J. Salánki

Age- and size-specific patterns of heavy metals in the organs of freshwater fish Abramis brama L. populating a low-contaminated site.

Concentrations of cadmium, copper, mercury, lead and zinc were determined by atomic absorption spectrophotometry in the muscle, gill and liver of bream Abramis brama L. to study the relationship between the heavy metal load of fish and their age and size, and the seasonal variation of pollutant loads. Fish were collected from the Western basin of Lake Balaton (Hungary) in October 1999 and May 2000. The average metal concentrations of different organs varied in the following ranges: Cd 0.42-2.10; Cu 1.77-56.2; Hg 0.01-0.19; Pb 0.44-3.24; Zn 10.9-82.5 microg g(-1) dry weight. The highest Cd, Cu, Pb and Zn concentrations were detected in the gill or liver of fish, whereas the highest Hg concentrations were measured in the muscle. In the liver of bream for cadmium, copper and mercury the Pearson correlation analysis revealed positive associations related to age and size (length, net weight), as well as for the mercury load of all three investigated organs. In the muscle and gill the copper, lead and zinc concentrations, similarly to the lead and zinc concentrations of the liver, the associations related to age and size were negative. The correlations between the heavy metal concentrations of organs and the individual condition factors of fish samples proved to have opposite trends compared to those related to the age and size of fish. The seasonal variations in the heavy metal load of bream could be attributed rather to the seasonal change in the condition factor of fish than to variations in the pollutant load of the site.

Heavy metals in animals of Lake Balaton

Abstract Hg, Cd, Cu, Pb, Zn, Fe and Mn concentrations were measured in Chironomidae larvae, Crustacea plankton, as well as in various organs of mussels and fishes collected from the open water area of Lake Balaton. The values were comparatively low. However, there were significant differences in the metal concentrations of species and tissue. Most Cd was found in the gill of Unio pictorum L., most Pb, Zn and Mn in the gill of Anodonta cygnea L., most Cu in Crustacea plankton and in the liver of Abramis brama L., and most Hg and Fe in Chironomidae larvae. Low concentrations occurred in fishes, the lowest in the flesh of Stizostedion lucioperca L. Accumulation of metals in organs as compared with their concentration in the lake water was in the range of 3.4 × 10 2 −2.6 × 10 3 for Hg; 7.0 × 10 2 −6.8 × 10 3 for Cd; 3.3 × 10 2 −9.7 × 10 3 for Cu; 6.9 × 10 2 −8.1 × 10 3 for Zn; 1.5 × 10 3 −2.4 × 10 4 for Pb; 3.5 × 10 2 −3.1 × 10 4 for Fe; and 5.0 × 10 1 −3.5 × 10 5 for Mn.

Molluscs in biological monitoring of water quality

Molluscs living in Lake Balaton accumulate persistent toxic substances, namely heavy metals, to a greater extent, than other organisms, and can serve as excellent passive biomonitors. Especially gills are good accumulators. Regular sampling showed that the level of Cd and Hg concentrations increased, while Pb contamination decreased during the past 20 years in mussels, corresponding probably to changes in pollution of the Lake. In functional, active monitoring various behavioral patterns of molluscs were employed. In mussels the periodicity of activity and rest (pumping activity vs. valve closure) is a sensitive indicator of unfavorable conditions and so of toxic substances. Low concentrations of inorganic and organic toxicants (heavy metals, PCBs, PAH compounds) cause reduction of the active and increase of the rest periods in a concentration dependent manner in a few hours. A second, suitable test for evaluating toxicity of chemicals is the measurement of the water flow through the exhalant siphon. Under the effect of toxicants the siphon activity, both the strength and duration of water flow changes characteristically within a few minutes. For both behavioral tests special techniques have been developed suitable for long duration recording, supported by mechano-electrical transduction and computerized data evaluation. In case of the pond snail (Lymnaea stagnalis L.) the behavior (positive/negative geotaxis and orientation) is disturbed in the presence of the above mentioned toxic chemicals. The execution and evaluation of the changes in the movement of the snail is based on video-recording and measurement of the direction and distance the animal performs in uncontaminated water and in the presence of the pollutants during the same period of time (0.5-4 h).

Physiological background for using freshwater mussels in monitoring copper and lead pollution

In studying the effect of copper (10 ± 0.57 µg Cu l−1 and 100 ± 3.01 µg Cu l−1) and lead (50 ± 1.12 µg Pb l−1 and 500 ± 12.5 µg Pb l−1) on the filtration activity of Anodonta cygnea L. it was found that both heavy metals resulted in significant shortening of the active periods, but little change occurred in the length of the rest periods. The concentrations of copper and lead were measured in the gill, foot, mantle, adductor muscle and kidney for 840 hours of exposure to 10.9 ± 5 µg Cu l−1 and 57.0 ± 19 µg Pb l−1 as well as during subsequent depuration. Uptake was observed after 72 hours of exposure. The highest copper concentration (59.1 ± 16.2 µg Cu g−1) was measured at 672 h in the mantle, and the highest lead value (143 ± 26.1 µg Pb−1) was obtained in the kidney. Depuration of copper was fastest from the foot, and from the adductor muscle for lead. The gill had the longest half-depuration time (> 840 h for copper and > 672 h for lead).

Seasonal and activity-dependent changes of the serotonin level in the C.N.S. and heart of the snail (Helix Pomatia L.)

Abstract 1. There is seasonal variation in the 5 HT level of the central nervous system and heart of the snail, Helic pomatia L.: in active animals the 5 HT content is higher in the cerebral ganglia, auricle, and ventricle in the autumn than at spring, while this pattern is reversed in the suboesophageal ganglion. 2. Snails kept in dry conditions at room temperature fall into a state of rest. Under such conditions an increase of the 5 HT level was observed in the C.N.S. and heart both in the summer as well as in the winter; the question remains as to what results from the decrease of the 5 HT utilization during the resting state of the animal. 3. There is a different seasonal variation of the 5 HT level in snails kept in a refrigerator: during the first winter months the 5 HT level of the ganglia increases; this is followed by a decrease, while in the summer an initial decrease with subsequent increase is observed. The 5 HT content of the heart showed an initial decrease both during the winter and the summer. 4. Arousal of the snails from hibernation in winter causes a decrease of the serotonin level of the ganglia. On cooling these animals again, the 5 HT level increases only to a moderate degree. 5. The variations of the 5 HT level in snails can be considered partly as the consequence of the change of the activity, but on the other hand the serotonin level can play a role in the determination of the activity of the animal.

The dynamics of mercury and cadmium uptake into different organs of Anodonta cygnea L.

Abstract The bioaccumulation of Hg and Cd into various organs of the freshwater mussel Anodonta cygnea was investigated during an 840 h experimental period. Parallel with the metal concentrations the periodicity of activity and the body weight of the animals were also checked. The accumulation of Hg in all of the investigated organs, and that of the Cd into the kidney have two phases, up to 24 h it was non linear, between 24 and 72 h it became linear in most organs up to 840 h, and could be characterized by a regression line. For Hg accumulation the gills while for Cd accumulation the kidney and viscera were exceptions, here saturation was observed after 504 and 672 h, respectively. The speed of Hg and Cd uptake was different in various organs of Anodonta cygnea. Into the kidney the accumulation of Hg was six times faster than that of Cd. As compared to the adductor muscles the Hg and Cd uptake of the kidney was 20 and 10 times faster, respectively. The factor of concentration was in all organs except adductor muscles over 1000, in case of the kidney the rate of bioconcentration for Hg reached nearly 100,000. The dry weight of organs dropped during the metal uptake by 20–60%, but no mortality was observed up to 840 h. In the presence of Hg and Cd the filtering activity of the mussels became reduced as a result of increase of inactive rest periods. Nevertheless, the decrease of activity did not prevent the linear uptake of metals into the animal

In vivo labeling of serotonin-containing neurons by 5,7-dihydroxytryptamine inAplysia

Intrahemocoelial administration of 5,7-dihydroxytryptamine (5,7-DHT) to Aplysia californica induces a transient (less than 4 h) behavioral alteration. About 5 weeks after 5,7-DHT treatment, 5-hydroxytryptamine (5-HT)-containing neurons develop dark brown pigmentation. These labeled 5-HT neurons have normal physiological and pharmacological properties when investigated electrophysiologically. This contrasts with the long-term neurotoxic effect of 5,7-DHT on vertebrate neurons. This technique will greatly facilitate visual identification of 5-HT-containing neurons and study of their physiology and actions.

NMDA-like receptors in the CNS of molluscs.

The properties of L-glutamate sensitive neurones in the fresh-water snail Lymnaea stagnalis were studied to determine whether or not NMDA type receptors are present in molluscan ganglia. Experiments were carried out in isolated ganglia and with dialysed neurones. In the neuro-secretory light yellow cells (LYC) both glutamate and NMDA (but not other glutamate agonists) induced prolonged depolarization and inward current. The sensitivity of the neurones for NMDA was lower than for glutamate. Both currents are carried by Na- and Ca-ions and have linear I-V characteristics. Mg-ions did not reduce either but glycine potentiated both glutamate and NMDA responses. It is concluded that in the molluscan central nervous system glutamate receptors have some of the characteristics of mammalian NMDA receptors.

Single neurone responses to tactile stimulation of the heart in the snail, Helix pomatia L.

SummaryThe electrical activity of the heart nerve and of single neurons in the suboesophageal ganglia were recorded during tactile stimulation of the heart. 15 neurons were identified which responded to heart stimulation by inhibiting or accelerating activity. Cells influenced by heart afferents are scattered in the visceral and in the right and left parietal ganglia.In most of the cases both decrease and increase of cell activity are caused by synaptic potentials, in some cases, however, the neuron is assumed to have a sensory character.The activity of three neurons influenced by heart stimulation was conducted into the heart nerve. These cells are central neurons of a heart-CNS-heart reflex.Some of the neurons located in the right parietal and visceral ganglia have no connection with the mechanoreceptors of the heart. Since their spikes propagate into the heart nerve, they probably take part in the extracardial regulation of heart activity.One of the neurons located in the visceral ganglion (cell V12) sends its axon into the heart nerve. The response of this neuron to heart stimulation was an increase in activity and an inhibition of the heart rate. This is an inhibitory neuron of the extracardial heart regulatory system.

Heavy metals regulate physiological and behavioral events by modulating ion channels in neuronal membranes of molluscs

The interaction of heavy metals (HgCl2, CdCl2, CuCl2, PbCl2 and ZnCl2) and neurotransmitters (ACh, 5HT and DA) was studied on the excitable membrane of identified neurons of Lymnaea stagnalis and Helix pomatia. It was shown that,(1)The excitability and chemosensitivity of molluscan neurons were modified under the influence of the heavy metals Hg2+, Cd2+, Cu2+, Pb2+ and Zn2+.(2)Change in excitability to transmitters occurred as a potentiation or depression of the evoked response both in duration of membrane polarization and in frequency of spike activity.(3)The chemosensitivity changes in various ways, namely:excitatory effect was totally eliminated;one component of the effect was depressed.Different neurons may show different reactions to the same heavy metal.(4)There were differences in the effects of various heavy metals. Hg2+ has a more generalized effect than Cd2+; Cu2+, Pb2+ and Zn2+ were less effective in a number of neurons. The heavy metal effect was dose dependent, too.(5)Both inward and outward currents, which were evoked by neurotransmitters or voltage induced, were modified in most of the tested neurons. Both an increase and decrease of the membrane permeability occurred in different neurons in response to the same or different heavy metals.(6)The changes can be interpreted as a result ofdirect effect on specific ionic channels;modification of receptors binding ACh, 5HT, or DA;modification of intracellular processes responsible for the regulation of membrane permeability.