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Contents The effects of prolonged, intermittent infusion of β-endorphin or naloxone into the third cerebral ventricle of follicular-phase ewes on the expression of genes encoding Gn RH and Gn RHR in the hypothalamus and Gn RHR in the anterior pituitary gland (AP) were examined by an enzyme-linked immunoabsorbent assay. Activation or blockade of μ-opioid receptors significantly decreased or increased the Gn RH concentration and Gn RHR abundance in the hypothalamus, respectively, and affected in the same way Gn RHR quantity in the AP gland. The changes in the levels of Gn RH and Gn RHR after treatment with β-endorphin as well as following action of naloxone were reflected in fluctuations of plasma LH concentrations. On the basis of these results, it is suggested that β-endorphinergic system in the hypothalamus of follicular-phase ewes affects directly or via β-endorphin-sensitive interneurons Gn RH and Gn RHR biosynthesis leading to suppression in secretory activity of the hypothalamic-pituitary axis. [ABSTRACT FROM AUTHOR]

Background: The inverse relationship between GnRH transcript level and GABA neurons activity has suggested that GABA at the hypothalamic level may exert a suppressive effect on subsequent steps of the GnRH biosynthesis. In the present study, we analyzed the effects of GABA type A receptor agonist (muscimol) or antagonist (bicuculline) on molecular mechanisms governing GnRH/LH secretion in follicular-phase sheep., Methods: ELISA technique was used to investigate the effects of muscimol and/or bicuculline on levels of post-translational products of genes encoding GnRH ligand and GnRH receptor (GnRHR) in the preoptic area (POA), anterior (AH) and ventromedial (VMH) hypothalamus, stalk/median eminence (SME), and GnRHR in the anterior pituitary (AP). Real-time PCR was chosen for determination of the effect of drugs on kisspeptin (Kiss 1) mRNA level in POA and VMH including arcuate nucleus (VMH/ARC), and on Kiss1 receptor (Kiss1r) mRNA abundance in POA-hypothalamic structures. These analyses were supplemented by RIA method for measurement of plasma LH concentration., Results: The study demonstrated that muscimol and bicuculline significantly decreased or increased GnRH biosynthesis in all analyzed structures, respectively, and led to analogous changes in plasma LH concentration. Similar muscimol- and bicuculline-related alterations were observed in levels of GnRHR. However, the expression of Kiss 1 and Kiss1r mRNAs in selected POA-hypothalamic areas of either muscimol- and bicuculline-treated animals remained unaltered., Conclusions: Our data suggest that GABAergic neurotransmission is involved in the regulatory pathways of GnRH/GnRHR biosynthesis and then GnRH/LH release in follicular-phase sheep conceivably via indirect mechanisms that exclude involvement of Kiss 1 neurons., (Copyright © 2019 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.)

There is no information in the literature regarding the effect of corticotropin-releasing hormone (CRH) on genes encoding gonadotrophin-releasing hormone (GnRH) and the GnRH receptor (GnRHR) in the hypothalamus or on GnRHR gene expression in the pituitary gland in vivo. Thus, the aim of the present study was to investigate, in follicular phase ewes, the effects of prolonged, intermittent infusion of small doses of CRH or its antagonist (α-helical CRH 9-41; CRH-A) into the third cerebral ventricle on GnRH mRNA and GnRHR mRNA levels in the hypothalamo-pituitary unit and on LH secretion. Stimulation or inhibition of CRH receptors significantly decreased or increased GnRH gene expression in the hypothalamus, respectively, and led to different responses in GnRHR gene expression in discrete hypothalamic areas. For example, CRH increased GnRHR gene expression in the preoptic area, but decreased it in the hypothalamus/stalk median eminence and in the anterior pituitary gland. In addition, CRH decreased LH secretion. Blockade of CRH receptors had the opposite effect on GnRHR gene expression. The results suggest that activation of CRH receptors in the hypothalamus of follicular phase ewes can modulate the biosynthesis and release of GnRH through complex changes in the expression of GnRH and GnRHR genes in the hypothalamo-anterior pituitary unit., (© CSIRO 2011 Open Access)

Using the Reverse Transcription-Polymerase Chain Reaction (RT-PCR) technique, the gonadotropin releasing-hormone (GnRH) mRNA and GnRH receptor (GnRH-R) mRNA were analyzed in the preoptic area (POA), anterior (AH) and ventromedial (VM) hypothalamus, stalk/median eminence (SME) and anterior pituitary gland (AP) of anestrous ewes subjected to short or prolonged footshock stimulation. No GnRH gene expression was detected in the SME and AP. The comparable levels of GnRH mRNA were found in the POA, AH and VM in control ewes. Short and prolonged footshock stimulation significantly increased GnRH mRNA in all analyzed tissue. The highest responses in GnRH mRNA to the short stress occurred in the POA whereas to the prolonged stress in the POA and VM. In non-stressed ewes the GnRH-R mRNA were detected in tissue continuum throughout the POA, AH, VM, SME and AP. The highest concentration of GnRH-R mRNA was detected in the SME. Short as well as prolonged stress stimuli caused an increase in GnRH-R mRNA levels in all analyzed tissue. The highest responses in GnRH-R mRNA expression were found in the VM. In spite of profound up-regulation of GnRH mRNA and GnRH-R mRNA under the short and prolonged stress conditions, the increase of luteinizing hormone (LH) secretion was noted only during acute stress. It is suggested that the increase of expression of GnRH and GnRH-R genes in anestrous ewes are not directly related to GnRH level and GnRH-R activity.