REGENERATION OF THE NEURAL LOBE OF THE HYPOPHYSIS AFTER EXTIRPATION OF THE MEDIAN EMINENCE IN RANA TEMPORARIA

1965 ◽  
Vol 60 (2) ◽  
pp. 181-186 ◽  
Author(s):  
K. Dierickx
Keyword(s):  
Median Eminence ◽  
Rana Temporaria ◽  
Neural Lobe

Role of catecholamines in regulating ovine median eminence blood flow

1990 ◽  
Vol 258 (5) ◽  
pp. R1242-R1249
Author(s):  
R. B. Page ◽  
M. Gropper ◽  
E. Woodard ◽  
J. Townsend ◽  
S. Davis ◽  
...  
Keyword(s):  
Blood Flow ◽  
Choroid Plexus ◽  
Median Eminence ◽  
Serum Prolactin ◽  
Dopamine Antagonist ◽  
Drug Infusion ◽  
Neural Lobe ◽  
Dopamine Infusion ◽  
D2 Agonist ◽  
Before And After

Blood flow was measured in the ovine median eminence and neural lobe before and after the intravenous infusion of dopamine (n = 7), the D1 agonist SKF 38393 (n = 4), the D2 agonist bromocriptine (n = 4), and the dopamine antagonist haloperidol (n = 5). It was also measured before and after the intracarotid infusion of dopamine into eight naive sheep and seven sheep pretreated with phenoxybenzamine. Radiolabeled microspheres were used to determine regional cerebral and regional neurohypophysial blood flows (RNHBF) in these 35 adult female sheep anesthetized with pentobarbital sodium. Samples for serum prolactin measurement by radioimmunoassay were obtained before and after drug infusion. Intravenous dopamine infusion did not change median eminence or neural lobe blood flow (RNHBF) but increased renal and choroid plexus blood flow. Intravenous haloperidol caused a significant fall in RNHBF and blood flow in choroid plexus, caudate nucleus, and kidneys. Intracarotid dopamine infusion decreased RNHBF but increased choroid plexus blood flow. RNHBF was significantly greater in the seven sheep pretreated with phenoxybenzamine than in the eight naive sheep. These findings do not support a role for dopamine in the regulation of median eminence blood flow. The last observation does add support to the hypothesis that norepinephrine or epinephrine interaction with alpha-receptors plays a role in the control of ovine median eminence blood flow and hence in the regulation of delivery of humoral messages from the brain to the anterior pituitary gland.

Regional neurohypophyseal blood flow and its control in adult sheep

1981 ◽  
Vol 241 (1) ◽  
pp. R36-R43 ◽  
Author(s):  
R. B. Page ◽  
D. J. Funsch ◽  
R. W. Brennan ◽  
M. J. Hernandez
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
White Matter ◽  
Arterial Blood Pressure ◽  
Median Eminence ◽  
Vascular System ◽  
Neural Lobe ◽  
Adult Sheep ◽  
Blood Flows ◽  
Arterial Blood

Regional neurohypophyseal and cerebral blood flows were measured by the radiolabeled microsphere technique in 30 adult sheep under light barbiturate anesthesia. Regional blood flows were determined under basal conditions. The responses of regional blood flow to alterations in arterial PCO2 and to changes in arterial blood pressure wee also determined. In addition, the relationship between regional neurohypophyseal blood flow and neurosecretory activity as judged by plasma arginine vasopressin levels was assessed. Under basal conditions median eminence blood flow averaged 461 ml.100 g-1.min-1 and did not significantly differ from neural lobe blood flow (436 ml.100 g-1.min-1). Blood flow in the neurohypophysis was about 8 times cortical and 16 times white matter blood flow in these animals. Median eminence and neural lobe blood flow proportionately increased far less than regional cortical or white matter blood flow under conditions of hypercarbia. With alteration of arterial blood pressure, regional neurohypophyseal blood flow remained constant beyond the limits of cerebral autoregulation. The neurohypophysis demonstrates a degree of blood flow homeostasis that exceeds that of any other brain area studied. Although the neurohypophysis is a diverticulum of the brain, its vascular system forms a unique functional as well as a unique anatomic unit.

HORMONAL CONTENT AND ULTRASTRUCTURE OF THE HYPOTHALAMO-NEUROHYPOPHYSIAL SYSTEM OF THE RAT AFTER INJECTION OF VINBLASTINE INTO THE MEDIAN EMINENCE

1977 ◽  
Vol 73 (2) ◽  
pp. 197-205 ◽  
Author(s):  
E. L. RODRÍGUEZ ◽  
ECHANDÍA, J. C. CAVICHIA ◽  
E. M. RODRÍGUEZ
Keyword(s):  
Electron Microscopy ◽  
Fine Structure ◽  
Median Eminence ◽  
Microscopic Analysis ◽  
Plasma Samples ◽  
Neural Lobe ◽  
Hormonal Content ◽  
Light Microscopic Analysis ◽  
Progressive Accumulation ◽  
Positive Materials

SUMMARY The effects of an injection of vinblastine (Vbl) into the median eminence on the structure, fine structure and antidiuretic hormone (ADH) content of the hypothalamo-neurohypophysial system in the rat is reported. The animals were studied on days 3, 8 and 25 after the injection of 1 or 5 mm-Vbl (3 μl). Significant changes were observed only in the 5 mm-Vbl-injected animals. Their median eminence extracts showed a progressive accumulation of ADH whereas ADH depletion occurred in the neural lobe extracts. On day 8 after injection, the animals exhibited strong polidipsia although considerable amounts of ADH still remained within the neural lobe. The ADH content of the plasma samples was consistently below the sensitivity of the method (5 μu.). The light microscopic analysis showed accumulation of Gomori-stainable products in the median eminence and a striking depletion of this material from the neural lobe. Electron microscopy revealed accumulation of neurosecretory vesicles and other inclusions proximal to the site of injection in the median eminence together with some evidence of nerve fibre degeneration. Few neurosecretory terminals were found in the neural lobe of the 8-day experimental rats. They had been engulfed by pituicytes for digestion. Recuperation of the normal ADH content of both median eminence and neural lobe was found to occur on day 25 after the Vbl injection. Simultaneously, the neural lobe refilled with Gomori-positive materials and neurosecretory terminals reappeared. The results suggest (1) reversible blockade of axoplasmic transport at the site of the Vbl injection; (2) reversible degeneration of neurosecretory terminals and (3) reversible blockade of ADH release in the surviving terminals of the neural lobe.

The Anterior Pituitary and Hypothalamus

2011 ◽  
Author(s):  
Sergio R. Ojeda
Keyword(s):  
Median Eminence ◽  
Anterior Pituitary ◽  
Neurosecretory Cells ◽  
Blood System ◽  
Portal Blood ◽  
Pituitary Hormone ◽  
Neural Lobe ◽  
Hypothalamic Hormones ◽  
Neural Origin ◽  
Trophic Hormones

The hypothalamic-pituitary complex represents the core of the neuroendocrine system. The hypothalamus is composed of a diversity of neurosecretory cells arranged in groups, which secrete their products either into the portal blood system that connects the hypothalamus to the adenohypophysis (see later) or directly into the general circulation after storage in the neurohypophysis (see Chapter 6). Because of the nature of their actions, the hypothalamic hormones are classified as releasing or inhibiting hormones. The hypothalamic hormones delivered to the portal blood system are transported to the adenohypophysis, where they stimulate or inhibit the synthesis and secretion of different trophic hormones. In turn, these hormones regulate gonadal, thyroid, and adrenal function, in addition to lactation, bodily growth, and somatic development. No attempt will be made in this chapter to cover the actions of the different pituitary trophic hormones on their target glands, because they are discussed in detail in other chapters. An exception to this is growth hormone (GH). Although Chapter 11 considers several aspects of the control and actions of GH, a broader discussion of its physiological actions will be presented here because GH is the only anterior pituitary hormone that does not have a clear-cut target gland. The pituitary gland has two parts: the neurohypophysis, of neural origin (see Chapter 6), and the adenohypophysis, of ectodermal origin. In embryonic development, an evagination from the roof of the pharynx pushes dorsally to reach a ventrally directed evagination from the base of the diencephalon. The dorsally projecting evagination, known as Rathke’s pouch , forms the adenohypophysis, whereas the ventrally directed evagination of neural tissue forms the neurohypophysis. The neurohypophysis has three parts: the median eminence, the infundibular stem, and the neural lobe itself. The median eminence represents the intrahypothalamic portion and lies just ventral to the floor of the third ventricle protruding slightly in the midline. The main part of the neurohypophysis, the neural lobe, is connected to the median eminence by the infundibular stem.

Corticoliberin activity of rat neurohypophysis is distinct from vasopressin

1981 ◽  
Vol 240 (6) ◽  
pp. E689-E693 ◽  
Author(s):  
M. Karteszi ◽  
E. Stark ◽  
G. Rappay ◽  
F. A. Laszlo ◽  
G. B. Makara
Keyword(s):  
Electrical Stimulation ◽  
Median Eminence ◽  
Brattleboro Rats ◽  
Neural Lobe ◽  
Experimental Conditions ◽  
Adrenal Axis ◽  
Corticosterone Secretion ◽  
Pituitary Adrenal Axis ◽  
Stimulation Of

Electrical stimulation of the neural lobe of the pituitary resulted in an increase of corticosterone secretion in both normal and Brattleboro rats. Bioassaying the corticoliberin (CRF) activity of stalk-median eminence and neural lobe extracts obtained from normal and Brattleboro rats revealed that the endogenous vasopressin was not a prerequisite of ACTH-releasing potency. Arginine-8-vasopressin failed to potentiate the CRF activity of the different extracts. These data suggest that a nonvasopressin substance(s) with CRF activity can be released from the neurohypophysis of the rat, and it may contribute to activating the pituitary-adrenal axis under certain experimental conditions.

Differences between median eminence and neural lobe in amphibians

1966 ◽  
Vol 74 (3) ◽  
pp. 308-316 ◽  
Author(s):  
Esteban M. Rodriguez
Keyword(s):  
Median Eminence ◽  
Neural Lobe

Portal vascular route from hypophysial stalk/neural lobe to adenohypophysis

1980 ◽  
Vol 239 (5) ◽  
pp. R463-R469 ◽  
Author(s):  
A. J. Baertschi
Keyword(s):  
Blood Flow ◽  
Median Eminence ◽  
General Circulation ◽  
Circulatory Arrest ◽  
Constant Current ◽  
Extracellular Potassium ◽  
Neural Lobe ◽  
Capillary Networks ◽  
Anterior Dorsal ◽  
Current Spread

Adenohypophysis, neural lobe, stalk, and median eminence are interconnected by capillary networks and portal vessels, but the directions of blood flow are not clearly understood. To test the hypothesis that peptides released from the hypothalamohypophysial tract (HHT) may reach the adenohypophysis, the HHT of anesthetized rats were stimulated electrically with 5-s trains of constant current (400 microA) biphasic impulses (0.2-1 ms) at 30 Hz, and extracellular potassium activity was recorded in various parts of the hypothalamohypophysial complex with microelectrodes (2- to 4-micrometer tip). Within HHT and neural lobe, K+ increased without delay (within 30 ms) from 2.20 +/- 0.25 (meq/l, mean +/- SE) and 2.65 +/- 0.40 to 4.50 +/- 0.60 and 7.60 +/- 0.85, respectively. Within the anterior dorsal regions of the adenohypophysis (AAH), K+ increased from 3.00 +/- 0.25 to 5.05 +/- 0.35, but with a delay of 1-4 s. Within the posterior regions of the dorsal adenohypophysis, the increase was barely significant (P < 0.1) and was delayed by 4-10 s. K+ responses in AAH to nicotine and HHT stimulation were abolished by circulatory arrest; thus K+ responses were not due to current spread or passive diffusion. Coagulation of long portal vessels did not diminish K+ responses in AHH. Results suggest that peptides released from HHT are not only secreted into the general circulation, but may reach the adenohypophysis through a portal vascular route.

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