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Genetically Encoded Activity Indicators
Published in Francesco S. Pavone, Shy Shoham, Handbook of Neurophotonics, 2020
Voltage sensitive dyes achieve a direct readout of neuronal electrical activity. Indeed, VSD imaging has allowed measurements of membrane potential transients with high spatial resolution (practically limited only by light scattering) as well as high temporal resolutions (practically limited only by data acquisition rates) in a variety of preparations including molluscs, fish, worms, and mammalians (Grinvald and Hildesheim, 2004; Baker et al., 2005; Homma et al., 2009; Antic et al., 2016). Low molecular weight (LMW) “organic” VSDs that respond quasi-instantaneously (within microseconds) to a change in membrane potential are able to faithfully image fast electrical signaling, including the shape and spread of fast action potentials (Vranesic et al., 1994). LMW VSDs can be used to bulk-stain membranes in tissues or be injected into single cells. Bulk-staining allows voltage imaging from a large number of cells simultaneously and with good spatial coverage but normally not with single cell resolution, while staining individual cells allows imaging of voltage transients in fine dendritic branches and axons with high spatial resolution (Antic et al., 2016). Activities of VSD-stained cells can be imaged by using simple epifluorescence wide-field imaging techniques that are often used at the level of population signals (Grinvald and Hildesheim, 2004; Baker et al., 2005; Homma et al., 2009), but dye-injected labeling of single neurons using VSDs also allows optical recordings that resolve subcellular structures including individual axons/dendrites (Zhou et al., 2007).
Voltage-Sensitive Dye and Intrinsic Signal Optical Imaging
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Vassiliy Tsytsarev, Reha S. Erzurumlu
VSDi is based on voltage-sensitive fluorescence probes that are fluorescent chemicals that change their optical features in response to the changes of the membrane potential. The molecules of the voltage-sensitive dyes bind to the external neural surface and play the role of energy transducers that transform changes in the transmembrane voltage into the changes in light absorption or emitted photons (Fromherz et al., 2008). Photosensitive devices record these changes. The voltage across the neural membrane generates a strong electric field, which affects voltage-sensitive dye molecule fluorescence properties. Changes in the transmembrane potential are linearly related to the fluorescence of the voltage-sensitive dye molecule, which follow the transmembrane voltage. The amplitudes of the VSDi signals are linearly correlated with changes in the membrane potential; therefore, these dyes are called potentiometric dyes.
Optical Cardiovascular Imaging
Published in Robert J. Gropler, David K. Glover, Albert J. Sinusas, Heinrich Taegtmeyer, Cardiovascular Molecular Imaging, 2007
Crystal M. Ripplinger, Guy Salama, Igor R. Efimov
Voltage-dependent changes in fluorescence of dye molecules are a consequence of interactions of the electric field with the dye molecules resulting in intra-and extra-molecular rearrangements of the dye in the membrane. Voltage-sensitive dyes are classified into two groups (8), fast and slow dyes, based on their response times and presumed molecular mechanisms. Only the fast probes are used in cardiac electrophysiology, due to their ability to respond to voltage changes in a matter of microseconds (9). The precise mechanisms underlying the voltage-dependent spectroscopic properties of fast voltage-sensitive dyes are still not fully understood. The electrochromic theory (10) states that a dye will be voltage sensitive if (i) the photon-produced excitation of the chromophore is accompanied by a shift in electric charge and (ii) the vector of intramolecular charge movement is parallel with the electric field gradient. Therefore, if charge movement in a dye molecule occurs perpendicular to the cell membrane, the dye’s fluorescence will be sensitive to changes in transmembrane potential. An alternative theory is the solvatochromic theory (11) which contends that dye molecules experience a change in the polarity of the lipid environment during reorientation produced by the voltage gradient. This dependency causes the spectral voltage-dependence of the chromophore.
Recent progress in electrophysiology and motility mapping of the gastrointestinal tract using multi-channel devices
Published in Journal of the Royal Society of New Zealand, 2020
Peng Du, Julia Y. H. Liu, Atchariya Sukasem, Anna Qian, Stefan Calder, John A. Rudd
The second trend of multi-channel recording is to increase the resolution power of the recording technique at a microscopic level. Zhang et al. (2019) demonstrated the feasibility of translating the optical mapping technique to record gastric slow-wave. The technique involves infusion of voltage-sensitive dye (di-4-ANEPPS) into the gastroepiploic artery and then using 450 or 505 nm laser light to excite the dye to emit fluorescence which was imaged between 607 and 695 nm. The advantage of optical mapping is the near-unlimited resolution power of the recording field. Another form of dye-loading mapping studies has allowed calcium transients in ICC within isolated small intestinal tissue to be recorded. Accompanied by confocal microscopy imaging of the same tissue, it has been possible to investigate the impact of drugs and cellular level changes to the functional behaviour of the ICC. One such finding from Malysz et al. (2016, 2017) demonstrated abnormal calcium transients in tissue preparation that has a high proportion of ICC that has been knocked out for the Ano1 channel, which is responsible for slow-wave pacemaking. These detailed tissue-level recordings form the basis for studying the detailed entrainment mechanisms of slow-wave at the microscopic levels, such as through incorporating existing ICC mathematical models into a tissue-level framework (Lees-Green et al. 2014; Qian et al. 2017).