R.C. Peters

Publications of R.C. Peters

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

  Authors: 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 20The 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.

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

  Authors: 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 thisThe 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.

• The electroreceptor organ of the catfish, Ictalurus melas, as a model for cisplatin-induced ototoxicity.

  Authors: R.C. Peters, P M Mommersteeg, P S Heijmen

  Neuroscience. 02/1999; 91(2):745-51.

  The ototoxic side-effects of the anti-cancer drug cisplatin (cis-diaminedichloroplatinum) have been widely investigated. However, the exact site of action remains unclear. In this study, theThe ototoxic side-effects of the anti-cancer drug cisplatin (cis-diaminedichloroplatinum) have been widely investigated. However, the exact site of action remains unclear. In this study, the electroreceptor organ of the freshwater catfish Ictalurus melas is used as a model for examining the acute effects of cisplatin. The sensory cells in the electroreceptor organ are homologous to the inner hair cells in the cochlea of mammals. The effects of cisplatin administration can be investigated by in vivo recording of the spike trains from the electroreceptor organ primary afferents. Exposure of electroreceptor organs to 330 microM cisplatin for 1 h causes the spontaneous activity to drop, the overall sensitivity to diminish and the shape of the frequency characteristics to change. These effects persist in the week after administration. Control levels have returned at day 22. These results demonstrate an acute and, with considerable hysteresis, reversible cisplatin effect on the electroreceptor organs, which is to a large extent consistent with the cisplatin-induced effects in isolated hair cells in mammals. The time-course of the effect supports the hypotheses that ion channels are blocked immediately by cisplatin administration, and that cisplatin metabolites disturb enzymatic cellular processes.

• Converging electroreceptor cells improve sensitivity and tuning.

  Authors: 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 primaryWe 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.

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

  Authors: 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 catfishAn 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.

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

  Authors: 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 ofAmpullary 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.

• The effect of hyperosmotic treatment on the functioning of ampullary electroreceptor organs.

  Authors: P S Heijmen, A Boele, R.C. Peters

  Neuroscience. 07/1996; 72(4):1107-15.

  The condition of the microvilli of the apical membrane in ampullary electroreceptor organs of the freshwater catfish, Ictalurus nebulosus, was manipulated by administration of hyperosmotic solutionsThe condition of the microvilli of the apical membrane in ampullary electroreceptor organs of the freshwater catfish, Ictalurus nebulosus, was manipulated by administration of hyperosmotic solutions (500 mM) in order to investigate to what extent the apical surface area determines the sensitivity and the shape of the frequency curves. Electrophysiological recordings demonstrated that hyperosmotic sucrose and glucose solutions reduce the sensitivity by 80%, and alter the shape of the frequency curves. The synaptic delay and the average spontaneous activity remained almost unchanged. Calculations with an equivalent electric circuit of an electroreceptor cell indicate that a reduction in apical surface area can account for these effects. Apparently, the sensitivity and the frequency curves in ampullary organs in freshwater catfish depend on the apical surface area. A hyperosmotic urea solution proved to be less suitable to investigate the effect of manipulations of the apical surface area. The almost total loss in sensitivity caused by administration of urea is caused by both shunting of the stimulus by leaky tight junctions and a reduced synaptic efficacy. The repetitive activity observed after exposure to glucose or sucrose must be attributed to malfunctioning of postsynaptic parts of the receptor organ.

• Vincristine disturbs spontaneous firing of the afferent nerve fibre in ampullary electroreceptor organs.

  Authors: P S Heijmen, D Kalmeijer, R.C. Peters

  Neuroscience. 06/1996; 72(2):585-91.

  Ampullary electroreceptor organs of the catfish were apically exposed to 0.3 mM vincristine in order to investigate the part played by the microtubular system in stimulus transduction. The mainAmpullary electroreceptor organs of the catfish were apically exposed to 0.3 mM vincristine in order to investigate the part played by the microtubular system in stimulus transduction. The main effects were repetitive firing of the afferent fibre, a reduction of the mean spontaneous activity and a reduction of the spike amplitude two to four days after exposure to vincristine. The mean sensitivity was less susceptible to vincristine than the spontaneous activity. Since the shape of the frequency curves remained unchanged and similar effects as described above were also observed after denervation, we conclude that vincristine most likely does not affect electroreceptor cell functioning, but causes degeneration of the afferent fibre.

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

  Authors: 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 actionSpontaneous 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.

• Identification of AMPA receptors in catfish electroreceptor organs.

  Authors: 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 ofSingle 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.

• In vitro electroreceptor organs for pharmacological studies.

  Authors: 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 receptorElectroreception 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.

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

  Authors: 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 withThe 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.

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

  Authors: 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 gammaThe 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.

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

  Authors: 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 dotThe 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.

  Authors: 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 the1. 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.

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

  Authors: 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 spontaneousThe 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.

• Resting discharge and sensitivity of ampullary electroreceptors in Clarias gariepinus related to convergence ratio during ontogeny.

  Authors: R C Peters, S van Ieperen

  Brain, behavior and evolution. 02/1989; 34(1):43-7.

  The ampullary electroreceptor organs of the teleost fish Clarias gariepinus converge to single afferent neurons. During the first 4 months of ontogeny the convergence ratio (CR) increases from 1 toThe ampullary electroreceptor organs of the teleost fish Clarias gariepinus converge to single afferent neurons. During the first 4 months of ontogeny the convergence ratio (CR) increases from 1 to 3. Extracellular single-unit recordings show that a 3-fold increase in CR results on average in a 3.6-fold increase in sensitivity measured at stimulus frequencies of 2, 8 and 20 Hz, and in a small but significant 1.1-fold increase in resting discharge. Adaptation of the primary afferents could account for the differences between changes in sensitivity and resting discharge.

• Denervation reveals two components of neurotransmission in electroreceptor synapses.

  Authors: R.C. Peters, E.L. Groen, M.M. van der Sluis, P F Teunis, K.A. Wilhelm

  Neuroscience. 01/1989; 27(3):1049-53.

  Denervation-induced changes in the synaptic efficacy of single electroreceptors in catfish (Ictalurus nebulosus, Teleostei) were studied in vivo under alfadolone anaesthesia. At 16 degrees C theDenervation-induced changes in the synaptic efficacy of single electroreceptors in catfish (Ictalurus nebulosus, Teleostei) were studied in vivo under alfadolone anaesthesia. At 16 degrees C the following effects were found 48 h post-operatively: (1) the average amplitude of the extra-dermally recorded spikes decreased from 100 to less than 20 microV; (2) the average resting discharge decreased from 40 to less than 25 spikes/s; (3) neither the sensitivity nor the frequency characteristic changed. The results indicate that the resting discharge and the modulation mechanism of sensory synapses are controlled by different biochemical mechanisms. The resting discharge seems to be related to the trophic function of the afferent nerve and to its generator region, whereas the modulation mechanism is apparently associated with the receptor cell.

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

  Authors: 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.

• Fish electroreception as a model for vincristine-induced neuropathies and a possible preventive role for Org 2766 treatment

  Authors: I.S.A. Neuman, P.S. Heijmen, R.C. Peters, G.S.F. Ruigt

  Comparative Biochemistry and Physiology Part C: Comparative Pharmacology.

  1. Subcutaneous injection of vincristine (more than 3 μg) in the catfish, Ictalurus nebulosus, produces a black spot on the skin with a grey surround. Doses between 1 and 3 μg give a less pronounced1. Subcutaneous injection of vincristine (more than 3 μg) in the catfish, Ictalurus nebulosus, produces a black spot on the skin with a grey surround. Doses between 1 and 3 μg give a less pronounced discolouration.2. Two to three days after injection of 5 μg vincristine, repetitive activity is detected in primary afferents of unstimulated electroreceptor organs close to the site of injection.3. Vincristine increases the phase-lag of the modulation of afferent activity in electroreceptor organs during electrical stimulation without a clear effect on the sensitivity of catfish electroreceptor organs.4. The amplitude of the action potentials of the primary afferents begins to decrease after 2 days; after3 days they gradually disappear in the background noise.5. Application of Org 2766, a potentially neurotrophic compound, at 2 days, but not 1 day, before vincristine application prevents vincristine effects on the phase shift.6. Preliminary electron-microscopical studies of the synapse shows a severe depletion of glycogen granules in the afferent nerve fibre after vincristine application,7. It is concluded that electroreceptor organs can be used to study neuropathies caused by vincristine, and that Org 2766 may be useful for preventive treatment of such neuropathies.