Asynchronization in Changes of Electrophysiology and Pathology of Spinal Cord Motor Neurons in Rats Following Middle Cerebral Artery Occlusion

Transsynaptic degeneration of ventral horn motor neurons exists but plays a minor role in lower motor system dysfunction in acute ischemic rats

BACKGROUND

As a leading cause of mortality and long-term disability, acute ischemic stroke can produce far-reaching pathophysiological consequences. Accumulating evidence has demonstrated abnormalities in the lower motor system following stroke, while the existence of Transsynaptic degeneration of contralateral spinal cord ventral horn (VH) neurons is still debated.

METHODS

Using a rat model of acute ischemic stroke, we analyzed spinal cord VH neuron counts contralaterally and ipsilaterally after stroke with immunofluorescence staining. Furthermore, we estimated the overall lower motor unit abnormalities after stroke by simultaneously measuring the modified neurological severity score (mNSS), compound muscle action potential (CMAP) amplitude, repetitive nerve stimulation (RNS), spinal cord VH neuron counts, and the corresponding muscle fiber morphology. The activation status of microglia and extracellular signal-regulated kinase 1/2 (ERK 1/2) in the spinal cord VH was also assessed.

RESULTS

At 7 days after stroke, the contralateral CMAP amplitudes declined to a nadir indicating lower motor function damage, and significant muscle disuse atrophy was observed on the same side; meanwhile, the VH neurons remained intact. At 14 days after focal stroke, lower motor function recovered with alleviated muscle disuse atrophy, while transsynaptic degeneration occurred on the contralateral side with elevated activation of ERK 1/2, along with the occurrence of neurogenic muscle atrophy. No apparent decrement of CMAP amplitude was observed with RNS during the whole experimental process.

CONCLUSIONS

This study offered an overview of changes in the lower motor system in experimental ischemic rats. We demonstrated that transsynaptic degeneration of contralateral VH neurons occurred when lower motor function significantly recovered, which indicated the minor role of transsynaptic degeneration in lower motor dysfunction during the acute and subacute phases of focal ischemic stroke.

Alterations in the spinal cord and ventral root after cerebral infarction in non-human primates

BACKGROUNDS

Cerebral infarction does not only cause focal injury in the ischemic site, but also secondary non-ischemic damage at the remote areas of nervous system associated with the primary focus.

OBJECTIVE

This study investigated the changes in the spinal cord and ventral root after middle cerebral artery occlusion (MCAO) in cynomolgus monkeys (Macaca fascicularis).

METHODS

Adult male cynonolgus monkeys (4-5 years, 5.5-7.5 kg) were subjected to MCAO (n = 6) or sham surgery (n = 4). After 12 weeks, spinal cords and the ventral roots were harvested. Morphometric alterations in the spinal cord were detected at C5 and L5 levels via immunofluorescence. The profiles of C5 and L5 ventral roots were displayed by toluidine blue staining and transmission electron microscopic examination.

RESULTS

Significant axonal loss in the contralateral corticospinal tract and abnormally enlarged axons in the ipsilateral were observed in monkeys with MCAO. The number of neurons in the contralateral ventral horn got declined while that in the ipsilateral was almost unaffected after MCAO compared with sham controls. Glial activation post-MCAO was observed in the bilateral corticospinal tract and the ventral horn. Aberrant nerve fibers appeared frequently in the contralateral ventral roots of MCAO monkey but rarely in the ipsilateral.

CONCLUSIONS

These results indicate that focal cerebral infarction leads to pathological alterations in the spinal cord and ventral roots in non-human primates.