Effect of tributyltin exposure on the embryonic development and behavior of a molluscan model species, Lymnaea stagnalis.

The presence of the organotin compound tributyltin (TBT) in aquatic ecosystems has been a serious environmental problem for decades. Although a number of studies described the negative impact of TBT on mollusks at different levels, investigations connected to its potential effects during embryogenesis have been neglected. For a better understanding of the impact of TBT on mollusks, in the present study, embryos of previously TBT-treated or not treated specimens of the great pond snail (Lymnaea stagnalis) were exposed to 100 ng L-1 TBT from egg-laying (single-cell stage) until hatching. According to our results, TBT significantly delayed hatching and caused shell malformation. TBT transiently decreased the locomotion (gliding) and also reduced the feeding activity, demonstrating for the first time that this compound can alter the behavioral patterns of molluscan embryos. The heart rate was also significantly reduced, providing further support that cardiac activity is an excellent indicator of metal pollution in molluscan species. At the histochemical level, tin was demonstrated for the first time in TBT-treated hatchlings with intensive reaction in the central nervous system, kidney, and hepatopancreas. Overall, the most notable effects were observed in treated embryos derived from TBT treated snails. Our findings indicate that TBT has detrimental effects on the development and physiological functions of Lymnaea embryos even at a sub-lethal concentration, potentially influencing their survival and fitness. Highlighting our observations, we have demonstrated previously unknown physiological changes (altered heart rate, locomotion, and feeding activity) caused by TBT, as well as visualized tin at the histochemical level in a molluscan species for the first time following TBT exposure. Further studies are in progress to reveal the cellular and molecular mechanisms underlying the physiological and behavioral changes described in the present study.

Presence, variation, and potential ecological impact of microplastics in the largest shallow lake of Central Europe.

The presence of microplastics (MPs) in the global ecosystem has generated a rapidly growing concern worldwide. Although their presence in the marine environment has been well-studied, much less data are available on their abundance in freshwaters. MPs alone and in combination with different chemicals has been shown to cause acute and chronic effects on algae and aquatic invertebrate and vertebrate species at different biological levels. However, the combined ecotoxicological effects of MPs with different chemicals on aquatic organisms are still understudied in many species and the reported data are often controversial. In the present study, we investigated, for the first time, the presence of MPs in Lake Balaton, which is the largest shallow lake of Central Europe and an important summer holiday destination. Moreover, we exposed neonates of the well-established ecotoxicological model organism Daphnia magna to different MPs (polystyrene [3 µm] or polyethylene [≤ 100 µm]) alone and in combination with three progestogen compounds (progesterone, drospirenone, levonorgestrel) at an environmentally relevant concentration (10 ng L-1) for 21 days. The presence of 7 polymer types of MPs in the size range of 50-100 µm was detected in Lake Balaton. Similarly to the global trends, polypropylene and polyethylene MPs were the most common types of polymer. The calculated polymer-independent average particle number was 5.5 particles m-3 (size range: 50 µm - 100 µm) which represents the values detected in other European lakes. Our ecotoxicological experiments confirmed that MPs and progestogens can affect D. magna at the behavioral (body size and reproduction) and biochemical (detoxification-related enzyme activity) levels. The joint effects were negligible. The presence of MPs may lead to reduced fitness in the aquatic biota in freshwaters such as Lake Balaton, however, the potential threat of MPs as vectors for progestogens may be limited.

Functional characterization and related evolutionary implications of invertebrate gonadotropin-releasing hormone/corazonin in a well-established model species.

In vertebrates, gonadotropin-releasing hormone (GnRH) peptide is the central mediator of reproduction. Homologous peptides have previously also been identified in molluscan species. However, emerging evidence suggests that these molecules might serve diverse regulatory functions and proposes to consider them as corazonin (CRZ). We previously isolated the full-length cDNA of the invGnRH/CRZ peptide (termed ly-GnRH/CRZ) in the well-established invertebrate model species, the great pond snail Lymnaea stagnalis; however, its predicted functions remain to be verified. In this study, we first confirmed the presence of the deduced active peptide from the central nervous system of L. stagnalis. Further, we performed in vivo and in vitro studies to explore the functions of ly-GnRH/CRZ. Injection of sexually mature specimens with synthetic active peptide had an inhibitory effect on locomotion and an acceleratory effect on egg-laying, but had no effect on feeding. The previously predicted modulatory effect of ly-GnRH/CRZ was supported by its identified co-localization with serotonin on the surface of the heart atria. Lastly, we demonstrated not only the presence of ly-GnRH/CRZ in the penial complex but also that ly-GnRH/CRZ-containing neurons project to the efferent penis nerve, suggesting ly-GnRH/CRZ may directly modulate the motor output of this peripheral tissue. Overall, our findings strongly support that ly-GnRH/CRZ is a multifunctional neuropeptide. These results contribute to the understanding of the GnRH superfamily and, more broadly, disciplines such as comparative endocrinology and neurobiology.

Issues, challenges, directives, and limitations concerning the improvement of environmental risk assessment of pharmaceutically active compounds.

Nowadays, when tons of different chemicals including pharmaceutically active compounds (PhACs) are known to be released into the environment, applying adequate risk assessment relating to the protection of the ecosystem is very important. A broad body of scientific papers expresses a growing demand for improvement of the method(s) for ecological/environmental risk assessment (ERA). Although certain issues about ERA often emerge in the community, most of them cannot be considered as real problems and its methodology was developed keeping several limitations in mind. Nevertheless, the current approaches can be improved in order to better serve the intended purposes. For example, there is a lack of an integrated, manageable ecotoxicological database. It is not uncommon for basic, but extremely important, influencing factors such as time of exposure, interactions between different compounds, and characteristics of different habitats to be ignored. Discussing under the basic regulatory framework used in the EU, this correspondence paper deals with these and other examples to present the current features of ERA, identify gaps in process and application, and propose possible improvements/directives.

Effects of chronic sublethal progestogen exposure on development, reproduction, and detoxification system of water flea, Daphnia magna.

The presence of sex steroid hormones in aquatic ecosystems is of rapidly growing concern worldwide since they can affect the different non-target species including cladocerans. Although data are available on the effects of estrogens on the well-established ecotoxicological model organism Daphnia magna, the molecular or behavioural alterations induced by environmentally relevant concentrations (from a few ng L-1 to a few hundred ng L-1 in average) of progestogens have not been investigated on this species. In the present study, we exposed neonates of D. magna to relevant equi-concentrations (1, 10, 100, 500 ng L-1) of mixtures of four progestogens (progesterone, drospirenone, gestodene, levonorgestrel) in short-term (6 days) and long-term (21 days) experiments. Significant alterations were observed at the molecular, cellular, and individual levels. During the short-term exposure, all of the mixtures increased the gene expression of glutathione S-transferase (GST) detoxification enzyme, moreover, the activity of GST was also significantly increased at the concentrations of 10, 100, and 500 ng L-1. In long-term exposure, the number of days until production of the first eggs was reduced at the 10 ng L-1 concentration compared to control, furthermore, the maximum egg number per individual increased at the concentrations of 1 and 10 ng L-1. Based on the authors' best knowledge, this is the first study to investigate the effects of progestogens in mixtures and at environmentally relevant concentrations on D. magna. Our findings contribute to the understanding of the possible physiological effects of human progestogens. Future research should be aimed at understanding the potential mechanisms (e.g., perception) underlying the changes induced by progestogens.

The Great Pond Snail (Lymnaea stagnalis) as a Model of Aging and Age-Related Memory Impairment: An Overview.

With the increase of life span, normal aging and age-related memory decline are affecting an increasing number of people; however, many aspects of these processes are still not fully understood. Although vertebrate models have provided considerable insights into the molecular and electrophysiological changes associated with brain aging, invertebrates, including the widely recognized molluscan model organism, the great pond snail (Lymnaea stagnalis), have proven to be extremely useful for studying mechanisms of aging at the level of identified individual neurons and well-defined circuits. Its numerically simpler nervous system, well-characterized life cycle, and relatively long life span make it an ideal organism to study age-related changes in the nervous system. Here, we provide an overview of age-related studies on L. stagnalis and showcase this species as a contemporary choice for modeling the molecular, cellular, circuit, and behavioral mechanisms of aging and age-related memory impairment.

Progestogen-induced alterations and their ecological relevance in different embryonic and adult behaviours of an invertebrate model species, the great pond snail (Lymnaea stagnalis).

The presence of oral contraceptives (basically applying estrogens and/or progestogens) poses a challenge to animals living in aquatic ecosystems and reflects a rapidly growing concern worldwide. However, there is still a lack in knowledge about the behavioural effects induced by progestogens on the non-target species including molluscs. In the present study, environmental progestogen concentrations were summarised. Knowing this data, we exposed a well-established invertebrate model species, the great pond snail (Lymnaea stagnalis) to relevant equi-concentrations (1, 10, 100, and 500 ng L-1) of mixtures of four progestogens (progesterone, drospirenone, gestodene, levonorgestrel) for 21 days. Significant alterations were observed in the embryonic development time, heart rate, feeding, and gliding activities of the embryos as well as in the feeding and locomotion activity of the adult specimens. All of the mixtures accelerated the embryonic development time and the gliding activity. Furthermore, the 10, 100, and 500 ng L-1 mixtures increased the heart rate and feeding activity of the embryos. The 10, 100, and 500 ng L-1 mixtures affected the feeding activity as well as the 1, 10, and 100 ng L-1 mixtures influenced the locomotion of the adult specimens. The differences of these adult behaviours showed a biphasic response to the progestogen exposure; however, they changed approximately in the opposite way. In case of feeding activity, this dose-response phenomenon can be identified as a hormesis response. Based on the authors' best knowledge, this is the first study to investigate the non-reproductive effects of progestogens occurring also in the environment on molluscan species. Our findings contribute to the global understanding of the effects of human progestogens, as these potential disruptors can influence the behavioural activities of non-target aquatic species. Future research should aim to understand the potential mechanisms (e.g., receptors, signal pathways) of progestogens induced behavioural alterations.