after Spinal Cord Contusion

“…46,47 This area was significantly larger in contusioned animals treated with PROG than in the vehicle group (Fig. 2C, SCI + PROG: 0.38 mm 2 -0.034 vs. SCI: 0.27 mm 2 -0.067, p < 0.05).…”

“…White matter tracts that occupy the outer rim of the cord such as the rubro-, raphe-, reticulo-and vestibulospinal tracts are part of the descending brainstem system that appear to provide important, if not essential, input to the central pattern generator (CPG) to initiate locomotion and produce complex and precise locomotor patterns. 46,47,62 Thus, axon sparing of these tracts by PROG treatment may underline the described locomotor recovery.…”

Chondroitinase ABC Combined with Neurotrophin NT-3 Secretion and NR2D Expression Promotes Axonal Plasticity and Functional Recovery in Rats with Lateral Hemisection of the Spinal Cord

“…Lateral hemisection of the thoracic spinal cord leads to transient severe impairment of hindlimb function ipsilateral to the injury (Hains et al, 2001;Ballermann and Fouad, 2006;Arvanian et al, 2009) with milder effects on the contralateral hindlimb. All the animals tested showed a similar pattern of recovery in the 2 weeks after injury.…”