Meroplankton dynamics in a saline,turbulent, turbid shallow lake (Neusiedlersee,Austria and Hungary)

Phytoplankton species composition, horizontal distribution, seasonal- and long-term dynamics are investigated in relation to some environmental factors, based on about 700 samples taken between 1968 and 1992 in the shallow, turbid, turbulent, saline Neusiedlersee (Austria/Hungary). We deduced:

1. The phytoplankton is relatively poor in species which is attributable to high salinity and turbidity. Blue-green algae of picoalgal size, meroplanktonic diatoms, green algae either with gelée or elongated form are the most important groups in the plankton;
2. No consequent horizontal differences in the distribution of phytoplankton biomass were found; the high contribution of diatoms (69%) and green algae (22%) is characteristic;
3. Despite the low percentage contribution (0.54%) of phytoplankton dry weight in total seston, the two variables correlate closely because of simultaneous resuspension after wind actions. The prevalence of both low phytoplankton/seston ratio and significant correlation between these two variables is indicative to the presence of a meroplankton;
4. Phytoplankton biomass, especially that of diatoms, varies within wide limits in the short term as a combined effect of growth/loss, transport by horizontal water currents and periodic resuspension from the sediment surface. Diatoms like Fragilaria, Surirella and Campylodiscus are involved especially. Parameters of population dynamics (growth rate, annual cycles, length of stationary phases, standing crop) were estimated based on moving averages. Growth rates were smaller than those of ‘normal’ planktonic species; however, the similarities of seasonal pattern suggest that the carrying capacity of the lake is very constant;
5. Picoalgal biomass is very high in the lake; its contribution to total biomass can exceed 75%, especially in spring. The large cellular chlorophyll a content of Neusiedlersee's phytoplankton can most probably be explained by this high picoalgal standing crop, which is not included in the routine biomass estimations;
6. Concerning long-term changes of phytoplankton, periodic appearances and disappearances are very characteristic. Annual average biomass of most species is growing for several (3–5) years, then declining with a similar rate and these periods are recurrent. Climatic drying-out periods, during which water level lowers, conductivity increases, nutrients and their ratios change following trend-like periodicities, and they are supposed to be responsible for the observed longterm periodicity of dominant species. An increased nutrient load in the seventies was superimposed on this cyclicity;
7. Most of the species can be found in smaller or larger amounts in the littoral microhabitats (canals, inner ponds) of the lake in periods when they are absent or very rare in the open water. Thus, these littoral microhabitats play a very important role in the survival and recruitment of planktonic populations to the open water.

     

Phytoplankton biomass and chlorophyll-a in some shallow lakes in central Europe

Based on 388 parallel data of phytoplankton biomass and chlorophyll-a of two shallow lakes and two ponds, the following results were obtained:

1. Relative chlorophyll-a content of phytoplankton biomass varied between 0.08–1.88%; chlorophyll-a concentration showed great differences among lakes.
2. Significant correlations (r = 0.68–0.92) were established between phytoplankton biomass and chlorophyll-a concentration. The regression in the artificial ponds was non-linear.
3. In parallel with the increase of average cell volume, a decrease in relative chlorophyll-a content was observed. A significant correlation (r = + 0.83) between the two variables was found. Relative chlorophyll-a content of phytoplankton is a log-function of average cell volume.

     

Effects of Environmental Perturbations on Short-Term Phytoplankton Production off Lawson's Bay,A Tropical Coastal Embayment

1. The phytoplankton cycle off Lawson's Bay, Waltair follows a bimodal pattern with a major peak during March–May; a minor peak during October–November months and with a low production during the summer months i.e., June–August.
2. During the summer months of 1957, 1958, 1960 and 1962 dumping of dredged spoil from the entrance channel of the harbour into the sea resulted in a natural enrichment of waters.
3. Following this enrichment, there was a qualitative and quantitative increase in the phytoplankters thus leading to the development of a bloom.
4. Only Thalassiosira subtilis and Chaetoceros curvisetus commonly bloomed during the four years.
5. The increase in gross production which varied from 3–13 fold and the high photosynthesis-respiration ratios 5.1 to 10.5 indicated that the bloom populations were in a healthy state.
6. The decrease of the populations to the initial levels suggests that some unknown factor, other than those investigated must have been operating.
7. Consequences of eutrophication of different origins on stimulation of phytoplankton production are briefly discussed.

     

Morphological and physiological properties of pheromone-triggered flipflopping descending interneurons of the male silkworm moth,Bombyx mori

1. The morphology of descending interneurons (DNs) which have arborizations in the lateral accessory lobe (LAL) of the protocerebrum, the higher order olfactory center, and have an axon in the ventral nerve cord (VNC), were characterized in the male silkworm moth, Bombyx mori.
2. Two clusters (group I, group II) of DNs which have arborizations mainly in the LALs were morphologically characterized. The axons of these DNs are restricted to the dorsal part of the each connective (Figs. 1–5).
3. Pheromonal responses of the group I and group II DNs were characterized. Flipflopping activity patterns, which have two distinct firing frequencies (high and low) in response to sequential pheromonal stimulation, were usually recorded (Figs.6–10).
4. Two types of flipflopping activity patterns were classified into those that had an antiphasic relationship (called the ‘FF’ type) between the left and right connectives and those with a synchronized relationship (‘ff’ type) (Figs. 8–12). We propose that some group II DNs show ‘FF’ flipflopping activity patterns (Fig. 10).
5. A state transition was usually elicited by less than 10 ng bombykol, the principal pheromone component. Extra impulses were elicited during constant light stimulation (Fig. 9).
6. Our results suggest that the LAL olfactory pathways might be important for producing flipflopping activity patterns (Fig. 11).

     

Succession in Zoo- and phytoplankton in a sewage stabilization pond

The investigations pertaining to zoo- and phytoplankton succession during prestabilization and stabilization of domestic waste water in a facultative pond operating at 1.22 meters depth with an average BOD loading of 336.3 kg per hectare per day and a retention period of 10 days revealed the following:

1. A photosynthetic sulphur bacterium Thiocystis violacea has been recorded during the second and third day along with a considerable population of ciliate protozoa and algae.
2. Chlorophytes were followed by euglenoids in the ecological succession and the latter became predominant after the pond stabilized.
3. Of the twelve protozoan species Halteria grandinella, Bursaria truncatella and Perispira ovum were associated with peaks of algae and vigorous photosynthesis in the stabilized pond water.
4. There ia a gradual improvement in the quality of the waste water with respect to reduction in bacteria and biochemical oxygen demand and enhancement in changes in physico-chemical factors till a relatively stable community is evolved.

     

Relationship between extracellular and cellular production in the sulphuric green bactreium Chlorobium limicola Nads. (Chlorobacteriaceae) as compared to primary production of phytoplankton

1. The authors examined the relationship between extracellular production of green hydrosulphuric bacteria (Chlorobium limicola Nads) and extracellular production of phytoplankton using radioactive carbon. Dark assimilation of carbon was also taken into consideration.
2. Mean values of extracellular production of phytoplankton were 58.40% (stand II) and 65.2% (stand I) of cellular production, and for extracellular production of Chlorobium limicola the values were respectively 44.7% (stand II) and 70.7% (stand I). On average 70.8% of carbon assimilated in the dark filtered outside the cell in case of phytoplankton, and 31.0%-in case of Chlorobium limicola.
3. Extracellular and cellular production in case of phytoplankton and Clorobium limicola was calculated for 1 square metre of the water column.

     

Response characteristics of wide-field non-habituating non-directional motion detecting neurons in the optic lobe of the locust,Locusta migratoria

1. Extracellular recordings from wide-field nonhabituating non-directional (ND) motion detecting neurons in the second optic chiasma of the locust Locusta migratoria are presented. The responses to various types of stepwise moving spot and bar stimuli were monitored (Fig. 1)
2. Stepwise motion in all directions elicited bursts of spikes. The response is inhibited at stimulus velocities above 5°/s. At velocities above 10°/s the ND neurons are slightly more sensitive to motion in the horizontal direction than to motion in the vertical direction (Fig. 2). The ND cells have a preference for small moving stimuli (Fig. 3).
3. The motion response has two peaks. The latency of the second peak depends on stimulus size and stimulus velocity. Increasing the height from 0.1 to 23.5° of a 5°/s moving bar results in a lowering of this latency time from 176 to 130 ms (Fig. 4). When the velocity from a single 0.1° spot is increased from 1 to 16°/s, the latency decreases from 282 to 180 ms (Figs. 5–6).
4. A change-of-direction sensitivity is displayed. Stepwise motion in one particular direction produces a continuous burst of spike discharges. Reversal or change in direction leads to an inhibition of the response (Fig. 7).
5. It shows that non-directional motion perception of the wide-field ND cells can simply be explained by combining self-and lateral inhibition.

     

Polarization sensitivity in crayfish lamina monopolar neurons

1. Polarization sensitivity (PS) was examined in photoreceptors and lamina monopolar cells (LMCs) in two species of crayfish, Procambarus clarkii and Pacifasticus leniusculus. The measurements were made with intracellular recordings and broad field illumination.
2. PS is about 40% greater in Pacifasticus than in Procambarus (Table 1). In both species the LMC stationary PS profiles (estimated with flashes) are similar to those of receptors (Figs. 1 and 2). Both receptor and LMC sensitivity profiles are well described by cos² θ functions (Fig. 3). PS was observed in all receptors and 78% of LMCs.
3. When stimulated with a rotating polarizer, receptors and LMCs exhibit membrane potential modulation with phase predicted by the stationary PS profile (Fig. 5). In photoreceptors, the polarization-elicited percent modulation falls off steeply as intensity increases. The LMC modulation is stronger than that in receptors and relatively insensitive to the mean intensity (Figs. 6 to 8). For low intensities the LMC modulation is 100%. The LMC dynamic behavior is consistent with either an opponency mechanism or strong but polarization-insensitive lateral inhibition.
4. Receptors and LMCs exhibit steady-state differential sensitivity to stationary e-vector orientation (Fig. 9).
5. About 10% of the LMC neurons exhibit PS maxima separated by 90°. These results imply a nonlinear summation of signals from orthogonal receptor channels (Fig. 10).

     

Wind-evoked evasive responses in flying cockroaches

1. A standing cockroach (Periplaneta americana) responds to the air displacement made by an approaching predator, by turning away and running. The wind receptors on the cerci, two posterior sensory appendages, excite a group of ventral giant interneurons that mediate this response. While flying, these interneurons remain silent, owing to strong inhibition; however, the dorsal giant interneurons respond strongly to wind. Using behavioral and electromyographic analysis, we sought to determine whether flying cockroaches also turn away from air displacement like that produced by an approaching flying predator; and if so, whether the cerci and dorsal giant interneurons mediate this response.
2. When presented with a wind puff from the side, a flying cockroach carries out a variety of maneuvers that would cause a rapid turn away and perhaps a dive. These are not evoked if the cerci are ablated (Figs. 4, 5, 6).
3. This evasive response appears to be mediated by a circuit separate from that mediating escape when the cockroach is standing (Fig. 7).
4. The dorsal giant interneurons respond during flight in a directional manner that is suited to mediate this behavior (Fig. 8).
5. Recordings of the wind produced by a moving model predator (Fig. 9), together with measurements of the behavioral latency of tethered cockroaches, suggest that the evasive response would begin just milliseconds before a predator actually arrives. However, as explained in the Discussion section, under natural conditions, the evasive response may well begin earlier, and could indeed be useful in escaping from predators.
6. If cockroaches had a wind-mediated yaw-correcting behavior, as locusts have, this could conflict with the wind-evoked escape. In fact, cockroaches show the opposite, yaw-enhancing response, mediated by the cerci, that does not present a conflict with escape (Figs. 10–14).

     

An analysis of amino acid composition of a few oxidoreductases by different methods

1. All methods used to analyze amino acid composition of different enzymes agree well with each other.
2. They lead to a relationship between amino acid composition and function of proteins.
3. Cytochrome oxidase is in a class by itself; copper-containing oxidases are closely related as expected.

     

The influence of different disturbance frequencies on the species richness,diversity and equitability of phytoplankton in shallow lakes

The relationships between the species richness, diversity and equitability of phytoplankton is discussed in the context of Connell's (1978, Science 199: 1304–1310) Intermediate Disturbance Hypothesis (IDH). The records of 759 vertical phytoplankton samples, which were obtained from four shallow central European lakes (Balaton, Neusiedlersee, and two small artificial ponds) at daily to weekly intervals were analysed.

1. The Shannon-Weaver function was used to measure diversity of the recorded species compositionof the phytoplankton. It is shown on fictitious data that compositional diversity is sensitive to the numberof coequilibrating species provided that the suspected interrelationship between diversity and ‘complexity’is amenable to the application of this method.
2. The disturbance scale that was developed on the basis of the field records fits well to Reynolds'(1988, Verh. int. Ver. Limnol. 23: 683–691) derivation: < 3 days qualifies as high frequency, approximatel3–8 days as intermediate frequency and > 8–9 days as low frequency of disturbance for phytoplankton.
3. Arithmetical means of the compositional diversity of phytoplankton under different frequencies ofdisturbance support the hypothesis that maximal diversity appears at intermediate frequencies.
4. There are different reasons for decrease in diversity at higher and lower frequencies. Inequitabilitydiminishes diversity at low disturbance; while species number decreases at high frequencies.
5. The case of Neusiedlersee calls attention to the fact that it is difficult, if at all possible, to differentiatebetween the indices under continuous stress and high frequency of disturbance in lakes in temperateregions. Similar species number-equitability pattern are induced by both and it is also presumablethat high frequency disturbance can itself effect a serious stress.
6. The striking effects that regular major periodic events (e.g. significant changes in the grazing pressureat the onset of the clear-water phase, autumnal cooling) in the plankton have on its species diversity areevident. Thus, the relative importance of intermediate frequency disturbances has its own seasonality:it is increasingly important in periods (partly in the spring, but mostly in the summer-autumn equilibriumphases), in which competition among phytoplankton species is increasing. This observation suggestsa way by which the stochasticity-based IDH can be incorporated into rather more deterministicexplanations (e.g. PEG-model; Sommer et al., 1986. Archiv für Hydrobiologie 106: 433–471) of planktonsuccession.
7. The most controversial issue and, therefore, the main difficulty, with IDH is that it not onlymaintains species richness in an ecosystem but it also supposes its presence. The lack of either earlyor late successional species in a given community can inactivate the mechanism. From the point of viewof the diversity-species richness relationship, the persistence of disturbance at given frequencies is ofgreater importance than the temporal alterations themselves in the evolutionary ecology of the phytoplankton.
8. For characteristically unperturbed phytoplankton communities (no case was studied here), equilibriumconcepts (niche diversification, etc.) should be more strongly applicable to their diversity andspecies richness.

     

Charkterisierung eines phagenähnlichen Partikels aus Zellen von Nitrobacter

1. Phage-like particles Nb₁ isolated from cells of Nitrobacter agilis were characterized after freeze etching and after treatment by fixation agents.
2. Ethanol-acetic acid fixed particles can be digested by the proteolytic enzyme papain.
3. Ethanol-acetic acid fixed particles show a loss in mass and volume after treatment with DNase. Under the same conditions RNase has no influence.
4. The chemical composition of the phage-like particle Nb₁ is discussed.

     

An ecological study of the Ponggol Estuary in Singapore

1. An ecological study of the Ponggol Estuary was conducted from July 1965 to June 1966 and the seasonal data on physical, chemical and biological characteristics were presented.
2. The Ponggol River represents a short, narrow and shallow estuary in Singapore. The river mouth is open throughout the year and water from eastern Johore Straits drains in twice a day at high tide. The upper reach, however, is left exposed at low tide.
3. The Ponggol River was classified as a vertically and laterally homogeneous estuary and was found to exhibit a mesohaline to polyhaline environment.
4. Significant hydrological gradients from the river mouth 10 the upper reach were noted in the river system. Salinity, dissolved oxygen and pH increased towards the mouth of the river and other parameters such as nutrients, dissolved organic matter and turbidity increased towards the source.
5. Although the river received organic pollutants at the upper reach the estuary was able to discharge them fairly rapidly through regular flushing by the tides. The transient rise of organic matter did not appear to impart any serious affect on the biota in the estuary.
6. Over 98% of the phytoplankton consisted of diatoms, most of which were brought into the estuary from eastern Johore Straits. Freshwater forms were relatively few.
7. Phytoplankton biomass was considerably higher than the adjoining waters. and was reduced at the upper reach due to high turbidity of the water.
8. 80% of the zooplankton was composed of dinoflagellates,Difflugia, copepods and bivalve larvae dominating at all sections of the estuary.
9. Percentage composition of the zooplankton showed that dinoflagellates and copepod nauplii predominated at high tide whileDifflugia and bivalve larvae were abundant at low tide.
10. Zooplankton standing crop, in general, was higher towards the source at high tide but the reverse was found at low tide, i.e. standing crop increased towards the river mouth. This was attributed to the process of concentration.
11. Species composition of zooplankton was found to be more or less similar to that of the eastern Johore Straits.
12. The nekton consisted predominantly of small and juvenile fish. Close correlation of fish and copepods was found to be statistically valid and it was concluded that the fish entered the estuary to feed rather than to spawn.
13. The squids formed an important catch of the beach seine unit and were caught throughout the year.
14. The fish population could be grouped into four categories: estuarine components, euryhaline components, marine components and migratory components.
15. Benthic invertebrates were abundant. Commercially important species consisted of prawns,Metapenaeus andPenaeus, and crabs,Neptunus pelagicus andScylla serrata.
16. The river bed was inhabited predominantly by molluscs and the distribution resembled that of the sheltered shore of muddy-sand type.

     

Basic processes of locomotor coordination in the rock lobster

Rock lobsters are able to perform long and stereotyped stepping sequences above a motor driven treadmill. Forward walking samples are estimated by mean of statistical methods to draw out the basic rules involved in the locomotor behaviour (Fig. 1).

- The spatial and temporal parameters defined in a single propulsive leg are either invariable in respect to the imposed speed, as the mean step length (L), the return stroke duration (Tr) and the pause times (T's, T'r), or speed dependent as the power stroke duration (Ts) and the whole period (Figs. 2 and 3).

- The interleg phase coupling is strong and stable in the ipsilateral rear pairs (4–5), these legs acting most of the time in absolute coordination (1:1) or in harmonic ratio (2:1). In the contralateral pairs (R4-L4, R5-L5) the legs roughly operate in antiphase, but the relationship appears much weaker and variable, with frequent episodes of relative coordination (Fig. 4).

- The time intervals between the ground contact of any leg and the swing initiation in the nearest ones appear somewhat constant and could be closely related to the mechanism of stepping synchronization. The “5 on - 4 off” delay, very stable and always positive, suggests that the rear legs could exert a predominant influence upon the rhythmical movements of the next anterior ipsilateral appendages (Fig. 5).

- To test the contralateral relationships, the treadmill belts can be decoupled in order to impose different walking speeds on each side. Such a conflicting stimulus reveals that:

1. The relative hierarchy always observed between the ipsilateral legs can be artificially created between the two sides (Fig. 6).
2. The driving influence of a given leg is closely linked to the intensity of EMG's discharges in its power stroke muscles.
3. The contralateral appendages are able to walk in absolute coordination despite a large speed difference between the two sides (up to 4 cm/s). Under such a constraint, the walking legs alter its invariable parameters (L and Tr) to reach a common step period and steadily maintain the alternating pattern (Figs. 6 and 7).

     

A study on the rate of water transport of the clam katelysia opima in relation to environmental conditions

1. The neutral red technique was employed to study the rate of filtration in Katelysia opima.
2. The weight specific water filtration was found to be greater for younger clams compared to the older ones.
3. The rate of water filtration increased with decreasing salinity.
4. Water filtration was found to increase as temperature increased, reaching a maximum at 35°C. but then sharply decreasing at 39°C.
5. Light had no significant effect on the rate of filtration.
6. Suspended matter was found to affect the rate of water filtration.
7. The rate of filtration was low at high pH and high in low pH.
8. The rate of water filtration was found to be faster during high tide than during low tide.
9. The presence of the parasitic crab, Pennotheris sp., in the mantle cavity of clams had a marked effect on the particle filtration.
10. Accidental cut of the siphon tips had no effect on the rate of filtration.

     

Rhythmicity of chromophore turnover of visual pigment in the Antarctic amphipod Orchomene plebs (Crustacea; Amphipoda)

1. Relative retinal amounts in the compound eye of the Antarctic amphipod Orchomene plebs were assessed during conditions of continuous summer daylight every 3 h over a period of 48 h. The habitat of the experimental animal is the bottom of the Ross Sea (78°S; 166°E) down to depths of at least 400 m; water temperature is a constant — 1.8° C. A periodicity of 12 h was detected with relative amounts of 11-cis retinal exhibiting peaks at midday and at midnight and troughs at 7.00 h and 19.00 h.
2. The result that 90% of retinoid were insoluble in n-hexane suggests that at least 90% of the measured retinoid were attached to membrane-bound proteins such as opsin.
3. Selective light adaptation showed that the visual pigments were thermostable and photoregenerable. The main absorbance peak of rhodopsin, compared with metarhodopsin, seems to be in the longer wavelengths.

     

The reproductive cycle in a typical estuarine mollusc Nausitora hedleyi Schepman based on a study of the Gonad Index

1. Previous work on the methods employed for the determination of the breeding season of shipworms is briefly reviewed.
2. The method adopted for studying the reproductive cycle by using the “gonad index” is described.
3. The reproductive cycle of Nausitora hedleyi is described in detail based on a study of the gonad index of different sexes collected at monthly intervals from the estuarine environment of Cochin harbour.
4. The fact that breeding is restricted as marked by seasonal activity is shown from the size and activity of the gonad during the different months of the year.
5. The environment, and the hydrographic conditions prevailing in the habitat of N. hedleyi in the Cochin harbour are described.

     

Summer algal communities and primary productivity in fish ponds

The paper presents data on primary productivity and phytoplankton communities in new experimental ponds which received the following treatments; ammonium nitrate and triplesuperphosphate, triplesuperphosphate, cracked corn (10% crude protein) and Auburn No. 3 fish feed (36% crude protein). Comparative data on algal communities were also obtained from production ponds which received feeds or fertilizers. Basic ecological data on macro-algae are also presented.

1. All nutrient additions to experimental ponds resulted in higher levels of gross photosynthesis and greater concentrations of chlorophyll a than were found in the control treatments. Fertilization with both nitrogen and phosphorus gave the highest values. Chlorophyll a and gross photosynthesis were higher in ponds receiving high protein content feed (Auburn No. 3) than in ponds to which low protein content feed (corn) was applied.
2. Persistent blooms of blue-green algae occurred in ponds receiving nitrogen and phosphorus fertilization. Phosphorus only fertilization produced blooms of blue-greens, but these blooms did not persist as in the ponds to which nitrogen was also added. Control ponds were dominated by green algae. Blue-green algae were seldom abundant in feed treatments.
3. Production ponds had high level of gross photosynthesis and large concentrations of chlorophyll a.
4. Many of the production ponds which received feed applications developed heavy blooms of blue-green algae.
5. The major species of blue-green algae observed in the present study were Oscillatoria sp., Raphidiopsis curvata, Anacystis nidulans, A. aeruginosa, Spirulina sp., and Anabaena circinalis. Heterocyst bearing forms, which can presumably fix nitrogen, were seldom noted in ponds that received continuous additions of nitrogen from fish feeds.
6. Macro-algae are abundant in many fish ponds. Data illustrating the competition of macro-algae with phytoplankton are presented.

     

Rigorous and extended application of information theory to the afferent visual system of the cat

1. Intracellular recording were obtained from P-cells of the LGN of the cat. The impulse trains of a single presynaptic retinal ganglion cell and the postsynaptic P-cell were separated by band-pass-filtering and subsequent amplitude discrimination.
2. The rates of information and transinformation for the visual channel from the eye to a ganglion cell and to the connected P-cell were calculated. Input signals to the channel were trains of light flashes of different rate, luminance and spatial distribution.
3. Transinformation was calculated without restrictive assumptions for the code.
4. The transient behaviour of the system in response to a flash was fully considered for information calculations. Additionally, it was ensured that the state of the (adaptive) channel was considered correctly.
5. Information theory was applied in an extended way. The time courses of information transfer were calculated for various flash stimuli and compared with each other.

     

The use of toxicokinetics for the safety assessment of drugs acting in the brain

Pharmacological and toxicological studies undertaken on drugs that affect the brain are frequently performed in disparate species under various experimental conditions, at doses often greatly in excess of those expected to be administered to humans, and the findings are extrapolated implicitly or explicitly with scant regard to differences in the biodisposition of the drugs. Such considerations are necessary since:

1. Species;
2. Strain;
3. Gender;
4. Route;
5. Dose;
6. Frequency and time of administration;
7. Temperature;
8. Coadministration of drugs; and
9. Surgical manipulation

are but some of the factors that have been shown to influence the kinetics and metabolism of drugs. This article, using MDMA and other phenylethylamines as examples, provides evidence for the need to measure the exoosure of the drugs and their active metabolites in blood and brain (toxicokinetics) in order that conclusions based only on dynamic, biochemical, or histological evidence are more pertinent. Further, the combined use of toxicokinetic-dynamic modeling can lead to a better appreciation of the mechanisms involved and a more useful approach to the calculation of safety margins.