NEURONS IN THE BRAINSTEM THAT EXPRESS NEUROPEPTIDE Y ARE SUFFICIENT TO SUPPRESS LUTEINIZING HORMONE PULSES IN MICE IN A GONADAL STEROID-DEPENDENT MANNER

Abstract

Pulsatile secretion of gonadotropin-releasing hormone/luteinizing hormone (GnRH/LH) is critical for gonad function. While it is known that stress suppresses GnRH/LH pulses, the precise mechanism for this inhibition of gonadotropin secretion is unknown. Neuropeptide Y (NPY) is expressed in several brain regions and is important for both hunger and stress circuits. In previous work, activation of norepinephrine (NE) neurons in the nucleus of the solitary tract (NTS) was sufficient to suppress LH pulses and induced sickness-like behavior. Since NTS NE neurons are heterogeneous and contribute to many physiological processes, we aimed to identify a subpopulation of NTS NE cells that are important for the suppression of LH secretion. Thus, we tested the hypothesis that chemogenetic activation of NTS NPY neurons is sufficient to suppress LH secretion in mice. To accomplish this, adult NPY-Cre transgenic male and female mice on a C57/BL6 background received a stimulatory Cre recombinase-dependent Designer Receptor Exclusively Activated by Designer Drugs (DREADD) virus, AAV1-hSyn-DIO-hM3D(Gq), bilaterally into the NTS. Littermate Cre negative mice were used as controls for all groups. Ten days after neurosurgery, mice were gonadectomized and received a SILASTIC implant containing either estradiol (females) or dihydrotestosterone (DHT; males) or empty/vehicle control implants. Ten days after gonadectomy, frequent blood samples were collected before and after administration of the DREADD agonist (Clozapine N-oxide; CNO), and LH concentrations were determined with enzyme-linked immunosorbent assays (ELISA). Neural tissue was collected following blood collection to assess transduction efficiency using immunohistochemistry and RNAscope. Per repeated measures ANOVA, mean LH concentrations were significantly reduced following CNO administration in Cre positive gonadectomized male and female mice, but not in Cre negative mice. In contrast, DHT-replaced gonadectomized males had no change in LH secretion following CNO in Cre positive and Cre negative mice, while preliminary evidence in estradiol-replaced gonadectomized females demonstrates that CNO can inhibit LH secretion in Cre positive animals. Together, these data demonstrate that NTS-NPY neurons are sufficient to suppress LH secretion in gonadectomized animals, but DHT abrogates this effect, which is consistent with the notion that androgens reduce the sensitivity to stress.