Cesarean birth elicits long-term effects on vasopressin and oxytocin neurons in the hypothalamic paraventricular nucleus of mice

The inflammatory response to birth requires MyD88 and is driven by both mother and offspring

Birth is an inflammatory event for the newborn, characterized by elevations in interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-α peripherally and/or centrally, as well as changes in brain microglia. However, the mechanism(s) underlying these responses is unknown. Toll-like receptors (TLRs) play crucial roles in innate immunity and initiate inflammatory cascades upon recognition of endogenous or exogenous antigens. Most TLR signaling depends on the adaptor molecule myeloid differentiation primary response 88 (MyD88). We independently varied MyD88 gene status in mouse dams and their offspring to determine whether the inflammatory response to birth depends on MyD88 signaling and, if so, whether that signaling occurs in the offspring, the mother, or both. We find that the perinatal surges in plasma IL-6 and brain expression of TNF-α depend solely on MyD88 gene status of the offspring, whereas postnatal increases in plasma IL-10 and TNF-α depend on MyD88 in both the pup and dam. Interestingly, MyD88 genotype of the dam primarily drives differences in offspring brain microglial density and has robust effects on developmental neuronal cell death. Milk cytokines were evaluated as a possible source of postnatal maternal influence; although we found high levels of CXCL1/GROα and several other cytokines in ingested post-partum milk, their presence did not require MyD88. Thus, the inflammatory response previously described in the late-term fetus and newborn depends on MyD88 (and, by extension, TLRs), with signaling in both the dam and offspring contributing. Unexpectedly, naturally-occuring neuronal cell death in the newborn is modulated primarily by maternal MyD88 gene status.

Lasting consequences on physiology and social behavior following cesarean delivery in prairie voles

Cesarean delivery is associated with diminished plasma levels of several 'birth-signaling' hormones, such as oxytocin and vasopressin. These same hormones have been previously shown to exert organizational effects when acting in early life. For example, our previous work found a broadly gregarious phenotype in prairie voles exposed to oxytocin at birth. Meanwhile, cesarean delivery has been previously associated with changes in social behavior and metabolic processes related to oxytocin and vasopressin. In the present study, we investigated the long-term neurodevelopmental consequences of cesarean delivery in prairie voles. After cross-fostering, vole pups delivered either via cesarean or vaginal delivery were studied throughout development. Cesarean-delivered pups responded to isolation differently in terms of their vocalizations (albeit in opposite directions in the two experiments), huddled in less cohesive groups under warmed conditions, and shed less heat. As young adults, we observed no differences in anxiety-like or alloparental behavior. However, in adulthood, cesarean-delivered voles of both sexes failed to form partner preferences with opposite sex conspecifics. In a follow-up study, we replicated this deficit in partner-preference formation among cesarean-delivered voles and were able to normalize pair-bonding behavior by treating cesarean-delivered vole pups with oxytocin (0.25 mg/kg) at delivery. Finally, we detected minor differences in regional oxytocin receptor expression within the brains of cesarean-delivered voles, as well as microbial composition of the gut. Gene expression changes in the gut epithelium indicated that cesarean-delivered male voles have altered gut development. These results speak to the possibility of unintended developmental consequences of cesarean delivery, which currently accounts for 32.9 % of deliveries in the U.S. and suggest that further research should be directed at whether hormone replacement at delivery influences behavioral outcomes in later life.