Ovulation is initiated by central positive feedback effects of estradiol stimulating a surge of gonadotropin-releasing hormone (GnRH) release. Estradiol feedback is conveyed to GnRH neurons by afferents expressing estrogen receptor alpha, including kisspeptin-expressing neurons in the anteroventral periventricular (AVPV) area. To determine if endocrine milieu modulates functional interactions between AVPV kisspeptin and GnRH neurons, optogenetics was used to stimulate AVPV kisspeptin neurons while recording GnRH neuron spiking activity or synaptic currents in brain slices from ovariectomized, estradiol-treated, and ovary-intact mice. Stimulation (20Hz) increased GnRH neuron firing rate in all hormone conditions. This effect was stronger during proestrus and was further increased in GnRH neurons receiving fast-synaptic transmission. A synaptic connection was not required, however, suggesting volume transmission occurs.
Starrett et al. (Sat,) studied this question.