Long-Term Motor Deficit and Diffuse Cortical Atrophy Following Focal Cortical Ischemia in Athymic Rats

Rodent Models of Post-Stroke Dementia

Post-stroke cognitive impairment is one of the most common complications in stroke survivors. Concomitant vascular risk factors, including aging, diabetes mellitus, hypertension, dyslipidemia, or underlying pathologic conditions, such as chronic cerebral hypoperfusion, white matter hyperintensities, or Alzheimer’s disease pathology, can predispose patients to develop post-stroke dementia (PSD). Given the various clinical conditions associated with PSD, a single animal model for PSD is not possible. Animal models of PSD that consider these diverse clinical situations have not been well-studied. In this literature review, diverse rodent models that simulate the various clinical conditions of PSD have been evaluated. Heterogeneous rodent models of PSD are classified into the following categories: surgical technique, special structure, and comorbid condition. The characteristics of individual models and their clinical significance are discussed in detail. Diverse rodent models mimicking the specific pathomechanisms of PSD could provide effective animal platforms for future studies investigating the characteristics and pathophysiology of PSD.

Long-term structural brain changes in adult rats after mild ischaemic stroke

Preclinical studies of remote degeneration have largely focused on brain changes over the first few days or weeks after stroke. Accumulating evidence suggests that neurodegeneration occurs in other brain regions remote to the site of infarction for months and even years following ischaemic stroke. Brain atrophy appears to be driven by both axonal degeneration and widespread brain inflammation. The evolution and duration of these changes are increasingly being described in human studies, using advanced brain imaging techniques. Here, we sought to investigate long-term structural brain changes in a model of mild focal ischaemic stroke following injection of endothlin-1 in adult Long–Evans rats (n = 14) compared with sham animals (n = 10), over a clinically relevant time-frame of 48 weeks. Serial structural and diffusion-weighted MRI data were used to assess dynamic volume and white matter trajectories. We observed dynamic regional brain volume changes over the 48 weeks, reflecting both normal changes with age in sham animals and neurodegeneration in regions connected to the infarct following ischaemia. Ipsilesional cortical volume loss peaked at 24 weeks but was less prominent at 36 and 48 weeks. We found significantly reduced fractional anisotropy in both ipsi- and contralesional motor cortex and cingulum bundle regions of infarcted rats (P < 0.05) from 4 to 36 weeks, suggesting ongoing white matter degeneration in tracts connected to but distant from the stroke. We conclude that there is evidence of significant cortical atrophy and white matter degeneration up to 48 weeks following infarct, consistent with enduring, pervasive stroke-related degeneration.

Hemispheric cortical atrophy and chronic microglial activation following mild focal ischemic stroke in adult male rats

Animal modeling has played an important role in our understanding of the pathobiology of stroke. The vast majority of this research has focused on the acute phase following severe forms of stroke that result in clear behavioral deficits. Human stroke, however, can vary widely in severity and clinical outcome. There is a rapidly building body of work suggesting that milder ischemic insults can precipitate functional impairment, including cognitive decline, that continues through the chronic phase after injury. Here we show that a small infarction localized to the frontal motor cortex of rats following injection of endothelin-1 results in an essentially asymptomatic state based on motor and cognitive testing, and yet produces significant histopathological change including remote atrophy and inflammation that persists up to 1 year. While there is understandably a major focus in stroke research on mitigating the acute consequences of primary infarction, these results point to progressive atrophy and chronic inflammation as additional targets for intervention in the chronic phase after injury. The present rodent model provides an important platform for further work in this area.

Focal Ischemic Injury to the Early Neonatal Rat Brain Models Cognitive and Motor Deficits with Associated Histopathological Outcomes Relevant to Human Neonatal Brain Injury

Neonatal arterial ischemic stroke is one of the more severe birth complications. The injury can result in extensive neurological damage and is robustly associated with later diagnoses of cerebral palsy (CP). An important part of efforts to develop new therapies include the on-going refinement and understanding of animal models that capture relevant clinical features of neonatal brain injury leading to CP. The potent vasoconstrictor peptide, Endothelin-1 (ET-1), has previously been utilised in animal models to reduce local blood flow to levels that mimic ischemic stroke. Our previous work in this area has shown that it is an effective and technically simple approach for modelling ischemic injury at very early neonatal ages, resulting in stable deficits in motor function. Here, we aimed to extend this model to also examine the impact on cognitive function. We show that focal delivery of ET-1 to the cortex of Sprague Dawley rats on postnatal day 0 (P0) resulted in impaired learning in a touchscreen-based test of visual discrimination and correlated with important clinical features of CP including damage to large white matter structures.

Ischemic Injury Does Not Stimulate Striatal Neuron Replacement Even during Periods of Active Striatal Neurogenesis

Ischemic damage to the adult rodent forebrain has been widely used as a model system to study injury-induced neurogenesis, resulting in contradictory reports regarding the capacity of the postnatal brain to replace striatal projection neurons. Here we used a software-assisted, confocal approach to survey thousands of cells generated after striatal ischemic injury in rats and showed that injury fails not only to stimulate production of new striatal projection neurons in the adult brain but also to do so in the neonatal brain at early postnatal ages not previously explored. Conceptually this is significant, because it shows that even during periods of active striatal neurogenesis, injury is not a sufficient stimulus to promote replacement of these neurons. Understanding the intrinsic capacity of the postnatal brain to replace neurons in response to injury is fundamental to the development of “self-repair” therapies.

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Phenotyping of thousands of cells generated after striatal ischemic injury

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Confirms previous reports on lack of injury-induced adult striatal neurogenesis

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No “self-repair” even during active periods of neonatal striatal neurogenesis