Behavioral and Neural Activity-Dependent Recanalization of Plugged Capillaries in the Brain of Adult and Aged Mice

Abstract

The capillaries of the brain, owing to their small diameter and low perfusion pressure, are vulnerable to interruptions in blood flow. These tiny occlusions can have outsized consequences on angioarchitecture and brain function; especially when exacerbated by disease states or accumulate with aging. A distinctive feature of the brain’s microvasculature is the ability for active neurons to recruit local blood flow. The coupling of neural activity to blood flow could play an important role in recanalizing obstructed capillaries. To investigate this idea, we experimentally induced capillary obstructions in mice by injecting fluorescent microspheres and then manipulated neural activity levels though behavioral or pharmacologic approaches. We show that engaging adult and aged mice with 12 h exposure to an enriched environment (group housing, novel objects, exercise wheels) was sufficient to significantly reduce the density of obstructed capillaries throughout the forebrain. In order to more directly manipulate neural activity, we pharmacologically suppressed or increased neuronal activity in the somatosensory cortex. When we suppressed cortical activity, recanalization was impaired given the density of obstructed capillaries was significantly increased. Conversely, increasing cortical activity improved capillary recanalization. Since systemic cardiovascular factors (changes in heart rate, blood pressure) could explain these effects on recanalization, we demonstrate that unilateral manipulations of neural activity through whisker trimming or injection of muscimol, still had significant and hemisphere specific effects on recanalization, even in mice exposed to enrichment where cardiovascular effects would be evident in both hemispheres. In summary, our studies reveal that neural activity bi-directionally regulates the recanalization of obstructed capillaries. Further, we show that stimulating brain activity through behavioral engagement (i.e., environmental enrichment) can promote vascular health throughout the lifespan.

High Throughput Detection of Capillary Stalling Events with Bessel Beam Two-Photon Microscopy

“…This provides an easy to calculate metric for vessel diameter, which we used to observe drops in stalling point prevalence around large dilation events (Figure 5c), as stalls were presumably cleared due to the transient increase in flow and perfusion pressure. This is consistent with recent work showing that environmental enrichment reduced the number of capillaries plugged by injected microspheres 29 . But here we show that there is on average fewer stalled capillaries around larger arterial dilation events in vivo , demonstrating the potential for dynamic reductions in stalling from spontaneous flow changes, not just under direct functional activation 13 .…”

“…The copyright holder for this preprint this version posted December 17, 2022. ; https://doi.org/10.1101/2022.12.16.520779 doi: bioRxiv preprint environmental enrichment reduced the number of capillaries plugged by injected microspheres 29 . But here we show that there is on average fewer stalled capillaries around larger arterial dilation events in vivo, demonstrating the potential for dynamic reductions in stalling from spontaneous flow changes, not just under direct functional activation 13 .…”

High throughput detection of capillary stalling events with Bessel beam two-photon microscopy

“…5(c)], as stalls were presumably cleared due to the transient increase in flow and perfusion pressure. This is consistent with recent work showing that environmental enrichment reduced the number of capillaries plugged by injected microspheres 33 . But here we show that there is on average fewer stalled capillaries around larger arterial dilation events in vivo , demonstrating the potential for dynamic reductions in stalling from spontaneous flow changes, not just under direct functional activation 13 .…”

“…This is consistent with recent work showing that environmental enrichment reduced the number of capillaries plugged by injected microspheres. 33 But here we show that there is on average fewer stalled capillaries around larger arterial dilation events in vivo , demonstrating the potential for dynamic reductions in stalling from spontaneous flow changes, not just under direct functional activation. 13 This effect was shown with large and isolated dilation events, but more sophisticated analysis can be done to better understand the relationship between stalling and neurovascular coupling, or even stalling and resting state oscillations.…”

Oxygen imaging of hypoxic pockets in the mouse cerebral cortex

“…To directly test whether capillary stalling elicits hypoxic pockets, microspheres (diameter: 4 μm) were delivered intravascularly (Fig. 3J) to occlude capillaries ( 28 , 29 ). We recorded O 2 dynamics and microspheres in the same field of view simultaneously at 1 Hz using a hybrid BLI-fluorescence microscope that uses the readout time of the BLI camera to record microsphere fluorescence with a second camera (Fig.…”