Background

Many neurological and psychiatric illnesses are caused by disorders of the cerebral circulation. A sudden interruption of the blood supply to distinct brain regions can lead to stroke, while a gradual reduction of continuous cerebral blood flow (CBF) impairs memory processes and contributes to the development of dementia (Farkas and Luiten, 2001; Matsuda, 2001; de la Torre, 2002). In the 2-VO rat model, there is a dramatic decrease in CBF to the brain during the acute ischemic phase (2-3 days post-operation) and the cortical and white matter areas have the largest decrease in blood flow, reaching 35%-45% of the control level (Otori et al., 2003). In the chronic ischemic phase (1-3 months post-operation), the CBF values begin to gradually recover at 1 week, but are still significantly lower than the control values 4 weeks after 2-VO induction (Schmidt-Kastner et al., 2001; Otori et al., 2003; Tomimoto et al., 2003). After 8 weeks to 3 months of 2-VO, only a slight reduction or virtually no reduction of flow has been reported (Otori et al., 2003). Finally, after 6 months of 2-VO, the CBF almost returns completely to normal (Choy et al., 2006), because other arterial sources of blood provide compensatory blood flow (via the circle of Willis, Figure 1) to areas that typically are supplied by the common carotid (Farkas et al., 2007). The 2-VO model exhibits characteristic features of human CCH condition, such as cerebral blood flow and metabolic changes (Ohta et al., 1997; Otori et al., 2003), learning and memory disturbances (Farkas and Luiten, 2001; Farkas et al., 2004b; Liu et al., 2005) and the neuropathologic changes (Kreutzberg, 1996; Farkas et al., 2004b; Panickar and Norenberg, 2005; Ohtaki et al., 2006; Eisel et al., 2006). Additionally, this model has been used to study cerebrovascular WM lesions (Wakita et al., 2002; Takizawa et al., 2003; Farkas et al., 2004a).

In the traditional 2-VO experiment, silk suture is used to ligate the bilateral common carotid artery, and an acute phase after the occlusion with dramatic CBF fall ensues. To improve the 2-VO model, researchers have tested some alternative methods. For example, a silicone collar cuff can be placed around the common carotid artery in order to reproduce the inflammatory response caused by atherosclerosis. However, this operation does not cause long-term memory impairment (de Bortoli et al., 2005). A study in which the two common carotid arteries were occluded at intervals of 1 week found that procedure leads to a progressive decrease in brain perfusion, and decreased mortality compared to procedures that occlude both arteries at once (Sarti et al., 2002a and 2002b). But an undesirable feature of these protocols is that the rats must undergo anesthesia twice a week, which can be stressful to the animal. Kitaguchia et al. (2009) use a 30 min delay between carotid arteries in the murine BCAS model to decrease mortality. Other research groups use ameroid constrictors in place of the silk suture. The ameroid constrictors consist of a titanium shell surrounding the hygroscopic casein material with the internal lumen. The casein component gradually absorbs water and thus expands, resulting in narrowing and occlusion of its encased arterial lumen. So the reduction of the CBF could be mild without a sharp drop (Hattori et al., 2015). Here, we described a protocol in detail for performing 2-VO in rat.


Figure 1. Schematic diagram of the circle of Willis in human (A) and rat (B). ACA (anterior cerebral artery); ACOA (anterior communicating artery); AICA (anterior inferior cerebellar artery); ASA (anterior spinal artery); BA (basilar artery); ICA (internal carotid artery); MCA (middle cerebral artery); PCA (posterior cerebral artery); PCOA (posterior communicating artery); SCA (superior cerebellar artery); VA (vertebral artery). This figure is adapted from Eszter Farkas et al. (2001).