title: Endogenous kisspeptin tone is a critical excitatory component of spontaneous GnRH activity and the GnRH response to NPY and CART.
abstract: OBJECTIVE
  Kisspeptin is the major excitatory regulator of gonadotropin-releasing hormone (GnRH) neurons and is responsible for basal GnRH/LH release and the GnRH/LH surge. Although it is widely assumed, based on mutations in kisspeptin and Kiss1R, that kisspeptin acts to sustain basal GnRH neuronal activity, there have been no studies to investigate whether endogenous basal kisspeptin tone plays a direct role in basal spontaneous GnRH neuronal excitability. It is also of interest to examine possible interactions between endogenous kisspeptin tone and other neuropeptides that have direct effects on GnRH neurons, such as neuropeptide Y (NPY) or cocaine- and amphetamine-regulated transcript (CART), since the activity of all these neuropeptides changes during states of negative energy balance.
  
  
  METHODS
  Loose cell-attached and whole-cell current patch-clamp recordings were made from GnRH-GFP neurons in hypothalamic slices from female and male rats.
  
  
  RESULTS
  Kisspeptin activated GnRH neurons in a concentration-dependent manner with an EC50 of 3.32 ± 0.02 nM. Surprisingly, a kisspeptin antagonist, Peptide 347, suppressed spontaneous activity in GnRH neurons, demonstrating the essential nature of the endogenous kisspeptin tone. Furthermore, inhibition of endogenous kisspeptin tone blocked the direct activation of GnRH cells that occurs in response to antagonism of NPY Y5 receptor or by CART.
  
  
  CONCLUSIONS
  Our electrophysiology studies suggest that basal endogenous kisspeptin tone is not only essential for spontaneous GnRH neuronal firing, but it is also required for the net excitatory effects of other neuropeptides, such as CART or NPY antagonism, on GnRH neurons. Therefore, endogenous kisspeptin tone could serve as the linchpin in GnRH activation or inhibition.
authors.affiliation: Division of Diabetes, Obesity, & Metabolism, Oregon National Primate Research Center, Oregon Health & Sciences University, Beaverton, Oreg., USA.
authors.forename: Saurabh
authors.initials: S
authors.lastname: Verma
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Kirigiti
authors.forename: Robert P
authors.initials: RP
authors.lastname: Millar
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Grove
authors.forename: M Susan
authors.initials: MS
authors.lastname: Smith
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000235:genetics; D000818:Animals; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D059648:Kisspeptins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D009419:Nerve Tissue Proteins / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D009478:Neuropeptide Y / Q000494:pharmacology*; D010052:Ovariectomy; D018408:Patch-Clamp Techniques; D011301:Preoptic Area / Q000166:cytology; D051381:Rats; D055647:Rats, Transgenic; D017208:Rats, Wistar; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein
chemical_list: C491406:Kiss1 protein, rat; D059648:Kisspeptins; D009419:Nerve Tissue Proteins; D009478:Neuropeptide Y; D026941:Sodium Channel Blockers; D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D007987:Gonadotropin-Releasing Hormone; D013779:Tetrodotoxin; D004958:Estradiol