Hyperpolarization-Activated Cation Channels Are Expressed in Rat Hypothalamic Gonadotropin-Releasing Hormone (GnRH) Neurons and Immortalized GnRH Neurons

Objectives: The current research was conducted to determine whether hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels are expressed in gonadotropin-releasing hormone (GnRH) neurons in the female rat hypothalamus and immortalized GnRH neurons (GT1-7 cells). Methods: Double-label fluorescence immunohistochemistry was used to colocalize HCN1-4 channels and GnRH in GnRH neurons in the female rat hypothalamus. Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry were used to analyze HCN channel gene expression in GT1-7 cells. Results: Double-label fluorescence immunohistochemistry showed that 43% of hypothalamic GnRH neurons immunostained for HCN2 and 90% of GnRH neurons immunostained for HCN3. RT-PCR and Western blot showed expression of all four HCN channel subunits in GT1-7 cells. Double-label immunocytochemistry showed cytoplasmic immunostaining of HCN2 and HCN3 in GT1-7 cells. Conclusions: This study demonstrates for the first time that HCN channels are expressed in GnRH neurons in the rat hypothalamus and GT1-7 cells. Our research supports the hypothesis that HCN channels may be involved in electrical bursting activity and pulsatile GnRH secretion in endogenous GnRH neurons and GT1-7 cells.