Sex hormones influence respiratory function across the lifespan and are integral to facilitating respiratory neuroplasticity, but the mechanisms remain undefined. One specific form of respiratory neuroplasticity, phrenic long-term facilitation (pLTF), is elicited by brief exposures to acute intermittent hypoxia (AIH). Removing the gonads (gonadectomy, GDX) in experimental rats of either sex eliminates pLTF, and pLTF is restored with administration of steroid hormones in both males and females. Reinforcing the importance of steroid hormones to neuroplasticity, females exhibit pLTF only during the proestrus phase of the estrus cycle, when circulating levels of estrogen are high. Here we present findings of a comprehensive study investigating the role of estrogen and G-protein coupled estrogen receptor (GPER) signaling to hypoxic ventilatory responses (HVR) and the expression of pLTF. Our prior work revealed that estrogen signaling via non-genomic receptor mechanisms was important for pLTF expression in females, and GPER is a membrane-bound receptor that has yet to be characterized in the phrenic motor network. We hypothesized: (1) GPER would be present in phrenic motor neurons in males and females and (2) spinal GPER expression would fluctuate in opposition to estrogen to females, as has been demonstrated in the brain. Using immunohistochemistry and advanced colocalization techniques, our findings showed that GPER is expressed equally in male and female phrenic motor neurons (regardless of female estrus cycle; p = 0.27), but it is lower in females during proestrus (when circulating estrogen is high, p = 0.01). Subsequently, we used whole-body plethysmography to assess the role of estrogen and GPER signaling to HVR by (1) comparing young intact and young-GDX female rats to aged female rats and (2) comparing young intact male and female rats after administration of GPER-antagonist or a placebo. We hypothesized that estrogen loss, through GDX or natural aging, would decrease sensitivity to hypoxia in females. We also hypothesized that administration of a GPER-antagonist drug would diminish the HVR in males and females. Consistent with prior studies, we found that estrogen loss from GDX did not impact HVR, but aged females showed a reduced magnitude hypoxic response (p < 0.01). GPER antagonism led to a decreased HVR magnitude in the males, but not females. Differences in metabolism were central to both findings. Finally, the role of GPER to pLTF was assessed using phrenic nerve recordings in anesthetized, mechanically ventilated rats. We hypothesized, based on preliminary findings, that the GPER-antagonist would abolish pLTF in females but not males. Injections of the GPER-antagonist G15, did not impact the magnitude of pLTF in either males or females (p = 0.86). However, females injected with G15 showed an interesting, time-dependent increase in phrenic amplitude in the absence of an AIH stimulus (i.e. the time control group; p < 0.01). These complex initial findings imply that the G15 exerts sex-specific influences on phrenic neural output. Funding sources: University of Minnesota BIRCWH/Women’s Health Research Program Seed Grant, NHLBI R01HL146477, University of Minnesota Rehabilitation Science Program. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Grittner et al. (Fri,) studied this question.