Electron microscope studies on the development of the external zone of the mouse median eminence

1971 ◽  
Vol 122 (4) ◽  
pp. 488-502 ◽  
Author(s):  
Laila Eurenius ◽  
Rune Jarsk�r
Keyword(s):  
Electron Microscope ◽  
Median Eminence ◽  
External Zone

scholarly journals Acute hypoxia activates neuroendocrine, but not presympathetic, neurons in the paraventricular nucleus of the hypothalamus: differential role of nitric oxide

2017 ◽  
Vol 312 (6) ◽  
pp. R982-R995 ◽  
Author(s):  
K. Max Coldren ◽  
De-Pei Li ◽  
David D. Kline ◽  
Eileen M. Hasser ◽  
Cheryl M. Heesch
Keyword(s):  
Nitric Oxide ◽  
Paraventricular Nucleus ◽  
Median Eminence ◽  
Nucleus Tractus Solitarius ◽  
Acute Hypoxia ◽  
Ventrolateral Medulla ◽  
Specific Cell ◽  
External Zone ◽  
Cell Phenotypes

Hypoxia results in decreased arterial Po2, arterial chemoreflex activation, and compensatory increases in breathing, sympathetic outflow, and neuroendocrine secretions, including increased secretion of AVP, corticotropin-releasing hormone (CRH), adrenocorticotropin hormone (ACTH), and corticosterone. In addition to a brain stem pathway, including the nucleus tractus solitarius (nTS) and the rostral ventrolateral medulla (RVLM), medullary pathways to the paraventricular nucleus of the hypothalamus (PVN) contribute to chemoreflex responses. Experiments evaluated activation of specific cell phenotypes within the PVN following an acute hypoxic stimulus (AH; 2 h, 10% O2) in conscious rats. Retrograde tracers (from spinal cord and RVLM) labeled presympathetic (PreS) neurons, and immunohistochemistry identified AVP- and CRH-immunoreactive (IR) cells. c-Fos-IR was an index of neuronal activation. Hypoxia activated AVP-IR (~6%) and CRH-IR (~15%) cells, but not PreS cells in the PVN, suggesting that sympathoexcitation during moderate AH is mediated mainly by a pathway that does not include PreS neurons in the PVN. Approximately 14 to 17% of all PVN cell phenotypes examined expressed neuronal nitric oxide synthase (nNOS-IR). AH activated only nNOS-negative AVP-IR neurons. In contrast ~23% of activated CRH-IR neurons in the PVN contained nNOS. In the median eminence, CRH-IR terminals were closely opposed to tanycyte processes and end-feet (vimentin-IR) in the external zone, where vascular NO participates in tanycyte retraction to facilitate neuropeptide secretion into the pituitary portal circulation. Results are consistent with an inhibitory role of NO on AVP and PreS neurons in the PVN and an excitatory role of NO on CRH secretion in the PVN and median eminence.

Many Peptides that Are Present in the External Zone of the Median Eminence Are Not Secreted into the Hypophysial Portal Blood of Sheep

1993 ◽  
Vol 57 (5) ◽  
pp. 765-775 ◽  
Author(s):  
Iain Clarke ◽  
David Jessop ◽  
Robert Millar ◽  
Margaret Morris ◽  
Steven Bloom ◽  
...  
Keyword(s):  
Median Eminence ◽  
Portal Blood ◽  
External Zone ◽  
Hypophysial Portal

scholarly journals Video-enhanced technique for detecting neurophysin, enkephalin, and somatostatin immunoreactivity in ultrathin sections of cat median eminence.

1986 ◽  
Vol 34 (11) ◽  
pp. 1405-1415 ◽  
Author(s):  
H D Coulter ◽  
R P Elde
Keyword(s):  
Median Eminence ◽  
Freeze Drying ◽  
Video Camera ◽  
Neuropeptide Immunocytochemistry ◽  
Serial Sections ◽  
External Zone ◽  
Freeze Dried ◽  
Ultrathin Sections ◽  
Low Levels ◽  
Somatostatin Immunoreactivity

A freeze-drying technique using epoxy-embedded ultrathin serial sections permits critical comparisons of neuropeptides in small fibers and varicosities of the nervous system by video-enhanced, light microscopic immunofluorescence. The desirability of the method was documented by data showing: retention of radioimmunoassayable somatostatin in freeze-substituted blocks of tissue as compared to its loss in tissue dehydrated in an alcohol series; feasibility of OsO4 vapor fixation of freeze-dried tissue and compatibility with neuropeptide immunocytochemistry, and utility of a silicon-intensified-tube video camera for recording low levels of fluorescence from ultrathin sections. Ultrathin serial sections, 150 nm thick, from the inner zone of freeze-dried median eminence of the cat revealed three populations of axons containing various combinations of neurophysin immunoreactivity and enkephalin immunoreactivity. Some elements contained neurophysin immunoreactivity alone, some contained both neurophysin immunoreactivity and enkephalin immunoreactivity, and a few elements contained enkephalin immunoreactivity alone. The adjacent external zone of the median eminence contained immunoreactivity for all three substances, but the structures in this region were too small to permit demonstration of coexistence in 150 nm thick sections.

scholarly journals Tanycyte Pyroglutamyl Peptidase II Contributes to Regulation of the Hypothalamic-Pituitary-Thyroid Axis through Glial-Axonal Associations in the Median Eminence

Endocrinology ◽  
2009 ◽  
Vol 150 (5) ◽  
pp. 2283-2291 ◽  
Author(s):  
Edith Sánchez ◽  
Miguel Angel Vargas ◽  
Praful S. Singru ◽  
Isel Pascual ◽  
Fidelia Romero ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Median Eminence ◽  
Anterior Pituitary ◽  
Cellular Localization ◽  
Third Ventricle ◽  
Male Rats ◽  
Mediobasal Hypothalamus ◽  
External Zone ◽  
The Third ◽  
In Cells

Pyroglutamyl peptidase II (PPII), a highly specific membrane-bound metallopeptidase that inactivates TRH in the extracellular space, is tightly regulated by thyroid hormone in cells of the anterior pituitary. Whether PPII has any role in the region where axons containing hypophysiotropic TRH terminate, the median eminence, is unknown. For this purpose, we analyzed the cellular localization and regulation of PPII mRNA in the mediobasal hypothalamus in adult, male rats. PPII mRNA was localized in cells lining the floor and infralateral walls of the third ventricle and coexpressed with vimentin, establishing these cells as tanycytes. PPII mRNA extended in a linear fashion from the tanycyte cell bodies in the base of the third ventricle to its cytoplasmic and end-feet processes in the external zone of the median eminence in close apposition to pro-TRH-containing axon terminals. Compared with vehicle-treated, euthyroid controls, animals made thyrotoxic by the ip administration of 10 μg l-T4 daily for 1–3 d, showed dramatically increased accumulation of silver grains in the mediobasal hypothalamus and an approximately 80% increase in enzymatic activity. PPII inhibition in mediobasal hypothalamic explants increased TRH secretion, whereas ip injection of a specific PPII inhibitor increased cold stress- and TRH-induced TSH levels in plasma. We propose that an increase in circulating thyroid hormone up-regulates PPII activity in tanycytes and enhances degradation of extracellular TRH in the median eminence through glial-axonal associations, contributing to the feedback regulation of thyroid hormone on anterior pituitary TSH secretion.

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