The neurobiology of pair bonding

Neural correlates of MDMA ("Ecstasy")-induced social interaction in rats

The popular drug 3,4 methylenedioxymethamphetamine (MDMA, "Ecstasy", "the Love Drug") produces feelings of love and closeness in humans and induces analogous prosocial and antiaggressive effects in laboratory animals. Here we examined the specific brain regions that may be involved in these prosocial effects. Male Wistar rats were pretreated with a moderate dose of MDMA (5 mg/kg) or vehicle and then either kept alone in a familiar test chamber for 60 min (groups MDMA-ALONE and VEHICLE-ALONE) or allowed to engage in social interaction in the familiar test chamber with an unfamiliar same-sex conspecific for 60 min (groups MDMA-SOCIAL and VEHICLE-SOCIAL). Rats in the MDMA-SOCIAL group showed much greater overall social interaction than rats in the VEHICLE-SOCIAL group, with microanalysis revealing increased general investigation of other rats but decreased anogenital sniffing. Analysis of neural activation across 39 brain regions using Fos immunohistochemistry showed the following results: (1) VEHICLE-SOCIAL and VEHICLE-ALONE groups did not differ in Fos expression, indicating that a social context per se did not affect Fos expression, (2) MDMA-treated groups showed significantly increased Fos expression relative to VEHICLE treated groups in 30 brain regions, (3) the MDMA-SOCIAL group showed augmented Fos expression relative to the MDMA-ALONE group in six brain regions including the caudate-putamen (medial), medial preoptic area, paraventricular thalamic nucleus, central amygdala, ventromedial hypothalamic nucleus, and the medial amygdala (posterodorsal), and (4) the MDMA-SOCIAL group (but not the MDMA-ALONE group) showed augmented Fos expression relative to the VEHICLE groups in the nucleus accumbens, ventral tegmental area and periaqueductal grey. These results indicate that a moderate dose of MDMA given in a social context causes considerably greater brain activation than the same dose given to solitary rats. This activation involves specific neural circuits that are known to regulate affiliative behavior, perhaps by modulating the incentive value of social stimuli. A possible role for the neuropeptide oxytocin in mediating the prosocial effects of MDMA is discussed.

When Sex Primes Love: Subliminal Sexual Priming Motivates Relationship Goal Pursuit

The studies reported here provide, for the first time, experimental evidence to support the claim that sexual interest and arousal are associated with motives to form and maintain a close relationship. In five studies, sex-related representations were cognitively primed, either subliminally or supraliminally, by exposing participants to erotic words or pictures as compared with neutral words or pictures. The effects of “sexual priming” on the tendencies to initiate and maintain a close relationship were assessed using various cognitive–behavioral and self-report measures. Supporting the hypotheses, subliminal but not supraliminal exposure to sexual primes increased (a) willingness to self-disclose, (b) accessibility of intimacy-related thoughts, (c) willingness to sacrifice for one's partner, and (d) preference for using positive conflict-resolution strategies. The article discusses implications of these findings for the role of sex in close relationships and offers a conceptualization of possible relational motives of the sexual behavioral system.

Coregulation, Dysregulation, Self-Regulation: An Integrative Analysis and Empirical Agenda for Understanding Adult Attachment, Separation, Loss, and Recovery

An integrative framework is proposed for understanding how multiple biological and psychological systems are regulated in the context of adult attachment relationships, dysregulated by separation and loss experiences, and, potentially, re-regulated through individual recovery efforts. Evidence is reviewed for a coregulatory model of normative attachment, defined as a pattern of interwoven physiology between romantic partners that results from the conditioning of biological reward systems and the emergence of felt security within adult pair bonds. The loss of coregulation can portend a state of biobehavioral dysregulation, ranging from diffuse psychophysiological arousal and disorganization to a full-blown (and highly organized) stress response. The major task for successful recovery is adopting a self-regulatory strategy that attenuates the dysregulating effects of the attachment disruption. Research evidence is reviewed across multiple levels of analysis, and the article concludes with a series of testable research questions on the interconnected nature of attachment, loss, and recovery processes.

Oxytocin facilitates the induction of long-term potentiation in the accessory olfactory bulb

When female mice are mated, they form a memory to the pheromonal signal of their male partner. Several lines of evidence indicate that the neural changes underlying this memory occur in the accessory olfactory bulb (AOB) at the first stage of the vomeronasal system. The formation of this memory depends on the mating-induced release of noradrenaline in the AOB. In addition to noradrenaline, the neuropeptide oxytocin (OT) is also released within the central nervous system during mating. Because OT has been implicated in social memory and its receptors are expressed in the AOB, we hypothesized that OT might promote the strength of synaptic transmission from mitral to granule cells in the AOB. To test this hypothesis, we analyzed the lateral olfactory tract-evoked field potential that represents the granule cell response to mitral cell activation and its plasticity in parasagittal slices of the AOB. Of the 10-, 20-, 50-, and 100-Hz stimulations tested, the 100-Hz stimulation was optimal for inducing long-term potentiation (LTP). OT paired with 100-Hz stimulation that only produced short-term potentiation enhanced LTP induction in a dose-dependent manner. OT-paired LTP was blocked by both the selective OT antagonist desGly-NH(2),d(CH(2))(5)[Tyr(Me)(2),Thr(4)]-ornithine vasotocin and the N-methyl-d-aspartate (NMDA) receptor antagonist dl-2-amino-5-phosphonovaleric acid. These results indicate that OT can function as a gate to modulate the establishment of NMDA receptor-dependent LTP at the mitral-to-granule cell synapse in the AOB.

The utility of behavioral models and modules in molecular analyses of social behavior

It is extremely difficult to trace the causal pathway relating gene products or molecular pathways to the expression of behavior. This is especially true for social behavior, which being dependent on interactions and communication between individuals is even further removed from molecular-level events. In this review, we discuss how behavioral models can aid molecular analyses of social behavior. Various models of behavior exist, each of which suggest strategies to dissect complex behavior into simpler behavioral 'modules.' The resulting modules are easier to relate to neural processes and thus suggest hypotheses for neural and molecular function. Here we discuss how three different models of behavior have facilitated understanding the molecular bases of aspects of social behavior. We discuss the response threshold model and two different approaches to modeling motivation, the state space model and models of reinforcement and reward processing. The examples we have chosen illustrate how models can generate testable hypotheses for neural and molecular function and also how molecular analyses probe the validity of a model of behavior. We do not champion one model over another; rather, our examples illustrate how modeling and molecular analyses can be synergistic in exploring the molecular bases of social behavior.

Bidirectional cannabinoid modulation of social behavior in adolescent rats

RATIONALE

Marijuana use in adolescents is a highly social activity, and interacting endocannabinoid and opioid systems may modulate social reward. However, cannabinoid exposure has been reported to reduce social behavior.

OBJECTIVES

The aim of this study was to elucidate the mechanisms underlying the paradoxical relationship between cannabinoid exposure and sociability.

MATERIALS AND METHODS

We investigated the effect of cannabinoid agonists with a different mechanism of action on social play behavior in adolescent rats. In addition, we examined whether endocannabinoid neurotransmission interacts with opioid and dopaminergic neurotransmission in the modulation of social play behavior.

RESULTS

The direct CB1 cannabinoid receptor agonist WIN55,212-2 reduced social play. However, the indirect cannabinoid agonist URB597, which inhibits the hydrolysis of the endocannabinoid anandamide, enhanced social play. This effect of URB597 depended upon stimulation of opioid and dopamine receptors. The well-known stimulatory effect of morphine on social play was attenuated by the CB1 cannabinoid receptor antagonist SR141716A, but independent of dopamine receptor stimulation. Combined treatment with ineffective doses of URB597 and morphine increased social play.

CONCLUSIONS

Cannabinoid neurotransmission can both enhance and inhibit social interaction in adolescent rats depending on how the endocannabinoid system is stimulated. Activation of cannabinoid receptors throughout the brain, which occurs during cannabis use, inhibits sociability. In contrast, on-demand release of endocannabinoids facilitates social interaction, which is magnified by indirect cannabinoid agonists through an interaction with opioid and dopaminergic neurotransmission. These results shed light on the paradoxical relationship between cannabis exposure and sociability and suggest that endocannabinoid degradation inhibitors hold promise for the treatment of social dysfunctions.

Female influences on pair formation, reproduction and male stress responses in a monogamous cavy (Galea monasteriensis)

We examined the possible existence of, and female contributions to, pair bonds, as well as the relation of social preference to mating selectivity, in a recently identified wild guinea pig, the Muenster yellow-toothed cavy (Galea monasteriensis). In Experiment 1, females housed for approximately 20 days in an apparatus in which they could choose to approach and interact with unfamiliar males typically exhibited a robust preference for one of two available males. DNA fingerprinting revealed a strong association between female choice and paternity. Experiment 2 examined the influence of the removal and return of the female on male plasma cortisol levels and behavior in established breeding pairs. A 2-h period of separation in the home enclosure elevated male cortisol levels. Return of the female to the home enclosure reduced male cortisol levels 2 h later, whereas continued separation did not. Reunion in either the home or novel enclosure increased socio-positive and courtship/sexual behavior, as well as time spent in proximity of the partner. Together, these results provide evidence for a substantial female influence on pair bond formation and maintenance in G. monasteriensis and further support for the existence of social and sexual monogamy in this species.

Alcohol preference in mice lacking the Avpr1a vasopressin receptor

[Arg(8)]-vasopressin (Avp), a nonapeptide hormone, is known to regulate blood pressure, water balance, and a variety of behaviors such as anxiety, aggression, and bonding. Although some evidence that Avp modifies ethanol consumption and some of the effects of ethanol on behavior have been reported, the role of Avp in alcohol consumption and preference is poorly understood. The Avp1a receptor (Avpr1a) is ubiquitously expressed in the central nervous system. To determine the role of Avp signaling on the behavioral effects of alcohol, we examined voluntary ethanol consumption in mice with targeted disruptions of the Avpr1a knockout (Avpr1a KO) gene. Avpr1a KO mice displayed both increased ethanol consumption and preference compared with wild-type (WT) mice. Enhanced ethanol consumption was dramatically and reversibly reduced by treatment with N-methyl-D-aspartic acid antagonists. Basal glutamate release was elevated around the striatum in Avpr1a KO mice. Elevation of extracellular glutamate was also produced in WT mice by local application of an Avpr1a antagonist though a dialysis probe, and this elevation was quickly reversed by stopping the perfusion. These results suggest that Avp can inhibit the release of glutamate from the presynaptic terminal via the Avp1a receptor and that elevation of glutamate levels owing to loss of the inhibitory effect via Avp-Avpr1a signaling may play an important role in the preference for ethanol.

Overview of cellular electrophysiological actions of vasopressin

The nonapeptide vasopressin acts both as a hormone and as a neurotransmitter/neuromodulator. As a hormone, its target organs include kidney, blood vessels, liver, platelets and anterior pituitary. As a neurotransmitter/neuromodulator, vasopressin plays a role in autonomic functions, such as cardiovascular regulation and temperature regulation and is involved in complex behavioral and cognitive functions, such as sexual behavior, pair-bond formation and social recognition. At the neuronal level, vasopressin acts by enhancing membrane excitability and by modulating synaptic transmission. The present review will focus on the electrophysiological effects of vasopressin at the cellular level. A large proportion of the experiments summarized here have been performed in in vitro systems, especially in brain and spinal cord slices of the rat. Vasopressin exerts a powerful excitatory action on motoneurons of young rats and mice. It acts by generating a cationic inward current and/or by reducing a potassium conductance. In addition, vasopressin enhances the inhibitory synaptic input to motoneurons. By virtue of these actions, vasopressin may regulate the functioning of neuronal networks involved in motor control. In the amygdala, vasopressin can directly excite a subpopulation of neurons, whereas oxytocin, a related neuropeptide, can indirectly inhibit these same neurons. In the lateral septum, vasopressin exerts a similar dual action: it excites directly a neuronal subpopulation, but causes indirect inhibition of virtually all lateral septal neurons. The actions of vasopressin in the amygdala and lateral septum may represent at least part of the neuronal substrate by which vasopressin influences fear and anxiety-related behavior and social recognition, respectively. Central vasopressin can modulate cardiovascular parameters by causing excitation of spinal sympathetic preganglionic neurons, by increasing the inhibitory input to cardiac parasympathetic neurons in the nucleus ambiguus, by depressing the excitatory input to parabrachial neurons, or by inhibiting glutamate release at solitary tract axon terminals. By acting in or near the hypothalamic supraoptic nucleus, vasopressin can influence magnocellular neuron activity, suggesting that the peptide may exert some control on its own release at neurohypophyseal axon terminals. The central actions of vasopressin are mainly mediated by receptors of the V(1A) type, although recent studies have also reported the presence of vasopressin V(1B) receptors in the brain. Major unsolved problems are: (i) what is the transduction pathway activated following stimulation of central vasopressin V(1A) receptors? (ii) What is the precise nature of the cation channels and/or potassium channels operated by vasopressin? (iii) Does vasopressin, by virtue of its second messenger(s), interfere with other neurotransmitter/neuromodulator systems? In recent years, information concerning the mechanism of action of vasopressin at the neuronal level and its possible role and function at the whole-animal level has been accumulating. Translation of peptide actions at the cellular level into autonomic, behavioral and cognitive effects requires an intermediate level of integration, i.e. the level of neuronal circuitry. Here, detailed information is lacking. Further progress will probably require the introduction of new techniques, such as targeted in vivo whole-cell recording, large-scale recordings from neuronal ensembles or in vivo imaging in small animals.

Variation in neural V1aR predicts sexual fidelity and space use among male prairie voles in semi-natural settings

Although prairie voles (Microtus ochrogaster) are socially monogamous, males vary in both sexual and spatial fidelity. Most males form pairbonds, cohabit with one female, and defend territories. Wandering males, in contrast, have expansive home ranges that overlap many males and females. In the laboratory, pairing is regulated by arginine vasopressin and its predominant CNS receptor, vasopressin 1a receptor (V1aR). We investigated individual differences in forebrain V1aR expression of male prairie voles in mixed-sex seminatural enclosures. Individual differences in V1aR were compared with space use measured by radio telemetry and paternity determined with microsatellite markers. Animals engaging in extra-pair fertilizations (EPFs) as either wanderers or paired residents overlapped significantly more in same- and opposite-sex home ranges. Surprisingly, neither social fidelity measured by space use nor sexual fidelity measured by paternity was associated with V1aR expression in the ventral pallidum (VPall) or lateral septum, areas causally related to pairbond formation. In contrast, V1aR expression in the posterior cingulate/retrosplenial cortex (PCing) and laterodorsal thalamus (LDThal), areas implicated in spatial memory, strongly covaried with space use and paternity. Animals engaging in EPFs either as wanderers or paired residents exhibited low levels of LDThal and PCing V1aR expression. Individual differences in brain and behavior parallel differences between prairie voles and promiscuous congeners. The concordance among space use, paternity, and V1aR in spatial circuits suggests a common link between the mechanisms of spatial behaviors and success at EPF. The combined data demonstrate how organismal biology can inform our understanding of individual and species differences in behavioral mechanisms.

Opposing regulation of pair bond formation by cAMP signaling within the nucleus accumbens shell

The formation of monogamous pair bonds, by prairie voles, is facilitated by activation of dopamine (DA) D2-like, but not D1-like, receptors within the nucleus accumbens (NAcc) shell. Because DA exerts opposing regulation of cAMP production depending on the subtype of receptor activated, we tested the hypothesis that DA regulation of pair bond formation is mediated via the cAMP signaling cascade. Consistent with activation of D2-like receptors, decreasing cAMP signaling, by blocking cAMP binding sites on protein kinase A (PKA), facilitated partner preference formation. Conversely, increasing cAMP signaling, by preventing the activation of inhibitory G-proteins, activating stimulatory G-proteins, or stimulating PKA prevented the formation of mating-induced partner preferences. These manipulations were effective in the shell, but not the core, of the NAcc. Together, these data demonstrate opposing regulation over pair bond formation by cAMP signaling within the NAcc shell.

Social bonds and posttraumatic stress disorder

Retrospective and prospective studies consistently show that individuals exposed to human-generated traumatic events carry a higher risk of developing Posttraumatic Stress Disorder (PTSD) than those exposed to other kinds of events. These studies also consistently identify perceptions of social support both before and after a traumatic event as an important factor in the determining vulnerability to the development of PTSD. We review the literature on interpersonal traumas, social support and risk for PTSD and integrate findings with recent advances in developmental psychopathology, attachment theory and social neuroscience. We propose and gather evidence for what we term the social ecology of PTSD, a conceptual framework for understanding how both PTSD risk and recovery are highly dependent on social phenomena. We explore clinical implications of this conceptual framework.

Diminished plasma oxytocin in schizophrenic patients with neuroendocrine dysfunction and emotional deficits

Polydipsic hyponatremic schizophrenic patients (PHS) exhibit enhanced plasma arginine vasopressin (pAVP) and hypothalamic pituitary adrenal (HPA) axis responses to stress that appear attributable to anterior hippocampal dysfunction. Neuroanatomic and electrophysiologic studies indicate oxytocin activity in PHS patients should also be affected. Furthermore, oxytocin normally diminishes HPA responses to stress and facilitates cognitive and behavioral functions impaired in schizophrenia, suggesting that diminished oxytocin activity could contribute to this subsets' neuropsychiatric disorder. In the present study, we measured plasma oxytocin levels at intervals before and after stress induction in six polydipsic hyponatremic (PHS), four polydipsic normonatremic (PNS), five nonpolydipsic normonatremic schizophrenic (NNS) patients and seven healthy controls. Most of these subjects also completed studies measuring their medial temporal lobe volumes, their hippocampal-mediated HPA feedback and their ability to discriminate different facial emotions (an oxytocin-sensitive measure which is markedly impaired in schizophrenia). Results demonstrated that 1) plasma oxytocin levels were lower (p=.006) in hyponatremic patients relative to the other three groups, whose levels were similar and did not change. Oxytocin levels across all subjects were 2) inversely correlated with anterior hippocampal (p=.004) (but not posterior hippocampal or amygdala volumes), and 3) directly correlated with the integrity of hippocampal-mediated HPA feedback (p=.039). Finally, 4) oxytocin levels predicted schizophrenic patients' ability to correctly identify facial emotions (p=.004). These preliminary data provide further evidence that neuroendocrine dysfunction in PHS reflects anterior hippocampal pathology and contributes to a characteristic neuropsychiatric syndrome.

Oxytocin attenuates amygdala responses to emotional faces regardless of valence

BACKGROUND

Oxytocin is known to reduce anxiety and stress in social interactions as well as to modulate approach behavior. Recent studies suggest that the amygdala might be the primary neuronal basis for these effects.

METHODS

In a functional magnetic resonance imaging study using a double-blind, placebo-controlled within-subject design, we measured neural responses to fearful, angry, and happy facial expressions after intranasal application of 24 IU oxytocin compared with placebo.

RESULTS

Oxytocin reduced right-sided amygdala responses to all three face categories even when the emotional content of the presented face was not evaluated explicitly. Exploratory whole brain analysis revealed modulatory effects in prefrontal and temporal areas as well as in the brainstem.

CONCLUSIONS

Results suggest a modulatory role of oxytocin on amygdala responses to facial expressions irrespective of their valence. Reduction of amygdala activity to positive and negative stimuli might reflect reduced uncertainty about the predictive value of a social stimulus and thereby facilitates social approach behavior.

Vasopressin: behavioral roles of an "original" neuropeptide

Vasopressin (Avp) is mainly synthesized in the magnocellular cells of the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) whose axons project to the posterior pituitary. Avp is then released into the blood stream upon appropriate stimulation (e.g., hemorrhage or dehydration) to act at the kidneys and blood vessels. The brain also contains several populations of smaller, parvocellular neurons whose projections remain within the brain. These populations are located within the PVN, bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and suprachiasmatic nucleus (SCN). Since the 1950s, research examining the roles of Avp in the brain and periphery has intensified. The development of specific agonists and antagonists for Avp receptors has allowed for a better elucidation of its contributions to physiology and behavior. Anatomical, pharmacological and transgenic, including "knockout," animal studies have implicated Avp in the regulation of various social behaviors across species. Avp plays a prominent role in the regulation of aggression, generally of facilitating or promoting it. Affiliation and certain aspects of pair-bonding are also influenced by Avp. Memory, one of the first brain functions of Avp that was investigated, has been implicated especially strongly in social recognition. The roles of Avp in stress, anxiety, and depressive states are areas of active exploration. In this review, we concentrate on the scientific progress that has been made in understanding the role of Avp in regulating these and other behaviors across species. We also discuss the implications for human behavior.

Topography in the preoptic region: differential regulation of appetitive and consummatory male sexual behaviors

Several studies have suggested dissociations between neural circuits underlying the expression of appetitive (e.g., courtship behavior) and consummatory components (i.e., copulatory behavior) of vertebrate male sexual behavior. The medial preoptic area (mPOA) clearly controls the expression of male copulation but, according to a number of experiments, is not necessarily implicated in the expression of appetitive sexual behavior. In rats for example, lesions to the mPOA eliminate male-typical copulatory behavior but have more subtle or no obvious effects on measures of sexual motivation. Rats with such lesions still pursue and attempt to mount females. They also acquire and perform learned instrumental responses to gain access to females. However, recent lesions studies and measures of the expression of the immediate early gene c-fos demonstrate that, in quail, sub-regions of the mPOA, in particular of its sexually dimorphic component the medial preoptic nucleus, can be specifically linked with either the expression of appetitive or consummatory sexual behavior. In particular more rostral regions can be linked to appetitive components while more caudal regions are involved in consummatory behavior. This functional sub-region variation is associated with neurochemical and hodological specializations (i.e., differences in chemical phenotype of the cells or in their connectivity), especially those related to the actions of androgens in relation to the activation of male sexual behavior, that are also present in rodents and other species. It could thus reflect general principles about POA organization and function in the vertebrate brain.

Psychobiologische Mechanismen sozialer Unterstützung

Zusammenfassung. Epidemiologische Studien können eindrucksvoll nachweisen, dass Personen, die in stabile soziale Netzwerke eingebunden sind, zufriedener, gesünder und auch länger leben als sozial isolierte Personen. Einerseits wird vermutet, dass dieser gesundheitsfördernde Effekt sozialer Unterstützung durch Verhaltensänderungen vermittelt wird, welche auf nahestehende Personen zurückführbar sind. Auf der anderen Seite wird ein direkter protektiver Effekt sozialer Unterstützung auf die körperliche Stressreaktivität angenommen, der unterschiedliche salutogenetische Wirkungen haben könnte. Die möglichen vermittelnden biologischen Mechanismen dieses Effekts werden zunehmend in Labor- und Feldstudien untersucht. In diesem Artikel geben wir einen Überblick über die Ergebnisse psychobiologischer Untersuchungen zu den Einflüssen sozialer Unterstützung auf der Ebene des Herz-Kreislauf-Systems, des endokrinen Systems und des Immunsystems. Abschließend gehen wir auf erste Studien ein, in denen die zentralnervösen Mechanismen sozialer Unterstützung experimentell untersucht wurden, und fassen die Ergebnisse in einem Modell zusammen.

Female-Directed Aggression Predicts Paternal Behavior, but Female Prairie Voles Prefer Affiliative Males to Paternal Males

In the socially monogamous prairie vole, Microtus ochrogaster, male affiliation and parental care are influenced by the neuropeptide arginine vasopressin and expression of its receptor V1aR. If parental care and adult affiliation can be considered a behavioral syndrome, females might use male affiliative behavior as a cue to choose a good father. We investigated three questions: (1) do females prefer affiliative males; (2) do males that are affiliative with females demonstrate paternal behavior with pups; and (3) is male V1aR expression related to male behavior or female preference? We evaluated paternal behavior of individual males, then offered sexually receptive females a choice between paternal and non-paternal males and measured the proportion of time each male spent engaging in affiliative behavior with the choosing female. Females showed a preference for more affiliative males, but affiliation was not predictive of paternal care. Thus females did not discriminate between paternal and non-paternal males. Perhaps surprisingly, paternal behavior was correlated with the relative amount of aggression males directed toward females. Finally, females did not discriminate between males with high or low V1aR expression and V1aR expression did not predict male affiliative behavior or parental care. These data suggest that male affiliative behavior, but not paternal care, is associated with female mate choice.

Evolution in the Social Brain

The evolution of unusually large brains in some groups of animals, notably primates, has long been a puzzle. Although early explanations tended to emphasize the brain's role in sensory or technical competence (foraging skills, innovations, and way-finding), the balance of evidence now clearly favors the suggestion that it was the computational demands of living in large, complex societies that selected for large brains. However, recent analyses suggest that it may have been the particular demands of the more intense forms of pairbonding that was the critical factor that triggered this evolutionary development. This may explain why primate sociality seems to be so different from that found in most other birds and mammals: Primate sociality is based on bonded relationships of a kind that are found only in pairbonds in other taxa.

Peripherally administered non-peptide oxytocin antagonist, L368,899, accumulates in limbic brain areas: a new pharmacological tool for the study of social motivation in non-human primates

Central administration of oxytocin (OT) antagonists inhibits maternal and sexual behavior in non-primates, providing the strongest experimental evidence that endogenous OT facilitates these behaviors. While there have been a few reports that ICV administration of OT increases social behaviors in monkeys, no studies to date have assessed the effects of OT antagonists. Therefore, we studied in rhesus monkeys whether L368,899, a non-peptide antagonist produced by Merck that selectively blocks the human uterine OT receptor, penetrates the CNS after peripheral administration and alters female maternal and sexual behavior. In two studies in four male monkeys, L368,899 was injected iv (1 mg/kg) after which (1) CSF samples were collected at intervals over 4 h and (2) brains were collected at 60 min. Assay of samples confirmed that iv-administered L368,899 entered CSF and accumulated in the hypothalamus, septum, orbitofrontal cortex, amygdala and hippocampus, but not other areas. An adult female monkey was tested for interest in either an infant or sexual behavior, receiving a different iv treatment prior to each test (1 or 3 mg/kg of L368,899 or saline). OT antagonist treatment reduced or eliminated interest in the infant and sexual behavior. These results, although preliminary, are the first to directly implicate endogenous OT in activation of primate maternal interest and sexual behavior. While it remains to be empirically demonstrated that peripherally administered L368,899 blocks central OT receptors, our behavioral findings suggest that this non-peptide antagonist may facilitate testing OT involvement in a variety of social and other behaviors in primates.

Neuronal activation by stimuli that predict sexual reward in female rats

Conditioned stimuli (CSs) associated with paced copulation induce a conditioned partner preference for males bearing the CS. Here we examined the activation of Fos immunoreactivity (Fos-IR) following exposure to a CS previously paired with either paced or nonpaced copulation. Ovariectomized, hormone-primed rats received 10 sequential conditioning trials at 4-day intervals. In experiment 1, females in the odor-paired group learned to associate an almond odor on a male with paced copulation and an unscented male with nonpaced copulation. In the odor-unpaired group, females received the opposite association. In experiment 2, females associated two different strains of male, Long-Evans or Wistar, with paced or nonpaced copulation, respectively. A preference test indicated that females in both experiments developed a conditioned preference for the pacing-related males, as indicated by significantly more solicitations toward the male and a preference to copulate with the pacing-related male. Subsequently, females were exposed to the CS (odor or strain) alone for 1 h prior to kill and preparation of their brains for immunocytochemistry. In both experiments, the CS associated with paced copulation produced significantly more Fos-IR in the piriform cortex, medial preoptic area, and ventral tegmental area, relative to the same odor or strain cues associated with nonpaced copulation. These findings provide evidence that the state associated with paced copulation can be conditioned to environmental stimuli such as neutral odors or strain cues, which earn an incentive value via classical conditioning. The significance of the brain areas activated is discussed with regard to their role in sexual and other motivated behaviors.

Role of the midbrain dopaminergic system in modulation of vocal brain activation by social context

In a well-studied model of social behaviour, male zebra finches sing directed song to court females and undirected song, used possibly for practice or advertisement. Although the two song types are similar, the level of neural activity and expression of the immediate early gene egr-1 are higher during undirected than during directed singing in the lateral part of the basal ganglia song nucleus AreaX (LAreaX) and its efferent pallial song nuclei lateral magnocellular nucleus of the anterior nidopallium (LMAN) and the robust nucleus of the arcopallium (RA). As social interactions are dependent on brain motivation systems, here we test the hypothesis that the midbrain ventral tegmental area-substantia nigra pars compacta (VTA-SNc) complex, which provides a strong dopaminergic input to LAreaX, is a source of this modulation. Using egr-1 expression, we show that GABAergic interneurons in VTA-SNc are more active during directed courtship singing than during undirected singing. We also found that unilateral removal of VTA-SNc input reduced singing-dependent gene expression in ipsilateral LAreaX during both social contexts but it did not eliminate social context differences in LAreaX. In contrast, such lesions reduced and eliminated the social context differences in efferent nuclei LMAN and RA, respectively. These results suggest that VTA-SNc is not solely responsible for the social context gene regulation in LAreaX, but that VTA-SNc input to LAreaX enhances the singing-regulated gene expression in this nucleus and, either through LAreaX or through direct projections to LMAN and RA, VTA-SNc is necessary for context-dependent gene regulation in these efferent nuclei.

Does maternal oxytocin protect the fetal brain?

By contrast to its inhibitory actions in adults, gamma-aminobutyric acid (GABA) is excitatory in the developing brain. The high intracellular chloride concentration [Cl(-)](i) in immature neurons causes a positive shift of the GABA(A) reversal potential so that opening of the GABA(A) channels results in depolarization due to chloride efflux. Because [Cl(-)](i) decreases during development, GABA becomes progressively inhibitory. A recent study has shown that a reduction in [Cl(-)](i) induced by endogenous oxytocin triggers a transient but profound switch of GABA actions from excitatory to inhibitory in the hippocampus of the rat fetus shortly before delivery and that this protects the fetal brain from hypoxic or hypoglycemic insult during delivery. The authors hypothesize that the oxytocin is derived from the maternal circulation, representing a novel form of communication between the brain of the mother and her offspring.

Vasopressin 1a receptor knockout mice have a subtle olfactory deficit but normal aggression

Two receptors for vasopressin (Avp) are expressed in the brain, the Avp 1a receptor (Avpr1a) and the Avp 1b receptor (Avpr1b). To investigate the role of Avpr1a in behaviors in mice more extensively, we generated a line of mice lacking a functional Avpr1a (knockout, Avpr1a(-/-)). We first performed a baseline phenotypic screen of the Avpr1a knockouts followed by a more detailed analysis of their circadian rhythms and olfactory function. When free-running in constant darkness, the Avpr1a(-/-) mice have a longer circadian tau than the wild types. There are also subtle olfactory deficits in Avpr1a(-/-) mice as measured in an olfactory habituation/dishabituation test and in the discrimination of female urine from male urine using an operant testing paradigm. An extensive body of research has shown that manipulation of the Avpr1a alters behavior, including aggression and social recognition. Therefore, we expected profound behavioral deficits in mice lacking the Avpr1a gene. Contrary to our expectations, social aggression, anxiety-like behavior and social recognition are unaffected in this line of Avpr1a knockout mice. These data suggest either that the Avpr1a is not as critical as we thought for social behavior in mice or, more likely, that the neural circuitry underlying aggression and other social behaviors compensates for the life-long loss of the Avpr1a. However, the olfactory deficits observed in the Avpr1a(-/-) mice suggest that Avp and Avpr1a drugs may affect behavior, in part, by modulation of chemosensory systems.

Anterior hypothalamic neural activation and neurochemical associations with aggression in pair-bonded male prairie voles

Male prairie voles (Microtus ochrogaster) display mating-induced pair bonding indicated by social affiliation with their female partners and aggression toward unfamiliar conspecifics. In the present study, we characterized their aggression associated with pair bonding and examined the related neuronal activation and neurochemical architecture. Males that were pair-bonded for 2 weeks displayed intense levels of aggression toward a female or male conspecific stranger but maintained a high level of social affiliation with their familiar female partners. These social interactions induced increases in neural activation, indicated by increased density of Fos-immunoreactive staining (Fos-ir) in several brain regions including the bed nucleus of the stria terminalis (BNST), medial preoptic area (MPOA), paraventricular nucleus (PVN), anterior cortical (AcA), and medial nuclei (MeA) of the amygdala. In the anterior hypothalamus (AH), increased density of Fos-ir staining was found specifically to be associated with aggression toward unfamiliar female or male strangers. In addition, higher densities of AH cells that were stained for tyrosine hydroxylase (TH) or vasopressin (AVP) were also labeled with Fos-ir in these males displaying aggression toward a conspecific stranger compared with males displaying social affiliation toward their female partner. Together, our results indicate that dopamine and vasopressin in the AH may be involved in the regulation of enduring aggression associated with pair bonding in male prairie voles.

Opposite effects of maternal separation on intermale and maternal aggression in C57BL/6 mice: link to hypothalamic vasopressin and oxytocin immunoreactivity

Early life stress, in particular child abuse and neglect, is an acknowledged risk factor for the development of pathological anxiety and aggression. In rodents, 3-h daily maternal separation (MS) during the first 2 weeks of life is an established animal model of early life stress and has repeatedly been shown to increase anxiety and stress responsiveness in adulthood. However, preclinical studies on the effects of postnatal stress on adult aggression are limited. The present study investigated whether MS affects intermale aggression and/or maternal aggression in C57BL/6 mice. In both adult male and virgin female mice, MS elevated anxiety-related behavior as tested on the elevated plus-maze, in the open field and during novel object exploration. The latency to attack an unknown male intruder, as assessed with the resident-intruder test, was significantly longer in MS male mice compared with control male mice. In contrast, the latency to attack a novel male intruder was significantly shorter in MS females compared with control females on days 3 and 5 of lactation. These opposite effects of MS can be explained by the fact that intermale and maternal aggression are two different forms of aggression, and hence, might be modulated by different neurobiological pathways. Indeed, in the paraventricular nucleus of the hypothalamus, MS was found to selectively increase vasopressin immunoreactivity in males, whereas MS selectively decreased oxytocin immunoreactivity in lactating females. In conclusion, MS has long-lasting and differential effects on adult intermale and maternal aggression in C57BL/6 mice. Alterations in hypothalamic vasopressin and oxytocin immunoreactivity may, in part, underlie the opposite effects of MS on intermale and maternal aggression. The MS paradigm represents a promising animal model to reveal underlying mechanisms of aggressive behavioral dysfunctions associated with early life stress.

Effects of different kinds of couple interaction on cortisol and heart rate responses to stress in women

In animal studies, positive social interaction and physical contact play a preeminent role in the control of behavioral and neuroendocrine responses to stress. The aim of this study was to determine whether specific kinds of couple interaction reduce hypothalamic-pituitary-adrenal (HPA) and autonomic responses to psychosocial stress in women. Sixty-seven women, aged 20-37 years, who had been married or cohabiting with a male partner for at least 12 months at the time of the study, were exposed to a standardized psychosocial laboratory stressor (Trier Social Stress Test). Participants were randomly assigned to three study groups differing in the type of a 10-min period of social interaction with their partner prior to stress: n=25 with no partner interaction, n=22 with verbal social support, and n=20 with physical contact (standardized neck and shoulder massage). Salivary free cortisol levels, plasma levels of oxytocin, heart rate, and psychological responses to stress were compared among the three study groups. Women with positive physical partner contact before stress exhibited significantly lower cortisol and heart rate responses to stress but no different plasma oxytocin levels compared to women who received social support or no social interaction. Verbal social support alone was not associated with reduced stress responsiveness. Our results are in line with previous human studies indicating reduced responsiveness to verbal social support by a spouse in women. More importantly, these findings imply a direct protective effect of touch on stress-related neurobiological systems as a possible underlying mechanism of health beneficial effects of positive couple interaction.

Social approach behaviors in oxytocin knockout mice: comparison of two independent lines tested in different laboratory environments

Oxytocin mediates social affiliation behaviors and social memory in rodents. It has been suggested that disruptions in oxytocin contribute to the deficits in reciprocal social interactions that characterize autism. The present experiments employed a new social approach task for mice which is designed to detect low levels of sociability, representing the first diagnostic criterion for autism. Two lines of oxytocin knockout mice were tested, the National Institute of Mental Health line in Bethesda, and the Baylor/Emory line at the University of North Carolina in Chapel Hill. Similar methods were used for each line to evaluate tendencies to spend time with a stranger mouse versus with an inanimate novel object with no social valence. Adult C57BL/6J males were tested identically, as controls to confirm the robustness of the methods used in the social task. Comprehensive phenotyping of general health, neurological reflexes, olfactory and other sensory abilities, and motor functions was employed to assess both lines. No genotype differences were detected in any of the control measures for either line. Normal sociability, measured as time spent with a novel stranger mouse as compared to time spent with a novel object, was seen in both the NIMH and the Baylor/Emory lines of oxytocin null mutants, heterozygotes, and wild-type littermate controls. Normal preference for social novelty, measured as time spent with a second novel stranger as compared to time spent with a more familiar mouse, was seen in both the NIMH and the Baylor/Emory lines of oxytocin null mutants, heterozygotes, and wild-type littermate controls, with minor exceptions. Similar behavioral results from two independent targeted gene mutations, generated with different targeting vectors, bred on different genetic backgrounds, and tested in different laboratory environments, corroborates the negative findings on sociability in oxytocin mutant mice. Intact tendencies to spend time with another mouse versus with a novel object, in both lines of oxytocin knockouts, supports an interpretation that oxytocin plays a highly specific role in social memory, but is not essential for general spontaneous social approach in mice.

Social experience organizes parallel networks in sensory and limbic forebrain

Successful social behavior can directly influence an individual's reproductive success. Therefore, many organisms readily modify social behavior based on past experience. The neural changes induced by social experience, however, remain to be fully elucidated. We hypothesize that social modulation of neural systems not only occurs at the level of individual nuclei, but also of functional networks, and their relationships with behavior. We used the green anole lizard (Anolis carolinensis), which displays stereotyped, visually triggered social behaviors particularly suitable for comparisons of multiple functional networks in a social context, to test whether repeated aggressive interactions modify behavior and metabolic activity in limbic-hypothalamic and sensory forebrain regions, assessed by quantitative cytochrome oxidase (a slowly accumulating endogenous metabolic marker) histochemistry. We found that aggressive interactions potentiate aggressive behavior, induce changes in activities of individual nuclei, and organize context-specific functional neural networks. Surprisingly, this experiential effect is not only present in a limbic-hypothalamic network, but also extends to a sensory forebrain network directly relevant to the behavioral expression. Our results suggest that social experience modulates organisms' social behavior via modifying sensory and limbic neural systems in parallel both at the levels of individual regions and networks, potentially biasing perceptual as well as limbic processing.

Sexual behavior of domesticated ruminants

Domesticated ruminants have lived in close association with humans for thousands of years and knowledge of the behavior of these organisms has contributed to their successful domestication, as well as to the management of animals in captivity, both extensive and intensive. Here we describe the reproductive behavioral endocrinology of cattle, goats and sheep. These relatively large and tame animals provide opportunities to conduct a wide range of behavioral studies from short-term to longitudinal or developmental in nature. Highlighted is some of the work from our laboratory describing the social, environmental and endocrine factors that influence the expression of sexual behavior in male and female goats.

Male and female brain evolution is subject to contrasting selection pressures in primates

The claim that differences in brain size across primate species has mainly been driven by the demands of sociality (the "social brain" hypothesis) is now widely accepted. Some of the evidence to support this comes from the fact that species that live in large social groups have larger brains, and in particular larger neocortices. Lindenfors and colleagues (BMC Biology 5:20) add significantly to our appreciation of this process by showing that there are striking differences between the two sexes in the social mechanisms and brain units involved. Female sociality (which is more affiliative) is related most closely to neocortex volume, but male sociality (which is more competitive and combative) is more closely related to subcortical units (notably those associated with emotional responses). Thus different brain units have responded to different selection pressures.

From affiliative behaviors to romantic feelings: A role of nanopeptides

Love is one of the most desired experiences. The quest for understanding human bonds, especially love, was traditionally a domain of the humanities. Recent developments in biological sciences yield new insights into the mechanisms underlying the formation and maintenance of human relationships. Animal models of reproductive behaviors, mother-infant attachment and pair bonding complemented by human studies reveal neuroendocrine foundations of prosocial behaviors and emotions. Amongst various identified neurotransmitters and modulators, which control affiliative behaviors, the particular role of nanopeptides has been indicated. New studies suggest that these chemicals are not only involved in regulating bonding processes in animals but also contribute to generating positive social attitudes and feelings in humans.

Regulating the Social Brain: A New Role for CD38

Centrally released oxytocin regulates maternal behavior, social memory, and social bonding. A recent paper by Jin et al. published in Nature demonstrates that the transmembrane receptor CD38 plays a critical role in regulating social behaviors by regulating the release of OT from hypothalamic neurons.

The adaptive value of sociality in mammalian groups

According to behavioural ecology theory, sociality evolves when the net benefits of close association with conspecifics exceed the costs. The nature and relative magnitude of the benefits and costs of sociality are expected to vary across species and habitats. When sociality is favoured, animals may form groups that range from small pair-bonded units to huge aggregations. The size and composition of social groups have diverse effects on morphology and behaviour, ranging from the extent of sexual dimorphism to brain size, and the structure of social relationships. This general argument implies that sociality has fitness consequences for individuals. However, for most mammalian species, especially long-lived animals like primates, there are sizable gaps in the chain of evidence that links sociality and social bonds to fitness outcomes. These gaps reflect the difficulty of quantifying the cumulative effects of behavioural interactions on fitness and the lack of information about the nature of social relationships among individuals in most taxa. Here, I review what is known about the reproductive consequences of sociality for mammals.

Patterning of frontal cortex subdivisions by Fgf17

The frontal cortex (FC) is the seat of higher cognition. The genetic mechanisms that control formation of the functionally distinct subdivisions of the FC are unknown. Using a set of gene expression markers that distinguish subdivisions of the newborn mouse FC, we show that loss of Fgf17 selectively reduces the size of the dorsal FC whereas ventral/orbital FC appears normal. These changes are complemented by a rostral shift of sensory cortical areas. Thus, Fgf17 functions similar to Fgf8 in patterning the overall neocortical map but has a more selective role in regulating the properties of the dorsal but not ventral FC.

CRF receptors in the nucleus accumbens modulate partner preference in prairie voles

Recent evidence suggests a role for corticotropin-releasing factor (CRF) in the regulation of pair bonding in prairie voles. We have previously shown that monogamous and non-monogamous vole species have dramatically different distributions of CRF receptor type 1 (CRF(1)) and CRF receptor type 2 (CRF(2)) in the brain and that CRF(1) and CRF(2) receptor densities in the nucleus accumbens (NAcc) are correlated with social organization. Monogamous prairie and pine voles have significantly lower levels of CRF receptor type 1 (CRF(1)), and significantly higher levels of type 2 (CRF(2)) binding, in NAcc than non-monogamous meadow and montane voles. Here, we report that microinjections of CRF directly into the NAcc accelerate partner preference formation in male prairie voles. Control injections of CSF into NAcc, and CRF into caudate-putamen, did not facilitate partner preference. Likewise, CRF injections into NAcc of non-monogamous meadow voles also did not facilitate partner preference. In prairie voles, this CRF facilitation effect was blocked by co-injection of either CRF(1) or CRF(2) receptor antagonists into NAcc. Immunocytochemical staining for CRF and Urocortin-1 (Ucn-1), two endogenous ligands for CRF(1) and CRF(2) receptors in the brain, revealed that CRF, but not Ucn-1, immunoreactive fibers were present in NAcc. This supports the hypothesis that local CRF release into NAcc could activate CRF(1) or CRF(2) receptors in the region. Taken together, our results reveal a novel role for accumbal CRF systems in social behavior.

Oxytocin improves "mind-reading" in humans

BACKGROUND

The ability to "read the mind" of other individuals, that is, to infer their mental state by interpreting subtle social cues, is indispensable in human social interaction. The neuropeptide oxytocin plays a central role in social approach behavior in nonhuman mammals.

METHODS

In a double-blind, placebo-controlled, within-subject design, 30 healthy male volunteers were tested for their ability to infer the affective mental state of others using the Reading the Mind in the Eyes Test (RMET) after intranasal administration of 24 IU oxytocin.

RESULTS

Oxytocin improved performance on the RMET compared with placebo. This effect was pronounced for difficult compared with easy items.

CONCLUSIONS

Our data suggest that oxytocin improves the ability to infer the mental state of others from social cues of the eye region. Oxytocin might play a role in the pathogenesis of autism spectrum disorder, which is characterized by severe social impairment.

Amphetamine reward in the monogamous prairie vole

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.

On switches and knobs, microsatellites and monogamy

Comparative studies in voles have suggested that a polymorphic microsatellite upstream of the Avpr1a locus contributes to the evolution of monogamy. A recent study challenged this hypothesis by reporting that there is no relationship between microsatellite structure and monogamy in 21 vole species. Although the study demonstrates that the microsatellite is not a universal genetic switch that determines mating strategy, the findings do not preclude a substantial role for Avpr1a in regulating social behaviors associated with monogamy.

Non-invasive measurement of small peptides in the common marmoset (Callithrix jacchus): a radiolabeled clearance study and endogenous excretion under varying social conditions

A non-invasive assay for measurement of oxytocin (OT) and vasopressin (AVP) in primates would enable researchers to study the relationship between the endocrine system and behavior without disturbing potentially endangered animals in their natural habitats. In order to test whether or not OT specifically would be measurable in the urine of a primate, 10 microCi of tritium-labeled OT were injected into the peripheral blood supply of four adult male common marmosets (Callithrix jacchus), with continuous urinary collection over 48 h. When urine was processed by HPLC separation and beta counting for radioactive clearance, the label was present in all samples in the fraction where OT elutes. Large amounts of OT were also seen in a fraction other than that containing the OT standard, indicating that OT is measurable but that it also undergoes substantial metabolic breakdown. In a second experiment, we isolated six common marmosets for 48 h and then exposed them to social contact to evaluate the effect of changing social stimuli on endogenous urinary measurement of both OT and AVP. Both were measured after HPLC separation to isolate the intact molecule and also to control for cross-reactivity with metabolites in subsequent RIA. Cortisol was also measured to objectively evaluate the stress response. A priori assumptions were that urinary OT and AVP would be lower during a period of isolation and higher during periods of social contact. These assumptions were met, leading us to conclude that peripheral OT and AVP are measurable via urinary assay and that such an assay is a valid means of evaluating social condition in this species.

Neuroendocrine mechanisms of stress and social interaction: implications for mental disorders

PURPOSE OF REVIEW

The purpose of the present review is to consider further evidence for the role of neuroendocrine mechanisms in mental disorders by focusing on recent trends and advances in the field of psychoneuroendocrinology.

RECENT FINDINGS

Recent studies confirm the importance of the hypothalamic-pituitary-adrenal axis for the development and course of mental disorders. Notably, the neuropeptide oxytocin has been shown to reduce the responsiveness of the hypothalamic-pituitary-adrenal axis to social stress and to improve social approach behavior. A better understanding of the neuroendocrine mechanisms of action underlying normal behavior has recently been translated to studies investigating novel therapeutic approaches using hormone administration.

SUMMARY

Neuroendocrine systems relevant to behavior clearly demonstrate their impact for the field of psychiatry. Further neuroendocrine research provides insight into the origins of mental disorders both from an etiological perspective and an interventional perspective.

Lending a hand: social regulation of the neural response to threat

Social contact promotes enhanced health and well-being, likely as a function of the social regulation of emotional responding in the face of various life stressors. For this functional magnetic resonance imaging (fMRI) study, 16 married women were subjected to the threat of electric shock while holding their husband's hand, the hand of an anonymous male experimenter, or no hand at all. Results indicated a pervasive attenuation of activation in the neural systems supporting emotional and behavioral threat responses when the women held their husband's hand. A more limited attenuation of activation in these systems occurred when they held the hand of a stranger. Most strikingly, the effects of spousal hand-holding on neural threat responses varied as a function of marital quality, with higher marital quality predicting less threat-related neural activation in the right anterior insula, superior frontal gyrus, and hypothalamus during spousal, but not stranger, hand-holding.

Distribution of vasopressin in the brain of the eusocial naked mole-rat

Naked mole-rats are eusocial rodents that live in large subterranean colonies in which one queen breeds with one to three males. All other animals are nonbreeding subordinates. The external features of male and female subordinates, including their genitalia, are remarkably monomorphic, as is their behavior. Because vasopressin (VP) is associated with social behaviors and sex differences in other species, its distribution in naked mole-rats was of interest. We used immunohistochemistry to examine VP in the brains of subordinate and breeding naked mole-rats of both sexes. As in other mammals, VP-immunoreactive (-ir) somata were found in the paraventricular (PVN) and supraoptic nuclei (SON) and VP-ir projections from these nuclei ran through the internal and external zone of the median eminence. However, naked mole-rats had very few VP-ir cells in the bed nucleus of the stria terminalis (BST) and none in the suprachiasmatic nucleus (SCN); the extensive network of fine-caliber VP-ir fibers usually seen in projection sites of the BST and SCN were also absent. Equally unexpected was the abundance of large-caliber VP-ir fibers in the dorsomedial septum. VP immunoreactivity was generally similar in all groups, with the exception of VP-ir cell number in the dorsomedial hypothalamus (DMH). Breeders had a population of labeled cells in the DMH that was absent, or nearly absent, in subordinates. Future studies on the function of VP in these areas are needed to determine how the atypical distribution of VP immunoreactivity relates to eusociality and the unusual physiology of naked mole-rats.

CD38 is critical for social behaviour by regulating oxytocin secretion

CD38, a transmembrane glycoprotein with ADP-ribosyl cyclase activity, catalyses the formation of Ca2+ signalling molecules, but its role in the neuroendocrine system is unknown. Here we show that adult CD38 knockout (CD38-/-) female and male mice show marked defects in maternal nurturing and social behaviour, respectively, with higher locomotor activity. Consistently, the plasma level of oxytocin (OT), but not vasopressin, was strongly decreased in CD38-/- mice. Replacement of OT by subcutaneous injection or lentiviral-vector-mediated delivery of human CD38 in the hypothalamus rescued social memory and maternal care in CD38-/- mice. Depolarization-induced OT secretion and Ca2+ elevation in oxytocinergic neurohypophysial axon terminals were disrupted in CD38-/- mice; this was mimicked by CD38 metabolite antagonists in CD38+/+ mice. These results reveal that CD38 has a key role in neuropeptide release, thereby critically regulating maternal and social behaviours, and may be an element in neurodevelopmental disorders.

Oxytocin Involvement in SSRI-Induced Delayed Ejaculation: A Review of Animal Studies

INTRODUCTION

Selective serotonin reuptake inhibitors (SSRIs) differ in the severity of induced ejaculation delay. Various studies indicate that oxytocin is involved in sexual behavior.

AIM

To review and evaluate the involvement of oxytocin in SSRI-induced ejaculation delay.

MAIN OUTCOME MEASURES

Oxytocine release, 5-hydroxytryptamine (5-HT) neurotransmission, and desensitization of 5-HT(1A) receptors.

METHODS

A review and critical analysis of animal studies investigating the interaction of serotonergic and oxytocinergic neurotransmission in relation to the ejaculation process.

RESULTS

Although acute treatment with the SSRIs fluoxetine and paroxetine immediately causes increased serotonin levels, delayed ejaculation does not occur. The increased serotonin levels induce oxytocin release via activation of 5-HT(1A) receptors, and this might compensate for the inhibitory actions of serotonin on sexual behavior. Chronic treatment with fluoxetine and paroxetine desensitizes 5-HT(1A) receptors on oxytocin neurons, and that might in part determine the onset of delayed ejaculation. Desensitization of 5-HT(1A) receptors is less strong following chronic treatment with the SSRIs fluvoxamine or citalopram, which may attenuate the degree of delayed ejaculation.

CONCLUSIONS

Preliminary data suggest that the severity of chronic SSRI treatment-induced delayed ejaculation and the differences between the various SSRIs in inducing ejaculation delay is related to gradual desensitization of 5-HT(1A) receptors on oxytocin neurons.