Goodman RL, Lopez JA, Bedenbaugh MN, Connors JM, Hardy SL< Hileman SM, Coolen LM, Lehman MN (2018) Evidence that the LH surge in ewes involves both neurokinin B-dependent and -independent actions of kisspeptin. Neuroscience 2018 Abstracts 773.20 / YY14. Society for Neuroscience, San Diego, CA.
Summary: It is generally recognized that kisspeptin plays a key role in induction of the LH surge in sheep and we have reported evidence that neurokinin B (NKB) does so as well. Specifically, disrupting NKB signaling in the retrochiasmatic area (RCh) using either an antagonist to its receptor, NK3R, or lesions of NK3R-containing neurons in the RCh with a saporin conjugate (NK3-SAP) reduced the amplitude of the estrogen-induced LH surge by 50%. Because a KISS1R antagonist (p271) also produced a 50% decrease in surge amplitude, we hypothesized that these two systems are organized in series with NKB actions in the RCh stimulating kisspeptin release. If this is the case, then the combination of NK3R lesions and a KISS1R antagonist should produce the same inhibition as either treatment alone. This experiment tested this prediction using a 2 x 2 design. Breeding season ewes were ovariectomized and immediately given an estradiol (E) implant sc and two progesterone implants (CIDRs) intravaginally that produced luteal phase levels of these steroids. Ewes then received bilateral injections of either NK3-SAP (n=6) or Blank-SAP (n=5) into the RCh. Three weeks later, an artificial follicular phase was produced by inserting four 3 cm long E implants 24 hrs after CIDR removal and either saline or p271 was infused into the lateral ventricle for 16-24 hrs after E implantation; LH was monitored every 2-4 hrs for two days. CIDRs were then reinserted and the protocol repeated in a cross-over design so that all ewes received saline and p271 treatment. In Blank-SAP ewes, p271 decreased the peak of the LH surge from 61.2 ± 7.6 to 27.4 ± 4.6 ng/mL and delayed it 8 hrs (from 26.5 ± 0.5 to 34.1 ± 1.2 hrs post E implantation). The NK3-SAP injections alone decreased the peak of the LH surge to 29.7 ± 10.7 ng/mL compared to Blank-SAP, but the peak was not further inhibited by p271 in these NK3-SAP-treated ewes (24.4 ± 1.4 ng/mL). However, p271 delayed the peak of the LH surge (from 28.8 ± 1.2 to 34.8 ± 2.1 hrs post E implantation) in the ewes injected with NK3-SAP. Based on these results, we propose that kisspeptin has two roles in the LH surge in ewes: it initiates the surge independent of NKB signaling in the RCh, and maintains LH secretion during the surge by a NKB-dependent system.