The interaction between mediobasohypothalamic dopaminergic and endorphinergic neuronal systems as a key regulator of reproduction: an hypothesis

Rasmussen, Dennis D.

doi:10.1007/bf03346826

Cited by 38 publications

(23 citation statements)

References 254 publications

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“…Involvement of extracellular mediators (i.e. norepinephrine, dopamine or neuropeptide Y) in the regulation of GnRH release has been extensively investigated in several species [8, 9, 10, 11, 12]. However, less is known about the intracellular mechanisms controlling release (exocytosis) of GnRH at the neuron terminal.…”

Section: Introductionmentioning

confidence: 99%

Calcium/Calmodulin-Dependent Protein Kinase II Involvement in Release of Gonadotropin-Releasing Hormone

et al. 1998

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Involvement of calcium/calmodulin-dependent protein kinase II (CaM kinase II) in regulation of GnRH release was tested by determining the effect of CaM kinase II antagonists (KN-62 or KN-93) on GnRH release from rat or cattle infundibular (stalk median eminence) explants. Preincubation of male rat infundibular explants for 30 min with KN-62 (0.5, 1, 5 or 10 µM) 1.5 h prior to the addition of 59.3 mM (high) K⁺ resulted in a dose-dependent suppression of GnRH release. A longer pretreatment period (2 h) of rat infundibular explants with KN-62 (1 or 10 µM) appeared to enhance the suppressive effect of the CaM kinase II antagonist. Exposure (2 h) of rat infundibular explants to 10 µM, but not 0.1 µM KN-93, resulted in a complete inhibition of high K⁺-induced GnRH release. Exposure of steer infundibular explant halves to KN-62 (50 or 100 µM) or KN-93 (50 µM) inhibited high K⁺-induced GnRH release. Likewise, treatment of heifer infundibular explant halves with KN-93 (50 µM) abolished high K⁺-induced GnRH release. The period of exposure required for KN-62 to elicit its effect was relatively short since exposure of KN-62 (100 µM) for only 91–150 min of incubation was sufficient to block high K⁺-induced GnRH release from steer infundibular explant halves. In conclusion, these results: (1) support the hypothesis that CaM kinase II is involved in GnRH release from the rat and cattle infundibulum, (2) demonstrate that the effect of CaM kinase II on GnRH release from cattle infundibula is independent of reproductive state, (3) confirm previous reports supporting Ca²⁺ and CaM involvement in GnRH release from rat and cattle infundibula and (4) establish that infundibular explants incubated in vitro are useful for studying selected mechanisms regulating hypothalamic neurohormone release from neuron terminals.

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Section: Introductionmentioning

confidence: 99%

Calcium/Calmodulin-Dependent Protein Kinase II Involvement in Release of Gonadotropin-Releasing Hormone

et al. 1998

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“…These studies suggest, that the MBH is a critical site reached by melatonin, involved in the photoperiodic control of gonadotropin secretion in sheep. This could be through an effect of melatonin on catecholamines located in or close to the MBH (Rassmussens, 1991). Chomicka et al (1994), showed that increase in the secretion of GnRH from the MBH during late anoestrus is accompanied by a decrease of dopamine release, the main inhibitor of GnRH in this area (Meyer and Goodman, 1985).…”

Section: Discussionmentioning

confidence: 99%

Seasonal changes of melatonin secretion in relation to the reproductive cycle in sheep

Misztal¹,

Romanowicz²,

Barcikowski³

1996

J. Anim. Feed Sci.

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The seasonal changes in circulating melatonin were determined in ewes and rams exposed to the natural photoperiod at 52°N during first year and in rams under the artificial daylength conditions (16D:8L), during the second year of the experiment. The changes in the luteotropin (LH) and testosterone (T) concentrations in blood plasma of rams were also monitored.The mean daily concentrations of plasma melatonin in the ewes varied through a year from 41+7 to 112 +13 pg/ml and a significant increase above the daily values occured during the first hour after sunset. The duration of nightly melatonin secretion was longer during the period of short day (10-12h), than under the long day conditions (8T0h). The mean nightly concentrations of circulating melatonin were highest from August to February: 171 +73 to 329+ 187 pg/ml for individual ewes.The mean concentrations of LH and testosterone in blood plasma of rams, under the natural photoperiod, were low during the period of sexual quiescence and the significantly high levels occured in August: 6.2 + 0.4 ng/ml and in October: 4.6 + 0.7 ng/ml, respectively. Shortening of daylength from 16 to 8 h in May evoked in rams an increase in duration of melatonin secretion from 6 to 14 h. This advanced reproductive function by 6 to 9 weeks, with the peak of LH and testosterone secretion noted at the beginning of July: 8.2 + 0.9 ng/ml and in August: 5.2 + 0.9 ng/ml, respectively. Nevertheless the duration of reproductive activity of rams during the second year of the experiment was shorter than under the natural photoperiodic conditions.

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“…Such a mechanism has been proposed for the hypothalamo-pituitary-gonadal axis in which sex steroids increase inhibitory opioid activity impinging upon hypothalamic GnRH neurones [18]. If a similar sys tem were to operate within the hypothalamo-pituitaryadrenal axis, naloxone would reverse the inhibitory effect of cortisol and addition of opioids to cells treated with cortisol would not be expected to have a further inhibitory effect.…”

Section: Discussionmentioning

confidence: 99%

“…For reasons which remain unclear, opioid peptides have been reported to stimulate, inhibit or have no effect on ACTH secretion [14][15][16][17], One possible explanation is that the way in which opioids act on hypothalamic neurones controlling ACTH secretion, is related to the glucocorti coid status of the animal. A system such as this has been documented for hypothalamic GnRH neurones, activity of which is regulated by opioid peptides in a sex-steroiddependent fashion [18], However, it is not known if a sim ilar feedback system functions within the hypothalamopituitary-adrenal axis.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Arginine Vasopressin Secretion from Cultured Ovine Hypothalamic Cells by Glucocorticoids and Opioid Peptides

Currie

Gillies²,

Brooks³

1994

Neuroendocrinology

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In sheep, arginine vasopressin (AVP) appears to be a more potent ACTH-releasing factor than ovine corticotrophin-releasing hormone. In order to investigate the neuroendocrine regulation of AVP secretion we have developed a novel system for maintaining fetal ovine hypothalamic neurones in serum-free culture. Hypothalamic neurones derived from fetal sheep at day 70 gestation (term = 145 days) secreted AVP under basal conditions and in response to repeated potassium-induced depolarizations, for up to 35 days in vitro. AVP secretion was time- and calcium-dependent. AVP secreted from ovine hypothalamic cells co-eluted with synthetic AVP on a Sephadex chromatography column and diluted in parallel with AVP standard in the radioimmunoassay. The addition of coritisol (150ΠM) to medium bathing ovine hypothalamic cells significantly inhibited basal, and potassium-induced AVP secretion without altering the AVP content of the cell cultures. Furthermore, the opioid peptide [D-Pro¹⁰]Dynorphin(_1–11) which acts via the ĸ opioid receptor, significantly inhibited basal and potassium-stimulated AVP secretion, an effect which was abolished when cells were cultured in the presence of cortisol. These data show that hypothalamic AVP is a site for negative feedback regulation within the ovine hypothalamic-pituitary-adrenal axis. Furthermore, these data suggest that the ĸ opioid system inhibits AVP secretion from ovine hypothalamic neurones, a response which is modulated by glucocorticoids.

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The interaction between mediobasohypothalamic dopaminergic and endorphinergic neuronal systems as a key regulator of reproduction: an hypothesis

Cited by 38 publications

References 254 publications

Calcium/Calmodulin-Dependent Protein Kinase II Involvement in Release of Gonadotropin-Releasing Hormone

Calcium/Calmodulin-Dependent Protein Kinase II Involvement in Release of Gonadotropin-Releasing Hormone

Seasonal changes of melatonin secretion in relation to the reproductive cycle in sheep

Modulation of Arginine Vasopressin Secretion from Cultured Ovine Hypothalamic Cells by Glucocorticoids and Opioid Peptides

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