Poster Presentation The International Congress of Neuroendocrinology 2014

The influence of Leptin on RFRP-3 neurons of mice in development and adulthood (#358)

Matthew C. Poling 1 , Alexander S. Kauffman 1
  1. UCSD, La Jolla, CA, United States

The neuropeptide RFamide-related peptide 3 (RFRP-3; encoded by the Rfrp gene) is the mammalian ortholog to GnIH. RFRP-3 injections can inhibit LH release and increase food intake, but a clear physiological role in adulthood or development remains unknown. We previously demonstrated that rodent Rfrp neurons reside exclusively in the hypothalamic dorsomedial nucleus (DMN) and can be categorized as high mRNA-expressing or low mRNA-expressing Rfrp neurons. Given RFRP-3’s reported orexigenic properties, we performed double-label in situ hybridization (ISH) for metabolic genes and found that while Rfrp neurons do not appear to coexpress NPY, TRH, or MC4R, a subset of Rfrp neurons express leptin receptor in both sexes. Next, we found that Rfrp mRNA is lower in adult gonadectomized ob/ob (leptin-deficient) mice of both sexes, with fewer high mRNA-expressing Rfrp cells than wildtypes. These results differ from a recent report indirectly showing absence of leptin receptor in RFRP-3 cells and normal RFRP-3-immunoreactive levels in estrogen-treated ob/ob mice. The latter difference may reflect a masking effect of estrogen replacement on RFRP-3 levels in the previous study. Given the observed lower Rfrp levels in adult ob/ob mice, we asked whether leptin may also regulate RFRP-3 neuron development. We discovered striking changes in Rfrp gene expression over juvenile development that correlate with the known juvenile “leptin surge,” a postnatal event that governs the development of hypothalamic feeding circuits. Moreover, we found leptin receptor coexpression in some juvenile Rfrp neurons, suggesting that the dramatic developmental changes in postnatal Rfrp expression may be leptin-driven. We tested this possibility by examining Rfrp development in ob/ob juveniles. Contrary to our hypothesis, we found no alteration in Rfrp neuron developmental pattern in ob/ob juveniles. Thus, leptin appears to regulate, directly or indirectly, some RFRP-3 neurons in adulthood, but is not required for normal development of the RFRP-3 system.