The response to monochromatic light flashes of the oxygen consumption of honeybee drone photoreceptors

Local measurements of the fall in oxygen pressure on stimulation of slices of the retina of the honeybee drone by flashes of light were made with oxygen microelectrodes and used to calculate the kinetics of the extra oxygen consumption (delta QO2) induced by each flash. The action spectrum for delta QO2 was obtained from response-intensity curves in response to brief (40 ms) monochromatic light flashes. The action spectrum of receptor potentials was obtained with the same experimental conditions. The two action spectra match closely: they deviate slightly from the photosensitivity spectrum of the drone rhodopsin (R). The deviation is thought to be due to wavelength-dependent light scattering and absorption in the preparation. In these experiments, the visual pigment was first illuminated with orange light, which is known to convert the bistable drone photopigment predominantly to the R state from the metarhodopsin (M) state. When long (300-900 ms) light flashes were used to elicit delta QO2, the responses to different wavelengths could not be matched in time course (as for the short flashes). Flashes producing large R-to-M conversions produced a prolonged delta QO2. The prolongation did not occur after double flashes, which produced both large R-to-M and M-to-R conversions. Similar changes in the length of afterpotentials in the photoreceptor cells and in a long-lasting decrease in photoreceptor intracellular K+ activity were found after long single or double flashes. The results are interpreted to show that the initial event for stimulation by light of metabolism in the drone retina is the same as that for stimulation of electrical responses (i.e., absorption of photons by R). Absorption of photons by M can produce an inhibitory effect on this stimulation.     

Correspondences in the Behavior of the Electroretinogram and of the Potentials Evoked at the Visual Cortex

Electrical potentials from the eye (ERG) and from the contralateral visual cortex were recorded in response to flashes of white and of colored light of various intensities and durations. The evoked potentials were found to parallel the behavior of the ERG in several significant respects. Selective changes in the ERG brought about by increasing the light intensity and by light adaptation led to parallel selective changes in the cortical responses. The dual waves (b₁, b₂) of the ERG were found to have counterparts in two cortical waves (c₁, c₂) which, in respect to changes in light intensity and to light adaptation, behaved analogously to the two retinal components. The responses evoked at high intensity showed only the diphasic c₁-potential. As stimulus intensity was lowered the c₁-wave decreased in magnitude and a delayed c₂-component appeared. The c₂-potential increased in amplitude as light intensity of the flash was further reduced. Eventually the c₂-wave, too, decreased as stimulus reduction continued. There was no wave length specificity in regard to either the duplex b-waves or duplex cortical waves. Both appeared at all wave lengths from 454 mµ to 630 mµ. The two cortical waves evoked by brief flashes of colored light showed all the behavior to changes in stimulus intensity and to light adaptation that occurred with white light.     

ELECTROPHYSIOLOGY OF EXTRAOCULAR PHOTORECEPTORS IN THE SQUID LOLIGO FORBESI(CEPHALOPODA: LOLIGINIDAE)

The electrophysiology of extraocular photoreception in the myopsidsquid, Loligo forbesi Steenstrup 1856 has been examined. Extracellulargenerator potentials were evoked by white light flashes. Intracellularrecordings from extraocular photoreceptor cells in the parolfactorybodies of the squid demonstrated that they had resting potentialsaround –40 mV, and were depolarised by flashes of white,but not red light (>650 nm). The evoked depolarisation consistedof a transient component, followed by a steady plateau component.The amplitude of depolarisation increased with the logarithmof the light intensity and was maintained for the duration ofthe light stimulus. Action potentials were seen in some recordingsand these increased in frequency during light flash stimulation. (Received 11 February 1997; accepted 10 May 1997)     

Bump amplitude,but not latency and time-course,can depend on position of illumination in Limulus photoreceptor cells

Bumps, the responses evoked by single photons in the ventral photoreceptor of Limulus polyphemus, were measured under voltage clamp conditions. The bumps were evoked by illuminating the photoreceptor either with a global flash or a small light spot (diameter about 5 m) which covers only 0.25% of the light-sensitive part of the cell membrane. The light energy of both flash types was adjusted so that each flash on average evoked one bump. Parameters of bumps evoked by local light spots in various membrane areas were compared with those evoked by light flashes which illuminated the whole photoreceptor. The results show that the bump amplitude depends on the location of the illumination. Membrane areas were found where the average value of the bump amplitude was either smaller or larger for a spot illumination than for a whole cell illumination. The latency and the shape (e.g. width) of the bumps does not depend on the location of the illumination.     

Dissociating sensory and cognitive contributions to visual persistence I. Photoreceptor response duration as a function of flash intensity, adaptation state, and candidate code

 Numerous careful behavioral studies of visual persistence have reported a variety of apparently contradictory effects. Variation of flash intensity has particularly been found to have both direct and inverse effects on subjective duration. This conflict has been addressed by theories which contain both sensory and cognitive components. Depending on the weight given to these components, one obtains theories which emphasize intensity dependence or task dependence. Few comparably detailed physiological studies of persistence exist. To clarify the issues raised by these theories, we examined the responses evoked in the model photoreceptor of the Limulus lateral eye. To explore the role of sensory variables, we manipulated adaptation state and flash intensity. To explore cognitive variables, the durations of the photoreceptor potentials (RPs) evoked in this model system were assessed by a mutually complementary and complete set of candidate sensory codes. Accordingly, sharp microelectrodes were used to record RPs intracellularly from single photoreceptor cells in response to 40-ms flashes whose intensity was varied over at least 3.6 log units. Two light adaptation states were used which differed in sensitivity by 3.5 log units. This model system made it possible to employ stringent objective assessments of data quality which ensured that only cells which had remained stable for several hours contributed to the present data. A variety of code-dependent trends were found: direct, inverse, invariant, and U-shaped trends related flash intensity to RP duration, while adaptation state interacted with some of these trends. Only some of the expectations which had generated this research were qualitatively corroborated and numerous quantitative discrepancies were found between data and theory. While caution is necessary when generalizing from neural responses to perception, these data indicate that two major gaps now exist in this field. First, both task and stimulus variables need to be exhaustively explored in more complete behavioral experiments. The present data make it more likely that sensory models and cognitive models simply address different aspects of the same phenomenon. Second, similarly detailed questions need to be posed to more central neural loci, particularly to those in the various visual cortices. Received: 5 July 2000 / Accepted in revised form: 14 February 2001     

The actin-binding interface of a myosin III is phosphorylated in vivo in response to signals from a circadian clock

Class III unconventional myosins are critical for the normal function of auditory hair cells and the function and maintenance of photoreceptors; however, the roles of class III myosins in these sensory cells are unknown. Class III myosins are unique in that they have a kinase domain at their N-terminus; thus, they may have both signaling and motor functions. In the horseshoe crab Limulus polyphemus, enhanced phosphorylation of an abundant, photoreceptor specific class III myosin at night correlates with well-characterized circadian changes in photoreceptor structure and function. Thus, the Limulus visual system may be particularly useful for investigating the properties, modulation, and functions of a class III myosin. Previously, we showed that two sites within the actin interface of full-length Limulus myosin III expressed in baculovirus are substrates for both cyclic AMP-dependent protein kinase and autophosphorylation. In the current study, mass spectrometry was used to show that these same sites are phosphorylated in the endogenous protein extracted from Limulus lateral eye, and that enhanced phosphorylation at these sites occurs in vivo in response to natural circadian clock input to these eyes. These findings demonstrate in vivo changes in myosin III phosphorylation in response to a natural stimulus. This phosphorylation may modulate myosin III-actin interactions.     

Reversal of Photoreceptor Polarity Recorded during the Graded Receptor Potential Response to Light in the Eye of Limulus

Intracellular electrodes were inserted into single photoreceptor units of the excised lateral eye of Limulus, and preparations were selected from which graded receptor potentials of relatively large amplitude could be recorded in response to light stimuli. The experimental data indicated that the graded receptor potential does not arise solely from a collapse of the resting membrane potential of the sensory cells of the eye, since a reversal of polarity of the photoreceptor unit could be demonstrated when the eye was stimulated by light. In the recovery period following stimulation, characteristic changes in the so-called resting potential were recorded. It is suggested that these changes in the so-called resting membrane potential are electrical signs of recovery processes occurring in the photoreceptor, because the potential changes were recorded when the eye was in darkness and because the magnitudes of the potential changes were a predictable function of the intensity and duration parameters of the preceding light stimulus.     

Circadian rhythms in Limulus photoreceptors. II. Quantum bumps

The light response of the lateral eye of the horseshoe crab, Limulus polyphemus, increases at night, while the frequency of spontaneous discrete fluctuations of its photoreceptor membrane potential (quantum bumps) decreases. These changes are controlled by a circadian clock in the brain, which transmits activity to the eye via efferent optic nerve fibers (Barlow, R. B., S. J. Bolanski, and M. L Brachman. 1977. Science. 197:86-89). Here we report the results of experiments in which we recorded from single Limulus photoreceptors in vivo for several days and studied in detail changes in their physiological and membrane properties. We found that: (a) The shape of (voltage) quantum bumps changes with the time of day. At night, spontaneous bumps and bumps evoked by dim light are prolonged. The return of the membrane potential to its resting level is delayed, but the rise time of the bump is unaffected. On average, the area under a bump is 2.4 times greater at night than during the day. (b) The rate of spontaneous bumps decreases at night by roughly a factor of 3, but their amplitude distribution remains unchanged. (c) The resting potential and resistance of the photoreceptor membrane do not change with the time of day. (d) the relationship between injected current and impulse rate of the second order neuron, the eccentric cell, also remains unchanged with the time of day. Thus the efferent input from the brain to the retina modulates some of the membrane properties of photoreceptor cells. Our findings suggest that the efferent input acts on ionic channels in the membrane to increase the sensitivity of the photoreceptor to light.     

Neural response mechanisms in the photoreceptive pineal organ of goldfish

In order to classify the different cell types involved in signal transmission of the photoreceptive pineal organ of the goldfish, Carassius auratus, intra- and extracellular electrical responses were recorded from photoreceptors and second-order neurons. Photoreceptor responses to light consisted of hyperpolarizing potentials up to 30 mV. The responses were graded with intensity and their voltage-intensity relation followed the hyperbolic function V/Vmax = In/In + sigma n. Latencies varied between 500 msec for responses near threshold and 60 msec for supersaturating flashes. The response duration increased up to 60 sec for flashes 2 log units above the saturation level. Action spectra of individual photoreceptors peaked at lambda max = 530 nm and corresponded to measurements of extracellular slow mass potentials or spike potentials. Slow mass potentials exhibited similar characteristics as intracellular recorded photoreceptor potentials with respect to latency, voltage-intensity curves and spectral sensitivity. Ganglion cells showed maintained discharges under conditions of steady illumination. The discharge rate changed inversely with the logarithm of steady illumination over a range of 8 log units. The response to light flashes was purely achromatic and consisted of inhibition of the maintained discharge. The physiological properties demonstrate that the pineal organ of the goldfish is an effective functional photoreceptor organ operating both in dim and in bright light. The light-induced hyperpolarization of photoreceptors lead to an inhibition of the nervous discharge of ganglion cells. The direct flow of information from photoreceptors to ganglion cells is the basic channel of data processing in the goldfish pineal.     

Receiver operating characteristic (ROC) analysis of neural code efficacies

 Nerve cell signals are different in form from the stimuli that evoke them and they exhibit complex spatio-temporal characteristics. This defines a neural coding problem which is addressed by two current theories: Multiple Meaning Theory holds that neural signals contain patterns that make statements about combinations of stimulus properties; the Task Dependence Hypothesis suggests that different features of identical neural signals mediate performance in different behavioral tasks. These coding issues were addressed by investigating the representation of sensory information in the distal nervous system after transduction of visual stimuli into bio-electric signals. The objects of study were light-evoked neural responses which had been intracellularly recorded from single retinula (photoreceptor) cells in Limulus lateral eyes. The efficacies with which sensory information was represented by various candidate neural codes were calculated using receiver operating characteristic (ROC) analyses to provide objective indices. The specific visual problem under investigation was discrimination between light flashes whose intensities differed by a very small amount. A wide range of light adaptation states and relative stimulus intensities were explored. Extremely stringent data quality standards were applied which restricted the investigation to cells whose potentials did not exhibit any statistically significant drift during the hours required for data collection. Seven cellular characterizations were simultaneously monitored to detect drift in a given cell’s potentials; these characterizations included the value of the membrane potential and the values of six candidate codes. These codes were: the area under the light-evoked receptor potential (RP), the mean value of the RP, the peak height of the RP, the slope of the onset of the RP, the duration required for the RP to drop from its peak by a given amount, and the duration required for the RP to end. The results were: (1) Light adaptation increases efficacy. (2) Thus, light adaptation trades sensitivity for acuity (as characterized by ROC discriminations). (3) Increasing relative light flash intensity also increases efficacy. (4) The efficacies of the various codes are significantly different and fall in the following order: area?peak=mean?duration-end=slope= duration-drop. These findings further demonstrate that arbitrary characterizations of stimulus-response relationships are very likely to be incomplete. They particularly indicate that many commonly used and quite conventional neural analysis strategies may substantially underestimate system performance. Received: 21 August 1995/Accepted in revised form: 19 April 1996     

Light-induced changes of sensitivity in Limulus ventral photoreceptors

The responses of Limulus ventral photoreceptors to brief test flashes and to longer adapting lights were measured under voltage clamp conditions. When the cell was dark adapted, there was a range of energy of the test flashes over which the peak amplitude of the responses (light-induced currents) was directly proportional to the flash energy. This was also true when test flashes were superposed on adapting stimuli but the proportionality constant (termed peak currently/photon) was reduced. The peak current/photon was attenuated more by brighter adapting stimuli than by less bright adapting stimuli. The peak current/photon is a measure of the sensitivity of the conductance-increase mechanism underlying the light response of the photo-receptor. The response elicited by an adapting stimulus had a large initial transient which declined to a smaller plateau. The peak current/photon decreased sharply during the declining phase of the transient and was relatively stable during the plateau. This indicates that the onset of light adaptation is delayed with respect to the onset of the response to the adapting stimulus. If the adaptational state just before the onset of each of a series of adapting stimuli was constant, the amplitude of the transient was a nearly linear function of intensity. When the total intensity was rapidly doubled (or halved) during a plateau response, the total current approximately doubled (or halved). We argue that the transition from transient to plateau, light-elicited changes of threshold, and the nonlinear function relating the plateau response to stimulus intensity all reflect changes of the responsiveness of the conductance-increase mechanism.     

Efferent control of temporal response properties of the Limulus lateral eye

The sensitivity of the Limulus lateral eye exhibits a pronounced circadian rhythm. At night a circadian oscillator in the brain activates efferent fibers in the optic nerve, inducing multiple changes in the physiological and anatomical characteristics of retinal cells. These changes increase the sensitivity of the retina by about five orders of magnitude. We investigated whether this increase in retinal sensitivity is accompanied by changes in the ability of the retina to process temporal information. We measured the frequency transfer characteristic (FTC) of single receptors (ommatidia) by recording the response of their optic nerve fibers to sinusoidally modulated light. We first measured the FTC in the less sensitive daytime state and then after converting the retina to the more sensitive nighttime state by electrical stimulation of the efferent fibers. The activation of these fibers shifted the peak of the FTC to lower frequencies and reduced the slope of the low-frequency limb. These changes reduce the eye's ability to detect rapid changes in light intensity but enhance its ability to detect dim flashes of light. Apparently Limulus sacrifices temporal resolution for increased visual sensitivity at night.     

Visual responses in teleosts. Electroretinograms, eye movements, and circadian rhythms.

We have recorded ocular potentials in response to brief flashes of light from two teleosts, the white perch (Roccus americana) and the green sunfish (Lepomis cyanellus). The animals were respired and maintained in an alert state for up to 2 d. Responses were recorded with corneal and transcleral electrodes. The responses of green sunfish were composed of electroretinogram (ERG) and eye movement potentials, whereas the responses in white perch contained only the ERG. Injection of curare abolished the sunfish eye movement potentials, unmasking the ERG. Observation under infrared illumination established a direct relationship between eye movements and the fast potentials which could be abolished by curare. We found no evidence of circadian changes in the amplitude of the ERG b-wave of either species. However, our results combined with those of a previous study of sunfish ocular potentials (Dearry, A., and B. Barlow, Jr. 1987. J. Gen. Physiol. 89: 745-770) suggest that the sunfish visual system exhibits rhythmic changes in oculomotor responses, which appear to be controlled by a circadian oscillator.     

Retrieval of delayed evoked potentials after amygdaloid stimulation

The effect of amygdaloid stimulation on retrieval of delayed evoked potentials recorded in the cortex, mesencephalic reticular formation, lateral geniculate body, and hippocampus was investigated in unanesthetized curarized cats. Delayed evoked potentials were produced to 10–400 combinations of flashes and hypothalamic stimulation and consisted of potentials arising in response to a conditioned stimulus after a delay equal to the interval between it and the unconditioned stimulus. Amygdaloid stimulation facilitated the retrieval of these potentials if they had first been extinguished or had not appeared during initial testing.Institute of Physiology, Academy of Medical Sciences of the USSR, Siberian Branch, Novosibirsk. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 300–304, May–June, 1976.     

Über das optische Auflösungsvermögen der Facettenaugen von Limulus

Summary The resolving power of the human eye and the apposition eye in insects is discussed on the basis of Fraunhofer's diffraction theory. It is then shown that diffraction does not play an important role in the Limulus facet eye. In spite of this the visual fields of neighboured ommatidia overlap strongly as Waterman has shown. A mathematical relation which describes the process of imaging the optical surroundings onto the generator potentials of the excentric cells of the receptors is presented. This relation takes into account the overlap of the visual fields and the logarithmic relation between light intensity and generator potential (MacNichol, Fuortes). On the basis of Hartline and Ratliff's reports on lateral inhibition in the Limulus eye it is shown that this process corrects the overlap and therefore increases the resolving power of the eye. The functional mechanism of lateral inhibition is in principle able to create an image of the optical surroundings in the optic nerve. It therefore can compensate for the dioptric apparatus in front of the receptor mosaic. The correction process in the Limulus eye is studied quantitatively and other cases of principle interest are investigated by means of an analog computer. The results are discussed and other inhibitory processes in the visual and auditory system etc. are mentioned.     

Intracellular optical physiology of the bee's eye

Summary Intracellular optical physiology is a newly developed, non-invasive technique for recording from single types of insect photoreceptor cells. An intact animal is mounted on the goniometer stage of a double-beam, incident-light microspectrophotometer. The stimulating beam delivers monochromatic flashes that evoke pupillary responses from photoreceptor cells in a localized region of the eye. The measuring beam delivers red or infrared illumination that continuously measures the changes in reflectance that accompany the pupillary response. In this paper on the worker bee we demonstrate two experimental conditions under which only one of the three spectral types of photoreceptor dominates the measured response.When the eye is dark-adapted, and increases in reflectance are measured with an infrared beam, threshold responses evoked by long flashes (40 s or more) are dominated by that cell type which is most sensitive to the stimulus. The following data were taken from the dorsal (ventral) poles of the bee's eye: At 350 nm, a quantum flux of 0.1 (0.05)×10 ¹² photons/cm ²/s/numerical aperture of 0.2 produces a threshold response that originates only from the UV-receptors. At 430 nm, a quantum flux of 0.6 (0.2) units produces a threshold response that is dominated by the blue-receptors. At 530 nm, a flux of 1.0 (0.1) units produces a threshold response that originates only from the green-receptors.When the eye is red-adapted, the pupillary responses to short flashes (10 s or less) are dominated by the green-receptors. Under this condition the pupillary action-spectrum for sensitized green-receptors is the same as the electrophysiological spectral sensitivity function of the minimally coupled green-receptor. This is true throughout the spectral range 350 nm–650 nm (Fig. 3).If the duration of stimulating flashes is increased to 40 s, the shape of the action spectrum is unchanged for wavelengths greater than 470 nm, but is significantly elevated, by as much as 1.8 log-units, for wave-lengths less than 420 nm (Fig. 4). In this case the UV-receptors dominate the pupillary response at short wavelengths, while the green-receptors dominate it at long wavelengths.We used these effects to determine that all three spectral types of receptor are present in the regions of both dorsal and ventral poles, as well as in the frontal region of the eye.This work was supported by grants EY01140 and EY00785 from the National Eye Institute, U.S.P.H.S. (to GDB), by the Connecticut Lions Eye Research Foundation (to GDB), and by a grant from the University of Zurich (to RW), and by grant 3.529.075 from the Swiss National Science Foundation (to RW) including a Senior Research Fellowship awarded to GDB. We thank Dr. Thomas Labhart for many helpful discussions and for allowing us to refer to his unpublished data, and Dr. Doekele Stavenga for his critical, constructive comments.     

Auditory responses in the torus semicircularis of the cane toad, Bufo marinus. I. Field potential studies

Field potentials have been recorded in the torus semicircularis of the toad, Bufo marinus, in response to brief tones presented in the free field. The amplitude of the potentials varied with the frequency of the stimulus and location of the electrode along the rostro-caudal axis of the torus. All frequencies in the auditory range evoked largest potentials when the stimulus was located in the contralateral auditory field. Potentials evoked by low to mid frequencies were largest when the stimulus was located near the line orthogonal to the long axis of the animal. For progressively higher frequencies, the optimal stimulus position was progressively more anterior in the contralateral field. In animals in which one eighth nerve had been sectioned, field potentials evoked by tones of low to mid frequency were less sensitive to changes in stimulus direction than in normal animals. However, the directional sensitivity of field potentials evoked by mid to high frequencies was similar in monaural and normal animals. These observations suggest that binaural neural integration is important in determining the directional sensitivity of field potentials in the torus evoked by low to mid frequencies but not for potentials evoked by mid to high frequencies.     

Electrophysiological organization of the eye of Aplysia

The eye of Aplysia californica was studied by electrophysiological and histological methods. It has a central spheroidal lens which is surrounded by a retina composed of several thousand receptor cells which are replete with clear vesicles, pigmented support cells, neurons which contain secretory granules, and glial cells. The thin optic nerve that connects the eye to the cerebral ganglion gives a simple "on" response of synchronized action potentials. Tonic activity occurs in the optic nerve in the dark and is dependent on previous dark adaptation. Micropipette recordings indicate that the ERG is positive (relative to a bathelectrode) on the outer surface of the eye and negative in the region of the distal segments of the receptors. Intracellular recordings show that receptor cells have resting potentials of 40–50 mv and respond to illumination with graded potentials of up to 55 mv. Dark-adapted receptors exhibit discrete bumps on the graded response to brief light flashes. Other elements in the retina that do not give large graded responses fall into two classes. One class responds to illumination with action potentials that are in synchrony with the extracellularly recorded compound optic nerve potentials. The other class is tonically active and is depolarized or hyperpolarized and inhibited upon illumination. It is apparent that complex excitatory and lateral inhibitory interactions occur among the elements of the retina.     

Sensory evoked potentials in unanesthetized unrestrained cuttlefish: a new preparation for brain physiology in cephalopods

Summary Up to five microelectrodes inserted through short hypodermic needles in the cranial cartilage of Sepia officinalis recorded potentials while the cuttlefish moved freely in a small enclosure. Compound field potentials and unit spikes were seen during ongoing, spontaneous activity and after sensory stimulation.Ongoing activity resembles that reported for octopus, with maximum power usually below 20 Hz. Amplitude varies greatly but has not been seen to shut off or turn on abruptly and globally as in octopus.Evoked potentials, focally large after flashes of light consist of several waves; the first is largest, positive and peaks at ca. 35 ms (called P35), followed by ca. P75, P95, N110 and smaller waves or oscillations lasting more than 0.5 s. The Upper Following Frequency (highest flashing rate the potentials can follow 1:1), without averaging, is >15 flashes/s (20–22 °C); at 20/s the 11 following lasts for 1 or 2 s. The Lower Fusion Frequency of averaged responses is < 30/s. Gentle tapping of the tank wall evokes local, brief, fast potentials. No responses have been found to loud air-borne clicks and tone bursts with principal energy at 300 Hz or to electric fields in the bath at 50–100 V/cm.In a few loci relatively large slow Omitted Stimulus Potentials have been seen following the end of a train of flashes at more than 5/s; these are by definition event related potentials and a special, central form of OFF response.Abbreviations EP evoked potential - ISI interstimulus interval - OSP omitted stimulus potential - VEP visual evoked potential