Factors controlling the expression of central progesterone receptors

Abstract

Progesterone, a steroid hormone is closely associated with a variety of behavioural and neuroendocrine functions. Studies were undertaken to identify the control of progesterone receptor (PR) expression in avian brain tissue. In the first study, glial cells taken from newly hatched ring doves (Streptopelia risoria) were cultured in vitro to examine their subsequent development and to identify those cells which expressed PR. Astrocytes, identified using an antibody against glial fibrillary acidic protein (GFAP) and oligodendrocytes, marked with an antibody to galactocerebroside (GaIC), were observed in culture 5 days after preparation. Over a period of 25 days both the astrocytes and oligodendrocytes altered in form from a protoplasmic to a filamentous morphology. PR expression, using a specific monoclonal antibody against the hinge region of the chicken oviduct progesterone receptor, occurred in both of these cell types and the immunostaining was essentially nuclear. However, PR-immunoreactivity (PRir) in oligodendrocytes was more pronounced when compared to PR-it in astrocytes. In a subsequent study glial cells were cultured with estrogen added to the medium. The development and differentiation of the glial cells was not effected, although a significant difference was observed in the intensity of PR immunofluorescence. The intensity of PR immunofluorescence was greater in those cells treated with estrogen. Addition of
tamoxifen failed to influence PR expression, however the length of time of culture with this estrogen antagonist was probably too short. An in situ immunocytochemical study was performed to localise the distribution of astrocytes in the newly hatched ring dove brain. Astrocytes were identified as being distributed throughout the brain with a greater density in the peripheral and ventricular areas. Studies to immunolocalise oligodendrocytes in situ were unsuccessful.
A second series of studies examined the distribution of PR-jr in the chicken (Gallus domesticus) brain and to quantify changes in expression during a period of high plasma estrogen concentration (laying) and one of low plasma estrogen concentration (brooding). Cell nuclei containing progesterone receptor were largely restricted to the medial and basal hypothalamic area with the highest density occurring in the preoptic area and the lateral hypothalamus. The distribution of cells containing PR-ir demonstrated a similar pattern in both laying and brooding birds. The number of PR-ir cells was consistently lower in brooding birds than in laying. The intensity of PR expression was also greater in laying birds compared to brooding birds, however, due to the small sample size this did not reach statistical significance. These studies have
demonstrated that progesterone receptors are localised in the avian brain and that in both young and adult birds, PR expression is sensitive to the presence of estrogen.