Photoelectric photometry

Braddick, H. J. J.

doi:10.1088/0034-4885/23/1/303

Cited by 25 publications

(9 citation statements)

References 36 publications

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“…With a large resting fluorescence, the noise in the measurements was predominantly due to random arrival of photons at the photodetector, and the signal-to-noise ratio was proportional to (i,)~/2 (Braddick, 1960). In this situation the signal-to-noise ratio depended upon the incident excitation intensity, the fraction of the emitted light reaching the detector, the quantum efficiency of the detector, as well as AI/I, (Cohen, Hille & Keynes, 1969).…”

Section: Resultsmentioning

confidence: 99%

Changes in axon fluorescence during activity: Molecular probes of membrane potential

et al. 1974

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Summary. The fluorescence of dyes added to squid giant axons was studied during action potentials and voltage-clamp steps. One goal was to find fluorescence changes related to the increases in membrane conductance that underlie propagation. A second goal was to find large changes in fluorescence that would allow optical monitoring of membrane potential in neurons and other cells. Attempts were made to measure fluorescence changes using over 300 different fluorescent molecules and positive results were obtained with more than half of these. No evidence was found that would relate any of the fluorescence changes to the increases in membrane conductance that accompany depolarization; most, instead, were correlated with the changes in membrane potential. The fluorescence changes of several dyes were relatively large; the largest changes during an action potential were 10 -3 of the resting intensity. They could be measured with a signal-to-noise ratio of better than 10:1 in a single sweep.Changes in the fluorescence of molecules added to axons have been studied in an effort to learn about alterations in membrane structure that occur during excitation (Tasaki, Carnay &Watanabe, 1969;Cohen, Landowne, Shrivastav &Ritchie, 1970; Conti, Tasaki &Wanke, 1971). Although it was suggested that ANS and TNS fluorescence changes were related to increases in membrane conductance, our experiments (Davila, Cohen, Salzberg &Shrivastav, 1974) indicated that these fluorescence changes were, in fact, potential dependent. With the hope that other dyes would provide information about the structural basis of the conductance

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Section: Resultsmentioning

confidence: 99%

Changes in axon fluorescence during activity: Molecular probes of membrane potential

et al. 1974

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“…The root mean square statistical noise in a light measurement made over a certain period is equal to the square root of the number of photons detected during that period (Braddick, 1960). Thus the percentage of noise is reduced by increasing the number of photons in each measurement.…”

Section: Optical Changes In Electric Organ 491 Methodsmentioning

confidence: 99%

Light scattering and birefringence changes during activity in the electric organ of Electrophorus electricus

Cohen¹,

Hille²,

Keynes³

1969

The Journal of Physiology

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SUMMARY1. In an attempt to obtain information about structural changes related to electrical activity in Electrophorus electroplates, we have determined the size and time course of the changes in light scattering and in birefringence that occur during and after the discharge of the electric organ.2. The changes in light intensity detected with a photomultiplier were never greater than 0-2 % for a single discharge, and were often much smaller than this, but records with an acceptable ratio of signal to noise could be obtained by signal-averaging techniques.3. A single stimulus led to a decrease, then an increase, and finally another decrease in the light scattered by slices of the main electric organ. These three phases were designated E 1, E 2 and E 3.4. E 1 started at the beginning of the action potential, and its peak was reached at the same time as the completion of repolarization, even when the repolarization was delayed by cooling or hastened by drawing larger currents from the tissue.5. E 2 was proportional to the integral of the current flowing through the slice of electric organ, and may arise from the swelling and shrinking of the tubules that stud the faces of the electroplates. It developed within a millisecond or two of the start of an applied current, and lasted for about 100 msec.6. E 3 was a variable decrease in scattering that lasted for some seconds. 7. A stimulus also led to a transient increase in the birefringence of the electric organ. The optical change followed the change in electrical potential across the innervated faces of the electroplates with a delay of somewhat under 50 pasec.

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“…With currently available light sources, there are random fluctuations in the number of photons emitted (and measured) per unit time; the root-mean-square (r.m.s.) deviation in the number measured is the square root of the average number (Braddick 1960;Malmstadt et al 1974). Thus, in a shot-noise-limited measurement, the signal-to-noise ratio is directly proportional to the square root of the number of measured photons and inversely proportional to the square root of the bandwidth of the photodetection system.…”

Section: Noise In Optical Measurementsmentioning

confidence: 99%

Wide-field and two-photon imaging of brain activity with voltage- and calcium-sensitive dyes

Homma

Baker

Liu

et al. 2009

Phil. Trans. R. Soc. B

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This review presents three examples of using voltage-or calcium-sensitive dyes to image the activity of the brain. Our aim is to discuss the advantages and disadvantages of each method with particular reference to its application to the study of the brainstem. Two of the examples use wide-field (onephoton) imaging; the third uses two-photon scanning microscopy. Because the measurements have limited signal-to-noise ratio, the paper also discusses the methodological aspects that are critical for optimizing the signal.The three examples are the following. (i) An intracellularly injected voltage-sensitive dye was used to monitor membrane potential in the dendrites of neurons in in vitro preparations. These experiments were directed at understanding how individual neurons convert complex synaptic inputs into the output spike train. (ii) An extracellular, bath application of a voltage-sensitive dye was used to monitor population signals from different parts of the dorsal brainstem. We describe recordings made during respiratory activity. The population signals indicated four different regions with distinct activity correlated with inspiration. (iii) Calcium-sensitive dyes can be used to label many individual cells in the mammalian brain. This approach, combined with two-photon microscopy, made it possible to follow the spike activity in an in vitro brainstem preparation during fictive respiratory rhythms.The organic voltage-and ion-sensitive dyes used today indiscriminatively stain all of the cell types in the preparation. A major effort is underway to develop fluorescent protein sensors of activity for selectively staining individual cell types.

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Photoelectric photometry

Cited by 25 publications

References 36 publications

Changes in axon fluorescence during activity: Molecular probes of membrane potential

Changes in axon fluorescence during activity: Molecular probes of membrane potential

Light scattering and birefringence changes during activity in the electric organ of Electrophorus electricus

Wide-field and two-photon imaging of brain activity with voltage- and calcium-sensitive dyes

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