Toxic effects of cadmium on reproduction, development, and hatching in the freshwater snail Lymnaea stagnalis for water quality monitoring

The cerebral neurosecretory caudodorsal cells (CDCs) of the freshwater pulmonate snail Lymnaea stagnalis control egg laying, an event that involves a pattern of stereotyped behaviors. The CDCs synthesize and release multiple peptides, among which is the ovulation hormone (CDCH). It is thought that each peptide controls a specific aspect of the processes involved in egg laying. We isolated and characterized a CDC-specific cDNA clone that encodes the ovulation hormone (CDCH). RNA blot analysis and in situ hybridization experiments demonstrated that the CDCs are the major cell groups in the cerebral ganglia that transcribe the CDCH gene. In addition to CDCH, the 259-amino acid-long CDCH preprohormone contains 11 other predicted peptides. The overall homology of the CDCH preprohormone with the egg-laying hormone (ELH) preprohormones of the marine opisthobranch snails Aplysia californica and A. parvula is very low (29 and 26%, respectively). However, a more detailed comparison revealed a highly differential pattern of conservation of peptide regions. Significant homology was found between the regions containing (1) CDCH and ELH, (2) repeated pentapeptides, (3) alpha-caudodorsal cell peptide and alpha-bag cell peptide, and (4) 2 regions representing as yet unidentified peptides. Insignificant homology was found when comparing regions containing the other predicted peptides. The conserved peptides probably control similar aspects of the egg-laying fixed action patterns in these distantly related gastropod species. The pentapeptide region exhibits the highest level of homology (75%); in addition, an extra pentapeptide has been generated on the CDCH precursor. This indicates a vital function of these peptides in Aplysia, as well as in Lymnaea species.

https://www.jneurosci.org/content/jneuro/8/11/4184.full.pdf

Isolation, characterization, and evolutionary aspects of a cDNA clone encoding multiple neuropeptides involved in the stereotyped egg-laying behavior of the freshwater snail Lymnaea stagnalis.

Publisher Summary This chapter describes how schistosomes profit from stress responses they elicit in their hosts. The complex life cycle of trematodes comprises at least two hosts—that is, one or more intermediate hosts and a definitive host. The parasitic worms that cause schistosomiasis (bilharzia) in man belong to these trematodes (genus Schistosoma ). Asexual multiplication occurs in the intermediate hosts (freshwater snails), whereas the parasites reach sexual maturity in the definitive hosts (man or other mammals). The major problems which schistosomes have to overcome during their life cycle are (1) they have to find compatible hosts to penetrate their skin and tissue, (2) they have to adapt to environmental stress induced by changes of physicochemical factors, (3) they have to evade immune attacks in their hosts, and (4) they have to obtain energy and space within their hosts to grow and reproduce prior to transmission. Apart from mechanical damage, interference of schistosomes with regulatory mechanisms in their host has to be mediated by parasite components of the parasite–host interface exposed to elements of these regulatory systems or by products secreted into the host.

How schistosomes profit from the stress responses they elicit in their hosts.

3 – Freshwater Snails (Basommatophora)

Publisher Summary This chapter discusses the morphological, neurophysiological, endocrinological, biochemical, and pharmacological characteristics of the caudo-dorsal cells (CDC), with particular reference to structure–function relationships. Three main factors have contributed to the present knowledge of the nature of the peptidergic CDC of Lymnaea stagnalis: the suitability of the cells for experimental studies, the multidisciplinary approach with which they have been investigated, and the detailed knowledge of various related aspects of the snail's biology, such as endocrinology, reproduction, the sensory system, the muscular system, the blood and connective tissue, and hydromineral regulation. Some of the results may increase the insight into structure and functioning of nervous systems in general. The quantitative electron microscopic analyses of the cyclic dynamics of CDC activity show the way in which a neuroendocrine system can meet the physiological demand for a sudden high titer of neurohormone to induce ovulation by synthesizing, transporting, and degrading secretory material in a timed, cyclic, and quantitative fashion. The clear relation between the electrical discharge and massive release of ovulation neurohormone of Lymnaea stagnalis (CDCH) demonstrates the significance of the simultaneous neural and endocrine character of the neuroendocrine cell.

Cytobiology of the Ovulation-Neurohormone Producing Neuroendocrine Caudo-Dorsal Cells of Lymnaea stagnalis

Ovipository activity decreases when specimens of the pond snail, Lymnaea stagnalis, are kept in closed jars that are not cleaned regularly. When the snails are transferred from dirty to clean water, egg-laying occurs within 3 h in over 90% of the animals. The number of eggs per egg mass laid after water change is directly related to the length of the period between the induced and the previous oviposition. The relationship is similar to that found when snails are injected with a very high dose (20-times threshold) of egg-laying hormone. The latency of oviposition, which depends on the dose of ovulation hormone, is not affected by the oviposition interval. The size of the egg capsule depends on the number of ripe eggs in the ovotestis and the packaging capacity of the female accessory sex organs. The role of a number of component factors of the water-change stimulus was studied. Elevated O2-content of the water, a clear jar and clean water all have a positive effect on egg-laying. Clean water is the most e...

Induction of egg-laying in the pond snail Lymnaea stagnalis by environmental stimulation of the release of ovulation hormone from the Caudo—Dorsal Cells

M. Wilbrink

Papers

Induction of egg-laying in the pond snail Lymnaea stagnalis by environmental stimulation of the release of ovulation hormone from the Caudo—Dorsal Cells

Effects of 2,2′-dichlorobiphenyl on egg laying in the pond snail Lymnaea stagnalis