Abstract
Purpose :
Regional increase of blood flow triggered by local neuronal activity is used to assess brain function in humans and animals. The underlying spatial mechanism is poorly understood. In particular, the capillaries surrounded by neuronal synapses, can sense their activity but have a lower capacity to change the blood flow than the remote arterioles. Our goal was to determine in the living mouse retina how the capillary signal propagates to the vasoactive arteriole.
Methods :
First, ten mice carrying a GCaMP6f calcium sensor under NG2 promoter were injected with a contrasting agent Evans Blue. In the isolated living retinas from these mice, individual capillary pericytes were activated by a patch pipette. Calcium signal and vasomotor response were simultaneously measured under the two-photon microscope. Second, in ten wildtype mice, retinal pericytes were individually injected with neurobiotin to assess cellular coupling. Both calcium imaging and neurobiotin experiments were conducted with and without a gap junction blocker. Finally, ten wildtype retinas were collected and stained for Cx43, Cx37 and Cx40 gap junctions. All statistical analyses were performed using t-test or ANOVA.
Results :
The pericytes from a transition zone between the capillary and arteriole were significantly more coupled to the neighboring pericytes and/or endothelial cells. In the same areas, calcium signaling and vasoconstriction initiated by an electrically stimulated pericyte propagated significantly further than in the areas adjacent to veins. Neurobiotin spread, propagation of calcium signaling, and vasomotor response were abolished by a gap junction blocker. Finally, we identified a unique pattern of Cx43-containing gap junctions in the transitional areas, which was not present in the rest of the vascular tree.
Conclusions :
We identified a functional domain of the vascular tree with an extensive coupling of the cells via Cx43-containing gap junctions. In this area, the initiation of the signal and the major changes of the vascular diameter were spatially separated and coordinated via gap junctions. This spatial separation may facilitate functional hyperemia by combining a sensitive signal reception in the capillaries with a strong vasomotor response of smooth muscle cells in the remote feeding arterioles.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.