Hypothalamus as an Endocrine Organ

Abstract

The endocrine hypothalamus constitutes those cells which project to the median eminence and secrete neurohormones into the hypophysial portal blood to act on cells of the anterior pituitary gland. The entire endocrine system is controlled by these peptides. In turn, the hypothalamic neuroendocrine cells are regulated by feedback signals from the endocrine glands and other circulating factors. The neuroendocrine cells are found in specific regions of the hypothalamus and are regulated by afferents from higher brain centers. Integrated function is clearly complex and the networks between and amongst the neuroendocrine cells allows fine control to achieve homeostasis. The entry of hormones and other factors into the brain, either via the cerebrospinal fluid or through fenestrated capillaries (in the basal hypothalamus) is important because it influences the extent to which feedback regulation may be imposed. Recent evidence of the passage of factors from the pars tuberalis and the median eminence casts a new layer in our understanding of neuroendocrine regulation. The function of neuroendocrine cells and the means by which pulsatile secretion is achieved is best understood for the close relationship between gonadotropin releasing hormone and luteinizing hormone, which is reviewed in detail. The secretion of other neurohormones is less rigid, so the relationship between hypothalamic secretion and the relevant pituitary hormones is more complex.

Understanding the trade-off between the environment and fertility in cows and ewes

“…Although CRH, AVP and beta-endorphin terminals are seen in the mPOA, there are no direct contacts with GnRH cell bodies in this area. Within the median eminence, abundant CRH (but no AVP) terminals are close to GnRH cell terminals in the external zone; whereas, beta-endorphin and dynorphin cell bodies and terminals are in the internal zone (Ghuman et al, 2011;Clarke, 2015). The presence of c-Fos (an early gene activation marker) indicates which cells are currently active: after in vivo insulin treatment in ewes, the number of activated noradrenergic neurones in the caudal brainstem increases markedly, along with significant activation of CRH and AVP neurones in the PVN.…”

The origins of the circumventricular organs

“…to share a large number of developmental mechanisms, and because they are connected to form a functional unit (Szarek et al 2010;Davis et al 2013;Clarke, 2015).…”

Expression of genes for Kisspeptin ( KISS1 ), Neurokinin B ( TAC3 ), Prodynorphin ( PDYN ), and gonadotropin inhibitory hormone ( RFRP ) across natural puberty in ewes

“…Puberty is typified by an increase in the secretion of gonadotropin releasing hormone (GnRH) which drives an increase in gonadotropins secretion from the pituitary gland (Clarke & Pompolo, 2005; Ojeda, Roth, et al, 2006), leading to activation of the gonads. GnRH neurons are controlled by a number of interactive neuronal pathways which are regulated by internal signals and external cues (Clarke, 2015; Clarke & Arbabi, 2015; Clarke, Campbell, Smith, Prevot, & Wray, 2011; Ojeda, Lomniczi, et al, 2006; Tena‐Sempere, 2012; Terasawa & Fernandez, 2001), many of which may be involved in the process of puberty. Although much is known about neuronal systems that regulate GnRH secretion, the neurochemical basis of integrated control of puberty remains only partially understood.…”

“…Puberty is typified by an increase in the secretion of gonadotropin releasing hormone (GnRH) which drives an increase in gonadotropins secretion from the pituitary gland (Clarke & Pompolo, 2005;, leading to activation of the gonads. GnRH neurons are controlled by a number of interactive neuronal pathways which are regulated by internal signals and external cues (Clarke, 2015;Clarke & Arbabi, 2015;Clarke, Campbell, Smith, Prevot, & Wray, DOI: 10.14814/phy2.14399…”