Abstract
In vivo calcium imaging is an incredibly powerful technique that provides simultaneous information on fast neuronal events, such as action potentials and subthreshold synaptic activity, as well as slower events that occur in the glia and surrounding neuropil. Bulk-loading methods that involve multiple injections can be used for single-cell as well as wide-field imaging studies. However, multiple injections result in inhomogeneous loading as well as multiple sites of potential cortical injury. We used convection-enhanced delivery to create smooth, continuous loading of a large area of the cortical surface through a solitary injection site and demonstrated the efficacy of the technique using confocal microscopy imaging of single cells and physiological responses to single-trial events of spontaneous activity, somatosensory-evoked potentials, and epileptiform events. Combinations of calcium imaging with voltage-sensitive dye and intrinsic signal imaging demonstrate the utility of this technique in neurovascular coupling investigations. Convection-enhanced loading of calcium dyes may be a useful technique to advance the study of cortical processing when widespread loading of a wide-field imaging is required.
Highlights
Neurovascular coupling refers to the relationship between local neural activity and subsequent changes in cerebral blood flow (CBF)
We evaluated the utility of calcium imaging when studying a variety of different neuronal processes, and we demonstrated that calcium can be imaged with cerebral blood volume (CBV) and oximetry simultaneously
Traditional multi-injection calcium staining creates inhomogeneous loading with islands of high concentration that decrease with distance from the injection site as the dye diffuses into the surrounding extracellular space [Fig. 1(b)] and multiple injections are employed to stain a large cortical area, which often results in an uneven staining [Fig. 1(b)]
Summary
Neurovascular coupling refers to the relationship between local neural activity and subsequent changes in cerebral blood flow (CBF). An important issue in resultant data interpretation pertains to the spatial and temporal precision of the hemodynamic changes in comparison to the underlying neuronal activity. The study of neurovascular coupling has primarily focused on the role of different cell types (e.g., neurons, astrocytes, and pericytes) and physiological parameters [e.g., lactate, NADH (nicotinamide adenine dinucleotide (NAD) + hydrogen (H)), O2, nitric oxide) on CBF changes.[5,6,7,8,9,10,11] in these studies, neuronal activity is typically recorded from a small group of neurons using a single electrode or a small population of loaded cells or even a single
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