title: Rapid inhibition of Ca2+ influx by neurosteroids in murine embryonic sensory neurones.
abstract: The non-genomic role of neuroactive steroids on [Ca2+]i transients induced by GABA receptor activation was investigated in cultured dorsal root ganglia (DRG) neurones at embryonic stage E13. [Ca2+]i measurements were performed with Fura-2 fast fluorescence microfluorimetry. Application of the GABAA receptor agonist muscimol (Musci) evoked an increase in [Ca2+]i, confirming the excitatory effect of GABA at this embryonic stage. The muscimol-induced [Ca2+]i response was inhibited by progesterone (Proges) and its primary metabolite allopregnanolone (Allo) in a rapid, reversible and dose-dependent manner. These calcium transients were suppressed in the absence of external Ca2+ or in the presence of Ni2+ + Cd2+ suggesting an involvement of voltage-activated Ca2+ channels. In contrast, none of these steroids affected the resting [Ca2+]i nor exhibited any inhibitory effect on 50 mM KCl-induced [Ca2+]i increases. In view of the well-established potentiation of GABAA receptor by direct binding of neurosteroids, the inhibitory effects described in this study seem to involve distinct mechanisms. This new inhibitory effect of progesterone is observed at low and physiological concentrations, is rapid and independent of RU38486, an antagonist of the classic progesterone receptor, probably involving a membrane receptor. Using RT-PCR, we demonstrated the expression of progesterone receptor membrane component 1 (Pgrmc1), encoding 25-Dx, a membrane-associated progesterone binding protein in DRG neurones at different stages of development. In conclusion, we describe for the first time a rapid effect of progestins on embryonic DRG neurones involving an antagonistic effect of progesterone and allopregnanolone on GABAA receptors.
authors.affiliation: INSERM U 583, Institut des Neurosciences de Montpellier, Hôpital St Eloi, BP 74103, 80 rue Augustin Fliche, F-34091 Montpellier, Cedex 5, France.
authors.forename: Cédric
authors.initials: C
authors.lastname: Viéro
authors.forename: Ilana
authors.initials: I
authors.lastname: Méchaly
authors.forename: Hervé
authors.initials: H
authors.lastname: Aptel
authors.forename: Sylvie
authors.initials: S
authors.lastname: Puech
authors.forename: Jean
authors.initials: J
authors.lastname: Valmier
authors.forename: Frédéric
authors.initials: F
authors.lastname: Bancel
authors.forename: G
authors.initials: G
authors.lastname: Dayanithi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000378:metabolism; D002478:Cells, Cultured; D002614:Chelating Agents / Q000378:metabolism; D004622:Embryo, Mammalian / Q000166:cytology*; D005456:Fluorescent Dyes / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D018755:GABA Agonists / Q000378:metabolism; D005727:Ganglia, Spinal / Q000166:cytology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009118:Muscimol / Q000378:metabolism; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000378:metabolism; D011280:Pregnanolone / Q000494:pharmacology*; D011374:Progesterone / Q000494:pharmacology*; D011963:Receptors, GABA-A / Q000378:metabolism; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism; D026941:Sodium Channel Blockers / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D002121:Calcium Channel Blockers; D002614:Chelating Agents; D005456:Fluorescent Dyes; D018755:GABA Agonists; D008565:Membrane Proteins; C508868:PGRMC1 protein, mouse; D026902:Potassium Channel Blockers; D011963:Receptors, GABA-A; D011980:Receptors, Progesterone; D026941:Sodium Channel Blockers; D009118:Muscimol; D011374:Progesterone; D005680:gamma-Aminobutyric Acid; D011280:Pregnanolone; D002118:Calcium; D016257:Fura-2