Changes in muscle-tendon unit length-force characteristics following experimentally induced photothrombotic stroke cannot be explained by changes in muscle belly structure

PURPOSE

The aim of this study was to assess the effects of experimentally induced photothrombotic stroke on structural and mechanical properties of rat m. flexor carpi ulnaris.

METHODS

Two groups of Young-adult male Sprague-Dawley rats were measured: stroke (n = 9) and control (n = 7). Photothrombotic stroke was induced in the forelimb region of the primary sensorimotor cortex. Four weeks later, muscle-tendon unit and muscle belly length-force characteristics of the m. flexor carpi ulnaris, mechanical interaction with the neighbouring m. palmaris longus, the number of sarcomeres in series within muscle fibres, and the physiological cross-sectional area were measured.

RESULTS

Stroke resulted in higher force and stiffness of the m. flexor carpi ulnaris at optimum muscle-tendon unit length, but only for the passive conditions. Stroke did not alter the length-force characteristics of m. flexor carpi ulnaris muscle belly, morphological characteristics, and the extent of mechanical interaction with m. palmaris longus muscle.

CONCLUSION

The higher passive force and passive stiffness at the muscle-tendon unit level in the absence of changes in structural and mechanical characteristics of the muscle belly indicates that the experimentally induced stroke resulted in an increased stiffness of the tendon.

Novel miRNA PC-5P-12969 in Ischemic Stroke

Circulating microRNAs (miRNAs) have been used effectively as peripheral biomarkers and mechanistic targets for human diseases such as stroke, Alzheimer's, and cancer. The purpose of our study is to determine noninvasive, blood-based early detectable biomarkers for ischemic stroke (IS). Based on our previous global miRNA sequencing study, four miRNAs were previously unreported (novel) in IS condition. Among these, miRNA PC-5P-12969 was exclusively expressed in the IS condition; otherwise, it was not expressed in normal condition, and therefore, we focused on miRNA PC-5P-12969 for further studies. In the present study, we investigated novel miRNA PC-5P-12969 for its expression levels using quantitative real-time PCR assay (qRT-PCR) in an in vitro, oxygen, and glucose deprivation/reoxygenation (OGD/R)-treated mouse primary hippocampal neuronal cells (HT22) and in an in vivo using a photothrombotic stroke model. In an in vitro study of stroke-induced HT22 cells, we found a two fold increase of PC-5P-12969 expression levels, in agreement with our original global miRNA study. In the cerebral cortex of photothrombotic stroke mice, we found significantly upregulated levels of PC-5P-12969 in 4 hours and 1 day post-stroke relative to the control mice. However, we did not find any change in the expression of PC-5P-12969 in the cerebellum (unaffected in IS) of both stroke and control mice. Based on findings from this study, together with our earlier original global microRNA study results, we conclude that PC-5P-12969 is a potential candidate of the peripheral marker and also a drug target for IS. This is the first study validating that the miRNA PC-5P-12969, might be a potential biomarker for IS.

Hemodynamic effects of intraoperative anesthetics administration in photothrombotic stroke model: a study using laser speckle imaging

Background

Previous neuroimaging studies have shown the hemodynamic effect of either preconditioning or postconditioning anesthesia in ischemic stroke model. However, the anesthetic effect in hemodynamics during and immediately after the stroke modeling surgery remains unknown due to the lack of appropriate anesthesia-free stroke model and intraoperative imaging technology. In the present study, we utilized our recently developed photothrombotic model of focal cerebral ischemia in conscious and freely moving rats, and investigated transient hemodynamic changes with or without isoflurane administration. Laser speckle imaging was applied to acquire real-time two-dimensional full-field cerebral blood flow (CBF) information throughout the surgical operations and early after.

Results

Significantly larger CBF reduction area was observed in conscious rats from 8 min immediately after the onset of stroke modeling, compared with anesthetized rats. Stroke rats without isoflurane administration also showed larger lesion volume identified by magnetic resonance imaging 3 h post occlusion (58.9%), higher neurological severity score 24 h post occlusion (28.3%), and larger infarct volume from 2,3,5-triphenyltetrazolium chloride staining 24 h post occlusion (46.9%).

Conclusions

Our results demonstrated that the hemodynamic features were affected by anesthetics at as early as during the stroke induction. Also, our findings about the neuroprotection of intraoperative anesthetics administration bring additional insights into understanding the translational difficulty in stroke research.