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Biomedical subjects

R Budelli

Publications and source records attributed to R Budelli.

At least 19 recordsLinked to original sources
PubMed2006

Peripheral electrosensory imaging by weakly electric fish.

Different species have developed different solutions to the problem of constructing a representation of the environment from sensory images projected onto sensory surfaces. Comprehension of how these images are formed is an essential first step in understanding the representation of external reality by a given sensory system. Modeling of the electrical sensory images of objects began with the discovery of electroreception and continues to provide general insights into the mechanisms of imaging. Progress in electric image research has made it possible to establish the physical basis of electric imaging, as well as methods to accurately predict the electric images of objects alone and as a part of a natural electric scene. In this review, we show the following. (1) The internal low resistance of the fish's body shapes the image in two different ways: by funneling the current generated by the electric organ to the sensory surface, it increases the fields rostrally, thus enhancing the perturbation produced by nearby objects; and by increasing the projected image. (2) The electric fish's self-generated currents are modified by capacitive objects in a distinctive manner. These modulations can be detected by different receptor types, yielding the possibility of "electric color." (3) The effects of different objects in a scene interact with each other, generating an image that is different from the simple addition of the images of individual objects, thus causing strong contextual effects.

Animals↗
PubMed2001

Dynamical behavior of a pacemaker neuron model with fixed delay stimulation.

In physiological and pathological conditions, many biological oscillators, such as pacemaker cells, operate under the influence of feedbacks. Fixed delay stimulation is a standard preparation to evaluate the effects of such influences. Through the study of the Hodgkin-Huxley model, we show that such recurrent excitation can lead to regular and irregular discharge trains with interdischarge intervals that are up to several multiples of the period of the oscillator. In other words, we show that recurrent excitation can considerably slow down the firings of the pacemaker. This result contrasts with previous studies of similar preparations that have reported that fixed delay stimulation leads to a bursting pattern in which regimes of high-frequency firing alternate with periods of quiescence. We elucidate the mechanisms underlying the behavior of the oscillator under fixed delay perturbation through the analysis of the dynamics of a well-known two-dimensional oscillator, namely, the Poincaré oscillator.

Biophysical Phenomena↗
PubMed2000

The electric image in weakly electric fish: perception of objects of complex impedance.

Weakly electric fish explore the environment using electrolocation. They produce an electric field that is detected by cutaneous electroreceptors; external objects distort the field, thus generating an electric image. The electric image of objects of complex impedance was investigated using a realistic model, which was able to reproduce previous experimental data. The transcutaneous voltage in the presence of an elementary object is modulated in amplitude and waveform on the skin. Amplitude modulation (measured as the relative change in the local peak-to-peak amplitude) consists of a 'Mexican hat' profile whose maximum relative slope depends on the distance of the fish from the object. Waveform modulation depends on both the distance and the electrical characteristics of the object. Changes in waveform are indicated by the amplitude ratio of the larger positive and negative phases of the local electric organ discharge on the skin. Using the peak-to-peak amplitude and the positive-to-negative amplitude ratio of this discharge, a perceptual space can be defined and correlated with the capacitance and resistance of the object. When the object is moved away, the perceptual space is reduced but keeps the same proportions (homothetically): for a given object, the positive-to-negative amplitude ratio is a linear function of the peak-to-peak amplitude. This linear function depends on the electrical characteristics of the object. However, there are 'families' of objects with different electrical characteristics that produce changes in the parameters of the local electric organ discharge that are related by the same linear function. We propose that these functions code the perceptual properties of an object related to its impedance.

Animals↗
PubMed1998

Electric fish measure distance in the dark.

Distance determination in animals can be achieved by visual or non-visual cues. Weakly electric fish use active electrolocation for orientation in the dark. By perceiving self-produced electric signals with epidermal electroreceptors, fish can detect, locate and analyse nearby objects. Distance discrimination, however, was thought to be hardly possible because it was assumed that confusing ambiguity could arise with objects of unknown sizes and materials. Here we show that during electrolocation electric fish can measure the distance of most objects accurately, independently of size, shape and material. Measurements of the 'electric image' projected onto the skin surface during electrolocation revealed only one parameter combination that was unambiguously related to object distance: the ratio between maximal image slope and maximal image amplitude. However, slope-to-amplitude ratios for spheres were always smaller than those for other objects. As predicted, these objects were erroneously judged by the fish to be further away than all other objects at an identical distance. Our results suggest a novel mechanism for depth perception that can be achieved with a single, stationary two-dimensional array of detectors.

Animals↗
PubMed1998

The electric image in weakly electric fish: physical images of resistive objects in Gnathonemus petersii.

The present study describes a measurement-based model of electric image generation in the weakly electric mormyrid fish Gnathonemus petersii. Measurements of skin impedance, internal resistivity and fish body dimensions have been used to generate an electrical-equivalent model of the fish and to calculate electrical images and equivalent dipole sources for elementary resistive objects. These calculations allow us to understand how exafferent and reafferent signals are sensed by electroreceptors. An object's electric image consists of the modulation of the transcutaneous voltage profile generated by the fish's own discharge. The results suggest a set of rules for electrolocation: (1) the side of the fish where modulation is larger indicates the side on which the object is situated; (2) the object's position in the electroreceptive field is indicated by the point of maximum modulation of the transcutaneous voltage; (3) the degree of focus of the image indicates the distance to the object. In addition, center-surround opposition originating at pre-receptor level is proposed. Both experimental measurements and modeling indicate that fish skin impedance is relatively low (400-11 000 cm 2 ) and mainly resistive. This low skin impedance appears to enhance the local electric organ discharge modulation, the center-surround effect, the signal-to-noise ratio for electrolocation and the active space for electrocommunication.

Animals↗
PubMed1996

Two-neuro networks. II. Leaky integrator pacemaker models.

The behavior of two pacemaker neurons simulated by leaky integrators and connected reciprocally by synapses was studied. In every case the firing of both neurons phase-locks. The resulting limit cycle may or may not show simultaneous firing of both neurons. When both synapses are excitatory, phase-locking with simultaneous neuronal firing is always present. When one synapse is excitatory and the other inhibitory, phase-locking is also present always, while the neurons may or may not fire simultaneously. For a restricted set of parameters, bistability appears; the initial conditions determine whether or not the limit cycle presents simultaneous firing. When both synapses are inhibitory, the system phase-locks without simultaneous firing for almost every set of parameters.

Biological Clocks↗
PubMed1995

The electric image in weakly electric fish: I. A data-based model of waveform generation in Gymnotus carapo.

Understanding how electrosensory images are generated and perceived in actively electrolocating fish requires the study of the characteristics of fish bodies as electric sources. This paper presents a model of Gymnotus carapo based on measurements of the electromotive force generated by the electric organ and the impedance of the passive tissues. A good agreement between simulated and experimentally recorded transcutaneous currents was obtained. Passive structures participate in the transformation of the electromotive force pattern into transcutaneous current profiles. These spatial filtering properties of the fish's body were investigated using the model. The shape of the transcutaneous current profiles depends on tissue resistance and on the geometry and size of the fish. Skin impedance was mainly resistive. The effect of skin resistance on the spatial filtering properties of the fish's body was theoretically analyzed. The model results show that generators in the abdominal and central regions produce most of the currents through the head. This suggests that the electric organ discharge (EOD), generated in the abdominal and central regions is critical for active electrolocation. In addition, the well-synchronized EOD components generated all along the fish produce large potentials in the far field. These components are probably involved in long-distance electrocommunication. Preliminary results of this work were published as a symposium abstract.

Animals↗
PubMed1991

Two-neurons network. I. Integrate and fire pacemaker models.

The behavior of two pacemakers simulated by integrate and fire oscillators reciprocally connected by synapses is studied. The activation of each synapse produces a sudden potential shift in the post-synaptic neuron. Two sorts of behaviour may occur when at least one synapse is excitatory. Phase-locking occurs for almost every set of parameters, and given certain initial conditions. Repetitive patterns in indifferent equilibrium appear in the presence of a given set of parameters and certain other initial conditions. Quasi-periodic behaviour corresponds to almost every set of parameters when both synapses are inhibitory, although repetitive patterns of firing in indifferent equilibrium occassionally occur.

Biological Clocks↗
PubMed1991

Food anticipatory yawning rhythm in the rat.

The effect of feeding schedules on the daily rhythm in spontaneous yawning activity was studied in high yawning (HY) Sprague-Dawley rats. If the animals are fed ad libitum and changed from a standard 12-12 light-dark (LD) illumination regime to constant light (LL), the normal predark circadian peak in yawning disappears, to be replaced, after 3 weeks, by two or more ultradian smaller peaks in yawning frequency. Restriction of food availability to 2-2:30 regular hours of the day, in rats under LL conditions, leads to the appearance of a significant preprandial (food anticipatory) peak in yawning. A similar eating-fasting daily cycle of 2-22 h in rats under LD conditions determines the disappearance of the pre-dark peak in yawning activity, and a significant shift in higher yawning frequency towards the couple of hours preceding food availability. This result suggests that restricted feeding is more potent than the LD transition in the entrainment of the daily rhythm in yawning activity.

Animals↗
PubMed1990

Serial dependency in the discharge pattern of dorsal spinocerebellar tract neurons: a computer simulation analysis.

We have developed a model in order to analyze the factors eventually responsible for the strong negative serial dependency between successive interspike intervals in the discharge of the Dorsal Spinocerebellar Tract (DSCT) neurons. This dependency is reflected, phenomenologically, by short intervals followed by long ones and, quantitatively, by the first order correlation coefficient (R1-2); which can be lower than -.6 (Jansen, Nicolaysen & Rudjord, 1966; Kröller and Grüsser, 1982). We have found that the lowest values of R1-2 are always related with model parameter values which were very similar to those obtained experimentally. It was observed that EPSP amplitude distribution plays an important role in the discharge patterns of the DSCT neurons. There is one fiber that elicits EPSPs greater than 6 mV, which is responsible for the genesis of the short intervals in the discharge. Long intervals are determined basically by a suprathreshold depolarization and the afterhyperpolarization processes.

Action Potentials↗
PubMed1988

Locking, intermittency, and bifurcations in a periodically driven pacemaker neuron: Poincaré maps and biological implications.

Slowly adapting stretch receptor (SAO) pacemaker neurons, driven with periodic tugs, were analyzed by way of Poincaré mappings (Appendix). Two behaviors were apparent. i) Intermittency characterized previously unclear situations: discharges shifted irregularly between prolonged epochs where spike phases (relative to tugs) and intervals barely changed (slid), and brief bursts with marked variations (skipped). ii) Locking was well-known: phases and intervals remained almost fixed, regardless of the initiation. Changing frequencies, map domains with locking (ordered according to spikes/tugs ratios), alternated with intermittent ones. The best fit for any experimental map was a curve, not straight but certainly unidimensional, continuous and monotonic; it varied characteristically with frequency. This suggested relations called diffeomorphisms, implying periodicity and quasi-periodicity. Outcomes, expanding previous knowledge and meaningful biologically, were i) a precise, exhaustive behavior list (including between behavior transitions) and ii) a thorough understanding or model. This, in turn, provides norms for more specific models (single-variable ones suffice), constraints upon basic mechanisms (one variable, reflecting several real ones combined, should behave as the phase), and forecasts for future experimentation (e.g., unexamined tug frequencies and amplitudes).

Animals↗
PubMed1987

Is GABA an afferent transmitter in the vestibular system?

This study was undertaken to determine the possible role of GABA as an afferent transmitter in the vestibular system of the axolotl. We studied the effects of GABA, muscimol, bicuculline and picrotoxin on the spontaneous spike discharge of the afferent fibers of the sacculi lagena and anterior semicircular canal. It was found that GABA and muscimol produce a very weak excitatory effect which does not mimic either the temporal course or the amplitude of the response of vestibular afferents to physiological stimuli. The GABA antagonist bicuculline has no significant effect on these fibers, and picrotoxin partially blocks the spontaneous activity in 33% of the fibers studied. These results indicate that GABA is probably not an afferent transmitter in the vestibular system as has previously been proposed.

Afferent Pathways↗
PubMed1984

Mechanisms of sensory adaptation in the isolated utricle.

The occurrence of receptor adaptation in utricular afferent fibers is now widely recognized. The experiments reported here explored the basic mechanisms of adaptation at the level of the receptor organ. Spike discharges from single utricular afferent fibers were recorded in isolated labyrinths of an elasmobranch, during three types of stimulation: (a) tilts in the gravity field, (b) vibrations, and (c) electrical polarization delivered through the nerve filaments from which recordings were also made. Experimental evidence supported the conclusion that polarization affects the discharge by acting at the level of the spike triggering mechanism, the point of the afferent fiber at which impulses normally arise. Three types of afferent fibers have been described: Types I and II fire spontaneously and show phasic-tonic responses to tilts. Type III fibers do not have spontaneous activity and respond to tilts in a phasic manner. Adaptation to polarizing currents was observed in all afferent fibers. Type II fibers adapted slowly to vibrations whereas types I and III afferent fibers did not. The functional processes situated near the spike triggering site of the sensory axon is referred to as neural whereas those occurring at earlier stages of transduction are called preneural. Adaptation to tilts exhibited two successive components: an early, fast phase and a late, slow one. Our results suggested that these phases can be related to the mechanisms of preneural and neural adaptation, respectively. Because the time course of adaptation to polarizing currents was similar in different afferent fibers, we concluded that preneural adaptation was the origin of the differences among afferent fibers that allowed their classification into phasic, phasic-tonic, and tonic groups. No attempts were made to separate the influence of mechanical coupling and transduction in the production of preneural adaptation.

Acoustic Stimulation↗
PubMed1984

Is the Na+,K+-ATPase symmetrically distributed in the neuroepithelium of the vestibular system in the axolotl (Ambyostoma mexicanum)?

This study was undertaken to assess the localization of the Na+,K+-ATPase in the neuroepithelial cells of the macula sacculi. In vitro perilymphatic (basolateral) perfusion with ouabain produced a significant drop in the membrane potential. Endolymphatic (apical) application of ouabain had practically no effect on membrane potentials. This suggests that Na+,K+-ATPase is asymmetrically distributed in the neuroepithelial cells.

Acoustic Maculae↗
PubMed1979

Statoacoustic properties of utricular afferents.

1. We classified the utricular afferents on the basis of their spontaneous acitivity and responses to tilts and vibrations. 2. Type I afferents fire spontaneously in a regular pattern; their responses to tilts consist of a phasic-tonic change in firing rate. They may respond to vibrations by increasing or decreasing their rate and show no adaptation. 3. The spontaneous activity and the responses to tilts of type II are similar to those observed in type I afferents. The differences become apparent when the preparation is subjected to a vibrational stimulus, since type II neurons increase their firing rate regardless of the stimulus frequency and show adaptation. 4. Type III neurons have no spontaneous activity. They respond to tilts by firing during the transition from one position to the other. They respond to a vibrational stimulus with maintained firing and show no adaptation. 5. We studied the dynamic responses of each type of neuron. We used sensitivity curves for the study of type III afferents and proposed a statistical method to define gain curves for the study of the other types. 6. The gain curves generated by type I neurons reach their maximum at frequencies of stimulation close to the spontaneous rate of firing. 7. In the gain curves of type II afferents the maximum corresponds to frequencies higher than their spontaneous activity. 8. Sensitivity curves and gain curves give similar results for type III fibers. The sensitivity curves of these afferents were classified into four subtypes. 9. We studied the responses of the three types of afferents to bursts of sinusoidal vibrations. 10. We concluded that the properties of types I and II fibers are fit to carry information about movements and position of the head, but also transmit acoustical information. Type III fibers are more adapted to provide information about acoustical stimuli, but can also convey information about head movements.

Acoustic Stimulation↗
PubMed1978

Multivalued stimulus-response relation in isolated elasmobranch utricles.

The relation between a maintained spatial orientation and the corresponding fully adapted discharge rate was multivalued in all the afferents tonically sensitive to maintained spatial orientation observed in isolated utricles of Rhinobates productus. The spread of rate values was of the order of changes produced by natural tilts. The occurrence of multivaluedness in isolated receptors indicated that peripheral issues are sufficient. Two factors contributed: firstly, the side from which the orientation had been reached (i.e. "hysteresis"): higher adapted rates occurred when the preceding orientation was characterized by lower rates and when the corresponding transition caused acceleration; secondly, "spontaneous" rate variations, some of which resembled markedly, and interacted with, the effects of tilts. It was not possible to identify the basic mechanisms underlying these factors. The multivaluedness in the coding of maintained position, because of its constancy and magnitude, cannot be ignored. It, as well as the sensitivity to fast transients, must be taken into account in utricular models, in evaluations of information transmission, and in psychophysical explorations.

Action Potentials↗
PubMed1978

The generation of resting membrane potentials in an inner ear hair cell system.

1. The macula sacculi in the mudpuppy is an inner ear sensory area accessible for intracellular recordings in vitro and in vivo. 2. The resting potentials recorded in vitro can be explained by the electrodiffusion theory assuming a uniform ionic selective in the membranes of the neuroepithelial cells. 3. The resting potentials recorded in vivo are significantly larger than predicted by the electrodiffusion theory, probably because of an electrogenic metabolic process present in the neuroepithelial cells. 4. An equivalent circuit is proposed to explain the resting electrogenesis in the neuroepithelial cells present in the sensory area.

Animals↗