When vertebrates face acute stressors, their bodies rapidly undergo a repertoire of physiological and behavioral adaptations, which is termed the stress response. Rapid changes in heart rate and blood glucose levels occur via the interaction of glucocorticoids and their cognate receptors following hypothalamic‐pituitary‐adrenal axis activation. These physiological changes are observed within minutes of encountering a stressor and the rapid time domain rules out genomic responses that require gene expression changes. Although behavioral changes corresponding to physiological changes are commonly observed, it is not clearly understood to what extent hypothalamic‐pituitary‐adrenal axis activation dictates adaptive behavior. We hypothesized that rapid locomotor response to acute stressors in zebrafish requires hypothalamic‐pituitary‐interrenal (HPI) axis activation. In teleost fish, interrenal cells are functionally homologous to the adrenocortical layer. We derived eight frameshift mutants in genes involved in HPI axis function: two mutants in exon 2 ofmc2r(adrenocorticotropic hormone receptor), five in exon 2 or 5 ofnr3c1(glucocorticoid receptor [GR]) and two in exon 2 ofnr3c2(mineralocorticoid receptor [MR]). Exposing larval zebrafish to mild environmental stressors, acute changes in salinity or light illumination, results in a rapid locomotor response. We show that this locomotor response requires a functioning HPI axis via the action ofmc2rand the canonical GR encoded bynr3c1gene, but not MR (nr3c2). Our rapid behavioral assay paradigm based on HPI axis biology can be used to screen for genetic and environmental modifiers of the hypothalamic‐pituitary‐adrenal axis and to investigate the effects of corticosteroids and their cognate receptor interactions on behavior.

In this study, rapid one step facile synthesis of silver nanoparticles (AgNPs) was done using culture supernatant of two Gram positive (B. thuringiensis and S. aureus) and Gram negative (E. coli and Salmonella typhimurium [STAgNP]) bacterial strains and were termed as “Bacillus thuringiensis,” “Staphylococcus aureus,” “Escherichia coli,” and “STAgNP,” respectively. Synthesized AgNPs were well characterized with the help of different standard techniques like FESEM, DLS, UV-Vis spectroscopy, and Fourier transform infrared. Mechanism of AgNPs synthesis was elucidated using in silico approach. In vivo cytotoxicity of synthesized AgNPs was assessed in embryonic Zebrafish model with the help of uptake, oxidative stress, and apoptosis induction experimental assays, and the mechanism was investigated through in silico approach at the molecular level. The result showed successful biosynthesis of 20–40 nm sized AgNPs stable with zeta potential of − 45 to − 35 mV having standard silver nanoparticles SPR peaks due to the interaction of reduced silver particles with amino acid residues of bapA proteins of the bacterial supernatant. In vivo cytotoxicity with embryonic Zebrafish was found to be dependent on biogenicity and concentration of biosynthesized AgNPs as consequence of oxidative stress induction and apoptosis due to the influential regulation of sod1 and tp53 genes clarified by pathway analysis with reference to experimental and computational results. The study suggested that cytotoxicity of biologically synthesized silver nanoparticles from bacteria depends on strain specificity with significant difference in use of Gram positive and Gram negative bacterial strains.

Toxicological impact of TiO₂nanoparticles synthesized by HEBM on embryonic zebrafish at molecular level.