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Proceedings of The Physiological Society
University of Central Lancashire (2002) J Physiol 543P, S224
Localization and distribution of progesterone receptors in the hypothalamus and pituitary of the domestic fowl (Gallus domesticus)
B. Das*, R.W. Lea* and P.J. Sharp
*University of Central Lancashire, Preston PR1 2HE and The Roslin Institute, Roslin, Midlothian EH25 9PS, UK
In avian species, gonadal steroids are closely involved with neuroendocrine events and the behaviour associated with the breeding cycle. The pre-ovulatory surge of progesterone in the domestic fowl is involved in the timing of oviposition and ovulation (Wilson & Sharp, 1976) and in addition, progesterone has a central action on the expression of appropriate nesting behaviour (Wood-Gush et al. 1977).
Previous studies using immunocytochemistry (ICC) have demonstrated the existence of central progesterone receptors in the hypothalamic region of the domestic fowl, but the identification of exact nuclei is as yet unclear (Kawashima et al. 1978; Sterling et al. 1987).
The purpose of this study is firstly to accurately identify the distribution of central and pituitary progesterone receptor immunoreactivity (PR-ir), and secondly to quantify any changes in PR-ir expression that may be associated with the stages of the breeding cycle.
Adult domestic fowl were terminally anaesthetized with an intramuscular injection of sodium pentobarbitone (60 mg kg-1 body weight) and the brain was perfused immediately through the two internal carotid arteries with 500 ml of Zamboni's fixative followed by 400 ml of 10 % sucrose. The tissue was frozen with isopentane and liquid nitrogen and 16 µm cryostat sections were collected and prepared for ICC. The expression of PR-ir was determined using a monoclonal antibody (clone H928; dilution 1:1000; Calbiochem) raised against the hinge region of the chicken progesterone receptor. Brains from laying hens (n = 4) and brooding hens (n = 4) were collected as matched pairs and processed accordingly.
PR-ir was confined to several discrete hypothalamic regions of the brain, the nucleus periventricularis hypothalami (PHN), nucleus paraventricularis (PVN), nucleus preopticus periventricularis (POP), organum vasculosum lamina terminalis (OVLT), nucleus suprachianmaticus (SCNm), nucleus preopticus medialis (POM), and tuberal region (Tu) (Kuenzel & Masson, 1988). Quantification studies demonstrated that the PHN, PVN, POM and POP of the brain of the laying (ly) hens does not possess a significantly greater number of PR-ir compared with the brains of broody (br) hens (P > 0.05), whereas OVLT, SCNm and Tu demonstrated a significantly greater number (P < 0.05). PR-ir was widespread in the anterior pituitary (Pit) of the laying hen but significantly depressed (P < 0.05, unpaired t test) in those glands taken from brooding birds.
These studies are consistent with progesterone having a central action associated with both neuroendocrine regulation and reproductive behaviour at different stages of the breeding cycle of the domestic fowl.
All procedures accord with current UK legislation.
Where applicable, experiments conform with Society ethical requirements