Activated vasotocin and galanin immunoreactivity in magnocellular supraoptic neurons of female chickens at oviposition

Vasotocin (AVT) is well known as hormone of the magnocellular hypothalamo-neurohypophysial system that is activated at oviposition in female chickens.

Objectives: In the present study, the time course of AVT and galanin (Gal) immunoreactivity (ir) in the hypothalamic supraoptic nucleus (SON) of chickens relative to the time of oviposition was investigated. Three different time points were selected: (1) four hours before the presumed oviposition, (2) immediately after oviposition, and (3) four hours after oviposition.

Methods: After perfusion of terminally anesthetized birds, brains were cut coronally at 40µm kryosections. The sections were incubated with guinea pig anti-porcine galanin antiserum diluted 1:600 and rabbit anti-AVT antiserum diluted 1:30,000. Fluorescent labeling was performed with goat anti guinea pig IgG linked to FITC to detect chicken Gal and goat anti rabbit antibody labeled with Alexa 555 for AVT to visualize both peptides in the same sections by confocal microscopy in multitracking mode.

Results: Highest AVT-ir and numbers of ir cells were recorded at oviposition. Gal-ir with up to 100% co-localization to AVT was seen only in the magnocellular neurons of the SON in hens immediately after oviposition. At four hours before presumed oviposition, the lowest ir and numbers of AVT cells were found. In contrast, four hours before as well as four hours after oviposition no Gal ir was detected in SON neurons.

Conclusions: These results demonstrate for the first time oviposition related increase of AVT ir and co-localisation with Gal in the SON of female chickens. These observations refine our previous reports of sexual dimorphic Gal ir in SON as restricted to female reproductive function. A paracrine and/or autocrine action of Gal is suggested for the oviposition related activation of AVT synthesis in the hypothalamo-neurohypophysial system.