Photothrombotic Ischemic Thalamic Stroke in Mice Recapitulates Spontaneous Pain Features of Central Post-Stroke Pain in Humans

Abstract

Central post-stroke pain (CPSP) is a highly distressing condition that develops in 50% of people who suffer a thalamic stroke, and is typically unresponsive to current clinical treatments. Hypoxic damage to the ventral posterolateral (VPL) and ventral posteromedial (VPM) sensory thalamic nuclei, in particular, precipitates CPSP. One barrier to developing treatments for CPSP is the lack of preclinical models of thalamic ischemic stroke. In this study, we present a novel mouse model of CPSP induced through targeted photothrombotic ischemia. After eliciting hypoxia in the sensory thalamus of male mice, we assessed pain behaviors over a four-week period. Stroke-affected mice exhibited a persistent spontaneous facial grimace from day four to week four post-stroke, indicative of pain. Hind-paw mechanical hypersensitivity indicative of altered nociception, characteristic of VPL and VPM hemorrhagic CPSP models, was not detected in our model. Immunofluorescence analysis revealed increased activated microglia (Iba1) and reactive astrocytes (GFAP). Iba1 fluorescence intensity in the VPL thalamus-but not the VPM thalamus-correlated with the severity of facial grimace at four weeks post-stroke. Clustering based on behavioral phenotypes identified a subpopulation of mice in which grimace pain spontaneously resolved, by four weeks post-stroke, relative to sham controls, suggesting that this model can be used to understand how stroke recovery may influence pain chronification. This model provides a valuable tool to investigate the cellular and circuit mechanisms underlying CPSP after an ischemic thalamic stroke. Significance StatementResearch into central post-stroke pain (CPSP) is hindered by the lack of preclinical models that match the clinical presentation of the condition. Although 87% of clinical strokes are ischemic, current CPSP preclinical models induce hemorrhagic strokes. To our knowledge, our mouse model is the first to induce CPSP by photothrombosis in the ventral posterolateral and posteromedial thalamus. Moreover, our study quantifies spontaneous pain, using a facial grimace score, in addition to nociception, whereas previous CPSP studies have relied exclusively on nociceptive tests. Finally, our model recapitulates some of the variability observed in clinical CPSP. We anticipate that this model will help dissect the roots of chronic pain after a thalamic stroke, and facilitate development of novel therapies for CPSP.