Gonadotropin-releasing hormone-1 neuronal activity is independent of cyclic nucleotide-gated channels.
Pulsatile release of GnRH-1 is essential for secretion of gonadotropin hormones. The frequency of GnRH-1 pulses is regulated during the reproductive cycle by numerous neurotransmitters. Cyclic nucleotide-gated (CNG) channels have been proposed as a mechanism to integrate the cAMP signal evoked by many neurotransmitters. This study reports the expression of the CNGA2 subunit in GnRH-1 neurons obtained from mouse nasal explants and shows the ability of GnRH-1 neurons to increase their activity in response to forskolin (activator of adenylyl cyclases), or 3-isobutyl-1-methylxanthine (inhibitor of phosphodiesterases) even after removal of gamma-aminobutyric acid (A)-ergic input. Next, the endogenous activity of adenylyl cyclases was evaluated as a component of the oscillatory mechanism of GnRH-1 neurons. Inhibition of endogenous activity of adenylyl cyclases did not alter GnRH-1 activity. The potential involvement of CNGA2 subunit in basal or induced activity was tested on GnRH-1 neurons obtained from CNGA2-deficient mice. Without up-regulation of CNGA1 or CNGA3, the absence of functional CNGA2 did not alter either the endogenous GnRH-1 neuronal activity or the response to forskolin, negating CNG channels from cAMP-sensitive mechanisms leading to changes in GnRH-1 neuronal activity. In addition, the potential role of CNGA2 subunit in the synchronization of calcium oscillations previously described was evaluated in GnRH-1 neurons from CNGA2-deficient explants. Synchronized calcium oscillations persisted in CNGA2-deficient GnRH-1 neurons. Taken together, these results indicate that CNGA2 channels are not necessary for either the response of GnRH-1 neurons to cAMP increases or the basal rhythmic activity of GnRH-1 neurons.
Constantin
Stéphanie
S
Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
Wray
Susan
S
D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics / Q000502:physiology*; D004594:Electrophysiology; D004622:Embryo, Mammalian; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D010507:Periodicity
C518240:Cnga2 protein, mouse; D054815:Cyclic Nucleotide-Gated Cation Channels; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP