Vasopressin excites preoptic kisspeptin neurons in an estrogen dependent manner in female mice (#116)
Kisspeptin is a critical regulator of the
hypothalamic-pituitary-gonadal axis, via its action on gonadotropin releasing
hormone (GnRH) neurons. In rodents, the preovulatory activation of GnRH neurons
is under the control of the suprachiasmatic nucleus (SCN), the central
biological clock. Kisspeptin-synthesizing neurons located in the rostral
periventricular area of the third ventricle of the hypothalamus (RP3V) are
thought to integrate these circadian signals with estrogen (E2)
feedback to appropriately time the preovulatory GnRH surge. Consistent with
this, kiss1 gene expression in the RP3V
as well as the luteinizing hormone surge are controlled by the vasopressin
(AVP)-rich dorsomedial SCN. Furthermore, RP3V kisspeptin neurons are innervated
by AVP-containing fibers originating in the SCN, suggesting that AVP might play
a key role in conveying circadian cues to RP3V kisspeptin neurons. Here, we
investigated the effect of exogenous AVP on the electrical activity of RP3V
kisspeptin neurons in acute brain slices from kisspeptin-IRES-Cre x R26 tGFP
female mice. Our results show that bath application of AVP causes a significant
and reversible increase in the spontaneous firing in a majority (>60 %) of RP3V
kisspeptin neurons from intact mice. This effect does not require fast synaptic
transmission, and involves the activation of type I AVP receptors. AVP-induced
increase in RP3V kisspeptin neuron firing is similar in slices from diestrous
and proestrous females, but is markedly reduced in slices from ovariectomized
(OVX) mice. Further experiments show that the AVP effect on RP3V kisspeptin
neurons is restored to ‘ovary-intact’ levels by in vivo treatment of OVX mice with E2 implants. Together
our results provide a cellular mechanism through which E2 may gate
the responsiveness of RP3V kisspeptin neurons to activation by the SCN.