Chemogenetic Activation of RFRP Neurons Reduces LH Pulse Frequency in Female but not Male Mice

The neuropeptide RFRP-3 (RFamide-related peptide-3) is thought to play a role in the negative regulation of fertility. However, the exogenous administration of RFRP-3 yields varying results depending on the dose and route of administration, sex of the subject, and many other variables. Manipulation of in vivo neuronal activity using DREADDs (designer receptor exclusively activated by designer drugs) technology enables investigation of cell type-specific neuronal activation in a manner that better reflects endogenous neuronal activity.

To test the effects of RFRP neuronal activation on pulsatile luteinizing hormone (LH) secretion.

We generated mice expressing the stimulatory hM3Dq designer receptor exclusively in RFRP cells using 2 different Cre-loxP-mediated approaches: (1) we bred mice to express hM3Dq in all Rfrp-Cre-expressing cells, including some that transiently expressed Rfrp-Cre neonatally (RFRP × hM3Dq mice), and (2) we stereotaxically injected Cre-dependent hM3Dq into the dorsomedial nucleus of RFRP-Cre mice to drive hM3Dq expression exclusively in a subpopulation of adult Rfrp-Cre neurons (RFRP-AAV-hM3Dq mice). We then investigated the effects of acute hM3Dq activation on LH pulse frequency in RFRP × hM3Dq mice, RFRP-AAV-hM3Dq mice, and their respective controls.

In both female RFRP × hM3Dq and RFRP-AAV-hM3Dq mice, chemogenetic activation of Cre-driven hM3Dq led to a significant 35% to 50% reduction in LH pulse frequency compared with controls, while no differences in pulse amplitude or mean LH concentration were observed. In marked contrast, RFRP activation did not cause any changes to LH pulse dynamics in male mice.

These data show for the first time that activation of neurons that have expressed Rfrp, or of a subset of adult RFRP neurons, can independently suppress LH pulsatility in female, but not male mice.