Which Aspects of Stroke Do Animal Models Capture? A Multitracer Micro-PET Study of Focal Ischemia with Endothelin-1

Abstract

Background: Cortical injections of the vasoconstrictor endothelin-1 (ET1) have widely been used to induce focal circumscribed ischemic lesions in the motor cortex of rodents in the context of stroke recovery studies. In order to apply this model correctly, it is essential to understand the time course of regional flow changes and of the development of penumbra and infarction. Methods: Multitracer micro-PET of ET1 focal ischemia in rats was performed using [¹¹C]-flumazenil ([¹¹C]FMZ) as a flow- and viability tracer and [¹⁸F]-fluoromisonidazole ([¹⁸F]FMISO) as hypoxia marker in order to characterize the physiological time-course of this model. Nine adult Sprague-Dawley rats received stereotaxic injections of ET1 into the right primary motor cortex, 3 served as controls. PET imaging was started 2, 3 and 20 h after the last ET1 injection. Histology was obtained at the end of the scans. Standardized uptake value ratios reflecting cerebral blood flow (CBF), [¹¹C]FMZ-binding and [¹⁸F]FMISO-retention were calculated for the region of hypoperfusion and the normoperfused cortex. Results: CBF in the hypoperfused cortex was significantly reduced (p < 0.01) at 5 h (0.58 ± 0.025), 6 h (0.54 ± 0.043) and 23 h (0.66 ± 0.024) compared to controls (1.00 ± 0.011) and moderately reduced (p < 0.05) in the remainder of the affected hemisphere at 5 h (0.93 ± 0.036). [¹¹C]FMZ-binding was within the control range at all time points. Significant [¹⁸F]FMISO-retention (1.16 ± 0.091, p < 0.05) was observed only after 6 h in the ischemic core that later turned into infarct. Conclusion: ET1 injections yield reproducible, slowly developing ischemic lesions with constant levels of hypoperfusion. This multitracer micro-PET study suggests that the ET1 model is appropriate for inducing chronic circumscribed ischemic lesions but seems to be less suited for studying acute stroke pathophysiology.

Ischemic stroke: experimental models and reality

“…Although endothelin is considered to play a key role in the induction of vasospasms after subarachnoid hemorrhage with subsequent infarcts in human patients, there are no data on its application in animal experiments to model this specific situation. Since ischemia develops slowly after endothelin-1 application and is accompanied only by minimal edema, this model again does not accurately mimic human stroke [112]. Similar to the photothrombotic model, it may be more useful for simulating lacunar stroke and for long-term studies with a focus on recovery mechanisms.…”

Long-Term Motor Deficit and Diffuse Cortical Atrophy Following Focal Cortical Ischemia in Athymic Rats

“…We chose a model of focal cortical ischemia induced through local injection of the vasoconstrictor endothelin-1 (ET-1). Previous studies have shown that cortical injection of ET-1 recapitulates important pathophysiological aspects of human ischemia including significant reduction in cortical blood flow, persisting up to 23 h (Schirrmacher et al, 2016), leading to hypoperfused tissue and development of an infarcted area associated with neuronal cell loss (Windle et al, 2006;Nguemeni et al, 2015;Weishaupt et al, 2016).…”

Acute characterization of tissue and functional deficits in a clinically translatable pig model of ischemic stroke

“…These needs have been met with poor therapeutic translation due to discrepencies in lissencephalic small animal stroke models including limited cerebral edema and swelling as well as variable MLS and mortality rates (108–110). Specifically in endothelin-1 (ET-1) rodent stroke models, animals exhibit a dose-dependent ischemic lesion with marginal ischemic edema making this model less suited for studying acute stroke pathophysiology (111–114). In contrast, our pig stroke model exhibited increased ipsilateral hemipshere swelling due to the development of cytotoxic edema and consquent MLS within 24 hours post-stroke.…”