Direct electrical stimulation softens the cervix in pregnant and nonpregnant rats

Vagus nerve stimulation in pregnant rats and effects on inflammatory markers in the brainstem of neonates

BackgroundVagus nerve stimulation (VNS) is an Food and Drug Administration-approved method delivering electrical impulses for treatment of depression and epilepsy in adults. The vagus nerve innervates the majority of visceral organs and cervix, but potential impacts of VNS on the progress of pregnancy and the fetus are not well studied.MethodsWe tested the hypothesis that VNS in pregnant dams does not induce inflammatory changes in the cardio-respiratory control regions of the pups' brainstem, potentially impacting the morbidity and mortality of offspring. Pregnant dams were implanted with stimulators providing intermittent low or high frequency electrical stimulation of the sub-diaphragmatic esophageal segment of the vagus nerve for 6-7 days until delivery. After birth, we collected pup brainstems that included cardio-respiratory control regions and counted the cells labeled for pro-inflammatory cytokines (interleukin (IL)-1β, IL-6, tumor necrosis factor-α) and high mobility group box 1.ResultsNeither pup viability nor number of cells labeled for pro-inflammatory cytokines in nucleus tractus solitarii or hypoglossal motor nucleus was impaired by VNS. We provide evidence suggesting that chronic VNS of pregnant mothers does not impede the progress or outcome of pregnancy.ConclusionVNS does not cause preterm birth, affect well-being of progeny, or impact central inflammatory processes that are critical for normal cardiovascular and respiratory function in newborns.

Prostaglandin dehydrogenase is a target for successful induction of cervical ripening

The cervix represents a formidable structural barrier for successful induction of labor. Approximately 10% of pregnancies undergo induction of cervical ripening and labor with prostaglandin (PG) E₂ or PGE analogs, often requiring many hours of hospitalization and monitoring. On the other hand, preterm cervical ripening in the second trimester predicts preterm birth. The regulatory mechanisms of this paradoxical function of the cervix are unknown. Here, we show that PGE₂ uses cell-specific EP2 receptor-mediated increases in Ca²⁺ to dephosphorylate and translocate histone deacetylase 4 (HDAC4) to the nucleus for repression of 15-hydroxy prostaglandin dehydrogenase (15-PGDH). The crucial role of 15-PGDH in cervical ripening was confirmed in vivo. Although PGE₂ or 15-PGDH inhibitor alone did not alter gestational length, treatment with 15-PGDH inhibitor + PGE₂ or metabolism-resistant dimethyl-PGE₂ resulted in preterm cervical ripening and delivery in mice. The ability of PGE₂ to selectively autoamplify its own synthesis in stromal cells by signaling transcriptional repression of 15-PGDH elucidates long sought-after molecular mechanisms that govern PG action in the cervix. This report details unique mechanisms of action in the cervix and serves as a catalyst for (i) the use of 15-PGDH inhibitors to initiate or amplify low-dose PGE₂-mediated cervical ripening or (ii) EP2 receptor antagonists, HDAC4 inhibitors, and 15-PGDH activators to prevent preterm cervical ripening and preterm birth.