Changes in expression of AVT and AVT receptor (VT1) gene in hypothalamus and shell gland in relation to egg laying in white leghorn hen R. Seth, a,b Y.X. Xu, b,c R. Grossmann, b and C.M. Chaturvedi a, * a Molecular Endocrinology Lab, Department of Zoology, Banaras Hindu University, Varanasi 221005, UP, India b Department Functional Genomics and Bioregulation, Institute for Animal Science and Animal Behaviour (FAL), Mariensee, 31535 Neustadt am R€ ubenberg, Germany c Nanjing Agricultural University, Nanjing, PR China Received 6 June 2003; revised 1 March 2004; accepted 4 March 2004 Available online 13 April 2004 Abstract Oviposition is a complex phenomenon involving various regulatory mechanisms at the neuroendocrine levels. Present study was designed to access the changes in arginine vasotocin (AVT) and its receptor (VT1) gene expression in relation to the time of egg laying of white leghorn hen. The expression of AVT gene (Northern blot analysis and in situ hybridization) in the hypothalamus and localization of ir-AVT in the magnocellular neurons of paraventricular nuclei was studied 2 h before ()2 h), immediately after (0 h) and 2 h after (+2 h) egg laying. Simultaneous changes in the AVT and VT1 receptor gene in the shell gland, which finally responds to AVT for smooth muscle contraction and expulsion of egg, were also determined by semi-quantitative reverse transcriptase-poly- merase chain reaction. The findings indicated increased hypothalamic AVT gene expression immediately after egg laying (0 h) when compared to 2 h before and 2 h after egg laying. AVT receptor gene expression in the shell gland also followed the same pattern. However, AVT gene expression in the shell gland, unlike that of hypothalamus was higher at )2 h compared to 0 and +2 h of oviposition. While highly significant increase was noted in plasma AVT concentration at the time of egg laying, other parameters such as plasma osmolality and ionic concentration (Na þ ,K þ , Ca 2þ , and Cl  ) did not show any change. It is suggested that in addition to increased hypothalamic AVT transcript and peripheral release, local synthesis of AVT in the shell gland (paracrine release) may contribute to the contraction of shell gland smooth muscles during egg laying. Moreover, these findings clearly indicate temporal correlation of AVT and its receptor gene expression in different tissues during oviposition. Ó 2004 Elsevier Inc. All rights reserved. 1. Introduction Oviposition or egg laying occurs almost daily after puberty during the reproductive phase of the life cycle in poultry birds. Oviposition is a complex phenomenon involving various regulatory mechanisms, mainly at the level of hypothalamus, hypophysis, ovary, and oviduct. Regulatory factors include follicular growth, ovulation, egg transport through the oviduct, and neuropeptide arginine vasotocin (AVT) and prostaglandin(s) (PG). Oviposition involves contraction of the smooth muscles of uterus (shell gland) and relaxation of the utero-vag- inal sphincter leading to egg expulsion from the oviduct. After the rupture of mature graffian follicle, the ovum travels down the infundibulum, magnum, isthmus, and finally reaches to the shell gland in albumen deposited form where it stays for about 20 h. During its stay in the shell gland the egg acquires shell before being laid. AVT has both oxytocic and antidiuretic properties and is selectively released during oviposition or hyper- tonic saline infusion in chickens (Koike et al., 1988; Nouwen et al., 1984; Sawyer, 1977; Shimada et al., 1986). Both, the sensitivity of uterine muscle to AVT and receptor density is maximal at oviposition (Koike et al., 1988; Saito et al., 1987). The ovary in laying hen contains large amount of AVT which varies in different * Corresponding author. Fax: +91-542-2368323. E-mail addresses: cmcbhu@indiatimes.com, sethrohit@uams.edu (C.M. Chaturvedi). 0016-6480/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ygcen.2004.03.003 www.elsevier.com/locate/ygcen General and Comparative Endocrinology 137 (2004) 177–186 GENERAL AND COMPARATIVE ENDOCRINOLOGY