F. Bretschneider

Publications

• 3.70

  Impact points

  Spontaneous nerve activity and sensitivity in catfish ampullary electroreceptor organs after tetanus toxin application.

  M.L. Struik, F. Bretschneider, R.C. Peters

  Pflügers Archiv : European journal of physiology. 04/2002; 443(5-6):903-7.

  The functioning of electroreceptor organs of Ictalurus sp. was investigated by inhibiting synaptic transmission by the administration of tetanus toxin in vitro. A piece of Ictalurus skin of about 20 mm diameter was mounted in an Ussing-type chamber. After establishing the normal functioning of the o... [more] The functioning of electroreceptor organs of Ictalurus sp. was investigated by inhibiting synaptic transmission by the administration of tetanus toxin in vitro. A piece of Ictalurus skin of about 20 mm diameter was mounted in an Ussing-type chamber. After establishing the normal functioning of the organ, tetanus toxin (TeTx) was applied basolaterally for 150 min in 66.7 pM and 400 pM concentrations, while the single unit nerve activity was recorded extracellularly. Spontaneous spike activity and the sensitivity of the electroreceptor organs were measured. The results show that TeTx reduces sensitivity to less then 20% of its original value, whereas the spontaneous activity is unaffected by the treatment. This indicates that the afferent nerve is capable of generating impulses independent of receptor cell neurotransmitter release. In the discussion we suggest two alternative mechanisms for the emergence of the spontaneous spike activity.
• 2.20

  Impact points

  Simultaneous measurements of calcium mobilization and afferent nerve activity in electroreceptor organs of anesthetized Kryptopterus bicirrhis.

  M.L. Struik, H.G. Steenbergen, A.S. Koster, F. Bretschneider, R.C. Peters

  Comparative biochemistry and physiology. Part A, Molecular & integrative physiology. 11/2001; 130(3):607-13.

  The transduction pathway of ampullary electroreceptor organs involves ionic currents. It has been shown that calcium, as well as sodium and potassium play important parts in this process. In this study we examine the stimulus-evoked changes in the Fura-2 ratio in electroreceptor cells. Furthermore, ... [more] The transduction pathway of ampullary electroreceptor organs involves ionic currents. It has been shown that calcium, as well as sodium and potassium play important parts in this process. In this study we examine the stimulus-evoked changes in the Fura-2 ratio in electroreceptor cells. Furthermore, we recorded stimulus-evoked Fura-2 ratio changes while Na+ and K+ channels were blocked by amiloride and TEA. Simultaneously, extracellular recordings of the afferent spike activity were made. The results show the presence of stimulus evoked fluctuations in the Fura-2 ratio. These fluctuations can be abolished by the application of Cd2+, TEA, and amiloride. The stimulus-evoked activity of the afferent nerve was decreased due to application of these drugs. We conclude that the transduction current is carried by Na+, K+, and probably Ca2+. This fits the existing model on transduction in electroreceptors.
• 2.22

  Impact points

  Low-dimensional dynamics in sensory biology. 1: Thermally sensitive electroreceptors of the catfish.

  H A Braun, K Schäfer, K Voigt, R Peters, F. Bretschneider, X Pei, L Wilkens, F Moss

  Journal of computational neuroscience. 12/1997; 4(4):335-47.

  We report the results of a search for evidence of periodic unstable orbits in the electroreceptors of the catfish. The function of these receptor organs is to sense weak external electric fields. In addition, they respond to the ambient temperature and to the ionic composition of the water. These qu... [more] We report the results of a search for evidence of periodic unstable orbits in the electroreceptors of the catfish. The function of these receptor organs is to sense weak external electric fields. In addition, they respond to the ambient temperature and to the ionic composition of the water. These quantities are encoded by receptors that make use of an internal oscillator operating at the level of the membrane potential. If such oscillators have three or more degrees of freedom, and at least one of which also exhibits a nonlinearity, they are potentially capable of chaotic dynamics. By detecting the existence of stable and unstable periodic orbits, we demonstrate bifurcations between noisy stable and chaotic behavior using the ambient temperature as a parameter. We suggest that the technique developed herein be regarded as an additional tool for the analysis of data in sensory biology and thus can be potentially useful in studies of functional responses to external stimuli. We speculate that the appearance of unstable orbits may be indicative of a state of heightened sensory awareness by the animal.
• 3.29

  Impact points

  Converging electroreceptor cells improve sensitivity and tuning.

  R.C. Peters, R J Brans, F. Bretschneider, E Versteeg, A Went

  Neuroscience. 12/1997; 81(1):297-301.

  We studied the effect of convergent clustering of ampullary electroreceptor organs on stimulus transduction and transmission in the catfish Icalurus melas by electrophysiologically recording primary afferent activity of single ampullae (singlets) and pairs (doublets) innervated by the same afferent.... [more] We studied the effect of convergent clustering of ampullary electroreceptor organs on stimulus transduction and transmission in the catfish Icalurus melas by electrophysiologically recording primary afferent activity of single ampullae (singlets) and pairs (doublets) innervated by the same afferent. Doublets were twice as sensitive as singlets, and showed sharper tuning around the best frequency. The slope of the phase curve in the doublets was slightly steeper than in the singlets. The spontaneous activity and scatter in interspike interval were not correlated with clustering. The implications of these findings for signal averaging in sensory neurons and their relevance for behaviour are discussed.
• 3.29

  Impact points

  Electrophysiological demonstration of N-methyl-D-aspartate receptors at the afferent synapse of catfish electroreceptor organs.

  G N Andrianov, F. Bretschneider, R.C. Peters

  Neuroscience. 09/1997; 79(4):1231-7.

  An excitatory amino acid, most probably L-glutamate, acts as a neurotransmitter at the receptor cell--afferent fibre synapses in the ampullary electroreceptor organs of the freshwater catfish Ictalurus nebulosus. In the present study, we have used an electrophysiological approach to investigate the ... [more] An excitatory amino acid, most probably L-glutamate, acts as a neurotransmitter at the receptor cell--afferent fibre synapses in the ampullary electroreceptor organs of the freshwater catfish Ictalurus nebulosus. In the present study, we have used an electrophysiological approach to investigate the presence of N-methyl-D-aspartate receptors at this level. N-Methyl-D-aspartate, dissolved in an Mg(2+)-containing (normal) solution, had no effect on afferent activity, not even at 5 mM. However, addition of 5 mM N-methyl-D-aspartate to an Mg(2+)-free solution evoked an enduring increase in firing rate. The application of N-methyl-D-aspartate combined with electrical sine wave stimulation produced a firing increase in the primary afferents, even in the presence of Mg2+ (1.5 mM). Glycine (0.01-0.001 mM) significantly potentiated the N-methyl-D-aspartate responses. Addition of antagonists of the actions of N-methyl-D-aspartate, 7-chlorokynurenic acid, DL-2-amino-5-phosphonovaleric acid and ketamine in concentrations of 0.5-2.0 mM led to a decrease in resting and stimulus-evoked activity. 7-Chlorokynurenic acid also blocked the responses to application of N-methyl-D-aspartate. The glycine agonist D-serine (0.01 mM) prevented the 7-chlorokynurenic inhibitory effect. These results suggest the involvement of N-methyl-D-aspartate receptors in mediating the actions of L-glutamate at the afferent synapses of the electroreceptor organs of the catfish.
• 3.29

  Impact points

  Caffeine reduces the efficacy of electroreceptor cell synapses: an electrophysiological single-unit in vivo study.

  R.C. Peters, E Versteeg, F. Bretschneider, R J Brans, A Went

  Neuroscience. 07/1997; 78(4):1229-38.

  Ampullary electroreceptor organs of catfish, Ictalurus melas, were exposed apically to caffeine solutions at concentrations of 0, 5, 7.5, 10, and 15 mM. Recording sinusoidally-modulated activity of single-unit afferents reveals a dose-dependent decrease in mean afferent activity and sensitivity. A r... [more] Ampullary electroreceptor organs of catfish, Ictalurus melas, were exposed apically to caffeine solutions at concentrations of 0, 5, 7.5, 10, and 15 mM. Recording sinusoidally-modulated activity of single-unit afferents reveals a dose-dependent decrease in mean afferent activity and sensitivity. A rebound effect of average activity occurs after caffeine is washed out. After 25 min exposure to 15 mM caffeine the peak of the gain curve shifts from 8 Hz to 4 Hz. The corresponding phase characteristic shows an increased phase lag with a maximum shift of 35 degrees at 20 Hz. The latency between stimulus and response increases from 12 to 19 ms; the recovery time after onset of the pulse decreases with 60 ms. The most probable explanation for the recorded effects is that caffeine reduces the availability of intracellular Ca2+ by blocking of the inositol triphosphate receptors in the endoplasmic reticulum. This in turn would affect many intracellular properties and processes. The unavailability of Ca2+ could reduce the synaptic efficacy and increase latency by suppressing fusion of synaptic vesicles with the presynaptic membrane and by depressing vesicle transport. The change in frequency response corresponds in part to reduction of the apical membrane surface area of the receptor cells, and in part to the increased latency. Accumulation of glutamate-containing vesicles could account for the higher mean activity and modulation amplitude in the lower frequency range after caffeine is washed out. Caffeine might act postsynaptically by inducing hyperpolarization of the terminals of the primary afferents.
• 3.70

  Impact points

  Periodic firing pattern in afferent discharges from electroreceptor organs of catfish.

  K Schäfer, H A Braun, R.C. Peters, F. Bretschneider

  Pflügers Archiv : European journal of physiology. 02/1995; 429(3):378-85.

  Spontaneous afferent activity was recorded from 26 single ampullary electroreceptive organs of freshwater catfish (Ictalurus nebulosus LeS) at various temperatures. Regular grouping of action potentials was apparent in this secondary sensory system at 35 degrees C and occasionally at 30 degrees C. I... [more] Spontaneous afferent activity was recorded from 26 single ampullary electroreceptive organs of freshwater catfish (Ictalurus nebulosus LeS) at various temperatures. Regular grouping of action potentials was apparent in this secondary sensory system at 35 degrees C and occasionally at 30 degrees C. Impulse groups consisted of up to seven impulses. The precise timing of impulse generation and the temporal sequence of impulses indicated that oscillating processes are involved. Expectation density functions were calculated for records of afferent activity obtained at various temperatures below 35 degrees C. In the majority of records the function was periodic. Impulse grouping and expectation density functions became more distinct in units exhibiting extremely high thresholds (i.e. being insensitive) to electrical stimuli. The results suggest that the oscillations originate from the postsynaptic membrane. The temporal pattern of impulse generation within impulse groups of ampullary electroreceptor organs and of specific warm and cold receptors was compared and found to be similar. Application of cadmium and menthol, which both reduce calcium entry, suppressed spontaneous activity in normal and insensitive electroreceptor systems, attenuated the sensitivity of normal receptors and modified the periodic pattern. This indicates that calcium is implicated in sensory transduction and in postsynaptic mechanisms. The data suggest that an oscillating process is one component of signal transmission in ampullary electroreceptor organs of teleost fish.
• 1.61

  Impact points

  Reduced-carrier single-sideband microscopy F. Bretschneider and PFM Teunis

  F. Bretschneider, PFM Teunis

  Journal of Microscopy. 08/1994; 175(2-175):121-134.

  We have investigated the theoretical and practical properties of different forms of contrast formation in the microscope based on anaxial illumination: so-called single-sideband (SSB) techniques. The use of anaxial illumination in transmitted-light microscopy, as described by Kachar (1985), is by it... [more] We have investigated the theoretical and practical properties of different forms of contrast formation in the microscope based on anaxial illumination: so-called single-sideband (SSB) techniques. The use of anaxial illumination in transmitted-light microscopy, as described by Kachar (1985), is by itself a form of phase contrast (asymmetric illumination contrast, or AIC), but needs enhancement via a video circuit coupled to the microscope. The addition of a partially absorbing mask in a proper, so-called conjugate plane in the microscope, known as a carrier-attenuation filter (CAF), improves contrast substantially. We have tested the imaging properties of this reduced-carrier, single-sideband imaging method (RC-SSB) using the transparent parts of a compact disc (CD), the tracks of which may be used as small objects with a controllable phase shift. In addition, the results have been compared both theoretically and experimentally with Zernike’s phase contrast, and with Nomarski DIC. The SSB technique has been shown to reveal transparent, sub-micron parts of living, unstained tissue, such as microvilli on sensory receptor cells of the transparent catfish, Kryptopterus. The high resolving power, together with the variable spatial-frequency contrast enhancement, makes it a powerful technique for the imaging of in-vivo subcellular details.
• 1.81

  Impact points

  Identification of AMPA receptors in catfish electroreceptor organs.

  G N Andrianov, R.C. Peters, F. Bretschneider

  Neuroreport. 06/1994; 5(9):1056-8.

  Single afferent unit recording in microampullae of the catfish revealed that bath-applied AMPA increases both resting discharge frequency and electrically evoked responses. The potency of AMPA is of the order of 10 microM. DNQX strongly inhibits the excitatory effects of AMPA. The results suggest th... [more] Single afferent unit recording in microampullae of the catfish revealed that bath-applied AMPA increases both resting discharge frequency and electrically evoked responses. The potency of AMPA is of the order of 10 microM. DNQX strongly inhibits the excitatory effects of AMPA. The results suggest the presence of AMPA receptors at the synaptic membrane of ampullary electroreceptor organs in the catfish.
• 2.30

  Impact points

  In vitro electroreceptor organs for pharmacological studies.

  G N Andrianov, F. Bretschneider, R.C. Peters, P F Teunis

  Journal of neuroscience methods. 09/1992; 44(1):1-6.

  Electroreception is a well-established sensory faculty in aquatic vertebrates. The general physiology of the receptor organs is comprehensively documented. The transduction mechanism of the receptor cells and the synaptic transmission mechanism are less well understood. Research has been hampered by... [more] Electroreception is a well-established sensory faculty in aquatic vertebrates. The general physiology of the receptor organs is comprehensively documented. The transduction mechanism of the receptor cells and the synaptic transmission mechanism are less well understood. Research has been hampered by the inaccessibility of the synaptic site. This paper describes how to prepare an in vitro preparation of ampullary electroreceptor organs which allows exposure of both the mucosal and the serosal sides of the receptor cells to superfusion of test solutions. The preparation is quite robust and has been shown to function reliably for more than 8 h. Furthermore, the use of in vitro electroreceptors organs as a model for pharmacological studies is evaluated.
• 3.29

  Impact points

  The emergence of electroreceptor organs in regenerating fish skin and concurrent changes in their transduction properties.

  P F Teunis, W Vredevoogd, C Weterings, F. Bretschneider, R.C. Peters

  Neuroscience. 02/1991; 45(1):205-12.

  The process of regeneration of skin patch denervated empullary electroreceptor organs of the African catfish Clarias gariepinus has been investigated at an ambient temperature of 28 degrees C with both electrophysiological and histological methods. At day 1 after denervation none of the receptor org... [more] The process of regeneration of skin patch denervated empullary electroreceptor organs of the African catfish Clarias gariepinus has been investigated at an ambient temperature of 28 degrees C with both electrophysiological and histological methods. At day 1 after denervation none of the receptor organs on the skin patch showed afferent activity. At this stage none of the ampullary organs previously recorded showed a normal appearance. Degenerative changes consisted of a decreased number of receptor cells and an often invisible lumen. At day 7 regeneration seems to start with a high density of primordial ampullary organs, more than a seven-fold increase compared to controls. In these units, the level of spontaneous activity is very low: compared to controls, more than a two-fold increase in mean interspike interval. At this stage, the sensitivity to electrical stimuli is already at the level of untreated control organs. At day 15 there is a lower, i.e. approximately normal, density of ampullary organs with a normal morphology. In these units both spontaneous firing and sensitivity returned to normal. It can be concluded that the functional dichotomy between spontaneous firing and sensitivity that was found in degenerating ampullary electroreceptor organs is also found during the process of their regeneration, although the underlying cellular changes may be totally different. The speed of recovery suggests that only regeneration of the distal part of the sectioned nerve fibers takes place.
• 3.29

  Impact points

  Quantitative aspects of transduction in an electroreceptor organ studied by means of experimental manipulation of the interspike interval.

  P F Teunis, F. Bretschneider, C van Groeningen, R.C. Peters, J J Bedaux

  Neuroscience. 02/1991; 42(1):283-9.

  The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firin... [more] The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firing threshold of the spike generator, and the scale parameter lambda provides a measure for the input rate of synaptic quanta. Here, we have studied the physiological meaning of the two parameters of the fitted gamma probability density function by manipulating the mean firing rate. This was done in two ways: "frequency clamp" stimulation and a change in temperature. Frequency clamp stimulation, compensating for adaptation of the response, keeps the afferent firing rate at a fixed value for a limited period. We show that within such a period not only the mean spike rate remains constant, but these spike trains can be regarded as renewal series: the spike generator is functionally uncoupled from the frequency-dependent parts of the transduction path. Concerning the gamma parameters, two types of responses are found: at strong excitation lambda increases, r does not change; with small stimuli r is inversely proportional to the stimulus strength, lambda remains unchanged. This is difficult to explain when stimulus transduction acts via the synaptic input rate only. Stimulation seems to influence the firing threshold of the spike generator directly. At strong inhibition a regular firing pattern suddenly takes over; the major part of the variability suddenly disappears from the spike train. A change in temperature causes a shift in lambda (Q10 approximately 2.3), but not in r. This points to a temperature effect on the input rate only.
• 3.29

  Impact points

  Synaptic noise in spike trains of normal and denervated electroreceptor organs.

  P F Teunis, F. Bretschneider, J J Bedaux, R.C. Peters

  Neuroscience. 02/1991; 41(2-3):809-16.

  The sequence of interspike intervals of the spontaneous activity in denervated electroreceptor organs of the catfish is analysed with several statistical techniques: visual inspection of dot displays, interval histograms, serial correlograms, tests for stationary and trends, and tests for renewal pr... [more] The sequence of interspike intervals of the spontaneous activity in denervated electroreceptor organs of the catfish is analysed with several statistical techniques: visual inspection of dot displays, interval histograms, serial correlograms, tests for stationary and trends, and tests for renewal properties, based on the spectrum of intervals. The interspike interval train of primary afferents can usually be treated as a renewal process. Following denervation, a number of non-renewal properties emerge. The interval histogram of the renewal spike trains can be fitted well with a gamma probability density function; non-renewal cases need a more complex approach. We propose that the stochastic fluctuations in interval duration arise from randomly occurring quantal depolarizations (Stein's model of stochastic neuronal excitations. Two important properties with regard to synaptic transduction are: afferent firing results from capture of a limited number of depolarizing quanta; and the quantal input rate and the threshold for firing appear to be correlated.

• Biomonitoring: cadmium deteriorates electro-orientation performance in catfish.

  I S Neuman, C van Rossum, F. Bretschneider, P F Teunis, R.C. Peters

  Comparative biochemistry and physiology. C, Comparative pharmacology and toxicology. 02/1991; 100(1-2):259-62.

  1. Exposure of catfish, Ictalurus nebulosus, to sublethal concentrations of cadmium deteriorates electro-orientation performance. 2. Cadmium, at a concentration of 40 micrograms/l, doubles the behavioural threshold for electric stimuli within 48 hr of exposure; both prolonged exposure and higher con... [more] 1. Exposure of catfish, Ictalurus nebulosus, to sublethal concentrations of cadmium deteriorates electro-orientation performance. 2. Cadmium, at a concentration of 40 micrograms/l, doubles the behavioural threshold for electric stimuli within 48 hr of exposure; both prolonged exposure and higher concentrations result in higher thresholds. The effect is reversible. 3. Electro-orientation performance can be used to monitor the quality of surface water.
• 3.70

  Impact points

  Ampullary electroreceptors in catfish (Teleostei): temperature dependence of stimulus transduction.

  K Schäfer, H A Braun, F. Bretschneider, P F Teunis, R.C. Peters

  Pflügers Archiv : European journal of physiology. 10/1990; 417(1):100-5.

  The response properties of ampullary electroreceptors have been studied in the catfish Ictalurus nebulosus at skin temperatures between 5 and 35 degrees C. A unimodal relationship between spontaneous activity and temperature was obtained. Mean (+/- SEM) peak discharge rate was 57.3 +/- 1.8 impulses ... [more] The response properties of ampullary electroreceptors have been studied in the catfish Ictalurus nebulosus at skin temperatures between 5 and 35 degrees C. A unimodal relationship between spontaneous activity and temperature was obtained. Mean (+/- SEM) peak discharge rate was 57.3 +/- 1.8 impulses s-1 at 25 degrees C; the receptors were active at 5 degrees C (15.0 impulses s-1) and at 35 degrees C (31.5 impulses s-1). There were no dynamic responses to temperature changes in either the warming or cooling direction. The shape of the frequency characteristic depended on temperature: the peak of the gain curve shifted to low frequencies at low temperatures. There was a concomitant change of the phase characteristic: the intersection at zero degree phase angle shifted to higher frequencies with an increase of temperature, thus increasing the lead at lower frequencies and decreasing the lag at higher frequencies. Latency after combined excitatory and inhibitory impulse stimulation was temperature dependent, ranging from 16.4 ms (5 degrees C) to 5.6 ms (35 degrees C). Application of the specific calcium channel blocker menthol (0.2 mM) suppressed spontaneous activity, the effect becoming more prominent at higher temperatures. Sensitivity to sinusoidal electrical stimulation was also impaired, but to a lesser degree and mainly at lower temperatures. We conclude that the filter properties of the receptor organ can be modelled by a band-pass filter in series with a latency, both of which are temperature dependent. These filter properties might be partially based on the activation kinetics of the transduction channels.

• Preliminary observations on the ampullary receptors of Ictalurus sp. (Teleostea, Ictaluridae) after autoplastic skin grafting, with a short note on their electrophysiology.

  P Guarnieri, R.C. Peters, F. Bretschneider, W J Loos, D Anzanel, C Zeni

  Bollettino della Società italiana di biologia sperimentale. 11/1987; 63(10):911-7.

• Transduction at electroreceptor cells manipulated by exposure of apical membranes to ionic channel blockers

  R.C. Peters, R. Zwart, W.J.G. Loos, F. Bretschneider

  Comparative Biochemistry and Physiology Part C: Comparative Pharmacology.

  1. Stimulus transduction in catfish electroreceptors was investigated electrophysiologically during local exposure to low-Ca2+ water and the ionic channel blockers verapamil, bepridil, Cd2+ TTX and TEA.2. Current through receptor cells is not carried by Ca-ions passing through voltage sensitive Ca-c... [more] 1. Stimulus transduction in catfish electroreceptors was investigated electrophysiologically during local exposure to low-Ca2+ water and the ionic channel blockers verapamil, bepridil, Cd2+ TTX and TEA.2. Current through receptor cells is not carried by Ca-ions passing through voltage sensitive Ca-channels in the apical membranes. Ca-channel Mockers act on compartments inside the receptor cells.3. Resting discharge rate and modulation of resting discharge can be manipulated independently. This is inconsistent with the concept that both parameters are controlled by neurotransmitter release only; more receptor cell functions must be involved.

• The actions of L-glutamate and its agonists on the ampullary electroreceptor organs of the catfish Ictalurus nebulosus

  G.N. Andrianov, F. Bretschneider, R.C. Peters

  Comparative Biochemistry and Physiology Part C: Comparative Pharmacology.

  1. Ampullary electroreceptors of the freshwater catfish, Ictalurus nebulosus, were examined for the effects of bath-applied l-glutamate (l-GLU) and its agonists quisqualate (Q), kainate (KA) and n-methyl-d-aspartate (NMDA). Resting discharge rate and stimulus-evoked activity in single afferent fiber... [more] 1. Ampullary electroreceptors of the freshwater catfish, Ictalurus nebulosus, were examined for the effects of bath-applied l-glutamate (l-GLU) and its agonists quisqualate (Q), kainate (KA) and n-methyl-d-aspartate (NMDA). Resting discharge rate and stimulus-evoked activity in single afferent fibers were recorded in an in vitro preparation.2. l-GLU (0.1–1 mM), Q (0.8–40 μM) and KA (10–250 μM) strongly increased both resting activity and stimulus-evoked activity in the afferent fibres. NMDA had no effect, even at a concentration of 5.0 mM.3. The potencies of l-GLU and its agonists, arbitrary defined as the concentrations which gave 50% of maximal frequency increase, were of the order of 7 μM (Q), 25 μM (KA) and 0.6 mM (l-GLU).4. The excitatory effects of l-GLU persisted in receptors suppressed by high Mg2+, indicating that l-GLU was acting at the postsynaptic site.5. The data presented are consistent with our current concept that the action of l-GLU in Ictalurus electroreceptors is mediated via Q/AMPA- and KA-types, but not the NMDA-type, of membrane receptors.

• Quantitative aspects of transduction in an electroreceptor organ studied by means of experimental manipulation of the interspike interval

  P.F.M. Teunis, F. Bretschneider, C. van Groeningen, R.C. Peters, J.J.M. Bedaux

  Neuroscience.

  The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firin... [more] The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firing threshold of the spike generator, and the scale parameter λ provides a measure for the input rate of synaptic quanta.Here, we have studied the physiological meaning of the two parameters of the fitted gamma probability density function by manipulating the mean firing rate. This was done in two ways: “frequency clamp” stimulation and a change in temperature.Frequency clamp stimulation, compensating for adaptation of the response, keeps the afferent firing rate at a fixed value for a limited period. We show that within such a period not only the mean spike rate remains constant, but these spike trains can be regarded as renewal series: the spike generator is functionally uncoupled from the frequency-dependent parts of the transduction path.Concerning the gamma parameters, two types of responses are found: at strong excitation λ increases, r does not change; with small stimuli r is inversely proportional to the stimulus strength, λ remains unchanged. This is difficult to explain when stimulus transduction acts via the synaptic input rate only. Stimulation seems to influence the firing threshold of the spike generator directly.At strong inhibition a regular firing pattern suddenly takes over; the major part of the variability suddenly disappears from the spike train.A change in temperature causes a shift in λ (Q10 ≈ 2.3), but not in r. This points to a temperature effect on the input rate only.

• The emergence of electroreceptor organs in regenerating fish skin and concurrent changes in their transduction properties

  P.F.M. Teunis, W. Vredevoogd, C. Weterings, F. Bretschneider, R.C. Peters

  Neuroscience.

  The process of regeneration of skin patch denervated empullary electroreceptor organs of the African catfish Clarias gariepinus has been investigated at an ambient temperature of 28°C with both electrophysiological and histological methods. At day 1 after denervation none of the receptor organs on t... [more] The process of regeneration of skin patch denervated empullary electroreceptor organs of the African catfish Clarias gariepinus has been investigated at an ambient temperature of 28°C with both electrophysiological and histological methods. At day 1 after denervation none of the receptor organs on the skin patch showed afferent activity. At this stage none of the ampullary organs previously recorded showed a normal appearance. Degenerative changes consisted of a decreased number of receptor cells and an often invisible lumen. At day 7 regeneration seems to start with a high density of primordial ampullary organs, more than a seven-fold increase compared to controls. In these units, the level of spontaneous activity is very low: compared to controls, more than a two-fold increase in mean interspike interval. At this stage, the sensitivity to electrical stimuli is already at the level of untreated control organs. At day 15 there is a lower, i.e. approximately normal, density of ampullary organs with a normal morphology. In these units both spontaneous firing and sensitivity returned to normal.It can be concluded that the functional dichotomy between spontaneous firing and sensitivity that was found in degenerating ampullary electroreceptor organs is also found during the process of their regeneration, although the underlying cellular changes may be totally different. The speed of recovery suggests that only regeneration of the distal part of the sectioned nerve fibers takes place.