Comparison of spinal vasculature in mouse and rat: investigations using MR angiography

The spinal vascular system is the conduit through which nutrition, cells and drugs access the parenchyma of the spinal cord (SC). This system is severely damaged as a principal consequence of the spinal cord injury (SCI). The initial vascular damage plays a critical role in establishing the course of the well-established postinjury cascade including compromised blood spinal cord permeability, hypoxia, activation of various factors and, subsequently, secondary injuries [1–6]. Rodent models play an important role in experimental studies of SCI [7, 8]. Rat model of SCI is more representative of what occurs in most closed human injuries. In this model, evolution of the neuropathology over time begins with an early phase of spreading hemorrhagic necrosis and edema, progressing to an intermediate phase of partial repair and tissue reorganization, and reaching a chronic phase characterized by the establishment of central cystic cavities with atrophic parenchyma and glial scarring. Recent trends indicate that mouse models of SCI are becoming more common [9–17]. The main reason behind this shift of focus is that genetically engineered mice offer opportunities to study the role of particular genes in the pathophysiology of SCI and thereby allow the development of more specific treatment strategies [18]. However, it is also recognized that the neuropathology of injured SC in mouse exhibits distinctly different spatio-temporal course than what is observed in rat. Specifically, mice exhibit a unique wound-healing response with typical characteristics of lesion site filling in with fibrous connective tissue matrix [9, 10, 19–23]. Magnetic resonance images can sensitively detect the differences between these pathological patterns in moderate injuries, induced with the device described in [17], in rat and mouse SCs (see Fig. 1). It is conceivable that the observed differences in the injury responses in mice and rats may be due to speciesspecific differences in the vascular organization of the spine. This establishes a strong motivation to study the arterial formation supplying blood from the descending aorta to the pial arteries as well as the distribution of blood in the parenchyma of the SC. We hypothesize that if the arterial vascularization (intraand extraparenchymal) were different in normal animals, the pathophysiology following an injury would naturally be different. These differences may subsequently lead to the specific neuropathological responses observed in injured mice and rats. Therefore, our aim in this study is to test this hypothesis by using magnetic resonance angiography (MRA) as an in vivo imaging tool to visualize the organization of the arterial network in normal mouse spine and parenchyma, and compare it with that of normal rat.