Thalamic alterations remote to infarct appear as focal iron accumulation and impact clinical outcome

Enhanced angiogenesis in the thalamus induced by a novel TSPO ligand ameliorates cognitive deficits after focal cortical infarction

Neuronal loss in the ipsilateral thalamus after focal cortical infarction participates in post-stroke cognitive deficits, and enhanced angiogenesis in the thalamus is expected to reduce neuronal damage. We hypothesize that novel translocator protein (TSPO) ligand, 2-Cl-MGV-1, can promote angiogenesis, attenuate neuronal loss in the thalamus, and ameliorate post-stroke cognitive deficits. Cortical infarction was induced by distal middle cerebral artery occlusion (dMCAO) in stroke-prone renovascular hypertensive rats. 2-Cl-MGV-1 or dimethyl sulfoxide was administered 24 h after dMCAO and then for 6 or 13 days. Spatial learning and memory were assessed using the Morris water maze. Neuronal loss, TSPO expression, angiogenesis, and intrinsic pathway were determined by immunofluorescence and immunoblotting 7 and 14 days after dMCAO. Cortical infarction caused post-stroke cognitive deficits and secondary neuronal loss with gliosis in the ipsilateral thalamus within 14 days of dMCAO. Increased angiogenesis and elevated expression of vascular TSPO were detected in the ipsilateral thalamus, and treatment with 2-Cl-MGV-1 enhanced angiogenesis by stimulating the PI3K-AKT-mTOR pathway. The effects of 2-Cl-MGV-1 on angiogenesis coincided with reduced neuronal loss in the thalamus and contributed to improvements in post-stroke cognitive deficits. Our findings suggest that 2-Cl-MGV-1 stimulates angiogenesis, ameliorates neuronal loss in the thalamus, and improves post-stroke cognitive deficits.

Dl-3-n-Butylphthalide Alleviates Secondary Brain Damage and Improves Working Memory After Stroke in Cynomolgus Monkeys

BACKGROUND

Remote secondary neurodegeneration is associated with poststroke cognitive impairment (PSCI). Dl-3-n-butylphthalide (NBP) improves PSCI clinically. However, whether it ameliorates PSCI by alleviating secondary neurodegeneration remains uncertain. Nonhuman primates provide more relevant models than rodents for human stroke and PSCI. This study investigated the effects of NBP on PSCI and secondary neurodegeneration in cynomolgus monkeys after permanent left middle cerebral artery occlusion (MCAO).

METHODS

Thirteen adult male cynomolgus monkeys were randomly assigned to sham (n=4), MCAO+placebo (n=5), and MCAO+NBP groups (n=4). The MCAO+placebo and MCAO+NBP groups received saline and NBP injections intravenously, respectively, starting at 6-hour postsurgery for 2 weeks, followed by soybean oil and NBP orally, respectively, for 10 weeks after MCAO. Infarct size was assessed at week 4 by magnetic resonance imaging. Working memory and executive function were evaluated dynamically using the delayed response task and object retrieval detour task, respectively. Neuron loss, glia proliferation, and neuroinflammation in the ipsilateral dorsal lateral prefrontal cortex, thalamus, and hippocampus were analyzed by immunostaining 12 weeks after MCAO.

RESULTS

Infarcts were located in the left middle cerebral artery region, apart from the ipsilateral dorsal lateral prefrontal cortex, thalamus, or hippocampus, with no significant difference between the MCAO+placebo and MCAO+NBP group. Higher success in delayed response task was achieved at weeks 4, 8, and 12 after NBP compared with placebo treatments (P<0.05), but not in the object retrieval detour task (all P>0.05). More neurons and less microglia, astrocytes, CD68-positive microglia, tumor necrosis factor-α, and inducible NO synthase were observed in the ipsilateral dorsal lateral prefrontal cortex and thalamus after 12 weeks of NBP treatment (P<0.05), but not in the hippocampus (P>0.05).

CONCLUSIONS

Our findings indicate that NBP improves working memory by alleviating remote secondary neurodegeneration and neuroinflammation in the ipsilateral dorsal lateral prefrontal cortex and thalamus after MCAO in cynomolgus monkeys.

Association between substantia nigra degeneration and functional outcome in patients with basal ganglia infarction

BACKGROUND AND PURPOSE

Cerebral infarction in the basal ganglia may cause secondary and delayed neuronal degeneration in the substantia nigra (SN). However, the clinical significance of SN degeneration remains poorly understood.

METHODS

This retrospective observational study included patients with acute ischemic stroke in the basal ganglia on initial diffusion-weighted imaging who underwent follow-up diffusion-weighted imaging between 4 and 30 days after symptom onset. SN degeneration was defined as a hyperintensity lesion in the SN observed on diffusion-weighted imaging. We compared functional outcomes at 3 months between patients with and without SN degeneration. A poor outcome was defined as a score of 3-6 (functional dependence or death) on the modified Rankin Scale.

RESULTS

Of 350 patients with basal ganglia infarction (median age = 74.0 years, 53.7% male), 125 (35.7%) had SN degeneration. The proportion of functional dependence or death was 79.2% (99/125 patients) in patients with SN degeneration, which was significantly higher than that in those without SN degeneration (56.4%, 127/225 patients, p < 0.001). SN degeneration was more frequent in patients with functional dependence or death (99/226 patients, 43.8%) than in those with functional independence (26/124 patients, 21.0%, p < 0.001). Multivariable logistic regression analysis showed a significant association between SN degeneration and functional dependence or death (odds ratio = 2.91, 95% confidence interval = 1.17-7.21, p = 0.021).

CONCLUSIONS

The study showed that patients with degeneration of SN were associated with functional dependence or death at 3 months, suggesting that secondary degeneration is a predictor of poor stroke outcomes and a potential therapeutic target.

Transplantation of hESCs-Derived Neural Progenitor Cells Alleviates Secondary Damage of Thalamus After Focal Cerebral Infarction in Rats

Human embryonic stem cells-derived neural progenitor cells (hESCs-NPCs) transplantation holds great potential to treat stroke. We previously reported that delayed secondary degeneration occurs in the ventroposterior nucleus (VPN) of ipsilateral thalamus after distal branch of middle cerebral artery occlusion (dMCAO) in adult male Sprague-Dawley (SD) rats. In this study, we investigate whether hESCs-NPCs would benefit the neural recovery of the secondary damage in the VPN after focal cerebral infarction. Permanent dMCAO was performed with electrocoagulation. Rats were randomized into Sham, dMCAO groups with or without hESCs-NPCs treatment. HESCs-NPCs were engrafted into the peri-infarct regions of rats at 48 h after dMCAO. The transplanted hESCs-NPCs survive and partially differentiate into mature neurons after dMCAO. Notably, hESCs-NPCs transplantation attenuated secondary damage of ipsilateral VPN and improved neurological functions of rats after dMCAO. Moreover, hESCs-NPCs transplantation significantly enhanced the expression of BDNF and TrkB and their interaction in ipsilateral VPN after dMCAO, which was reversed by the knockdown of TrkB. Transplantated hESCs-NPCs reconstituted thalamocortical connection and promoted the formation of synapses in ipsilateral VPN post-dMCAO. These results suggest that hESCs-NPCs transplantation attenuates secondary damage of ipsilateral thalamus after cortical infarction, possibly through activating BDNF/TrkB pathway, enhancing thalamocortical projection, and promoting synaptic formation. It provides a promising therapeutic strategy for secondary degeneration in the ipsilateral thalamus post-dMCAO.

Iron homeostasis imbalance and ferroptosis in brain diseases

Brain iron homeostasis is maintained through the normal function of blood-brain barrier and iron regulation at the systemic and cellular levels, which is fundamental to normal brain function. Excess iron can catalyze the generation of free radicals through Fenton reactions due to its dual redox state, thus causing oxidative stress. Numerous evidence has indicated brain diseases, especially stroke and neurodegenerative diseases, are closely related to the mechanism of iron homeostasis imbalance in the brain. For one thing, brain diseases promote brain iron accumulation. For another, iron accumulation amplifies damage to the nervous system and exacerbates patients' outcomes. In addition, iron accumulation triggers ferroptosis, a newly discovered iron-dependent type of programmed cell death, which is closely related to neurodegeneration and has received wide attention in recent years. In this context, we outline the mechanism of a normal brain iron metabolism and focus on the current mechanism of the iron homeostasis imbalance in stroke, Alzheimer's disease, and Parkinson's disease. Meanwhile, we also discuss the mechanism of ferroptosis and simultaneously enumerate the newly discovered drugs for iron chelators and ferroptosis inhibitors.

Vascular tortuosity is related to reduced thalamic volume after middle cerebral artery occlusion

The mechanisms underlying secondary brain injury in remote areas remains unclear. This study aimed to investigate the relationship between vascular tortuosity and thalamic volume.

METHODS

In this study, we retrospectively analyzed sixty-five patients with unilateral middle cerebral artery occlusion (MCAO) who underwent magnetic resonance angiography. We compared the vascular tortuosity in patients with MCAO and controls, and analyzed the relationship between vascular tortuosity and thalamic volume.

RESULTS

Compared with controls, the MCAO group exhibited a significantly smaller thalamus volume on the affected side (5874 ± 183 mm³ vs. 5635 ± 383 mm³, p < 0.0001). The vascular tortuosity of the posterior cerebral artery (PCA) was higher in the MCAO group than in the controls (82.8 ± 17.3 vs. 76.7 ± 17.3, p = 0.040). Logistic regression analysis revealed that PCA tortuosity was an independent risk factor for reduced thalamic volume after MCAO (p = 0.034). In the subgroup analysis, only the 4-7-day group was not statistically different in thalamic volume between the MCAO and control groups. In the MCAO group, patients older than 60 years and female patients had a more tortuous PCA.

CONCLUSION

Reduced thalamic volume after MCAO was associated with a tortuous PCA. After MCAO, PCA tortuosity increased more significantly in patients aged >60 years and in female patients.

Microstructural Gray Matter Integrity Deteriorates After an Ischemic Stroke and Is Associated with Processing Speed

Microstructural changes after an ischemic stroke (IS) have mainly been described in white matter. Data evaluating microstructural changes in gray matter (GM) remain scarce. The aim of the present study was to evaluate the integrity of GM on longitudinal data using mean diffusivity (MD), and its influence on post-IS cognitive performances. A prospective study was conducted, including supra-tentorial IS patients without pre-stroke disability. A cognitive assessment was performed at baseline and 1 year, including a Montreal Cognitive Assessment, an Isaacs set test, and a Zazzo cancelation task (ZCT): completion time and number of errors. A 3-T brain MRI was performed at the same two time-points, including diffusion tensor imaging for the assessment of GM MD. GM volume was also computed, and changes in GM volume and GM MD were evaluated, followed by the assessment of the relationship between these structural changes and changes in cognitive performances. One hundred and four patients were included (age 68.5 ± 21.5, 38.5% female). While no GM volume loss was observed, GM MD increased between baseline and 1 year. The increase of GM MD in left fronto-temporal regions (dorsolateral prefrontal cortex, superior and medial temporal gyrus, p < 0.05, Threshold-Free Cluster Enhancement, 5000 permutations) was associated with an increase time to complete ZCT, regardless of demographic confounders, IS volume and location, GM, and white matter hyperintensity volume. GM integrity deterioration was thus associated with processing speed slowdown, and appears to be a biomarker of cognitive frailty. This broadens the knowledge of post-IS cognitive impairment mechanisms.

Normal-Appearing White Matter Deteriorates over the Year After an Ischemic Stroke and Is Associated with Global Cognition

Normal-appearing white matter (NAWM) is a hub of plasticity, but data relating to its influence on post-ischemic stroke (IS) outcome remain scarce. The aim of this study was to evaluate the relationship between NAWM integrity and cognitive outcome after an IS. A longitudinal study was conducted including supra-tentorial IS patients. A 3-Tesla brain MRI was performed at baseline and 1 year, allowing the analyses of mean fractional anisotropy (FA) and mean diffusivity (MD) in NAWM masks, along with the volume of white matter hyperintensities (WMH) and IS. A Montreal Cognitive Assessment (MoCA), an Isaacs set test, and a Zazzo's cancellation task were performed at baseline, 3 months and 1 year. Mixed models were built, followed by Tract-based Spatial Statistics (TBSS) analyses. Ninety-five patients were included in the analyses (38% women, median age 69 ± 20). FA significantly decreased, and MD significantly increased between baseline and 1 year, while cognitive scores improved. Patients who decreased their NAWM FA more over the year had a slower cognitive improvement on MoCA (β =  - 0.11, p = 0.05). The TBSS analyses showed that patients who presented the highest decrease of FA in various tracts of white matter less improved their MoCA performances, regardless of WMH and IS volumes, demographic confounders, and clinical severity. NAWM integrity deteriorates over the year after an IS, and is associated with a cognitive recovery slowdown. The diffusion changes recorded here in patients starting with an early preserved white matter structure could have long term impact on cognition.

Neuronal Alterations in Secondary Thalamic Degeneration Due to Cerebral Infarction: A 11 C-Flumazenil Positron Emission Tomography Study

Studies using animal experiments have shown secondary neuronal degeneration in the thalamus after cerebral infarction. Neuroimaging studies in humans have revealed changes in imaging parameters in the thalamus, remote to the infarction. However, few studies have directly demonstrated neuronal changes in the thalamus in vivo. The purpose of this study was to determine whether secondary thalamic neuronal damage may manifest as a decrease in central benzodiazepine receptors in patients with cerebral infarction and internal carotid artery or middle cerebral artery disease.

Corpus callosum lesions are associated with worse cognitive performance in cerebral amyloid angiopathy

The impact of vascular lesions on cognition is location dependent. Here, we assessed the contribution of small vessel disease lesions in the corpus callosum to vascular cognitive impairment in cerebral amyloid angiopathy, as a model for cerebral small vessel disease. Sixty-five patients with probable cerebral amyloid angiopathy underwent 3T magnetic resonance imaging, including a diffusion tensor imaging scan, and neuropsychological testing. Microstructural white-matter integrity was quantified by fractional anisotropy and mean diffusivity. Z-scores on individual neuropsychological tests were averaged into five cognitive domains: information processing speed, executive functioning, memory, language and visuospatial ability. Corpus callosum lesions were defined as haemorrhagic (microbleeds or larger bleeds) or ischaemic (microinfarcts, larger infarcts and diffuse fluid-attenuated inversion recovery hyperintensities). Associations between corpus callosum lesion presence, microstructural white-matter integrity and cognitive performance were examined with multiple regression models. The prevalence of corpus callosum lesions was confirmed in an independent cohort of memory clinic patients with and without cerebral amyloid angiopathy (n = 82). In parallel, we assessed corpus callosum lesions on ex vivo magnetic resonance imaging in cerebral amyloid angiopathy patients (n = 19) and controls (n = 5) and determined associated tissue abnormalities with histopathology. A total number of 21 corpus callosum lesions was found in 19/65 (29%) cerebral amyloid angiopathy patients. Corpus callosum lesion presence was associated with reduced microstructural white-matter integrity within the corpus callosum and in the whole-brain white matter. Patients with corpus callosum lesions performed significantly worse on all cognitive domains except language, compared with those without corpus callosum lesions after correcting for age, sex, education and time between magnetic resonance imaging and neuropsychological assessment. This association was independent of the presence of intracerebral haemorrhage, whole-brain fractional anisotropy and mean diffusivity, and white-matter hyperintensity volume and brain volume for the domains of information processing speed and executive functioning. In the memory clinic patient cohort, corpus callosum lesions were present in 14/54 (26%) patients with probable and 2/8 (25%) patients with possible cerebral amyloid angiopathy, and in 3/20 (15%) patients without cerebral amyloid angiopathy. In the ex vivo cohort, corpus callosum lesions were present in 10/19 (53%) patients and 2/5 (40%) controls. On histopathology, ischaemic corpus callosum lesions were associated with tissue loss and demyelination, which extended beyond the lesion core. Together, these data suggest that corpus callosum lesions are a frequent finding in cerebral amyloid angiopathy, and that they independently contribute to cognitive impairment through strategic microstructural disruption of white-matter tracts.

Post-Stroke Cognitive Impairment and Dementia

Poststroke cognitive impairment and dementia (PSCID) is a major source of morbidity and mortality after stroke worldwide. PSCID occurs as a consequence of ischemic stroke, intracerebral hemorrhage, or subarachnoid hemorrhage. Cognitive impairment and dementia manifesting after a clinical stroke is categorized as vascular even in people with comorbid neurodegenerative pathology, which is common in elderly individuals and can contribute to the clinical expression of PSCID. Manifestations of cerebral small vessel disease, such as covert brain infarcts, white matter lesions, microbleeds, and cortical microinfarcts, are also common in patients with stroke and likewise contribute to cognitive outcomes. Although studies of PSCID historically varied in the approach to timing and methods of diagnosis, most of them demonstrate that older age, lower educational status, socioeconomic disparities, premorbid cognitive or functional decline, life-course exposure to vascular risk factors, and a history of prior stroke increase risk of PSCID. Stroke characteristics, in particular stroke severity, lesion volume, lesion location, multiplicity and recurrence, also influence PSCID risk. Understanding the complex interaction between an acute stroke event and preexisting brain pathology remains a priority and will be critical for developing strategies for personalized prediction, prevention, targeted interventions, and rehabilitation. Current challenges in the field relate to a lack of harmonization of definition and classification of PSCID, timing of diagnosis, approaches to neurocognitive assessment, and duration of follow-up after stroke. However, evolving knowledge on pathophysiology, neuroimaging, and biomarkers offers potential for clinical applications and may inform clinical trials. Preventing stroke and PSCID remains a cornerstone of any strategy to achieve optimal brain health. We summarize recent developments in the field and discuss future directions closing with a call for action to systematically include cognitive outcome assessment into any clinical studies of poststroke outcome.

Reactive Astrocytes Prevent Maladaptive Plasticity after Ischemic Stroke

Restoration of functional connectivity is a major contributor to functional recovery after stroke. We investigated the role of reactive astrocytes in functional connectivity and recovery after photothrombotic stroke in mice with attenuated reactive gliosis (GFAP^-/-Vim^-/-). Infarct volume and longitudinal functional connectivity changes were determined by in vivo T2-weighted magnetic resonance imaging (MRI) and resting-state functional MRI. Sensorimotor function was assessed with behavioral tests, and glial and neural plasticity responses were quantified in the peri-infarct region. Four weeks after stroke, GFAP^-/-Vim^-/- mice showed impaired recovery of sensorimotor function and aberrant restoration of global neuronal connectivity. These mice also exhibited maladaptive plasticity responses, shown by higher number of lost and newly formed functional connections between primary and secondary targets of cortical stroke regions and increased peri-infarct expression of the axonal plasticity marker Gap43. We conclude that reactive astrocytes modulate recovery-promoting plasticity responses after ischemic stroke.

Secondary thalamic neuroinflammation after focal cortical stroke and traumatic injury mirrors corticothalamic functional connectivity

While cortical injuries, such as traumatic brain injury (TBI) and neocortical stroke, acutely disrupt the neocortex, most of their consequent disabilities reflect secondary injuries that develop over time. Thalamic neuroinflammation has been proposed to be a biomarker of cortical injury and of the long-term cognitive and neurological deficits that follow. However, the extent to which thalamic neuroinflammation depends on the type of cortical injury or its location remains unknown. Using two mouse models of focal neocortical injury that do not directly damage subcortical structures-controlled cortical impact and photothrombotic ischemic stroke-we found that chronic neuroinflammation in the thalamic region mirrors the functional connections with the injured cortex, and that sensory corticothalamic regions may be more likely to sustain long-term damage than nonsensory circuits. Currently, heterogeneous clinical outcomes complicate treatment. Understanding how thalamic inflammation depends on the injury site can aid in predicting features of subsequent deficits and lead to more effective, customized therapies.

A pilot [11C]PBR28 PET/MRI study of neuroinflammation and neurodegeneration in chronic stroke patients

Neuroinflammation occurs in response to acute ischemic stroke, and has been speculated to underlie secondary poststroke pathologies, such as depression, that often develop over time poststroke. However, no study has examined whether neuroinflammation is present in chronic stroke patients (e.g., ​≥ ​1 year poststroke). This study tested whether neuroinflammation is present in chronic stroke patients, and is associated with neurodegeneration, using [¹¹C]PBR28 PET and diffusion MRI.

Eight patients with middle cerebral artery (MCA) ischemic stroke incurred 1–3 years prior and 16 healthy controls underwent [¹¹C]PBR28 PET to measure glial activation and diffusion MRI to measure microstructural integrity by mean diffusivity (MD) and fractional anisotropy (FA) using an integrated PET/MRI scanner. Group differences in [¹¹C]PBR28 binding, MD and FA were analyzed voxelwise across the whole brain excluding the infarct zone defined as voxels containing the infarct in any patient.

Compared to controls, patients showed elevations in [¹¹C]PBR28 binding in several brain regions outside the infarct zone, including regions with presumed direct neuroanatomical connections to the infarct (e.g., ipsilesional internal capsule and thalamus) and those without known direct connections (e.g., contralesional thalamus and cingulate gyrus). Patients also showed widespread elevations in MD, with a subset of these regions having reduced FA. In patients, MD was more elevated in regions with co-localized elevations in [¹¹C]PBR28 binding than in contralateral regions without elevations in [¹¹C]PBR28 binding.

This pilot study supports the presence of extensive glial activation along with widespread loss in microstructural integrity in non-infarcted tissue in a cohort of patients with chronic MCA stroke. The loss in microstructural integrity was greater in regions with co-localized glial activation. It is possible that stroke risk factors (e.g., hypertension) contributed to these tissue changes in patients.

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Chronic neuroinflammation speculated to underlie secondary poststroke pathologies such as depression.

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Measured neuroinflammation in chronic stroke patients using [¹¹C]PBR28 PET.

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First study showing extensive neuroinflammation in non-infarcted tissue in chronic stroke patients.

Is Cerebral Amyloid-β Deposition Related to Post-stroke Cognitive Impairment?

Approximately two-thirds of ischemic stroke patients suffer from different levels of post-stroke cognitive impairment (PSCI), but the underlying mechanisms of PSCI remain unclear. Cerebral amyloid-β (Aβ) deposition, a pathological hallmark of Alzheimer's disease, has been discovered in the brains of stroke patients in some autopsy studies. However, less is known about the role of Aβ pathology in the development of PSCI. It is hypothesized that cerebral ischemic injury may lead to neurotoxic Aβ accumulation in the brain, which further induces secondary neurodegeneration and progressive cognitive decline after stroke onset. In this review, we summarized available evidence from pre-clinical and clinical studies relevant to the aforementioned hypothesis. We found inconsistency in the results obtained from studies in rodents, nonhuman primates, and stroke patients. Moreover, the causal relationship between post-stroke cerebral Aβ deposition and PSCI has been uncertain and controversial. Taken together, evidence supporting the hypothesis that brain ischemia induces cerebral Aβ deposition has been insufficient so far. And, there is still no consensus regarding the contribution of cerebral amyloid pathology to PSCI. Other non-amyloid neurodegenerative mechanisms might be involved and remain to be fully elucidated.

Neurofilament Light Chain (NfL) in Blood-A Biomarker Predicting Unfavourable Outcome in the Acute Phase and Improvement in the Late Phase after Stroke

Increased sensitivity of methods assessing the levels of neurofilament light chain (NfL), a neuron-specific intermediate filament protein, in human plasma or serum, has in recent years led to a number of studies addressing the utility of monitoring NfL in the blood of stroke patients. In this review, we discuss that elevated blood NfL levels after stroke may reflect several different neurobiological processes. In the acute and post-acute phase after stroke, high blood levels of NfL are associated with poor clinical outcome, and later on, the blood levels of NfL positively correlate with secondary neurodegeneration as assessed by MRI. Interestingly, increased blood levels of NfL in individuals who survived stroke for more than 10 months were shown to predict functional improvement in the late phase after stroke. Whereas in the acute phase after stroke the injured axons are assumed to be the main source of blood NfL, synaptic turnover and secondary neurodegeneration could be major contributors to blood NfL levels in the late phase after stroke. Elevated blood NfL levels after stroke should therefore be interpreted with caution. More studies addressing the clinical utility of blood NfL assessment in stroke patients are needed before the inclusion of NfL in the clinical workout as a useful biomarker in both the acute and the chronic phase after stroke.

Determining the effect of aging, recovery time, and post-stroke memantine treatment on delayed thalamic gliosis after cortical infarct

Secondary injury following cortical stroke includes delayed gliosis and eventual neuronal loss in the thalamus. However, the effects of aging and the potential to ameliorate this gliosis with NMDA receptor (NMDAR) antagonism are not established. We used the permanent distal middle cerebral artery stroke model (pdMCAO) to examine secondary thalamic injury in young and aged mice. At 3 days post-stroke (PSD3), slight microgliosis (IBA-1) and astrogliosis (GFAP) was evident in thalamus, but no infarct. Gliosis increased dramatically through PSD14, at which point degenerating neurons were detected. Flow cytometry demonstrated a significant increase in CD11b⁺/CD45^int microglia (MG) in the ipsilateral thalamus at PSD14. CCR2-RFP reporter mouse further demonstrated that influx of peripheral monocytes contributed to the MG/Mϕ population. Aged mice demonstrated reduced microgliosis and astrogliosis compared with young mice. Interestingly, astrogliosis demonstrated glial scar-like characteristics at two years post-stroke, but not by 6 weeks. Lastly, treatment with memantine (NMDAR antagonist) at 4 and 24 h after stroke significantly reduced gliosis at PSD14. These findings expand our understanding of gliosis in the thalamus following cortical stroke and demonstrate age-dependency of this secondary injury. Additionally, these findings indicate that delayed treatment with memantine (an FDA approved drug) provides significant reduction in thalamic gliosis.

Characterizing Diaschisis-Related Thalamic Perfusion and Diffusion After Middle Cerebral Artery Infarction

[Figure: see text].

Plasma neurofilament light chain levels predict improvement in late phase after stroke

BACKGROUND AND PURPOSE

Although functional recovery is most pronounced in the first 6 months after stroke, improvement is possible also in the late phase. The value of plasma neurofilament light chain (NfL), a biomarker of axonal injury and secondary neurodegeneration, was explored for the prediction of functional improvement in the late phase after stroke.

METHODS

Baseline plasma NfL levels were measured in 115 participants of a trial on the efficacy of multimodal rehabilitation in the late phase after stroke. The association between NfL levels, impairment in balance, gait and cognitive domains, and improvement 3 and 9 months later was determined.

RESULTS

Plasma NfL levels were associated with the degree of impairment in all three domains. Individuals with meaningful improvement in balance and gait capacity had higher plasma NfL levels compared with non-improvers (p = 0.001 and p = 0.018, respectively). Higher NfL levels were associated with improvement in balance (odds ratio [OR] 2.34, 95% confidence interval [CI] 1.35-4.27, p = 0.004) and gait (OR 2.27, 95% CI 1.25-4.32, p = 0.009). Elevated plasma NfL levels showed a positive predictive value for cognitive improvement, and this effect was specific for the intervention targeting the cognitive domain. The association of NfL levels with cognitive improvement withstood correction for baseline impairment, age and total years of schooling (OR 7.54, 95% CI 1.52-45.66, p = 0.018).

CONCLUSIONS

In addition to its established role as a biomarker in the acute phase, elevated circulating NfL levels may predict functional improvement in the late phase after stroke. Our results should prompt further studies into the use of plasma NfL as a biomarker in the late phase after stroke.

Unique Subtype of Microglia in Degenerative Thalamus After Cortical Stroke

BACKGROUND AND PURPOSE

Stroke disrupts neuronal functions in both local and remotely connected regions, leading to network-wide deficits that can hinder recovery. The thalamus is particularly affected, with progressive development of neurodegeneration accompanied by inflammatory responses. However, the complexity of the involved inflammatory responses is poorly understood. Herein we investigated the spatiotemporal changes in the secondary degenerative thalamus after cortical stroke, using targeted transcriptome approach in conjunction with histology and flow cytometry.

METHODS

Cortical ischemic stroke was generated by permanent occlusion of the left middle cerebral artery in male C57BL6J mice. Neurodegeneration, neuroinflammatory responses, and microglial activation were examined in naive and stroke mice at from poststroke days (PD) 1 to 84, in both ipsilesional somatosensory cortex and ipsilesional thalamus. NanoString neuropathology panel (780 genes) was used to examine transcriptome changes at PD7 and PD28. Fluorescence activated cell sorting was used to collect CD11c⁺ microglia from ipsilesional thalamus, and gene expressions were validated by quantitative real-time polymerase chain reaction.

RESULTS

Neurodegeneration in the thalamus was detected at PD7 and progressively worsened by PD28. This was accompanied by rapid microglial activation detected as early as PD1, which preceded the neurodegenerative changes. Transcriptome analysis showed higher number of differentially expressed genes in ipsilesional thalamus at PD28. Notably, neuroinflammation was the top activated pathway, and microglia was the most enriched cell type. Itgax (CD11c) was the most significantly increased gene, and its expression was highly detected in microglia. Flow-sorted CD11c⁺ microglia from degenerative thalamus indicated molecular signatures similar to neurodegenerative disease-associated microglia; these included downregulated Tmem119 and CX3CR1 and upregulated ApoE, Axl, LpL, CSF1, and Cst7.

CONCLUSIONS

Our findings demonstrate the dynamic changes of microglia after stroke and highlight the importance of investigating stroke network-wide deficits. Importantly, we report the existence of a unique subtype of microglia (CD11c⁺) with neurodegenerative disease-associated microglia features in the degenerative thalamus after stroke.

Impact of sleep quality on post-stroke anxiety in stroke patients

OBJECTIVE

To explore whether poor sleep is associated with post-stroke anxiety (PSA) in Chinese patients with acute ischemic stroke (AIS) and to verify whether poor sleep is a predictor of PSA.

METHODS

A total of 327 patients with AIS were enrolled and followed up for 1 month. Sleep quality within 1 month before stroke was evaluated using the Pittsburgh Sleep Quality Index (PSQI) at admission. The patients were divided into the poor sleep group (PSQI > 7, n = 76) and good sleep group (PSQI ≤ 7, n = 251). One month after stroke, patients with obvious anxiety symptoms and a Hamilton Anxiety Scale score >7 were diagnosed with PSA.

RESULTS

Eighty-seven patients (26.6%) were diagnosed with PSA. Compared to the good sleep quality group, the incidence of PSA in patients with poor sleep quality was higher (42.1% vs. 21.9%, p = .001). Poor sleep quality is more common in patients with PSA (35.6% vs. 18.8%, p = .001). A logistic regression analysis indicated that poor sleep quality was significantly associated with PSA (OR: 2.265, 95% CI: 1.262-4.067, p = .003). After adjusting for conventional and identified risk factors, poor sleep quality was found to be independently associated with PSA (OR: 2.676, 95% CI: 1.451-4.936, p = .001).

CONCLUSIONS

Poor sleep quality before stroke was associated with PSA and may be an independent risk factor of PSA 1 month after AIS onset.

Cerebral Small Vessel Disease MRI Features Do Not Improve the Prediction of Stroke Outcome

OBJECTIVE

To determine whether the total small vessel disease (SVD) score adds information to the prediction of stroke outcome compared to validated predictors, we tested different predictive models of outcome in patients with stroke.

METHODS

White matter hyperintensity, lacunes, perivascular spaces, microbleeds, and atrophy were quantified in 2 prospective datasets of 428 and 197 patients with first-ever stroke, using MRI collected 24 to 72 hours after stroke onset. Functional, cognitive, and psychological status were assessed at the 3- to 6-month follow-up. The predictive accuracy (in terms of calibration and discrimination) of age, baseline NIH Stroke Scale score (NIHSS), and infarct volume was quantified (model 1) on dataset 1, the total SVD score was added (model 2), and the improvement in predictive accuracy was evaluated. These 2 models were also developed in dataset 2 for replication. Finally, in model 3, the MRI features of cerebral SVD were included rather than the total SVD score.

RESULTS

Model 1 showed excellent performance for discriminating poor vs good functional outcomes (area under the curve [AUC] 0.915), and fair performance for identifying cognitively impaired and depressed patients (AUCs 0.750 and 0.688, respectively). A higher SVD score was associated with a poorer outcome (odds ratio 1.30 [1.07-1.58], p = 0.0090 at best for functional outcome). However, adding the total SVD score (model 2) or individual MRI features (model 3) did not improve the prediction over model 1. Results for dataset 2 were similar.

CONCLUSIONS

Cerebral SVD was independently associated with functional, cognitive, and psychological outcomes, but had no clinically relevant added value to predict the individual outcomes of patients when compared to the usual predictors, such as age and baseline NIHSS.

Experimental cortical stroke induces aberrant increase of sharp-wave-associated ripples in the hippocampus and disrupts cortico-hippocampal communication

The functional consequences of ischemic stroke in the remote brain regions are not well characterized. The current study sought to determine changes in hippocampal oscillatory activity that may underlie the cognitive impairment observed following distal middle cerebral artery occlusion (dMCAO) without causing hippocampal structural damage. Local field potentials were recorded from the dorsal hippocampus and cortex in urethane-anesthetized rats with multichannel silicon probes during dMCAO and reperfusion, or mild ischemia induced by bilateral common carotid artery occlusion (CCAO). Bilateral change of brain state was evidenced by reduced theta/delta amplitude ratio and shortened high theta duration following acute dMCAO but not CCAO. An aberrant increase in the occurrence of sharp-wave-associated ripples (150-250 Hz), crucial for memory consolidation, was only detected after dMCAO reperfusion, coinciding with an increased occurrence of high-frequency discharges (250-450 Hz). dMCAO also significantly affected the modulation of gamma amplitude in the cortex coupled to hippocampal theta phase, although both hippocampal theta and gamma power were temporarily decreased during dMCAO. Our results suggest that MCAO may disrupt the balance between excitatory and inhibitory circuits in the hippocampus and alter the function of cortico-hippocampal network, providing a novel insight in how cortical stroke affects function in remote brain regions.

Diaschisis revisited: quantitative evaluation of thalamic hypoperfusion in anterior circulation stroke

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CT perfusion reveals thalamic hypoperfusion in acute anterior circulation stroke.

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This indirect phenomenon is referred to as ipsilateral thalamic diaschisis (ITD).

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Quantitative analysis indicates that ITD is a non-binary phenomenon.

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ITD is associated with lesion extent and involvement of the lentiform nucleus.

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Stroke outcome was not associated with ITD parameters.

Purpose

Ipsilateral thalamic diaschisis (ITD) refers to the phenomenon of thalamic hypoperfusion or hypometabolism due to a distant cerebral injury. To further investigate the characteristics and spectrum of ITD, we analyzed quantitative measurements of thalamic hypoperfusion in acute anterior circulation stroke.

Methods

We selected consecutive patients with large-vessel occlusion (LVO) anterior circulation stroke and available CT perfusion (CTP) examination on admission who underwent endovascular thrombectomy. Thalamic perfusion parameters on CTP were tested between ipsi- and contralesional thalamus and ischemic territory. Values were compared with thresholds from CTP analysis software. Associations of thalamic perfusion parameters with acute imaging and clinical data were determined in uni- and multivariate logistic regression analyses.

Results

Ninety-nine patients were included. All perfusion parameters indicated significant non-ischemic hypoperfusion of the thalamus, not reaching the levels of ischemia in the middle cerebral artery territory due to LVO (all p < 0.002). Multiple perfusion parameters exhibited significant association with ischemic lesion extent (relative cerebral blood flow [CBF]: β =  − 0.23, p = 0.022; Δtime to drain: β = 0.33, p < 0.001; ΔTmax: β =  − 0.36, p < 0.001) and involvement of the Lentiform Nucleus (Δmean transit time: β = 0.64, p = 0.04; Δtime to drain: β = 0.81, p = 0.01; ΔTmax: β =  − 0.82, p = 0.01). Symptom severity on admission exhibited minor significant association with reduction of thalamic CBF in uncorrected analysis (Odds ratio: 0.05, p = 0.049), but short- and long-term outcomes were unaffected by perfusion status. ITD reached guideline-based software-threshold levels in only one patient.

Conclusions

ITD in acute stroke is a non-binary phenomenon affected by lesion extent and involvement of the lentiform nucleus. We found uncorrected association of ITD with early clinical presentation, but no association with short- or long-term outcome was evident. Relevant misclassification of ITD by guideline-based CTP software was not indicated, which needs further dedicated testing.

Automated MRI-based volumetry of basal ganglia and thalamus at the chronic phase of cortical stroke

Purpose

We aimed at assessing the potential of automated MR morphometry to assess individual basal ganglia and thalamus volumetric changes at the chronic phase after cortical stroke.

Methods

Ninety-six patients (mean age: 65 ± 18 years, male 55) with cortical stroke at the chronic phase were retrospectively included. Patients were scanned at 1.5 T or 3 T using a T1-MPRAGE sequence. Resulting 3D images were processed with the MorphoBox prototype software to automatically segment basal ganglia and thalamus structures, and to obtain Z scores considering the confounding effects of age and sex. Stroke volume was estimated by manual delineation on T2-SE imaging. Z scores were compared between ipsi- and contralateral stroke side and according to the vascular territory. Potential relationship between Z scores and stroke volume was assessed using the Spearman correlation coefficient.

Results

Basal ganglia and thalamus volume Z scores were lower ipsilaterally to MCA territory stroke (p values < 0.034) while they were not different between ipsi- and contralateral stroke sides in non-MCA territory stroke (p values > 0.37). In MCA territory stroke, ipsilateral caudate nucleus (rho = − 0.34, p = 0.007), putamen (rho = − 0.50, p < 0.001), pallidum (rho = − 0.44, p < 0.001), and thalamus (rho = − 0.48, p < 0.001) volume Z scores negatively correlated with the cortical stroke volume. This relation was not influenced by cardiovascular risk factors or time since stroke.

Conclusion

Automated MR morphometry demonstrated atrophy of ipsilateral basal ganglia and thalamus at the chronic phase after cortical stroke in the MCA territory. The atrophy was related to stroke volume. These results confirm the potential role for automated MRI morphometry to assess remote changes after stroke.

Advances in Studies on Stroke-Induced Secondary Neurodegeneration (SND) and Its Treatment

Background:

The occurrence of secondary neurodegeneration has exclusively been observed after the first incidence of stroke. In humans and rodents, post-stroke secondary neurodegeneration (SND) is an inevitable event that can lead to progressive neuronal loss at a region distant to initial infarct. SND can lead to cognitive and motor function impairment, finally causing dementia. The exact pathophysiology of the event is yet to be explored. It is seen that the thalami, in particular, are susceptible to cause SND. The reason behind this is because the thalamus functioning as the relay center and is positioned as an interlocked structure with direct synaptic signaling connection with the cortex. As SND proceeds, accumulation of misfolded proteins and microglial activation are seen in the thalamus. This leads to increased neuronal loss and worsening of functional and cognitive impairment.

Objective:

There is a necessity of specific interventions to prevent post-stroke SND, which are not properly investigated to date owing to sparsely reproducible pre-clinical and clinical data. The basis of this review is to investigate about post-stroke SND and its updated treatment approaches carefully.

Methods:

Our article presents a detailed survey of advances in studies on stroke-induced secondary neurodegeneration (SND) and its treatment.

Results:

This article aims to put forward the pathophysiology of SND. We have also tabulated the latest treatment approaches along with different neuroimaging systems that will be helpful for future reference to explore.

Conclusion:

In this article, we have reviewed the available reports on SND pathophysiology, detection techniques, and possible treatment modalities that have not been attempted to date.

Impaired glymphatic system in secondary degeneration areas after ischemic stroke in rats

BACKGROUND

Pathomechanism of secondary degeneration in remote regions after ischemic stroke has not been totally clarified. Contrast-enhanced MRI with injecting Gd-DTPA in cisterna magna (CM) is regarded as an efficient method to measure glymphatic system function in brain. Our research aimed at evaluating glymphatic system changes in secondary degeneration areas by contrast-enhanced MRI.

METHODS

Ischemic stroke was induced by left middle cerebral artery occlusion (MCAO) model. A total of 12 Sprague-Dawley rats were randomly divided into three groups: control group with sham operations (n=4), the group of acute phase (1 day after MCAO) (n=4), and the group of subacute phase (7 days after MCAO) (n=4). Contrast-enhanced MRI was performed in 1days or 7days after operations respectively. All rats received an intrathecal injection of Gd-DTPA (2μl/min, totally 20μl) and high-resolution 3D T1-weighted MRI for 6 h. The time course of the signal-to-noise ratio (SNR) in substantia Nigra (SN) and ventral thalamic nucleus (VTN) was evaluated between two hemispheres in all rats.

RESULTS

In control group without ischemia, time-to-peak of SNR in SN was earlier than that in VTN. There were no differences of SNR between two hemispheres after intrathecal Gd-DTPA administration. In the group of acute phase, MRI revealed similar time course and time-to-peak of SNR between ipsilateral and contralateral VTN, while a tendency of higher SNR in ipsilateral SN than contralateral SN at 4h, 5h, 6h after Gd-DTPA injection. And time-to-peak of SNR was similar in bilateral SN. In the group of subacute phase, time-to-peak of SNR was similar in bilateral VTN, while longer in ipsilateral SN compared with contralateral side. In addition, SNR in T1WI in ipsilateral was significantly higher than SNR in contralateral SN and VTN at 5h (VTN, P= 0.003; SN, P=0.004) and 6h (VTN, P=0.015; SN, P=0.006) after Gd-DTPA injection.

CONCLUSION

Glymphatic system was impaired in ipsilateral SN and VTN after ischemic stroke, which may contribute to neural degeneration.

Association of serum biomarker neurofilament light concentration with post-stroke depression: A preliminary study

OBJECTIVE

To investigate serum neurofilament light (sNfL) levels in acute ischemic stroke and to assess whether sNfL are related to the severity of disease and a potential prognostic marker of post-stroke depression (PSD) during a 3-month follow-up period.

METHODS

This was a single-center prospective cohort study. The sNfL concentration was measured in baseline samples using the Simoa platform- Single Molecule Array technology. A psychiatrist administered the Structural Clinical Interview for Diagnostic and Statistical Manual IV to all patients and made a diagnosis of PSD 3 months after stroke. The logistic regression was used to examine the association between sNfL and PSD.

RESULTS

In total, 236 ischemic stroke cases were included and finished the follow-up. In the follow-up, 55 patients were defined as PSD, thus the incidence rate was 23.3% (95% confidence intervals [CI]: 17.9%-28.7%). Significant differences were observed between the sNfL levels in patients with PSD (124.8 pg/ml [interquartile range {IQR}: 59.6-159.2]) and in patients without PSD (35.9 pg/ml [IQR: 18.2-60.4]) levels (P < 0.001). After adjusting for age, family history of depression, marital status, National Institutes of Health and Stroke Scale score, C-reactive protein and homocysteine levels, sNfL levels independently predicted the development of post-stroke depression. The crude and adjusted odds ratios [OR] (and 95%CI) of PSD associated with an IQR increase for sNfL were 3.38(2.29, 4.98) and 2.65(1.59, 4.04), respectively. According to receiver operating characteristic curves (ROC) curves, the cut-off value of sNfL to predict PSD was 111.4 pg/ml with an area under the curve (AUC) of 0.84(95% CI, 0.78-0.90) and with the highest sensitivity (61.8%) and specificity (95.4%).

CONCLUSIONS

In this study, elevated level of sNfL is associated with higher risk of 3-month depression in patients with ischemic stroke and makes early diagnoses of depression. The study needs replication to ensure the validity of our preliminary results.

Inflammatory Responses in the Secondary Thalamic Injury After Cortical Ischemic Stroke

Stroke is one of the major causes of chronic disability worldwide and increasing efforts have focused on studying brain repair and recovery after stroke. Following stroke, the primary injury site can disrupt functional connections in nearby and remotely connected brain regions, resulting in the development of secondary injuries that may impede long-term functional recovery. In particular, secondary degenerative injury occurs in the connected ipsilesional thalamus following a cortical stroke. Although secondary thalamic injury was first described decades ago, the underlying mechanisms still remain unclear. We performed a systematic literature review using the NCBI PubMed database for studies that focused on the secondary thalamic degeneration after cortical ischemic stroke. In this review, we discussed emerging studies that characterized the pathological changes in the secondary degenerative thalamus after stroke; these included excitotoxicity, apoptosis, amyloid beta protein accumulation, blood-brain-barrier breakdown, and inflammatory responses. In particular, we highlighted key findings of the dynamic inflammatory responses in the secondary thalamic injury and discussed the involvement of several cell types in this process. We also discussed studies that investigated the effects of blocking secondary thalamic injury on inflammatory responses and stroke outcome. Targeting secondary injuries after stroke may alleviate network-wide deficits, and ultimately promote stroke recovery.

Relationship Between Olfactory Disturbance After Acute Ischemic Stroke and Latent Thalamic Hypoperfusion

Odor detection, recognition, and identification were assessed in 19 acute ischemic stroke patients who had no magnetic resonance imaging-detectable thalamic lesions but in whom technetium-99m ethyl cysteinate dimer single photon emission tomography revealed thalamic hypoperfusion. Although these patients were unaware of reduced olfactory function, they exhibited significantly lower scores in tests for odor identification and recognition threshold as compared with 9 ischemic stroke controls that had normal thalamic hypoperfusion. However, absolute odor detection thresholds were similar in the 2 groups. These results demonstrate the usefulness of cerebral perfusion scintigraphy in assessing sensory loss after ischemic stroke and provide further evidence for the role of the thalamus in olfaction.

Characterizing ipsilateral thalamic diaschisis in symptomatic cerebrovascular steno-occlusive patients

The clinical significance of ipsilateral thalamic diaschisis (ITD) occurring after stroke is unknown. To characterize ITD, we investigate its hemodynamic, structural, and clinical implications. A single-institution prospective cross-sectional study was conducted using 28 symptomatic cerebrovascular steno-occlusive patients undergoing both BOLD-CVR and Diamox-challenged 15(O)-H2O-PET. Follow-up was at least three months. In addition, 15 age-matched healthy subjects were included. ITD was diagnosed based on a BOLD-CVR thalamic asymmetry index (TAI) > +2 standard deviations from healthy subjects. Cerebral blood flow differences were assessed using a PET-based TAI before and after Diamox challenge. Thalamic volume masks were determined using Freesurfer. Neurological status at symptom onset and after three months was determined with NIHSS and mRS scores. ITD was diagnosed in 15 of 28 (57%) patients. PET-TAI before and after Diamox challenge were increased in patients with ITD, indicating an ipsilateral thalamic blood flow decrease. Patients with ITD exhibited a marked ipsilateral thalamic volume decrease as compared to patients without ITD and healthy subjects. Furthermore, patients with ITD had worse NIHSS and mRS at symptom onset and after three months follow-up, even after adjustment for stroke volume. The presence of ITD is characterized by thalamic volume reduction, reduced thalamic blood flow, and worse neurological performance unrelated to stroke volume.

Serum Neurofilament Light Predicts Severity and Prognosis in Patients with Ischemic Stroke

Serum neurofilaments are markers of axonal injury. We investigated whether serum neurofilament light (sNfL) is a potential prognostic marker of functional outcome in Chinese patients with acute ischemic stroke (AIS). From May 2015 to December 2018, consecutive patients with AIS from the Department of Neurology of the Second Hospital of Jilin University were included. sNfL concentration was tested at baseline, and stroke severity was analyzed at admission using the NIHSS score. Functional outcome was assessed at discharge by the modified Rankin scale (mRS). The sNfL concentration was tested in 343 patients with a median value of 17.8 (IQR, 13.4-25.2) pg/ml. sNfL concentration paralleled lesion size (P = 0.035). At admission, 174 patients were defined as moderate-to-high stroke (NIHSS ≥ 5); the sNfL concentration in those patients were higher than that observed in patients with minor clinical severity [21.2 (IQR, 15.1-31.7) vs. 14.9 (11.8-19.4) pg/ml, P < 0.001]. For each 1 quartile increase of sNfL concentration, the unadjusted and adjusted risk of moderate-to-high stroke increased by 202% (with the OR of 3.04 (95% CI 2.15-4.32), P < 0.001) and 102% [2.02 (1.10-3.16), P = 0.001), respectively. At discharge, 85 patients (24.8%) had poor functional outcome (mRS, 3-6); the sNfL concentration in those patients were higher than that observed in patients with good outcome [24.1 (IQR, 18.8-33.9) vs. 15.7 (11.9-21.8) pg/ml, P < 0.001]. For each 1 quartile increase of sNfL concentration, the unadjusted and adjusted risk of poor outcome increased by 236% [with the OR of 3.36 (95% CI 2.23-5.06), P < 0.001] and 102% [2.29 (1.37-3.82), P < 0.001], respectively. The results show sNfL is meaningful blood biomarker to monitor stroke severity and functional outcome in ischemic stroke, suggesting that sNfL may play a role in stroke progression.

Brain iron content in systemic iron overload: A beta-thalassemia quantitative MRI study

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Iron overload is a life-threatening condition in beta-thalassemia.

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Data on brain involvement in systemic iron overload are conflicting.

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MRI quantification of brain tissue iron content is feasible in a voxel-based approach.

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No iron tissue excess is evident in beta-thalassemia but in the choroid plexuses.

Objective

Multisystem iron poisoning is a major concern for long-term beta-thalassemia management. Quantitative MRI-based techniques routinely show iron overload in heart, liver, endocrine glands and kidneys. However, data on the brain are conflicting and monitoring of brain iron content is still matter of debate.

Methods

This 3T-MRI study applied a well validated high-resolution whole-brain quantitative MRI assessment of iron content on 47 transfusion-dependent (mean-age: 36.9 ± 10.3 years, 63% females), 23 non-transfusion dependent (mean-age: 29.2 ± 11.7 years, 56% females) and 57 healthy controls (mean-age: 33.9 ± 10.8 years, 65% females). Clinical data, Wechsler Adult Intelligence Scale scores and treatment regimens were recorded. Beside whole-brain R2* analyses, regional R2*-values were extracted in putamen, globus pallidum, caudate nucleus, thalamus and red nucleus; hippocampal volumes were also determined.

Results

Regional analyses yielded no significant differences between patients and controls, except in those treated with deferiprone that showed lower R2*-values (p<0.05). Whole-brain analyses of R2*-maps revealed strong age-R2* correlations (r²=0.51) in both groups and clusters of significantly increased R2*-values in beta-thalassemia patients in the hippocampal formations and around the Luschka foramina; transfusion treatment was associated with additional R2* increase in dorsal thalami. Hippocampal formation R2*-values did not correlate with hippocampal volume; hippocampal volume did not differ between patients and controls. All regions with increased R2*-values shared a strict anatomical contiguity with choroid plexuses suggesting a blooming effect as the likely cause of R2* increase, in agreement with the available histopathologic literature evidence.

Conclusion

According to our MRI findings and the available histopathologic literature evidence, concerns about neural tissue iron overload in beta-thalassemia appear to be unjustified.

Active learning strategy and hybrid training for infarct segmentation on diffusion MRI with a U-shaped network

Automatic and reliable stroke lesion segmentation from diffusion magnetic resonance imaging (MRI) is critical for patient care. Methods using neural networks have been developed, but the rate of false positives limits their use in clinical practice. A training strategy applied to three-dimensional deconvolutional neural networks for stroke lesion segmentation on diffusion MRI was proposed. Infarcts were segmented by experts on diffusion MRI for 929 patients. We divided each database as follows: 60% for a training set, 20% for validation, and 20% for testing. Our hypothesis was a two-phase hybrid learning scheme, in which the network was first trained with whole MRI (regular phase) and then, in a second phase (hybrid phase), alternately with whole MRI and patches. Patches were actively selected from the discrepancy between expert and model segmentation at the beginning of each batch. On the test population, the performances after the regular and hybrid phases were compared. A statistically significant Dice improvement with hybrid training compared with regular training was demonstrated ( p < 0.01 ). The mean Dice reached 0.711 ± 0.199 . False positives were reduced by almost 30% with hybrid training ( p < 0.01 ). Our hybrid training strategy empowered deep neural networks for more accurate infarct segmentations on diffusion MRI.

The new insights into human brain imaging after stroke

Over the last two decades, developments of human brain stroke imaging have raised several questions about the place of new MRI biomarkers in the acute management of stroke and the prediction of poststroke outcome. Recent studies have demonstrated the main role of perfusion-weighted imaging in the identification of the best cerebral perfusion profile for a better response after reperfusion therapies in acute ischemic stroke. A major issue remains the early prediction of stroke outcome. While voxel-based lesion-symptom mapping emphasized the influence of stroke location, the analysis of the brain parenchyma underpinning the stroke lesion showed the relevance of prestroke cerebral status, including cortical atrophy, white matter integrity, or presence of chronic cortical cerebral microinfarcts. Moreover, besides the evaluation of the visually abnormal brain tissue, the analysis of normal-appearing brain parenchyma using diffusion tensor imaging and magnetization transfer imaging or spectroscopy offered new biomarkers to improve the prediction of the prognosis and new targets to follow in therapeutic trials. The aim of this review was to depict the main new radiological biomarkers reported in the last two decades that will provide a more thorough prediction of functional, motor, and neuropsychological outcome following the stroke. These new developments in neuroimaging might be a cornerstone in the emerging personalized medicine for stroke patients.

Four Social Brain Regions, Their Dysfunctions, and Sequelae, Extensively Explain Autism Spectrum Disorder Symptomatology

Autism spectrum disorder (ASD) is a challenging neurodevelopmental disorder with symptoms in social, language, sensory, motor, cognitive, emotional, repetitive behavior, and self-sufficient living domains. The important research question examined is the elucidation of the pathogenic neurocircuitry that underlies ASD symptomatology in all its richness and heterogeneity. The presented model builds on earlier social brain research, and hypothesizes that four social brain regions largely drive ASD symptomatology: amygdala, orbitofrontal cortex (OFC), temporoparietal cortex (TPC), and insula. The amygdala's contributions to ASD largely derive from its major involvement in fine-grained intangible knowledge representations and high-level guidance of gaze. In addition, disrupted brain regions can drive disturbance of strongly interconnected brain regions to produce further symptoms. These and related effects are proposed to underlie abnormalities of the visual cortex, inferior frontal gyrus (IFG), caudate nucleus, and hippocampus as well as associated symptoms. The model is supported by neuroimaging, neuropsychological, neuroanatomical, cellular, physiological, and behavioral evidence. Collectively, the model proposes a novel, parsimonious, and empirically testable account of the pathogenic neurocircuitry of ASD, an extensive account of its symptomatology, a novel physiological biomarker with potential for earlier diagnosis, and novel experiments to further elucidate the mechanisms of brain abnormalities and symptomatology in ASD.

Neurodegeneration of the Substantia Nigra after Ipsilateral Infarct: MRI R2* Mapping and Relationship to Clinical Outcome

Background The substantia nigra (SN) is suspected to be affected after remote infarction, in view of its large array of connections with the supratentorial brain. Whether secondary involvement of SN worsens overall clinical outcome after a supratentorial stroke has not previously been studied. Purpose To assess longitudinal changes in SN R2* by using MRI in the setting of ipsilesional supratentorial infarct and the relationship of SN signal change to clinical outcome. Materials and Methods Participants prospectively included from 2012 to 2015 were evaluated at 24-72 hours (baseline visit) and at 1 year with MRI to quantify R2*. The SN was segmented bilaterally to calculate an R2* asymmetry index (SN-AI); greater SN-AI indicated greater relative R2* in the ipsilateral compared with contralateral SN. The 95th percentile of R2* (hereafter, SN-AI₉₅) was compared according to infarct location with mixed linear regression models. We also conducted voxel-based comparisons of R2* and identified individual infarcted voxels associated with high SN-AI₉₅ through voxel-based lesion-symptom mapping. Multivariable regression models tested the association between SN-AI₉₅ and clinical scores. Results A total of 181 participants were evaluated (127 men, 54 women; mean age ± standard deviation, 64.2 years ± 13.1; 75 striatum infarcts, 106 other locations). Visual inspection, SN-AI₉₅, and average maps consistently showed higher SN R2* at 1 year if ipsilateral striatum was infarcted than if it was not (SN-AI₉₅, 4.25 vs -0.88; P < .001), but this was not observed at baseline. The striatal location of the infarct was associated with higher SN-AI₉₅ at 1 year independently from infarct volume, SN-AI₉₅ at baseline, microbleeds, age, and sex (β = 4.99; P < .001). Voxel-based lesion-symptom mapping confirmed that striatum but also insula, internal capsule, and external capsule were associated with higher SN-AI₉₅ at 1 year. SN-AI₉₅ was an independent contributor of poor motor outcome (Box and Block Test, β = -.62 points; P = .01). Conclusion In patients with stroke, greater substantia nigra R2*, likely reflective of greater iron content, can be observed at 1 year ipsilateral from remote infarcts of specific location, which is associated with worse motor function. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Vernooij in this issue.

Brain Iron Deposits in Thalamus Is an Independent Factor for Depressive Symptoms Based on Quantitative Susceptibility Mapping in an Older Adults Community Population

Objectives: With the trend of an aging population, an increasing prevalence of late-life depression has been identified. Several studies demonstrated that iron deposition was significantly related to the severity of symptoms in patients with depression. However, whether brain iron deposits influence depressive symptoms is so far unclear in the community of older adults. We measured iron deposition in deep intracranial nucleus by quantitative susceptibility mapping (QSM) and aimed to explore the relationship between iron deposition and depressive symptoms. Methods: We reviewed the data of a community population from CIRCLE study, which is a single-center prospective observational study that enrolled individuals above 40 years old with cerebral small vessel disease (SVD), while free of known dementia or stroke. We evaluated regional iron deposits on QSM, measured the volume of white matter hyperintensities (WMHs) on T2 fluid-attenuated inversion recovery, and assessed depressive symptoms by Hamilton depression scale (HDRS). We defined depressive symptom as HDRS > 7. Results: A total of 185 participants were enrolled. Participants in depressive symptom group had higher QSM value in thalamus than control group (18.79 ± 14.94 vs 13.29 ± 7.64, p = 0.003). The QSM value in the thalamus was an independent factor for the presence of depressive symptoms (OR = 1.055; 95% CI: 1.011-1.100; p = 0.013). The regional QSM values in other areas were not associated with HDRS score (all p > 0.05). No significant correlations were observed between WMHs volume and HDRS score (p > 0.05), or regional QSM values and WMHs volume (all p > 0.05). Conclusions: Our study demonstrated that iron deposits in the thalamus were related to the depressive symptoms in older adults.

The Involvement of Iron in Traumatic Brain Injury and Neurodegenerative Disease

Traumatic brain injury (TBI) consists of acute and long-term pathophysiological sequelae that ultimately lead to cognitive and motor function deficits, with age being a critical risk factor for poorer prognosis. TBI has been recently linked to the development of neurodegenerative diseases later in life including Alzheimer’s disease, Parkinson’s disease, chronic traumatic encephalopathy, and multiple sclerosis. The accumulation of iron in the brain has been documented in a number of neurodegenerative diseases, and also in normal aging, and can contribute to neurotoxicity through a variety of mechanisms including the production of free radicals leading to oxidative stress, excitotoxicity and by promoting inflammatory reactions. A growing body of evidence similarly supports a deleterious role of iron in the pathogenesis of TBI. Iron deposition in the injured brain can occur via hemorrhage/microhemorrhages (heme-bound iron) or independently as labile iron (non-heme bound), which is considered to be more damaging to the brain. This review focusses on the role of iron in potentiating neurodegeneration in TBI, with insight into the intersection with neurodegenerative conditions. An important implication of this work is the potential for therapeutic approaches that target iron to attenuate the neuropathology/phenotype related to TBI and to also reduce the associated risk of developing neurodegenerative disease.

Sensorimotor stroke alters hippocampo-thalamic network activity

Many stroke survivors experience persisting episodic memory disturbances. Since hippocampal and para-hippocampal areas are usually spared from the infarcted area, alterations of memory processing networks remote from the ischemic brain region might be responsible for the observed clinical symptoms. To pinpoint changes in activity of hippocampal connections and their role in post-stroke cognitive impairment, we induced ischemic stroke by occlusion of the middle cerebral artery (MCAO) in adult rats and analyzed the functional and structural consequences using activity-dependent manganese (Mn²⁺) enhanced MRI (MEMRI) along with behavioral and histopathological analysis. MCAO caused stroke lesions of variable extent along with sensorimotor and cognitive deficits. Direct hippocampal injury occurred in some rats, but was no prerequisite for cognitive impairment. In healthy rats, injection of Mn²⁺ into the entorhinal cortex resulted in distribution of the tracer within the hippocampal subfields into the lateral septal nuclei. In MCAO rats, Mn²⁺ accumulated in the ipsilateral thalamus. Histopathological analysis revealed secondary thalamic degeneration 28 days after stroke. Our findings provide in vivo evidence that remote sensorimotor stroke modifies the activity of hippocampal-thalamic networks. In addition to potentially reversible alterations in signaling of these connections, structural damage of the thalamus likely reinforces dysfunction of hippocampal-thalamic circuitries.

Serum neurofilament light: A biomarker of neuroaxonal injury after ischemic stroke

OBJECTIVE

To explore the utility of serum neurofilament light chain (NfL) as a biomarker for primary and secondary neuroaxonal injury after ischemic stroke (IS) and study its value for the prediction of clinical outcome.

METHODS

We used an ultrasensitive single-molecule array assay to measure serum NfL levels in healthy controls (n = 30) and 2 independent cohorts of patients with IS: (1) with serial serum sampling at hospital arrival (n = 196), at days 2, 3, and 7 (n = 89), and up to 6 months post stroke; and (2) with standardized MRI at baseline and at 6 months post stroke, and with cross-sectional serum sampling at 6 months (n = 95). We determined the temporal profile of serum NfL levels, their association with imaging markers of neuroaxonal injury, and with clinical outcome.

RESULTS

Patients with IS had higher serum NfL levels compared with healthy controls starting from admission until 6 months post stroke. Serum NfL levels peaked at day 7 (211.2 pg/mL [104.7-442.6], median [IQR]) and correlated with infarct volumes (day 7: partial r = 0.736, p = 1.5 × 10^-15). Six months post stroke, patients with recurrent ischemic lesions on MRI (n = 19) had higher serum NfL levels compared to those without new lesions (n = 76, p = 0.002). Serum NfL levels 6 months post stroke further correlated with a quantitative measure of secondary neurodegeneration obtained from diffusion tensor imaging MRI (r = 0.361, p = 0.001). Serum NfL levels 7 days post stroke independently predicted modified Rankin Scale scores 3 months post stroke (cumulative odds ratio [95% confidence interval] = 2.35 [1.60-3.45]; p = 1.24 × 10^-05).

CONCLUSION

Serum NfL holds promise as a biomarker for monitoring primary and secondary neuroaxonal injury after IS and for predicting functional outcome.

Mapping of thalamic magnetic susceptibility in multiple sclerosis indicates decreasing iron with disease duration: A proposed mechanistic relationship between inflammation and oligodendrocyte vitality

Recent advances in susceptibility MRI have dramatically improved the visualization of deep gray matter brain regions and the quantification of their magnetic properties in vivo, providing a novel tool to study the poorly understood iron homeostasis in the human brain. In this study, we used an advanced combination of the recent quantitative susceptibility mapping technique with dedicated analysis methods to study intra-thalamic tissue alterations in patients with clinically isolated syndrome (CIS) and multiple sclerosis (MS). Thalamic pathology is one of the earliest hallmarks of MS and has been shown to correlate with cognitive dysfunction and fatigue, but the mechanisms underlying the thalamic pathology are poorly understood. We enrolled a total of 120 patients, 40 with CIS, 40 with Relapsing Remitting MS (RRMS), and 40 with Secondary Progressive MS (SPMS). For each of the three patient groups, we recruited 40 controls, group matched for age- and sex (120 total). We acquired quantitative susceptibility maps using a single-echo gradient echo MRI pulse sequence at 3 T. Group differences were studied by voxel-based analysis as well as with a custom thalamus atlas. We used threshold-free cluster enhancement (TFCE) and multiple regression analyses, respectively. We found significantly reduced magnetic susceptibility compared to controls in focal thalamic subregions of patients with RRMS (whole thalamus excluding the pulvinar nucleus) and SPMS (primarily pulvinar nucleus), but not in patients with CIS. Susceptibility reduction was significantly associated with disease duration in the pulvinar, the left lateral nuclear region, and the global thalamus. Susceptibility reduction indicates a decrease in tissue iron concentration suggesting an involvement of chronic microglia activation in the depletion of iron from oligodendrocytes in this central and integrative brain region. Not necessarily specific to MS, inflammation-mediated iron release may lead to a vicious circle that reduces the protection of axons and neuronal repair.