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• The relatively low level of physical violence between men is an evolutionary puzzle. • I use evolutionary game theory to model the evolution of male competitiveness. • Male-male competition determines both reproductive and productive resources. • I identify necessary conditions for high levels of male competitiveness to evolve. Since a man's reproductive success depends on his ability to outcompete other men, male competitiveness may be expected to have been exposed to strong selective pressure throughout human history. Accordingly, the relatively low level of physical violence observed between men has been viewed as a puzzle. What could have limited the eagerness of men to out-compete each other? I study the evolution of male competitiveness in a model where men compete for both reproductive and productive resources. I show that high levels of male competitiveness are then consistent with evolution by natural selection if (a) the ecology is generous enough for men to supply little or no food to their children, (b) competing is not too costly in terms of productive resources, and (c) relatedness among males is low enough. While the main analysis takes women to passively accept the husband that emerges from the male-male competition, the results are qualitatively robust to allowing for female mate choice following the male-male competition game. Possible implications for our understanding of the evolution of marriage systems are discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Quantum nonlocality and quantum contextuality are the most curious properties that change our understanding of nature, and were observed independently in recent decades. One important question is whether both properties can be observed simultaneously. In this paper, we show that in a qutrit-qutrit system we can observe quantum nonlocality and quantum contextuality at the same time. From the perspective of quantum information, our experiment proves in principle that the two resources, quantum nonlocality and quantum contextuality, can be utilized simultaneously. [ABSTRACT FROM AUTHOR]

Species comparisons indicate that scent-marking may differ as a function of mating system and co-housing with the opposite sex (“pairing”). We previously demonstrated that pairing may decrease male solicitation to unfamiliar females in the monogamous Peromyscus californicus but not in the non-monogamous P. leucopus . Whether urine scent-marking of females changes following pairing and whether scent-marking of paired males varies in response to scent-marks of their cagemate versus those of an unfamiliar female has not been examined. Therefore, we tested P. californicus and P. leucopus for within and between species differences in urine scent-marking of: 1) paired and non-paired females in an unscented arena, and 2) paired males in response to their female cagemate’s or an unfamiliar female’s scent-marks (counter-marking). Consistent with previous findings, P. californicus of both sexes deposited more urine scent-marks and covered greater surface area than P. leucopus . In both species, female scent-marking did not differ according to pairing status and male counter-marking did not differ in response to the scent-marks of their female cagemate versus an unfamiliar female. More females of both species and more P. leucopus, but not P. californicus, males scent-marked more around the perimeter than centrally. Potential explanations for these findings are discussed. [ABSTRACT FROM AUTHOR]

Perceptions of trustworthiness are an important predictor of social outcomes, such as monetary exchanges, criminal sentencing, and the attainment of leadership roles. Higher testosterone levels predict both lower voice pitch and untrustworthy behavior, across economic and mating contexts. Here, we tested the influence of voice pitch on perceptions of trustworthiness across general, economic, and mating-related (mate poaching, infidelity) contexts. We found that the context of trust and the sex of the speaker both changed how voice pitch affected perceived trustworthiness. Listeners were more trusting of higher-pitched female voices in economic and mate poaching contexts, but trusted lower-pitched female voices more in general. Listeners were more trusting of higher-pitched male voices in economic and mating-related contexts, and also tended to perceive higher-pitched male voices as more trustworthy in general. Listeners' attributions of trustworthiness were generally unrelated to perceptions of attractiveness from similarly-pitched voices, indicating that trust-related attributions were independent of preferences for higher- or lower-pitched voices. Furthermore, perceptions of general trustworthiness were associated with perceptions of economic trust, but were not consistently associated with perceptions of mating-related trust. These findings provide evidence that voice pitch alone is sufficient to influence trust-related perceptions, and demonstrates that listeners use voice pitch as a cue to trustworthy behavior. [ABSTRACT FROM AUTHOR]

Many factors, including the demonstrator’s sex, status, and familiarity, shape the nature and magnitude of social learning. Given the important role of pair bonds in socially-monogamous animals, we predicted that these intimate relationships would promote the use of social information, and tested this hypothesis in zebra finches ( Taeniopygia guttata ). Observer birds witnessed either their mate or another familiar, opposite-sex bird eat from one, but not a second novel food source, before being allowed to feed from both food sources themselves. Birds used social information to make foraging decisions, but not all individuals used this information in the same way. While most individuals copied the foraging choice of the demonstrator as predicted, paired males did not, instead avoiding the feeder demonstrated by their mate. Our findings reveal that sex and pairing status interact to influence the use of social information and suggest that paired males might use social information to avoid competing with their mate. [ABSTRACT FROM AUTHOR]

Early experience and social context interact to alter the phenotype of complex social behaviors. These early experiences can also result in alterations to cortical organization and connections. Given the ability of the neuropeptide oxytocin (OT) to modulate social and reproductive behavior, OT is likely involved in these cortical processes. However, little is known about the distribution of OT and OT receptors (OTR) within the neocortex. Using autoradiographic and neuroanatomical techniques, we characterized the cortical distribution of OT receptors (OTR) in prairie voles, a socially monogamous rodent species. We found that OTR density was low in the primary sensory areas (including primary somatosensory and auditory regions) but was quite high in association regions (including temporal and parietal association areas, and prelimbic regions). In the primary motor area as well as the temporal and parietal association areas, we observed differences in OTR density across cortical layers. Specifically, cortical layers 2/3 and 5 exhibited greater OTR density than layer 4. Our results point to a role for OT in integrating sensory and motor in the prairie vole brain, providing a complementary mechanism for the modulation of social interactions. Given the ability of early social experience and developmental manipulations of OT to affect the brain and behavior, these results suggest a novel mechanism for how OT may influence cortical organization. [ABSTRACT FROM AUTHOR]

Pair bonding in humans and other socially monogamous species can have positive effects on health and well-being. These attachments also come with the potential for challenges such as separation, jealousy, or grief. Much of the work on the neurobiology of pair bonding in non-human primates has been carried out in coppery titi monkeys (Plecturocebus cupreus), a monogamous South American monkey, although these studies have been primarily in males. In the current study, we utilized female titi monkeys to experimentally examine responses to their monogamous male partner vs. a male stranger or being alone. Positron emission tomography (PET) scans were performed on eight adult female titi monkeys from well-established pairs. We used a within-subjects design in which each female underwent three different conditions after the fluorodeoxyglucose F18 (FDG) injection: a) the subject was reunited with her partner, b) encountered a stranger, or c) was alone in the experimental cage. Behavioural observations were recorded, and plasma assayed for cortisol. Females housed alone showed higher cortisol compared with either the partner or stranger conditions. FDG uptake was higher in the amygdala and hippocampus when interacting with the stranger than the partner. Proximity modulated the relationship between social condition and FDG uptake in several areas. Females entered into mutual proximity more frequently with the partner than with the stranger. Female titi monkeys have different physiological, neural, and behavioural reactions to being with their partner, a stranger male, or being alone. [ABSTRACT FROM AUTHOR]

A prominent body of research spanning disciplines has been focused on the potential underlying role for oxytocin in the social signatures of monogamous mating bonds. Behavioral differences between monogamous and non-monogamous vole species, putatively mediated by oxytocinergic function, constitute a key source of support for this mechanism, but it is unclear to what extent this hormone–behavior linkage extends to the primate order. In a preregistered experiment, we test if oxytocin receptor blockade affects affiliative behavior in mixed-sex pairs of Eulemur , a genus of strepsirrhine primate containing both monogamous and non-monogamous species. Inconsistent with past studies in monogamous voles or monkeys, we do not find confirmatory evidence in Eulemur that monogamous pairs affiliate more than non-monogamous pairs, nor that oxytocin receptor blockade of one pair member selectively corresponds to reduced affiliative or scent-marking behavior in monogamous species. We do, however, find exploratory evidence of a pattern not previously investigated: simultaneously blocking oxytocin receptors in both members of a monogamous pair predicts lower rates of affiliative behavior relative to controls. Our study demonstrates the value of non-traditional animal models in challenging generalizations based on model organisms, and of methodological reform in providing a potential path forward for behavioral oxytocin research. • We administer an oxytocin receptor antagonist (OTA) to monogamous and non-monogamous lemurs. • Confirmatory analyses do not find consistent evidence for previously reported OTA effects. • Exploratory analyses suggest OTA effects may arise during joint administration to both members of monogamous dyads. • Oxytocin may not be key to monogamous mating bonds in the same way across mammalian models. [ABSTRACT FROM AUTHOR]

Monogamy of quantum correlations is a vibrant area of research because of its potential applications in several areas in quantum information ranging from quantum cryptography to co-operative phenomena in many-body physics. In this paper, we investigate conditions under which monogamy is preserved for functions of quantum correlation measures. We prove that a monogamous measure remains monogamous on raising its power, and a non-monogamous measure remains non-monogamous on lowering its power. We also prove that monogamy of a convex quantum correlation measure for arbitrary multipartite pure quantum state leads to its monogamy for mixed states in the same Hilbert space. Monogamy of squared negativity for mixed states and that of entanglement of formation follow as corollaries of our results. [ABSTRACT FROM AUTHOR]

Prairie voles are unusual mammals in that, like humans, they are capable of forming socially monogamous pair bonds, display biparental care, and engage in alloparental behaviors. Both mu and kappa opioid receptors are involved in behaviors that either establish and maintain, or result from pair bond formation in these animals. Mu and kappa opioid receptors both utilize inhibitory G-proteins in signal transduction mechanisms, however the efficacy by which these receptor subtypes stimulate G-protein signaling across the prairie vole neuraxis is not known. Utilizing [ 35 S]GTPγS autoradiography, we characterized the efficacy of G-protein stimulation in coronal sections throughout male and female prairie vole brains by [ d -Ala 2 ,NMe-Phe 4 ,Gly-ol 5 ]-enkephalin (DAMGO) and U50,488H, selective mu and kappa opioid agonists, respectively. DAMGO stimulation was highest in the forebrain, similar to that found with other rodent species. U-50,488H produced greater stimulation in prairie voles than is typically seen in mice and rats, particularly in select forebrain areas. DAMGO produced higher stimulation in the core versus the shell of the nucleus accumbens (NAc) in females, while the distribution of U-50,488H stimulation was the opposite. There were no gender differences for U50,488H stimulation of G-protein activity across the regions examined, while DAMGO stimulation was greater in sections from females compared to those from males for NAc core, entopeduncular nucleus, and hippocampus. These data suggest that the kappa opioid system may be more sensitive to manipulation in prairie voles compared to mice and rats, and that female prairie voles may be more sensitive to mu agonists in select brain regions than males. [ABSTRACT FROM AUTHOR]

Social environment has direct effects on an animal's behavior, physiology and neurobiology. In particular, adult neurogenesis is notably affected by a variety of social manipulations, including social isolation. We hypothesized that social isolation should have particularly acute effects on neurogenesis in a highly social (monogamous and bi-parental) species such as Peromyscus californicus , the California mouse. Adult male and female P. californicus mice were housed in isolation or in same-sex pairs for 4 or 24 days. At the end of each period, either cell proliferation or cell survival was quantified with BrdU label and neuronal markers (either TuJ1 or NeuN). After 4 days, isolated males had greater cellular proliferation in the dentate gyrus of the hippocampus (DG) than pair housed males. After 24 days, isolate females demonstrated greater cell survival in the DG than paired females. Males demonstrated a similar, but non-significant pattern. No differences in cellular proliferation or cell survival were found in the subventricular zone (SVZ), or medial amygdala (MeA). These results add to the evidence which demonstrates that neurogenic responses to environmental conditions are not identical across species. These data may be critical in understanding the functional significance of neurogenesis as it relates to the interactions between social systems, social environment and the display of social behaviors. [ABSTRACT FROM AUTHOR]

The opioid system is involved in infant–mother bonds and adult–adult bonds in many species. We have previously shown that μ opioid receptors (MORs) and κ opioid receptors (KORs) are involved in regulating the adult attachment of the monogamous titi monkey. The present study sought to determine the distribution of MOR and KOR in the titi monkey brain using receptor autoradiography. We used [ 3 H][D-Ala 2 ,N-Me-Phe 4 ,Gly 5 -ol]-enkephalin (DAMGO) to label MORs and [ 3 H]U69,593 to label KORs. MOR binding was heterogeneous throughout the titi monkey brain. Specifically, MOR binding was observed in the cingulate gyrus (CG), striatum, septal regions, diagonal band, amygdala, hypothalamus, hippocampus, and thalamus. Binding was particularly dense in the septum, medial amygdala, paraventricular nucleus of the hypothalamus, mediodorsal thalamus with moderate binding in the nucleus accumbens. Consistent with other primate species, MOR were also observed in “neurochemically unique domains of the accumbens and putamen” (NUDAPs). In general KOR binding was more homogenous. KORs were primarily found in the CG, striatum, amygdala and hippocampus. Dense KOR binding was observed in the claustrum. Relative MOR and KOR binding in the titi monkey striatum was similar to other humans and primates, but was much lower compared to rodents. Relative MOR binding in the titi monkey hypothalamus was much greater than that found in rodents. This study was the first to examine MOR and KOR binding in a monogamous primate. The location of these receptors gives insight into where ligands may be acting to regulate social behavior and endocrine function. [ABSTRACT FROM AUTHOR]

The μ opioid receptor (MOR) and κ opioid receptor (KOR) have been implicated in pair-bond formation and maintenance in socially monogamous species. Utilizing monogamous titi monkeys ( Callicebus cupreus ), the present study examined the potential role opioids play in modulating the response to separation, a potent challenge to the pair-bond. In Experiment 1, paired male titi monkeys were separated from their pair-mate for 30-min and then received saline, naloxone (1.0 mg/kg), morphine (0.25 mg/kg), or the KOR agonist, U50,488 (0.01, 0.03, or 0.1 mg/kg) in a counter-balanced fashion, immediately prior to a 30-min reunion with their mate. Blood samples were collected immediately prior to and after the reunion. Males receiving morphine approached females less, initiated contact less, and females broke contact with the males less. The increase in cortisol in response to naloxone was greater compared to vehicle, and the increase in cortisol in response to the high dose of U50,488 compared to vehicle approached significance. In Experiment 2, paired males were treated with the KOR antagonist, GNTI (0.1, 0.3, or 1.0 mg/kg), or saline 24 h prior to a 60-min separation from their mate. Blood samples were collected at the time of injection and immediately before and after separation. Administration of the low dose of GNTI decreased the locomotor component of the separation response compared to vehicle. The present study found that the opioid system is involved in both the affiliative and separation distress components of a pair-bond, and these components are regulated by different opioid receptors. [ABSTRACT FROM AUTHOR]

Studying how host characteristics and ecology affect the mating systems of symbiotic crustaceans offers an opportunity to understand how ecological factors contribute to the evolution of different animal mating systems. In theory, symbiotic crustaceans should display social monogamy with long-term heterosexual pairing when hosts are relatively small in body size and structurally simple, and when hosts have relatively low abundance in habitats where the risk of mortality for symbionts (e.g., predation) away from hosts is high. We test this prediction in the mating system of the flotsam crab ( Planes major ) and its facultative association with loggerhead sea turtles ( Caretta caretta ). First, we found that the overall population and sex distributions were non-random and crabs inhabited host turtles as heterosexual pairs more frequently than expected by chance, which supports the hypothesis that P . major is socially monogamous on C . caretta . Second, we found that male crabs pair with females regardless of their reproductive state, male–female pairs do not display size-assortative pairing, crab body size and host turtle body size are not correlated, and crabs display reverse sexual dimorphism in body size and conventional sexual dimorphism in weaponry. These results do not support the hypothesis that social monogamy in P . major is always long term. Instead, our results suggest that the duration of social monogamy in P . major is likely variable and may involve some degree of host switching and intra-sexual (mostly male–male) competition. Our results were only partially consistent with theoretical considerations for how host characteristics and ecology affect the mating systems of symbiotic crustaceans, and future studies should focus on quantifying the degree and direction of host switching to better understand the factors that affect the duration of monogamous pairing when P . major associates with C . caretta . [ABSTRACT FROM AUTHOR]

• IN OXT attenuates male aggression during pre-courtship encounters. • IN OXT does not alter male aggression during resident intruder encounters. • IN OXT increases paternal responsiveness during a paternal care challenge. • IN OXT in fathers does not influence total paternal care or vocalizations. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

A variety of recent data demonstrate that vasoactive intestinal polypeptide (VIP) and VPAC receptors (which bind VIP, and to a lesser extent, pituitary adenylatecyclase activating peptide) are important for numerous social behaviors in songbirds, including grouping and aggression, although VIP relates to these behaviors in a site-specific manner. In order to determine the global effects of central VPAC receptor activation on social behavior, we here infused a VPAC receptor antagonist or vehicle twice daily into the lateral ventricle of colony-housed male and female zebra finches and quantified a wide range of behaviors. Aggressive behaviors were not altered by ventricular infusions, consistent with known opposing, site-specific relationships of VIP innervation to aggression. Courtship and self-maintenance behaviors were likewise not altered. However, VPAC antagonism produced significant deficits in pair bonding. Antagonist subjects took longer to form a pair bond and were paired for significantly fewer observation sessions relative to control subjects (median 1.5 of 6 observation sessions for antagonist subjects versus 4 for control subjects). Antagonist subjects were also significantly less likely to be paired in the final observation session. Based on the known distribution of VPAC receptors in finches and other vertebrates, we propose that VPAC receptors may mediate pair bonding via a variety of brain areas that are known to be important for the establishment of partner preferences in voles, including the lateral septum, ventral tegmental area, nucleus accumbens and ventral pallidum. [ABSTRACT FROM AUTHOR]

Highlights: [•] Vasopressin 1a receptor binding is diffuse and widespread in the titi monkey brain. [•] Oxytocin receptor binding is much more limited, with the densest binding in the hippocampus. [•] There is considerable interspecies variation in neuropeptide receptor expression in primates. [•] ALS-II-69 is a selective antagonist for the titi monkey oxytocin receptor. [•] SR49059 is a selective antagonist for the titi monkey vasopressin 1a receptor. [Copyright &y& Elsevier]

Highlights: [•] Sex difference found in rostrocaudal distribution of OXA cells in prairie voles. [•] Reproductive experience increased OXA-ir cells in female prairie voles. [•] Reproductive experience did not increase OXA-ir cells in male prairie voles. [•] Males showed more OXA-ir cells after long cohabitation with a female, regardless of mating. [•] Increase in OXA-ir cells in experienced females perhaps related to mating, mothering or lactation. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this paper was to determine aspects of the reproductive biology of captively bred Fenneropenaeus merguiensis under commercial broodstock production conditions that relate to the design and implementation of genetic improvement programmes for this species. First, we tested whether there is evidence for polygamy vs monogamy by genotyping females, the material found in their thelycums, and material that leaches out of the thelycum using DNA microsatellite loci. All genotypes in all animals and tissues tested could be accounted for using a monogamy model. Second we compared the accuracy of pedigrees formed under assumptions of monogamy vs polygamy. Pedigrees were formed using microsatellite genotypes from 73 dams and 400 offspring. Sibship groups and dam–offspring groups from pedigrees developed assuming monogamy almost always had the same mtDNA haplotypes, suggesting a high accuracy of the pedigrees, but those formed under the assumption of polygamy were less accurate, and together these results also support the monogamy model. Third, we assessed the between family variance in offspring family numbers from two sets of mass spawnings of about 40 inseminated females per spawn. About half of the offspring originated from just 20 percent of the dams, i.e. many dams contributed few offspring. These data can help predict optimal sample sizes required for accurate future estimates of genetic parameters. [Copyright &y& Elsevier]

Highlights: [•] Women prefer lower-pitched male voices over higher-pitched male voices. [•] Lower-pitched male voices are perceived as more likely to commit infidelity. [•] We tested if perceptions of fidelity predicted women’s voice preferences. [•] Perceptions of fidelity predicted short- over long-term voice preferences. [Copyright &y& Elsevier]

Summary: The role of opioid receptors in infant–mother attachment has been well established. Morphine, a preferential μ opioid receptor (MOR) agonist, attenuates separation distress vocalizations and decreases physical contact between infant and mother. However, there is little research on how opioid receptors are involved in adult attachment. The present study used the monogamous titi monkey (Callicebus cupreus) to explore the role of opioid receptors in the behavioral and physiological components of pair-bonding. In Experiment 1, paired male titi monkeys (N =8) received morphine (0.1, 0.5, or 1.0mg/kg), the opioid antagonist naloxone (1.0mg/kg), vehicle, or a disturbance control and were filmed with their pair-mate for 1h. In Experiment 2, the same eight males received morphine (0.25mg/kg), naloxone (1.0mg/kg), vehicle, or a disturbance control and were filmed for an hour without their pair-mates. All video sessions were scored for social and non-social behaviors. Blood was sampled immediately prior to drug administration and at the end of the hour session. Plasma was assayed for cortisol, oxytocin, and vasopressin. In Experiment 1, opioid manipulation had no effect on affiliative behaviors; however, morphine dose-dependently decreased locomotor behavior and increased scratching. In Experiment 2 in which males were separated from their pair-mates, naloxone increased locomotion. Morphine dose-dependently attenuated the rise in cortisol, while naloxone potentiated the increase of cortisol. The cortisol increase following naloxone administration was greater when a male was alone compared to when the male was with his pair-mate. Naloxone increased vasopressin but only when the male was tested without his pair-mate. The present study found that the absence of a pair-mate magnified naloxone's effects on stress-related hormones and behaviors, suggesting that the presence of a pair-mate can act as a social buffer against the stress-inducing effects of naloxone. [Copyright &y& Elsevier]

Abstract: Differences in the social organization and behavior of male mammals are attributable to species differences in neurochemistry, including differential expression of steroid hormone receptors. However, the distribution of progestin receptors (PR) in a socially monogamous and spontaneously parental male rodent has never been examined. Here we determined if PR exists and is regulated by testicular hormones in forebrain sites traditionally influencing socioreproductive behaviors in male prairie voles (Microtus ochrogaster). We hypothesized that PR expression in male prairie voles would differ from that described in other male rodents because PR activity inhibits parental behaviors and social memory in laboratory mice and rats. Adult male prairie voles received a sham surgery, were gonadectomized, or were gonadectomized and implanted with a testosterone-filled capsule. PR immunoreactivity (PRir) was measured four weeks later in areas of the hypothalamus and extended amygdala. A group of gonadally intact female prairie voles was included to reveal possible sex differences. We found considerable PRir in all sites examined. Castration reduced PRir in males'' medial preoptic nucleus, anteroventral periventricular nucleus, ventromedial hypothalamus, and posterodorsal medial amygdala, and it was maintained in these sites by testosterone. This is the first study to examine PR expression in brain sites involved in socioreproductive behaviors in a socially monogamous and spontaneously paternal male rodent. Our results mostly reveal cross-species conservation in the distribution and hormone sensitivity of PR expression. Because PR interferes with aspects of sociality in other male rodents, PR may eventually be found to have different neurobiological actions in male prairie voles. [Copyright &y& Elsevier]

Summary: Adult male prairie voles (Microtus ochrogaster) are highly gregarious and socially monogamous, which is dissimilar to most other male rodents but reminiscent of many primates, including humans. This has resulted in prairie voles becoming a premier model in which to study the neural and hormonal basis of complex social behaviors, as well as the atypical development of these behaviors. This research is impeded by the complete lack of knowledge about the gonadal steroid environment during early development in this species. In many other animals, testicular hormones released during perinatal life permanently organize the neural substrates underlying later social behaviors in males, so knowledge about the presence or possibly even absence of testosterone in male prairie vole pups would provide important insight into their neurobehavioral development. In this study, male and female prairie vole pups were sacrificed 1, 2, 3, 4 or 5 days after birth and radioimmunoassay used to determine plasma levels of testosterone. We found that testosterone was detectable in both sexes on all days and that levels were significantly higher in males than females. Testosterone in neonatal males was sometimes as high as breeding males sampled one day after the birth of a litter. This study is the first to examine circulating testosterone in neonatal prairie voles, or any other species of Microtus, and the results indicate similarity to other rodents. This is surprising because some previous studies manipulating gonadal hormones in neonatal prairie voles have found limited effects on their neurobehavioral development, suggesting the existence of some unique, yet-to-be-revealed aspects of their neuroendocrine profile during early life. [ABSTRACT FROM AUTHOR]

Background: In specific vole and primate species the neuropeptide oxytocin plays a central role in the regulation of pair-bonding behavior. Here we investigate the extent to which genetic variants in the oxytocin receptor gene (OXTR) are associated with pair-bonding and related social behaviors in humans. Methods: We first genotyped twelve single nucleotide polymorphisms (SNPs) in the TOSS (Twin and Offspring Study in Sweden) (n = 2309) and the TCHAD (Swedish Twin Study of Child and Adolescent Development) (n = 1240), comprising measures of self-reported pair-bonding behavior. In the TOSS sample we further investigated one of the SNPs for measures of marital status and quality. Moreover, in the TCHAD sample we explored the longitudinal relationship between precursors of pair-bonding during childhood and subsequent behavior in romantic relationships. Finally, in the TCHAD study and in the Child and Adolescent Twin Study of Sweden (CATSS) (n = 1771), the association between the same SNP and childhood behaviors was investigated. Results: One SNP (rs7632287) in OXTR was associated with traits reflecting pair-bonding in women in the TOSS and TCHAD samples. In girls the rs7632287 SNP was further associated with childhood social problems, which longitudinally predicted pair-bonding behavior in the TCHAD sample. This association was replicated in the CATSS sample in which an association between the same SNP and social interaction deficit symptoms from the autism spectrum was detected. Conclusion: These results suggest an association between variation in OXTR and human pair-bonding and other social behaviors, possibly indicating that the well-described influence of oxytocin on affiliative behavior in voles could also be of importance for humans. [ABSTRACT FROM AUTHOR]

Abstract: Love, attachment, and truth of human monogamy have become important research themes in neuroscience. After the introduction of functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET), neuroscientists have demonstrated increased interest in the neurobiology and neurochemistry of emotions, including love and affection. Neurobiologists have studied pair-bonding mechanisms in animal models of mate choice to elucidate neurochemical mechanisms underlying attachment and showed possible roles for oxytocin, vasopressin, and dopamine and their receptors in pair-bonding and monogamy. Unresolved is whether these substances are also critically involved in human attachment. The limited number of available imaging studies on love and affection is hampered by selection bias on gender, duration of a love affair, and cultural differences. Brain activity patterns associated with romantic love, shown with fMRI, overlapped with regions expressing oxytocin receptors in the animal models, but definite proof for a role of oxytocin in human attachment is still lacking. There is also evidence for a role of serotonin, cortisol, nerve growth factor, and testosterone in love and attachment. Changes in brain activity related to the various stages of a love affair, gender, and cultural differences are unresolved and will probably become important research themes in this field in the near future. In this review we give a resume of the current knowledge of the neurobiology of love and attachment and we discuss in brief the truth of human monogamy. [Copyright &y& Elsevier]

Abstract: Neurons synthesizing dopamine (DA) are widely distributed in the brain and implicated in a tremendous number of physiological and behavioral functions, including socioreproductive behaviors in rodents. We have recently been investigating the possible involvement of sex- and species-specific TH-immunoreactive (TH-ir) cells in the male prairie vole (Microtus ochrogaster) principal bed nucleus of the stria terminalis (pBST) and posterodorsal medial amygdala (MeApd) in the chemosensory control of their monogamous pairbonding and parenting behaviors. These TH-ir cells are not immunoreactive for dopamine-beta-hydroxylase (DBH), suggesting they are not noradrenergic but possibly DAergic. A DAergic phenotype would require them to contain aromatic l-amino acid decarboxylase (AADC) and here we examined the existence of cells immunoreactive for both TH and AADC in the pBST and MeApd of adult virgin male and female prairie voles. We also investigated the presence of TH/AADC cells in the anteroventral periventricular nucleus (AVPV), medial preoptic area (MPO), arcuate nucleus (ARH), zona incerta (ZI), substantia nigra (SN) and ventral tegmental area (VTA). Among our findings were: (1) the pBST and MeApd each contained completely non-overlapping distributions of TH-ir and AADC-ir cells, (2) the AVPV contained surprisingly few AADC-ir cells and almost no TH-ir cells contained AADC-ir, (3) approximately 60% of the TH-ir cells in the MPO, ARH, and ZI also contained AADC-ir, (4) unexpectedly, only about half of TH-ir cells in the SN and VTA contained AADC-ir, and (5) notable populations of AADC-ir cells were found outside traditional monoamine-synthesizing regions, including some sites that do not contain AADC-ir cells in adult laboratory rats or cats (medial septum and cerebral cortex). In the absence of the chemical requirements to produce DA, monoenzymatic TH-ir cells in the virgin adult prairie vole pBST, MeApd, and elsewhere in their brain may instead produce l-DOPA as an end product and use it as a neurotransmitter or neuromodulator, similar to what has been observed for monoenzymatic TH-synthesizing cells in the laboratory rat brain. [Copyright &y& Elsevier]

Abstract: Pair-bonded relationships form during periods of close spatial proximity and high sociosexual contact. Like other monogamous species, marmosets form new social pairs after emigration or ejection from their natal group resulting in periods of social isolation. Thus, pair formation often occurs following a period of social instability and a concomitant elevation in stress physiology. Research is needed to assess the effects that prolonged social isolation has on the behavioral and cortisol response to the formation of a new social pair. We examined the sociosexual behavior and cortisol during the first 90-days of cohabitation in male and female Geoffroy''s tufted-ear marmosets (Callithrix geoffroyi) paired either directly from their natal group (Natal-P) or after a prolonged period of social isolation (ISO-P). Social isolation prior to pairing seemed to influence cortisol levels, social contact, and grooming behavior; however, sexual behavior was not affected. Cortisol levels were transiently elevated in all paired marmosets compared to natal-housed marmosets. However, ISO-P marmosets had higher cortisol levels throughout the observed pairing period compared to Natal-P marmoset. This suggests that the social instability of pair formation may lead to a transient increase in hypothalamic–pituitary–adrenal (HPA) axis activity while isolation results in a prolonged HPA axis dysregulation. In addition, female social contact behavior was associated with higher cortisol levels at the onset of pairing; however, this was not observed in males. Thus, isolation-induced social contact with a new social partner may be enhanced by HPA axis activation, or a moderating factor. [Copyright &y& Elsevier]

Abstract: Theory suggests that symbiotic species should be monogamous and form long-lasting heterosexual pairs in/on hosts when inhabiting scarce and small hosts in environments where predation risk away from hosts is high (e.g., tropical subtidal). This prediction was tested with Pontonia mexicana which inhabits the relatively small and scarce amber pen-shell Pinna carnea in the tropical Caribbean. In agreement with theory, P. mexicana were found dwelling as heterosexual pairs in the mantle cavity of pen-shell individuals with more frequency than expected by chance alone. However, additional observations suggested that male–female pairing of P. mexicana does not last long. First, males paired with females that were close to molt and become sexually receptive more frequently than expected by chance alone. In monogamous species in which pairing appears to be long lasting, males occur with females in the same host, independent of the reproductive condition of the female. Second, the body size of paired shrimps was poorly correlated and the relationship between host and shrimp body size was weak. If males and females of P. mexicana were staying within host individuals for long periods of time, a tight correlation between host and shrimp size and between males and females in a pair would have been found. Lastly, sexual dimorphism in terms of cheliped size was evident; males invested considerably more resources to this body structure compared to females. In monogamous species in which pairing appears to be long-term, sexual dimorphism is low or absent given that sexual selection is weak in this mating system. Overall, our data suggests that monogamy in P. mexicana does not last long and that males switch among host individuals in search of receptive females. Manipulative experiments are necessary to understand the conditions favoring short- and long-term monogamy in symbiotic crustaceans. [Copyright &y& Elsevier]

Abstract: We examined intergenerational and epigenetic effects of early handling manipulations on the social behavior of the prairie vole (Microtus ochrogaster), a monogamous rodent. Laboratory-born parents and their newborn pups were assigned to either a MAN0 “zero handling” manipulation (transfer with a cup during weekly cage changes) or a MAN1 “gloved handling” manipulation (transfer with a gloved hand). Previous studies from our laboratory () showed that MAN0 juvenile males that received this manipulation as pups are less alloparental and that MAN0 adult females that received this manipulation as pups display impaired pair-bonding. In the present study, when MAN0 and MAN1 pups reached adulthood, they were mated in three combinations (MAN1 female×MAN1 male; MAN0 female×MAN1 male; MAN1 female and MAN0 male). Once the pairs produced offspring, we examined their parental behavior towards their own pups. The offspring of these pairings (F2 generation) also were tested as juveniles for alloparental behavior. MAN1 females paired with a MAN0 male displayed higher levels of parenting behaviors. In the F2 generation, juvenile offspring with a MAN0 parent were less alloparental than were offspring from other pairs. These results suggest that early experiences can be transmitted intergenerationally. [Copyright &y& Elsevier]

Abstract: The monogamous social behaviors of prairie voles (Microtus ochrogaster) require olfactory inputs, which are processed by the posterodorsal medial amygdala (MeApd) and principal bed nucleus of the stria terminalis (pBST). The male prairie vole MeApd and pBST contain hundreds of cells densely immunoreactive for tyrosine hydroxylase (TH-ir). Female prairie voles have relatively few of these cells, but we previously found that the number of these TH-ir cells is greatly increased in females by exogenous estradiol. We here hypothesized that the number of TH-ir cells in their MeApd and pBST would also increase during the natural hormone surges associated with females'' induced estrus. We found that the number of TH-ir cells in both sites did significantly increase after females cohabitated for two days with an unfamiliar male. However, this increase did not require the presence of ovaries and even tended to occur in the pBST of females cohabitating for two days with unfamiliar females. We then determined if the greater number of TH-ir cells after heterosexual pairing was transient by examining two groups of long-term pairbonded females (primiparous and multiparous), and found these females also had significantly more TH-ir cells in the pBST and/or MeApd compared to unmated controls. Thus, social novelty arising from cohabitation with unfamiliar conspecifics produces a reoccurring increase in the number of TH-ir cells in the female prairie vole extended olfactory amygdala. Ovarian hormones are not necessarily required. This increase in catecholaminergic cells may facilitate acquisition and retention of olfactory memories necessary for social recognition in this species. [Copyright &y& Elsevier]

Abstract: We studied female preferences for familiar and unfamiliar males. The subjects were laboratory-born house mice: (1) non-commensal Mus musculus domesticus from the eastern part of Syria along the Euphrates River; and (2) commensal M. m. musculus from the Czech Republic. Pair-choice preference tests have revealed that oestrous females of both populations sniffed towards unfamiliar males more than familiar males. In the case of females exhibiting postpartum oestrus, this preference was less pronounced and statistically not significant. Thus, our mice clearly exhibited the behavioural pattern known from commensal populations of polygynous and/or promiscuous M. m. domesticus. We found no inverse tendency to seek proximity to the familiar male that has been previously reported from closely related and presumably monogamous aboriginal mouse Mus spicilegus. We conclude that neither commensal M. m. musculus, nor non-commensal M. m. domesticus, are likely to share a monogamous mating system with mound-building mice. [Copyright &y& Elsevier]

Abstract: Male prairie voles (Microtus ochrogaster) are a valuable model in which to study the neurobiology of sociality because, unlike most mammals, they pair bond after mating and display paternal behaviors. Research on the regulation of these social behaviors has highlighted dopamine (DA) neurotransmission in both pair bonding and parenting. We recently described large numbers of dopaminergic cells in the male prairie vole principal nucleus of the bed nucleus of the stria terminalis (pBST) and posterodorsal medial amygdala (MeApd), but such cells were very few in number or absent in the non-monogamous species we examined, including meadow voles. This suggests that DA cells in these sites may be important for sociosexual behaviors in male prairie voles. To gain some insight into the function of these DAergic neurons in male prairie voles, we examined expression of the immediate-early genes (IEGs) Fos and Egr-1 in tyrosine hydroxylase (TH)–immunoreactive (TH-ir) cells of the pBST and MeApd after males interacted or not with one of several social stimuli. We found that IEGs were constitutively expressed in some TH-ir neurons under any social condition, but that IEG expression in these cells decreased after a 3.5-h social isolation. Thirty-minute mating bouts (but not 6- or 24-h bouts) that included ejaculation elicited greater IEG expression in TH-ir cells than did non-ejaculatory mating, interactions with a familiar female sibling, or interactions with pups. Furthermore, Fos expression in TH-ir cells was positively correlated with the display of copulatory, but not parental, behaviors. These effects of mating were not found in other DA-rich sites of the forebrain (including the anteroventral periventricular preoptic area, periventricular anterior hypothalamus, zona incerta, and arcuate nucleus). Thus, activity in DAergic cells of the male prairie vole pBST and MeApd is influenced by their social environment, and may be particularly involved in mating and its consequences, including pair bonding. [Copyright &y& Elsevier]

Abstract: The partner preference test (PPT) is commonly used to examine sexual and social preferences in rodents. The test offers experimental subjects a choice between two stimulus animals, and time spent with each is used to calculate a preference score. In monogamous prairie voles (Microtus ochrogaster), the PPT has been paramount to the study of pair bonding. Although powerful, use of the PPT in voles has depended primarily on human manual scoring. Manual scoring is time-consuming and is susceptible to bias and fatigue, limiting the use of the PPT in high-throughput studies. Here we compared manual scoring (real-time and 16×) and two automated scoring metrics: “social proximity” and “immobile social contact”. We hypothesized that “immobile social contact” would provide data most comparable to manually scored “huddling”, and thus be the most sensitive measure of partner preference in prairie voles. Each automated metric produced data that highly correlated with manual scoring (R >0.90); however, “immobile social contact” more closely reflected manually scored huddling (R =0.99; P <0.001). “Social proximity” and “immobile social contact” were then used to detect group partner preferences in four data sets that varied by cohabitation length and sex. “Immobile social contact” revealed a significant partner preference in each data set; “social proximity” detected partner preferences in only three of the four. Our results demonstrate the utility of automated systems in high-throughput PPTs, and further confirm that automated systems capable of scoring “immobile social contact” yield results indistinguishable from manual scoring. [Copyright &y& Elsevier]

Abstract: The mating systems of internal parasites are inherently difficult to investigate although they have important implications for the evolutionary biology of the species, disease epidemiology, and are important considerations for control measures. Using parentage analyses, three topics concerning the mating biology of Schistosoma mansoni were investigated: the number of mates per adult male and female, variance in reproductive success among individuals, and the potential role for sexual selection on male body size and also mate choice for genetically dissimilar individuals. Results indicated that schistosomes were mostly monogamous, and evidence of only one mate change occurred over a period of 5–6weeks. One male was polygynous and contained two females in its gynecophoral canal although offspring were only detected for one of the females. Even though they were primarily monogamous and the sex ratio near even, reproductive success was highly variable, indicating a potential role for sexual selection. Male body size was positively related to reproductive success, consistent with sexual selection via male–male competition and female choice for large males. However, relatedness of pairs was not associated with their reproductive success. Finally, genetically identical individuals differed significantly in their reproductive output and identical males in their body size, indicating important partner and environmental effects on these traits. [Copyright &y& Elsevier]

Abstract: We present an interesting monogamy equation for -dimensional pure states, by which a quantity is found to characterize the tripartite entanglement with the GHZ type and W type entanglements as a whole. In particular, we, for the first time, reveals that for any quantum state of a pair of qubits, the difference between the two remarkable entanglement measures, concurrence and negativity, characterizes the W type entanglement of tripartite pure states with the two-qubit state as reduced density. [Copyright &y& Elsevier]

One of the fundamental traits of quantum entanglement is the restricted shareability among multipartite quantum systems, namely monogamy of entanglement, while it is well known that monogamy inequalities are always satisfied by entanglement measures with convexity. Here we present a measure of entanglement, logarithmic convex-roof extended negativity (LCREN) satisfying important characteristics of an entanglement measure, and investigate the monogamy relation for logarithmic negativity and LCREN both without convexity. We show exactly that the α th power of logarithmic negativity, and a newly defined good measure of entanglement, LCREN, obey a class of general monogamy inequalities in multiqubit systems, 2 ⊗ 2 ⊗ 3 systems and 2 ⊗ 2 ⊗ 2 n systems for α ≥ 4 ln 2. We provide a class of general polygamy inequalities of multiqubit systems in terms of logarithmic convex-roof extended negativity of assistance (LCRENoA) for 0 ≤ β ≤ 2. Given that the logarithmic negativity and LCREN are not convex, these results are surprising. Using the power of the logarithmic negativity and LCREN, we further establish a class of tight monogamy inequalities of multiqubit systems, 2 ⊗ 2 ⊗ 3 systems and 2 ⊗ 2 ⊗ 2 n systems in terms of the α th power of logarithmic negativity and LCREN for α ≥ 4 ln 2. We also show that the β th power of LCRENoA obeys a class of tight polygamy inequalities of multiqubit systems for 0 ≤ β ≤ 2. • Give a measure of entanglement, logarithmic convex-roof extended negativity (LCREN). • Find that the logarithmic negativity and the LCREN satisfy monogamy of entanglement. • Establish a class of general monogamy inequalities. [ABSTRACT FROM AUTHOR]

Abstract: The formation and maintenance of social bonds in adulthood is an essential component of human health. However studies investigating the underlying neurobiology of such behaviors have been scarce. Microtine rodents offer a unique comparative animal model to explore the neural processes responsible for pair bonding and its associated behaviors. Studies using monogamous prairie voles and other related species have recently offered insight into the neuroanatomical, neurobiological, and neurochemical underpinnings of social attachment. In this review, we will discuss the utility of the microtine rodents in comparative studies by exploring their natural history and social behavior in the laboratory. We will then summarize the data implicating vasopressin, oxytocin, and dopamine in the regulation of pair bonding. Finally, we will discuss the ways in which these neurochemical systems may interact to mediate this complex behavior. [Copyright &y& Elsevier]

Abstract: Stress and anxiety play a role in many psychological processes including social behavior. The present study examines the effects of urocortin II (UCN II) on spontaneous parental behavior in adult prairie voles (Microtus ochrogaster). UCN II was found to increase passive parental behavior in voles while not affecting any stress-related measures. Delineating the mechanism of this change will aid in our understanding of the regulation of parenting. [Copyright &y& Elsevier]

Abstract: The neurobiology of social bonding, despite its relevance to human mental health, has been studied primarily in rodents. In this study we used position emission tomography (PET), registered with structural magnetic resonance imaging (MRI) to investigate central glucose uptake in 17 males of a monogamous primate species, the titi monkey (Callicebus cupreus). Twelve pair-bonded males (including six with a lesion of the prefrontal cortex) and five lone males were scanned. The five lone males were re-scanned 48 h after pairing with a female. Significant differences in glucose uptake were found between males in long-term pair-bonds and lone males in areas including the nucleus accumbens, ventral pallidum, medial preoptic area, medial amygdala, and the supraoptic nucleus of the hypothalamus. In paired before and after comparisons, males showed significant changes following pairing in the right nucleus accumbens and ventral pallidum but not in other areas. Lesioned males showed significantly higher uptake in the posterior cingulate cortex than all other males. These results indicate some basic similarities between rodents and primates in the formation and maintenance of selective social bonds, but emphasize the importance of studying long-term maintenance in addition to short-term formation of social bonds. [Copyright &y& Elsevier]

Abstract: Recent studies have shown that the neural regulation of pair bonding in the monogamous prairie vole (Microtus ochrogaster) is similar to that of drug seeking in more traditional laboratory rodents. Therefore, strong interactions between social behavior and drug reward can be expected. Here, we established the prairie vole as a model for drug studies by demonstrating robust amphetamine-induced conditioned place preferences in this species. For both males and females, the effects of amphetamine were dose-dependent, with females being more sensitive to drug treatment. This study represents the first evidence of drug reward in this species. Future studies will examine the effects of social behavior on drug reward and the underlying neurobiology of such interactions. [Copyright &y& Elsevier]

Abstract: Developmental exposure to oxytocin (OT) or oxytocin antagonists (OTAs) has been shown to cause long-lasting and often sexually dimorphic effects on social behaviors in prairie voles (Microtus ochrogaster). Because regulation of social behavior in monogamous mammals involves central receptors for OT, arginine vasopressin (AVP), and dopamine, we examined the hypothesis that the long-lasting, developmental effects of exposure to neonatal OT or OTA might reflect changes in the expression of receptors for these peptides. On postnatal day 1, prairie voles were injected intraperitoneally with either OT (1 mg/kg), an OTA (0.1 mg/kg), saline vehicle, or were handled only. At approximately 60 days of age, vasopressin V1a receptors, OT receptors (OTR) and dopamine D2 receptor binding were quantified using receptor autoradiography in brain tissue taken from males and females. Significant treatment effects on V1a binding were found in the bed nucleus of the stria terminalis (BNST), cingulate cortex (CgCtx), mediodorsal thalamus (MdThal), medial preoptic area of the hypothalamus (MPOA), and lateral septum (LS). The CgCtx, MPOA, ventral pallidum, and LS also showed significant sex by treatment interactions on V1a binding. No significant treatment or sex differences were observed for D2 receptor binding. No significant treatment difference was observed for OTR receptor binding, and only a marginal sex difference. Changes in the neuropeptide receptor expression, especially the V1a receptor, may help to explain sexually dimorphic changes in behavior that follow comparable neonatal manipulations. [Copyright &y& Elsevier]

Abstract: Reduced levels of estrogen receptor alpha (ERα) in the medial amygdala (MeA) and bed nucleus of stria terminalis (BST) have been hypothesized to play a significant role in the expression of male behaviors associated with monogamy. Therefore, the regulation of ERα could be a critical factor in determining male behavior and the evolution of monogamy. Central expression of ERα immunoreactivity was compared in hybrid offspring from crosses between two phenotypically distinct populations of prairie voles (Microtus ochrogaster). Illinois voles (IL) are socially monogamous and display low levels of ERα, while Kansas voles (KN) display some characteristics associated with polygyny and have higher levels of ERα. In offspring from hybrid crosses, the pattern of ERα expression was dependent upon parentage; the two types of hybrid crosses did not produce the same ERα pattern in the offspring. In the BST and MeA, hybrid males expressed ERα patterns consistent with those of males from their mother’s population, while hybrid females had ERα patterns typical of females belonging to their father’s population. The parental-specific patterns of ERα expression are suggestive of genomic imprinting, therefore, the vole ERα (Esr1) gene was cloned and sequenced, and examined for allele-specific expression. Results from this study indicate that while maternal factors may play a major role the expression of ERα in their male offspring, genomic imprinting is unlikely to be involved, suggesting another mechanism is responsible. [Copyright &y& Elsevier]

Abstract: Human hair and eye color is unusually diverse in northern and eastern Europe. The many alleles involved (at least seven for hair color) and their independent origin over a short span of evolutionary time indicate some kind of selection. Sexual selection is particularly indicated because it is known to favor color traits and color polymorphisms. In addition, hair and eye color is most diverse in what used to be, when first peopled by hunter-gatherers, a unique ecozone of low-latitude continental tundra. This type of environment skews the operational sex ratio (OSR) of hunter-gatherers toward a male shortage in two ways: (1) men have to hunt highly mobile and spatially concentrated herbivores over longer distances, with no alternate food sources in case of failure, the result being more deaths among young men; (2) women have fewer opportunities for food gathering and thus require more male provisioning, the result being less polygyny. These two factors combine to leave more women than men unmated at any one time. Such an OSR imbalance would have increased the pressures of sexual selection on early European women, one possible outcome being an unusual complex of color traits: hair- and eye-color diversity and, possibly, extreme skin depigmentation. [Copyright &y& Elsevier]

Abstract: Comparisons between monogamous and promiscuous vole species have proven useful in examining neurobiological mechanisms underlying social attachment. Reward processing is important for social attachment, and the medial prefrontal cortex (mPFC) exerts a direct influence on reward pathways. Dopamine (DA), oxytocin (OT), and arginine vasopressin (AVP) all have been implicated in the regulation of social attachment in monogamous voles. Therefore, we used radiolabeled ligands to examine dopamine D1- and D2-like, OT, and AVP V1a receptor binding densities in the mPFC of monogamous and promiscuous voles. Species differences were found; monogamous voles had higher densities of D2-like and OT receptor binding and lower densities of D1-like and V1a receptor binding than did promiscuous voles. Sex differences also were found; females had higher densities of OT receptor binding but lower densities of V1a receptor binding than did males in both species. Further, the laminar distribution of receptor binding indicates the possibility of an interaction between DA and OT systems in the mPFC in the regulation of social attachment. Differences in D1- and D2-like receptor binding between species are discussed in terms of how they might modulate cortical activity and subsequent DA release in the nucleus accumbens (NAcc). [Copyright &y& Elsevier]

Abstract: Endocrine-disrupting chemicals (EDCs) are synthetic chemicals that arise from sources such as pesticides and have the ability to mimic or inhibit gonadal steroid hormones. The objective of this research was to examine the effects of EDCs on the behaviors associated with monogamy and the expression of related neuropeptide receptors. Pine voles, a novel experimental mammal, were chosen because they display strong monogamous pair bonding. Female pine voles were orally administered estrogenic diethylstilbestrol (DES) and methoxychlor (MXC) or oil control throughout gestation and lactation of pups. Exposed pups were tested as adults. Preference for the mate and maternal behaviors were assessed. While the ability to form partner preferences was intact, DES-exposed females showed increased aggression toward a stranger, while MXC exposed females showed a strong trend toward spending more time alone. Oxytocin (OT) receptor binding in the brain was assessed for possible effects on this behaviorally important neuropeptide signaling system. The cingulate cortex showed a reduction in OT binding in the MXC group. These findings demonstrate that exposure to EDCs during pre- and neonatal development can alter female adult neural phenotype and behavior related to monogamous behavior traits. [Copyright &y& Elsevier]

Abstract: Induction of partner preferences in monogamous prairie voles (Microtus ochrogaster) was used to examine the possibility that blockade of glucocorticoid receptors may be rewarding in females of this species. We first examined the ability of either a mineralocorticoid receptor antagonist (spironolactone) or a glucocorticoid receptor antagonist (RU-486) to induce partner preferences in females. Peripheral administration of either of the antagonists was capable of inducing partner preferences, although the effective dose for RU-486 was an order of magnitude lower than that for spironolactone. We then examined a potential interaction of glucocorticoid receptor with central dopamine in pair bonding by treating females with i.c.v. dopamine receptor antagonists (haloperidol, SCH23390, or eticlopride) prior to peripheral administration of RU-486. All of the dopamine antagonists were capable of reversing the effects of glucocorticoid receptor blockade on pair bonding. These results establish the ability for acute blockade of glucocorticoid to induce pair bonds in female voles. Further, this effect appears to be mediated via an interaction with central dopamine systems. Together these findings support the possibility that, unlike other model systems, reductions in glucocorticoid receptor activity may enhance reward in female prairie voles. [Copyright &y& Elsevier]

Abstract: Dopamine is known to play a critical role in social attachment in monogamous voles. However, little is known about the neurochemical regulation of central dopamine release during pair bond formation. Here we examine the effects on partner preference formation in male prairie voles of neurochemical manipulations in the ventral tegmental area (VTA), a major source of dopamine to brain regions implicated in pair bonding. Administration of NBQX, an AMPA receptor antagonist, or bicuculline, a GABA receptor antagonist, into the VTA induced partner preferences within 6 h in the absence of mating. We also found that, after unilateral administration of NBQX into the VTA, neuronal activation, as indicated by the expression of the immediate early gene c-fos, was decreased in the nucleus accumbens, prefrontal cortex, and medial amygdala, but was unchanged in the lateral septum and in a control region, the arcuate nucleus. These results confirm a role for the VTA in partner preference formation in monogamous voles and extend the list of neurochemicals important in pair bonding to include glutamate and GABA. [Copyright &y& Elsevier]

Abstract: Reward mechanisms are involved in pair bond formation in monogamous prairie voles. Given the potential role of CART (cocaine- and amphetamine-regulated transcript) in reward, and its possible role as a third neurohypophysial hormone, we examined the brain distribution of CART mRNA and peptide in monogamous prairie voles compared to congener promiscuous meadow voles. Large species differences in CART mRNA distribution were apparent in the nucleus accumbens, bed nucleus of the stria terminalis, hippocampus, and cortex. CART peptide distribution largely mirrored, but did not exactly match, CART mRNA distribution. Dramatic species differences also existed in CART peptide distribution, including the medial preoptic area, nucleus accumbens, central amygdala, lateral septum, and cortex. In contrast, several brain regions were highly conserved between prairie and meadow voles, including many subnuclei examined within the hypothalamus and olfactory tubercle. Taken together, these data suggest a potential role for CART in the regulation of pair bond formation between monogamous mates and suggest potential brain regions involved in its neural circuitry. Our findings also point to novel avenues of investigation regarding the brain mechanisms for the evolution of diverse social organization. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to determine the presence of estrogen receptor alpha (ERα) and the relationship between neurons that express ERα and produce vasopressin (AVP) in the paraventricular nucleus of the hypothalamus (PVN) in new world mice of the genus Peromyscus. Brains were collected from male and female Peromyscus californicus, Peromyscus leucopus, Peromyscus maniculatus, and Peromyscus polionotus, and double labeled for the expression of ERα and AVP immunoreactivity (IR). The number of cells expressing ERα-IR and AVP-IR was determined in the medial and posterior region of the PVN. The results indicate that Peromyscus is the first taxonomic group reported to have ERα widely distributed in the PVN, occurring in both medial and posterior regions of the PVN. While estrogen can regulate the production of AVP, AVP and ERα were rarely colocalized. There was, however, a significant inverse relationship between the number of cells that expressed ERα-IR and the number expressing AVP-IR. There were no sex differences in the expression of ERα-IR or AVP-IR. [Copyright &y& Elsevier]

Pair bonding represents social attachment between mates and is common among monogamous animals. The prairie vole (Microtus ochrogaster) is a monogamous rodent in which mating facilitates pair bond formation. In this review, we first discuss how prairie voles have been used as an excellent model for neurobiological studies of pair bonding. We then primarily focus on male prairie voles to summarize recent findings from neuroanatomical, neurochemical, cellular, molecular, and behavioral studies implicating vasopressin (AVP), oxytocin (OT), and dopamine (DA) in the regulation of pair bonding. Possible interactions among these neurochemicals in the regulation of pair bonding, the brain areas important for pair bond formation, and potential sexually dimorphic mechanisms underlying pair bonding are also discussed. As analogous social bonds are formed by humans, investigation of the neurochemical regulation of pair bond formation in prairie voles may be beneficial for our understanding of the mechanisms associated with normal and abnormal social behaviors in humans. [Copyright &y& Elsevier]