Visible Light Stimulation Research Articles

Reversible low-light induced photoswitching of crowned spiropyran-DO3A complexed with gadolinium(III) ions.

Photoswitchable spiropyran has been conjugated to the crowned ring system DO3A, which improves its solubility in dipolar and polar media and stabilizes the merocyanine isomer. Adding the lanthanide ion gadolinium(III) to the macrocyclic ring system leads to a photoresponsive magnetic resonance imaging contrast agent that displays an increased spin-lattice relaxation time (T1) upon visible light stimulation. In this work, the photoresponse of this photochromic molecule to weak light illumination using blue and green light emitting diodes was investigated, simulating the emission spectra from bioluminescent enzymes. Photon emission rate of the light emitting diodes was changed, from 1.75 × 1016 photons·s−1 to 2.37 × 1012 photons·s−1. We observed a consistent visible light-induced isomerization of the merocyanine to the spiropyran form with photon fluxes as low as 2.37 × 1012 photons·s−1 resulting in a relaxivity change of the compound. This demonstrates the potential for use of the described imaging probes in low light level applications such as sensing bioluminescence enzyme activity. The isomerization behavior of gadolinium(III)-ion complexed and non-complexed spiropyran-DO3A was analyzed in water and ethanol solution in response to low light illumination and compared to the emitted photon emission rate from over-expressed Gaussia princeps luciferase.

Intrinsic optical imaging of stimulus-modulated physiological responses in amphibian retina

We demonstrated near-infrared light imaging of stimulus-modulated physiological activities in an isolated frog retina using transient intrinsic optical responses (TIORs). While low-strength visible-light stimuli evoked TIORs with positive polarity, strengthened stimuli elicited additional negative TIORs. Our experimental study and physiological analysis suggest that the negative TIORs are associated with photoreceptor response, and the positive TIORs result primarily from dynamic changes of postphotoreceptor response during retinal activation. In coordination with the sophisticated design of visible-light stimulation protocols, optical imaging of TIORs promises an important application for noninvasive assessment of retinal photoreceptor and inner neurons.

Visual Stimulus–Induced Changes in Human Near-Infrared Fundus Reflectance

Imaging studies from anesthetized feline, primate, and human retinas have revealed near-infrared fundus reflectance changes induced by visible light stimulation. In the present study, the spatial and temporal properties of similar changes were characterized in normal, awake humans. Five normal human subjects were studied. A modified fundus camera was used to image changes in retinal reflectance of 780-nm near-infrared light imaged onto a 12-bit charge-coupled device (CCD) camera in response to a green (540 nm) visual stimulus. During 60 seconds of recording (frame rate, 3 Hz) 10 cycles were recorded, during each of which 3 seconds of blank and then 3 seconds of either vertical bar or blank stimulus was projected. The change in the average near-infrared reflectance of the stimulated retinal region relative to an equal-sized nonstimulated region (r is the ratio of reflectance between the two retinal areas) was analyzed with a mixed model for repeated measures. The mixed model showed a significant average decrease in r of 0.14% (95% CI, -0.25 to -0.03) over all subjects induced by bar stimulus cycles, with a gradual return to baseline after stimulus offset, compared with only a 0.04% (95% CI, -0.11-+0.20) decrease in r induced by blank, nonstimulated cycles. The mixed model for individuals showed a decreasing linear trend in r over time during bar stimulation, but no decrease for blank cycles in three of five subjects. There was a localized decrease in reflectance in response to 780-nm near-infrared light in the retinal region exposed to a visual stimulus, which was significant in three of five subjects. It is presumed that the reflectance change represents the functional activity of the retina in response to a visual stimulus.

Near-infrared imaging of fast intrinsic optical responses in visible light-activated amphibian retina

High performance functional imaging is needed for dynamic measurements of neural processing in retina. Emerging techniques for visual prosthesis also require advanced methodology for reliable validation of electromagnetic stimulation of the retina. Imaging of fast intrinsic optical responses associated with neural activation promises a variety of technical advantages over traditional single and multichannel electrophysiological techniques for these purposes, but the application of fast optical signals for neural imaging has been limited by low signal-to-noise ratio and high background light intensity. However, by using an optimized near-infrared probe light and improved optical system, we improve the optical signals substantially, allowing single pass measurements with approximately micron resolution. We image fast intrinsic optical responses with different optical modalities, i.e., bright field, dark field, and cross-polarization, from isolated retina activated by visible light stimulation. At single cell resolution, bright-field imaging discloses the maxima of optical responses approximately 5% dI/I, where dI is the dynamic optical change and I is the baseline light intensity. Dark-field imaging techniques further enhance the sensitivity of optical measurements, and show the maxima of optical responses exceeding 10% dI/I. Cross-polarized imaging provides optical sensitivity similar to dark-field imaging, but different patterns of neural activation are observed.

Regional variations in the relative sensitivity to UV light in the mouse retina.

About 3% of all mouse photoreceptors are cones. An earlier electrophysiological study indicated that there were two classes of cone in the mouse retina having peak sensitivities (lambda max) of about 360 nm and 511 nm. Recent immunocytochemical results show there are two types of cones that have distinctive regional segregation patterns. We used regional stimulation of the retina in conjunction with electroretinogram (ERG) flicker photometry to see if the two cone types identified electrophysiologically are regionalized in a fashion suggested by the anatomical results. We find they are. Relative sensitivity to ultraviolet and visible light stimulation qualitatively parallels that predicted by immunocytochemical labelling. One result of this remarkable regionalization of cone types is that the mouse retina is relatively more sensitive to ultraviolet light stimulation when that light is directed toward the ventral half of the retina.

Photovoltaic Effects in Liquid Crystal Cells Containing Organic Dyes

Abstract Dye sensitization on photovoltaic phenomena under visible light stimulation are described in smectic, nematic, and isotropic phases of p-cyano-p'-n-octylbiphenyl cells with a symmetrical electrode arrangement. Methyl red is used as a sensitizer. The dependence of short-circuit photocurrents on excitation light intensity, light pulse width, temperature, and the cell thickness are measured. The photocurrent consists of three components, that is, the small negative peak with a fast response, the second positive peak following after the first peak, and the third negative peak with a slow response. The second and the third components of the photocurrents cannot be observed in the solid crystalline state. Both of them decrease with an increase in the cell thickness, and their response time becomes shorter as the temperature rises. These two components are induced by the diffusion processes of the carriers produced by the light stimulation.

Mechanism of the Formation of X-Ray-Induced Phosphenes: I. Electrophysiological Investigations

To explore one possible mechanism of the formation of phosphenes detected by astronauts during space flights, the x-ray stimulation of the photoreceptor cells of the eye was investigated. The albino rat's retina, maintained in culture by perfusion, was used for this study. The electrophysiological response (ERG) induced by x rays was found to be identical to the one produced by a visible light stimulation. Under our experimental procedure, only a direct interaction between incident radiation and retina induced such as ERG. Irrespective of whether the experiment was performed using the isolated retina or the whole animal, we found that the ERG amplitude was proportional to the logarithm of the exposure on the retina. A comparative study indicated that, to obtain the same ERG amplitude, the incident energy on the retina must be about 5 x 10/sup 6/ times larger for x rays (E = 40 keV) than for visible light (lambda = 489 nm). The analysis of these results leads us to assume that the x rays act on the rod's photosensitive molecule, rhodopsin.

X-ray induced behavioral reactions and detection mechanisms in the shrimp

Red Ghost Shrimp, Callianassa californiensis, were shown from behavioral and electrophysiological studies to respond to ionizing radiation. When exposed to X-rays at 52 R/sec, the majority of intact animals could detect and avoid further irradiation by escaping into a shielded section of the test chamber. Animals continued to display escape responses after removal of eyestalks and antennae. Significant avoidance activity also occurred with partial-body exposure and indicated the existence of a radiation-sensitive receptor on the abdomen. Electroretinograms elicited by beta- and X-radiation sources corresponded closely with the waveforms produced by visible light stimulation. Electroantennograms were recorded from isolated antennules following stimulation with glutamic acid, beta-, and X-radiation. Biphasic on-off phases were recorded with an intermediate phase present during the longer duration exposures. Similarly, bioelectrical potentials were recorded from swimmeret preparations with exposure to beta- and X-radiation. The electrophysiological evidence indicates that the eye, antennules, and possibly chemoreceptors on the abdominal segments serve as routes for detection of ionizing radiations.

Fluorescence différée et émissions photostimulées du carbazole et de la diphénylamine dans une matrice rigide d'éther à 77 °K

The isothermal delayed fluorescence along with the visible (6000 Å) photostimulated fluorescence and phosphorescence emissions have been recorded and analyzed in the following systems: diphénylamine (DPA) – ether rigid glass and carbazole (C) – ether rigid glass at 77°K. The electron–cation recombination after visible light stimulation has been analyzed in terms of a kinetic model already described (10). The triplet quantum yields of the DPA and C molecules are calculated and compared to the existing experimental values. The rate constant ratio (β) of populating the first triplet (T1) relative to populating the first excited singlet (S1) after the recombination event has taken place, is equal to about 2 in both systems investigated here. A value of 4.4 was obtained for indole and tryptophan in the same matrix. This difference can only be explained in terms of various singlet state energies for these molecules and also in terms of the stimulating energies used in these experiments.

Isothermal and Photostimulated Emissions of Indole and Tryptophan in Two Polar Matrices at 77 °K

The isothermal delayed fluorescence along with the visible photostimulated fluorescence and phosphorescence emissions have been recorded and studied for the following systems: a 10−3 M solution of indole in an ether glassy matrix, a 10−3 M solution of indole in an ethylene glycol–water glassy matrix (EG–W) (70–30 by volume), a 10−3M solution of tryptophan in an EG–W glassy matrix (70–30 by volume). All these experiments have been performed at the temperature of liquid nitrogen. It has also become possible to record the action spectra of the photostimulated emissions which give us information about the entities playing an active part in the recombination processes. The electron–cation recombination after visible light stimulation has been analyzed in terms of a kinetic model based on the assumption that upon neutralization an intermediate state is formed from which the molecule decides what its spin multiplicity will be. It was found that in an EG–W glass at 77 °K about 80% of the recombination events lack the energy necessary to reach the first excited singlet state of the amines studied. In an ether glass this percentage decreases to about 28%. This result is qualitatively in accord with the fact that the photostimulated electrons are more stabilized in an EG–W glass by an amount of energy equal to 1.5 eV.