Immortalized gonadotropin-releasing hormone neurons (GT1-7 cells) exhibit synchronous bursts of action potentials.
Although it has been assumed that synchronized firing of gonadotropin-releasing hormone (GnRH) neurons is necessary for pulsatile GnRH secretion, there is no clear evidence for this. In the present study we simultaneously recorded spontaneous action potentials from multiple cells. Immortalized GnRH neurons (GT1-7 cells) were cultured on a multi-electrode dish (MED) and action potentials recorded by an extracellular recording method. One to two weeks after the beginning of culture, spontaneous action potentials appeared, exhibiting bursts composed of 5-10 action potentials. Burst activity was intermittent and periodic with mean burst intervals of 13.3 s. Furthermore, burst activity was recorded almost simultaneously from several micro-electrodes, suggesting that electrical activities of GT1-7 cells were synchronized with each other. Periodic bursts were completely and reversibly blocked by 1-5 microM tetrodotoxin, indicating that voltage-dependent Na(+) channels are involved in their generation. gamma-Aminobutyric acid (GABA) given at a 10-microM concentration shortened inter-burst intervals, whereas 10 microM bicuculline lengthened them. Finally, the gap junctional blockers n-octyl alcohol (1 mM) and carbenoxolone (100 microM) reversibly blocked periodic burst activity. The present study provides direct evidence that the electrical activity of GT1-7 cells exhibits synchronous and periodic bursts composed of action potentials. In addition, endogenous GABA is involved in GT1-7 cells in determining burst frequency. Although the precise mechanism of synchronized burst activities needs to be clarified, gap junctional communications among GT1-7 cells are at least partially involved.
Funabashi
T
T
Department of Physiology, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan.
Suyama
K
K
Uemura
T
T
Hirose
M
M
Hirahara
F
F
Kimura
F
F
D020003:1-Octanol / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D001640:Bicuculline / Q000494:pharmacology; D002229:Carbenoxolone / Q000494:pharmacology; D002461:Cell Line, Transformed; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D018756:GABA Antagonists / Q000494:pharmacology; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018756:GABA Antagonists; D007987:Gonadotropin-Releasing Hormone; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D002229:Carbenoxolone; D020003:1-Octanol; D011188:Potassium; D001640:Bicuculline