Expression of hypothalamic arginine vasotocin gene in response to water deprivation and sex steroid administration in female Japanese quail.

Arginine vasotocin (AVT) is a neurohypophyseal hormone involved in reproductive function and control of osmoregulation in birds. In view of the dual function of AVT, the present experiment was designed to observe the effect of water deprivation (WD) and sex steroid [estradiol benzoate (EB) and testosterone propionate (TP)] treatment independently, as well as simultaneously, on the profile/activity of the hypothalamic AVT system. WD resulted in a significant increase in plasma osmolality, sodium ion concentration and AVT concentration, but administration of sex steroids had no significant influence on these parameters. By contrast, the amount of hypothalamic AVT transcript (northern analysis) and the size of immunoreactive vasotocin (ir-AVT) neurons and hybridization signals (in the form of silver grains), representing AVT mRNA in corresponding neurons of paraventricular nuclei (PVN), increased significantly in all the treated groups compared with controls. Our findings indicate that although sex steroid administration has no effect on plasma osmolality and AVT concentration, unlike water deprivation, it may stimulate the profile/activity of AVT neurons of PVN, supporting the possibility of sex steroid receptors on these neurons. It is concluded that in quail, osmotic stress not only upregulates the expression of the AVT gene in existing neurons but also recruits many more neurons to increase the rate of AVT synthesis and secretion, while sex steroids appear to have a stimulatory effect only on the existing number of neurons and only at the level of transcription/translation and hence may influence/modulate hypothalamic AVT gene expression in response to osmotic stress. This study also suggests an interrelationship between reproduction and AVT system/function in birds.