Michel Descamps

Cadmium and Lead Accumulation in the Earthworm Eisenia fetida (Savigny) and its Impact on Cholinesterase and Metabolic Pathway Enzyme Activity

Abstract The uptake of cadmium and lead was studied in the earthworm Eisenia fetida (Annelida: Oligochaeta) using an artificial soil exposure. Although cadmium and lead are bioconcentrated in Eisenia fetida tissue, bioaccumulation is not shown for concentrations below 100 ppm for lead, individuals eliminating as much metal as they ingest or the interactions between lead and organic matter in our substratum reduce the bioavailability of lead at low concentration. The cholinesterase activity was not inhibited when individuals were exposed for 8 weeks to either 8 or 80 ppm of cadmium or 100 or 2,000 ppm of lead. Results are different from those reported in another species Eisenia fetida andrei (= E. andrei) showing an inhibitory effect of lead on ChE activity; thus, differences in cholinesterase inhibition reflects the existence of two separate species. No effect of cadmium and lead on the activity of esterases, malate dehydrogenase, phosphoglucomutase and glutamate oxalate transferase was found in our experimental conditions, but we observed the disappearance of the fast moving band after electrophoretic separation for phosphoglucose isomerase.

Cadmium and lead kinetics during experimental contamination and decontamination of the centipede Lithobius forficatus L.

Kinetics of cadmium decontamination in Lithobius forficatus, performed in autumn experiments showed a decrease in Cd level, from about 30 mg/kg dw at the beginning of the experiment to about 12 mg/kg dw ten weeks later. Kinetics of cadmium contamination in animals showed in a first time a dramatic increase in Cd levels (up to a mean 80 mg/kg dw). Then a regular decrease was observed, although the animals were regularly fed with cadmium contamined larvae. Difference between animals fed or not with cadmium containing diet ranged from 18 mg/kg dw to only 8 mg/kg dw at the end of the experimental series. Experiments conducted either in autumn or in spring showed comparable aspects in the evolution of level curves, if not the same values. Natural decontamination of lead in animals showed results that were not convincing, depending at least of the dose level present in animals. Therefore, when experimental intoxication was performed, a natural detoxification process took place where Pb levels in animals first increased dramatically and then regularly decreased which was assumed to be evidence of an active excretion. Moreover, animals living in an artificially lead polluted soil and fed with lead-free diet also showed a rapid increase in Pb level followed by a plateau. From these studies, it can be concluded that these centipedes can be contaminated both by food intake and by ion regain through the tegument.

Conversion of different putative ecdysteroid precursors in Lithobius forficatus L. (Myriapoda: Chilopoda)

Abstract The biosynthetic pathway of ecdysteroids has been investigated in the centipede Lithobius forficatus . By using various labeled putative precursors already known to be efficiently converted into ecdysone and 20-hydroxyecdysone by insects and crustaceans, it was found that the reactions always stopped at 2-deoxyecdysone, and that this compound was only epimerized and conjugated at the C-3 position. Ecdysone was efficiently converted into 20-hydroxyecdysone, whereas 20-hydroxylation was not effective with 2-deoxyecdysteroids. None of the tested precursors was hydroxylated at the C-2 position. In addition, in vivo labeling experiments with [ 3 H]cholesterol led only the formation of unidentified products. Therefore, the origin of the already reported ecdysone and 20-hydroxyecdysone in these animals remains still conjectural. The “ecdysial glands” (i.e. the putative molting glands) and gonads proved the most effective tissues to convert 2,22,25-trideoxyecdysone into 2-deoxyecdysone in vitro , although at rather low levels. By contrast, this compound was very efficiently converted in vivo . The present data raise many unanswered questions, and they point out that classical inserct schemes are not applicable in the present case. It might thus well be that divergent pathways have evolved in arthropods, and this problem awaits further investigations.

Ultrastructural and autometallographic studies of the nephrocytes of Lithobius forficatus L. (Myriapoda, Chilopoda): role in detoxification of cadmium and lead

Abstract Ultrastructural and autometallographic investigations of the nephrocytes of the centipede Lithobius forficatus (Myriapoda : Chilopoda) and their role in detoxification of cadmium and lead are presented. This cell-type exhibits the characteristic features of podocytes, i.e. the typical pedicel-basal lamina complex and the well-developed lysosomal vacuolar system. Ultrastructural study demonstrated that heavy metals, such as cadmium and lead, may cause intracellular injuries. The autometallographic procedure showed that large electron-dense granules, referred to as cytosomes in the ultrastructural study, are the main organelles of the nephrocytes to accumulate heavy metals. Consequently, these cells may play an important role in the detoxification process.

Activation of neurosecretory protocerebral cells by 20-hydroxyecdysone in Lithobius forficatus L. (Myriapoda chilopoda)

In Lithobius forficatus, the influence of 20-hydroxyecdysone on the brain cells has been studied by autoradiography and electron microscopy. The hormone supply leads to an increase in the synthetic activity of the pars intercerebralis neurosecretory cells (p.i. NSC), particularly of the BS cell type. The neurosecretory cells of the frontal lobes (A type) and the p.i. ordinary neurons are not stimulated.

Influence of putative neurotransmitters on brain electrical activity in Lithobius Forficatus L. (Myriapoda Chilopoda)

Various putative neurotransmitters and related drugs were tested on the electrical activity of the brain of L. forficatus, at various times during the year. Indirect evidence exists for a depressant action from GABA. Ach, 5HT, NA and DA have stimulatory effects. However, DA effects were found to vary with the season, suggesting a role in the control of an annual cycle.