Multimodal exercises simultaneously stimulating cortical and brainstem pathways after unilateral corticospinal lesion

Characterization of Axon Damage, Neurological Deficits, and Histopathology in Two Experimental Models of Intracerebral Hemorrhage

Spontaneous intracerebral hemorrhage (ICH) is one of the most lethal forms of stroke. From the limited previous studies and our preliminary data, white matter is considered a key predictor of the outcome and potential target of recovery. The traditional ICH model induced by injection of autologous blood or bacterial collagenase into striatum (ST) demonstrated a spontaneous functional recovery within one or 2 months. We hypothesis that an internal capsule (IC) lesion might lead to long-term axonal damage and long lasting functional deficits. Thus in this study, a modified internal capsule ICH model was conducted in rats, and the axonal damage, neurological deficits, histopathology as well as electrophysiology were characterized. The finding demonstrated that compared to ST group, the modified IC lesioned model exhibited a relatively smaller lesion volume with consistent axonal loss/degeneration and long-lasting neurological dysfunction at 2 months after ICH. Functionally, the impairment of the mNSS, ratio of contralateral forelimb usage, four limb stand index, contralateral duty cycle and ipsilateral SSEPs amplitude remained significant at 56 days. Structurally, the significant loss of PKCγ in ipsilateral cortical spinal tracts of IC group and the consistent axonal degeneration with several axonal retraction bulbs and enlarged tubular space was observed at 56 days after ICH. This study suggested that a modified IC lesioned model was proved to have long lasting neurological deficits. A comprehensive understanding of the dynamic progression after experimental ICH should aid further successful clinic translation in animal ICH studies, and provide new insights into the role of whiter matter injury in the mechanism and therapeutic targets of ICH.

Multimodal cortical and subcortical exercise compared with treadmill training for spinal cord injury

BACKGROUND AND PURPOSE

Spared fibers after spinal cord injury (SCI) tend to consist predominantly of subcortical circuits that are not under volitional (cortical) control. We aim to improve function after SCI by using targeted physical exercises designed to simultaneously stimulate cortical and spared subcortical neural circuits.

METHODS

Participants with chronic motor-incomplete SCI enrolled in a single-center, prospective interventional crossover study. Participants underwent 48 sessions each of weight-supported robotic-assisted treadmill training and a novel combination of balance and fine hand exercises, in randomized order, with a 6-week washout period. Change post-intervention was measured for lower extremity motor score, soleus H-reflex facilitation; seated balance function; ambulation; spasticity; and pain.

RESULTS

Only 9 of 21 enrolled participants completed both interventions. Thirteen participants completed at least one intervention. Although there were no statistically significant differences, multimodal training tended to increase short-interval H-reflex facilitation, whereas treadmill training tended to improve dynamic seated balance.

DISCUSSION

The low number of participants who completed both phases of the crossover intervention limited the power of this study to detect significant effects. Other potential explanations for the lack of significant differences with multimodal training could include insufficient engagement of lower extremity motor cortex using skilled upper extremity exercises; and lack of skill transfer from upright postural stability during multimodal training to seated dynamic balance during testing. To our knowledge, this is the first published study to report seated posturography outcomes after rehabilitation interventions in individuals with SCI.

CONCLUSION

In participants with chronic incomplete SCI, a novel mix of multimodal exercises incorporating balance exercises with skilled upper extremity exercises showed no benefit compared to an active control program of body weight-supported treadmill training. To improve participant retention in long-term rehabilitation studies, subsequent trials would benefit from a parallel group rather than crossover study design.

Structural and functional improvements due to robot-assisted gait training in the stroke-injured brain

Robot-assisted gait training (RAGT) can improve walking ability after stroke. Because the underlying mechanisms are still unknown, we analyzed changes in post-stroke injured brains after RAGT. Ten non-ambulatory patients receiving inpatient rehabilitation were examined within 3 months of stroke onset. RAGT consisted of 45min of training, 3days per week. We acquired diffusion tensor imaging (DTI) data before and after 20 sessions of RAGT. Fractional anisotropy (FA) maps were then used to determine neural changes after RAGT. Fugl-Meyer motor assessment of the lower extremity, motricity index of the lower extremity, functional ambulation category, and trunk control tests were also conducted before training, after 10 and 20 RAGT sessions, and at the 1-month follow-up. After RAGT, the supplementary motor area of the unaffected hemisphere showed increased FA, but the internal capsule, substantia nigra, and pedunculopontine nucleus of the affected hemisphere showed decreased FA. All clinical outcome measures improved after 20 sessions of RAGT. Our findings indicate that RAGT can facilitate plasticity in the intact supplementary motor area, but not the injured motor-related areas, in the affected hemisphere.

Injury-induced decline of intrinsic regenerative ability revealed by quantitative proteomics

Neurons differ in their responses to injury, but the underlying mechanisms remain poorly understood. Using quantitative proteomics, we characterized the injury-triggered response from purified intact and axotomized retinal ganglion cells (RGCs). Subsequent informatics analyses revealed a network of injury-response signaling hubs. In addition to confirming known players, such as mTOR, this also identified new candidates, such as c-myc, NFκB, and Huntingtin. Similar to mTOR, c-myc has been implicated as a key regulator of anabolic metabolism and is downregulated by axotomy. Forced expression of c-myc in RGCs, either before or after injury, promotes dramatic RGC survival and axon regeneration after optic nerve injury. Finally, in contrast to RGCs, neither c-myc nor mTOR was downregulated in injured peripheral sensory neurons. Our studies suggest that c-myc and other injury-responsive pathways are critical to the intrinsic regenerative mechanisms and might represent a novel target for developing neural repair strategies in adults.

Acute changes in soleus H-reflex facilitation and central motor conduction after targeted physical exercises

We tested the acute effect of exercises targeted simultaneously at cortical and brainstem circuits on neural transmission through corticobulbar connections. Corticobulbar pathways represent a potential target for rehabilitation after spinal cord injury (SCI), which tends to spare brainstem circuits to a greater degree than cortical circuits. To explore this concept, able-bodied volunteers (n=20) underwent one session each of three exercises targeted at different nervous system components: treadmill walking (spinal locomotor circuits), isolated balance exercise (brainstem and other pathways), and multimodal balance plus skilled hand exercise (hand motor cortex and corticospinal tract). We found that short-interval soleus H-reflex facilitation increased after one session of balance and multimodal exercise by 13.2±4.0% and 8.3±4.7%, and slightly decreased by 1.9±4.4% after treadmill exercise (p=0.042 on ANOVA across exercise type). Increases in long-interval H-reflex facilitation were not significantly different between exercises. Both balance and multimodal exercise increased central motor conduction velocity by 4.3±2.6% and 4.5±2.8%, whereas velocity decreased by 4.3±2.7% after treadmill exercise (p=0.045 on ANOVA across exercise type). In conclusion, electrophysiological transmission between the motor cortex and spinal motor neurons in able-bodied subjects increased more following one session of balance exercise than treadmill exercise.