Models of neurodegenerative disease - Alzheimer's anatomical and amyloid plaque imaging

Abstract

Alzheimer's disease (AD) is an important social and economic issue for our societies. The development of therapeutics against this severe dementia requires assessing the effects of new drugs in animal models thanks to dedicated biomarkers. According to the amyloid cascade hypothesis, β-amyloid deposits are at the origin of most of the lesions associated with AD. These extracellular deposits are therefore one of the main targets in therapeutical strategies. Aβ peptides can be revealed histologically with specific dyes or antibodies, or by magnetic resonance microscopy (μMRI) that uses their association with iron as a source of signal. The microscopic size of the lesions necessitates the development of specific imaging protocols. Most protocols use T (2)-weighted sequences that reveal the aggregates as hypointense spots. This chapter describes histological methods that reveal amyloid plaques with specific stains and MR-imaging protocols for in vivo and ex vivo MR imaging of AD mice.

Fig. 1

In vivo 3D acquisition of a mouse brain: sagittal (top), coronal (left) and axial (right) views. Cerebral ventricles filled with CSF appear hyperintense on these images (arrows). The measure of their volumes can be used as an index of atrophy.

Fig. 2

Mouse setup for in vivo MR imaging. The animal is held still with tooth and ear bars. The isoflurane anesthesia is delivered via a face mask. Respiration is recorded through a pressure pad and body temperature is recorded through a rectal probe.

Fig. 3

Mouse intracardiac perfusion. The top picture shows the rib cage cut off and the butterfly needle inserted into the left ventricle (LV). The bottom picture shows the material used: formalin beakers and PBS beaker, peristaltic pump (a), butterfly needle (b), forceps, scissors (c), surgical board and draining bucket (d). RA = right atrium.

Fig. 4

Mouse brain holder for ex vivo imaging. The brain sample is held still in a 10-mL syringe filled with Fluorinert.

Fig. 5

Hypointense spots detected at the level of the hippocampus with MRI (top, A-C) match anti-Aβ staining (D), Congo red staining (E) and Perls’ staining (F). This indicates that, in the mouse model that we used, these spots correspond to amyloid plaques and that they are loaded with iron.