Molecular biology and regulation of the hypothalamic hormones

Plasticity of Anterior Pituitary Gonadotrope Cells Facilitates the Pre-Ovulatory LH Surge

Gonadotropes cells located in the anterior pituitary gland are critical for reproductive fitness. A rapid surge in the serum concentration of luteinizing hormone (LH) secreted by anterior pituitary gonadotropes is essential for stimulating ovulation and is thus required for a successful pregnancy. To meet the requirements to mount the LH surge, gonadotrope cells display plasticity at the cellular, molecular and morphological level. First, gonadotrope cells heighten their sensitivity to an increasing frequency of hypothalamic GnRH pulses by dynamically elevating the expression of the GnRH receptor (GnRHR). Following ligand binding, GnRH initiates highly organized intracellular signaling cascades that ultimately promote the synthesis of LH and the trafficking of LH vesicles to the cell periphery. Lastly, gonadotrope cells display morphological plasticity, where there is directed mobilization of cytoskeletal processes towards vascular elements to facilitate rapid LH secretion into peripheral circulation. This mini review discusses the functional and organizational plasticity in gonadotrope cells including changes in sensitivity to GnRH, composition of the GnRHR signaling platform within the plasma membrane, and changes in cellular morphology. Ultimately, multimodal plasticity changes elicited by gonadotropes are critical for the generation of the LH surge, which is required for ovulation.

60 YEARS OF NEUROENDOCRINOLOGY: The structure of the neuroendocrine hypothalamus: the neuroanatomical legacy of Geoffrey Harris

In November 1955, Geoffrey Harris published a paper based on the Christian A Herter Lecture he had given earlier that year at Johns Hopkins University in Baltimore, MD, USA. The paper reviewed the contemporary research that was starting to explain how the hypothalamus controlled the pituitary gland. In the process of doing so, Harris introduced a set of properties that helped define the neuroendocrine hypothalamus. They included: i) three criteria that putative releasing factors for adenohypophysial hormones would have to fulfill; ii) an analogy between the representation of body parts in the sensory and motor cortices and the spatial localization of neuroendocrine function in the hypothalamus; and iii) the idea that neuroendocrine neurons are motor neurons and the pituitary stalk functions as a Sherringtonian final common pathway through which the impact of sensory and emotional events on neuroendocrine neurons must pass in order to control pituitary hormone release. Were these properties a sign that the major neuroscientific discoveries that were being made in the early 1950s were beginning to influence neuroendocrinology? This Thematic Review discusses two main points: the context and significance of Harris's Herter Lecture for how our understanding of neuroendocrine anatomy (particularly as it relates to the control of the adenohypophysis) has developed since 1955; and, within this framework, how novel and powerful techniques are currently taking our understanding of the structure of the neuroendocrine hypothalamus to new levels.

Acute effects of acephate and methamidophos and interleukin-1 on corticotropin-releasing factor (CRF) synthesis in and release from the hypothalamus in vitro

Acute effects of Ace, Meth and IL-1 on AChE activity, ACh and CRF mRNA levels in, and CRF-release from the hypothalamus were studied in vitro. The hypothalamus samples were dissected from the rat brain and were incubated in vitro with IL-1, Ace or Meth in the presence or absence of Dex, Atrop, PTL, PROP and GABA. Ace and Meth, but not IL-1, inhibited AChE activity, while all three compounds; (1) increased ACh and CRF mRNA levels in and CRF release from; (2) activated the CRE promoter region of CRF-gene in: and (3) increased cFos binding to the AP-1 region of the CRF-gene in the hypothalamus. Dex suppressed the effects of IL-1, possibly by inducing the nGRE regulatory sites of the CRF-gene. Dex, however, did not modulate the effects of Ace and Meth on the hypothalamus, which may be attributed to the failure of Dex to modulate the CRF-gene's nGRE regulatory sites. Atrop caused 80-90% inhibition of the effects of IL-1, but caused only 50-65% inhibition of the effects of Ace or Meth on CRF mRNA levels in and CRF release from the hypothalamus. PTL did not affect, while PROP slightly attenuated the effects of IL-1 and the insecticides on the hypothalamus. GABA attenuated the effects of the insecticides but not the effects of IL-1 on the hypothalamus. This suggests that the IL-1-induced augmentation of CRF synthesis in and release from the hypothalamus is mediated through a cholinergic pathway, while the insecticide-induced augmentation of CRF synthesis in and release from the hypothalamus is mediated through the cholinergic and GABAergic pathways. The insecticides, but not IL-1, disrupt feedback regulation of CRF synthesis in and release from the hypothalamus.

Release of corticotropin after administration of corticotropin-releasing hormone in depressed patients in relation to the dexamethasone suppression test

The possible hypersecretion involvement of corticotropin-releasing hormone (CRH) in the pathophysiology of hypothalamic-pituitary-adrenocortical axis disturbances in patients with major depressive episode and with an abnormal dexamethasone suppression test (DST) was investigated. The corticotropin (ACTH) and cortisol response to the injection of 45 micrograms of synthetic human CRH at 1630 were analyzed in 24 inpatients with normal (suppressors) or abnormal (nonsuppressors) DST. The outcome of the DST was analyzed using 3 cut-off points for the cortisol levels. The clinical assessments included two rating scales. The results showed that nonsuppressors had a significantly lower ACTH response to CRH stimulation than suppressors at all cut-off points (calculated as net area under the curve and as the difference between the peak and the baseline level) despite no significant differences in the severity of depression.