Gender-related changes in the avian vasotocin system during ontogeny

The arginine vasotocin (AVT) system of the avian brain includes a sexually dimorphic part that extends from the caudal part of preoptic region through the medial part of the bed nucleus of stria terminalis (BSTm) to the later al septum. It is composed of the parvocellular neurons located in the BSTm and the dense innervation of the medial preoptic region and lateral septum. In this part of the brain, AVT expression is stronger in males than in fem ales in a few bird species investigated to date. This review focuses on the ontogeny of sexual differences in the vasotocinergic system of two gallina ceous species, domestic chicken and Japanese quail, and on the role of gona dal hormones in organizing during development and maintaining in adulthood these differences. Parvocellular AVT neurons become discernible in the BSTm of males and females during the second half of embryonic development. Thes e cells undergo a profound and irreversible sexual differentiation during o ntogenetic development. Recent findings demonstrate a dual role of estrogen s in the organization and activation of sex differences in the AVT system. During the embryonic period of ontogeny, estrogens differentiate the AVT sy stem in a sexually dimorphic manner in parallel with the differentiation of sexual behavior, while in adulthood estrogens, locally produced from testo sterone in the male brain, activate AVT synthesis in the BSTm. The sexually dimorphic part of the AVT system is sensitive to a number of abiotic facto rs such as light, temperature, and water availability. It is suggested that sex dimorphic vasotocinergic systems could be implicated in processes of s ocial recognition in various behavioral contexts. Microsc. Res. Tech. 55:27 -36, 2001. (C) 2001 Wiley-Liss, Inc.