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Tamiki Hikake, Shinji Hayashi, Taisen Iguchi and Tomomi Sato

IGF1 knockout (IGF1KO) mice show a reduced number of prolactin (PRL) producing cells (PRL cells); however, the role of IGF1 in PRL cell proliferation and differentiation in immature mice is unclear. In this study, ontogenic changes in the percentages of PRL cells, GH producing cells (GH cells), and 5-bromo-2′-deoxyuridine (BrdU)-labeled cells in the anterior pituitary of male IGF1KO mice during the postnatal period were investigated. The percentage of PRL cells in IGF1KO mice was significantly lower at day 20 compared with that in wild-type (WT) mice, while GH cells in IGF1KO mice were significantly increased from day 10. From days 5 to 20, the percentage of BrdU-labeled cells in WT and IGF1KO mice was similar. PRL cells and GH cells are thought to originate from the same progenitor cells, therefore, PRL cells in IGF1KO mice are not able to differentiate because progenitor cells have already committed to be GH cells. However, IGF1, 17β-estradiol (E2), epidermal growth factor (EGF), or IGF1 plus E2 treatments increased the PRL cell number in the pituitaries in vitro of 10-day-old WT and IGF1KO mice. This fact suggests that these factors are involved in PRL cell proliferation and differentiation. In addition, the increase of PRL cells in IGF1KO mice stimulated by E2 or EGF was less than that of WT mice. Thus, IGF1 plays a crucial role in PRL cell proliferation and differentiation in mouse pituitaries by regulating the differentiation of progenitor cells and mediating the actions of E2 and EGF.

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Cleyde Vanessa Vega Helena, Maristela de Oliveira Poletini, Gilberto Luiz Sanvitto, Shinji Hayashi, Celso Rodrigues Franci and Janete Aparecida Anselmo-Franci

We have previously shown that the locus coeruleus (LC) is essential for triggering surges of LH. Since LC neurons are responsive to estradiol, which induces progesterone receptor (PR) expression, this study aimed to investigate whether LC neurons express the α-estradiol receptor (αER) and PR as well as comparing such responses to that observed in the preoptic area (POA). Female rats were perfused at 10, 14 and 16 h on each day of the estrous cycle, and a blood sample was collected for estradiol, progesterone and LH measurements. αER- and PR immunoreactive (ir) neurons were detected in POA and LC by immunocytochemistry (ICC). Higher plasma estradiol levels were observed on the day of proestrus, when a smaller number of αER-ir POA neurons were detected. An increase in the number of αER-ir neurons were observed at 16 h of proestrus and estrus. The number of PR-ir neurons increased in POA only at 16 h of proestrus, and remained unchanged during all other days and times. The profile of αER-ir and PR-ir neurons in LC changed over the estrous cycle, with a lower expression on metestrus morning and reaching a peak on diestrus afternoon before declining on the day of proestrus. However, on estrus afternoon, αER-ir neurons increased, while PR-ir neurons decreased which may be related to the prolactin surge of estrus. These data show that LC neurons express αER and PR and seem to be more sensitive to variations in estradiol than POA. Also, the fluctuation in αER and PR observed for LC neurons seems to accompany the hormonal events that occur during the estrous cycle. This profile of αER and PR expression might be related to the ability of estradiol and progesterone in regulating the activity of LC neurons, which could be associated to the control mechanisms of LH and prolactin release.