Gonadotropin-releasing hormone-1 neuronal activity is independent of hyperpolarization-activated cyclic nucleotide-modulated channels but is sensitive to protein kinase a-dependent phosphorylation.
Pulsatile release of GnRH-1 stimulates the anterior pituitary and induces secretion of gonadotropin hormones. GnRH-1 release is modulated by many neurotransmitters that act via G protein-coupled membrane receptors. cAMP is the most ubiquitous effector for these receptors. GnRH-1 neurons express hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel protein in vivo. HCN channels are involved in neuronal pacemaking and can integrate cAMP signals. cAMP-dependent protein kinase (PKA) is also activated by cAMP signals, and PKA-dependent phosphorylation modulates voltage-activated channels. In this report, these two pathways were examined in GnRH-1 neurons as integrators of forskolin (FSK)-induced stimulation. The HCN3 isoform was detected in GnRH-1 neurons obtained from mouse nasal explants. ZD7288, a HCN channel blocker, significantly reduced the efficiency of FSK to stimulate GnRH-1 neurons, whereas blockade of PKA with Rp-adenosine-3',5'-cyclic monophosphorothioate triethylammonium did not attenuate the FSK-induced stimulation. To ensure that disruption of HCN channels on GnRH-1 neurons was responsible for reduction of FSK stimulation, experiments were performed removing gamma-aminobutyric acid (GABA), the major excitatory input to GnRH-1 neurons in nasal explants. Under these conditions, Rp-adenosine-3',5'-cyclic monophosphorothioate triethylammonium, but not ZD7288, altered the FSK-induced response of GnRH-1 neurons. These studies indicate that PKA-dependent phosphorylation is involved in the FSK-induced stimulation of GnRH-1 neurons rather than HCN channels, and HCN channels integrate the FSK-induced stimulation on GABAergic neurons. In addition, blockade of HCN channels did not modify basal GnRH-1 neuronal activity when GABAergic input was intact or removed, negating a role for these channels in basal GABAergic or GnRH-1 neuronal activity.
Constantin
Stephanie
S
Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Wray
Susan
S
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics / Q000378:metabolism*; D005260:Female; D058787:GABA-A Receptor Antagonists; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007150:Immunohistochemistry; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009588:Nitrogen Mustard Compounds / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D011247:Pregnancy; D011743:Pyrimidines / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D046509:Tissue Culture Techniques
D054815:Cyclic Nucleotide-Gated Cation Channels; D058787:GABA-A Receptor Antagonists; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D009588:Nitrogen Mustard Compounds; D015221:Potassium Channels; D011743:Pyrimidines; D011963:Receptors, GABA-A; C082246:ICI D2788; D005576:Colforsin; D007987:Gonadotropin-Releasing Hormone; C100119:imidazole mustard; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases