Specialized subpopulations of kisspeptin neurons communicate with GnRH neurons in female mice.

The neuropeptide kisspeptin is a potent stimulator of GnRH neurons and has been implicated as a major regulator of the hypothalamus-pituitary-gonadal axis. There are mainly two anatomically segregated populations of neurons that express kisspeptin in the female hypothalamus: one in the anteroventral periventricular nucleus (AVPV) and the other in the arcuate nucleus (ARC). Distinct roles have been proposed for AVPV and ARC kisspeptin neurons during reproductive maturation and in mediating estrogen feedback on the hypothalamus-pituitary-gonadal axis in adults. Despite their pivotal role in the regulation of reproductive physiology, little is known about kisspeptin neuron connectivity. Although previous data suggest heterogeneity within the AVPV and ARC kisspeptin neuron populations, how many and which of these potential kisspeptin neuron subpopulations are actually communicating with GnRH neurons is not known. Here we used a combinatorial genetic transsynaptic tracing strategy to start to analyze the connectivity of individual kisspeptin neurons with the GnRH neuron population in female mice with a single-cell resolution. We find that only subsets of AVPV and ARC kisspeptin neurons are synaptically connected with GnRH neurons. We demonstrate that the majority of kisspeptin neurons within the AVPV and ARC does not communicate with GnRH neurons. Furthermore, we show that all kisspeptin neurons within the AVPV connected to GnRH neurons are estrogen sensitive and that most of these express tyrosine hydroxylase. Our data demonstrate functional specialization within the two kisspeptin neuron populations.