Phosphodiesterase expression targeted to gonadotropin-releasing hormone neurons inhibits luteinizing hormone pulses in transgenic rats

Paruthiyil, Sreenivasan; Majdoubi, Mohammed El; Conti, Marco; Weiner, Richard I.

doi:10.1073/pnas.012678999

Cited by 25 publications

(24 citation statements)

References 55 publications

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“…This increases cell excitability and enhances firing of action potentials, leading to depolarization and elevation of [Ca 2ϩ ] i . The exact manner in which cAMP contributes to the episodic mode of GnRH secretion has yet to be determined, but its importance in the control of GnRH release is indicated by a recent study in rats expressing an active phosphodiesterase transgene in their GnRH neurons (34). However, it is likely that cAMP is essential but not alone sufficient for the generation of pulsatile GnRH release.…”

Section: Discussionmentioning

confidence: 99%

An agonist-induced switch in G protein coupling of the gonadotropin-releasing hormone receptor regulates pulsatile neuropeptide secretion

Krsmanović

Navarro

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

127

103

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The pulsatile secretion of gonadotropin-releasing hormone (GnRH) from normal and immortalized hypothalamic GnRH neurons is highly calcium-dependent and is stimulated by cAMP. It is also influenced by agonist activation of the endogenous GnRH receptor (GnRH-R), which couples to Gq/11 as indicated by release of membrane-bound ␣q/11 subunits and increased inositol phosphate͞Ca 2؉ signaling. Conversely, GnRH antagonists increase membrane-associated ␣q/11 subunits and abolish pulsatile GnRH secretion. GnRH also stimulates cAMP production but at high concentrations has a pertussis toxinsensitive inhibitory effect, indicative of receptor coupling to Gi. Coupling of the agonist-activated GnRH-R to both Gs and Gi proteins was demonstrated by the ability of nanomolar GnRH concentrations to reduce membrane-associated ␣s and ␣i3 levels and of higher concentrations to diminish ␣i3 levels. Conversely, ␣i3 was increased during GnRH antagonist and pertussis toxin treatment, with concomitant loss of pulsatile GnRH secretion. In cholera toxin-treated GnRH neurons, decreases in ␣s immunoreactivity and increases in cAMP production paralleled the responses to nanomolar GnRH concentrations. Treatment with cholera toxin and 8-bromo-cAMP amplified episodic GnRH pulses but did not affect their frequency. These findings suggest that an agonist concentration-dependent switch in coupling of the GnRH-R between specific G proteins modulates neuronal Ca 2؉ signaling via Gs-cAMP stimulatory and Gi-cAMP inhibitory mechanisms. Activation of Gi may also inhibit GnRH neuronal function and episodic secretion by regulating membrane ion currents. This autocrine mechanism could serve as a timer to determine the frequency of pulsatile GnRH release by regulating Ca 2؉ -and cAMPdependent signaling and GnRH neuronal firing.

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Section: Discussionmentioning

confidence: 99%

An agonist-induced switch in G protein coupling of the gonadotropin-releasing hormone receptor regulates pulsatile neuropeptide secretion

Krsmanović

Navarro

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

127

103

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“…On the other hand, decreasing cAMP levels by the expression of a constitutively active PDE4D1 inhibited forskolin-induced cAMP production and GnRH secretion [37]. Furthermore, decreasing cAMP levels in vivo by the overexpression of PDE4D1 targeted to GnRH neurons not only reduced the release of GnRH but also decreased the fertility rate in rats [38, 39]. However, despite the importance of the AC/cAMP signaling pathway as a central modulator of GnRH secretion, very little was known about the AC family in GnRH neurons.…”

Section: Discussionmentioning

confidence: 99%

GABA Inhibition of Cyclic AMP Production in Immortalized GnRH Neurons Is Mediated by Calcineurin-Dependent Dephosphorylation of Adenylyl Cyclase 9

Martin¹,

Jacobi²,

Nava³

et al. 2007

Neuroendocrinology

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The neurotransmitter γ-aminobutyric acid (GABA) is an important modulator of gonadotropin-releasing hormone (GnRH), and consequently of reproduction. GABA, acting via ionotropic GABA_A receptors, exerts a biphasic effect on GnRH secretion in immortalized GnRH cells. The initial increase in GnRH secretion is triggered by a sharp rise in [Ca²⁺]_i, while the progressive decline of GnRH levels that follows is paralleled by reduced levels of intracellular cAMP. The experiments described here were designed to explore the potential signaling pathways involved in this novel GABA_A ionotropic inhibition of cAMP synthesis in GT1–7 cells. Using RT-PCR and real-time PCR, we found that GT1–7 cells express 8 of 9 known membrane adenylyl cyclase (AC) isoforms, including a large proportion of AC3 and AC9, as well as AC5 and AC6, all of which are negatively regulated by increases in [Ca²⁺]_i. In contrast, isoforms of AC that are positively regulated by [Ca²⁺]_i were barely detectable (AC1) or undetectable (AC8). Pharmacological activation of L-type voltage-operated calcium channels with BayK 8644 produced a decrease in [cAMP]_i similar to that induced by GABA, while blocking these calcium channels with verapamil reversed the effect of GABA on cAMP synthesis. Furthermore, blocking calcineurin with deltamethrin, FK-506 or cyclosporin A blocked the inhibitory effect of GABA on [cAMP]_i, supporting the involvement of AC9 in this effect. In addition, blocking Ca²⁺/calmodulin-dependent protein kinase II (CamKII) with KN-62 partially reversed the action of GABA, suggesting that AC3 may also be involved in this effect. Finally, GABA increased phosphatase activity in a calcium-dependent manner, an effect blocked by calcineurin inhibitors. Collectively, our results show that the ionotropic action of GABA via the activation of GABA_A receptors can decrease AC activity in immortalized GnRH neurons, and that the effect of GABA appears to be mediated by a transient increase in [Ca²⁺]_i followed by activation of calcineurin and CamKII, leading to dephosphorylation of AC9 and phosphorylation of AC3, respectively, and subsequently reducing the synthesis of cAMP.

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“…We previously showed that the frequency of LH pulses in OVX GPR-4 rat was significantly decreased relative to WT littermate controls [18]. We extended these findings to determine if pulsatile FSH secretion was also affected and whether there was concordance between LH and FSH pulses.…”

Section: Resultsmentioning

confidence: 50%

“…Expression of PDE4D1 was specifically targeted to GnRH neurons in the GPR-4 rat transgenic line using the promoter/enhancer regions of the rat GnRH gene [18]. The transgene consisted of 3 kb of the promoter/enhancer region of the rat GnRH gene inserted upstream of the B intron of the rabbit β-globin gene.…”

Section: Methodsmentioning

confidence: 99%

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Pulsatile Luteinizing Hormone and Follicle-Stimulating Hormone Secretion and Gonadotropin Subunit mRNA Levels in the Ovariectomized GPR-4 Transgenic Rat

Majdoubi¹,

Paruthiyil²,

Weiner³

2003

Neuroendocrinology

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Genetic targeting of the cAMP-specific phosphodiesterase 4D1 (PDE4D1) to gonadotropin-releasing hormone (GnRH) neurons in the GPR-4 transgenic rat resulted in decreased luteinizing hormone (LH) pulse frequency in castrated female and male rats. A similar decrease in the intrinsic GnRH pulse frequency was observed in GT1 GnRH cells expressing the PDE4D1 phosphodiesterase. We have extended these findings in ovariectomized (OVX) GPR-4 rats by asking what effect transgene expression had on pulsatile LH and follicle-stimulating hormone (FSH) secretion, plasma and pituitary levels of LH and FSH, and levels of the α-glycoprotein hormone subunit (α-GSU), LH-β and FSH-β subunit mRNAs. In OVX GPR-4 rats the LH pulse frequency but not pulse amplitude was decreased by 50% compared to wild-type littermate controls. Assaying the same samples for FSH, the FSH pulse frequency and amplitude were unchanged. The plasma and anterior pituitary levels of LH in the GPR-4 rats were significantly decreased by approximately 45%, while the plasma but not anterior pituitary level of FSH was significantly decreased by 25%. As measured by real-time RT-PCR, the mRNA levels for the α-GSU in the GPR-4 rats were significantly decreased by 41%, the LH-β subunit by 38% and the FSH-β subunit by 28%. We conclude that in the castrated female GPR-4 rats the decreased GnRH pulse frequency results in decreased levels of LH and FSH and in the α- and β-subunit mRNA levels.

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Phosphodiesterase expression targeted to gonadotropin-releasing hormone neurons inhibits luteinizing hormone pulses in transgenic rats

Cited by 25 publications

References 55 publications

An agonist-induced switch in G protein coupling of the gonadotropin-releasing hormone receptor regulates pulsatile neuropeptide secretion

An agonist-induced switch in G protein coupling of the gonadotropin-releasing hormone receptor regulates pulsatile neuropeptide secretion

GABA Inhibition of Cyclic AMP Production in Immortalized GnRH Neurons Is Mediated by Calcineurin-Dependent Dephosphorylation of Adenylyl Cyclase 9

Pulsatile Luteinizing Hormone and Follicle-Stimulating Hormone Secretion and Gonadotropin Subunit mRNA Levels in the Ovariectomized GPR-4 Transgenic Rat

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