Both Estrogens and Androgens Alter Neurokinin 3 Receptor (NK3R)- or Kappa-Opioid Receptor (KOR)-Modulated Activity in Arcuate Kisspeptin Neurons
Presentation Number: OR16-1
Date of Presentation: March 6th, 2015
Kristen A Ruka* and Suzanne M Moenter
University of Michigan, Ann Arbor, MI
Gonadotropin-releasing hormone (GnRH) is released in a pulsatile pattern that is essential for fertility. Gonadal steroid feedback alters this pattern, but GnRH neurons themselves rarely express the necessary steroid receptors. Therefore, feedback is likely mediated by steroid-sensitive afferents, such as arcuate neurons that coexpress kisspeptin, neurokinin B (NKB), and dynorphin, also known as KNDy neurons. Kisspeptin stimulates GnRH neurons, and NKB stimulates KNDy neurons via NK3R, while dynorphin inhibits KNDy neurons via KOR. In KNDy neurons from intact vs. gonadectomized (GDX) male mice, NK3R-mediated stimulation of action potential firing is attenuated, while KOR-mediated inhibition of firing is enhanced, supporting steroid negative feedback via both NK3R and KOR. Testosterone can be metabolized to estradiol (E2) in the brain, and most KNDy neurons express both estrogen receptor alpha and androgen receptor. Both steroid classes can suppress arcuate kisspeptin mRNA. However, E2 but not dihydrotestosterone (DHT, an androgen that cannot be converted to E2) appears to be essential for negative feedback on GnRH neuron activity in mice. Therefore, we hypothesized that estrogens, not androgens, modulate KNDy neuron firing responses to activation of NK3R or KOR in males. To test this hypothesis, adult male Tac2 (NKB)-GFP mice were GDX and either untreated or implanted with Silastic capsules containing E2 or DHT. Extracellular electrophysiological recordings were taken from KNDy neurons in acutely prepared coronal brain slices. Frequency of action potential firing was averaged over the last 2 minutes of an untreated control period and compared with average frequency over the last 2 minutes of a 5 minute bath application of either the NK3R agonist senktide (SK) or dynorphin. As in previous studies, preliminary data from GDX mice show a trend toward increased KNDy neuron firing frequency in response to SK (control 0.0±0.0 Hz, SK 8.9±2.7 Hz, p=0.063, n=5). Consistent with our hypothesis, this effect is attenuated in cells from E2-implanted mice (control 0.0±0.0 Hz, SK 1.9±0.8 Hz, p=0.063, n=6; E2 SK vs. GDX SK p<0.05). Interestingly, the response to SK treatment in KNDy neurons after DHT implantation is similar to that after E2 (control 0.0±0.0 Hz, SK 1.5±0.7 Hz, p<0.05, n=8; DHT SK vs. GDX SK p<0.05, DHT SK vs. E2 SK p>0.9). Preliminary data also suggest that dynorphin reduces firing rate in all animal models tested and that this inhibition may be more effective in cells from either E2- or DHT-implanted mice. These data are consistent with the action of estrogens and, in contrast to our hypothesis, also androgens in the alteration of NK3R- and KOR-mediated responses in KNDy neurons from GDX male mice. Future studies will test through which receptors estradiol acts to mediate these changes and whether the effects are direct on KNDy neurons.
Nothing to Disclose: KAR, SMM