Cervical sprouting of corticospinal fibers after thoracic spinal cord injury accompanies shifts in evoked motor responses

Abstract

deficits [1]. Small injuries can result in transient impairments, but the mechanisms of recovery are poorly understood [2]. At the cortical level, rearrangements of the sensory and motor representation maps often parallel recovery [3, 4]. Results and discussion In the sensory system, studies have shown thatAdult female Lewis rats were anesthetized, and their left cortical and subcortical mechanisms contribute to motor cortex was exposed and stimulated by a tungsten map rearrangements [5, 6], but for the motor system microelectrode as described in the supplemental materials the situation is less clear. Here we show that large-section, with the aim to identify an area that yields consisscale structural changes in the spared rostral part tent and exclusive hind-limb (HL) responses. Consistent of the spinal cord occur simultaneously with shifts with previous studies [8, 9], this was found to be the case of a hind-limb motor cortex representation after for stimulations at 2 mm caudal to bregma and 1.5-2.5 mm traumatic spinal-cord injury. By intracortical lateral to the midline. Stimulation at these coordinates microstimulation, we defined a cortical area that usually activated hind-limb flexor muscles and, more consistently and exclusively yielded hind-limb rarely, extensor muscles. In two animals, muscles of the muscle responses in normal adult rats. Four weeks tail base were activated. We determined the stimulus after a bilateral transsection of the corticospinal threshold by increasing stimulus intensities and recording tract (CST) in the lower thoracic spinal cord, we again the lowest intensity at which a consistent movement was stimulated this cortical field and found forelimb, observed [7]. The average threshold was 49.6 A (Ϯ 18.1 whisker, and trunk responses, thus demonstrating standard deviation [SD], n ϭ 32), and animals with threshreorganization of the cortical motor olds above 100 A were not used for physiological evaluarepresentation. Anterograde tracing of corticospinal tion. After the stimulation, the animals received an addifibers originating from this former hind-limb area tional dose of anaesthetic (xylazine), and the scalp wasrevealed that sprouting greatly increased the sutured. Subsequently, the spinal cord was exposed at a normally small number of collaterals that lead into mid-thoracic level (T8), and the dorsal columns, including the cervical spinal cord rostral to the lesion. We the main component of the corticospinal tract (CST), were conclude that the corticospinal motor system has transsected bilaterally as described [10]. Care was taken greater potential to adapt structurally to lesions than not to compromise the dorsolaterally running rubrospinal was previously believed and hypothesize that this tract (Figure 1). In a control group, the spinal cord was spontaneous growth response is the basis for the exposed but not transsected (sham operation). The tissue observed motor representation rearrangements overlying the spinal cord was sutured, and the animals and contributes to functional recov...

Increased Close Appositions between Corticospinal Tract Axons and Spinal Sympathetic Neurons after Spinal Cord Injury in Rats

“…Confirming previous reports (Fouad et al, 2001;Weidner et al, 2001;Raineteau et al, 2002), spinal injury elicited substantial sprouting of the corticospinal tract rostral to the lesion. The trajectories of these collaterals were not limited to regions well supplied with collaterals of the CST in intact rats.…”

“…First, after transection, the corticospinal tract of the rat collateralizes abundantly into new regions of the dorsal horn and intermediate zone (Fouad et al, 2001). Second, sprouting corticospinal tract axons (CST) make new connections with somatic interneurons above incomplete spinal lesions.…”

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

“…BDNF infused into the rat motor cortex enhanced rostral sprouting, but not regeneration, of corticospinal tract axons injured by thoracic spinal cord dorsal funiculotomies [115]. When we applied this approach after thoracic spinal cord dorsal over-hemisection, the collateral sprouting of corticospinal tract axons and innervation of cervical spinal cord propriospinal interneurons we previously observed [25] was enhanced [116]. Intrathecal infusion of BDNF or pegylated BDNF caudal to thoracic spinal cord transection or contusive injury similarly promoted cholinergic axon sprouting, stimulated hindlimb air-stepping, and improved both hindlimb joint movements and Basso, Beattie, and Bresnahan open field locomotor rating scale scores [117,118].…”

“…Here, as well, axon collateral sprouting appears to be involved. For example, we found that rat hindlimb corticospinal tract axons axotomized in the thoracic spinal cord dorsal funiculus sprouted axons into the cervical spinal cord gray matter [25]. Associated with this was novel forelimb and trunk muscle activity being evoked by hindlimb motor cortex stimulation.…”

Prominent Role of the Spinal Central Pattern Generator in the Recovery of Locomotion after Partial Spinal Cord Injuries

“…The recovery of locomotion after partial lesions may depend on multiple cooperative mechanisms that can be regrouped under the general heading of neuroplasticity (Wolpaw and Tennissen, 2001;Nudo, 2006;Rossignol, 2006). After partial SCI, the regeneration of damaged fibers and/or sprouting of undamaged fibers may contribute to recovery (Fouad et al, 2001;Raineteau and Schwab, 2001; Raineteau et al, 2002;Bareyre et al, 2004; Ballermann and Fouad, 2006). Plastic changes within descending pathways could suggest that inputs from the brain and brainstem supplant functions normally performed by the spinal locomotor CPG.…”