Prithvi K. Shah

Variability in step training enhances locomotor recovery after a spinal cord injury.

Performance of a motor task is improved by practicing a specific task with added ‘challenges’ to a training regimen. We tested the hypothesis that, in the absence of brain control, the performance of a motor task is enhanced by training using specific variations of that task. We utilized modifications of step performance training to improve the ability of spinal rats to forward step. After a complete thoracic spinal cord transection, 20 adult rats were divided randomly to bipedally step on a treadmill in the forward, sideward, or backward direction for 28 sessions (20u2003min, 5u2003days/week) and subsequently tested for their ability to step in the forward direction. Although the animals from all trained groups showed improvement, the rats in the sideward‐trained and backward‐trained groups had greater step consistency and coordination along with higher peak amplitudes and total integrated activity of the rectified electromyographic signals from selected hindlimb muscles per step during forward stepping than the rats in the forward‐trained group. Our results demonstrate that, by retaining the fundamental features of a motor task (bipedal stepping), the ability to perform that motor task can be enhanced by the addition of specific contextual variations to the task (direction of stepping). Our data suggest that the forward stepping neuronal locomotor networks are partially complemented by synchronous activation of interneuronal/motoneuronal populations that are also a part of the sideward or backward stepping locomotor networks. Accordingly, the overlap and interaction of neuronal elements may play a critical role in positive task transference.

Use of quadrupedal step training to re-engage spinal interneuronal networks and improve locomotor function after spinal cord injury

Can lower limb motor function be improved after a spinal cord lesion by re-engaging functional activity of the upper limbs? We addressed this issue by training the forelimbs in conjunction with the hindlimbs after a thoracic spinal cord hemisection in adult rats. The spinal circuitries were more excitable, and behavioural and electrophysiological analyses showed improved hindlimb function when the forelimbs were engaged simultaneously with the hindlimbs during treadmill step-training as opposed to training only the hindlimbs. Neuronal retrograde labelling demonstrated a greater number of propriospinal labelled neurons above and below the thoracic lesion site in quadrupedally versus bipedally trained rats. The results provide strong evidence that actively engaging the forelimbs improves hindlimb function and that one likely mechanism underlying these effects is the reorganization and re-engagement of rostrocaudal spinal interneuronal networks. For the first time, we provide evidence that the spinal interneuronal networks linking the forelimbs and hindlimbs are amenable to a rehabilitation training paradigm. Identification of this phenomenon provides a strong rationale for proceeding toward preclinical studies for determining whether training paradigms involving upper arm training in concert with lower extremity training can enhance locomotor recovery after neurological damage.

Sub-threshold spinal cord stimulation facilitates spontaneous motor activity in spinal rats

BackgroundEpidural stimulation of the spinal cord can be used to enable stepping on a treadmill (electrical enabling motor control, eEmc) after a complete mid-thoracic spinal cord transection in adult rats. Herein we have studied the effects of eEmc using a sub-threshold intensity of stimulation combined with spontaneous load-bearing proprioception to facilitate hindlimb stepping and standing during daily cage activity in paralyzed rats.MethodsWe hypothesized that eEmc combined with spontaneous cage activity would greatly increase the frequency and level of activation of the locomotor circuits in paralyzed rats. Spontaneous cage activity was recorded using a specially designed swivel connector to record EMG signals and an IR based camcorder to record video.Results and conclusionThe spinal rats initially were very lethargic in their cages showing little movement. Without eEmc, the rats remained rather inactive with the torso rarely being elevated from the cage floor. When the rats used their forelimbs to move, the hindlimbs were extended and dragged behind with little or no flexion. In contrast, with eEmc the rats were highly active and the hindlimbs showed robust alternating flexion and extension resulting in step-like movements during forelimb-facilitated locomotion and often would stand using the sides of the cages as support. The mean and summed integrated EMG levels in both a hindlimb flexor and extensor muscle were higher with than without eEmc. These data suggest that eEmc, in combination with the associated proprioceptive input, can modulate the spinal networks to significantly amplify the amount and robustness of spontaneous motor activity in paralyzed rats.

Plasticity of subcortical pathways promote recovery of skilled hand function in rats after corticospinal and rubrospinal tract injuries.

The corticospinal and rubrospinal tracts are the predominant tracts for controlling skilled hand function. Injuries to these tracts impair grasping but not gross motor functions such as overground locomotion. The aim of the present study was to determine whether or not, after damage to both the corticospinal and rubrospinal tracts, other spared subcortical motor pathway can mediate the recovery of skilled hand function. Adult rats received a bilateral injury to the corticospinal tract at the level of the medullar pyramids and a bilateral ablation of the rubrospinal axons at C4. One group of rats received, acutely after injury, two injections of chondroitinase-ABC at C7, and starting at 7days post-injury were enrolled in daily reaching and grasping rehabilitation (CHASE group, n=5). A second group of rats received analogous injections of ubiquitous penicillinase, and did not undergo rehabilitation (PEN group, n=5). Compared to rats in the PEN group, CHASE rats gradually recovered the ability to reach and grasp over 42days after injury. Overground locomotion was mildly affected after injury and both groups followed similar recovery. Since the reticulospinal tract plays a predominant role in motor control, we further investigated whether or not plasticity of this pathway could contribute to the animals recovery. Reticulospinal axons were anterogradely traced in both groups of rats. The density of reticulospinal processes in both the normal and ectopic areas of the grey ventral matter of the caudal segments of the cervical spinal cord was greater in the CHASE than PEN group. The results indicate that after damage to spinal tracts that normally mediate the control of reaching and grasping in rats other complementary spinal tracts can acquire the role of those damaged tracts and promote task-specific recovery.

Neuromodulation of motor-evoked potentials during stepping in spinal rats

The rat spinal cord isolated from supraspinal control via a complete low- to midthoracic spinal cord transection produces locomotor-like patterns in the hindlimbs when facilitated pharmacologically and/or by epidural electrical stimulation. To evaluate the role of epidural electrical stimulation in enabling motor control (eEmc) for locomotion and posture, we recorded potentials evoked by epidural spinal cord stimulation in selected hindlimb muscles during stepping and standing in adult spinal rats. We hypothesized that the temporal details of the phase-dependent modulation of these evoked potentials in selected hindlimb muscles while performing a motor task in the unanesthetized state would be predictive of the potential of the spinal circuitries to generate stepping. To test this hypothesis, we characterized soleus and tibialis anterior (TA) muscle responses as middle response (MR; 4-6 ms) or late responses (LRs; >7 ms) during stepping with eEmc. We then compared these responses to the stepping parameters with and without a serotoninergic agonist (quipazine) or a glycinergic blocker (strychnine). Quipazine inhibited the MRs induced by eEmc during nonweight-bearing standing but facilitated locomotion and increased the amplitude and number of LRs induced by eEmc during stepping. Strychnine facilitated stepping and reorganized the LRs pattern in the soleus. The LRs in the TA remained relatively stable at varying loads and speeds during locomotion, whereas the LRs in the soleus were strongly modulated by both of these variables. These data suggest that LRs facilitated electrically and/or pharmacologically are not time-locked to the stimulation pulse but are highly correlated to the stepping patterns of spinal rats.

Alkaline Ceramidase 3 Deficiency Results in Purkinje Cell Degeneration and Cerebellar Ataxia Due to Dyshomeostasis of Sphingolipids in the Brain.

Dyshomeostasis of both ceramides and sphingosine-1-phosphate (S1P) in the brain has been implicated in aging-associated neurodegenerative disorders in humans. However, mechanisms that maintain the homeostasis of these bioactive sphingolipids in the brain remain unclear. Mouse alkaline ceramidase 3 (Acer3), which preferentially catalyzes the hydrolysis of C18:1-ceramide, a major unsaturated long-chain ceramide species in the brain, is upregulated with age in the mouse brain. Acer3 knockout causes an age-dependent accumulation of various ceramides and C18:1-monohexosylceramide and abolishes the age-related increase in the levels of sphingosine and S1P in the brain; thereby resulting in Purkinje cell degeneration in the cerebellum and deficits in motor coordination and balance. Our results indicate that Acer3 plays critically protective roles in controlling the homeostasis of various sphingolipids, including ceramides, sphingosine, S1P, and certain complex sphingolipids in the brain and protects Purkinje cells from premature degeneration.

Evaluation of optimal electrode configurations for epidural spinal cord stimulation in cervical spinal cord injured rats.

BACKGROUNDnEpidural spinal cord stimulation is a promising technique for modulating the level of excitability and reactivation of dormant spinal neuronal circuits after spinal cord injury (SCI). We examined the ability of chronically implanted epidural stimulation electrodes within the cervical spinal cord to (1) directly elicit spinal motor evoked potentials (sMEPs) in forelimb muscles and (2) determine whether these sMEPs can serve as a biomarker of forelimb motor function after SCI.nnnNEW METHODnWe implanted EMG electrodes in forelimb muscles and epidural stimulation electrodes at C6 and C8 in adult rats. After recovering from a dorsal funiculi crush (C4), rats were tested with different stimulation configurations and current intensities to elicit sMEPs and determined forelimb grip strength.nnnRESULTSnsMEPs were evoked in all muscles tested and their characteristics were dependent on electrode configurations and current intensities. C6(-) stimulation elicited more robust sMEPs than stimulation at C8(-). Stimulating C6 and C8 simultaneously produced better muscle recruitment and higher grip strengths than stimulation at one site.nnnCOMPARISON WITH EXISTING METHOD(S)nClassical method to select the most optimal stimulation configuration is to empirically test each combination individually for every subject and relate to functional improvements. This approach is impractical, requiring extensively long experimental time to determine the more effective stimulation parameters. Our proposed method is fast and physiologically sound.nnnCONCLUSIONSnResults suggest that sMEPs from forelimb muscles can be useful biomarkers for identifying optimal parameters for epidural stimulation of the cervical spinal cord after SCI.

Spinal Epidural Stimulation Strategies: Clinical Implications of Locomotor Studies in Spinal Rats:

Significant advancements in spinal epidural stimulation (ES) strategies to enable volitional motor control in persons with a complete spinal cord injury (SCI) have generated much excitement in the field of neurorehabilitation. Still, an obvious gap lies in the ability of ES to effectively generate a robust locomotor stepping response after a complete SCI in rodents, but not in humans. In order to reveal potential discrepancies between rodent and human studies that account for this void, in this review, we summarize the findings of studies that have utilized ES strategies to enable successful hindlimb stepping in spinal rats. Recent clinical and preclinical evidence indicates that motor training with ES plays a crucial role in tuning spinal neural circuitry to generate meaningful motor output. Concurrently administered pharmacology can also facilitate the circuitry to provide near optimal motor performance in SCI rats. However, as of today, the evidence for pharmacological agents to enhance motor function in persons with complete SCI is insignificant. These and other recent findings discussed in this review provide insight into addressing the translational gap, guide the design of relevant preclinical experiments, and facilitate development of new approaches for motor recovery in patients with complete SCIs.

Rodent estrous cycle response to incomplete spinal cord injury, surgical interventions, and locomotor training.

Estrous cycle disruption after spinal cord injury (SCI) in female rats is a common phenomenon. It remains unknown, however, if the aberrant estrous cycle is a result of an injury to the spinal cord itself or due to the general stress associated with surgical interventions. We addressed this issue by determining estrous cyclicality in female rats after a spinal cord hemisection (HX), implantation of EMG wires into selected hind limb muscles, and/or injections of tracer dyes into the spinal cord. Because it is known that aerobic exercise can enhance the recovery of locomotor function in rodents with an incomplete SCI, we also determined if locomotor training positively impacts the disrupted estrous cycle after an HX. Estrous cycle assessments were made during a 5-8 week period in 27 female rats before and after HX, EMG, and/or dye injection surgeries and in HX rats that recovered spontaneously or underwent locomotor training. Our results show that estrous cyclicality was disrupted (cycle length >5 days) in approximately 76%, 46%, and 50% of the rats after HX, EMG, and dye injection surgeries, respectively. The cyclicality, however, was disrupted for a longer period after HX than after EMG or dye injection surgeries. Furthermore, estrous cycle mean length was shorter in the trained than nontrained HX group. These results suggest that estrous cycle disruption after a major SCI is a consequence of both the direct injury to the spinal cord and to the associated stress. Moreover, moderate aerobic exercise initiated early after a spinal cord HX returns the duration of the estrous cycle toward normal.

In vivo 31P NMR spectroscopy assessment of skeletal muscle bioenergetics after spinal cord contusion in rats

PurposeMuscle paralysis after spinal cord injury leads to muscle atrophy, enhanced muscle fatigue, and increased energy demands for functional activities. Phosphorus magnetic resonance spectroscopy (31P-MRS) offers a unique non-invasive alternative of measuring energy metabolism in skeletal muscle and is especially suitable for longitudinal investigations. We determined the impact of spinal cord contusion on in vivo muscle bioenergetics of the rat hind limb muscle using 31P-MRS.MethodsA moderate spinal cord contusion injury (cSCI) was induced at the T8–T10 thoracic spinal segments. 31P-MRS measurements were performed weekly in the rat hind limb muscles for 3xa0weeks. Spectra were acquired in a Bruker 11xa0T/470xa0MHz spectrometer using a 31P surface coil. The sciatic nerve was electrically stimulated by subcutaneous needle electrodes. Spectra were acquired at rest (5xa0min), during stimulation (6xa0min), and recovery (20xa0min). Phosphocreatine (PCr) depletion rates and the pseudo first-order rate constant for PCr recovery (kPCr) were determined. The maximal rate of PCr resynthesis, the in vivo maximum oxidative capacity (Vmax) and oxidative adenosine triphosphate (ATP) synthesis rate (Qmax) were subsequently calculated.ResultsOne week after cSCI, there was a decline in the resting total creatine of the paralyzed muscle. There was a significant reduction (~24xa0%) in kPCr measures of the paralyzed muscle, maximum in vivo mitochondrial capacity (Vmax) and the maximum oxidative ATP synthesis rate (Qmax) at 1xa0week post-cSCI. During exercise, the PCr depletion rates in the paralyzed muscle one week after injury were rapid and to a greater extent than in a healthy muscle.ConclusionsUsing in vivo MRS assessments, we reveal an acute oxidative metabolic defect in the paralyzed hind limb muscle. These altered muscle bioenergetics might contribute to the host of motor dysfunctions seen after cSCI.