In mammals, the meiotic cell cycle of oocytes starts during embryogenesis and then pauses. Much later, in preparation for fertilization, oocytes within preovulatory follicles resume meiosis in response to luteinizing hormone (LH). Before LH stimulation, the arrest is maintained by diffusion of cyclic (c)GMP into the oocyte from the surrounding granulosa cells, where it is produced by the guanylyl cyclase natriuretic peptide receptor 2 (NPR2). LH rapidly reduces the production of cGMP, but how this occurs is unknown. Here, using rat follicles, we show that within 10 min, LH signaling causes dephosphorylation and inactivation of NPR2 through a process that requires the activity of phosphoprotein phosphatase (PPP)-family members. The rapid dephosphorylation of NPR2 is accompanied by a rapid phosphorylation of the cGMP phosphodiesterase PDE5, an enzyme whose activity is increased upon phosphorylation. Later, levels of the NPR2 agonist C-type natriuretic peptide decrease in the follicle, and these sequential events contribute to the decrease in cGMP that causes meiosis to resume in the oocyte.

Recent reports indicate that, in addition to treating hypertension, renal denervation (RDN) also mitigates renal inflammation. However, since RDN decreases renal perfusion pressure, it is unclear whether these effects are due to the direct effects of RDN on inflammatory signaling or secondary to decreased arterial pressure (AP). Therefore, this study was conducted to elucidate the contribution of renal nerves to renal inflammation in the DOCA-salt rat, a model in which RDN decreases AP and abolishes renal inflammation. In Experiment 1, we assessed the temporal changes in renal inflammation by measuring renal cytokines and AP in DOCA-salt rats. Uninephrectomized (1K) adult male Sprague Dawley rats that received surgical renal denervation (RDN) or sham (Sham) were administered DOCA (100mg, s.c.) and 0.9% saline for 21 days. AP was measured by radiotelemetry, and urinary cytokine excretion were measured repeatedly. In Experiment 2, the contribution of renal nerves in renal inflammation was assessed in a 2-kidney DOCA-salt rat to control for renal perfusion pressure. DOCA-salt treatment was administered after unilateral (U-)RDN. In Experiment 1, DOCA-salt induced increases in AP and renal inflammation (assessed by urinary cytokines) were attenuated by RDN versus Sham. In Experiment 2, GRO/KC, MCP-1, and macrophage infiltration were lower in the denervated kidney vs. the contralateral Sham kidney. No differences in T-cell infiltration were observed. Together, these data support the hypothesis that renal nerves mediate, in part, the development of renal inflammation in the DOCA-salt rat independent of hypertension. The mechanisms and cellspecificity mediating these effects require further investigation.

Emerging evidence suggests an interaction between renal inflammation and afferent renal nerves in some preclinical models of hypertension. In this study we tested the hypothesis that the inflammatory cytokine IL-1β interacts with afferent renal nerves in the pathogenesis of the DOCA-salt mouse model of hypertension. Specifically, we compared the effect of total renal denervation (TRDN) and afferent RDN (ARDN) on the development of DOCA-salt hypertension to that observed in animals receiving the IL-1 receptor antagonist anakinra. In the first study , 10-week-old male C57BL6/J mice were implanted with radiotelemeters for measurement of mean arterial pressure (MAP). DOCA was administered via subcutaneous pellet containing 50 mg of DOCA, controls received a drug free pellet. Uni-nephrectomy, pellet insertion, salt treatment, TRDN, ARDN, or sham denervation were all performed on the same day. TRDN and ARDN was performed through peri-axonal application of phenol and capsaicin respectively. In the second study , the IL-1 receptor antagonist anakinra (75mg/kg) or vehicle control (0.9% saline) was delivered via intraperitoneal injection daily 10 days post-induction of hypertension. Renal cytokine protein was quantified by Multiplex ELISA. All values reported are mean + SEM, all groups n=5. In the first study , MAP increased in sham treated DOCA-salt mice +43 ± 1 mmHg from baseline by the end of the 3 rd week of DOCA-salt. This response was attenuated by 40% in TRDN (+26 ± 4 mmHg) and by 44% in ARDN DOCA-salt mice (+24 ± 3 mmHg). IL-1β was increased in DOCA-salt kidneys (2.1 ± 0.4 pg/mg) compared to control kidneys (0.36 ± 0.1 pg/mg). In the second study , anakinra similarly attenuated the increase in MAP by 45% (+21 ± 2 mmHg) compared to vehicle controls (+38 ± 1 mmHg). Neither ARDN nor IL-1 receptor antagonism had any effect on renal inflammatory cytokines IL-1β, IL-6, or TNFα. The comparable attenuation in the MAP response to DOCA-salt ARDN and anakinra treated groups as well as the unchanged inflammatory phenotype is consistent with a common mechanism of action. We hypothesize that intrarenal IL-1β activates sympathoexcitatory renal afferent nerves to increase MAP in DOCA-salt mice. Future studies are needed to directly test this hypothesis.

Perhaps because they are a small minority of the total population of renal afferents, myelinated renal afferents (MRA ) have been the least studied. Yet, they are promising targets for neuromodulation because of their low thresholds for electrical stimulation. We are studying the calibers, branching patterns, terminal morphologies, and intrarenal targets of MRA. We identify the myelin sheaths and axons of MRA using antibodies to myelin protein zero and heavy‐chain neurofilament, respectively. The diameters of a majority of MRA range between 1 and 4 u. The diameters of a small minority range between 6 and 10u. Thus, the diameters of MRA are distinctly bimodal. Unmyelinated terminal segments of MRA arise from the myelinated segments of axons at two sites. First, an unmyelinated segment of axon projects from the end of each MRA. Second, unmyelinated segments arise as axon collaterals at nodes of Ranvier along the course of the myelinated axon. Most unmyelinated segments end without any terminal specialization. However, some terminate in small “bulbs, that are approximately twice the diameter of the axon. We have not observed receptor‐related, connective tissue specializations surrounding either type of termination. The distal myelinated portions of MRA are frequently tortuous, sometimes forming hairpin turns and loops. These complex features result in spatial concentrations of nodes of Ranvier, concentrations of unmyelinated collaterals, and concentrations of receptors. A marked narrowing at the origin of each unmyelinated segment suggests the presence of a spike‐initiation zone. The majority of MRA terminate deep in the renal cortex, most often in the extracellular space and frequently within bundles of connective tissue. Some terminations closely appose, but never penetrate, the renal tubular system. However, a small number of MRA appear to penetrate the walls of small arteries and venules. Terminations of MRA show no consistent relationship to glomeruli. The functions of MRA are, thus far, uncertain. Their terminations in the extracellular space would permit them to respond to changes in the composition of the extracellular fluid. However, their associations with connective tissue in the extracellular space could also provide them with mechanoreceptor properties. Their presence in the walls of the vasculature could mediate either chemoreceptor or mechanoreceptor functions. The distinctly bimodal distribution of the diameters of MRA suggests that they may participate in more than one physiological function. From a clinical perspective, the differences in stimulation thresholds afforded by those differences in axon caliber could facilitate selective neuromodulation of multiple physiological processes. Support or Funding Information Supported by SPARC Award 1U01DK116320‐02, JW Osborn, Jr., PI