Research reportDistribution of estrogen receptor alpha and beta immunoreactive profiles in the postnatal rat brain
Introduction
Estrogens are lipophilic molecules, which are crucial for the neuronal differentiation of the brain during ontogeny. These steroids regulate brain function(s) either by genomic or non-genomic mechanisms (see Ref. [40]). Non-genomic actions occur via putative membrane receptors, which trigger rapid physiological responses. Genomic action is initiated, by estrogen’s binding with specific receptors, which activate gene expression at the nuclear level. At present, two estrogen receptors (ERs) have been identified termed alpha (ERα) [20] and beta (ERβ). The latter was recently cloned from rat prostate [23]. Both ERs have a specific binding affinity for estradiol and are capable of activating the transcription of an estrogen response element reporter gene construct [23]. These ERs share a high degree of homology in the N-terminal DNA binding domain, but less in the C-terminal DNA binding domain [23]. The existence of two ERs suggests that estrogens mediate different cellular events via one or the other or a combination of these receptor subtypes [49], [52].
Most investigations of the expression of the protein and message for ERs within the mammalian brain have been performed on tissue obtained from adults [5], [6], [9], [7], [17], [19], [21], [24], [42], [48], [54], [57], [58], [59], [67]. Specifically in the rat brain ERα and ERβ containing structures have been found throughout the adult neuraxis [5], [24], [26], [57], [58], [80]. However, despite the large amount of data indicating that estrogen plays a fundamental role in the sexual differentiation of the brain [22], [30], [31], [34] the precise localization and temporal distribution of ERs during development remain unknown. In the neonatal rat brain ERα immunoreactive profiles have been found in the diencephalon, amygdala [79], cerebral cortex [81] and ERβ containing cells were found in the cerebellum [18] and cerebral cortex [81]. Currently, there are no immunohistochemical studies detailing the distribution of ERα or ERβ throughout the entire postnatal rat brain. Therefore, the aim of the present study was to compare the distribution of ERβ to ERα immunoreactive profiles during the postnatal development of the rat brain. In addition, co-localization of these ERs was determined using a dual confocal immunofluorescence method. The data obtained from these studies will contribute to our understanding of the functions of ERs throughout the neuraxis during postnatal development.
Section snippets
Subjects
Four postnatal (P) rats (Fisher 344) of each sex, from P3, P7 and P14 days were used in the present study (a total of 24 pups). Each cohort was maintained on a 12:12 light–dark cycle at 20 °C in the animal care facility. All procedures were approved by the local Animal Care committee and were performed according to the NIH standards for animal care and use. The dams were given food and water available ad libitum. All rats were deeply anesthetized with an overdose of pentobarbital (100 mg/kg) and
General considerations
With the exception of the cerebral cortex (Fig. 4), no variations in the distribution of ERβ and ERα immunoreactive (ir) nuclei were observed within the brain across the postnatal ages examined (P3, P7 and P14) or between sexes. A topographic comparison of these receptors revealed that distribution of ERα-ir is more widespread than ERβ-ir within the postnatal developing rat brain (see Table 1, Fig. 1). ERβ and ERα-ir profiles appeared as a brown precipitate within the cell nucleus, whereas
General considerations
The present investigation revealed a widespread distribution of ERα and ERβ-ir nuclei at P3, P7 and P14, although ERα-ir was more extensive throughout the postnatal rat brain. Evaluation of these postnatal time points did not display distributional differences between the sexes for each ER. On the other hand, the only variation in the distribution of these receptors across the postnatal ages examined was observed within the cerebral cortex. In general, our findings support and expand the
Acknowledgements
This project was supported by AG16765, AG10688 and AG14449. We wish to thank M. Nadeem and W. Sun for histological and photographic assistance.
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