Medial Eminence

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Medial Eminence

<table class="infobox infobox-cell">
<tr>
<th class="infobox-header" colspan="2">Medial Eminence</th>
</tr>
<tr>
<td class="label">Category</td>
<td>Cell Types</td>
</tr>
<tr>
<td class="label">Brain Region</td>
<td>Hypothalamus</td>
</tr>
<tr>
<td class="label">Neuron Type</td>
<td>Neuroendocrine/Portal neurons</td>
</tr>
<tr>
<td class="label">Species</td>
<td>Human, Mouse, Rat</td>
</tr>
<tr>
<td class="label">Circumventricular Organ</td>
<td>Yes (lacks blood-brain barrier)</td>
</tr>
<tr>
<td class="label">Taxonomy</td>
<td>ID</td>
</tr>
<tr>
<td class="label">Cell Ontology (CL)</td>
<td>[CL:4023035](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_4023035)</td>
</tr>
<tr>
<td class="label">Marker</td>
<td>Cell Type</td>
</tr>
<tr>
<td class="label">Vimentin</td>
<td>Tanycytes</td>
</tr>
<tr>
<td class="label">GFAP</td>
<td>Tanycytes</td>
</tr>
<tr>
<td class="label">OATP1C1</td>
<td>Tanycytes</td>
</tr>
<tr>
<td class="label">MCT8</td>
<td>Tanycytes</td>
</tr>
<tr>
<td class="label">Leptin Receptor</td>
<td>Tanycytes</td>
</tr>
<tr>
<td class="label">Dopamine</td>
<td>Neuronal terminals</td>
</tr>
<tr>
<td class="label">Somatostatin</td>
<td>Neuronal terminals</td>
</tr>
<tr>
<td class="label">GnRH</td>
<td>Neuronal terminals</td>
</tr>
<tr>
<td class="label">CRH</td>
<td>Neuronal terminals</t

...

Medial Eminence

Introduction

Medial Eminence is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

The Medial Eminence (ME) is a circumventricular organ located in the floor of the third ventricle that lacks a blood-brain barrier and serves as a gateway for neuroendocrine communication between the brain and pituitary gland. This specialized structure plays critical roles in hypothalamic-pituitary axis regulation, metabolic sensing, and serves as a neural stem cell niche with significant implications for neurodegenerative diseases[@rodrguez2005][@prevot2010].

Overview

Multi-Taxonomy Classification

Taxonomy Database Cross-References

Morphology & Electrophysiology

Morphology: lateral ganglionic eminence derived neuron (source: Cell Ontology)
Morphology can be inferred from Cell Ontology classification

External Database Links

[Cell Ontology (CL:4023035)](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_4023035)
[OBO Foundry (CL:4023035)](http://purl.obolibrary.org/obo/CL_4023035)
[Allen Brain Cell Atlas](https://portal.brain-map.org/atlases-and-data/bkp/abc-atlas)
[CellxGene Census](https://cellxgene.cziscience.com/)
[Human Cell Atlas](https://www.humancellatlas.org/)

Anatomy and Histology

Gross Anatomy

The medial eminence is located in the infundibular region of the hypothalamus, forming the floor of the third ventricle. It appears as a prominent bulge that connects the hypothalamus to the posterior pituitary gland. The ME is bounded laterally by the arcuate nucleus and superiorly by the ventromedial hypothalamus[@bleier1972].

Microscopic Structure

The medial Eminence contains several specialized cell types and structures:

Tanycytes

Tanycytes are specialized ependymal cells that line the ventricular surface and extend long processes into the underlying brain parenchyma. These cells are classified into two main subtypes[@akmel2022][@goodman2015]:

α-tanycytes: Located primarily in the dorsal ME, with processes extending to the median eminence outer layer
β-tanycytes: Found predominantly in the ventral ME, with processes terminating on portal capillaries

Tanycytes express distinctive molecular markers including vimentin, GFAP, and various thyroid hormone transporters (OATP1C1, MCT8). They possess tight junctions at their apical surface, creating a barrier between the cerebrospinal fluid and the underlying tissue[@brightman1969].

Herring Bodies

Herring bodies are axonal swellings from hypothalamic neurosecretory neurons that contain dense core vesicles filled with neurohormones. These structures store and regulate the release of hypothalamic releasing and inhibiting hormones into the portal capillary system[@dellmann1971].

Portal Capillary System

The median eminence contains an extensive portal capillary network that connects the hypothalamic nuclei to the anterior pituitary. This portal system allows for rapid, direct communication without entering the systemic circulation[@page1977].

Blood-Brain Barrier Properties

Unlike most brain regions, the medial Eminence lacks a functional blood-brain barrier (BBB), making it a circumventricular organ. This property allows[@weindl1973]:

Direct sensing of blood-borne molecules (hormones, cytokines, nutrients)
Gateway for neuroendocrine signaling
Potential route for drug delivery to the CNS

Molecular Markers

The medial Eminence expresses a distinctive set of molecular markers[@roa2011][@fliers1994]:

Normal Physiological Functions

Neuroendocrine Regulation

The medial Eminence serves as the primary gateway for hypothalamic-pituitary communication[@guillemin1966][@harris1978]:

Portal System Function: Direct vascular connection between hypothalamic neurons and anterior pituitary endocrine cells

Hormone Transport: Enables rapid delivery of releasing/inhibiting factors to the pituitary

Feedback Sensing: Allows hypothalamic neurons to detect circulating hormone levels

Hypothalamic Hormones Released via ME

Thyrotropin-releasing hormone (TRH): Stimulates TSH and prolactin release
Somatostatin (SST): Inhibits growth hormone release
Dopamine (DA): Inhibits prolactin secretion
Gonadotropin-releasing hormone (GnRH): Stimulates LH/FSH release
Corticotropin-releasing hormone (CRH): Stimulates ACTH release
Growth hormone-releasing hormone (GHRH): Stimulates GH release

Tanycyte Functions

Tanycytes in the medial Eminence perform multiple critical functions[@rodrguez2010][@garcia2016]:

Barrier Regulation: Gatekeeping between CSF and blood, controlling molecular passage

Transport: Mediate thyroid hormone, leptin, and glucose transport into the brain

Neurogenesis: Serve as neural stem cells, capable of generating new neurons

Energy Sensing: Communicate metabolic state to hypothalamic regulatory centers

Receptor Expression: Express receptors for hormones and nutrients (leptin, insulin, thyroid hormone)

Metabolic Sensing

The medial Eminence is critically involved in energy homeostasis[@balland2014][@sleiman2019]:

Leptin Signaling: Tanycytes transport leptin from the blood to hypothalamic neurons
Glucose Sensing: Detect blood glucose levels and modulate feeding behavior
Thyroid Hormone Regulation: Control CNS thyroid hormone availability
mTOR Pathway: Integrate nutritional signals via mechanistic target of rapamycin

Role in Neurodegenerative Diseases

Alzheimer's Disease

The medial Eminence shows significant pathology in Alzheimer's disease (AD)[@braak2012][@scheltens2016]:

Tau Pathology

Tanycytes accumulate hyperphosphorylated tau protein
Disruption of tanycyte barrier function
Impaired thyroid hormone transport to the brain
Correlation with neurofibrillary tangle distribution

Thyroid Hormone Dysregulation

Reduced thyroid hormone transport across the ME
Contributes to cerebral hypothyroidism in AD
May accelerate cognitive decline
Thyroid dysfunction is a known AD risk factor

Metabolic Dysfunction

Impaired leptin signaling
Disrupted energy homeostasis
Contributes to hypothalamic dysfunction
Links metabolic syndrome to AD pathogenesis

Parkinson's Disease

The medial Eminence is affected in Parkinson's disease (PD)[@jellinger1997][@wakabayashi2007]:

Hypothalamic Involvement

Lewy body pathology extends to hypothalamic nuclei
Disrupted neuroendocrine regulation
Autonomic dysfunction originates partly from ME pathology

Sleep-Wake Cycle Disruption

Altered ME function affects circadian regulation
Contributes to REM sleep behavior disorder
Sleep disturbances precede motor symptoms

Autonomic Dysregulation

Impaired cardiovascular control
Gastrointestinal dysfunction
Thermoregulatory abnormalities

Huntington's Disease

Hypothalamic pathology in Huntington's disease (HD) involves the medial Eminence[@van2019][@politis2008]:

Loss of orexin/hypocretin neurons
Metabolic disturbances
Sleep disorders
Early hypothalamic dysfunction

Multiple System Atrophy

MSA involves autonomic nuclei in the hypothalamic region[@wenning2004]:

Cardiovascular dysregulation
Urinary dysfunction
Sleep architecture disruption

Transcriptomic Profile

Single-cell RNA sequencing has identified distinct cell populations in the medial Eminence[@chen2017][@romanov2020]:

α-tanycytes: Dorsal region, neural stem cell properties

β-tanycytes: Ventral region, barrier function

Neuronal terminals: Neurosecretory axons

Endothelial cells: Portal vasculature

Pericytes: Capillary support

Microglia: Immune surveillance

Therapeutic Implications

Drug Delivery

The lack of blood-brain barrier makes the medial Eminence a potential target for CNS drug delivery[@thorne2004][@dhuria2010]:

Macromolecule Delivery: Proteins, peptides, and antibodies may access CNS
Neurodegenerative Therapies: Direct delivery of disease-modifying compounds
Pituitary Tumors: Access to pituitary via portal system
Gene Therapy: Potential route for viral vector delivery

Hormone-Based Therapies

Thyroid Hormone Therapy

Levothyroxine treatment considerations
T3/T4 transport modulation
Targeting tanycyte function

Metabolic Modulators

Leptin analog therapy
mTOR inhibitors
Metabolic disease management

Regenerative Medicine

The neural stem cell properties of tanycytes offer therapeutic potential[@xie2019]:

Endogenous neurogenesis activation
Cell replacement strategies
Tissue repair mechanisms

Research Directions

Current research focuses on several key areas[@lee2020][@rizzoti2021]:

Tanycyte Biology: Understanding stem cell properties and regeneration

Blood-CSF Barrier: Dynamics of molecular transport

Metabolic Sensing: Integration of nutritional and hormonal signals

Disease Mechanisms: Role in neurodegeneration progression

Therapeutic Targeting: Drug delivery and regenerative approaches

Aging: Age-related changes in ME function

External Links

[PubMed](https://pubmed.ncbi.nlm.nih.gov/) - Biomedical literature
[Alzheimer's Disease Neuroimaging Initiative](https://adni.loni.usc.edu/) - Research data
[Allen Brain Atlas](https://brain-map.org/) - Brain gene expression data

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Medial Eminence

Medial Eminence

Medial Eminence

Introduction

Overview

Multi-Taxonomy Classification

Taxonomy Database Cross-References

Morphology & Electrophysiology

External Database Links

Anatomy and Histology

Gross Anatomy

Microscopic Structure

Tanycytes

Herring Bodies

Portal Capillary System

Blood-Brain Barrier Properties

Molecular Markers

Normal Physiological Functions

Neuroendocrine Regulation

Hypothalamic Hormones Released via ME

Tanycyte Functions

Metabolic Sensing

Role in Neurodegenerative Diseases

Alzheimer's Disease

Tau Pathology

Thyroid Hormone Dysregulation

Metabolic Dysfunction

Parkinson's Disease

Hypothalamic Involvement

Sleep-Wake Cycle Disruption

Autonomic Dysregulation

Huntington's Disease

Multiple System Atrophy

Transcriptomic Profile

Therapeutic Implications

Drug Delivery

Hormone-Based Therapies

Thyroid Hormone Therapy

Metabolic Modulators

Regenerative Medicine

Research Directions

See Also

External Links