Objectives: 

The peptide arginine vasotocin (AVT), homologous to mammalian arginine vasopressin, is involved in fish in many aspects of physiology and behaviour, such as osmoregulation, biological rhythms, reproduction, metabolism or responses to stress. Since a decrease in appetite is a general response to stress in fish and other vertebrates, we investigated here the role of AVT as a possible food intake regulator in the rainbow trout.

Materials: 

We used intracerebroventricular injections for central administration of AVT to rainbow trout (Oncorhynchus mykiss) at doses of 1 ng/g body mass or 4 ng/g body mass. In a first experiment we evaluated the temporal response of food intake after AVT treatment. In a second experiment, we investigated the effects of central AVT administration on the response of typical stress markers (plasma cortisol, glucose and lactate levels), as well as brain serotonergic, noradrenergic and dopaminergic activity. In addition, the mRNA levels of genes involved in food intake regulation (neuropetide Y, pro-opiomelanocortin, cocaine and amphetamine-regulated transcript and corticotropin-releasing factor, CRF) and in CRF- (CRF-binding protein) and AVT-signaling (pro-AVT and AVT receptor), were also assessed after AVT treatment.

Results: 

Food intake was strongly reduced in trout exposed to AVT, which recovered normal food intake levels 72 hours after central AVT administration of the peptide. AVT also induced an increase in the plasma levels of cortisol and glucose and a decrease in the hypothalamic mRNA levels of the AVT-receptor gene.The serotonergic activity was increased in the telencephalon and the hypothalamus of AVT-treated fish.

Conclusions: 

Our results showed that AVT is a potent anorexigenic factor in fish and that AVT action was mediated by HPI axis activation. The appetite-regulating peptides seem not to be involved in the food intake-suppressing action of the AVT, although the involvement of CRF signaling is unclear.