ABSTRACT
Following ischemic stroke, substance P (SP)-mediated neurogenic inflammation is associated with profound blood-brain barrier (BBB) dysfunction, cerebral edema, and elevated intracranial pressure (ICP). SP elicits its effects by binding the neurokinin 1 tachykinin receptor (NK1-R), with administration of an NK1-R antagonist shown to ameliorate BBB dysfunction and cerebral edema in rodent and permanent ovine stroke models. Given the importance of reperfusion in clinical stroke, this study examined the efficacy of NK1-R antagonist treatment in reducing cerebral edema and ICP in an ovine model of transient middle cerebral artery occlusion (tMCAo). Anesthetized sheep (n = 24) were subject to 2-hours tMCAo and randomized (n = 6/group) to receive early NK1-R treatment (days 1-3 post-stroke), delayed NK1-R treatment (day 5 post-stroke), or saline vehicle. At 6-days post-stroke animals were re-anaesthetized and ICP measured, followed by MRI to evaluate infarction, edema and BBB dysfunction. Following both early and delayed NK1-R antagonist administration, ICP was significantly reduced on day 6 compared to vehicle animals (p < 0.05), accompanied by a reduction in cerebral edema, midline shift and BBB dysfunction (p < 0.05). This study demonstrates that NK1-R antagonist treatment is an effective novel therapy for cerebral edema and elevated ICP following stroke in an ovine model, warranting future clinical evaluation.
ABSTRACT
Background: Assessment of functional impairment following ischaemic stroke is essential to determine outcome and efficacy of intervention in both clinical patients and pre-clinical models. Although paradigms are well described for rodents, comparable methods for large animals, such as sheep, remain limited. This study aimed to develop methods to assess function in an ovine model of ischaemic stroke using composite neurological scoring and gait kinematics from motion capture. Methods: Merino sheep (n = 26) were anaesthetised and subjected to 2 hours middle cerebral artery occlusion. Animals underwent functional assessment at baseline (8-, 5-, and 1-day pre-stroke), and 3 days post-stroke. Neurological scoring was carried out to determine changes in neurological status. Ten infrared cameras measured the trajectories of 42 retro-reflective markers for calculation of gait kinematics. Magnetic resonance imaging (MRI) was performed at 3 days post-stroke to determine infarct volume. Intraclass Correlation Coefficients (ICC's) were used to assess the repeatability of neurological scoring and gait kinematics across baseline trials. The average of all baselines was used to compare changes in neurological scoring and kinematics at 3 days post-stroke. A principal component analysis (PCA) was performed to determine the relationship between neurological score, gait kinematics, and infarct volume post-stroke. Results: Neurological scoring was moderately repeatable across baseline trials (ICC > 0.50) and detected marked impairment post-stroke (p < 0.05). Baseline gait measures showed moderate to good repeatability for the majority of assessed variables (ICC > 0.50). Following stroke, kinematic measures indicative of stroke deficit were detected including an increase in stance and stride duration (p < 0.05). MRI demonstrated infarction involving the cortex and/or thalamus (median 2.7 cm3, IQR 1.4 to 11.9). PCA produced two components, although association between variables was inconclusive. Conclusion: This study developed repeatable methods to assess function in sheep using composite scoring and gait kinematics, allowing for the evaluation of deficit 3 days post-stroke. Despite utility of each method independently, there was poor association observed between gait kinematics, composite scoring, and infarct volume on PCA. This suggests that each of these measures has discreet utility for the assessment of stroke deficit, and that multimodal approaches are necessary to comprehensively characterise functional impairment.
ABSTRACT
BACKGROUND AND PURPOSE: Cerebral edema and elevated intracranial pressure (ICP) are the leading cause of death in the first week following stroke. Despite this, current treatments are limited and fail to address the underlying mechanisms of swelling, highlighting the need for targeted treatments. When screening promising novel agents, it is essential to use clinically relevant large animal models to increase the likelihood of successful clinical translation. As such, we sought to develop a survival model of transient middle cerebral artery occlusion (tMCAO) in the sheep and subsequently characterize the temporal profile of cerebral edema and elevated ICP following stroke in this novel, clinically relevant model. METHODS: Merino-sheep (27M;31F) were anesthetized and subject to 2 h tMCAO with reperfusion or sham surgery. Following surgery, animals were allowed to recover and returned to their home pens. At preselected times points ranging from 1 to 7 days post-stroke, animals were re-anesthetized, ICP measured for 4 h, followed by imaging with MRI to determine cerebral edema, midline shift and infarct volume (FLAIR, T2 and DWI). Animals were subsequently euthanized and their brain removed for immunohistochemical analysis. Serum and cerebrospinal fluid samples were also collected and analyzed for substance P (SP) using ELISA. RESULTS: Intracranial pressure and MRI scans were normal in sham animals. Following stroke, ICP rose gradually over time and by 5 days was significantly (p < 0.0001) elevated above sham levels. Profound cerebral edema was observed as early as 2 days post-stroke and continued to evolve out to 6 days, resulting in significant midline shift which was most prominent at 5 days post-stroke (p < 0.01), in keeping with increasing ICP. Serum SP levels were significantly elevated (p < 0.01) by 7 days post-tMCAO. CONCLUSION: We have successfully developed a survival model of ovine tMCAO and characterized the temporal profile of ICP. Peak ICP elevation, cerebral edema and midline shift occurred at days 5-6 following stroke, accompanied by an elevation in serum SP. Our findings suggest that novel therapeutic agents screened in this model targeting cerebral edema and elevated ICP would most likely be effective when administered prior to 5 days, or as early as possible following stroke onset.
