Effects of aggressive temperament on endogenous oxytocin levels in adult titi monkeys

Room size and offspring presence impact pair-bonded primate affiliation

Primates live in a variety of social groupings and vary in the expression of species-typical behaviors depending upon social conditions. Coppery titi monkeys (Plecturocebus cupreus) are pair-bonding, territorial primates often used to study neurobiology and social behavior in captivity at the California National Primate Research Center (CNPRC). At the center, titi monkeys are housed in cages of standardized size. However, the number of cages--and thus families--per room varies based upon the room size (small or large). Anecdotal evidence suggests titi monkeys behave differently in the two different room sizes. To empirically test this, we measured rates of pair-bonding related affiliation in 23 pairs of titi monkeys. We predicted that monkeys in small rooms would show higher rates of affiliation compared to large rooms. We used a between- and within- subjects design in which all subjects moved from either small to large or large to small rooms. Affiliative behavior was recorded via bihourly instantaneous scan samples. We found that titi monkey pairs affiliated significantly more in small rooms compared to large rooms (partial R2 = 0.1468, t(33) = -3.729, p-value < .0005). We also confirmed that the presence of offspring negatively impacts pair affiliation rates (partial R2 = 0.2240, t(33) = -0.181, p-value = 0.0011). The results of this study suggest that titi monkey pair behavior is influenced by room size, and thus the number of neighboring groups. Management decisions should consider the implications that housing may have on the results of social behavior research.

Sows' Responses to Piglets in Distress: An Experimental Investigation in a Natural Setting

Domestic pigs (Sus scrofa) possess complex socio-cognitive skills, and sows show high inter-individual variability in maternal behaviour. To evaluate how females-reared under natural conditions-react to the isolation calls of their own piglets or those of other females, we conducted observations and experimental trials. In January-February 2021, we conducted all-occurrences sampling on affiliation, aggression, and lactation (daily, 7:30-16:30 h) on six lactating and four non-lactating females at the ethical farm Parva Domus (Turin, Italy). The trials (30 s each, n = 37/sow) consisted of briefly catching and restraining a piglet. We recorded the sow response (none/reactive/proactive movement towards the piglet; self-directed anxiety behaviours such as body shaking) before and during the trial and under control conditions. Increased levels of anxiety behaviour in sows were accompanied by an increased frequency of responses. Less aggressive sows and lactating sows showed the highest frequencies of response. Finally, the isolation calls' maximum intensity had an influence on the type of response observed, with higher proactive response frequencies following lower intensity isolation calls. Our results suggest that being under lactation could play a key role in increasing sow response levels and that specific acoustic features may influence the response.

Neural correlates and effect of jealousy on cognitive flexibility in the female titi monkey (Plecturocebus cupreus)

Jealousy is a social emotion that manifests as behavioral reactions from an individual toward a threat to a valuable relationship. Monogamous species exhibit jealousy-type behaviors as an adaptive response to preserve the relationship. Jealousy is also a complex, negatively-valenced emotion which may include fear of loss, anxiety, suspiciousness, and anger. Negative emotion may impair cognitive processes such as cognitive flexibility, an ability important for coping with new situations. However, little is known about how complex social emotions influence cognitive flexibility. To understand the interaction between jealousy and cognitive flexibility, we examined the neural, physiological, and behavioral factors involved in jealousy and cognitive flexibility in female titi monkeys. We presented subjects with a jealousy provoking scenario, followed by a reversal learning task and a PET scan with a glucose-analog radiotracer. We found that female titi monkeys reacted to a jealousy provoking scenario with increased locomotor behavior and higher glucose uptake in the cerebellum; however, hormone measures and were not affected. As only two females demonstrated cognitive flexibility, the effects of jealousy were difficult to interpret. Locomotion behavior was also negatively correlated with glucose uptake in brain areas linked with motivation, sociality, and cognitive flexibility. Surprisingly, glucose uptake in the orbitofrontal cortex (OFC) was significantly decreased during jealousy scenarios, while uptake in the anterior cingulate cortex (ACC) was decreased during reversal tasks. Our findings suggest that the presence of an intruder produces less visible behavioral reactions in female titis than in males, while still reducing activity in the OFC.

The role of stress phenotypes in understanding childhood adversity as a transdiagnostic risk factor for psychopathology

Childhood adversity is a leading transdiagnostic risk factor for psychopathology, being associated with an estimated 31-62% of childhood-onset disorders and 23-42% of adult-onset disorders (Kessler et al., 2010). Major unresolved theoretical challenges stem from the nonspecific and probabilistic nature of the links between childhood adversity and psychopathology. The links are nonspecific because childhood adversity increases risk, through a range of mechanisms, for diverse forms of psychopathology and are probabilistic because not all individuals exposed to childhood adversity develop psychopathology. In this article, we propose a path forward by focusing on stress phenotypes, defined as biobehavioral patterns activated in response to stressors that can disrupt future functioning when persistent (e.g., reward seeking, social withdrawal, aggression). This review centers on the accumulating evidence that psychopathology appears to be more strongly predicted by behavior and biology during states of stress. Building on this observation, our theoretical framework proposes that we can model pathways from childhood adversity to psychopathology with greater specificity and certainty by understanding stress phenotypes, defined as patterns of behavior and their corresponding biological substrates that are elicited by stressors. This approach aims to advance our conceptualization of mediating pathways from childhood adversity to psychopathology. Understanding stress phenotypes will bring us closer to "precision mental health," a person-centered approach to identifying, preventing, and treating psychopathology. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

The neural circuits of monogamous behavior

The interest in studying the neural circuits related to mating behavior and mate choice in monogamous species lies in the parallels found between human social structure and sexual behavior and that of other mammals that exhibit social monogamy, potentially expanding our understanding of human neurobiology and its underlying mechanisms. Extensive research has suggested that social monogamy, as opposed to non-monogamy in mammals, is a consequence of the neural encoding of sociosensory information from the sexual partner with an increased reward value. Thus, the reinforced value of the mate outweighs the reward value of mating with any other potential sexual partners. This mechanism reinforces the social relationship of a breeding pair, commonly defined as a pair bond. In addition to accentuated prosocial behaviors toward the partner, other characteristic behaviors may appear, such as territorial and partner guarding, selective aggression toward unfamiliar conspecifics, and biparental care. Concomitantly, social buffering and distress upon partner separation are also observed. The following work intends to overview and compare known neural and functional circuits that are related to mating and sexual behavior in monogamous mammals. We will particularly discuss reports on Cricetid rodents of the Microtus and Peromyscus genus, and New World primates (NWP), such as the Callicebinae subfamily of the titi monkey and the marmoset (Callithrix spp.). In addition, we will mention the main factors that modulate the neural circuits related to social monogamy and how that modulation may reflect phenotypic differences, ultimately creating the widely observed diversity in social behavior.

Effects of Chronic and Acute Intranasal Oxytocin Treatments on Temporary Social Separation in Adult Titi Monkeys (Plecturocebus cupreus)

In socially monogamous titi monkeys, involuntary separation from a pair mate can produce behavioral distress and increased cortisol production. The neuropeptide oxytocin (OXT) is thought to play an important role in the separation response of pair-bonded species. Previous studies from our lab have shown that chronic intranasal oxytocin (IN OXT) during development can have long-term effects on adult social behavior. In the current study, we examined the chronic and acute effects of IN OXT or Saline (SAL) on the subjects’ response to a brief separation from their pair mates. Subjects with a history of chronic IN OXT or SAL treatment during development received a single dose of OXT or SAL as adults 30 min before being separated from their pair mate. Chronic treatment consisted of a daily dose of IN OXT (0.8 IU/kg) or SAL (control) from 12 to 18 months of age. Subjects (N = 29) were introduced to a pair mate at 30 months of age. After the pairs had cohabitated for 5 months, pairs underwent two “Brief Separation” (OXT and SAL) and two “Non-Separation” (OXT and SAL) test sessions. Vocalizations and locomotion were measured as behavioral indices of agitation or distress during the Brief Separation and Non-Separation periods (30 min each). We collected blood samples after the Brief Separation and Non-Separation periods to measure cortisol levels. Our results showed subjects treated with chronic OXT had a reduction in long call and peep vocalizations compared to subjects treated with chronic SAL. Subjects treated with chronic SAL and acute OXT produced more peeps and long calls compared to animals treated with acute SAL; however, patterns in this response depended on sex. Cortisol and locomotion were significantly higher during the Brief Separation period compared to the Non-Separation period; however, we did not find any treatment or sex effects. We conclude that chronic IN OXT given during development blunts the separation response, while acute OXT in chronic SAL subjects had sexually dimorphic effects, which could reflect increased partner seeking behaviors in males and increased anxiety in females.

Intranasal oxytocin reduces pre-courtship aggression and increases paternal response in California mice (Peromyscus californicus)

Oxytocin (OXT) is a neuropeptide that can facilitate prosocial behavior and decrease social stress and anxiety but can also increase aggression in some contexts. We investigated whether acute pulses of intranasal (IN) OXT influenced social behavior during social challenges that are likely to occur throughout the lifespan of a wild mouse. To test this, we examined the acute effects of IN OXT in the male California mouse (Peromyscus californicus), a monogamous, biparental, and territorial rodent, using a within-subjects longitudinal design. Social challenges included a pre-courtship male-female encounter conducted during the (1) initial aggressive and not the following affiliative phase of courtship, (2) same-sex resident intruder test, and (3) parental care test. Consecutive tests and doses were separated by at least two weeks. Males were treated with intranasal infusions of 0.8 IU/kg OXT or saline controls 5-min before each behavioral test, receiving a total of three treatments of either IN OXT or saline control. We predicted that IN OXT would 1) decrease aggression and increase affiliation during the pre-courtship aggression phase, 2) increase aggression during resident intruder paradigms, and 3) increase paternal care and vocalizations during a paternal care test. As predicted, during pre-courtship aggression with a novel female, IN OXT males displayed less contact aggression than control males, although with no change in affiliative behavior. However, post-pairing, during the resident intruder test, IN OXT males did not differ from control males in contact aggression. During the paternal care test, IN OXT males were quicker to approach their pups than control males but did not differ in vocalizations produced, unlike our previous research demonstrating an effect on vocalizations in females. In summary, during pre-courtship aggression and the paternal care test, IN OXT reduced antisocial behavior; however, during the resident intruder test, IN OXT did not alter antisocial behavior. These data suggest that IN OXT promotes prosocial behavior specifically in social contexts that can lead to affiliation.

Long term effects of chronic intranasal oxytocin on adult pair bonding behavior and brain glucose uptake in titi monkeys (Plecturocebus cupreus)

Intranasal oxytocin (IN OXT) administration has been proposed as a pharmacological treatment for a range of biomedical conditions including neurodevelopmental disorders. However, studies evaluating the potential long-lasting effects of chronic IN OXT during development are still scarce. Here we conducted a follow-up study of a cohort of adult titi monkeys that received intranasal oxytocin 0.8 IU/kg (n = 15) or saline (n = 14) daily for six months during their juvenile period (12 to 18 months of age), with the goal of evaluating the potential long-lasting behavioral and neural effects one year post-treatment. Subjects were paired with an opposite-sex mate at 30 months of age (one year post-treatment). We examined pair affiliative behavior in the home cage during the first four months and tested for behavioral components of pair bonding at one week and four months post-pairing. We assessed long-term changes in brain glucose uptake using ¹⁸FDG positron emission tomography (PET) scans. Our results showed that OXT-treated animals were more affiliative across a number of measures, including tail twining, compared to SAL treated subjects (tail twining is considered the "highest" type of affiliation in titi monkeys). Neuroimaging showed no treatment differences in glucose uptake between SAL and OXT-treated animals; however, females showed higher glucose uptake in whole brain at 23 months, and in both the whole brain and the social salience network at 33 months of age compared to males. Our results suggest that chronic IN OXT administration during development can have long-term effects on adult social behavior.

An improved sample extraction method reveals that plasma receptor for advanced glycation end-products (RAGE) modulates circulating free oxytocin in mice

The receptor for advanced glycation end-products (RAGE) binds oxytocin (OT) and transports it from the blood to the brain. As RAGE's OT-binding capacity was lost in RAGE knockout (KO) mice, we predicted that circulating concentrations of unbound (free) OT should be elevated compared to wild-type (WT) mice. However, this hypothesis has not yet been investigated. Unfortunately, the evaluation of the dynamics of circulating free and bound plasma OT is unclear in immunoassays, in part because of interference from plasma proteins. A radioimmunoassay (RIA) is considered the gold standard method for overcoming this issue, but is more challenging to implement; thus, commercially available enzyme-linked immunosorbent assays (ELISAs) are more commonly used. Here, we developed a pre-treatment method to remove the interference-causing components from plasma before performing ELISA. The acetonitrile protein precipitation (PPT) approach was reliable, with fewer steps needed to measure free OT concentrations than by solid-phase extraction of plasma samples. PPT-extracted plasma samples yielded higher concentrations of OT in RAGE KO mice than in WT mice using ELISA. After peripheral OT injection, free OT plasma levels spiked immediately then rapidly declined in WT mice, but remained high in KO mice. These results suggest that plasma samples with PPT pre-treatment appear to be superior and that circulating soluble RAGE can most likely serve as a buffer for plasma OT, which indicates a novel physiological function of RAGE.

Relationships between cortisol and urinary androgens in female titi monkeys (Plecturocebus cupreus)

Steroid hormones are critical to the regulation of sociosexual behavior. Their role in the formation of pair bonds is complicated by the relative scarcity of this social system in mammals, as well as species and taxonomic differences in endocrine systems. In the present study, we experimentally manipulated the hypothalamic-pituitary-adrenal axis in female titi monkeys (Plecturocebus cupreus), a neotropical monkey studied for its strong, selective pair bonds. We validated an assay for plasma and urinary cortisol in this species, showing a strong suppression of cortisol following dexamethasone injection, and a significant but somewhat blunted response to adrenocorticotrophin hormone (ACTH) stimulation. Urinary androgens did not change in response to dexamethasone or ACTH. Plasma and urinary cortisol were moderately correlated, whereas urinary cortisol and androgens were only correlated when extreme cortisol values were included. In this study, we laid groundwork for studying the role of glucocorticoids and androgens (and eventually, their interactions with peptides) in the behavioral endocrinology of pair bonds in female titi monkeys.

Coppery titi monkey (Plecturocebus cupreus) pairs display coordinated behaviors in response to a simulated intruder

Mate guarding and coordinated behaviors between partners are important for the maintenance of monogamous pair bonds. To study the effects of a perceived unfamiliar social intruder on females' behavior, we used coppery titi monkeys (Plecturocebus cupreus). We examined the effects of male aggressive temperament on females' behavior and the effects of each behavior performed by the male on the same female behavior. Using a mirror, we simulated a social intruder in the home territory and scored behaviors using an established ethogram. Based on our analysis of self-directed behaviors, females do not recognize themselves in the mirror. We then used general linear mixed models to predict percent change in females' behaviors as a function of (a) males' temperament, (b) males' behavior, and (c) an interaction between males' temperament and behavior. Male temperament did not significantly predict female behavior for any of our best fitting models. For percent change in female lip-smacking, male lip-smacking significantly predicted female lip-smacking (β = 0.74, SE = 0.22, t = 3.39; p = .004). There was a positive correlation between male and female agonistic behaviors such as back-arching/tail-lashing (β = 0.51, SE = 0.23, t = 2.22; p = .04) and for anxiety-related behaviors such as leaving the partner (β = 0.50, SE = 0.19, t = 2.68; p = .015), locomotion duration (β = 0.19, SE = 0.06, t = 2.98; p = .02), and locomotion frequency (β = 0.71, SE = 0.14, t = 5.17; p < .001). These findings on coordination of pair-mate behaviors may explain how titi monkeys display pair bond strength and ensure their reproductive success.

An Animal Model for Mammalian Attachment: Infant Titi Monkey (Plecturocebus cupreus) Attachment Behavior Is Associated With Their Social Behavior as Adults

Close social bonds are integral for good health and longevity in humans and non-human primates (NHPs), yet we have very little understanding of the neurobiological differences between healthy and unhealthy relationships. Our current understanding of social bonding is grounded in Bowlby’s theory of attachment. Work done with human infants and adult couples has suggested that attachment behavior developed in infancy remains stable through development into adulthood. Unfortunately, knowledge of the neurobiological correlates of attachment behavior has been limited due to a lack of animal models with both infant and adult attachments similar to humans. To address this, we measured behavioral responses to separation from their primary attachment figure in infant and adult titi monkeys (Plecturocebus cupreus). In Experiment 1, we tested for a linear relationship between the subject’s response to separation as an infant and their response to separation as an adult. We found greater decreases in infant locomotor behavior in the presence, as opposed to absence, of their primary attachment figure to be indicative of decreased anxiety-like behavior in the presence, as opposed to absence, of their adult pair mates during a novelty response task. In Experiment 2, we increased our sample size, accounted for adverse early experience, and tested a different outcome measure, adult affiliative behavior. We hypothesized that the level of intensity of an infant’s response to separation would explain affiliative behavior with their mate as an adult, but adverse early experience could change this relationship. When we compared infant response to separation to adult affiliative behavior during the first 6 months of their first adult pair bond, we observed a linear relationship for infants with typical early experience, but not for infants with adverse early experience. Infants with a greater change in locomotive behavior between the father and alone conditions were more affiliative with their first adult pair mate. These data support the use of titi monkeys as an appropriate animal model for further investigation of the neurobiology underlying attachment behavior.

Oxytocin, vasopressin, and primate behavior: Diversity and insight

It has become increasingly clear that the nonapeptide hormones oxytocin and vasopressin have more diverse behavioral and physiological effects across species and across individuals than was initially recognized. To reflect this variation, we would like to introduce our Special Issue, entitled Oxytocin and Vasopressin in Primate Behavior, by celebrating the diversity that is found across the articles within it. While every article directly addresses the topic of this Special Issue, they also vary in many characteristics: the species studied, the methods used, and the perspectives taken. By highlighting the interesting ways in which these articles differ from one another, we can gain unique insights into the subject that ties them together: our understanding of oxytocin and vasopressin and the behavior of primates. Nonhuman primates are critical intermediates between rodents and humans and are the best models for human biology and behavior, especially with respect to complex cognitive social constructs, such as visual social attention, face processing, and vocal communication. While rodent studies have laid an important and foundational framework for our understanding of nonapeptides, brains, and behavior, these studies cannot fully recapitulate human phenomena. Therefore, we hope the articles presented here contribute to a greater understanding on the role of oxytocin and vasopressin in primate physiology and behavior and help to further advance the application of this knowledge to human biology.