3 research outputs found
Depressing Antidepressant: Fluoxetine Affects Serotonin Neurons Causing Adverse Reproductive Responses in Daphnia magna
Selective
serotonin reuptake inhibitors (SSRIs) are widely used
antidepressants. As endocrine disruptive contaminants in the environment,
SSRIs affect reproduction in aquatic organisms. In the water flea Daphnia magna, SSRIs increase offspring production
in a food ration-dependent manner. At limiting food conditions, females
exposed to SSRIs produce more but smaller offspring, which is a maladaptive
life-history strategy. We asked whether increased serotonin levels
in newly identified serotonin-neurons in the Daphnia brain mediate these effects. We provide strong evidence that exogenous
SSRI fluoxetine selectively increases serotonin-immunoreactivity in
identified brain neurons under limiting food conditions thereby leading
to maladaptive offspring production. Fluoxetine increases serotonin-immunoreactivity
at low food conditions to similar maximal levels as observed under
high food conditions and concomitantly enhances offspring production.
Sublethal amounts of the neurotoxin 5,7-dihydroxytryptamine known
to specifically ablate serotonin-neurons markedly decrease serotonin-immunoreactivity
and offspring production, strongly supporting the effect to be serotonin-specific
by reversing the reproductive phenotype attained under fluoxetine.
Thus, SSRIs impair serotonin-regulation of reproductive investment
in a planktonic key organism causing inappropriately increased reproduction
with potentially severe ecological impact
Bacteria-Mediated Effects of Antibiotics on <i>Daphnia</i> Nutrition
In
polluted environments, contaminant effects may be manifested
via both direct toxicity to the host and changes in its microbiota,
affecting bacteria–host interactions. In this context, particularly
relevant is exposure to antibiotics released into environment. We
examined effects of the antibiotic trimethoprim on microbiota of Daphnia magna and concomitant changes in the host
feeding. In daphnids exposed to 0.25 mg L<sup>–1</sup> trimethoprim
for 24 h, the microbiota was strongly affected, with (1) up to 21-fold
decrease in 16S rRNA gene abundance and (2) a shift from balanced
communities dominated by <i>Curvibacter</i>, <i>Aquabacterium,</i> and <i>Limnohabitans</i> in controls to significantly
lower diversity under dominance of <i>Pelomonas</i> in the
exposed animals. Moreover, decreased feeding and digestion was observed
in the animals exposed to 0.25–2 mg L<sup>–1</sup> trimethoprim
for 48 h and then fed <sup>14</sup>C-labeled algae. Whereas the proportion
of intact algal cells in the guts increased with increased trimethoprim
concentration, ingestion and incorporation rates as well as digestion
and incorporation efficiencies decreased significantly. Thus, antibiotics
may impact nontarget species via changes in their microbiota leading
to compromised nutrition and, ultimately, growth. These bacteria-mediated
effects in nontarget organisms may not be unique for antibiotics,
but also relevant for environmental pollutants of various nature
Identification of Metabolic Pathways in <i>Daphnia magna</i> Explaining Hormetic Effects of Selective Serotonin Reuptake Inhibitors and 4‑Nonylphenol Using Transcriptomic and Phenotypic Responses
The molecular mechanisms explaining
hormetic effects of selective
serotonin reuptake inhibitors (SSRIs) and 4-nonylphenol in <i>Daphnia magna</i> reproduction were studied in juveniles and
adults. Transcriptome analyses showed changes in mRNA levels for 1796
genes in juveniles and 1214 genes in adults (out of 15 000
total probes) exposed to two SSRIs (fluoxetine and fluvoxamine) or
to 4-nonylphenol. Functional annotation of affected genes was improved
by assuming the annotations of putatively homologous <i>Drosophila</i> genes. Self-organizing map analysis and partial least-square regression
coupled with selectivity ratio procedures analyses allowed to define
groups of genes with specific responses to the different treatments.
Differentially expressed genes were analyzed for functional enrichment
using Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes databases.
Serotonin metabolism, neuronal developmental processes, and carbohydrates
and lipid metabolism functional categories appeared as selectively
affected by SSRI treatment, whereas 4-nonylphenol deregulated genes
from the carbohydrate metabolism and the ecdysone regulatory pathway.
These changes in functional and metabolic pathways are consistent
with previously reported SSRIs and 4-nonylphenol hormetic effects
in <i>D. magna</i>, including a decrease in reserve carbohydrates
and an increase in respiratory metabolism