Histological and Morphometric Analyses for Rat Carotid Balloon Injury Model

Experiments aimed at analyzing the response of blood vessels to mechanical injury and ensuing remodeling responses often employ the highly characterized carotid artery balloon injury model in laboratory rats. This approach utilizes luminal insertion of a balloon embolectomy catheter into the common carotid artery with inflation and withdrawal resulting in an injury characterized by vascular endothelial cell (EC) denudation and medial wall distension. The adaptive response to this injury is typified by robust vascular smooth muscle cell (SMC) replication and migration, SMC apoptosis and necrosis, enhanced synthesis and deposition of extracellular matrix (ECM) components, partial vascular EC regeneration from the border zones, luminal narrowing, and establishment of a neointima in time-dependent fashion. Evaluation of these adaptive responses to blood vessel injury can include acute and longer term qualitative and quantitative measures including expression analyses, activity assays, immunostaining for a plethora of factors and signals, and morphometry of neointima formation and gross mural remodeling. This chapter presents a logical continuation of Chapter 1 that offers details for performing the rat carotid artery balloon injury model in a standard laboratory setting by providing commonly used protocols for performing histological and morphometric analyses in such studies. Moreover, procedures, caveats, and considerations included in this chapter are highly relevant for alternative animal vascular physiology/pathophysiology studies and in particular those related to mechanisms of vascular injury and repair. Included in this chapter are specifics for in situ perfusion-fixation, tissue harvesting and processing for both snap-frozen and paraffin-embedded protocols, specimen embedding and sectioning, slide preparation, several standard histological staining steps, and routine morphological assessment.