P F Teunis

Publications of P F Teunis

• Analysis of three-dimensional ciliary beating by means of high-speed stereomicroscopy.

  Authors: P F Teunis, H Machemer

  Biophysical journal. 08/1994; 67(1):381-94.

  Results are presented on the analysis of three-dimensional motion of compound cilia or cirri in voltage-clamped specimens of the protozoan Stylonychia mytilus. Time series of three-dimensional dataResults are presented on the analysis of three-dimensional motion of compound cilia or cirri in voltage-clamped specimens of the protozoan Stylonychia mytilus. Time series of three-dimensional data were obtained by using the anaxial illumination method for simultaneous recording of stereoscopic video images. Data processing involved the following steps: determination of a reference coordinate system based solely on features present in each stereo-pair; tracing of cirral axes in digitized images, conversion to parameter curves by means of least-squares polynomial approximation, conversion of pairs of two-dimensional data to a series of three-dimensional data; correction for distortion due to projective shortening and conversion to a series of polynomial triplets, and analysis of the periodical components of the motion pattern in the frequency domain. Reconstructed beating cycles show typical differences between hyperpolarization-induced ciliary activity and depolarization-induced ciliary activity. Reconstructions of the motion of the basal segment of a cirrus are in agreement with existing data. Analysis of the curvature and torsion of a cirral axis during beating does not reveal any simple pattern of propagated activity within the axoneme. The return stroke may be subdivided into two phases. First, a curvature peak develops proximally. Secondly, a region with increased torsion arises more distally and spreads out in proximal direction. Both curvature and torsion return to minimal values by the beginning of the power stroke.

• 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.

• 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.