Introduction: Typhlonectes compressicauda is a viviparous gymnophionan amphibian living in tropical areas of South America. This lengthened amphibian is submitted to seasonal variations characterized by the rainy season (from January to June) and the dry season (from July to December). The mineral homeostasis in amphibians is partly ensured by the neurohormones arginine-vasotocin (AVT), and mesotocin (MST). These two hormones were localized in the hypothalamus, and their receptors, mesotocin receptors (MTR) and vasotocin receptors (VTR2) in the kidney. The aim of the study was to better understand the physiology of the hydromineral regulation of the studied species.
Material and methods: The specimens of T. compressicauda male and female adult were divided into 6 groups: males in the rainy season, males in the dry season, females pregnant in the rainy season, females pregnant in the dry season, females not pregnant in the rainy season, females not pregnant in the dry season. We studied the expression of hormones (AVT, MST) and their receptors (MTR, VTR2) in the hypothalamus and the kidney, respectively, by immunohistochemical and histological techniques. We also studied the expression of aquaporin-2 (AQP2), a water-channel protein in the kidney.
Results: We found that the MST (diuretic hormone) and its receptor were more intensively expressed during the rainy season, whereas the period of maximal AVT (anti-diuretic hormone) and VTR2 expression was the dry season. A quantitative analysis showed significant differences in the number of labeled cells in the hypothalamus depending on the seasonal variation. The expression of AQP2 was observed in renal tubules during both seasons with an increased intensity during the dry season.
Conclusion: The expression of the MST/AVT in brain, their receptors MTRs/VTR2, and AQP2 in kidney changed in T. compressicauda according to the seasonal variations. A direct relationship between the seasonal cycle and reproduction cycle was demonstrated in this species.
Keywords: Amphibian; IHC; Typhlonectes compressicauda; aquaporin; gymnophiona; mesotocin; vasotocin; vasotocin receptors.