Role of cortical microbleeds in cognitive impairment: In vivo behavioral and imaging characterization of a novel murine model

Open science and data sharing in cognitive neuroscience with MouseBytes and MouseBytes

Open access to rodent cognitive data has lagged behind the rapid generation of large open-access datasets in other areas of neuroscience, such as neuroimaging and genomics. One contributing factor has been the absence of uniform standardization in experiments and data output, an issue that has particularly plagued studies in animal models. Touchscreen-automated cognitive testing of animal models allows standardized outputs that are compatible with open-access sharing. Touchscreen datasets can be combined with different neuro-technologies such as fiber photometry, miniscopes, optogenetics, and MRI to evaluate the relationship between neural activity and behavior. Here we describe a platform that allows deposition of these data into an open-access repository. This platform, called MouseBytes, is a web-based repository that enables researchers to store, share, visualize, and analyze cognitive data. Here we present the architecture, structure, and the essential infrastructure behind MouseBytes. In addition, we describe MouseBytes+, a database that allows data from complementary neuro-technologies such as imaging and photometry to be easily integrated with behavioral data in MouseBytes to support multi-modal behavioral analysis.

Lack of direct involvement of a diazepam long-term treatment in the occurrence of irreversible cognitive impairment: a pre-clinical approach

Several observational studies have found a link between the long-term use of benzodiazepines and dementia, which remains controversial. Our study was designed to assess (i) whether the long-term use of benzodiazepines, at two different doses, has an irreversible effect on cognition, (ii) and whether there is an age-dependent effect. One hundred and five C57Bl/6 male mice were randomly assigned to the 15 mg/kg/day, the 30 mg/kg/day diazepam-supplemented pellets, or the control group. Each group comprised mice aged 6 or 12 months at the beginning of the experiments and treated for 16 weeks. Two sessions of behavioral assessment were conducted: after 8 weeks of treatment and after treatment completion following a 1-week wash-out period. The mid-treatment test battery included the elevated plus maze test, the Y maze spontaneous alternation test, and the open field test. The post-treatment battery was upgraded with three additional tests: the novel object recognition task, the Barnes maze test, and the touchscreen-based paired-associated learning task. At mid-treatment, working memory was impaired in the 15 mg/kg diazepam group compared to the control group (p = 0.005). No age effect was evidenced. The post-treatment assessment of cognitive functions (working memory, visual recognition memory, spatial reference learning and memory, and visuospatial memory) did not significantly differ between groups. Despite a cognitive impact during treatment, the lack of cognitive impairment after long-term treatment discontinuation suggests that benzodiazepines alone do not cause irreversible deleterious effects on cognitive functions and supports the interest of discontinuation in chronically treated patients.

Dysfunction of the Blood-brain Barrier in Cerebral Microbleeds: from Bedside to Bench

Cerebral microbleeds (CMBs) are a disorder of cerebral microvessels that are characterized as small (<10 mm), hypointense, round or ovoid lesions seen on T2*-weighted gradient echo MRI. There is a high prevalence of CMBs in community-dwelling healthy older people. An increasing number of studies have demonstrated the significance of CMBs in stroke, dementia, Parkinson's disease, gait disturbances and late-life depression. Blood-brain barrier (BBB) dysfunction is considered to be the event that initializes CMBs development. However, the pathogenesis of CMBs has not yet been clearly elucidated. In this review, we introduce the pathogenesis of CMBs, hypertensive vasculopathy and cerebral amyloid angiopathy, and review recent research that has advanced our understanding of the mechanisms underlying BBB dysfunction and CMBs presence. CMBs-associated risk factors can exacerbate BBB breakdown through the vulnerability of BBB anatomical and functional changes. Finally, we discuss potential pharmacological approaches to target the BBB as therapy for CMBs.

Beneficial effects of atorvastatin on sex-specific cognitive impairment induced by a cerebral microhaemorrhage in mice

BACKGROUND AND PURPOSES

Cerebral microhaemorrhages (CMHs) are associated with cognitive decline in humans. In rodents, CMHs induces cognitive impairment in male mice along with sex-specific cortical and hippocampal changes affecting neural, glial and vascular functions. Statins, have been proposed to prevent cognitive decline. We tested here the action of atorvastatin on CMH-induced cognitive impairment in a murine model of CMH.

EXPERIMENTAL APPROACH

Using a multimodal approach combining behavioural tests, in vivo imaging, biochemistry and molecular biology, the effects of oral administration of atorvastatin on the sex-specific changes induced by a cortical CMH were studied in male and female mice (C57BL/6J) at 6-week post-induction using a collagenase-induced model.

KEY RESULTS

Atorvastatin caused specific effects according to the sex-specific CMH-induced changes. In males, atorvastatin improved the visuospatial memory, induced a local modulation of microglial response and enhanced brain-derived neurotrophic factor (BDNF)-tropomyosin receptor kinase B (trkB) and vascular endothelial growth factor (VEGF) expression in the cortex. In the hippocampus, atorvastatin increased glucose metabolism and modulated astrocytes morphology. In females, atorvastatin did not modulate visuospatial memory despite the increased expression of cortical BDNF and the decrease in the number of hippocampal astrocytes. Atorvastatin also induced a decrease in the expression of cortical oestrogen receptors but did not modify body weight nor serum cholesterol levels in both sexes.

CONCLUSION AND IMPLICATIONS

Atorvastatin modulated the sex-specific cognitive impairment induced by the CMH with a pathophysiological impact mainly within the cortical area. It could represent a promising candidate for future sex-stratified clinical trials in patients with CMH.

Age and diet modify acute microhemorrhage outcome in the mouse brain

Cerebral microhemorrhages (CMHs) are considered as asymptomatic lesions, but might impair cognition in non-demented elderly individuals. The aging process includes poor vascular health, enhanced at midlife by metabolic disturbances upon high-fat diet (HFD). The onset of CMHs could thus have more serious consequences in midlife subjects with metabolic disturbances. This hypothesis was tested through the induction of multiple CMHs, using cyclodextrin nanoparticles injection, in mice at midlife (14 month old) or at a younger stage (5 month old) after 12 months or 3 months of normal diet or HFD (40% of animal fat) respectively. When induced at 14 months of age, CMHs were not larger but were more numerous (+25%) in mice on HFD compared with mice on normal diet. They slowed down the locomotor activity significantly but caused neither a change in the working memory nor a difference in the visual recognition memory decline. When induced at 5 months of age, CMHs provoked slighter locomotor and cognitive symptoms, regardless the diet. No spontaneous progression of CMHs toward larger hemorrhages was observed after onset when HFD was prolonged up to midlife. Consistently, no precipitated cognitive decline was observed. Middle-age plus time of metabolic disturbances represent enhanced risk factors for CMH outcome.

Sex Differences in Cognitive Impairment Induced by Cerebral Microhemorrhage

It has been suggested that cerebral microhemorrhages (CMHs) could be involved in cognitive decline. However, little is known about the sex-dependency of this effect. Using a multimodal approach combining behavioral tests, in vivo imaging, biochemistry, and molecular biology, we studied the cortical and hippocampal impact of a CMH in male and female mice (C57BL/6J) 6 weeks post-induction using a collagenase-induced model. Our work shows for the first time that a single cortical CMH exerts sex-specific effects on cognition. It notably induced visuospatial memory impairment in males only. This sex difference might be explained by cortical changes secondary to the lesion. In fact, the CMH induced an upregulation of ERα mRNA only in the female cortex. Besides, in male mice, we observed an impairment of pathways associated to neuronal, glial, or vascular functions: decrease in the P-GSK3β/GSK3β ratio, in BDNF and VEGF levels, and in microvascular water mobility. The CMH also exerted spatial remote effects in the hippocampus by increasing the number of astrocytes in both sexes, increasing the mean area occupied by each astrocyte in males, and decreasing hippocampal BDNF in females suggesting a cortical-hippocampal network impairment. This work demonstrates that a CMH could directly affect cognition in a sex-specific manner and highlights the need to study both sexes in preclinical models.

Remote brain hemorrhage after IV thrombolysis: Role of preexisting lesions

OBJECTIVE

To test the hypothesis that remote intracerebral hemorrhages (r-ICHs) after IV thrombolysis occur in preexisting brain lesions.

METHOD

We prospectively collected baseline data from consecutive patients treated with IV thrombolysis for cerebral ischemia and reviewed their baseline MRI scans to identify preexisting lesions in those who developed r-ICH. We evaluated outcomes with the modified Rankin Scale (mRS) and defined good outcomes as scores of 0 to 2 or similar to the preexisting mRS score.

RESULTS

Of 944 patients, 24 (2.5%) had r-ICH: lobar in 14, deep in 7, and both in 3. Sixteen of them (1.7% of all patients, 66.7% of those with r-ICH) were asymptomatic. Of the 41 r-ICHs found in these patients, 17 (41%) occurred within a lesion present before thrombolysis: 6 cerebral microbleeds (CMBs), 6 old and 1 recent infarct, and 4 areas of white matter hyperintensity. Patients with r-ICH were more likely to have strictly lobar CMBs (p = 0.049). They were 10 years older (p = 0.007), had a 16-mm Hg higher systolic blood pressure (p = 0.035) at baseline, and had more CMBs (p = 0.007). r-ICHs were better predicted by clinical (age, baseline systolic blood pressure) than imaging (purely lobar CMBs and having >5 CMBs) variables. r-ICHs tended to be associated with worse outcomes.

CONCLUSION

We identified preexisting brain lesions in nearly half of the patients with r-ICH. All were of vascular origin, supporting the hypothesis that r-ICHs occur in preexisting brain lesions. Higher-field machines could help identifying preexisting lesions in those who developed r-ICH in an apparently normal area.