The Duplex Nature of the Retina of the Nocturnal Gecko as Reflected in the Electroretinogram

The effect of light and dark adaptation on the electrical activity in two species of nocturnal gecko, Hemidactylus turcicus and Tarentola mauritanica was studied. The electroretinogram of both species changes from the scotopic type in the dark-adapted state to the photopic type after strong light adaptation. For the scotopic response fusion frequencies up to 18 flashes per sec. are obtained in both species. For the photopic response fusion frequencies up to 50 flashes per sec. are seen in Tarentola, and up to 25 flashes per sec. in Hemidactylus. Proceeding from dark to light adaptation the increment threshold (dI) is measured at different levels of adaptive illumination (I). At low levels of illumination the dI/I ratio is found to be small and at high levels of illumination to be large. No difference in the dI/I ratio is obtained for test lights of 462 and 605 mµ. During dark adaptation the change of threshold after exposure to moderate and weak lights (up to 10³ times dark threshold) is rather fast. After light adaptation to strong light (10⁶ times dark threshold) duplex dark adaptation curves are seen with a break separating a fast and a slow phase of dark adaptation. The significance of these results from a retina which possesses sense cells of only one type is discussed.     

CRITICAL INTENSITY AND FLASH DURATION FOR RESPONSE TO FLICKER: WITH ANAX LARVAE

Determinations of the flicker response curve (F – log I_m) with larvae of Anax junius (dragonfly) for various ratios t_L/t_D of light time to dark time in a flash cycle provide relations between t_L/t_D and the parameters of the probability integral fundamentally describing the F – log I function, including the variability of I. These relations are quantitatively of the same form as those found for this function in the sunfish, and are therefore non-specific. Their meaning for the theory of reaction to visual flicker is discussed. The asymmetry of the Anax curve, resulting from mechanical conditions affecting the reception of light by the arthropod eye, is (as predicted) reduced by relative lengthening of the fractional light time in a cycle.     

Cation-dependent light-induced structural changes in visual receptor membranes

A stearamide spin probe was used to study the light-induced structural changes in Rod Outer Segment Membranes in the presence of sodium and calcium ions. The correlation time (τ_C) for the reorientation of the probe was calculated in the dark and light. In the presence of sodium ions, τ_C = 3.3 × 10^?9 sec in the dark, and 2.7 × 10^?9sec in the light while the opposite was noticed in the presence of calcium ions, τ_C = 2.9 × 10^?9 sec in the dark and 3.6 × 10^?9 sec in the light. The correlation times for reorientation of the probe were also calculated in aqueous glycerol solutions of varying viscosities at 20°C. Comparison of the values of τ_C (dark and light) suggests a change in local mobility in the ROS corresponding to a macroscopic viscosity difference of approximately 150 cp. The significance of calcium ion interaction with negatively charged groups and the formation of a Schiff base is emphasized.     

Photocontrol of Hypocotyl Elongation in De-Etiolated Cucumis sativus L. : Long Term, Fluence Rate-Dependent Responses to Blue Light

Hypocotyl growth in Cucumis sativus L. cv Ridge Greenline is inhibited by increasing blue light (B) fluence rate in a near log linear fashion once a low fluence threshold is exceeded. Deviation from log linearity at the highest fluence rate used here is due to light perceived by the cotyledons and this effect is assigned to phytochrome. This response can be removed by Norflurazon treatment, without affecting the rest of the fluence response curve.

There is also some activation of phytochrome by lower fluence rates of B, an effect which contributes to the overall inhibition of growth. Responses to photostationary state and cycling rate indicate, however, that B does not primarily act via phytochrome, but through a specific blue light photoreceptor.

     

The responses of the pupil of Gekko gekko to external light stimulus

1. The responses of the pupil of a nocturnal gecko (Gekko gekko) to external light stimulus were studied. 2. The responses of the pupil are determined by light entering the pupil and not by light acting directly on the iris. 3. The responses of the pupil are very uniform in sensitivity including spectral sensitivity for light coming in different directions to the eye. 4. The possible change in area of the pupil is more than 300-fold and probably represents an effort to shield the pure rod retina from saturating light intensities. 5. The pupil continues to contract sharply for changes in external light intensity which give retinal illuminations corresponding to 10⁶ quanta/sec. striking a retinal rod. 6. There is a large degree of spatial summation of the response; circular external light fields subtending 5 and 140° giving the same illumination at the pupil give approximately the same pupil response. 7. The spectral sensitivity curve agrees with the absorption curve of an extracted pigment from a closely related gecko described by Crescitelli in the followig paper. It is similar to the human scotopic curve but its maximum is displaced about 20 to 30 mµ towards the red end of the spectrum. The fall in sensitivity towards the red end of the spectrum is described by the equation See PDF for Equation     

Assessment of Macular Function during Vitrectomy: New Approach Using Intraoperative Focal Macular Electroretinograms

Purpose

To describe a new technique to record focal macular electroretinograms (FMERGs) during vitrectomy to assess macular function.

Methods

Intraoperative FMERGs (iFMERGs) were recorded in ten patients (10 eyes) who undergo vitrectomy. iFMERGs were elicited by focal macular stimulation. The stimulus light was directed to the macular area through a 25 gauge (25G) glass fiber optic bundle. Background light was delivered through a dual chandelier-type light fiber probe. Focal macular responses elicited with combinations of stimulus and background luminances were analyzed.

Results

A stimulus luminance that was approximately 1.75 log units brighter than the background light was able to elicit focal macular responses that were not contaminated by stray light responses. Thus, a stimulus luminance of 160 cd/m² delivered on a background of 3 cd/m² elicited iFMEGs from only the stimulated area. This combination of stimulus and background luminances did not elicit a response when the stimulus was projected onto the optic nerve head. The iFMERGs elicited by a 10° stimulus with a duration of 100 ms and an interstimulus interval of 150 ms consisted of an a-, b-, and d-waves, the oscillatory potentials, and the photopic negative response (PhNR).

Conclusions

Focal ERGs with all components can be recorded from the macula and other retinal areas during vitreous surgery. This new technique will allow surgeons to assess the function of focal areas of the retina intraoperatively.     

THE FLICKER RESPONSE CONTOUR FOR THE CRAYFISH. I

The F - log I curve for threshold response to visual flicker has been determined for the crayfish Cambarus bartoni. As predicted on the basis of the higher curvature of the optic surface, the flicker response contour is more asymmetrical than for bee and dragonfly nymph under comparable conditions of temperature and light time fraction of flash cycle. The mechanical origin of this asymmetry is thus confirmed, and is further supported by the similar forms of the F - log I curves in bee, dragonfly larva, and crayfish in the lower portion of the curves (up to F = 70 per cent F_max.). The slope of the fundamental curve for crayfish, deduced by analysis of the data, is lower than for bee, dragonfly nymph, or Asellus. This signifies a wider spread of the effective distribution of elemental log I thresholds involvable in the response to flicker, and may be traced either to the greater curvature of the eye-surfaces or to their position upon movable pedicles. The results are therefore consistent with the statistical conception of the nature of effects recognizable as due to the activity of excitable elements.     

THE PHOTOTROPIC EXCITATION OF LIMAX

The photic orientation of Limax creeping geotropically upon a vertical plate is such that the phototropic vector determining the angular deflection β from the vertical path is proportional to log I. This is proved by the fact that with horizontal illumination tan β is directly proportional to log I; with non-horizontal light rays from a small source the ratio See PDF for Equation is directly proportional to log I (where A = the angle between light rays and the path of orientation), the vector diagram of the field of excitation being in this case not a right-angled triangle.     

Ionic Dependence of Reversal Voltage of the Light Response in Limulus Ventral Photoreceptors

The light-induced current as measured using a voltage clamp (holding voltage at resting potential) is attenuated when sodium ions in the bathing solution, Na_o, are replaced by Tris, choline, or Li or when NaCl is replaced by sucrose. After replacement of NaCl by sucrose, the reversal voltage, V_rev, for the light response becomes more negative. In this case, the slope of the V_rev vs. log Na_o near Na_o = 425 mM is approximately 55 mV/decade increase of Na_o (mean for 13 cells). The slope decreases at lower values of Na_o. Choline is not impermeant and partially substitutes for Na; the slope of V_rev vs. log Na_o is 20 mV/decade (mean for three cells). V_rev does not change when Na is replaced by Li. Decreases in the bath concentrations of Ca, Mg, Cl, or K do not affect V_rev. When Na_o = 212 mM, V_rev becomes more positive when K_o is increased. Thus, light induces a change in membrane permeability to Na and probably also to K.     

Differentiation of Nerve Terminals in the Crayfish Opener Muscle and Its Functional Significance

Junctional potentials (jp's) recorded from superficial distal fibers of the crayfish opener muscle are up to 50 times larger than jp' in superficial central fibers when the single motor axon that innervates the muscle is stimulated at a frequency of 1/sec or less. At 80/sec, in contrast, central jp's are up to four times larger than those observed in distal fibers. The tension produced by single muscle fibers of either type is directly proportional to the integral of the time-voltage curve minus an excitation-contraction coupling threshold of 3 mv. Distal fibers therefore produce almost all the total muscle tension at low frequencies of stimulation and central fibers add an increasingly greater contribution as their nerve endings begin to facilitate in response to increased rate of motor discharge. Differentiation of muscle membrane characteristics (input resistance, space constant, time constant) cannot account for these differences in facilitation ratios. The mechanism of neuronal differentiation is not based upon the size or effectiveness of transmitter quanta, since equal sized jp's have equal variances;: mjp sizes and variances are also equal. No differences were found between fiber types in rates of transmitter mobilization, density of innervation, or the relationship between transmitter release and terminal depolarization. Single terminals on distal fibers were found to release transmitter with a greater probability than central terminals. More effective invasion of distal terminals by the nerve impulse at low frequencies can account for the difference.     

CRITICAL ILLUMINATION FOR RESPONSE TO FLICKERED LIGHT,WITH DRAGONFLY LARVAE (ANAX), IN RELATION TO AREA OF EYE

Arthropods with large convex eyes provide curves of critical illumination for response as a function of flicker frequency (or of visual acuity) which depart from the probability integral type characteristically found for F – log I with vertebrates. By means of experiments with Anax nymphs in which various parts of the eye have been opaqued it is shown that the special shape of the flicker curve is due to the mechanical disadvantage of the periphery of the eye in the reception of light, which is overcome by higher intensities. It is not due to a fixed spatial pattern of intrinsic individual excitabilities of the ommatidia. Reduction of retinal area decreases F_max., and increases log I for F/F_max. = 50 per cent. The direct proportionality of I_m to P.E._1I is independent of area. Certain relations of these facts to the theory of response to flicker have been discussed.     

Sedentary Behavior and Light Physical Activity Are Associated with Brachial and Central Blood Pressure in Hypertensive Patients

Background

Physical activity is recommended as a part of a comprehensive lifestyle approach in the treatment of hypertension, but there is a lack of data about the relationship between different intensities of physical activity and cardiovascular parameters in hypertensive patients. The purpose of this study was to investigate the association between the time spent in physical activities of different intensities and blood pressure levels, arterial stiffness and autonomic modulation in hypertensive patients.

Methods

In this cross-sectional study, 87 hypertensive patients (57.5 ± 9.9 years of age) had their physical activity assessed over a 7 day period using an accelerometer and the time spent in sedentary activities, light physical activities, moderate physical activities and moderate-to-vigorous physical activities was obtained. The primary outcomes were brachial and central blood pressure. Arterial stiffness parameters (augmentation index and pulse wave velocity) and cardiac autonomic modulation (sympathetic and parasympathetic modulation in the heart) were also obtained as secondary outcomes.

Results

Sedentary activities and light physical activities were positively and inversely associated, respectively, with brachial systolic (r = 0.56; P < 0.01), central systolic (r = 0.51; P < 0.05), brachial diastolic (r = 0.45; P < 0.01) and central diastolic (r = 0.42; P < 0.05) blood pressures, after adjustment for sex, age, trunk fat, number of antihypertensive drugs, accelerometer wear time and moderate-to-vigorous physical activities. Arterial stiffness parameters and cardiac autonomic modulation were not associated with the time spent in sedentary activities and in light physical activities (P > 0.05).

Conclusion

Lower time spent in sedentary activities and higher time spent in light physical activities are associated with lower blood pressure, without affecting arterial stiffness and cardiac autonomic modulation in hypertensive patients.     

Negative Phototaxis in Blepharisma japonicum

The protozoan Blepharisma japonicum showed negative phototaxis caused by transient reversal of the direction of ciliary beat and changes of swimming velocity induced with varying intensities of light. The ciliary reversal occurred at 1–2 sec after a sudden increase in light intensity. When light intensity was decreased, no response was observed. Moreover, the ciliates swam fast in light areas but slowly in dark areas; the mean velocity of swimming was 80 μ m/sec at 5 × 10² lux but reached about 400 μMm/sec at 5 × 10³ lux. In addition, the cell body elongated in response to light application; the mean length of the body was 308 μm at 5 × 10² lux, which increased to 397 μ m at 10⁴ lux. Such body elongation seems to contribute to rapid swimming. Negative phototaxis may be an important behavior in B. japonicum because the organisms are killed by exposure to strong light.     

DARK ADAPTATION IN DINEUTES

The level of dark adaptation of the whirligig beetle can be measured in terms of the threshold intensity calling forth a response. The course of dark adaptation was determined at levels of light adaptation of 6.5, 91.6, and 6100 foot-candles. All data can be fitted by the same curve. This indicates that dark adaptation follows parts of the same course irrespective of the level of light adaptation. The intensity of the adapting light determines the level at which dark adaptation will begin. The relation between log aI ₀ (instantaneous threshold) and log of adapting light intensity is linear over the range studied.     

Implication of Urinary Complement Factor H in the Progression of Immunoglobulin A Nephropathy

Background

After activation, the complement system is involved in the pathogenesis of Immunoglobulin A nephropathy (IgAN). Complement factor H (CFH) is a crucial inhibitory factor of the alternative pathway of the complement system. The study investigated the effects of urinary CFH levels on IgAN progression.

Methods

A total of 351patients with IgAN participated in this study. They were followed up for an average of 51.8±26.6 months. Renal outcome was defined as a composite endpoint, that included instances of end-stage renal disease (ESRD),≥ 50% decline in estimated glomerular filtration rate (eGFR) or doubling of plasma creatinine levels. Urinary CFH levels were measured by enzyme-linked immunosorbent assay and calculated as the ratio of urinary CFH over creatinine (uCFH/uCr).

Results

In the whole cohort, uCFH/uCr values were associated with disease progression either as continuous [log(uCFH/uCr)] or categorical traits (dichotomous and quartile variables) after adjusting for eGFR, proteinuria, mean arterial blood pressure, histological grading and immunosuppressive therapy in the Cox proportional hazard model. Kaplan-Meier analysis showed that higher uCFH/uCr values at baseline predicted worse renal outcome during follow-up (log-rank, P<0.001). Receiver operating characteristic curve (ROC) analysis showed that log(uCFH/uCr) had predictive value for renal outcome (area under curve [AUC]=0.745), and the AUC increased to 0.805 after being incorporated into baseline eGFR and proteinuria. In subgroup analysis with eGFR≥60 mL/min/1.73m², log(uCFH/uCr) had better predictive value (AUC= 0.724, P=0.002) for renal outcome compared to eGFR (AUC = 0.582, P=0.259) and proteinuria (AUC = 0.615, P=0.114).

Conclusions

Urinary CFH levels are associated with renal function decline and increased urinary CFH levels are a risk factor for progression of IgA nephropathy.     

The Feeding Behavior of Adult Root-knot Nematodes (Meloidogyne incognita) in Rose Balsam and Tomato

Meloidogyne incognita is a parasitic root-knot nematode that causes considerable yield loss in a wide range of plants. In this study we documented the movement of adult female nematodes for more than 2 hr in micro-slices of infected tomato (Solanum lycopersicum) and rose balsam (Impatiens balsamina) plants using light and video microscopy. Stylet thrusting was followed by short pumping actions of the esophagus, dorsal esophageal gland ampulla, and metacorpal bulb. Regular thrusting was normally accompanied by head turning and always preceded continuous stylet thrusting aimed at a single point (for 20 to 90 sec). Females often held the stylet in a protruded position, while pulsating the metacorpus bulb, for about 30 sec. Subsequently, the stylet was paused in a retracted position for 5 to 40 sec. This sequence of behavior took 290 to 380 sec to complete. The procedure developed in this study provides a useful cytological technique to investigate the interaction between root-knot nematodes and the giant cells formed by infected plants. Scanning electron microscopy revealed that the head of the adult nematode was located in the narrow intercellular spaces among several giant cells. The anterior part of the head of the adult was folded like a concertina, whereas that of the second-stage juvenile was not. The labial disc and medial lips of second-stage juveniles seemed expanded and sturdy, whereas those of the adult were star-shaped, appeared to be contracted, and softer. These morphological differences in the heads of adult and second-stage juveniles are discussed with respect to their movement.     

The effect of light adaptation on the dynamic properties of phototransduction in the fly,Phormia regina

The static and dynamic characteristics of phototransduction were studied in photoreceptors of the compound eye of the fly Phormia regina (Calliphoridae) using a green light emitting diode driven by a controlled current source. The LED provides sufficiently intense light to investigate the behaviour of the receptors over about half of the dark adapted range of the response versus log intensity curve. The effects of constant adapting light intensities upon the step response and upon the frequency response and coherence functions were examined. Using both methods the effect of light adaptation upon receptor sensitivity can be closely approximated by a similar linear dependence of log sensitivity upon log adapting intensity. However, there was no reliably detectable effect of light adaptation upon the time constant of the response over the range of adapting intensities used.Abbreviation LED Light Emitting Diode     

DARK ADAPTATION AND THE DARK GROWTH RESPONSE OF PHYCOMYCES

Light-adapted sporangiophores of the fungus Phycomyces respond to sudden darkening by a temporary decrease in the rate of elongation, after a latent period of several minutes. The reaction time of this "dark growth" response is compound like that of the "light growth" response. It is, moreover, shorter the more intense the previous illumination. The rate of dark adaptation following adaptation to a very large range of light intensities is found to be proportional to the logarithm of the preceding light intensity. It is shown that a constant amount of dark adaptation takes place before the response occurs. On the assumption that changes in the rate of growth reflect changes in the concentration of a substance which at constant light intensity is in equilibrium with a light-sensitive material, possible equations for such a photostationary state are examined. The most reasonable formulation requires that the partial velocity of the "light" reaction be taken proportional to log I instead of to I directly.     

A pulsed N.M.R study of D2O bound to 1,2 dipalmitoyl phosphatidylcholine

Spin lattice relaxation times in both the lab and rotating frame, have been measured for deuterons (²H) in a number of unsonicated dispersions of 1,2 dipalmitoyl phosphatidylcholine in D₂O over a range of resonant frequencies from 13 MHz to 1 MHz for temperatures from ?20°C to 65°C.The proton (¹H) spin lattice relaxation time for the lecithin was measured for resonant frequencies of 8.5 MHz, and 40 MHz over a similar range of temperatures.The results agree with broadline measurements by Salsbury et al. [1], and for the liquid crystal phase are consistent with an anisotropic tumbling model of the water molecules bound to the lecithin headgroup. This tumbling occurs with correlation times of ≤10^?10 sec and ≈ 10^?6 sec about axes parallel to and perpendicular to the bisector of the D-O-D angle within a D₂O molecule, hydrogen bonded to the negatively charged phosphate headgroup.     

Dynamics of Excitation and Inhibition in the Light-Adapted Limulus Eye in situ

The dynamics of spike discharge in eccentric cell axons from the in situ lateral eye of Limulus, under small sinusoidal modulation of light to which the eye is adapted, are described over two decades of light intensity and nearly three decades of frequency. Steady-state lateral inhibition coefficients, derived from the very low-frequency response, average 0.04 at three interommatidial spacings. The gain vs. frequency of a singly illuminated ommatidium is described closely from 0.004 to 0.4 cps by the linear transfer function s^0.25; this function also accounts approximately for the measured phase leads, the small signal adaptation following small step inputs, and for Pinter's (1966) earlier low-frequency generator potential data. We suggest that such dynamics could arise from a summation in the generator potential of distributed intensity-dependent relaxation processes along the dendrite and rhabdome. Analysis of the dynamic responses of an eccentric cell with and without simultaneously modulated illumination of particular neighbors indicates an effect equivalent to self-inhibition acting via a first-order low-pass filter with time constant 0.42 sec, and steady-state gain near 4.0. The corresponding filters for lateral inhibition required time constants from 0.35 to 1 sec and effective finite delay of 50–90 msec.