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.