title: Rise in intracellular calcium via a nongenomic effect of allopregnanolone in fetal rat hypothalamic neurons.
abstract: This study examines the early effects of 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone on cytosolic free calcium concentration ([Ca2+]i in primary cultures of fetal rat hypothalamic neurons. Microspectrofluorimetry of fluorescent Ca2+(-)sensitive indicator Fura-2 was used to quantify these changes. Allopregnanolone (1 pM to 100 nM) increased [Ca2+]i within 2-3 sec, in a dose dependent manner, with an EC50 of 10 +/- 4 nM. The stimulatory effect of allopregnanolone was attributable principally to a Ca2+ influx, as shown by the strong inhibition of external Ca2+ removal or by the calcium channel blocker nifedipine. The effect was stereospecific because the allopregnanolone isomer 3 beta-hydroxy-5 alpha-pregnan-20-one had no effect on [Ca2+]i. Among two other steroids examined, progesterone had no effect on [Ca2+]i, but 17 beta-estradiol evoked a rise in [Ca2+]i, although to a lesser extent than allopregnanolone. The allopregnanolone-induced [Ca2+]i rise was inhibited by picrotoxin and bicuculline but was unaffected by tetrodotoxin or by pretreatment of neurons with pertussis toxin. These results are consistent with a membrane site of action for allopregnanolone associated with GABAA receptors, leading to rapid changes in [Ca2+]i in fetal rat hypothalamic neurons.
authors.affiliation: Laboratoire de Neurobiologie Endocrinologique, URA 1197 CNRS, Université Montpellier II, France.
authors.forename: G
authors.initials: G
authors.lastname: Dayanithi
authors.forename: L
authors.initials: L
authors.lastname: Tapia-Arancibia
mesh_terms: D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects; D004594:Electrophysiology; D005333:Fetus / Q000166:cytology; D018757:GABA Modulators / Q000494:pharmacology*; D007031:Hypothalamus / Q000196:embryology*; D009474:Neurons / Q000378:metabolism*; D037342:Pertussis Toxin; D010852:Picrotoxin / Q000494:pharmacology; D011280:Pregnanolone / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D001640:Bicuculline; D002118:Calcium; D018757:GABA Modulators; D037342:Pertussis Toxin; D010852:Picrotoxin; D011280:Pregnanolone; D010566:Virulence Factors, Bordetella