Friendships-i.e. selective peer relationships-are an important aspect of human behavior, but are rare in rodent species. Meadow voles are seasonally social rodents that form non-reproductive social groups in winter/short day lengths that are selective in nature. Across rodents, oxytocin neurons in the paraventricular nucleus (PVN) of the hypothalamus are typically active during socially salient events, including interaction with novel individuals as well as social separation. To assess whether familiar and novel peer interactions produce different patterns of immunolabeling in a species that forms bonds with familiar individuals, we measured oxytocin neuron immunoreactivity and colabeling with the immediate early gene product cFos. Oxytocin labeling and oxytocin/cFos colabeling were higher after interaction with a novel same-sex conspecific than after reunion with a peer partner. Colabeling was also high after 24 h separation without reunion. Circulating corticosterone concentrations paralleled PVN oxytocin neuron activity. We also investigated whether oxytocin signaling was photoperiod dependent and could contribute to seasonal differences in meadow vole social behavior. Oxytocin receptor densities are known to be higher in multiple brain regions in short day lengths in meadow voles, but we found no concomitant change in PVN oxytocin positive cell count. Together these studies indicate that seasonal changes in behavior correlate with oxytocin signaling at the receptor level, while short term experiences modulated oxytocin neuron activity differentially by social context.
© 2025. The Author(s).

Oxytocin, often called the "love hormone," is well-known for its roles in childbirth and lactation. Beyond these traditional functions, it plays a vital role in emotional and social behaviors, mood regulation, stress responses, and various physiological processes. Blood oxytocin levels are typically low under basal conditions but increase significantly during labor, breastfeeding, sexual activity, and positive social interactions. However, reported plasma oxytocin levels in humans and rodents vary widely across studies. In this study, we reviewed plasma oxytocin levels in rats from research conducted over the past decade, emphasizing the notable discrepancies observed between studies. Furthermore, we investigated the effects of two anesthetic protocols (inhaled isoflurane and a combination of three anesthetics) and the proteinase inhibitor aprotinin on plasma oxytocin levels in adult male rats. Our findings revealed that neither the anesthetics nor aprotinin significantly affected plasma oxytocin levels. We also discussed potential factors contributing to the marked differences in reported rat blood oxytocin levels.

Shelter environments can be inherently stressful for dogs, a highly social species that forms strong attachment bond with humans. This study evaluated stress responses in 26 shelter dogs during routine veterinary examinations, analyzing behavioral scores alongside physiological and hormonal parameters, including heart rate, body temperature, cortisol (CRT), oxytocin (OXT), serotonin (5-HT), tryptophan (TRP), and interleukin-6 (IL-6). A significant negative correlation was observed between OXT and CRT (ρ = -0.540, p = 0.007), particularly in dogs exhibiting relaxed behavior. OXT was also negatively correlated with body temperature (ρ = -0.435, p = 0.034), supporting its potential role in modulating stress-induced hyperthermia. No significant associations were found between TRP, 5-HT, IL-6, or other physiological measures and behavioral scores. The absence of correlation between TRP and 5-HT may be due to blood-brain barrier regulation, while IL-6's lack of association suggests further investigation is needed to clarify its role in canine stress responses. These findings highlight OXT's possible buffering effect on the hypothalamic-pituitary-adrenal axis and suggest that behavioral assessment may offer a more sensitive measure of canine stress than hormonal or physiological parameters alone. Future studies with larger and more diverse samples are needed to confirm and expand upon these results.

Reciprocity is one of the most prominent explanations for the evolution of stable cooperation. Although reciprocity has been studied for decades in numerous animal species and behavioural contexts, its underlying proximate mechanisms remain unclear. Domestic dogs provide a useful model species for the study of proximate mechanisms, though there are currently inconsistent findings regarding dogs' propensity to reciprocate. Here, we investigated whether, after minimal training, pet dogs would press a button, which remotely controlled a food dispenser, to deliver food to an enclosure occupied by a helpful conspecific that had provided them with food or an unhelpful conspecific that had not provided them with food. We included an asocial control condition in which the enclosure was unoccupied and a social facilitation control in which the food delivery mechanism was non-functional. Whether subjects were familiar with the helpful and unhelpful conspecifics was also varied. In addition, to investigate potential mechanisms underlying reciprocity, we measured subjects salivary oxytocin concentration before and after they experienced the helpful and unhelpful acts. There was no effect of the previous helpfulness or the familiarity of the partner on the number of times subjects pressed the button. However, there was also no effect of the presence of a partner or the operationality of the food delivery mechanism on the number of button presses, indicating that subjects were not pressing the button to provision the partner. Moreover, the experience of the helpful or unhelpful act did not influence subjects' salivary oxytocin concentration. Variation in findings of reciprocity across studies appears to correspond with differing training protocols. Subjects' understanding of the task in the current study may have been constrained by the limited training received. Additional tests to verify subjects' understanding of such tasks are warranted in future studies.

Alcohol consumption to facilitate social interaction is an important drinking motive. Here, we tested whether alcohol influences trust in others via modulation of oxytocin and/or androgens. We also aimed at confirming previously shown alcohol effects on positive affect and risk-taking, because of their role in facilitating social interaction.
This randomized, controlled, within-subject, parallel group, alcohol-challenge experiment investigated the effects of alcohol (versus water, both mixed with orange juice) on perceived trustworthiness via salivary oxytocin (primary and secondary endpoint) as well as testosterone, dihydrotestosterone, positive affect, and risk-taking (additional endpoints). We compared 56 male participants in the alcohol condition (1.07 ± 0.18 per mille blood alcohol concentration) with 20 in the control condition.
The group (alcohol versus control condition) × time (before [versus during] versus after drinking) interactions were not significantly associated with perceived trustworthiness (η2 < 0.001) or oxytocin (η2 = 0.003). Bayes factors provided also substantial evidence for the absence of these effects (BF01 = 3.65; BF01 = 7.53). The group × time interactions were related to dihydrotestosterone (η2 = 0.018 with an increase in the control condition) as well as positive affect and risk-taking (η2 = 0.027 and 0.007 with increases in the alcohol condition), but not significantly to testosterone.
The results do not verify alcohol effects on perceived trustworthiness or oxytocin in male individuals. However, they indicate that alcohol (versus control) might inhibit an increase in dihydrotestosterone and confirm that alcohol amplifies positive affect and risk-taking. This provides novel mechanistic insight into social facilitation as an alcohol-drinking motive.
© 2023. The Author(s).