Artery targeted photothrombosis widens the vascular penumbra, instigates peri-infarct neovascularization and models forelimb impairments

Abstract

The photothrombotic stroke model generates localized and reproducible ischemic infarcts that are useful for studying recovery mechanisms, but its failure to produce a substantial ischemic penumbra weakens its resemblance to human stroke. We examined whether a modification of this approach, confining photodamage to arteries on the cortical surface (artery-targeted photothrombosis), could better reproduce aspects of the penumbra. Following artery-targeted or traditional photothrombosis to the motor cortex of mice, post-ischemic cerebral blood flow was measured using multi-exposure speckle imaging at 6, 48, and 120 h post-occlusion. Artery-targeted photothrombosis produced a more graded penumbra at 48 and 120 h. The density of isolectin B4+ vessels in peri-infarct cortex was similarly increased after both types of infarcts compared to sham at 2 weeks. These results indicate that both models instigated post-ischemic vascular structural changes. Finally, we determined whether the strength of the traditional photothrombotic approach for modeling upper-extremity motor impairments extends to the artery-targeted approach. In adult mice that were proficient in a skilled reaching task, small motor-cortical infarcts impaired skilled-reaching performance for up to 10 days. These results support that artery-targeted photothrombosis widens the penumbra while maintaining the ability to create localized infarcts useful for modeling post-stroke impairments.

Multimodal mapping of neural activity and cerebral blood flow reveals long-lasting neurovascular dissociations after small-scale strokes

“…We did not measure motor deficits in this study. Recent studies showed that the artery targeted photothrombosis of similar and larger sizes than those induced in this study led to forelimb impairments in skilled reaching tasks but were difficult to detect using less sensitive behavioral assessments (17,40). Further investigations that combine sensitive behavioral assessments and simultaneous measurements of neuronal structural changes and electrical activities will help to elucidate the underlying mechanisms of functional recovery.…”

“…Furthermore, this refined model of photothrombosis produces a more graded vascular penumbra than traditional photothrombosis while maintaining the ability to create localized infarcts (17). The conventional view of brain injury is that the magnitude of the deficit is coarsely correlated to the infarct size when controlled for other influences including age, morbidity and stroke locations (35).…”

“…This allowed us to monitor the infarct formation in vivo ( Figure S2) and to capture the variations of CBF and neuronal electrical activity from pre-stroke baseline to during the formation of the lesion and after. We chose to selectively occlude arteriole branches in the imaging field of view (Figure 2A) and harnessed the spatially graded ischemia induced by this refined method of artery-targeted photothrombosis (17). By implanting 2D NET arrays at multiple distances from the infarct, we recorded at multiple locations and sampled varying levels of ischemia (Figure 2B-2D).…”

“…We measured the spatial extent of the tissue under ischemia and the infarct size in two means: the area under 20% CBF of the pre-stroke baseline from in vivo MESI of CBF at the end of the acute session ( Figure 5A), and the lesion volume identified in postmortem Nissl staining at 8 weeks after photothrombosis ( Figure 5B). A previous study showed that tissue damage identified from histological analysis paralleled regions of severe CBF deficits and that MESI estimates of ≤20% baseline CBF served as a reliable in vivo estimate of the ischemic core (17). We used the area under severe CBF deficits in MESI as a measure of infarct dimension and examined its correlation with the severity of reduction in neurovascular coupling.…”

“…By patterned illumination using a digital micromirror device (DMD), we induced targeted photothrombotic occlusion within individual or multiple surface arteriole branches to provide fine control over lesion location, size and onset time (16). In addition, by confining photodamage to arteries on the cortical surface, this modified technique produces a more graded penumbra than traditional photothrombosis (17). Finally, we performed all measurements including the induction of stroke on awake, head-fixed animals to remove the confounding impacts of anesthetic agents on neural activity, hemodynamics, and neurovascular coupling (18)(19)(20).…”