White matter lesions, cerebral inflammation and cognitive function in a mouse model of cerebral hypoperfusion.

Development of specific treatments for vascular dementia requires appropriate animal models. Bilateral carotid artery stenosis (BCAS) employs metal coils wrapped around both common carotid arteries to induce cerebral hypoperfusion, white matter lesions and memory impairment in mice. We focused on the relationship of memory impairment induced by BCAS to white matter lesions demonstrated by ex vivo magnetic resonance imaging (MRI). We found a significant effect of BCAS on perceptual learning in the novel object recognition test and on number of errors and latency to platform in the radial arm water maze. MRI analysis revealed a significant effect of BCAS on diffusion tensor imaging (DTI) parameters in white matter areas. After correction for multiple testing, significantly lower fractional anisotropy (FA) values were found in the corpus callosum and anterior commissure and significantly higher mean diffusivity values in the internal capsule. Focusing on the corpus callosum, we found that correlations between FA and number of errors on the RAWM test were significant after controlling for treatment. We further found that the effects of BCAS on cognition were partly mediated by its effects on white matter integrity. Immunofluorescence studies demonstrated significantly higher microglia cell density and soma size in the corpus callosum of BCAS mice compared to controls, and these parameters were correlated with the imaging data. The results of this study indicate that cognitive deficits induced by cerebral hypoperfusion due to BCAS result in part from microglia activation and disruption of white matter integrity, supporting the face and construct validity of this unique model of vascular dementia.

Effect of chronic unpredictable stress on mice with developmental under-expression of the Ahi1 gene: behavioral manifestations and neurobiological correlates.

The Abelson helper integration site 1 (Ahi1) gene plays a pivotal role in brain development and is associated with genetic susceptibility to schizophrenia, and other neuropsychiatric disorders. Translational research in genetically modified mice may reveal the neurobiological mechanisms of such associations. Previous studies of mice heterozygous for Ahi1 knockout (Ahi1+/-) revealed an attenuated anxiety response on various relevant paradigms, in the context of a normal glucocorticoid response to caffeine and pentylenetetrazole. Resting-state fMRI showed decreased amygdalar connectivity with various limbic brain regions and altered network topology. However, it was not clear from previous studies whether stress-hyporesponsiveness reflected resilience or, conversely, a cognitive-emotional deficit. The present studies were designed to investigate the response of Ahi1+/- mice to chronic unpredictable stress (CUS) applied over 9 weeks. Wild type (Ahi1+/+) mice were significantly affected by CUS, manifesting decreased sucrose preference (p < 0.05); reduced anxiety on the elevated plus maze and light dark box and decreased thigmotaxis in the open field (p < 0.01 0.05); decreased hyperthermic response to acute stress (p < 0.05); attenuated contextual fear conditioning (p < 0.01) and increased neurogenesis (p < 0.05). In contrast, Ahi1+/- mice were indifferent to the effects of CUS assessed with the same parameters. Our findings suggest that Ahi1 under-expression during neurodevelopment, as manifested by Ahi1+/- mice, renders these mice stress hyporesponsive. Ahi1 deficiency during development may attenuate the perception and/or integration of environmental stressors as a result of impaired corticolimbic connectivity or aberrant functional wiring. These neural mechanisms may provide initial clues as to the role Ahi1 in schizophrenia and other neuropsychiatric disorders.