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

Abstract

Background: Motor dysfunction is common in stroke patients. Clinical electrophysiological studies suggest that transsynaptic degeneration occurred in the lower motor neurons, while pathological evidence is lacked. This study aimed to combine the electrophysiological and pathological results to prove the existence of transsynaptic degeneration in the motor system after stroke.

Methods: Modified neurologic severity score, electrophysiological, and pathological assessments were evaluated in rats before middle cerebral artery occlusion (MCAO), and at 24 hours, 7 days, and 14 days after MCAO. Paired and independent-sample t-tests were applied to assess the changes of electrophysiological and pathological data.

Results: Compound motor action potential amplitude in the paretic side was significantly lower than the nonparetic side at both 24 hours (61.9 ± 10.4 vs. 66.6 ± 8.9, P < 0.05) and 7 days (60.9 ± 8.4 vs. 67.3 ± 9.6, P < 0.05) after MCAO. Motor unit number estimation of the paretic side was significantly less than the nonparetic side (379.0 ± 84.6 vs. 445.0 ± 89.5, P < 0.05) at 7 days after MCAO. Until 14 days after stroke, the pathological loss of motor neurons was detected. Motor neurons in 14-day MCAO group were significantly decreased, compared with control group (5.3 ± 0.7 vs. 7.3 ± 1.8, P < 0.05).

Conclusions: Both electrophysiological and pathological studies showed transsynaptic degeneration after stroke. This study identified the asynchronization in changes of electrophysiology and pathology. The abnormal physiological changes and function impairment can be detected in the early stage and recovered quickly, while the pathological loss of motor neuron can be detected only in a later stage.

Figure 1

(a) Schematic representation of the electrophysiology tests. R1: The active recording electrode; R2: The reference recording electrode; S1: The cathode of the stimulating electrode; S2: The anode of stimulating electrode; G: The ground electrode. (b and c) Compound muscle action potential and motor unit number estimation examples.

Figure 2

(a and b) The max difference of bilateral compound muscle action potential (CMAP) amplitude and motor unit number estimation (MUNE) showed at 7 days after the operation. (c-e) The number of anterior/posterior horn neurons was decreasing over the time. Active astrocytes showed in the early time after middle cerebral artery occlusion. Vertical bars represented standard deviation. GFAP: Glial fibrillary acidic protein.

Figure 3

(a-c) Motoneurons with neuron-specific nuclear protein (Immunohistochemical [IHC] staining, original magnification ×40), B-cell lymphoma/leukaemia-2 (IHC, ×100), B-cell lymphoma/leukaemia-2 associated X expressions (IHC, ×100), respectively. (d) Neuron-specific nuclear protein staining neurons in the posterior horn. Neurons of Rexed layers I–III (white Rome number) in three nonoverlapping areas (white rectangle) were counted (IHC, ×100). (e) Glial fibrillary acidic protein positive astrocytes (red arrow) (IHC, ×200).