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.
