Genetic calcium detector

Although genetically encoded calcium probes have started to be used in the live recording of neuronal activity, their low sensitivity and expression levels have not allowed the detection of single action potentials. Recently, Wallace et al. overcame this considerable problem by delivering the sensor protein D3cpv using an adeno-associated viral vector. The brain exerts its high-order function through the dynamic interactions of myriad neurons. Individual neurons work as functional elements within a topologically defined network. The mechanisms underlying the neural information processing, however, have not been fully elucidated, principally due to the experimental difficulty in monitoring large neuronal populations at the single cell resolution for long periods. To solve this problem, fluorescent calcium indicator proteins (FCIPs), i.e., genetically encoded reporters which alter their fluorescent properties in response to an increase in calcium ion activities, have recently been employed [1]. In neurons where the FCIP gene has been introduced under the downstream influence of an appropriate promoter, spike activity may be captured as a change in fluorescence intensity, as action potentials evoke transient calcium elevations through an activation of voltage-sensitive calcium channels. In a recent report [2], an experimental group has fine-tuned the properties of FCIP and enhanced its expression level in order to reliably detect single spikes within both in vitro and in vivo preparations.