Nicotine inhibition of pulsatile GnRH secretion is mediated by GABAA receptor system in the cultured rat embryonic olfactory placode.
In past work, we suggested that nicotine inhibition of in vivo pulsatile LH release is not mediated by opiate receptors known to be involved in the inhibition of LH release. In the present study, we examined whether nicotine inhibits the pulsatile gonadotropin-releasing hormone (GnRH) release, and whether this inhibition of GnRH release by nicotine is mediated by the GABA receptor system, by checking in vitro pulsatile GnRH release from cultured GnRH neurons obtained from olfactory placodes of rat embryos at E13.5. The mean interpulse interval of pulsatile GnRH release into the medium was 34.2+/-2.0 min in the control period and increased to 95.3+/-19.0 min (n=6) in the period of nicotine treatment at a concentration of 500 nM, showing an inhibitory effect of nicotine on pulsatile GnRH release. The GABA(A) receptor antagonist bicuculline used alone at a concentration of 20 microM caused no significant changes in the pulsatile GnRH release, but when used in combination with 500 nM of nicotine, bicuculline blocked the nicotine inhibition of GnRH release. In a separate experiment, nicotine treatment at a concentration of 500 nM significantly increased GABA release. These results suggest that, in the cultured embryonic olfactory placode, nicotine stimulates GABA release, which then inhibits GnRH release through GABA(A) receptor system.
Kimura
Fukuko
F
Department of Neuroendocrinology, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan. fukuko@med.yokohama-u.ac.jp
Shinohara
Kazuyuki
K
Funabashi
Toshiya
T
Daikoku
Shigeo
S
Suyama
Kumiko
K
Mitsushima
Dai
D
Sano
Akane
A
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004475:Ectoderm / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004622:Embryo, Mammalian / Q000166:cytology; D018756:GABA Antagonists / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D066298:In Vitro Techniques; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009538:Nicotine / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000494:pharmacology; D009833:Olfactory Pathways / Q000166:cytology / Q000187:drug effects* / Q000196:embryology / Q000378:metabolism; D010507:Periodicity; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000187:drug effects*; D019147:Vomeronasal Organ / Q000166:cytology / Q000187:drug effects / Q000196:embryology / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018756:GABA Antagonists; D018722:Nicotinic Agonists; D011963:Receptors, GABA-A; D007987:Gonadotropin-Releasing Hormone; D005680:gamma-Aminobutyric Acid; D009538:Nicotine; D001640:Bicuculline