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PubMed1990

Activation kinetics of retinal cones and rods: response to intense flashes of light.

Cone photoreceptors are less sensitive to light and the duration of their photoresponse is shorter than that of rods. In salamander rods and cones, we identified 3 components in membrane currents activated by bright flashes of light: an early receptor current (ERC) resulting from charge displacement within visual pigments, a saturation photocurrent generated by the closure of the cGMP-sensitive channels, and a putative Na-Ca exchanger current. The time courses of both the ERC and the onset of the saturation photocurrent were similar in rods and cones. The putative Na-Ca exchanger current, on the other hand, is 4- to 8-fold faster in cones. The onset of the saturation photocurrent consisted of a delay followed by a fast relaxation with an exponential time course. In both photoreceptor types the delay and the time course of the fast relaxation are dependent on light intensity and reach a limiting value when about 1% of the photopigment is bleached. The limiting value of the delay, about 8 msec, and of the relaxation time constant, about 2 msec, are nearly identical in rods and cones. The near identity of these parameters implies that at least 2 kinetic steps in the activation response of rods and cones are quantitatively similar. These findings suggest that the functional differences between rods and cones may arise from disparities in the processes that restore the components of the phototransduction cascade to their dark level and not from differences in the activation processes.

Animals↗
PubMed1989

[Human flash visually evoked cortical potentials under different levels of halothane anesthesia].

Flash visually evoked cortical potentials (FVECPs) were recorded in 13 surgical patients under different levels of halothane anesthesia, altering the rate of stimulus frequency from 0.5 Hz to 10 Hz. VECPs were obtained in the awake state under premedication with atropine sulphate, and at end-tidal halothane concentrations of 0.38%, 0.75%, 1.13% and 1.5%. The peak latency of P1 (the major positive component with a latency of about 100 msec) progressively increased from 116.7 +/- 3.3 msec (mean +/- SE) in the awake state to 124.3 +/- 6.3 msec, 136.5 +/- 5.2 msec, 151.5 +/- 5.2 msec and 166.3 +/- 8.7 msec with increasing halothane concentration. Significant reductions in P1 amplitude were observed to 2 Hz, 5 Hz and 10 Hz stimuli, whereas there were no significant changes in amplitude to 0.5 Hz and 1 Hz stimuli. P1 amplitude plotted against stimulus frequency had a maximum at 10 Hz in the awake state. This curve gradually and preferentially attenuated at higher frequencies as halothane concentration increased.

Adult↗
PubMed1989

[Clinical application of time dependent perimetry (9). The relations between stimulus area and double flash resolution, and critical flicker frequency].

Double flash resolution (DFR) and critical flicker fusion frequency (CFF) at the center of the visual field and the 5 degrees superior visual field were measured in normal subjects as a function of the stimulus area. Six stimulus sizes, ranging from a visual angle of 5' to 3 degrees 36' were used. The following results were obtained. First, the CFF increased as the stimulus area became larger at both the center and the 5 degrees superior visual field. Secondly, at the center of the visual field, the DFR initially increased as the stimulus area became larger and then decreased. Thirdly, at the 5 degrees superior visual field, this inhibitory phenomenon was also encountered with great individual variations and was not so evident as at the center of the visual field. Fourthly, the increasing rate of sensitivity was found to be greater at the 5 degrees superior visual field than at the center of the visual field in both CFF and DFR. From these results, we speculated that the CFF was detected by the transient system, which exhibited a weaker or no surround inhibition, and that the DFR in the center of the visual field was detected by the sustained system, which exhibited great surround inhibition. The DFR at the 5 degrees superior visual field could be detected by both transient and sustained systems.

Adult↗
PubMed1988

Protons in the thylakoid membrane-sequestered domains can directly pass through the coupling factor during ATP synthesis in flashing light.

Thylakoid membranes contain sequestered domains in which protons are held in a metastable state out of equilibrium with those in the inner (lumen) or the outer aqueous bulk phases unless the membranes are made leaky by, for instance, the addition of uncouplers. Previously, it has not been clear whether such sequestered domain protons are: 1) directly on a localized pathway into the CF0-CF1; 2) on an ultimately delocalized pathway comprising domains----lumen----CF0-CF1; or 3) perhaps not importantly involved in any way with proton gradient-linked ATP formation. Recent developments now permit a test of the above possibilities. The test for the possible mode of involvement of domain protons in energy coupling utilized single turnover flashes to energize electric field-driven ATP formation, as influenced by both the proton depletion level of the sequestered domains and whether the thylakoids were prepared in a way to show either a localized or delocalized proton gradient response in ATP formation (this response is reversibly controlled by incubation in low (localized coupling mode) or high KCl (delocalized mode) incubations (Beard, W. A., and Dilley, R. A. (1986) FEBS Lett. 201, 57-62; Chiang, G. and Dilley, R. A. (1987) Biochemistry 26, 4911-1916). Using thylakoids showing delocalized coupling responses, there was no influence of the reversible depletion of the sequestered domain buffering pool on the delta psi-driven ATP formation onset lag. Lumenal protons rather than domain protons in that case appear to be the first to be driven through the CF0-CF1 complex by the delta psi field. However, using thylakoids prepared to be in the localized gradient coupling mode, protons in the domains, rather than those in the lumen, are the first to pass through the CF0-CF1 complex in the onset of energization. We conclude that the sequestered domain protons, in the latter case only, are obligatorily in the main proton diffusion pathway for energization of ATP formation and are the first protons (rather than lumen protons) driven through the CF1-CF0 complex by a delta psi field.

Adenosine Triphosphate↗
PubMed1988

[The visual P300 (pattern flash P300) in the physiologic aging process].

For studying the relationship between the PFP300 (Pattern Flash elicited P300) and age we investigated 73 healthy subjects - 34 males, 39 females - between 18 and 60 years of age by presenting randomly two different checkerboards A (16 X 16 caskets visual angle = 50') and B (64 X 64 caskets visual angle = 12.5') to them (A:B = 80:20). The subjects' task was to keep a running count in their heads of the infrequent B-stimuli only. The resulting A- and B-responses were derived from Oz to Fz (Cz was ground). The results were as follows: 1. Comparing the PFP300-parameters between age group I (N = 46, 18-30 years) and age group II (N = 27, 31-60 years) we found that in the elder group both the N250-latencies (in B-potentials) and the PFP300a-latencies (in A-potentials) are significantly prolonged (p less than or equal to 0.01). The ascending PFP300a-amplitudes, however, remain (still?) unchanged. 2. Regression analyses between the PFP300-parameters and age for the total group revealed significant relationships for both the N250- (r = 0.35, P less than or equal to 0.01) and PFP300a-latencies (r = 0.78, P less than or equal to 0.01) and PFP300a-latencies (r = 0.78, P less than or equal to 0.01). In contrast to this, we could only find a zero correlation for the ascending PFP300a-amplitudes. 3. The coefficient of the regression line was 0.71 ms/year for the N250-latency and 1.09 ms/year for the PFP300a-latency. These findings indicate that one has to build age-matched control groups for applying PFP300 to pathophysiological processes.

Adolescent↗
PubMedDate not supplied

[Electroencephalographic changes in response to the equilibrium test and rhythmic light flashes].

Reliable diagnosis of CNS noise resistance is very important in the selection of operators, pilots and cosmonauts. This dictated a study the purpose of which was to investigate neocortex biopotentials of 74 test subjects during equilibrium tests in the presence or absence of 12 Hz light flashes. Electrocardiographic and stabilographic recordings were taken from 6 sites of the left neocortex during equilibrium tests (standing on toes) and during light stimulation. EEGs were processed through correlation-spectral analysis by means of Electronika-60 and EC-1035 computers. During light stimulation 35 "nonsusceptible" subjects maintained equilibrium for as long as 80-100% of the normal time while 39 "susceptible" subjects maintained it for only 10-30% of the normal time. In response to light stimulation susceptible subjects showed distinct rearrangement of the autospectral and coherence functions. The spectral density increased by 115-170% and the coherence of biopotentials that corresponded to the light stimulation frequency grew by 42-70% (p less than 0.01). Peaks of the function maxima occurred at 12 Hz. At the same time the density and coherence of biopotentials in the frequency range 6-8 Hz decreased by 50-58% and 15-28%, respectively (p less than 0.01). The above changes were more pronounced in the neocortex areas related to movement organization, viz. premotor, motor and sensorimotor areas. In the non-susceptible subjects light stimulation induced no changes in EEG. It is concluded that noise resistance of the motor control system depends on the CNS capacity to prevent the rhythm of light stimulation to occur in EEGs of motor areas.

Adult↗
PubMed1987

Death from electrical arc flash burns. A report of 2 cases.

Two cases of fatal accidental electrocution involving high-tension cables are reported in which autopsy revealed the presence of flash burns and, more significantly, multiple circumscribed and cavitated lesions associated with arcing. Attention is drawn to the danger of 'near-contact' with high-tension cables. The autopsy findings of severe internal injuries, which may be associated with the blast of the electrical discharge or occur secondary to a fall are discussed. In the absence of an adequate history, the autopsy findings may help to elucidate more accurately the circumstances of death and the type of electrical injury involved in fatal electrocution.

Adult↗
PubMed1986

Visual acuity and the flash visually evoked cortical potential in albinos.

The flash visually evoked cortical potential (VECP) was recorded in 18 human albinos. In some individuals P2 (latency 100-120 msec) formed the major component while in others P1 (latency 60-80 msec) was the largest component and dominated the response. The relative amplitude of P1 compared to P2 was calculated, and the results compared to the levels of monocular Snellen Visual Acuity measured. A relationship was found such that the greater the amplitude of P1 compared to P2, the lower the level of acuity. (Group 1: rs = -0.509, P less than 0.05. Group 2: rs = -0.536, P less than 0.05).

Adolescent↗
PubMed1986

Flash and pattern electroretinograms in normal and laser-induced glaucomatous primate eyes.

Experimental glaucoma was produced in one eye of five cynomolgus monkeys with the argon laser delivering 100-200 50-mu spots at 1200-1500 mW power and 0.5 sec to 360 degrees of the mid-trabecular meshwork. Monocular electroretinograms (ERGs) were recorded prior to and 2, 3, and 4 mo following the laser treatment. In the laser-treated (glaucoma) eyes, normal flash ERGs were observed using 1-Hz stimulation; however, pattern ERGs (PERGs) elicited using steady-state counterphase modulation of a 0.51 cpd square wave grating showed statistically significant reductions of amplitude. Only small reductions of PERG amplitude were seen with a 1.25 cpd grating. In three animals, abnormalities of the PERG occurred prior to clinically significant cupping of the optic nervehead. Moreover, reductions of PERG amplitude were progressive and associated with the magnitude of cupping of the optic nervehead and elevation of intraocular pressure. PERG amplitude did not change following acute reductions in intraocular pressure in the glaucoma eyes. Several control experiments were conducted to insure that results were not due to alterations in pupil size, refractive state, or accommodation in the glaucoma eyes. The authors believe they now have a monkey model for the electrophysiologic study of glaucoma.

Animals↗
PubMedDate not supplied

Flash evoked cortical and subcortical potentials in neuro-ophthalmology.

Visual evoked cortical and sub-cortical potentials are complementary to the electroretinogram in neuro-ophthalmology. By combining monocular stimulation with recordings from over the visual cortex of each cerebral hemisphere it is possible to accurately locate lesions which are both pre and post chiasmal. Chiasmal lesions can also be correctly identified using these techniques. The visual evoked sub-cortical potential, probably arising from a lateral geniculate or tectal site allows further post chiasmal variation. Flash and pattern reversal stimulation provide different information about the functioning of the visual system including the primary visual cortex and the association areas.

Brain Diseases↗
PubMed1985

Flash photolysis studies on the CO complexes of ferrous cytochrome P-450scc and cytochrome P-45011 beta. Effects of steroid binding on the photochemical and ligand binding properties.

Upon irradiation by a light flash (100-J), the carbon monoxide complex of cytochrome P-450scc was fully photodissociated in both the presence and absence of cholesterol, while less than 20% of the CO complex was photodissociable with those of deoxycorticosterone-bound and -free forms of cytochrome P-45011 beta. When the quantum yield of the reaction was measured for each photodissociable portion, the values were 0.5 and 1.0 for the substrate-free and -bound forms of cytochrome P-450scc, and 0.03 and 0.8 for the substrate-free and -bound forms of cytochrome P-45011 beta, respectively. Thus, CO complexes of these enzymes become more photosensitive upon binding with the specific substrates. Steroid binding also affected kinetic constants of reactions between the ferrous enzymes and CO. The rate constants for the CO recombination at 15 degrees C were 2.7 X 10(6) and 2.3 X 10(5) M-1 s-1 for the substrate-free and -bound forms of cytochrome P-450scc, and were 7.0 X 10(5) and 5.4 X 10(3) M-1 s-1 for the substrate-free and -bound forms of cytochrome P-45011 beta, respectively. The rate constants for the CO dissociation also decreased upon the steroid bindings. The products of the enzyme reactions, pregnenolone and corticosterone, had similar effects on the kinetic constants. From these findings, we postulate that the binding of a steroid to the substrate site of each enzyme alters the bonding character of CO with the heme-iron, thereby affecting both photochemical and kinetic properties of the CO complex. The nature of the photoindissociable portion of the CO complex of cytochrome P-45011 beta is also discussed.

Adrenal Cortex↗
PubMed1979

[Responses of cat suprasylvian gyrus neurons to light flashes of different wave lengths].

Unit responses in the cat's suprasylvian gyrus to the light flashes of different wavelength were studied. 80% of colour-coding units were found in the suprasylvian gyrus, especially in the Clare-Bishop area. Four groups of neurons differently responding to different spectral regions are distinguished. The possible principle of stimulus wavelength information coding in the suprasylvian units is discussed.

Animals↗
PubMed1977

[Cerebral potentials related to visual stimulation. Pattern inversion and flash].

Distinguishing between electroencephalogram (EEG) and event-related potentials (ERP) as indicators of brain electrical activity, methodological considerations pertaining to the recording of ERP to visual stimulation (evoked potentials, EP) are presented. Visual EP may be either steady-state or transient, depending upon stimulation used (repetitive versus transient) and method of analysis (frequency domain versus time domain). While both have diagnostic applications, this paper concentrates on transient visual EP. Based on the contention that intra and interindividual EP variability is the single most important issue in clinical practice, it presents data comparing two widely employed techniques (checkerboard reversal and flash stimulation) with respect to their stability in normal populations and their diagnostic sensitivity in demyelinating disease.

Adult↗
PubMed1983

[Changes in the RNA content in neurons and oligodendrogliocytes of the retinal ganglion layer in the frog resulting from stimulation with flashing light].

With Rana temporaria, the RNA content was studied cytophotometrically in large neurons of the retina ganglionic layer and in their satellites--oligodendrocytes. Due to light stimulation, the distribution and content of RNA in large neurons and satellite glia are rather specific. A 2 hour stimulation by flashing light with a frequency of 2 Hz (illumination intensity of 70 lx) resulted in increased concentration and amount of RNA both in the structures of large neurons and in the satellite glia, these changes being more pronounced in the former.

Animals↗
PubMed1983

[Changes in the spatial distribution of the neuronal activity in the visual cortex after stimulation with flashes of diffuse light].

At different stages of development of the response to flash, grouping of excited neurons of the guinea pig 17th area occurs within the same cortical microzones separated by narrow inhibition zones common to the neighbouring excited ones. The ensembles of excited neurons have the form of columns narrowing into depth. The grouping of cells into a silent gap indicates the grouping of inhibiting neurons. Three subgroups are differentiated by the character of averaged dynamics of impulse activity in ensembles, the essential moment of their interrelationship being the reciprocity. The one subgroup in deep layers is characterized by stability of the focus at different stages of the response development and seems to express the grouping of corticofugal neurons. The ensembles are considered to be one of the forms of activity of the structured morphofunctional cortical units, i.e. the columns.

Animals↗
PubMed1984

Formation and decay of the primary oxygen compound of cytochrome oxidase at room temperature as observed by stopped flow, laser flash photolysis and rapid scanning.

Rapid kinetic and scanning techniques were employed to observe the reaction of dioxygen with fully reduced cytochrome oxidase at room temperature following stopped flow flash photolysis of the CO compound of the enzyme. The initial product of the reaction was an oxygen compound with a spectral profile quite similar to that of the cytochrome oxidase-CO compound. The second order rate constant for formation of the primary oxygen compound was 1.1 X 10(8) M-1 S-1 at pH 7.4 and 25 degrees C. With an off rate constant of 1.9 X 10(3) S-1, the calculated dissociation constant was 1.8 X 10(-5) M. The apparent activation energy was 16.7 kJ/mol. The primary oxygen compound underwent further reaction which was independent of oxygen concentration with a rate constant of 1.2 X 10(3) S-1, and the product was Intermediate III ( Orii , Y. (1982) in Oxygenases and Oxygen Metabolism ( Nozaki , M., Yamamoto, S., Ishimura , Y., Coon , M. J., Ernster , L., and Estabrook , R., eds) pp. 137-149, Academic Press, New York), an oxidized species presumably identical to the "oxygen pulsed" oxidase. Thus, this reaction was ascribed to intramolecular electron transfer to the oxygen in the compound. The energy of activation was 49.8 kJ/mol below 18 degrees C but above that the rate constant was independent of temperature, and a "tunneling" mechanism was suggested for the intramolecular electron transfer.

Animals↗
PubMed1984

Lateralization of the flash visual-evoked cortical potential in human albinos.

Investigations were undertaken to determine which particular components of the flash visual-evoked cortical potential (VECP) lateralize on monocular stimulation in human albinos. Our results demonstrate that only the major positive component shows clear lateralization. Statistical analysis revealed that the latency lateralization was significant (P less than 0.001) while the amplitude lateralization was not.

Adolescent↗