Ammonia-N exposure alters neurohormone levels in the hemolymph and mRNA abundance of neurohormone receptors and associated downstream factors in the gills of Litopenaeus vannamei.

Abstract

Effects of ammonia-N (0.05, 2, 10 and 20 mg l-1) on the neuroendocrine regulation of ammonia transport were investigated in Litopenaeus vannamei The results showed that corticotrophin-releasing hormone, adrenocorticotropic hormone, dopamine, noradrenaline and 5-hydroxytryptamine concentrations in all ammonia-N groups increased significantly between 3 and 12 h. Cortisol increased significantly between 3 and 24 h. All hormones except crustacean hyperglycemic hormone were reduced to control levels. mRNA abundance of guanylyl cyclase increased significantly during the experiment. Dopamine receptor D4 and α2 adrenergic receptor mRNA abundance in treatments decreased significantly at the beginning, and eventually returned to the control level, whereas mRNA abundance of the 5-HT7 receptor increased significantly only within the first 12 h. Changes in protein kinase (PKA, PKG) mRNA abundance were similar to the patterns of biogenic amines and crustacean hyperglycemic hormone, peaking at 6 and 12 h, respectively, whereas PKC mRNA abundance decreased within 24 h. 14-3-3 protein, FXYD2 and cAMP-response element binding protein mRNA abundance increased significantly and peaked at 6 h. β-catenin and T-cell factor mRNA abundance increased significantly throughout the experiment and peaked at 12 h. The upregulation of Rh protein, K+ channel, Na+/K+-ATPase, V-type H+-ATPase and vesicle associated membrane protein (VAMP) mRNA, together with downregulation of Na+/K+/2Cl- cotransporter mRNA, indicated an adjustment of general branchial ion-/ammonia-regulatory mechanisms. Meanwhile, hemolymph ammonia concentration was significantly increased in most ammonia-N exposure groups. Histological investigation revealed the hepatopancreatic damage caused by ammonia-N. Results suggest that hormones, biogenic amines and Wnt/β-catenin play a principal role in adapting to ammonia-N exposure and facilitating ammonia transport.