Daily and LPS-induced variation of endocrine mediators in cururu toads (Rhinella icterica)

ABSTRACT

Increased plasma glucocorticoids (corticosterone – CORT, in amphibians) and melatonin (MEL) are associated with the daily activity phase and with environmental darkness, respectively. Besides, CORT and MEL also play pivotal immunomodulatory roles in several vertebrates. Herein we described the daily profile of plasma MEL and CORT for Rhinella icterica toads in captivity. Thereafter, we investigated the effects of lipopolysaccharide (LPS)-induced systemic inflammation on the production of CORT and MEL in the R. icterica. Captive toads showed CORT and MEL diurnal variation typical of nocturnal species, with increased values for CORT at ZT12 (18 h) and MEL peak at ZT18 (24 h). LPS-induced hormonal changes included increased plasma CORT and decreased ocular and plasma MEL when compared to those from toads treated with saline 2 h post-injection. Our results demonstrated the presence of a diurnal CORT and MEL variation in toads. We also showed the crosstalk between CORT and MEL during the toad’s systemic inflammation in response to an immune challenge with LPS. Additionally, our results demonstrated that anuran eyes’ MEL production might be regulated during the inflammatory processes.

KEYWORDS:

• Amphibian
• corticosterone
• daily variation
• inflammation
• melatonin

Acknowledgements

We would like to thank Benedito Santos for his help during fieldwork and the lab technicians Eduardo Braga and Débora Moura. This research was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (Grant numbers: 2013/00900-1 and 2013/13691-1); and by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) through a master degree fellowship to PROB. F.R. Gomes is a research fellow (#302308/2016-4) and R.P.Markus is a senior fellow (#312256/2018-3) of the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The data is available in the Mendeley Data. DOI: https://10.17632/nc7z59bnf8.1

Additional information

Funding

This research was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) [Grant numbers: 2013/00900-1 and 2013/13691-1].