Poly-Arginine Peptides R18 and R18D Improve Functional Outcomes After Endothelin-1-Induced Stroke in the Sprague Dawley Rat.

We have previously demonstrated that R18 and its d-enantiomer, R18D, are neuroprotective at 24 hours following intraluminal filament occlusion of the middle cerebral artery (MCAO) in the rat. This study examined R18 and R18D effectiveness in improving functional outcomes at up to 56 days poststroke following endothelin-1-induced MCAO. Peptides were administered intravenously at doses of 100, 300, or 1000 nmol/kg, 60 minutes after MCAO. Functional recovery poststroke was assessed using multiple forelimb placing tests and horizontal ladder test, and NA-1 (TAT-NR2B9c), a neuroprotective currently in phase 3 clinical stroke trials, was used as a benchmark. The study demonstrated that R18 (300 and 1000 nmol/kg) was the most effective peptide in improving functional outcomes, followed by R18D (300 and 1000 nmol/kg), and NA-1 (300 and 100 nmol/kg). Furthermore, R18 at doses of 300 and 1000 nmol/kg was the most effective agent in restoring pre-stroke body weight, while R18 and R18D at doses of 300 and 1000 nmol/kg, but not NA-1 also significantly reduced the number of animals requiring hand feeding 48 hours after stroke. This study confirms that R18 and R18D are effective in improving long-term functional outcomes after stroke, and suggests that R18 may be more effective than NA-1.

Bilateral ischaemic lesions of the medial prefrontal cortex are anxiogenic in the rat.

OBJECTIVE: Stroke patients often suffer from delayed disturbances of mood and cognition. In rodents, the prefrontal cortex (PFC) is involved in both higher order cognition and emotion. Our objective was to determine if bilateral focal ischaemic lesions restricted to the medial prefrontal cortex (mPFC) could be used to model post-stroke anxiety and/or cognitive deficits. METHODS: Groups of adult male Sprague-Dawley rats (n=9) received bilateral injections of either endothelin-1 (ET-1) (400 pmol) or vehicle (artificial cerebrospinal fluid) into the mPFC and were tested at various times using both a test of temporal order memory and in an elevated plus maze. Lesions were verified histologically. RESULTS: ET-1 lesioned rats had reduced mobility on post-surgery day 8 that had resolved by day 29 at which time they spent significantly more time in the closed arm of the plus maze CONCLUSION: We conclude that ischaemic lesions localised to the mPFC can be used to model post-stroke anxiety in rats.

Effects of endothelin-induced prefrontal cortical lesions on delay discounting in the rat.

Stroke is one of the most prominent causes of neurological disability, and the number of stroke cases worldwide is expected to grow due to increases in both average life span and population. As such, new methods for both acute treatment and poststroke rehabilitation will be increasingly necessary. Although a number of approaches to restoring motor function poststroke are in development, there are few methods to alleviate the cognitive deficits caused by this disease. As well, there are very few preclinical models of stroke with a specific focus on higher-order cognitive functions. The goal of the current experiments was to examine the effects of bilateral ischemic lesions, produced by targeted microinjections of endothelin-1 (ET-1) in the medial (mPFC) and orbital (oPFC) prefrontal cortices of adult male Sprague-Dawley rats (n = 39) on inhibitory control as measured through a delay discounting paradigm. The ET-1 injections to the mPFC and oPFC resulted in average lesion volumes of 17.98 mm3 ± 2.841 mm3 (Mean ± SE) and 26.05 mm3 ± 4.052 mm3 (Mean ± SE), respectively. During delay discounting testing, wherein animals were offered a small, immediately available food reward versus a large, but delayed reward, it was found that animals with lesions to the oPFC were more likely to choose the immediately available reward as compared to their mPFC or control counterparts. We conclude that using ET-1 in the oPFC may be a new and viable method to study the effects of ischemic lesions on higher-order cognitive dysfunction poststroke. (PsycINFO Database Record

Prefrontal Ischemia in the Rat Leads to Secondary Damage and Inflammation in Remote Gray and White Matter Regions.

Secondary damage processes, such as inflammation and oxidative stress, can exacerbate an ischemic lesion and spread to adjacent brain regions. Yet, few studies investigate how regions remote from the infarct could also suffer from degeneration and inflammation in the aftermath of a stroke. To find out to what extent far-remote brain regions are affected after stroke, we used a bilateral endothelin-1-induced prefrontal infarct rat model. Brain regions posterior to the prefrontal cortical infarct were analyzed for ongoing neurodegeneration using FluoroJadeB (FJB) and for neuroinflammation using Iba1 and OX-6 immunohistochemistry 28 days post-stroke. The FJB-positive dorsomedial nucleus of the thalamus (DMN) and retrosplenial area (RSA) of the cortex displayed substantial neuroinflammation. Significant neuronal loss was only observed within the cortex. Significant microglia recruitment and activation in the FJB-positive internal capsule indicates remote white matter pathology. These findings demonstrate that even regions far remote from an infarct are affected predictably based on anatomical connectivity, and that white matter inflammation is an integral part of remote pathology. The delayed nature of this pathology makes it a valid target for preventative treatment, potentially with an extended time window of opportunity for therapeutic intervention using anti-inflammatory agents.

Ischemic lesions localized to the medial prefrontal cortex produce selective deficits in measures of executive function in rats.

Ischemic stroke is one of the leading causes of neurological disability worldwide, and it has been estimated that about one quarter of stroke survivors experience some measurable long-term cognitive impairments. Many higher order cognitive deficits occur because of damage to the prefrontal cortex (PFC), which is one of the main areas of the brain responsible for executive functioning in mammals. Currently, there are few animal models that examine the effects of stroke on executive function. In this study we used bilateral micro-injections (1µl) of the vasoconstricting peptide endothelin-1 (ET-1) into the medial PFC in male Sprague-Dawley rats (or vehicle control, N=17-18 per group) in order to model ischemic lesions in the medial PFC. The effects of these lesions on executive function were assessed using tests of set-shifting and temporal object recognition. ET-1 injections in the medial PFC resulted in replicable and specific lesions within the PFC with an average infarct volume of 16.63±2.71mm(3). The ischemic lesions resulted in specific contextual set-shifting deficits within the maze, including an increased number of trials to criterion and a significant difference in learning curves. However, no deficits in temporal order memory processing were noted between sham and stroke animals. We conclude that ischemic lesions localized to the mPFC result in selective but not generalized deficits in executive function in rats.