the mammalian genes encoding arginine vasopressin. Removal of the 19-amino acid N-terminal signal peptide generates the prohormone, which is hydrolysed to AVT (derived from amino acids 20-28) and neurophysin VT (derived from amino acids 32-161). The existence of two AVT preprohormones with different sequences in fishes (such as chum salmon, Oncorhynchus keta) is evidence for gene duplication. Physiological Effects AVT combines both antidiuretic and reproductive activities similar to those of oxytocin and vasopressin. The physiological actions of AVT in birds are mediated through diverse receptor subtypes VT1, VT2, VT3 and VT4. AVT and synthetic analogs injected into monkeys cause reabsorption of osmotically free water and changes in excretion of sodium and potassium ions in the kidneys. AVT produces distinct effects on the reproductive functions of male and female domestic chickens. In laying hens, AVT synthesised in magnocellular diencephalic neurons is released into circulation in a highly coordinated manner, contributing to the peripheral control of oviposition. In males, parvocellular AVT cells located in the limbic system (bed nucleus of stria terminalis) express AVT. This expression is sensitive to gonadal steroids and is correlated with sexual differentiation of masculine behavior such as courtship vocalization and copulation. Behavioral Effects Several animal studies have been conducted that explore the behavioral effects of AVT. The main findings of these studies have revealed that AVT plays an integral role in the pair bonding behavior and social hierarchy in non-mammalian vertebrates. In a study conducted with zebra finches, increased levels of AVT were linked to an increase in aggressive, competitive behavior in non-paired male finches, but were subsequently related to an increase in defensive behavior after the finches had been paired. However, this study also found that blocking AVT receptors did not directly affect pair bonding ability. The shift in behaviors were explained by the location of the release of AVT in the brain. Competitive aggressive behavior was found to be linked with AVT release in the BSTm, whereas defensive, nest-protecting behavior was linked with AVT release in the neurons of the Hypothalamus and Paraventricular Nucleus. In a study conducted with male Japanese quail, AVT was found to have an effect on later social interactions amongst the species. Immediately after injection with AVT, the quails displayed less aggressive behavior (pecking). However, the next day, the quail that were injected with AVT displayed more dominant behavior towards familiar birds, but not unfamiliar birds. This study shows that AVT