Involvement of Cerebral Blood Flow on Neurological and Behavioral Functions after Subarachnoid Hemorrhage in Mice

Optimization and evaluation of an experimental subarachnoid hemorrhage model in mice

Subarachnoid hemorrhage (SAH) occurs when blood enters the subarachnoid space, typically due to aneurysm rupture, triggering complex pathophysiological processes. A reliable animal model is crucial for simulating SAH and investigating mechanisms of brain white matter injury. SAH was induced in C57BL/6J mice using an intraluminal perforation technique. Various filaments were tested to determine the optimal one, and filament depth was carefully measured. Postoperative evaluations included monitoring body weight, blood distribution on the skull, and clot formation. Cerebral blood flow was assessed, and neurological function was evaluated using modified Garcia scores, open field tests, and gait analysis. Myelin integrity was assessed by Luxol fast blue staining, and immunofluorescence was used to examine myelin, microglia, and neuronal integrity in the cortex and striatum. Using 4 - 0 polypropylene filaments advanced to 13 ± 1 mm at a 15-20 degree, we established a stable SAH mouse model with a success rate of 91.43% and a mortality rate of 6.25%. The SAH group showed motor impairments at 48 h post-surgery, along with myelin damage in the corpus callosum and striatum, oligodendrocyte damage, and neuronal injury.Our improved intraluminal perforation technique offers a stable and standardized SAH model, providing a reliable platform for studying SAH pathophysiology and testing new therapies.

Time-of-Day-Dependent Effects of Rehabilitation on Motor Recovery After Experimental Focal Cerebral Ischemia

BACKGROUND

Rehabilitation is an efficacious method to improve poststroke motor dysfunction. Various rehabilitative techniques have become popular in this field of research. However, it has not been reported whether better outcomes can be achieved if rehabilitation training is conducted at the optimal time of the day.

METHODS

A model of photothrombotic ischemic stroke was used in C57/BL6 mice, and poststroke 24-hour activity cycles were evaluated. We found an activity peak around Zeitgeber time (ZT)13 (21:00) and a trough around ZT20 (04:00) during the dark phase. In addition, we selected ZT6 (14:00) as the daytime training group (corresponding to the ZT13 training group, ZT20 training group, and ZT6 training group, respectively). The 3 groups underwent treadmill training for 4 weeks. Functional and histological recovery levels were compared among groups. In addition, bulk RNA sequencing analysis was used to explore the possible molecular mechanisms.

RESULTS

The results showed that stroke-induced mice maintained a regular nocturnal locomotor rhythm with reduced amplitude. Motor recovery was greater in the ZT13 training group than in the ZT6 group, with a trend toward better outcomes at ZT13 than ZT20. The ZT13 group also showed superior neuronal survival and neurogenesis compared with ZT6, while improvements between ZT13 and ZT20 were less pronounced. Bulk RNA sequencing suggested that synaptic plasticity, calcium signaling, cAMP signaling, and MAPK signaling pathways contributed to neural repair differences between ZT13 and ZT6. In addition, the results showed a similar pattern of motor recovery in female and aged mice trained at ZT13 compared with ZT6, reinforcing the benefits of time-of-day training.

CONCLUSIONS

In conclusion, rehabilitative training during the most active phase is beneficial for enhanced recovery outcomes. Our study suggests that rehabilitation should be conducted when the body is in an optimal physiological state-that is, a time-of-day-dependent rehabilitation strategy.

Microthrombosis at the Ultra-early Stages after Experimental Subarachnoid Hemorrhage Results in Early Brain Injury

INTRODUCTION

Early Brain Injury (EBI) significantly contributes to poor neurological outcomes and death following subarachnoid hemorrhage (SAH). The mechanisms underlying EBI post-SAH remain unclear. This study explores the relationship between serial cerebral blood flow (CBF) changes and neurological symptoms, as well as the mechanisms driving CBF changes in the ultra-early stages after experimental SAH in mice.

METHODS

SAH was induced by endovascular perforation in male ddY mice. Mice were sacrificed at 6, 12, 24, and 48 h after behavioral tests using the modified neurological score and grid walking test, and CBF was measured via Laser Speckle Flow Imaging (LSFI). Neurofunctional evaluation, CBF analysis, and Western blotting were used to assess SAH-induced damage.

RESULTS

Neurological symptoms were significantly worse at 12 h post-SAH compared to sham (9.5 ± 1.7 vs. 25.6 ± 0.63, respectively; p < 0.0001). CBF was significantly reduced at 12 h post- SAH compared to sham (35.34 ± 8.611 vs. 91.06 ± 12.45, respectively; p < 0.0001). Western blotting revealed significantly elevated thrombin and matrix metalloproteinase 9 levels 12 h post-SAH (p < 0.05).

CONCLUSION

Our results suggest that microthrombus formation peaked at 12 h post-SAH, potentially causing EBI and worsening neurological symptoms. Microthrombus formation in the ultraearly stages may represent a novel therapeutic target for managing EBI.

The urotensin II receptor triggers an early meningeal response and a delayed macrophage-dependent vasospasm after subarachnoid hemorrhage in male mice

Subarachnoid hemorrhage (SAH) can be associated with neurological deficits and has profound consequences for mortality and morbidity. Cerebral vasospasm (CVS) and delayed cerebral ischemia affect neurological outcomes in SAH patients, but their mechanisms are not fully understood, and effective treatments are limited. Here, we report that urotensin II receptor UT plays a pivotal role in both early events and delayed mechanisms following SAH in male mice. Few days post-SAH, UT expression is triggered by blood or hemoglobin in the leptomeningeal compartment. UT contributes to perimeningeal glia limitans astrocyte reactivity, microvascular alterations and neuroinflammation independent of CNS-associated macrophages (CAMs). Later, CAM-dependent vascular inflammation and subsequent CVS develop, leading to cognitive dysfunction. In an SAH model using humanized UTh+/h+ male mice, we show that post-SAH CVS and behavioral deficits, mediated by UT through Gq/PLC/Ca2+ signaling, are prevented by UT antagonists. These results highlight the potential of targeting UT pathways to reduce early meningeal response and delayed cerebral ischemia in SAH patients.

Incidence and Factors in Delayed Neurological Deficits after Subarachnoid Hemorrhage in Mice

Background

Delayed cerebral ischemia (DCI) is one of the most feared complications in aneurysmal subarachnoid hemorrhage (SAH). Animal models are crucial to studying the disease mechanisms and potential treatments. DCI in rodents was thought to not exist; herein we examine literature and our experience with DCI in rodents.

Methods

Daily behavioral performance was assessed every day from day 1 to up to 7 days post-SAH on mice from 5 different studies that used the endovascular perforation model. Performance was graded using an 8-test sensorimotor neuroscore previously described. The daily neuroscore was then used to identify the incidence and timing of delayed neurological deficits, a clinical surrogate for DCI. A total number of 298 mice (134 males, 164 females) were subjected to SAH. Fifty-one mice had histological staining done to identify infarct volume.

Results

The overall incidence of DND was 33.9%; 27.6% in males and 39.0% in females, but this difference was not statistically significant. The overall incidence of delayed death was 21.1%, and there was no significant difference for delayed mortality in females versus male mice. There is a non-statistically significant trend towards increased infarct volume in mice suffering DND.

Conclusions

Mice with endovascular puncture induced SAH develop DND at rates comparable to human patients. Future work needs to correlate the DND seen with decreased regional cerebral blood flow, another hallmark of DCI, but in spite of this need, researchers may use the murine models to test therapies for DCI after SAH.

Female mice display sex-specific differences in cerebrovascular function and subarachnoid haemorrhage-induced injury

BACKGROUND

In male mice, a circadian rhythm in myogenic reactivity influences the extent of brain injury following subarachnoid haemorrhage (SAH). We hypothesized that female mice have a different cerebrovascular phenotype and consequently, a distinct SAH-induced injury phenotype.

METHODS

SAH was modelled by pre-chiasmatic blood injection. Olfactory cerebral resistance arteries were functionally assessed by pressure myography; these functional assessments were related to brain histology and neurobehavioral assessments. Cystic fibrosis transmembrane conductance regulator (CFTR) expression was assessed by PCR and Western blot. We compared non-ovariectomized and ovariectomized mice.

FINDINGS

Cerebrovascular myogenic reactivity is not rhythmic in females and no diurnal differences in SAH-induced injury are observed; ovariectomy does not unmask a rhythmic phenotype for any endpoint. CFTR expression is rhythmic, with similar expression levels compared to male mice. CFTR inhibition studies, however, indicate that CFTR activity is lower in female arteries. Pharmacologically increasing CFTR expression in vivo (3 mg/kg lumacaftor for 2 days) reduces myogenic tone at Zeitgeber time 11, but not Zeitgeber time 23. Myogenic tone is not markedly augmented following SAH in female mice and lumacaftor loses its ability to reduce myogenic tone; nevertheless, lumacaftor confers at least some injury benefit in females with SAH.

INTERPRETATION

Female mice possess a distinct cerebrovascular phenotype compared to males, putatively due to functional differences in CFTR regulation. This sex difference eliminates the CFTR-dependent cerebrovascular effects of SAH and may alter the therapeutic efficacy of lumacaftor compared to males.

FUNDING

Brain Aneurysm Foundation, Heart and Stroke Foundation and Ted Rogers Centre for Heart Research.

Laser Speckle Flowmetry for the Prognostic Estimation Study of Permanent Focal Ischemia in Mice

The distal middle cerebral artery occlusion (dMCAO) model that mainly targets the cortex and causes low mortality is developed for the study of permanent focal ischemia, and it is highly appropriate for the study in the aged population. The two most common methods used to establish dMCAO models are dMCAO alone and dMCAO plus ipsilateral common carotid artery occlusion (CCAO). Up to now, studies on the prognosis of the two types of dMCAO models and the accuracy of cerebral blood flow (CBF) in predicting prognosis have not yet been reported. In the present study, we established permanent focal ischemia models in two groups of aged mice by dMCAO alone or by dMCAO plus ipsilateral common carotid artery occlusion (CCAO). CBF was evaluated by laser speckle flowmetry (LSF) before and after surgery. Cerebral infarction was assessed by TTC staining at day 2 after surgery and MAP2 staining at day 21 after surgery. In addition, behavioral outcomes were evaluated using the modified Garcia scoring system, adhesive removal test, and foot-fault test. Our results showed that compared with those in the dMCAO alone group, the mice in the dMCAO plus CCAO group had a larger cerebral infarct size and more severe neurological deficits. According to the results of the correlation analysis, the area of the ischemic core region on CBF imaging in the dMCAO group was helpful in predicting the infarct volume. In addition, the total CBF of the ischemic area in the dMCAO plus CCAO group showed a significant correlation with Garcia scores 3 days after surgery, but there was no significant correlation of CBF imaging with the foot-fault test 7 days after surgery. These results suggest that the total CBF of the ischemic area might be helpful to predict the severity of neurological damage at the acute stage.