The purpose of this article is to examine a previously unrecognized role for the vasopressin–oxytocin (VP-OT) system in mammalian “stress-response hormesis.” The current review adds hormesis to the long list of beneficial effects of OT. Hormesis, a biphasic adaptive response to low-level stressors, is introduced here to contextualize the dynamic roles of oxytocin and vasopressin. As with hormesis, the properties of the VP-OT system are context-, time-, and dose-sensitive. Here we suggest that one key to understanding hormesis is the fact that VP and OT and their receptors function as an integrated system. The VP-OT system is capable of changing and adapting to challenges over time, including challenges necessary for survival, reproduction and sociality. Prior research suggests that many beneficial effects of OT are most apparent only following stressful experiences, possibly reflecting interactions with VP, its receptors and other components of the hypothalamic–pituitary–adrenal axis. The release of OT is documented following various kinds of hormetic experiences such as birth, vigorous exercise, ischemic events and the ingestion of emetics, including psychedelics. The phasic or cyclic modulation of VP and related “stress” hormones, accompanied or followed by the release of OT, creates conditions that conform to the core principles of hormesis. This concept is reviewed here in the context of other hormones including corticotropin releasing hormone (CRH) and urocortin, as well as cytokines. In general, VP and classic “stress hormones” support an active response, helping to quickly mobilize body systems. OT interacts with all of these, and may subsequently re-establish homeostasis and precondition the organism to deal with future stressors. However, the individual history of an organism, including epigenetic modifications of classical stress hormones such as VP, can moderate the effects of OT. Oxytocin’s effects also help to explain the important role of sociality in mammalian resilience and longevity. A hormetic perspective, focusing on a dynamic VP-OT system, offers new insights into emotional and physical disorders, especially those associated with the management of chronic stress, and helps us to understand the healing power of social behavior and perceived safety.

The brain is composed of cells having distinct genomic DNA sequences that arise post-zygotically, known as somatic genomic mosaicism (SGM). One form of SGM is aneuploidy—the gain and/or loss of chromosomes—which is associated with mitotic spindle defects. The mitotic spindle orientation determines cleavage plane positioning and, therefore, neural progenitor cell (NPC) fate during cerebral cortical development. Here we report receptor-mediated signaling by lysophosphatidic acid (LPA) as a novel extracellular signal that influences cleavage plane orientation and produces alterations in SGM by inducing aneuploidy during murine cortical neurogenesis. LPA is a bioactive lipid whose actions are mediated by six G protein-coupled receptors, LPA₁–LPA₆. RNAscope and qPCR assessment of all six LPA receptor genes, and exogenous LPA exposure in LPA receptor (Lpar)-null mice, revealed involvement ofLpar1andLpar2in the orientation of the mitotic spindle.Lpar1signaling increased non-vertical cleavage in vivo by disrupting cell–cell adhesion, leading to breakdown of the ependymal cell layer. In addition, genomic alterations were significantly increased after LPA exposure, through production of chromosomal aneuploidy in NPCs. These results identify LPA as a receptor-mediated signal that alters both NPC fate and genomes during cortical neurogenesis, thus representing an extracellular signaling mechanism that can produce stable genomic changes in NPCs and their progeny. Normal LPA signaling in early life could therefore influence both the developing and adult brain, whereas its pathological disruption could contribute to a range of neurological and psychiatric diseases, via long-lasting somatic genomic alterations.

• Oxytocin is an ancient adaptive hormone that promotes social affiliation to maximize fitness and longevity. • Oxytocin is a multifaceted hormone that regulates stress responses at all levels of cellular organization within individuals. • Oxytocin's dual actions on sociability and inflammation highlight its powerful capacity as a modulator of human health.

Decreases in social behavior are a hallmark aspect of acute “sickness behavior” in response to infection. However, immune insults that occur during the perinatal period may have long-lasting consequences for adult social behavior by impacting the developmental organization of underlying neural circuits. Microglia, the resident immune cells of the central nervous system, are sensitive to immune stimulation and play a critical role in the developmental sculpting of neural circuits, making them likely mediators of this process. Here, we investigated the impact of a postnatal day (PND) 4 lipopolysaccharide (LPS) challenge on social behavior in adult mice. Somewhat surprisingly, neonatal LPS treatment decreased sociability in adult female, but not male mice. LPS-treated females also displayed reduced social interaction and social memory in a social discrimination task as compared to saline-treated females. Somatostatin (SST) interneurons within the anterior cingulate cortex (ACC) have recently been suggested to modulate a variety of social behaviors. Interestingly, the female-specific changes in social behavior observed here were accompanied by an increase in SST interneuron number in the ACC. Finally, these changes in social behavior and SST cell number do not appear to depend on microglial inflammatory signaling, because microglia-specific genetic knock-down of myeloid differentiation response protein 88 (MyD88; the removal of which prevents LPS from increasing proinflammatory cytokines such as TNFα and IL-1β) did not prevent these LPS-induced changes. This study provides novel evidence for enduring effects of neonatal immune activation on social behavior and SST interneurons in females, independent of microglial inflammatory signaling.