Translational Structural and Functional Signatures of Chronic Alcohol Effects in Mice.

BACKGROUND: Alcohol acts as an addictive substance that may lead to alcohol use disorder. In humans, magnetic resonance imaging showed diverse structural and functional brain alterations associated with this complex pathology. Single magnetic resonance imaging modalities are used mostly but are insufficient to portray and understand the broad neuroadaptations to alcohol. Here, we combined structural and functional magnetic resonance imaging and connectome mapping in mice to establish brain-wide fingerprints of alcohol effects with translatable potential. METHODS: Mice underwent a chronic intermittent alcohol drinking protocol for 6 weeks before being imaged under medetomidine anesthesia. We performed open-ended multivariate analysis of structural data and functional connectivity mapping on the same subjects. RESULTS: Structural analysis showed alcohol effects for the prefrontal cortex/anterior insula, hippocampus, and somatosensory cortex. Integration with microglia histology revealed distinct alcohol signatures, suggestive of advanced (prefrontal cortex/anterior insula, somatosensory cortex) and early (hippocampus) inflammation. Functional analysis showed major alterations of insula, ventral tegmental area, and retrosplenial cortex connectivity, impacting communication patterns for salience (insula), reward (ventral tegmental area), and default mode (retrosplenial cortex) networks. The insula appeared as a most sensitive brain center across structural and functional analyses. CONCLUSIONS: This study demonstrates alcohol effects in mice, which possibly underlie lower top-down control and impaired hedonic balance documented at the behavioral level, and aligns with neuroimaging findings in humans despite the potential limitation induced by medetomidine sedation. This study paves the way to identify further biomarkers and to probe neurobiological mechanisms of alcohol effects using genetic and pharmacological manipulations in mouse models of alcohol drinking and dependence.

Standardized Post-Mortem Examination and Fixation Procedures for Mutant and Treated Mice.

A procedure for post-mortem examination (or necropsy) of mice is provided. The aim is to obtain a "holistic" picture of organs and systems at the anatomical and histological levels. The major issue is tissue preservation, which is achieved by rapid transfer into a fixative solution, usually neutral buffered formalin. Fixation is the first of the four basic steps in histopathological analyses of tissues, which also include embedding, sectioning, and staining. The protocols provided here describe routine methods for tissue fixation, as these methods are integral parts of any necropsy procedure. There is also a Strategic Planning section that addresses the overall approach to histopathological evaluation, as well as specifics such as age and gender of the mice, cohort size, and controls. Curr. Protoc. Mouse Biol. 1:17-53. © 2011 by John Wiley & Sons, Inc.

Tissue collection for systematic phenotyping in the mouse.

In this unit, a procedure for post-mortem examination of mice and tissue collection is provided. This procedure is performed for post-mortem analysis of anatomical defects (necropsy) and histological analysis and/or tissue collection destined for molecular biology applications. In both cases, tissue preservation is the major issue, but the way to achieve it depends on the objective. When histological analysis is the aim, tissue preservation is achieved by rapid transfer into fixative solutions. In contrast, molecular biology applications require rapid freezing of tissue samples to preserve mRNA integrity. Consequently, performing both procedures simultaneously may be at the expense of the final product quality.

Histopathology in mouse metabolic investigations.

Due to the small size of the mouse, evaluating its clinical phenotype is sometimes problematic. In contrast, mouse models are readily accessible to post-mortem analyses at any time during the course of a disease and prior to its clinical onset. RNA, protein, and histological analyses following sacrifice represent a powerful means to identify affected cell types and molecular events underlying the altered phenotype, and therefore to understanding the signaling or metabolic pathways involved. In this unit, an overview of post-mortem analyses is provided with a strong emphasis on the principles of routine histology, including tissue fixation, processing, embedding, and staining with hematoxylin and eosin. There are also several protocols for staining with specialized histological stains used in the metabolic field to detect intracellular lipids, intracellular lipid "ghosts", cholesterol esters, polysaccharides, mitochondria, pathological collagen deposits, and atherosclerotic plaques.