= Median eminence
The <median eminence> is a region at the base of the <hypothalamus> where neurosecretory terminals release regulatory <hormones> near the first <capillary bed> of the <hypophyseal portal system>. It is an interface between hypothalamic <neurons> and the vascular route to the <anterior pituitary>. A <GnRH> terminal here is a site of release; the <neuron>'s <soma> need not occupy the same location.<Vascular endothelial cells promote acute plasticity in ependymoglial cells of the neuroendocrine brain by Sandrine De Seranno and others>[Introduction and Abstract: median-eminence neurosecretory interface]{ref}
Access to the <capillaries> also depends on neighboring <glial cells>, including <tanycytes>. In a 2004 study, female-rat tissue containing the <median eminence> was incubated for 30 minutes with or without added <arginine>, a substrate for <nitric oxide> production. <Immunoelectron microscopy> identified <GnRH>-containing terminals. In treated preparations, the investigators observed structural changes bringing terminals into direct contact with the space beside the <capillaries>. Complementary cell-culture experiments implicated signals from <endothelium> in glial remodeling.<Vascular endothelial cells promote acute plasticity in ependymoglial cells of the neuroendocrine brain by Sandrine De Seranno and others>[Abstract; Figure7:500micromolar L-arginine,30min and immunogold localization]{ref}
The comparison is illuminating because the route is more than a fixed pipe connecting two glands. The arrangement of <neurons>, <glial cells> and <blood vessels> can alter access to the release surface. A microscopic structural observation and a measurement of circulating <hormone> nevertheless remain different kinds of evidence: proximity alone does not quantify how much <GnRH> enters the <blood>.
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