Sexually dimorphic immunoreactivity of galanin and colocalization with arginine vasotocin in the chicken brain (Gallus gallus domesticus).

The bed nucleus of the stria terminalis medialis (BSTM) of adult chickens (Gallus gallus domesticus) was previously shown to synthesize arginine vasotocin (AVT) in males only and coincides spatially and temporally with steroid activity regulating male reproductive behavior. Galanin has been shown to be a potent modulator of the behavioral and neuroendocrine responses in the mammalian BSTM and in other sexually dimorphic brain regions. In the present study of adult chickens the morphological relationship of AVT and galanin was examined by immunohistochemical analysis of two limbic structures, the BSTM and the lateral septum (SL). The analysis also included the hypothalamic nuclei supraopticus (SON) and paraventricularis (PVN). In males galanin and AVT were both synthesized in the BSTM, while in females neither galanin nor AVT was present. Furthermore, in the males galanin and AVT were colocalized in the majority of neurons within BSTM and in fibers of the SL. In both sexes galanin neurons in the PVN were scattered between the distinct clusters of AVT neurons and there was no colocalization of galanin and AVT in single PVN neurons. Furthermore, AVT immunoreactivity was significantly higher in the SON than in the PVN in both sexes. In the SON, galanin was colocalized with AVT in significantly more neurons in hens than in males (P

Characterization and immunohistochemical visualization of the vasotocin VT2 receptor in the pituitary gland of the chicken, Gallus gallus.

Arginine vasotocin is a neurohypophysial hormone in lower vertebrates including birds. Its actions are mediated through G-protein coupled receptors that belong to the vasopressin/oxytocin receptor family. Our laboratory recently cloned a vasotocin receptor, designated the VT2 receptor (VT2R), which shares high sequence identity at both the nucleotide and amino acid level with the mammalian V1b vasopressin receptor (V1bR). In the present study, we report development and use of an antibody to the VT2R to obtain anatomical evidence for testing the hypothesis that the VT2R is the avian homolog of the mammalian V1bR. Results verified the specificity of the antibody and demonstrated a receptor distribution occurring predominantly in the cephalic lobe of the pars distalis and co-localizing with adrenocorticotropin in corticotrophs. With respect to VT2R distribution and cell-type localization in pituitary gland, evidence presented support its similarity with the mammalian V1bR. In contrast to the mammalian V1bR, VT2R expression was not observed in chicken brain. Further research will be required to determine which receptor/s in the arginine vasotocin/mesotocin family are expressed in brain and mediate regulatory functions of vasotocin in the central nervous system.

Effects of estrogens during embryonal development on crowing in the domestic fowl.

In the domestic fowl, crowing is typically a male-specific vocal behavior while the females normally do not crow. These sex differences in vocalization may result from organizational actions of estrogens during specific periods of embryonic development. To further investigate the role of estrogens in differentiation of crowing and development of the acoustic characteristics of crow calls, male domestic fowls were treated on Incubation Day 8 with estradiol benzoate (EB) or either oil or saline vehicles. On the same incubation day, the female fowls were treated with an aromatase inhibitor, fadrozole, or saline vehicle. An adulthood vocalization of cocks and hens was recorded during corresponding tests of sexual behavior. The exposure to EB or fadrozole had no effect on sexual differentiation of the gonads and all fadrozole-treated hens laid eggs at a rate similar to the control hens that received saline. While the levels of plasma testosterone at adulthood did not differ in treated and untreated cocks, the incidence of crowing rate was significantly lower in cocks that were exposed to estradiol. Acoustic analysis revealed a considerable reduction in duration and acoustic energy of calls while the main frequency characteristics were not changed. Four out of the seven tested fadrozole-treated hens demonstrated regularly crow-like vocalization with shorter duration and lower energy of calls in comparison to crows of the control males. These findings point out to a role for estradiol in organization of crowing behavior and a specific temporal pattern of the crowing call.

Sex dimorphism in the avian arginine vasotocin system with special emphasis to the bed nucleus of the stria terminalis.

The avian neuropeptide arginine vasotocin (AVT) originally characterized as the antidiuretic hormone (, Endocrinol. 66, 860-871) is produced by neurosecretory cells within the brain. Numerous neuroanatomical studies that employed immunocytochemical and in situ hybridization techniques revealed such cells in the following anatomical brain locations: (a) preoptic area including supraoptic nucleus; (b) paraventricular nucleus; (c) the bed nucleus of the stria terminalis (BnST) (, J. Hirnforsch. 27, 559-566;, J. Neuroendcrinol. 5, 281-288;, Cell Tiss. Res. 287, 69-77;, J. Comp. Neurol. 369, 141-157). The BnST which influences reproduction and sexual behavior shows sex differences in morphology, steroid responsiveness and synthesis of neuropeptides including AVT (, Brain Res. 657, 171-184). AVT is the main endocrine regulator of fluid balance in avian species and, in addition, is involved in oviposition in these species. Our recent studies clearly demonstrated that AVT secretion after osmotic stimulation is sexually dimorphic. In order to investigate whether AVT is expressed and synthesized in the BnST in a sexually dimorphic manner we have used in situ hybridization technique and immunocytochemistry to analyze AVT gene expressing neurons in the parvocellular (small-celled nulei) BnST of adult male and female chickens. In cocks, AVT peptide-containing neurons were detected in the parvocellular BnST and the lateral septal area, whereas no AVT immunoreactive neurons were detected in the corresponding regions of the hen. Even after osmotic stimulation AVT gene expression in neurons of the parvocellular BnST of hens was not upregulated (, Cell Tiss. Res. 287, 69-77). These results demonstrate: (a) AVT gene expression in the BnST of chickens; and (b) a strong sexual dimorphism in this region. Furthermore, AVT synthesis is regulated on the transcriptional level independent from osmotic stimuli. Thus, sex steroids might be the main regulator of AVT gene expression in the BnST. In this paper we not only review the sexual dimorphic vasotocinergic system in the BnST, we also focus on the ontogeny of sex differences and the role of gonadal hormones in organization and retention of these differences.