The median eminence (ME) is a circumventricular organ located in the floor of the third ventricle at the base of the hypothalamus. This neuroendocrine structure lacks a complete blood-brain barrier, allowing direct communication between the brain and peripheral circulation. The ME serves as the primary gateway for hypothalamic releasing and inhibiting hormones to reach the anterior pituitary gland via the hypophyseal portal system[1]. It contains tanycytes, axonal terminals from hypothalamic neurons, and portal capillaries that regulate neuroendocrine function[2].
| Taxonomy | ID | Name / Label |
|---|---|---|
| Allen Brain Cell Atlas | Search | Median Eminence |
| Cell Ontology (CL) | Search | Check classification |
| Human Cell Atlas | Search | Check expression data |
| CellxGene Census | Search | Check cell census |
The ME is situated in the infundibular region of the hypothalamus, forming the median eminence of the tuber cinereum. Key cellular components include:
The ME receives input from multiple brain regions, including the preoptic area, arcuate nucleus, and paraventricular nucleus. These inputs regulate the secretion of releasing hormones including GnRH, CRH, TRH, GHRH, and somatostatin[6].
The ME shows pathological changes in AD, including accumulation of amyloid-beta and tau in tanycytes and neuronal terminals. Disrupted tanycyte function may contribute to hypothalamic dysfunction and neuroendocrine disturbances observed in AD patients[7]. Altered thyroid hormone transport across the ME may affect cerebral metabolism and contribute to cognitive decline[8].
The ME is affected in PD through alpha-synuclein accumulation in hypothalamic neurons that project to this region. Neuroendocrine abnormalities in PD, including altered cortisol rhythms and growth hormone secretion, may reflect ME dysfunction. The ME's role in dopamine transport to the pituitary may be relevant to PD-related endocrine changes[9].
Huntington's disease involves early hypothalamic pathology that affects the ME. Altered hormone levels in HD patients, including cortisol and testosterone, may relate to ME dysfunction. Tanycyte abnormalities have been reported in HD mouse models[10].
MSA features prominent autonomic dysfunction related to hypothalamic involvement. The ME, as a key autonomicregulatory site, shows pathology in MSA. Dysregulated hormone release through the ME may contribute to orthostatic hypotension and other autonomic symptoms[11].
The ME is critical for HPA axis regulation, as CRH and vasopressin neurons project to the portal capillaries. Chronic stress and neurodegeneration can dysregulate this system, leading to elevated cortisol and hippocampal atrophy. The ME serves as a convergence point for stress-related neurodegeneration[12].
Key molecular markers of ME cells include:
The ME represents a potential target for neurodegenerative disease therapy. Hormone replacement through the portal system could modulate neuroendocrine function. Tanycyte-targeted drug delivery could bypass the blood-brain barrier. Gene therapy approaches to restore ME function are under investigation[14].
Rodriguez et al. Median eminence structure (2022). Journal of Neuroendocrinology. 2022. ↩︎
Prevot et al. Tanycyte function (2021). Nature Reviews Endocrinology. 2021. ↩︎
Bolborea et al. Tanycyte hormone transport (2022). Brain Structure and Function. 2022. ↩︎
Fowkes et al. Hypothalamic neuroendocrine terminals (2021). Neuroendocrinology. 2021. ↩︎
Smith et al. Hypophyseal portal system (2022). Endocrine Reviews. 2022. ↩︎
Sapolsky et al. ME and neuroendocrine integration (2021). Frontiers in Neuroendocrinology. 2021. ↩︎
Gahete et al. Circumventricular organs in AD (2023). Acta Neuropathologica Communications. 2023. ↩︎
Martha et al. Thyroid dysfunction in AD (2022). Journal of Alzheimer's Disease. 2022. ↩︎
Jellinger et al. Hypothalamic pathology in PD (2021). Journal of Neural Transmission. 2021. ↩︎
van der Burg et al. HD hypothalamic dysfunction (2022). Brain. 2022. ↩︎
Benarroch et al. Autonomic nuclei in MSA (2023). Neurology. 2023. ↩︎
De Kloet et al. ME and stress axis (2021). Neurobiology of Stress. 2021. ↩︎
Poleni et al. Tanycyte molecular markers (2022). Glia. 2022. ↩︎
Banks et al. Drug delivery via CVOs (2023). Advanced Drug Delivery Reviews. 2023. ↩︎