Estrogen Permits Vasopressin Signaling in Preoptic Kisspeptin Neurons in the Female Mouse

Abstract

The cellular mechanisms governing the impact of the central circadian clock on neuronal networks are incompletely understood. We examine here the influence of the suprachiasmatic nucleus output neuropeptide arginine-vasopressin (AVP) on the activity of preoptic area kisspeptin neurons. These cells integrate circadian and hormonal signals within the neuronal network that regulates fertility in females. Electrophysiological recordings in brain slices from kisspeptin-GFP mice showed that AVP dose-dependently increased the firing rate of most kisspeptin neurons. These actions were mediated directly at the kisspeptin neuron. Experiments in mice expressing the calcium indicator GCaMP3 in kisspeptin neurons enabled simultaneous monitoring of intracellular calcium concentrations ([Ca 2ϩ ] i ) in multiple cells and revealed that AVP increased [Ca 2ϩ ] i in Ͼ80% of diestrous kisspeptin neurons via a mechanism involving voltage-gated calcium channels. We next examined whether AVP signaling in kisspeptin neurons was time and ovarian cycle dependent. AVP exerted the same effects on diestrous and proestrous days of the ovarian cycle, whether hours before [zeitgeber time 4 (ZT4)-ZT6] or just before (ZT10) the expected time of the proestrous preovulatory luteinizing hormone surge. Remarkably, however, AVP signaling was critically dependent on circulating ovarian steroids as AVP no longer excited preoptic kisspeptin neurons in ovariectomized mice, an effect that was fully restored by estradiol treatment. Together, these studies show that AVP exerts a potent and direct stimulatory influence upon the electrical activity and [Ca 2ϩ ] i of most preoptic kisspeptin neurons. Unexpectedly, estrogen is found to permit circadian AVP signaling at preoptic kisspeptin neurons rather than dynamically modulate its activity throughout the estrous cycle.

Definition of the hypothalamic GnRH pulse generator in mice

“…Brain slice calcium imaging was carried out as previously reported (41). In brief, brain slices (as above) were illuminated through a 40× immersion objective, using the xenon arc light source (300 W; filtered by a GFP filter cube, excitation 460 to 480 nm; Olympus) and the shutter of a Lambda DG-4 (Sutter Instruments).…”

Control of puberty onset and fertility by gonadotropin-releasing hormone neurons

“…Although not proven specifically for the RP3V kisspeptin population, the selective deletion of Εrα from all kisspeptin neurons abolishes the LH surge in mice 63 . The RP3V kisspeptin cells also receive synaptic inputs from suprachiasmatic nucleus vasopressin neurons 64,65 , although it remains unclear precisely how they modulate RP3V kisspeptin activity in a circadiandependent manner [66][67][68] . Nevertheless, it is widely believed that RP3V kisspeptin neurons integrate a circadian vasopressin input with the fluctuating levels of oestradiol across the oestrous cycle to become fully activated only on the afternoon of pro-oestrus to stimulate GnRH neurons that, in turn, trigger the preovulatory GnRH surge 53,57,66,67 (FIG.…”

Ablation of KNDy Neurons Results in Hypogonadotropic Hypogonadism and Amplifies the Steroid-Induced LH Surge in Female Rats

“…Kisspeptin neurons in the AVPV and adjacent periventricular region are particularly important for the LH surge (64). AVPV neurons are modulated by estrogen positive feedback (65), receive circadian signals (66), project to GnRH neurons (67), and are activated during the surge (29). Because the diffusion of NK 3 -SAP does not extend to the rostral hypothalamus, AVPV kisspeptin neurons are not lesioned in KNDy-ablated rats (31).…”