A refined model of chronic cerebral hypoperfusion resulting in cognitive impairment and a low mortality rate in rats

Abstract

Objective: The cognitive deficits of vascular dementia and the vasoocclusive state of moyamoya disease have often been mimicked with bilateral stenosis/occlusion of the common carotid artery (CCA) or internal carotid artery. However, the cerebral blood flow (CBF) declines abruptly in these models after ligation of the CCA, which differs from "chronic" cerebral hypoperfusion. While some modified but time-consuming techniques have used staged occlusion of both CCAs, others used microcoils for CCA stenosis, producing an adverse effect on the arterial endothelium. Thus, the authors developed a new chronic cerebral hypoperfusion (CCH) model with cognitive impairment and a low mortality rate in rats.

Methods: Male Sprague-Dawley rats were subjected to unilateral CCA occlusion and contralateral induction of CCA stenosis (modified CCA occlusion [mCCAO]) or a sham operation. Cortical regional CBF (rCBF) was measured using laser speckle flowmetry. Cognitive function was assessed using a Barnes circular maze (BCM). MRI studies were performed 4 weeks after the operation to evaluate cervical and intracranial arteries and parenchymal injury. Behavioral and histological studies were performed at 4 and 8 weeks after surgery.

Results: The mCCAO group revealed a gradual CBF reduction with a low mortality rate (2.3%). White matter degeneration was evident in the corpus callosum and corpus striatum. Although the cellular density declined in the hippocampus, MRI revealed no cerebral infarctions after mCCAO. Immunohistochemistry revealed upregulated inflammatory cells and angiogenesis in the hippocampus and cerebral cortex. Results of the BCM assessment indicated significant impairment in spatial learning and memory in the mCCAO group. Although some resolution of white matter injury was observed at 8 weeks, the animals still had cognitive impairment.

Conclusions: The mCCAO is a straightforward method of producing a CCH model in rats. It is associated with a low mortality rate and could potentially be used to investigate vascular disease, moyamoya disease, and CCH. This model was verified for an extended time point of 8 weeks after surgery.

Keywords: BCCAO = bilateral CCA occlusion; BCCAS = bilateral CCA stenosis; BCM = Barnes circular maze; CBF = cerebral blood flow; CCA = common carotid artery; CCH = chronic cerebral hypoperfusion; CV = cresyl violet; DBP = diastolic blood pressure; DFn = degrees of freedom in the numerator; LFB = luxol fast blue; LSF = laser speckle flowmetry; MRA = MR angiography; PBS = phosphate-buffered saline; PR = pulse rate; ROI = region of interest; SBP = systolic blood pressure; TOF = time of flight; VA = vertebral artery; WM = white matter; carotid artery stenosis; cerebral blood flow; cerebral hypoperfusion; mCCAO = modified CCA occlusion; moyamoya disease; rCBF = regional CBF; vascular dementia; vascular disorders; white matter injury.