An analysis of four different methods of producing focal cerebral ischemia with endothelin-1 in the rat

Endothelin-1 (ET-1), a potent vasoconstrictor, reduces local blood flow to levels that produce ischemic injury when injected directly into brain tissue. The purpose of this study was to compare 4 different methods of inducing focal ischemia with ET-1: (1) topical application to the forelimb motor region of the cortex, (2) intracerebral injection into the forelimb motor region of the cortex, (3) a combination of intracortical and intrastriatal injections and 4. injection of ET-1 adjacent to the middle cerebral artery (MCA). We examined the effect of delivery method and dose of ET-1 on lesion size, inter-animal variability and behavioral outcome on 3 separate tests of motor function and limb preference. We calculated success rate as the percentage of animals that survived surgery and developed a significant impairment (>20% decrease in performance post-surgery) in the staircase-reaching test. All 4 methods produced similar deficits in the staircase, balance beam, and cylinder tests, but the application of ET-1 adjacent to the MCA, though widely used, provided the lowest success rate. The combined cortical and striatal ET-1 produced a high success rate and consequently we examined cerebral blood flow (CBF), the apparent diffusion coefficient (ADC) and T2-weighted magnetic resonance imaging (MRI) changes for this model. We found that infarct volume measured using T2-weighted MRI correlated with histological measurements and that ADC and CBF together predicted which areas will suffer permanent injury. The combined cortical and striatal injection model offers a number of advantages for studies of recovery of function.