Visualization of brain activity from in vitro to in vivo

Abstract

In order to understand the function of neuronal circuits, the spatio-temporal activity of multiple neurons have to be measured. In this regards, imaging of neuronal activity using fluorescence dyes is one of the most promising techniques. We conducted imaging studies on nervous tissues of in vitro and in vivo preparations using several different fluorescence dyes. Ca²⁺ is an important messenger in signal transduction of neurons and the intracellular Ca²⁺ concentration ([Ca²⁺]_i) is known to increase during the cell excitation. We made the Ca²⁺ imaging study in the brain slice preparations. [Ca²⁺]_i was measured using a high-speed cooled-CCD imaging system equipped with a excitation wavelength changer. In the basal ganglia striatal slices from mice, we observed the spontaneous [Ca²⁺]_i changes from individual neurons and glial cells. Long lasting spontaneous [Ca²⁺]_i changes, which lasted up to about 100 s, were found in both neurons and glial cells. In the visual cortical slice preparation, we measured the [Ca^{2+]_i changes of the neuronal population evoked by electrical stimulations. We could measure the signal propagation in the neuronal network of the visual cortex, and study the functional neuronal connections in the visual cortex. The membrane potential changes of neuronal population can be imaged with a voltage sensitive dye. In vivo membrane potential imaging reveal how the visual signals are encoded in the visual cortex and how signals propagate in the intact visual cortex. A flash of light applied to contralateral eye induced focal activation in the primary visual cortex in accord with the retinotopic map. In summary, imaging can visualize the population of the neuronal activity and have great potentials to reveal the spatiotemporal properties of the functional network from in vitro to in vivo.}