Hormone gene expression changes in the zebrafish caudal neurosecretory system under acute environmental challenges

The caudal neurosecretory system (CNSS) is a neuroendocrine complex, found only in fishes, suggested to be involved in osmoregulation and thermo-adaptation. Although being discovered 70 years ago, the CNSS has been understudied and its physiological significance remains poorly understood. The zebrafish ( Danio rerio ) is a well-established model organism for functional studies, yet, so far, the role of the CNSS has not really been investigated in this species. In the present study, we attempted to identify environmental factors whose variations induce changes in CNSS activity. Juvenile zebrafish were submitted to acute (2 h, 8 h, and 24 h) pH, salinity, and temperature challenges, and CNSS activity was quantified by measuring the expression levels of peptide hormone-encoding genes using quantitative PCR. Our findings revealed that temperature challenge affected the expression of the largest number of gene, followed by salinity and pH challenges. This suggested that, in the zebrafish, the CNSS is involved in thermo-adaptation and osmoregulation, which is consistent with what has been reported in other species, and showed that the zebrafish is a relevant model to study the function of the CNSS.