Assessing cognitive function following medial prefrontal stroke in the rat

Research trends and hotspots of post-stroke cognitive impairment: a bibliometric analysis

Background: Post-stroke cognitive impairment (PSCI) is a major complication of stroke that affects more than one-third of stroke survivors, threatening their quality of life and increasing the risk of disability and death. Although various studies have described the etiology, epidemiology, and risk factors of PSCI, there are a limited number of comprehensive and accurate reports on research trends and hotspots in this field. Therefore, this review aimed to evaluate research trends, hotspots, and frontiers in PSCI using bibliometric analysis. Methods: We screened the literature spanning 20 years in the Web of Science Core Collection: Science Citation Index Expanded (SCI-Expanded) database from 1 January 2003 to 31 December 2022. We included all eligible literature reports based on our comprehensive search strategy, inclusion criteria, and exclusion criteria. The analysis of annual publications, countries/regions, institutions, journals, co-cited references, and keywords was conducted using CiteSpace and VOSviewer, and the hotspots and major findings of PSCI were summarized. Results: A total of 1,024 publications were included in this review. We found that the number of publications on PSCI increased annually. These publications were published in 75 countries or regions by over 400 institutions. Although Chinese institutions had the highest number of publications, their international influence was limited. The United States showed a strong influence in the field. The journal "Stroke" published the most publications (57) with a high impact factor and was considered the most co-cited journal. The most frequently cited references focused on the prevalence, incidence, neuropsychological assessment scales, criteria, and guidelines of PSCI. The strongest citation burst keywords for PSCI were "neurotrophic factor" and "synaptic plasticity", which were regarded as research focuses and research hotspots, respectively. Conclusion: This review provided a comprehensive summary of the literature of PSCI, identified the authoritative and frequently cited literature and journals, clarified the trends in PSCI research, and highlighted the hotspots in this field. Currently, studies on the mechanisms and treatment of PSCI are limited, and we hope that this review has effectively highlighted the research trajectory of PSCI and will lay the foundation for more innovative research in the future.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

The effects of acamprosate on prefrontal cortical function are mimicked by CaCl2 and they are influenced by the history of alcohol exposure

Alcohol use disorder is associated with functional changes in the medial prefrontal cortex (mPFC), which include altered glutamatergic transmission and deficits in executive functions that contribute to relapse. Acamprosate (calcium-bis N-acetylhomotaurinate) reduces alcohol craving and relapse, effects that are thought to be mediated by acamprosate's ability to ameliorate alcohol-induced dysregulation of glutamatergic signaling. Treatment with acamprosate and its active moiety calcium (CaCl2) both improve deficits in cognitive flexibility in postdependent mice following chronic intermittent ethanol (CIE) exposure. Here, we show that mice that self-administered alcohol under goal-directed conditions (i.e., operant responding on a fixed-ratio schedule) also display similar deficits in cognitive flexibility and altered glutamatergic signaling in the mPFC, both of which were improved with acamprosate or CaCl2. However, under conditions shown to bias behavior towards habitual responding (operant self-administration after CIE exposure, or on a variable interval schedule), alcohol-induced changes to glutamatergic transmission were unaffected by either acamprosate or CaCl2 treatment. Together, these findings suggest that the variable effects of acamprosate on synaptic signaling may reflect a shift in mPFC networks related to the loss of behavioral control in habitual alcohol-seeking.

Tailoring of chitosan/diacrylated pluronic system as a versatile nanoplatform for the amelioration of radiation-induced cognitive dysfunction

Rutin (RUT) is a biologically active flavonoid that is reported to modulate radiation-induced brain dysfunctions. However, RUT's poor water solubility and low brain bioavailability limit its clinical use. To increase its brain bioavailability, RUT was loaded onto nanoplatforms based on chitosan/diacrylated pluronic (CS/DA-PLUR) nanogels synthesized by gamma radiation. The optimized formulation was investigated as a carrier system for RUT. Based on pilot experiments' results, the cranial radiation (CR) dose that induced cognitive dysfunction was selected. In the main experiment, rats were pre-treated orally with either free RUT or RUT-CS/DA-PLUR. Rats' cognitive and motor functions were assessed; 24 h later, rats were sacrificed, and the whole brain was separated for histopathological examination and biochemical estimation of brain content of acetylcholine esterase (AChE), neurotransmitters, oxidative stress markers, and interleukin-1β. CR produced prominent impairment in spatial and non-spatial learning memory, motor coordination, and muscular strength. Moreover, histopathological and biochemical alterations in brain contents of neurotransmitters, oxidative stress, and interleukin-1β were induced by CR. Conversely, RUT-CS/DA-PLUR, but not free RUT, successfully guarded against all the detrimental effects induced by CR. Based on the current findings, loading of RUT enhanced its bioavailability and therapeutic effectiveness by restoring the cognitive functions impaired by CR.

Possible Engagement of Nicotinic Acetylcholine Receptors in Pathophysiology of Brain Ischemia-Induced Cognitive Impairment

Post-stroke disabilities like cognitive impairment impose are complex conditions with great economic burdens on health care systems. For these comorbidities, no effective therapies have been identified yet. Nicotinic acetylcholine receptors (nAChRs) are multifunctional receptors participating in various behavioral and neurobiological functions. During brain ischemia, the increased glutamate accumulation leads to neuronal excitotoxicity as well as mitochondrial dysfunction. These abnormalities then cause the increased levels of oxidants, which play key roles in neuronal death and apoptosis in the infarct zone. Additionally, recall of cytokines and inflammatory factors play a prominent role in the exacerbation of ischemic injury. As well, neurotrophic factors' insufficiency results in synaptic dysfunction and cognitive impairments in ischemic brain. Of note, nAChRs through various signaling pathways can participate in therapeutic approaches such as cholinergic system's stimulation, and reduction of excitotoxicity, inflammation, apoptosis, oxidative stress, mitochondrial dysfunction, and autophagy. Moreover, the possible roles of nAChRs in neurogenesis, synaptogenesis, and stimulation of neurotrophic factors expression have been reported previously. On the other hand, the majority of the above-mentioned mechanisms were found to be common in both brain ischemia pathogenesis and cognitive function tuning. Therefore, it seems that nAChRs might be known as key regulators in the control of ischemia pathology, and their modulation could be considered as a new avenue in the multi-target treatment of post-stroke cognitive impairment.

Specific stimulation of PV+ neurons at early stage ameliorates prefrontal ischemia-induced spatial working memory impairment

Prefrontal ischemia can cause impairments in learning and memory, executive functions and cognitive flexibility. However, the related cellular mechanisms at the early stage are still elusive. The present study used ischemic stroke in medial prefrontal cortex and systemically investigated the electrophysiological changes of the parvalbumin (PV⁺) interneurons 12 h post ischemia. We found that I_h and the related voltage sags in PV⁺ interneurons are downregulated post ischemia, which correlates with hyperpolarization of the membrane potentials and increased input resistance in these interneurons. Consistent with the suppression of I_h, postischemic PV⁺ interneurons exhibited a reduction in excitability and exerted a less inhibitory control over the neighboring pyramidal excitatory neurons. Moreover, we found that specifically chemogenetic activation of PV⁺ neurons at early stage ameliorated prefrontal ischemia-induced spatial working memory dysfunction in T-maze without effects on the locomotor coordination and balance. In contrast, suppression of PV⁺ neurons by blockade of I_h leaded to further aggravate the damage of spatial memory. These findings indicate that dysfunctional I_h in the PV⁺ neuron postischemia induces the imbalance of excitation and inhibition, which might represent a novel mechanism underlying the prefrontal ischemia-induced cognitive impairment.

The role of the medial prefrontal cortex in cognition, ageing and dementia

Humans require a plethora of higher cognitive skills to perform executive functions, such as reasoning, planning, language and social interactions, which are regulated predominantly by the prefrontal cortex. The prefrontal cortex comprises the lateral, medial and orbitofrontal regions. In higher primates, the lateral prefrontal cortex is further separated into the respective dorsal and ventral subregions. However, all these regions have variably been implicated in several fronto-subcortical circuits. Dysfunction of these circuits has been highlighted in vascular and other neurocognitive disorders. Recent advances suggest the medial prefrontal cortex plays an important regulatory role in numerous cognitive functions, including attention, inhibitory control, habit formation and working, spatial or long-term memory. The medial prefrontal cortex appears highly interconnected with subcortical regions (thalamus, amygdala and hippocampus) and exerts top-down executive control over various cognitive domains and stimuli. Much of our knowledge comes from rodent models using precise lesions and electrophysiology readouts from specific medial prefrontal cortex locations. Although, anatomical disparities of the rodent medial prefrontal cortex compared to the primate homologue are apparent, current rodent models have effectively implicated the medial prefrontal cortex as a neural substrate of cognitive decline within ageing and dementia. Human brain connectivity-based neuroimaging has demonstrated that large-scale medial prefrontal cortex networks, such as the default mode network, are equally important for cognition. However, there is little consensus on how medial prefrontal cortex functional connectivity specifically changes during brain pathological states. In context with previous work in rodents and non-human primates, we attempt to convey a consensus on the current understanding of the role of predominantly the medial prefrontal cortex and its functional connectivity measured by resting-state functional MRI in ageing associated disorders, including prodromal dementia states, Alzheimer's disease, post-ischaemic stroke, Parkinsonism and frontotemporal dementia. Previous cross-sectional studies suggest that medial prefrontal cortex functional connectivity abnormalities are consistently found in the default mode network across both ageing and neurocognitive disorders such as Alzheimer's disease and vascular cognitive impairment. Distinct disease-specific patterns of medial prefrontal cortex functional connectivity alterations within specific large-scale networks appear to consistently feature in the default mode network, whilst detrimental connectivity alterations are associated with cognitive impairments independently from structural pathological aberrations, such as grey matter atrophy. These disease-specific patterns of medial prefrontal cortex functional connectivity also precede structural pathological changes and may be driven by ageing-related vascular mechanisms. The default mode network supports utility as a potential biomarker and therapeutic target for dementia-associated conditions. Yet, these associations still require validation in longitudinal studies using larger sample sizes.

Covert strokes prior to Alzheimer's disease onset accelerate peri-lesional pathology but not cognitive deficits in an inducible APP mouse model

It is estimated that up to 1 in 3 healthy middle-aged adults will have had a covert stroke during their lifetime. Furthermore, post-stroke, survivors are more than twice as likely to develop dementia. In the present study, we aimed to model the impact of focal subclinical ischemia prior to the onset of AD pathogenesis in a preclinical model. We utilized endothelin-1 to induce ischemia in an iducible transgenic mouse model of Alzheimer's disease, APPsi:tTA, allowing for temporal control of APP gene expression. We induced the focal subclinical ischemic events in the absence of APP expression, thus prior to AD onset. T2 structural magnetic resonance imaging confirmed the volume and location of focal subclinical ischemic lesions to the medial prefrontal cortex. Following recovery from surgery and 7 weeks of APP expression, we found that two subclinical ischemic lesions resulted in a significant localized increase in amyloid load and in microglial activation proximal to the lesion. However, no differences were found in astrogliosis. A battery of behaviour tests was conducted, in which no significant differences were detected in activities of daily living and cognitive function between stroked and sham cohorts. Overall, our results demonstrated that APP expression was the sole driving force behind behavioural deficits. In conclusion, our results suggest that a history of two subclinical strokes prior to AD onset does not worsen early disease trajectory in a mouse model.

Mir363-3p Treatment Attenuates Long-Term Cognitive Deficits Precipitated by an Ischemic Stroke in Middle-Aged Female Rats

Cognitive impairment and memory loss are commonly seen after stroke and a third of patients will develop signs of dementia a year after stroke. Despite a large number of studies on the beneficial effects of neuroprotectants, few studies have examined the effects of these compounds/interventions on long-term cognitive impairment. Our previous work showed that the microRNA mir363-3p reduced infarct volume and sensory-motor impairment in the acute stage of stroke in middle-aged females but not males. Thus, the present study determined the impact of mir363-3p treatment on stroke-induced cognitive impairment in middle-aged females. Sprague–Dawley female rats (12 months of age) were subjected to middle cerebral artery occlusion (MCAo; or sham surgery) and injected (iv) with mir363-3p mimic (MCAo + mir363-3p) or scrambled oligos (MCAo + scrambled) 4 h later. Sensory-motor performance was assessed in the acute phase (2–5 days after stroke), while all other behaviors were tested 6 months after MCAo (18 months of age). Cognitive function was assessed by the novel object recognition test (declarative memory) and the Barnes maze (spatial memory). The MCAo + scrambled group showed reduced preference for a novel object after the stroke and poor learning in the spatial memory task. In contrast, mir363-3p treated animals were similar to either their baseline performance or to the sham group. Histological analysis showed significant deterioration of specific white matter tracts due to stroke, which was attenuated in mir363-3p treated animals. The present data builds on our previous finding to show that a neuroprotectant can abrogate the long-term effects of stroke.

Molecular, circuit, and anatomical changes in the prefrontal cortex in chronic pain

The prefrontal cortex undergoes functional and structural reorganization in chronic pain conditions in both rodents and humans. We provide an illustrated overview of the molecular, functional, and connectivity pathology occurring in the prefrontal cortex in chronic pain states.

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

Development of new stroke therapies requires animal models that recapitulate the pathophysiological and functional consequences of ischemic brain damage over time-frames relevant to the therapeutic intervention. This is particularly relevant for the rapidly developing area of stem cell therapies, where functional replacement of circuitry will require maturation of transplanted human cells over months. An additional challenge is the establishment of models of ischemia with stable behavioral phenotypes in chronically immune-suppressed animals to allow for long-term survival of human cell grafts. Here we report that microinjection of endothelin-1 into the sensorimotor cortex of athymic rats results in ischemic damage with a sustained deficit in function of the contralateral forepaw that persists for up to 9 months. The histological post-mortem analysis revealed chronic and diffuse atrophy of the ischemic cortical hemisphere that continued to progress over 9 months. Secondary atrophy remote to the primary site of injury and its relationship with long-term cognitive and functional decline is now recognized in human populations. Thus, focal cortical infarction in athymic rats mirrors important pathophysiological and functional features relevant to human stroke, and will be valuable for assessing efficacy of stem cell based therapies.

β-Caryophyllene Reduces DNA Oxidation and the Overexpression of Glial Fibrillary Acidic Protein in the Prefrontal Cortex and Hippocampus of d-Galactose-Induced Aged BALB/c Mice

Aging is associated with detrimental cellular and cognitive changes, making it an important public health concern; yet, many of these changes may be influenced by nutritional interventions. The natural sesquiterpene β-caryophyllene (BCP) has anti-inflammatory and antioxidant effects that are mediated by cannabinoid type-2 receptor activation, and these actions promote neuroprotection in different animal models that involve a cognitive damage. Consequently, whether chronic administration of BCP might prevent the age-related cellular and cognitive damage in a model of aging induced by chronic d-galactose (GAL) consumption was assessed here. Male BALB/c mice were administered BCP (10 mg/kg, oral), GAL (300 mg/kg, intraperitoneal), or GAL+BCP, and long-term memory and cognitive flexibility were evaluated in the normal and the reverse phases of Morris water maze test. In addition, immunohistochemistry was performed on prefrontal and hippocampal brain slices to detect glial acidic fibrillary protein and DNA oxidation. Although GAL administration reduced cognitive flexibility (P = .0308), this functional damage was not reversed by administering BCP. However, GAL administration also elevated the total number of astrocytes and their interactions in the hippocampus, and increasing DNA oxidation in the prefrontal cortex. BCP administration impeded the rise in the total number of astrocytes (P = .0286) and the DNA oxidation (P = .0286) in mice that received GAL. Hence, although BCP did not improve cognitive flexibility, it did produce a neuroprotective effect at the molecular and cellular level in the GAL model of aging.

Assessment of spatial learning and memory in the Barnes maze task in rodents-methodological consideration

Among the methods valuable for assessing spatial learning and memory impairments in rodents, the Barnes maze (BM) task deserves special attention. It is based on the assumption that the animal placed into the aversive environment should learn and remember the location of an escape box located below the surface of the platform. Different phases of the task allow to measure spatial learning, memory retrieval, and cognitive flexibility. Herein, we summarize current knowledge about the BM procedure, its variations and critical parameters measured in the task. We highlight confounding factors which should be taken into account when conducting BM task, discussing briefly its advantages and disadvantages. We then propose an extended version of the BM protocol which allows to measure different aspects of spatial learning and memory in rodents. We believe that this review will help to standardize the BM methodology across the laboratories and eventually make the results comparable.

Protective effect of Centella asiatica against D-galactose and aluminium chloride induced rats: Behavioral and ultrastructural approaches

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder and the commonest cause of dementia among the aged people. _D-galactose (D-gal) is a senescence agent, while aluminium is a known neurotoxin linked to pathogenesis of AD. The combined administration of rats with d-gal and aluminium chloride (AlCl₃) is considered to be an easy and a cheap method to obtain an animal model of AD. The plant Centella asiatica (CA) is reported to exert neuroprotective effects both in vitro and in vivo. Therefore, this study explored the protective effects of CA on cognition and brain ultrastructure in d-gal and AlCl₃ induced rats.

MATERIALS AND METHODS

Rats were exposed to d-gal 60 mg/kg/b.wt/day + AlCl₃ 200 mg/kg/b.wt/day and CA (200, 400 and 800 mg/kg/b.wt/day) and 1 mg/kg/b.wt/day of donepezil for 70 days. Different cognitive paradigms viz. T maze spontaneous alternation, modified elevated plus maze and novel object recognition test, were used to evaluate full lesions of the hippocampus, spatial learning and memory and non-spatial learning and memory respectively. Nissl's staining was used to determine the survival of hippocampus CA1 pyramidal cells, while transmission electron microscopy was used to check the ultrastructural changes.

RESULTS

The results revealed that d-gal and AlCl₃ could significantly impair behavior and cognitive functions, besides causing damage to the hippocampal CA1 pyramidal neurons in rats. In addition, it also caused ultrastructural morphological alterations in rat hippocampus. Conversely, co-administration o;f CA, irrespective of the dosage used, alleviated the cognitive impairments and pathological changes in the rats comparable to donepezil.

CONCLUSION

In conclusion the results suggest that CA could protect cognitive impairments and morphological alterations caused by d-gal and AlCl₃ toxicity in rats. Biochemical and molecular studies are ongoing to elucidate the probable pharmacodynamics of CA.

Neuropathic Pain Creates an Enduring Prefrontal Cortex Dysfunction Corrected by the Type II Diabetic Drug Metformin But Not by Gabapentin

Chronic pain patients suffer from pain-related cognitive deficits, even when taking commonly prescribed analgesics. These deficits are likely related to pain-related maladaptive plasticity in the frontal cortex. We sought to model cognitive deficits in mice with neuropathic pain to examine maladaptive morphological plasticity in the mPFC and to assess the effects of several therapeutics. We used an attentional set-shifting task in mice with spared nerve injury (SNI) who received either a single intrathecal injection of an analgesic dose of clonidine, 7 d of 100 mg/kg gabapentin, or 7 d of 200 mg/kg metformin. Male SNI mice were significantly more impaired in the set-shifting task than females. This deficit correlated with a loss of parvalbumin (PV) and reductions in axon initial segment (AIS) length in layers 5/6 of the infralimbic (IL) cortex. Acute pain relief with clonidine had no effect on set-shifting performance, whereas pain relief via 7 day treatment with gabapentin worsened the impairment in both SNI and sham mice. Gabapentin reversed the PV loss in the IL but had no effect on AIS length. Treatment with the AMPK-activator metformin completely reversed the pain-related cognitive impairment and restored AIS length in the IL but had little effect on PV expression. Our findings reveal that neuropathic pain-related cognitive impairments in male mice are correlated to bilateral morphological changes in PV interneurons and layer 5/6 IL pyramidal neuron AIS. Pain relief with metformin can reverse some of the functional and anatomical changes.SIGNIFICANCE STATEMENT Cognitive impairments are a comorbidity of neuropathic pain but are inadequately addressed by existing therapeutics. We used a neuropathic pain model in mice to demonstrate that male (but not female) mice show a robust pain-related deficit in attentional set-shifting, which is associated with structural plasticity in axon initial segments in the infralimbic cortex. These deficits were completely reversed by 7 day treatment with the antidiabetic drug metformin, suggesting that this drug can be repurposed for the treatment of neuropathic pain and its cognitive comorbidities. Our findings have implications for our understanding of how neuropathic pain causes structural plasticity in the brain, and they point to a marked sexual dimorphism in neuropathic pain mechanisms in mice.

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.

Morphological and functional evidence of increased excitatory signaling in the prelimbic cortex during ethanol withdrawal

Excessive alcohol consumption in humans induces deficits in decision making and emotional processing, which indicates a dysfunction of the prefrontal cortex (PFC). The present study aimed to determine the impact of chronic intermittent ethanol (CIE) inhalation on mouse medial PFC pyramidal neurons. Data were collected 6-8 days into withdrawal from 7 weeks of CIE exposure, a time point when mice exhibit behavioral symptoms of withdrawal. We found that spine maturity in prelimbic (PL) layer 2/3 neurons was increased, while dendritic spines in PL layer 5 neurons or infralimbic (IL) neurons were not affected. Corroborating these morphological observations, CIE enhanced glutamatergic transmission in PL layer 2/3 pyramidal neurons, but not IL layer 2/3 neurons. Contrary to our predictions, these cellular alterations were associated with improved, rather than impaired, performance in reversal learning and strategy switching tasks in the Barnes maze at an earlier stage of chronic ethanol exposure (5-7 days withdrawal from 3 to 4 weeks of CIE), which could result from the anxiety-like behavior associated with ethanol withdrawal. Altogether, this study adds to a growing body of literature indicating that glutamatergic activity in the PFC is upregulated following chronic ethanol exposure, and identifies PL layer 2/3 pyramidal neurons as a sensitive target of synaptic remodeling. It also indicates that the Barnes maze is not suitable to detect deficits in cognitive flexibility in CIE-withdrawn mice.

Cyclosporin A-Mediated Activation of Endogenous Neural Precursor Cells Promotes Cognitive Recovery in a Mouse Model of Stroke

Cognitive dysfunction following stroke significantly impacts quality of life and functional independance; yet, despite the prevalence and negative impact of cognitive deficits, post-stroke interventions almost exclusively target motor impairments. As a result, current treatment options are limited in their ability to promote post-stroke cognitive recovery. Cyclosporin A (CsA) has been previously shown to improve post-stroke functional recovery of sensorimotor deficits. Interestingly, CsA is a commonly used immunosuppressant and also acts directly on endogenous neural precursor cells (NPCs) in the neurogenic regions of the brain (the periventricular region and the dentate gyrus). The immunosuppressive and NPC activation effects are mediated by calcineurin-dependent and calcineurin-independent pathways, respectively. To develop a cognitive stroke model, focal bilateral lesions were induced in the medial prefrontal cortex (mPFC) of adult mice using endothelin-1. First, we characterized this stroke model in the acute and chronic phase, using problem-solving and memory-based cognitive tests. mPFC stroke resulted in early and persistent deficits in short-term memory, problem-solving and behavioral flexibility, without affecting anxiety. Second, we investigated the effects of acute and chronic CsA treatment on NPC activation, neuroprotection, and tissue damage. Acute CsA administration post-stroke increased the size of the NPC pool. There was no effect on neurodegeneration or lesion volume. Lastly, we looked at the effects of chronic CsA treatment on cognitive recovery. Long-term CsA administration promoted NPC migration toward the lesion site and rescued cognitive deficits to control levels. This study demonstrates that CsA treatment activates the NPC population, promotes migration of NPCs to the site of injury, and leads to improved cognitive recovery following long-term treatment.

Chronic Fluoxetine Induces Activity Changes in Recovery From Poststroke Anxiety, Depression, and Cognitive Impairment

Poststroke depression (PSD) is a common outcome of stroke that limits recovery and is only partially responsive to chronic antidepressant treatment. In order to elucidate changes in the cortical-limbic circuitry associated with PSD and its treatment, we examined a novel mouse model of persistent PSD. Focal endothelin-1-induced ischemia of the left medial prefrontal cortex (mPFC) in male C57BL6 mice resulted in a chronic anxiety and depression phenotype. Here, we show severe cognitive impairment in spatial learning and memory in the stroke mice. The behavioral and cognitive phenotypes were reversed by chronic (4-week) treatment with fluoxetine, alone or with voluntary exercise (free-running wheel), but not by exercise alone. To assess chronic cellular activation, FosB+ cells were co-labeled for markers of glutamate/pyramidal (VGluT1-3/CaMKIIα), γ-aminobutyric acid (GAD67), and serotonin (TPH). At 6 weeks poststroke versus sham (or 4 days poststroke), left mPFC stroke induced widespread FosB activation, more on the right (contralesional) than on the left side. Stroke activated glutamate cells of the mPFC, nucleus accumbens, amygdala, hippocampus, and raphe serotonin neurons. Chronic fluoxetine balanced bilateral neuronal activity, reducing total FosB and FosB/CamKII+ cells (mPFC, nucleus accumbens), and unlike exercise, increasing FosB/GAD67+ cells (septum, amygdala) or both (hippocampus, raphe). In summary, chronic antidepressant but not exercise mediates recovery in this unilateral ischemic PSD model that is associated with region-specific reversal of stroke-induced pyramidal cell hyperactivity and increase in γ-aminobutyric acidergic activity. Targeted brain stimulation to restore brain activity could provide a rational approach for treating clinical PSD.

Test repositioning for functional assessment of neurological outcome after experimental stroke in mice

Stroke is a cerebrovascular pathology for which the only approved treatment is fibrinolysis. Several studies have focused on the development of new drugs but none has led to effective therapies to date, due, among others, to the difficulty to evaluate clinical deficits in experimental animal models. The present study aims to explore the applicability of known behavioral tests not commonly used in ischemia for the neurological assessment of mice after experimental stroke in different brain areas. A total of 225 CD1 male mice were randomly assigned to permanent middle cerebral artery occlusion by ligature (pMCAO) or permanent anterior cerebral artery occlusion by photothrombosis (pACAO) models. Modified neuroseverity score, footprint test, forced swim test and elevated plus maze were performed. Under these experimental conditions, modified neuroseverity score showed neurological impairment early after experimental stroke in both models. By contrast, the footprint test and the elevated plus maze detected short-term neurological deterioration in the pMCAO model but not in the pACAO model. Furthermore, the forced swim test identified depression-like behavior in mice after ischemia only when the left hemisphere was affected. In conclusion, we propose the repositioning of known neurobehavioral tests, but not commonly used in the stroke field, for the fast detection of neurological impairments early after ischemia, and even specific to discriminate the territory affected by arterial occlusion as well as the hemisphere where brain damage occurs. All these findings may prove useful to improve the experimental design of neuroprotective drugs in order to bridge the gap between experimental studies and clinical trials.

Persistent post-stroke depression in mice following unilateral medial prefrontal cortical stroke

Post-stroke depression (PSD) is a common outcome following stroke that is associated with poor recovery. To develop a preclinical model of PSD, we targeted a key node of the depression-anxiety circuitry by inducing a unilateral ischemic lesion to the medial prefrontal cortex (mPFC) stroke. Microinjection of male C57/BL6 mice with endothelin-1 (ET-1, 1600 pmol) induced a small (1 mm(3)) stroke consistently localized within the left mPFC. Compared with sham control mice, the stroke mice displayed a robust behavioral phenotype in four validated tests of anxiety including the elevated plus maze, light-dark, open-field and novelty-suppressed feeding tests. In addition, the stroke mice displayed depression-like behaviors in both the forced swim and tail suspension test. In contrast, there was no effect on locomotor activity or sensorimotor function in the horizontal ladder, or cylinder and home cage activity tests, indicating a silent stroke due to the absence of motor abnormalities. When re-tested at 6 weeks post stroke, the stroke mice retained both anxiety and depression phenotypes. Surprisingly, at 6 weeks post stroke the lesion site was infiltrated by neurons, suggesting that the ET-1-induced neuronal loss in the mPFC was reversible over time, but was insufficient to promote behavioral recovery. In summary, unilateral ischemic lesion of the mPFC results in a pronounced and persistent anxiety and depression phenotype with no evident sensorimotor deficits. This precise lesion of the depression circuitry provides a reproducible model to study adaptive cellular changes and preclinical efficacy of novel interventions to alleviate PSD symptoms.