Absent LH signaling rescues the anxiety phenotype in aging female mice

Clinical studies and experimental data together support a role for pituitary gonadotropins, including luteinizing hormone (LH), otherwise considered solely as fertility hormones, in age–related cognitive decline. Furthermore, rising levels of LH in post–menopausal women have been implicated in the high prevalence of mood disorders. This study was designed to examine the effect of deficient LH signaling on both cognitive and emotional behavior in 12–month–old Lhcgr ^−/− mice. For this, we established and validated a battery of five tests, including Dark–Light Box (DLB), Y–Maze Spontaneous Alternation, Novel Object Recognition (NOR), and contextual and cued Fear Conditioning (FCT) tests. We found that 12–month–old female wild type mice display a prominent anxiety phenotype on DLB and FCT. This phenotype was not seen in 12–month–old female Lhcgr ^−/− mice, indicating full phenotypic rescue. Furthermore, there was no effect of LHCGR depletion on recognition memory or working spatial memory on NOR and Y–maze testing, respectively, in 12–month–old mice, notwithstanding the absence of a basal phenotype in wild type littermates. The latter data do not exclude an effect of LH on cognition documented in previous studies. Finally, 12–month–old male mice and 3–month–old male and female mice did not consistently display deficits on any test. The data collectively document, for the first time, that loss of LH signaling reverses age–related emotional disturbances, a prelude to future targeted therapies that block LH action.