Possible involvement of the ampullary electroreceptor system in detection of frequency-modulated electrocommunication signals in Eigenmannia

Behavioral and electrophysiological experiments were conducted to examine whether frequency-modulated electrocommunication signals are detected by the ampullary electroreceptor system in Eigenmannia. First, frequency-modulated electric organ discharges were found to contain a low-frequency component that could be detected by the ampullary system. Second, fish were successfully trained to distinguish a frequency-modulated signal, which contained a low-frequency component as in natural signals, from an artificial signal in which the low-frequency component was eliminated but still modulated in frequency. Subsequently, the trained fish responded without reinforcement to a low-frequency sinusoidal signal which mimicked the low-frequency component in the frequency-modulated signal, suggesting that the fish used the ampullary system to detect frequency modulation. Finally, physiological recording from ampullary afferent fibers demonstrated that they respond to frequency-modulated signals as predicted from the signal's low-frequency component. Electrophysiological study also showed that detection of frequency modulation by the ampullary system is immune to the presence of other constant electric organ discharges. Accepted: 28 June 1998     

Evidence for transmitter operated electrical synapses (TOES) in ampullary electroreceptor organs

Afferent fibres of ampullary electroreceptor organs in electrosensitive fish fire spontaneously, that is, they fire without external stimulus. In the past it has been postulated that the spontaneous activity originates from a sustained level of neurotransmitter release delivered by the electroreceptor cells. The spontaneous activity can be modulated by electrical stimuli. Blocking of the chemical synapse, however, reduces the susceptibility to electrical stimuli to 2% or less, but the spontaneous activity to 60% only. By evaluating existing experimental evidence it is concluded that spontaneous firing of afferents is based on two processes. (1) A membrane bound oscillator, which does not depend on transmitter release, is almost free of frequency fluctuations, and is described by Hodgkin/Huxley-equations (HH-equations). (2) Release of neurotransmitter, which increases the firing level, adds frequency noise, and raises the susceptibility of the afferent to electrical stimuli. There is evidence that neurotransmitter release acts as a gating process, which makes the generator area of the afferents directly accessible to electrical stimuli from the outside. Apparently, the activated synapse behaves as a transmitter operated electrical synapse (TOES).     

Adenosine triphosphatases in electroreceptor organs (ampullary organs and mormyromasts) of Gnathonemus petersii Mormyridae

Summary Cytochemical techniques were used for the light and electron microscopical localization of ATPase in the ampullary organ and the mormyromast, both cutaneous electroreceptors inGnathonemus petersii (Mormyridae).At the light microscope level, two different techniques gave the same results, namely that high concentrations of the enzyme are present in the mormyromast and certain epidermal cells and weak concentrations in the ampullary organ.The enzyme was localized at the ultrastructural level using the lead capture method. It was found in the cytoplasm of type III accessory cells of the ampullary organ, in the apical cytoplasm of SC1 sensory cells and the accessory cells surrounding them and on the membrane of the SC2 sensory cells of the mormyromast. The ATPase of these various cells was inhibited byp-chloromercuribenzoate.The enzyme in the mormyromast SC1 and their accessory cells was not dependent on Mg²⁺ ions. However, that in the type III accessory cells of the ampullary organ and in the SC2 of the mormyromast was strictly dependent on Mg²⁺. In addition, there was a Ca²⁺-dependent ATPase in the microvilli of the SC2 of certain mormyromasts.     

A cross-interval spike train analysis: the correlation between spike generation and temporal integration of doublets

A stochastic spike train analysis technique is introduced to reveal the correlation between the firing of the next spike and the temporal integration period of two consecutive spikes (i.e., a doublet). Statistics of spike firing times between neurons are established to obtain the conditional probability of spike firing in relation to the integration period. The existence of a temporal integration period is deduced from the time interval between two consecutive spikes fired in a reference neuron as a precondition to the generation of the next spike in a compared neuron. This analysis can show whether the coupled spike firing in the compared neuron is correlated with the last or the second-to-last spike in the reference neuron. Analysis of simulated and experimentally recorded biological spike trains shows that the effects of excitatory and inhibitory temporal integration are extracted by this method without relying on any subthreshold potential recordings. The analysis also shows that, with temporal integration, a neuron driven by random firing patterns can produce fairly regular firing patterns under appropriate conditions. This regularity in firing can be enhanced by temporal integration of spikes in a chain of polysynaptically connected neurons. The bandpass filtering of spike firings by temporal integration is discussed. The results also reveal that signal transmission delays may be attributed not just to conduction and synaptic delays, but also to the delay time needed for temporal integration. Received: 3 March 1997 / Accepted in revised form: 6 November 1997     

The electroreceptive ampullary organs of urodeles

The system of lateral-line organs in urodeles was examined by the use of various light- and electron-microscopical techniques. The results show that, in addition to the well-known mechanoreceptive neuromast organs, a second type of receptor can be identified. This second type of organ was presumably seen by earlier workers, but they seemingly failed to point out the distinction between the two organs. The presently described organs are anatomically similar to the ampullary organs of various anamniotic species such as Brachiopterygii, sturgeons, lungfish, and silurids. In all these species the ampullary organs display only one afferent fiber but no efferent innervation and are situated around an ampullary enlargement in or below the epidermis as in urodeles. All ampullary receptors including those of urodeles are very sensitive to weak electrical fields. Similar to the situation in teleosts, the ampullae of urodeles show numerous microvilli but no kinocilia. All other nonteleostean ampullary receptors appear to possess only kinocilia as apical specializations but no microvilli. Current evidence suggests that the electroreceptive ampullary organs are as phylogenetically old as all other vertebrate sensory systems; they are now known to be relatively common among anamniotic vertebrates. Since all ampullary receptors share many common characteristics, it is assumed that they were derived from one phylogenetic precursor but have evolved certain peculiarities in each species not shared by other ampullary receptors.     

Axonal spike generation near the giant neuron soma computed by the Hodgkin-Huxley equation

The behavior of the antidromic spike and the origin of the axonal spike evoked by direct stimulation of the soma were studied with the aid of the Hodgkin-Hexley equation. It is suggested that the mechanisms responsible for electrical excitation of the axon are qualitatively and quantitatively similar to those described by Hodgkin and Huxley for the squid axon. The amplitude of the antidromic spike diminishes rapidly close to the soma. In the example studied, only subthreshod changes of membrane potential take place in the soma. During direct stimulation of the soma the site of primary origin of the axonal spike depends on the strength of the stimulating current. With an increase in its strength the site of primary generation of the spike moves closer to the soma.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 4, pp. 422–427, July–August, 1975.     

Electrical model of the electroreceptor of the ampulla of Lorenzini

On the basis of experimental data [2] a model of electrical processes taking place on the receptor epithelium of the ampulla of Lorenzini was developed. The basic assumption made in the model is that the apical membrane of the receptor cell has a stationary current-voltage characteristic curve with a region of negative resistance. The model explains logically the unusual sign of the spike response of the ampullae (excitation on application of a cathode to the apical surface of the epithelium) and experimental data obtained by various workers [2,7–10], including some concerned with the most complex forms of electrical and spike responses.     

Simulation analysis of effects of adrenaline on spike generation in olfactory receptor cells

Adrenaline is known to affect action potentials induced by the step current injection in an olfactory receptor cell (ORC). It is unclear, however, whether it also modulates action potentials induced by odor stimuli. In the present study, the effects of adrenaline on action potentials in ORCs were investigated quantitatively using a computer simulation. Adrenaline suppressed simulated action potentials induced by step current injection near threshold, and increased spike frequency to strong stimuli by 8-25%. Similar effects were obtained by applying a pseudo-transduction current to a model cell. Surprisingly, adrenaline markedly increased spike frequency to strong stimuli by 30-140%, and increased the slope of the stimulus-response relation compared with that of the step current injection. This suggests that adrenaline enhances odorant contrast in olfactory perception by modulating signal encoding of ORCs.     

The optical spike.

Among the signs of activity in excitable membranes, the action current (electrical spike) has been extensively studied. Recently, a new approach with optical methods has been rewarding. In nerves, a transient, rapid change of light scanning, birefringence and induced fluorescence can be observed during the passage of the action current. These optical effects are synchronous with the electrical spike and are therefore called the optical spikes. Birefringence decreases during excitation in the giant axon of the squid, the walking nerves of Maia, the vagus nerve of the rabbit, but it increases in the olfactory nerve of the pike, which contains 4 million nonmedullated nerve fibres. Light scattering increases or decreases depending on the angle of observation. Vitally stained nerves with fluorescent probes show an increase and a shift in the wavelength distribution of the fluorescent spike.     

Activity of central neurons of the electroreceptor system ofGlyptosternum reticulatum

Two types of electroreceptive neurons — tonic and phasic — were found in acute experiments with extracellular recording of unit activity from the lateral lobes of the medulla in the Turkestan catfishGlyptosternum reticulatum. Tonic neurons were more sensitive to the potential gradient in water (the threshold for most neurons was 1–6 µV/cm) than phasic neurons, they possessed spontaneous activity (mean frequency 4–10 spikes/sec), and their response characteristics depended significantly on the intensity and duration of stimulation. Phasic neurons had no spontaneous activity; their sensitivity was about one order of magnitude lower than that of the tonic neurons, and the response was independent of the parameters of the stimuli. The probable mechanisms of differentiation of neurons into two types, with a possible link with the characteristics of the receptor formations or with the functional organization of the corresponding brain centers, are discussed.     

SARS冠状病毒的刺突蛋白

严重急性呼吸系统综合征(severe acute respiratory syndrome,SARS)是由严重急性呼吸系统综合征冠状病毒(SARS corona-vims,SARS-CoV)引起的呼吸系统疾病。SARS-CoV的刺突蛋白(spike protein)具有S1和S2两个独特的功能结构域,研究发现两者都是进行疫苗和抗体研究的理想和有效的靶点。对非典疫苗的研究生产非常有价值,对预防和治疗SARS也有重大意义。     

Activity-dependent suppression of spontaneous spike generation in the Retzius neurons of the leech Hirudo medicinalis L.

We report on factors affecting the spontaneous firing pattern of the identified serotonin-containing Retzius neurons of the medicinal leech. Increased firing activity induced by intracellular current injection is followed by a ‘post-stimulus-depression’ (PSD) without spiking for up to 23 s. PSD duration depends both on the duration and the amplitude of the injected current and correlates inversely with the spontaneous spiking activity. In contrast to serotonin-containing neurons in mammals, serotonin release from the Retzius cells presumably does not mediate the observed spike suppression in a self-inhibitory manner since robust PSD persists after synaptic isolation. Moreover, single additional spikes elicited at specific delays after spontaneously occurring action potentials are sufficient to significantly alter the firing pattern. Since sub-threshold current injections do not affect the ongoing spiking pattern and PSD persists in synaptically isolated preparations our data suggest that PSD reflects an endogenous and ‘spike-dependent’ mechanism controlling the spiking activity of Retzius cells in a use-dependent way.