Smith MA, Williams H, Krajewski SJ, Mcmullen NT, Rance NE (2011) Arcuate NK3 receptor-expressing KNDy neurons are essential for estrogen modulation of LH secretion and body weight in the female rat. Neuroscience 2011 Abstracts 712.07. Society for Neuroscience, Washington, DC.
Summary: Arcuate kisspeptin, neurokinin B, and dynorphin (KNDy) neurons have been proposed to mediate estrogen negative feedback in multiple species. To determine if these neurons are essential for this feedback, we ablated KNDy neurons in the arcuate nucleus of female rats using [MePhe7]Neurokinin B, a selective NK3 receptor (NK3R) agonist, conjugated to Saporin ([MePhe7]NKB-SAP, Advanced Targeting Systems, San Diego, CA). The specificity of this conjugate for NK3R-expressing KNDy neurons is described in a separate abstract (see Krajewski et al., Soc. Neurosci. Abstr. 2011). Twenty-four female rats were ovariectomized (OVX) and received bilateral arcuate microinjections of either [MePhe7]NKB-SAP or a scrambled peptide conjugated to Saporin (Blank-SAP controls). 20-23 days later, animals were implanted with s.c. silastic capsules containing 17β-estradiol (E2), and animals were sacrificed 11 days later. Blood samples for RIA of serum LH were taken at time of OVX and injections (baseline), 20-23 days post-OVX, and 11 days after E2-treatment. Because OVX and E2-treatment have well-described effects on body weight, animals were weighed at the same three time points. In control animals, OVX induced a 13-fold rise in serum LH, which returned to baseline 11 days after E2 replacement. In contrast, OVX had no effect on serum LH in [MePhe7]NKB-SAP animals. There was a small decrease in serum LH 11 days after E2 replacement in [MePhe7]NKB-SAP animals, but the magnitude of this change was much less than seen in control animals. Control animals also exhibited a 20% increase in body weight 20-23 days after OVX, followed by a significant reduction after E2 replacement. Surprisingly, neither OVX nor E2 replacement affected body weight in [MePhe7]NKB-SAP-treated animals. Rather, these animals showed a steady increase in body weight throughout the experiment, at rates comparable to intact female rats or OVX rats treated with E2 (Williams et al., Endocrinology, 2010). Immunohistochemical studies showed near-complete destruction of KNDy neurons in the arcuate nucleus of [MePhe7]NKB-SAP animals. There was preservation of proopiomelanocortin and neuropeptide Y immunoreactivity in the arcuate nucleus and GnRH-immunoreactive fibers in the median eminence. These data provide compelling evidence that arcuate KNDy neurons play an essential role in estrogen negative feedback on LH secretion as well as the estrogen modulation of body weight.