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Involvement of kndy neurons in luteinizing hormone surges induced by steroids

Helena CV, Toporikova N, Kalil B, Stathopoulos AM, Anselmo-Franci JA, Bertram R (2014) Involvement of kndy neurons in luteinizing hormone surges induced by steroids. Neuroscience 2014 Abstracts 543.11. Society for Neuroscience, Washington, DC.

Summary: A subset of hypothalamic arcuate neurons that coexpress kisspeptin, neurokinin B and dynorphin (KNDy neurons) has been postulated to be critical for puberty onset and regulation of luteinizing hormone (LH) secretion. A method for targeted ablation of KNDy neurons was recently developed using the molecular neurotoxin saporin conjugated to the selective NK3R agonist [MePhe7]Neurokinin B (Nk3-SAP). Ovariectomized rats were microinjected bilaterally into the arcuate nucleus with Blank-SAP or Nk3-SAP. One set of rats was transcardiacally perfused 1, 2 or 3 weeks after the injections and immunocytochemistry for kisspeptin was performed in the arcuate nucleus region. The number of KNDy neurons was significantly decreased after 1 week of the toxin injection, however maximal fiber ablation was only achieved 3 weeks after the microinjections. Another group of rats was treated with oil (OVO), estradiol (OVE) or estradiol plus progesterone (OVEP). One week later, rats had their jugular vein cannulated and blood samples were taken at 10am and hourly from 3 until 6pm. Selective ablation of KNDy neurons of OVO rats significantly reduced basal LH levels at all time points studied. Basal LH levels in OVE and OVEP animals did not differ between groups, yet KNDy ablation increased peak LH levels in the afternoon of OVE and OVEP rats. A third group of OVE animals was microinjected with norbinaltorphimine (nor-BNI), a kappa opioid receptor antagonist, directly into the anteroventral periventricular nucleus (AVPV) one hour before the expected LH surge. The blockage of dynorphin receptors intra-AVPV significantly increased the LH surge, similar to the effect of KNDy ablation in OVE rats. Our results suggest that KNDy neurons provide inhibition to AVPV kisspeptin neurons through dynorphin and thus regulate the size of the LH surge induced by estradiol or estradiol plus progesterone.

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