Abstract
This chapter discusses the observations on the development of the median eminence (ME) during ontogenesis that has been obtained mainly in recent years. Information of this kind is of particular importance for the evaluation of the establishment of the direct and the feedback regulations of the neuroendocrine system. At the level of the ME hypothalamic neurohormones are released from the neurosecretory axons to the hypophyseal portal circulation and transferred to the adenohypophysis, thus directly regulating this gland. In turn, adenohypophyseal hormones ascend via the same portal circulation to the ME, and finally to the hypothalamic neuroendocrine centers contributing to their short feedback regulation. At the level of the ME, neurohormones are discharged from the supraependymal axons to the cerebrospinal fluid (CSF). A part of the neurohormones circulating in the CSF penetrates through the CSF-brain barrier and controls the neuroendocrine centers in an ultrashort feedback manner. Another part is transferred via tanycytes to the hypophyseal portal circulation reinforcing the direct regulation of the adenohypophyseal functions. The axonal pathways for the transfer of adenohypophyseotropic neurohormones to the median eminence in rats are established by the end of fetal life.
Published Version
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