Prenatal Testosterone Excess Decreases Neurokinin 3 Receptor Immunoreactivity within the Arcuate Nucleus KNDy cell population

摘要

Prenatal exposure of the ovine fetus to excess testosterone (T) leads to neuroendocrine disruptions in adulthood, evidenced by defects in responsiveness to the ability of gonadal steroids to regulate GnRH secretion. In the ewe, neurones of the arcuate nucleus (ARC), which co-expresses kisspeptin, neurokinin B (NKB) and dynorphin (termed KNDy cells), play a key role in steroid feedback control of GnRH and show altered peptide expression after prenatal T-treatment. KNDy cells also colocalise NKB receptors (NK3R), and it has been proposed that NKB may act as an autoregulatory transmitter in KNDy cells where it participates in the mechanisms underlying steroid negative feedback. In addition, recent evidence suggests that NKB/NK3R signaling may be involved in the positive feedback actions of oestradiol leading to the GnRH/LH surge in the ewe. Thus we hypothesise that decreased expression of NK3R in KNDy cells may be present in the brains of prenatal T-treated animals, potentially contributing to reproductive defects. Using single- and dual-label immunocytochemistry we found that NK3R-positive cells in diverse areas of the hypothalamus; however, after prenatal T-treatment, decreased numbers of NK3R immunoreactive (IR) cells were seen only in the ARC. Moreover, dual-label confocal analyses revealed a significant decrease in the percentage of KNDy cells (using kisspeptin as a marker) that colocalised NK3R. To investigate how NKB ultimately affects GnRH secretion in the ewe, we examined GnRH neurones in the POA and mediobasal hypothalamus (MBH) for the presence of NK3R. Although, consistent with earlier findings, we found no instances of NK3R colocalization in GnRH neurones in either the POA or MBH, >70% GnRH neurones in both areas were contacted by NK3R-IR presynaptic terminals suggesting that, in addition to its role at KNDy cell bodies, NKB may regulate GnRH neurones by presynaptic actions. In summary, decreased NK3R within KNDy cells in prenatal T-treated sheep complement previous observations of decreased NKB and dynorphin in the same population, and may contribute to deficits in the feedback control of GnRH/LH secretion in this animal model. The possibility that NKB agonists may be able to ameliorate the severity of neuroendocrine deficits in prenatal T-treated animals remains to be explored.