P S Wolters

Netherlands Institute for Neuroscience, Amsterdamo, North Holland, Netherlands

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Publications (19)44.09 Total impact

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    ABSTRACT: Cultured neuronal networks from dissociated rat cortical tissue show spontaneous firing activity from about the end of the first week in vitro. Multielectrode recordings have shown slow developmental changes in the firing activity at the individual electrode sites. Here we report that a short period of low-frequency electrical stimulation is able to induce lasting changes in the spontaneous firing activity, significantly larger than developmental changes over similar periods of time.
    Advances in Cognitive Neurodynamics, Edited by R Wang, F Gu, E Shen, 12/2008: pages 53-57;
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    ABSTRACT: Reverberating spontaneous synchronized brain activity is believed to play an important role in neural information processing. Whether and how external stimuli can influence this spontaneous activity is poorly understood. Because periodic synchronized network activity is also prominent in in vitro neuronal cultures, we used cortical cultures grown on multielectrode arrays to examine how spontaneous activity is affected by external stimuli. Spontaneous network activity before and after low-frequency electrical stimulation was quantified in several ways. Our results show that the initially stable pattern of stereotypical spontaneous activity was transformed into another activity pattern that remained stable for at least 1 h. The transformations consisted of changes in single site and culture-wide network activity as well as in the spatiotemporal dynamics of network bursting. We show for the first time that low-frequency electrical stimulation can induce long-lasting alterations in spontaneous activity of cortical neuronal networks. We discuss whether the observed transformations in network activity could represent a switch in attractor state.
    Biophysical Journal 07/2008; 94(12):5028-39. · 3.67 Impact Factor
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    ABSTRACT: To properly observe induced connectivity changes after training sessions, one needs a network model that describes individual relationships in sufficient detail to enable observation of induced changes and yet reveals some kind of stability in these relationships. We analyzed spontaneous firing activity in dissociated rat cortical networks cultured on multi-electrode arrays by means of the conditional firing probability. For all pairs (i, j) of the 60 electrodes, we calculated conditional firing probability (CFP(i,j)[tau]) as the probability of an action potential at electrode j at t = tau, given that one was detected at electrode i at t = 0. If a CFP(i,j)[tau] distribution clearly deviated from a flat one, electrodes i and j were considered to be related. For all related electrode pairs, a function was fitted to the CFP-curve to obtain parameters for 'strength' and 'delay' (i.e. maximum and latency of the maximum of the curve) of each relationship. In young cultures the set of identified relationships changed rather quickly. At 16 days in vitro (DIV) 50% of the set changed within 2 days. Beyond 25 DIV this set stabilized: during a week more than 50% of the set remained intact. Most individual relationships developed rather gradually. Moreover, beyond 25 DIV relational strength appeared quite stable, with coefficients of variation (100 x SD/mean) around 25% in periods of approximately 10 h. CFP analysis provides a robust method to describe the underlying probabilistic structure of highly varying spontaneous activity in cultured cortical networks. It may offer a suitable basis for plasticity studies, in the case of changes in the probabilistic structure. CFP analysis monitors all pairs of electrodes instead of just a selected one. Still, it is likely to describe the network in sufficient detail to detect subtle changes in individual relationships.
    Journal of Neural Engineering 07/2007; 4(2):54-67. · 3.28 Impact Factor
  • Journal of Experimental Social Psychology - J EXP SOC PSYCHOL. 01/2007;
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    ABSTRACT: Networks of cortical neurons were grown over multi electrode arrays to enable simultaneous measu-rement of action potentials from 60 electrodes. All possible pairs of electrodes (i,j) were tested for syn-chronized activity. We calculated conditional firing probability (CFPi,j[τ]) as the probability of an action potential at electrode j at t=τ, given that a spike was detected at i at t=0. If a CFPi,j[τ] distribution clearly deviated from flat, electrodes i and j were considered related. A function was fitted to each CFP-curve to obtain parameters for strength and delay. In young cultures the set of identified relationships changed rather quickly. At 16 days in vitro (DIV) 50% of the set changed within one day. Beyond 25 DIV this set stabilized: during a period of a week more than 50% of the set remained intact. Most individual relationships developed rather gradually. Moreover, beyond 25 DIV relational strength appeared quite stable during periods of ≈ 10 hours, with coefficients of variation (100×SD/mean) of ≈ 25% on average. CFP analysis provides a robust method to describe the stable underlying probabilistic structure of highly varying spontaneous activity in cultured cortical networks. It may offer a suitable basis for plasticity studies, in which induced changes should exceed spontaneous fluctuations. CFP analysis is likely to describe the network in sufficient detail to detect subtle changes in individual relationships. Analysis of data continuously recorded for ≈ 6 weeks, showed that highest stability is reached after ≈ 25 DIV, suggesting the 4th and 5th week as a suitable period for plasticity studies.
    IEEE Transactions on Biomedical Engineering - IEEE TRANS BIOMED ENG. 01/2006;
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    ABSTRACT: When dissociated cortical tissue is brought into culture, neurons readily grow out by forming axonal and dendritic arborizations and synaptic connections. These developing neuronal networks in vitro display spontaneous firing activity from about the end of the first week in vitro. When cultured on multielectrode arrays firing activity can be recorded from many neurons simultaneously over long periods of time. These experimental approaches provide valuable data for studying firing dynamics in neuronal networks in relation to an ongoing development of neurons and synaptic connectivity in the network. This chapter summarizes recent findings on the characteristics and developmental changes in the spontaneous firing dynamics. These changes include long-lasting transient periods of increased firing at individual sites on a time scale of days to weeks, and an age-specific repetitive pattern of synchronous network firing (network bursts) on a time scale of seconds. Especially the spatio-temporal organization of firing within network bursts showed great stability over many hours. In addition, a progressive day-to-day evolution was observed, with an initial broadening of the burst firing rate profile during the 3rd week in vitro (WIV) and a pattern of abrupt onset and precise spike timing from the 5th WIV onwards. These developmental changes are discussed in the light of structural changes in the network and activity-dependent plasticity mechanisms. Preliminary findings are presented on the pattern of spike sequences within network burst, as well as the effect of external stimulation on the spatio-temporal organization within network bursts.
    Progress in brain research 02/2005; 147:173-88. · 4.19 Impact Factor
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    ABSTRACT: Paired organotypic explants from rat occipital cortex were cultured for up to three weeks in the presence of selective blockers of amino acid receptor blockers, during which period spontaneous action potential generation was monitored electrophysiologically. In contrast to isolated explants (Corner, M.A., van Pelt, J., Wolters, P.S., Baker, R.E.and Nuytinck, R.H. (2002) Physiological e.ects of sustained blockade of excitatory synaptic transmission on spontaneously active developing neuronal networks--an inquiry into the reciprocal linkage between intrinsic biorhythms and neuroplasticity in early ontogeny. Neurosci. Biobehav. Rev., 26: 127-185), which upregulated their initially depressed spontaneous bursting activity only under conditions of N-methyl D-aspartate (NMDA) receptor blockade, cross-innervated co-cultures showed a large degree of functional recovery even when combined NMDA and AMPA receptor blockade was carried out. This compensatory activity could be eliminated by acute addition of a selective kainate receptor blocker to the medium. When kainate along with AMPA and NMDA receptor mediated activity was chronically suppressed, however, considerable functional recovery--in the form of recurrent burst discharges--took place gradually over a period of three weeks in vitro. These spontaneous bursts disappeared rapidly upon treatment with the muscarinic receptor blocker, atropine, but continuous low-level firing emerged at the same time. Similar "tonic" background activity was induced in control cultures as well, but without any noticeable reduction in burst discharges. Co-cultured neocortex explants, in which cyto-morphological maturation proceeds to a far greater degree than in isolated explants (Baker, R.E.and van Pelt, J. (1997) Co-cultured but not isolated cortical explants display normal dendritic development: a longterm quantitative study. Dev. Brain Res., 98: 21-27) are evidently capable of an astonishing degree of functional compensation for loss of excitatory synaptic drive during development. It could be shown, furthermore, that such homeostatic responses are not mediated largely by a weakening of inhibitory mechanisms in the absence of spontaneous firing. Chronic inhibitory synaptic blockade, on the other hand, led to intensified bursting activity which gradually normalized over a 3-week culture period. The cellular basis for this reversal of the disinhibited state, as well as for the residual neuronal firing even after cholinergic mechanisms have been largely eliminated, is at present unknown. The degree to which immature cortical networks attempt to compensate for altered levels of physiological activity, as documented in the present report, is another indication of how important such activity can be for normal development (see Corner, M.A., van Pelt, J., Wolters, P.S., Baker, R.E. and Nuytinck, R.H. (2002) Physiological e.ects of sustained blockade of excitatory synaptic transmission on spontaneously active developing neuronal networks-an inquiry into the reciprocal linkage between intrinsic biorhythms and neuroplasticity in early ontogeny. Neurosci. Biobehav. Rev., 26: 127-185).. At the same time, the large variations in overall firing levels and "macro-scale" temporal patterns from culture to culture within a given series, despite all attempts at identical preparation of the explants, can only mean that the "set-points" for such regulation are themselves subject to unknown ontogenetic factors which, apparently, are nonuniformly distributed even within a restricted region of the neocortex. On the other hand, it was striking to note that, regardless of age or treatment, an unexpected degree of consistency in temporal patterning existed at "mini-" and "micro-" time-scales (viz., EEG delta and beta frequency ranges, respectively) even when network bursting tendencies became greatly reduced in favor of tonic firing.
    Progress in brain research 02/2005; 147:231-48. · 4.19 Impact Factor
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    ABSTRACT: Extracellular action potentials were recorded from developing dissociated rat neocortical networks continuously for up to 49 days in vitro using planar multielectrode arrays. Spontaneous neuronal activity emerged toward the end of the first week in vitro and from then on exhibited periods of elevated firing rates, lasting for a few days up to weeks, which were largely uncorrelated among different recording sites. On a time scale of seconds to minutes, network activity typically displayed an ongoing repetition of distinctive firing patterns, including short episodes of synchronous firing at many sites ( network bursts). Network bursts were highly variable in their individual spatio-temporal firing patterns but showed a remarkably stable underlying probabilistic structure (obtained by summing consecutive bursts) on a time scale of hours. On still longer time scales, network bursts evolved gradually, with a significant broadening (to about 2 s) in the third week in vitro, followed by a drastic shortening after about one month in vitro. Bursts at this age were characterized by highly synchronized onsets reaching peak firing levels within less than ca. 60 ms. This pattern persisted for the rest of the culture period. Throughout the recording period, active sites showed highly persistent temporal relationships within network bursts. These longitudinal recordings of network firing have, thus, brought to light a reproducible pattern of complex changes in spontaneous firing dynamics of bursts during the development of isolated cortical neurons into synaptically interconnected networks.
    IEEE Transactions on Biomedical Engineering 12/2004; · 2.35 Impact Factor
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    ABSTRACT: Spontaneous action potentials were recorded longitudinally for 4-7 weeks from dissociated rat occipital cortex cells cultured on planar multi-electrode plates, during their development from isolated neurons into synaptically connected neuronal networks. Activity typically consisted of generalized bursts lasting up to several seconds, separated by variable epochs of sporadic firing at some of the active sites. These network bursts displayed discharge patterns with age-dependent firing rate profiles, and durations significantly increasing in the 3rd week in vitro and decreasing after about 1 month in vitro, when they evolved into short events with prompt onsets. These findings indicate that after about a month in vitro these cultured neuronal networks have developed a degree of excitability that allows almost instantaneous triggering of generalized discharges. Individual neurons tend to fire in specific and persistent temporal relationships to one another within these network bursts, suggesting that network connectivity maintains a core topology during its development.
    Neuroscience Letters 06/2004; 361(1-3):86-9. · 2.03 Impact Factor
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    ABSTRACT: Spontaneous bioelectric activity (SBA) taking the form of extracellularly recorded spike trains (SBA) has been quantitatively analyzed in organotypic neonatal rat visual cortex explants at different ages in vitro, and the effects investigated of both short- and long-term pharmacological suppression of glutamatergic synaptic transmission. In the presence of APV, a selective NMDA receptor blocker, 1-2- (but not 3-)week-old cultures recovered their previous SBA levels in a matter of hours, although in imitation of the acute effect of the GABAergic inhibitor picrotoxin (PTX), bursts of action potentials were abnormally short and intense. Cultures treated either overnight or chronically for 1-3 weeks with APV, the AMPA/kainate receptor blocker DNQX, or a combination of the two were found to display very different abnormalities in their firing patterns. NMDA receptor blockade for 3 weeks produced the most severe deviations from control SBA, consisting of greatly prolonged and intensified burst firing with a strong tendency to be broken up into trains of shorter spike clusters. This pattern was most closely approximated by acute GABAergic disinhibition in cultures of the same age, but this latter treatment also differed in several respects from the chronic-APV effect. In 2-week-old explants, in contrast, it was the APV+DNQX treated group which showed the most exaggerated spike bursts. Functional maturation of neocortical networks, therefore, may specifically require NMDA receptor activation (not merely a high level of neuronal firing) which initially is driven by endogenous rather than afferent evoked bioelectric activity. Putative cellular mechanisms are discussed in the context of a thorough review of the extensive but scattered literature relating activity-dependent brain development to spontaneous neuronal firing patterns.
    Neuroscience & Biobehavioral Reviews 04/2002; 26(2):127-85. · 10.28 Impact Factor
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    R E Baker, P Wolters, J van Pelt
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    ABSTRACT: Dendritic/axonal growth has been examined in long-term organotypic neocortical explants taken from neonatal rat pups and grown either as isolated slices or as co-cultures. The quantitative light microscopic measurement of dendritic and axonal branching patterns within both types of explants was carried out on Golgi-stained materials. Spontaneous bioelectric activity (SBA) was blocked within both types of explants using a combination of APV and DNQX, NMDA and non-NMDA receptor antagonists, respectively. No extracellularly measurable SBA was observed to occur in the silenced explants in the presence of both antagonists but reappeared following wash-out with control medium. In both control and silenced explants, the overall cellular organization of the slice was maintained throughout the culturing period, with distinguishable pyramidal and non-pyramidal neurons located within the same layers and with the same orientations as observed in situ. The major findings of the present study show the following. (i) Pyramidal neurones chronically exposed to APV/DNQX exhibited no basal dendritic growth in co-cultured explants, while growth of apical dendritic lengths was similar to control values in the absence of SBA. (ii) Pyramidal neurones, nonetheless, exhibited significant terminal segment growth under SBA blockade which was correlated with a concomitant decrease in number of basal dendrites. (iii) Axonal growth in co-cultures was not sustained in silenced pyramidal neurones. (iv) Non-pyramidal neurones showed significant total dendritic and axonal growth in co-cultures following APV/DNQX treatment. (v) Non-pyramidal cells in co-cultures experienced an increase in terminal segment length at 2 weeks which declined in the third week. This increase-decrease was correlated with a decrease-increase in the total number of dendritic segments during the second and third weeks, respectively. (vi) In isolated explants the only departure from control growth curves was a significant increase in terminal segment length which was offset by a similar decrease in number of dendritic segments under APV/DNQX growth conditions. Thus the chronic loss of glutamate-mediated SBA differentially effected pyramidal and non-pyramidal neurones in isolated and co-cultured explants, with pyramidal neurones experiencing the more pronounced effects. We conclude that SBA effects the dynamics of neuritic elongation and branching and that these changes are most dramatically seen in co-cultures which cross-innervate one another, presumably via pyramidal axons. We hypothesize that the activity-dependent changes associated with reduction in pyramidal dendritic and axonal growth may be associated with neurotrophin receptor production/maturation.
    Developmental Brain Research 01/1998; 104(1-2):31-9. · 1.78 Impact Factor
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    ABSTRACT: Activity-dependent processes are involved in neurite outgrowth and synaptogenesis. The authors expect that during neural network formation neuronal morphogenesis and synaptic connectivity are reciprocally dependent on the emerging bioelectric activity in the network. The authors want to study whether and how bioelectric activity is involved in the formation of network structure. A multielectrode recording facility has been constructed for the long-term registration of action potentials of individual neurons during network development in both organotypic and dissociated rat cerebral cortex tissue cultures. Long-term recordings of action potentials with good signal-to-noise ratios have been obtained. Experiments to correlate these activity levels with quantitative data on neuronal morphological development are in progress. Uncorrelated periodic fluctuations at a time scale of about ten minutes have been observed
    Engineering in Medicine and Biology Society, 1996. Bridging Disciplines for Biomedicine. Proceedings of the 18th Annual International Conference of the IEEE; 12/1996
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    ABSTRACT: In primary cultures of fetal rat cerebral cortex chronic manipulation of the level and/or pattern of bioelectric activity leads to plastic changes in bioelectric activity, opposite to those seen during the manipulation. This suggests the presence of adaptive mechanisms which regulate functional development in the neuronal network. Since NMDA receptors play an important role in early postnatal bioelectric activity and have been implicated in activity-dependent plasticity in vivo, the involvement of NMDA and non-NMDA receptors in spontaneously occurring bioelectric activity was investigated in cultured rat cerebral cortex by assaying the effects of NMDA and non-NMDA antagonists on neuronal firing. In addition, the physiological consequences of chronic suppression of bioelectric activity were investigated following development in the presence of tetrodotoxin. NMDA receptors appeared at all ages to be more crucial for spontaneous bioelectric activity than non-NMDA receptors, although their relative importance decreased during the first 3 weeks. Whereas the NMDA antagonist APV strongly reduced burst firing, the non-NMDA antagonist DNQX tended to increase burst firing slightly. Following chronic suppression of bioelectric activity, non-variable burst firing was increased, thus replicating previous findings in cerebral cortex culture grown under different conditions. The prominence of NMDA receptor activation in spontaneous bioelectric activity in early cultures suggests a role for these receptors in activity-dependent functional plasticity, as found in vivo.
    International Journal of Developmental Neuroscience 03/1993; 11(1):25-32. · 2.69 Impact Factor
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    ABSTRACT: Changes in neurite outgrowth parameters and in the immunolocalization of the neuronal growth-associated protein B-50 (GAP-43) were studied in cultured neocortex as a function of development. In addition, we studied the effects of chronic blockade of bioelectric activity (BEA) with tetrodotoxin (TTX) on these parameters. Axonal outgrowth rate in control cultures reached a maximum at 8 days in vitro (DIV) and declined to a low level at 21 DIV. B-50 staining shifted from the perikaryon to the axons and growth cones during the first 3 DIV. In axons the intensity of B-50 staining increased towards the growth cone. Within growth cones, the central/basal region and filopodia were intensely stained, whereas lamellipodia showed only marginal staining. Growth cone size gradually decreased after 3 DIV, due to the successive loss of lamellipodia and filopodia, and became club-shaped during the second week, until by 21 DIV growth cones were completely lost, and axons started retracting and degenerated. In the central area of the cultures, growth cones also decreased in size with time, but became stabilized as presynaptic elements onto other neurons. Acute addition of TTX did not affect the outgrowth rate at 6 DIV. Chronic TTX treatment led to an earlier retraction and degeneration of axons than in control cultures and to a loss of B-50-stained cells and varicosities during the third week, but did not affect growth cone morphology or B-50 staining. The regressive phenomena are probably due to an increased neuronal cell death shown to occur after chronic TTX treatment. The developmental changes in axonal elongation rate and growth cone morphology may be related to developmental changes in the content and/or phosphorylation of B-50 (GAP-43, which are studied in the same cultures in the following paper (Ramakers et al. (1991) Int. J. Devl Neurosci. 9, 231-241].
    International Journal of Developmental Neuroscience 02/1991; 9(3):215-30. · 2.69 Impact Factor
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    ABSTRACT: Binding sites for the vasopressin (VP) antagonist d(CH2)5Tyr(Me)VP, were located in various brain areas (e.g. the lateral septum, amygdala, choroid plexus and nucleus of the solitary tract) using light microscopic autoradiography. A number of areas (e.g. suprachiasmatic and arcuate nucleus, pineal gland) which previously showed no VP binding were labelled in the present study. The olfactory nucleus and ventromedial hypothalamic nucleus were not labelled. It therefore appears that d(CH2)5Tyr(Me)VP is capable of discriminating between VP and oxytocin binding sites and a more sensitive means of detecting VP binding sites than VP alone.
    Neuroscience Letters 10/1987; 80(2):121-6. · 2.03 Impact Factor
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    ABSTRACT: An autoradiographical oxytocin (OXT) labeling procedure using frozen, unfixed tissue sections resulted in very dense labeling of the mammary gland. Binding sites for OXT were also found in various forebrain areas, including the hippocampus, especially the ventral subiculum and taenia tecta, central amygdala, posterior part of the anterior olfactory nucleus, claustrum, nucleus accumbens, bed nucleus of the stria terminalis, ventromedial hypothalamic nucleus, and the posterior pituitary. The ependyma of the lateral ventricle and/or the chorioid plexus near the lateral septum was labeled as well. These data support the hypothesis that OXT plays a role in a number of centrally regulated processes.
    Brain Research 01/1986; 359(1-2):320-5. · 2.88 Impact Factor
  • F W Van Leeuwen, P Wolters
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    ABSTRACT: Specific binding sites for arginine-vasopressin (VP) were demonstrated in various major target areas of VP in the rat brain and kidney by light microscopic autoradiography. In the kidney moderate and intense labelling was found in the cortical and medullar areas, respectively. Within the brain intense labelling was shown in the lateral septum, which lends further support to the hypothesis that VP acts as a neurotransmitter. In the hypophysis moderate and heavy labelling was found in the anterior and neural lobes, respectively, which is in agreement with the idea that VP influences hypophyseal functioning.
    Neuroscience Letters 11/1983; 41(1-2):61-6. · 2.03 Impact Factor
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    ABSTRACT: Spontaneous firing rates have been recorded in dissociated rat cortical neuronal networks cultured on multielectrode arrays before and after a period of electrical stimulation. The question was studied whether low-frequency electrical stimulation induces changes in spontaneous firing rates in the period thereafter. It was found that a period of low-frequency stimulation has significant and lasting effects on the spontaneous firing rates at the individual electrodes in the array and, thus, on the total firing rate at all the electrodes. The changes include significant increases and decreases in the spontaneous firing rates, as well as the activation of initially silent neurons, and the silencing of initially active neurons. These findings demonstrate that low-frequency stimulation protocols, as used in the literature for test-ing the effect of high-frequency tetanic stimulation protocols in plasticity studies, may by themselves induce changes in such cultured cortical neuronal networks.

Publication Stats

582 Citations
44.09 Total Impact Points

Institutions

  • 2007–2008
    • Netherlands Institute for Neuroscience
      Amsterdamo, North Holland, Netherlands
    • Universiteit Twente
      • Department of Biomedical Signals and Systems (BSS)
      Enschede, Provincie Overijssel, Netherlands
  • 2004
    • Koninklijke Nederlandse Akademie van Wetenschappen
      Amsterdamo, North Holland, Netherlands
  • 1983–2004
    • Sociaal en Cultureel Planbureau
      's-Gravenhage, South Holland, Netherlands
  • 2002
    • University of Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 1987
    • Maritime Research Institute Netherlands
      Wageningen, Gelderland, Netherlands