A highly sensitive fluorescent indicator dye for calcium imaging of neural activity in vitro and in vivo

Abstract

Calcium imaging of individual neurons is widely used for monitoring their activity in vitro and in vivo. Synthetic fluorescent calcium indicator dyes are commonly used, but the resulting calcium signals sometimes suffer from a low signal-to-noise ratio (SNR). Therefore, it is difficult to detect signals caused by single action potentials (APs) particularly from neurons in vivo. Here we showed that a recently developed calcium indicator dye, Cal-520, is sufficiently sensitive to reliably detect single APs both in vitro and in vivo. In neocortical neurons, calcium signals were linearly correlated with the number of APs, and the SNR was > 6 for in vitro slice preparations and > 1.6 for in vivo anesthetised mice. In cerebellar Purkinje cells, dendritic calcium transients evoked by climbing fiber inputs were clearly observed in anesthetised mice with a high SNR and fast decay time. These characteristics of Cal-520 are a great advantage over those of Oregon Green BAPTA-1, the most commonly used calcium indicator dye, for monitoring the activity of individual neurons both in vitro and in vivo.

Functional imaging of neuronal activity of auditory cortex by using Cal-520 in anesthetized and awake mice

“…However, this widely used synthetic indicator has insufficient sensitivity to detect Ca 2+ transients evoked by single action potentials under in vivo conditions [26]. This sensitivity is extremely important in studies of the topographic organization of the Au1, because many cortical neurons respond to sound stimulation with only one or two spikes, particularly in layer 2/3 [27,28].…”

“…Cal-520 is a recently reported synthetic Ca 2+ indicator that has such required properties [26]. It has been used in studies of the neocortex, such as barrel and auditory cortices in anesthetized animals [26,37], subcortical regions such as the superior colliculus [38], and the cerebellum [26,39].…”

“…Cal-520 is a recently reported synthetic Ca 2+ indicator that has such required properties [26]. It has been used in studies of the neocortex, such as barrel and auditory cortices in anesthetized animals [26,37], subcortical regions such as the superior colliculus [38], and the cerebellum [26,39]. In cultured human neuroblastoma SH-SY5Y cells, Cal-520 has been demonstrated to be an optimal indicator for tracking localized subcellular changes, as compared with other synthetic Ca 2+ dyes including OGB-1 and fluo-8 and three GECIs (GCaMP6-slow, -medium and -fast variants) [40].…”

Efficient multi-site two-photon functional imaging of neuronal circuits

“…With the development of a genetically encoded calcium indicators [1,2] and bulk loaded calcium-sensitive dyes [3,4] that report changes in intracellular calcium, one can reconstruct the network connectivity by looking at the correlated activity of neurons. In addition, there are also genetically encoded voltage indicators [5] and voltage-sensitive dyes [6] that precisely report the fast changes in the membrane potential allowing one to study the propagation of action potentials along the dendritic tree of a neuron via single [7][8][9] and twophoton excitation [10].…”

A new strategy for specific imaging of neural cells based on peptide-conjugated gold nanoclusters

“…Noninvasive imaging of the neural cells of the central nervous system is a promising strategy for theranostics, however, it still remains challenging due to some drawbacks such as low signal-to-noise ratio resulting from the scattering of fluorescence signals by thick brain tissues 1,2 and low strict single-cell resolution. 3 The principal barriers to detecting neural cells in vivo are the tissue specificity of fluorescence-based imaging and the poor cell penetration ability of materials used in the neural cell imaging to blood-brain barrier (BBB).…”