Heterogeneity of Sensory-Induced Astrocytic Ca Dynamics During Functional Hyperemia.

Astrocytic Ca fluctuations associated with functional hyperemia have typically been measured from large cellular compartments such as the soma, the whole arbor and the endfoot. The most prominent Ca event is a large magnitude, delayed signal that follows vasodilation. However, previous work has provided little information about the spatio-temporal properties of such Ca transients or their heterogeneity. Here, using an awake, two-photon fluorescence-imaging model, we performed detailed profiling of delayed astrocytic Ca signals across astrocytes or within individual astrocyte compartments using small regions of interest next to penetrating arterioles and capillaries along with vasomotor responses to vibrissae stimulation. We demonstrated that while a 5-s air puff that stimulates all whiskers predominantly generated reproducible functional hyperemia in the presence or absence of astrocytic Ca changes, whisker stimulation inconsistently produced astrocytic Ca responses. More importantly, these Ca responses were heterogeneous among subcellular structures of the astrocyte and across different astrocytes that resided within the same field of view. Furthermore, we found that whisker stimulation induced discrete Ca "hot spots" that spread regionally within the endfoot. These data reveal that astrocytic Ca dynamics associated with the microvasculature are more complex than previously thought, and highlight the importance of considering the heterogeneity of astrocytic Ca activity to fully understanding neurovascular coupling.