Suppression of Luteinizing Hormone Secretion in Female Mice by a Urocortin 2-CRHR2 Signaling Pathway

Physiologic stress elicits impairment of reproductive function, in part, by the suppression of luteinizing hormone (LH) secretion. Two populations of kisspeptin-synthesizing neurons in the hypothalamus play essential roles in controlling the pulsatile and surge modes of LH secretion and are potential direct targets of stress-activated neural circuits; however, the mechanism(s) for impairment of kisspeptin cells during stress remain unclear. Here, we conducted 4 experiments to test the hypothesis that corticotropin-releasing hormone receptor 2 (CRHR2) signaling contributes to impaired pulsatile and surge LH secretion via direct actions on kisspeptin cells. First, we observed that cells expressing a specific ligand of CRHR2, urocortin 2 (UCN2), show enhanced c-Fos in the paraventricular nucleus (PVN) following acute hypoglycemia, a metabolic stressor that rapidly suppresses LH pulses by impairing arcuate kisspeptin neuron activation. Second, we determined that central injection of UCN2 rapidly inhibits LH pulses. Furthermore, UCN2 disrupts evening expression of the estradiol-induced LH surge and reduces kisspeptin cell activation in the rostral periventricular hypothalamic region (RP3V). Next, we identified CRHR2 in a majority of both arcuate and RP3V kisspeptin cells. Finally, we observed that UCN2 cells in the PVN are activated following chemogenetic stimulation of catecholamine neurons in the nucleus of the solitary tract. Together these data demonstrate that UCN2-CRHR2 signaling disrupts the pulsatile and surge modes of LH secretion via direct suppression of kisspeptin cells. Furthermore, these findings suggest UCN2 cells in the PVN are regulated by metabolic stress and brainstem norepinephrine signaling pathways that convey stress cues to the hypothalamus.