Concurrent observations of astrocytic Ca²⁺ activity and multisite extracellular potentials from an intact cerebral cortex

In basic neuroscience, the attention has been recently focused on the role played by the protoplasmic astrocytes in modulating the activity of nearby neurons or else on assisting a long-term/sustained communication between these neurons and the surrounding microvasculature. However, to understand the physiological mechanisms underlying such a multiscale interactions in space and time, novel methodologies are required. This paper reports about an experimental setting and a procedure that was developed to obtain concurrently twophoton astrocytic Ca² imaging and multisite large-scale extracellular potentials as recorded by a silicon-based probe. Solutions to several technical drawbacks (e.g. removal of photoelectric artifacts, the establishment of safety ranges for microinjection) are provided which are intrinsic to the technology and procedure utilized. Through the use of SR101 to stain protoplasmic astrocytes, it was possible to combine functional information represented by the Ca² activity in individual astrocytes and the LFPs with geometrical descriptors of the astrocytic/ vessel networks. Spatial distributions of neurons (Nissl fluorescent - yellow), astrocytes (sulforhodamine 101 - green) and vessels (FITC-dextran - red) in a coronal section of the barrel cortex. This postmortem brain section was obtained from a perfused brain following the in vivo experiment.