Imaging neuronal and astrocytic Ca2+ transients and hemodynamic responses evoked by single stimulation in rodent cortex

As transient intracellular Ca2+ changes play an important role in many essential processes including neuronal and astrocytic plasticity, tracking brain activity via Ca2+ is crucial. Unlike hemodynamics, Ca(2+ )change must be measured optically using an ionic fluorescent Ca2+ indicator. Here, we combine our highly sensitive multimodality optical imaging platform with genetically encoded Ca2+ indicator (GCaMP6f) expressed in neurons or astrocytes in somatosensory cortex, which enables simultaneous tracking of single-stimulation-evoked neuronal, astrocytic Ca2+ transients along with the corresponding hemodynamic responses at high spatiotemporal resolutions. We imaged neuronal and astrocytic Ca2+ transients from mouse cortex in response to a single electrical pulse (3mA, 0.3ms). Our results show that the neuronal Ca2+ responses were strong (Delta F/F-N =6.4 +/- 0.29%), fast (latency tau(N) =6 +/- 2.7ms) and of short duration (Delta t(N) =537 +/- 34ms) whereas the astrocyte responses were weak, slow and long-lasting (i.e., Delta F/F-A =1.7 +/- 0.1%, tau(A) =313 +/- 65ms, Delta t(A) =993 +/- 48ms). The synchronized activities among astrocytes were temporally less correlated than those among neurons. These results demonstrate the capability of optical detection of cell-specific Ca2+ activities from synchronized neuronal, astrocyte ensembles concurrently with the hemodynamic responses within the neuro-glio-vascular network, which can facilitate the study of the roles of astrocytes in the neurovascular coupling process. We also report time-lapse image results to analyze the interactions between stimuli-evoked neurovascular response versus the spontaneous cortical slow oscillations for brain functional studies.