• The Korean Journal of Zoology
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• v.37 no.4
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• pp.504-513
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• 1994

The present study was carried out 1) to show the ontogenic development of CA-and GnRH-containing nerve fobres in the median eminence, 2) to simultaneously demonstrate the synaptic contact between these two nenre fibres in the rat median eminence at the ultrastructural level using light and electron microscopic doublelabel immunostainlngs. GnRH-and CA-nenre terminals were detectable in the median eminence at embryonic day 19.5. The CA-newe terminals were obsenred in the entire legion of the extern31 lavers, while GnRH-newe terminals only in the lateral portion. At the 14th postnatal daw, both %ropes of nerve terminals showed a very similar distribution to those of adult one. In the median eminence of adult rats, a substantial overlap existed in the distribution of GnRH fibres with CA-containing nerve fibres. This overlap was most intense throughout the external palisade zone. Furthermore, an electron microscopic double label immunostaining showed that there was a close apposition of CA- and GnRH-nenre fobres. These axo-axonic contacts occurred frequently in the internal and palisade zones, i.e. at the level of the fobre preterminals. These morphological results suggest that the CA-mediated GnRH secretion may occur via sxo-axonic interaction in the median eminence.

• The Korean Journal of Pharmacology
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• v.23 no.2
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• pp.57-75
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• 1987

Two modalities of gonadotropin secretion, pulsatile gonadotropin and preovulatory gonadotropin surge, have been identified in the mammals. Pulsatile gonadotropin secretion is modulated by the pulsatile pattern of GnRH release and complex ovarian steroid feedback actions. The neural mechansim that regulates the pulsatile release of GnRH in the hypothalamus is called "GnRH pulse generator". Ovarian steroids, estradiol and progesterone, appear to exert thier feedback effects both directly on the pituitary to modulate gonadotropin release and on a hypothalamic site to modulate GnRH release; estradiol primarily affects the amplitude while progesterone decreases the frequency of the pulsatile GnRH. Steroid hormones are known to affect catecholamine transmission in brain. MBH-POA is richly innervated by NE systems and close apposition of NE terminals and GnRH cell bodies occurs in the MBH as well as in the POA. NE normally facilitates pulsatile LH release by acting through ${\alpha}-receptor$ mechanism. However, precise nature of facilitative role of NE transmission in maintaining pulsatile LH has not been clearly understood. Close apposition of DA and GnRH terminals in ME might permit DA to influence GnRH release. Action of DA transmission probably is mediated by axo-axonic contacts between GnRH and DA fibers in the ME. Dopamine transmission does not normally regulate pulsatile LH release, but under certain conditions, increased DA transmission inhibit LH pulse. Endogenous opioid acts to suppress the secretion of GnRH into hypophysial portal circulation, thereby inhibiting gonadotropin secretion. However, an interaction between endogenenous opioid peptides and gonadotropin release is a complex one which involves ovarian hormones as well. LH secretion appears to be most suppressed by endogenenous opioids during the luteal phase, at a time of elevated progesterone secretion. The arcuate nucleus contains not only cell bodies for GnRH and ${\beta}-endorphin$ but also a dense aborization of fibers suggesting that GnRH release is changed by the interactions between GnRH and ${\beta}-endorphin$ cell bodies within the arcuate nucleus. The frequency and amplitude of pulsatile LH release seem to be increased during the preovulatory gonadotropin surge. Estradiol exerts positive feedback action on the hypothalamo-pituitary axis to trigger preovulatory LH surge. GnRH is also crucial hormonal stimulus for preovulatory LH surge. It is unlikely, however, that increased secretion of GnRH during the preovulatory gonadotropin surge represents an obligatory neural signal for generation of the LH discharge in primates including human. Modulation of preovulatory LH surge by catecholamines has been studied almost exclusively in rats. NE and E may be involved in distinct way to accumulate GnRH in the MBH and its release into the hypophysial portal system during the critical period for LH surge on proestrus in rats. However, the mechanisms whereby augmented adrenergic transmission may facilitate the formation and accumulation of GnRH in the ME-ARC nerve terminals before the LH surge have not been clearly understood.

• Korean Journal of Animal Reproduction
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• v.19 no.2
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• pp.119-127
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• 1995

These studies were carried out to examine the estradiol-17$\beta$ levelsin plasma and ovarian tissues, as well as the contents of collagen and catecholamines in the uterus, and to determine the effects of GnRH administrations of uterine involution in postpartum Korean native goats. Plasma concentrations of estradiol-17$\beta$ were 63.81$\pm$8.00 pg/ml at day 1 of kidding, declined to 36.78$\pm$22.90 ng/ml at day 24 and decreased progressively to 27.81$\pm$17.06 and 12.46$\pm$8.13 pg/ml at days 30 and 36 postpartum, respectively. In ovarian tissues, the concentrations of estaiol-17$\beta$ were increased just before parturition and decreased immediately after parturition. The plasma estradiol-17$\beta$ levels were slightly higher on days 12 and then decreased gradually after parturition. The concentraitons of estradiol-17$\beta$ in the ovaries of postpartum goats were increased at day 36 after treatments with GnRH. The total hydroxyproline contents in the uterus was slightly higher prior to parturition and decreased gradually with the postpartum intervals after parturition. Hydroxyproline concentraitons in the uterus were decreased at days 24 and 36 postpartum after treatments with GnRH. The norepinephrine concentrations in myometrium from the pregnant and postpartum goats were correspondingly low both immediately before and after partuition. Norepinephrine concentrations in the pregnant horn of the uterus were increased from days 12 to 36 of postpartum and those levels of the non-pregnant horn were also increased from days 24 to 36 postpartum. Slightly higher concentrations were present in the non-pregnant horn in comparison to the pregnant horn but these differences were not significant. Postpartum, the uterine norepinephrine concentration was slightly increased at day 36 after treatments with GnRH. Dopamine concentrations were greater than those of norepinephrine. The concentrations of dopamine in the uterus of pregnant goats was not significantly different from that in the postpartum animals. Dopamine concentraitons of pregnant horn in postpartum goats were increased at day 24 after treatments with GnRH.

• Development and Reproduction
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• v.5 no.1
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• pp.9-16
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• 2001

Biogenic monoamines are divided into three categories; catecholamines(dopamine, norepinephrine, and epinephrine), indoleamine(serotonin and melatonin) and histamine. Among them, serotonin has been intensively studied by many researchers with a broad spectrum of biomedical interests. A concise overview of serotonin-related topics such as biosynthetic pathway, receptor subtypes, and roles in reproduction will be provided. In particular, serotonergic efffect on the regulation of hypothalamus-pituitary-gonad hormonal axis and sexual behaviors will be emphasized. Though our Knowledge on the biological roles and its clinical applications are still limited, these topics are quite promising subjects which will be helpful for improving our 'quality of life' in near future.