Hypothalamus, median eminence

Hypothalamus/median eminence Thyrotropin-releasing hormone (TRH) Somatostatin Peptides... 

The hypothalamic releasing factors regulate release of the anterior pituitary trophic hormones. As summarized in Figure 52-1, the releasing factors are produced in various neuronal groups within the hypothalamus and are transported to the median eminence for release into the portal circulation to the anterior pituitary. Neurons in the hypothalamus also produce the hormones oxytocin and vasopressin, which are released by the posterior pituitary into the blood. Therefore, it is not surprising that behavior and experience, which influence the hypothalamus, sometimes alter the secretion of these hypothalamic releasing factors and hormones. 

The intermediate length systems include the tuberoinfundibular system, which projects from the arcuate and periventricular nuclei into the intermediate lobe of the pituitary and the median eminence. This system is responsible for the regulation of such hormones as prolactin. The inter hypothalamic neurons send projections to the dorsal and posterior hypothalamus, the lateral septal nuclei and the medullary periventricular group, which are linked to the dorsal motor nucleus of the vagus such projections may play a role in the effects of dopamine on the autonomic nervous system. 

Growth hormone releasing hormone 24 tex produces vasodilation high levels in hypothalamus and median eminence... 

Male New Zealand White rabbits (2200 g) were exposed to 750 ppm [3.25 g/m ] ethylbenzene for 12 h per day for seven days. Twelve or 24 h following the final day of exposure, the rabbits were killed and their brains dissected. Ethylbenzene depleted both striatal and tubero-infundibular dopamine levels (Mutti et al, 1988). In male Sprague-Dawley rats exposed to 2000 ppm [8.70 g/m ] ethylbenzene for 6 h per day for three consecutive days and killed 16-18 h following the last exposure, ethylbenzene increased dopamine and noradrenaline levels and turnover in the hypothalamus and the median eminence. Ethylbenzene exposure also reduced the secretion of prolactin and increased dopamine turnover within the dopamine-cholecystokinin-8 immunoreactive nerve terminals of the nucleus accumbens (Andersson et al, 1981). 

The tuberoinfundibular system, which originates in the arcuate nucleus of the hypothalamus and projects to the median eminence. 

The BBB is found throughout the brain and spinal cord except for a small number of isolated regions of brain that line the ventricles, the large cavities in the middle of the brain. These circumventricular organs (CVOs) include the choroid plexus (a patch of tissue that lines the floors of the ventricles and manufactures cerebrospinal fluid), the median eminence of the hypothalamus, the subfornical organ at the roof of the third ventricle and the area postrema at the base of the fourth ventricle. 

Fig. 1. Location of dopaminergic perikarya (Au-A15) are depicted schematically on frontal sections (B-F) through the diencephalon of the rat. Section A is a sagittal view of the rat brain depicting the rostrocaudal location of frontal sections B-F. Abbreviations AH, anterior hypothalamus ARC, arcuate nucleus BST, bed nucleus of the stria terminalis f, fornix ic, internal capsule inf, infundibulum me, median eminence mt, mamillothalamic tract OC, optic chiasm ot, optic tract PH, posterior hypothalamus PIT, pituitary gland PeV, periventricular nucleus PVN, paraventricular nucleus RCH, retrochiasmatic area SON, supraoptic nucleus VMN, ventromedial nucleus ZI, zona incerta.

The rapid (i.e. less than 4 h) activation of TH in the median eminence by prolactin that constitutes the tonic component of prolactin stimulation does not require protein synthesis, but is probably associated with effects on the catalytic properties of this enzyme. Pasqualini and coworkers (1994) demonstrated in vitro that prolactin acts directly on TH in the mediobasal hypothalamus to trigger the phosphorylation of this enzyme. This effect, possibly mediated by protein kinase C, makes the enzyme less susceptible to inhibition by newly synthesized DA. That is, prolactin-induced short-term activation of TH results from the removal of end-product inhibition of the enzyme. Conversely, the acute reduction in TH activity measured in vitro in median eminence removed from rats 4 h after administration of bromocriptine is prevented by the coadministration of prolactin (Arbogast and Voogt, 1995). This can also be prevented by an inhibitor of phosphoprotein phosphatases, suggesting that rapid suppression of TH activity secondary to the bromocriptine-induced hypoprolactinemia may also result from dephosphorylation of the enzyme. 

Tramu G, Beauvillain JC, Croix D, Leonardelli J (1981) Comparative immunocytochemical localization of enkephalin and somatostatin in the median eminence, hypothalamus and adjacent areas of the guinea-pig brain. Brain Res 275 235-255. 

The master coordinator of hormonal activity in mammals is the hypothalamus, which acts on input that it receives from the central nervous system. Hormone secretion from the anterior pituitary gland is regulated by releasing hormones secreted by the hypothalamus. Neuroendocrine neurons in the hypothalamus project axons to the median eminence, at the base of the brain these neurons release substances into small blood vessels that travel directly to the anterior pituitary gland (the hypothalamo-hypophysial portal vessels). While the anterior pituitary... 

GRF has been isolated and characterized from a human tumor of the pancreas (61) as well as from rat (62), porcine (63), bovine (64), caprine (65), ovine (65), and human (65) hypothalamus stalk-median eminence. It is a 40-44-amino-acid peptide hormone produced in the arcuate nucleus of the hypothalamus and released from neurosecretory nerve terminals of these arcuate neurons, and it is carried by the hypothalamo-hypophysial portal circulation to the anterior pituitary gland where it stimulates growth hormone (GH) secretion (66). 

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