Maternal behavior deficits in nulliparous oxytocin knockout mice

Normal maternal behavior, but increased pup mortality, in conditional oxytocin receptor knockout females

Oxytocin (Oxt) and the Oxt receptor (Oxtr) are implicated in the onset of maternal behavior in a variety of species. Recently, we developed two Oxtr knockout lines: a total body knockout (Oxtr-/-) and a conditional Oxtr knockout (OxtrFB/FB) in which the Oxtr is lacking only in regions of the forebrain, allowing knockout females to potentially nurse and care for their biological offspring. In the current study, we assessed maternal behavior of postpartum OxtrFB/FB females toward their own pups and maternal behavior of virgin Oxtr-/- females toward foster pups and compared knockouts of both lines to wildtype (Oxtr+/+) littermates. We found that both Oxtr-/- and OxtrFB/FB females appear to have largely normal maternal behaviors. However, with first litters, approximately 40% of the OxtrFB/FB knockout dams experienced high pup mortality, compared to fewer than 10% of the Oxtr+/+ dams. We then went on to test whether or not this phenotype occurred in subsequent litters or when the dams were exposed to an environmental disturbance. We found that regardless of the degree of external disturbance, OxtrFB/FB females lost more pups on their first and second litters compared to wildtype females. Possible reasons for higher pup mortality in OxtrFB/FB females are discussed.

Ultrasonic vocalizations in mouse models for speech and socio-cognitive disorders: insights into the evolution of vocal communication

Comparative analyses used to reconstruct the evolution of traits associated with the human language faculty, including its socio-cognitive underpinnings, highlight the importance of evolutionary constraints limiting vocal learning in non-human primates. After a brief overview of this field of research and the neural basis of primate vocalizations, we review studies that have addressed the genetic basis of usage and structure of ultrasonic communication in mice, with a focus on the gene FOXP2 involved in specific language impairments and neuroligin genes (NL-3 and NL-4) involved in autism spectrum disorders. Knockout of FoxP2 leads to reduced vocal behavior and eventually premature death. Introducing the human variant of FoxP2 protein into mice, in contrast, results in shifts in frequency and modulation of pup ultrasonic vocalizations. Knockout of NL-3 and NL-4 in mice diminishes social behavior and vocalizations. Although such studies may provide insights into the molecular and neural basis of social and communicative behavior, the structure of mouse vocalizations is largely innate, limiting the suitability of the mouse model to study human speech, a learned mode of production. Although knockout or replacement of single genes has perceptible effects on behavior, these genes are part of larger networks whose functions remain poorly understood. In humans, for instance, deficiencies in NL-4 can lead to a broad spectrum of disorders, suggesting that further factors (experiential and/or genetic) contribute to the variation in clinical symptoms. The precise nature as well as the interaction of these factors is yet to be determined.

The neurobiology of pair bonding: insights from a socially monogamous rodent

The formation of enduring relationships between adult mates (i.e., pair bonds) is an integral aspect of human social behavior and has been implicated in both physical and psychological health. However, due to the inherent complexity of these bonds and the relative rarity with which they are formed in other mammalian species, we know surprisingly little about their underlying neurobiology. Over the past few decades, the prairie vole (Microtus ochrogaster) has emerged as an animal model of pair bonding. Research in this socially monogamous rodent has provided valuable insight into the neurobiological mechanisms that regulate pair bonding behaviors. Here, we review these studies and discuss the neural regulation of three behaviors inherent to pair bonding: the formation of partner preferences, the subsequent development of selective aggression toward unfamiliar conspecifics, and the bi-parental care of young. We focus on the role of vasopressin, oxytocin, and dopamine in the regulation of these behaviors, but also discuss the involvement of other neuropeptides, neurotransmitters, and hormones. These studies may not only contribute to the understanding of pair bonding in our own species, but may also offer insight into the underlying causes of social deficits noted in several mental health disorders.

The role of oxytocin in mother-infant relations: a systematic review of human studies

BACKGROUND

Oxytocin is associated with the establishment and quality of maternal behavior in animal models. Parallel investigations in humans are now under way. This article reviews the current research examining the role of oxytocin in mother-infant relations, attachment, and bonding in humans.

METHODS

A systematic search was made of three electronic databases and other bibliographic sources for published research studies that examined oxytocin and mother-infant relations in humans, including attachment, maternal behavior, parenting, and mother-infant relations.

RESULTS

Eight studies were identified, all of which were unique in their methodologies, populations studied, and measures used. Seven studies found significant and strong associations between levels or patterns of oxytocin and aspects of mother-infant relations or attachment.

CONCLUSIONS

Oxytocin appears to be of crucial importance for understanding mother-infant relationships. The findings of this review suggest that the pioneering, but preliminary, research undertaken to date is promising and that replication with larger samples is needed. Research that draws on more robust measures of attachment and bonding, as well as improved measures of oxytocin that include both central and peripheral levels, will elucidate the role of oxytocin in human mother-infant relationships. As the production of oxytocin is by no means restricted to mothers, the extension of the oxytocin studies to fathering, as well as to alloparental caregiving, would be an intriguing next step.

Using transgenic mouse models to study oxytocin's role in the facilitation of species propagation

Oxytocin and its receptor are important for a wide range of effects, from social memory to uterine contractions. It is an evolutionarily well-conserved hormone that is particularly important in social and gregarious animals. Research on small mammals has yielded a rich literature on oxytocin's many functions. Recently a new tool has been created that has furthered our understanding of oxytocin's role in behavior: transgenic mice that lack either the ability to synthesize oxytocin or the oxytocin receptor itself. The study of these lines, while still in its infancy, is already bearing fruit and offers the promise of insight into some human disorders characterized by aberrant social behavior.

Oxytocin signal and social behaviour: comparison among adult and infant oxytocin, oxytocin receptor and CD38 gene knockout mice

Oxytocin in the hypothalamus is the biological basis of social recognition, trust, love and bonding. Previously, we showed that CD38, a proliferation marker in leukaemia cells, plays an important role in the hypothalamus in the process of oxytocin release in adult mice. Disruption of Cd38 (Cd38 (-/-)) elicited impairment of maternal behaviour and male social recognition in adult mice, similar to the behaviour observed in Oxt and oxytocin receptor (Oxtr) gene knockout (Oxt (-/-) and Oxtr (-/-), respectively) mice. Locomotor activity induced by separation from the dam was higher and the number of ultrasonic vocalisation calls was lower in Cd38 (-/-) than Cd38( +/+) pups. However, these behavioural changes were much milder than those observed in Oxt (-/-) and Oxtr (-/-) mice, indicating less impairment of social behaviour in Cd38 (-/-) pups. These phenotypes appeared to be caused by the high plasma oxytocin levels during development from the neonatal period to 3-week-old juvenile mice. ADP-ribosyl cyclase activity was markedly lower in the knockout mice from birth, suggesting that weaning for mice is a critical time window of plasma oxytocin differentiation. Breastfeeding was an important exogenous source of plasma oxytocin regulation before weaning as a result of the presence of oxytocin in milk and the dam's mammary glands. The dissimilarity between Cd38 (-/-) infant behaviour and those of Oxt (-/-) or Oxtr (-/-) mice can be explained partly by this exogenous source of oxytocin. These results suggest that secretion of oxytocin into the brain in a CD38-dependent manner may play an important role in the development of social behaviour.

The challenge of translation in social neuroscience: a review of oxytocin, vasopressin, and affiliative behavior

Social neuroscience is rapidly exploring the complex territory between perception and action where recognition, value, and meaning are instantiated. This review follows the trail of research on oxytocin and vasopressin as an exemplar of one path for exploring the "dark matter" of social neuroscience. Studies across vertebrate species suggest that these neuropeptides are important for social cognition, with gender- and steroid-dependent effects. Comparative research in voles yields a model based on interspecies and intraspecies variation of the geography of oxytocin receptors and vasopressin V1a receptors in the forebrain. Highly affiliative species have receptors in brain circuits related to reward or reinforcement. The neuroanatomical distribution of these receptors may be guided by variations in the regulatory regions of their respective genes. This review describes the promises and problems of extrapolating these findings to human social cognition, with specific reference to the social deficits of autism.

Oxytocin and the neural mechanisms regulating social cognition and affiliative behavior

Oxytocin is produced in the hypothalamus and released into the circulation through the neurohypophyseal system. Peripherally released oxytocin facilitates parturition and milk ejection during nursing. Centrally released oxytocin coordinates the onset of maternal nurturing behavior at parturition and plays a role in mother-infant bonding. More recent studies have revealed a more general role for oxytocin in modulating affiliative behavior in both sexes. Oxytocin regulates alloparental care and pair bonding in female monogamous prairie voles. Social recognition in male and female mice is also modulated by oxytocin. In humans, oxytocin increases gaze to the eye region of human faces and enhances interpersonal trust and the ability to infer the emotions of others from facial cues. While the neurohypopheseal oxytocin system has been well characterized, less is known regarding the nature of oxytocin release within the brain. Here we review the role of oxytocin in the regulation of prosocial interactions, and discuss the neuroanatomy of the central oxytocin system.

Oxytocin: the great facilitator of life

Oxytocin (Oxt) is a nonapeptide hormone best known for its role in lactation and parturition. Since 1906 when its uterine-contracting properties were described until 50 years later when its sequence was elucidated, research has focused on its peripheral roles in reproduction. Only over the past several decades have researchers focused on what functions Oxt might have in the brain, the subject of this review. Immunohistochemical studies revealed that magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei are the neurons of origin for the Oxt released from the posterior pituitary. Smaller cells in various parts of the brain, as well as release from magnocellular dendrites, provide the Oxt responsible for modulating various behaviors at its only identified receptor. Although Oxt is implicated in a variety of "non-social" behaviors, such as learning, anxiety, feeding and pain perception, it is Oxt's roles in various social behaviors that have come to the fore recently. Oxt is important for social memory and attachment, sexual and maternal behavior, and aggression. Recent work implicates Oxt in human bonding and trust as well. Human disorders characterized by aberrant social interactions, such as autism and schizophrenia, may also involve Oxt expression. Many, if not most, of Oxt's functions, from social interactions (affiliation, aggression) and sexual behavior to eventual parturition, lactation and maternal behavior, may be viewed as specifically facilitating species propagation.

Evidence of dysregulated peripheral oxytocin release among depressed women

OBJECTIVE

Oxytocin is a hypothalamic neuropeptide that plays a key role in mammalian female reproductive function. Animal research indicates that central oxytocin facilitates adaptive social attachments and modulates stress and anxiety responses. Major depression is prevalent among postpubertal females, and is associated with perturbations in social attachments, dysregulation of the hypothalamic-pituitary-adrenal stress axis, and elevated levels of anxiety. Thus, depressed women may be at risk to display oxytocin dysregulation. The current study was developed to compare patterns of peripheral oxytocin release exhibited by depressed and nondepressed women.

METHODS

Currently depressed (N = 17) and never-depressed (N = 17) women participated in a laboratory protocol designed to stimulate, measure, and compare peripheral oxytocin release in response to two tasks: an affiliation-focused Guided Imagery task and a Speech Stress task. Intermittent blood samples were drawn over the course of two, 1-hour sessions including 20-minute baseline, 10-minute task, and 30-minute recovery periods.

RESULTS

The 10-minute laboratory tasks did not induce identifiable, acute changes in peripheral oxytocin. However, as compared with nondepressed controls, depressed women displayed greater variability in pulsatile oxytocin release over the course of both 1-hour sessions, and greater oxytocin concentrations during the 1-hour affiliation-focused imagery session. Oxytocin concentrations obtained during the imagery session were also associated with greater symptoms of depression, anxiety, and interpersonal dysfunction.

CONCLUSIONS

Depressed women are more likely than controls to display a dysregulated pattern of peripheral oxytocin release. Further research is warranted to elucidate the clinical significance of peripheral oxytocin release in both depressed and nondepressed women.

Locomotor activity, ultrasonic vocalization and oxytocin levels in infant CD38 knockout mice

Oxytocin (OT), a neurohormone involved in reproduction, plays a critical role in social behavior in a wide range of mammalian species from rodents to humans. The role of CD38 in regulating OT secretion for social behavior has been demonstrated in adult mice, but has not been examined in pups or during development. Separation from the dam induces stress in 7-day-old mouse pups. During such isolation, locomotor activity was higher in CD38 knockout (CD38(-/-)) pups than in wild-type (CD38(+/+)) or heterozygous (CD38(+/-)) controls. The number of ultrasonic vocalizations was lower in CD38(-/-) pups than in CD38(+/+) pups. However, the difference between the two genotypes was less severe than that in OT knockout or OT receptor knockout mice. To explain this, we measured plasma OT levels. The level was not lower in CD38(-/-) pups during the period 1-3 weeks after birth, but was significantly reduced after weaning (>3 weeks). ADP-ribosyl cyclase activities in the hypothalamus and pituitary were markedly lower from 1 week after birth in CD38(-/-) mice and were consistently lower thereafter to the adult stage (2 months old). These results showed that the reduced severity of behavioral abnormalities in CD38(-/-) pups was due to partial compensation by the high level of plasma OT.

A conditional knockout mouse line of the oxytocin receptor

Oxytocin plays important roles in reproductive physiology and various behaviors, including maternal behavior and social memory. Its receptor (Oxtr) is present in peripheral tissues and brain, so a conditional knockout (KO, -/-) would be useful to allow elimination of the receptor in specific sites at defined times. We created a line of mice in which loxP sites flank Oxtr coding sequence (floxed) enable Cre recombinase-mediated inactivation of the receptor. We expressed Cre recombinase in these mice either in all tissues (Oxtr(-/-)) or the forebrain (Oxtr(FB/FB)) using the Ca(2+)/calmodulin-dependent protein kinase IIalpha promoter. The latter KO has reduced Oxtr binding beginning 21-28 d postnatally, leading to prominent reductions in the lateral septum, hippocampus, and ventral pallidum. The medial amygdala is spared, and there is significant retention of binding within the olfactory bulb and nucleus and neocortex. We did not observe any deficits in the general health, sensorimotor functions, anxiety-like behaviors, or sucrose intake in either Oxtr(-/-) or Oxtr(FB/FB) mice. Females of both KO types deliver pups, but only the Oxtr(FB/FB) mice are able to eject milk. Oxtr(-/-) males show impaired social memory for familiar females, whereas the Oxtr(FB/FB) males appear to recognize their species but not individuals. Our results confirm the importance of oxytocin in social recognition and demonstrate that spatial and temporal inactivation of the Oxtr will enable finer understanding of the physiological, behavioral, and developmental roles of the receptor.

From ultrasocial to antisocial: a role for oxytocin in the acute reinforcing effects and long-term adverse consequences of drug use?

Addictive drugs can profoundly affect social behaviour both acutely and in the long-term. Effects range from the artificial sociability imbued by various intoxicating agents to the depressed and socially withdrawn state frequently observed in chronic drug users. Understanding such effects is of great potential significance in addiction neurobiology. In this review we focus on the 'social neuropeptide' oxytocin and its possible role in acute and long-term effects of commonly used drugs. Oxytocin regulates social affiliation and social recognition in many species and modulates anxiety, mood and aggression. Recent evidence suggests that popular party drugs such as MDMA and gamma-hydroxybutyrate (GHB) may preferentially activate brain oxytocin systems to produce their characteristic prosocial and prosexual effects. Oxytocin interacts with the mesolimbic dopamine system to facilitate sexual and social behaviour, and this oxytocin-dopamine interaction may also influence the acquisition and expression of drug-seeking behaviour. An increasing body of evidence from animal models suggests that even brief exposure to drugs such as MDMA, cannabinoids, methamphetamine and phencyclidine can cause long lasting deficits in social behaviour. We discuss preliminary evidence that these adverse effects may reflect long-term neuroadaptations in brain oxytocin systems. Laboratory studies and preliminary clinical studies also indicate that raising brain oxytocin levels may ameliorate acute drug withdrawal symptoms. It is concluded that oxytocin may play an important, yet largely unexplored, role in drug addiction. Greater understanding of this role may ultimately lead to novel therapeutics for addiction that can improve mood and facilitate the recovery of persons with drug use disorders.

Brain oxytocin: a key regulator of emotional and social behaviours in both females and males

In addition to various reproductive stimuli, the neuropeptide oxytocin (OXT) is released both from the neurohypophysial terminal into the blood stream and within distinct brain regions in response to stressful or social stimuli. Brain OXT receptor-mediated actions were shown to be significantly involved in the regulation of a variety of behaviours. Here, complementary methodological approaches are discussed which were utilised to reveal, for example, anxiolytic and anti-stress effects of OXT, both in females and in males, effects that were localised within the central amygdala and the hypothalamic paraventricular nucleus. Also, in male rats, activation of the brain OXT system is essential for the regulation of sexual behaviour, and increased OXT system activity during mating is directly linked to an attenuated anxiety-related behaviour. Moreover, in late pregnancy and during lactation, central OXT is involved in the establishment and fine-tuned maintenance of maternal care and maternal aggression. In monogamous prairie voles, brain OXT is important for mating-induced pair bonding, especially in females. Another example of behavioural actions of intracerebral OXT is the promotion of social memory processes and recognition of con-specifics, as revealed in rats, mice, sheep and voles. Experimental evidence suggests that, in humans, brain OXT exerts similar behavioural effects. Thus, the brain OXT system seems to be a potential target for the development of therapeutics to treat anxiety- and depression-related diseases or abnormal social behaviours including autism.

Reduced ultrasonic vocalizations in vasopressin 1b knockout mice

The neuropeptides oxytocin and vasopressin have been implicated in rodent social and affiliative behaviors, including social bonding, parental care, social recognition, social memory, vocalizations, territoriality, and aggression, as well as components of human social behaviors and the etiology of autism. Previous investigations of mice with various manipulations of the oxytocin and vasopressin systems reported unusual levels of ultrasonic vocalizations in social settings. We employed a vasopressin 1b receptor (Avpr1b) knockout mouse to evaluate the role of the vasopressin 1b receptor subtype in the emission of ultrasonic vocalizations in adult and infant mice. Avpr1b null mutant female mice emitted fewer ultrasonic vocalizations, and their vocalizations were generally at lower frequencies, during a resident-intruder test. Avpr1b null mutant pups emitted ultrasonic vocalizations similar to heterozygote and wildtype littermates when separated from the nest on postnatal days 3, 6, 9, and 12. However, maternal potentiation of ultrasonic vocalizations in Avpr1b null and heterozygote mutants was absent, when tested at postnatal day 9. These results indicate that Avpr1b null mutant mice are impaired in the modulation of ultrasonic vocalizations within different social contexts at infant and adult ages.

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.

Hypocretin-1 dose-dependently modulates maternal behaviour in mice

Increases in neuronal activity of hypocretin (HCRT), a peptide involved in arousal, and in HCRT-1 receptor mRNA expression have recently been identified in association with lactation. HCRT is released within brain regions regulating maternal behaviour and it is possible that increased HCRT neurotransmission during lactation supports maternal care. The present study examined for the first time the behavioural effects of HCRT on lactating mice. At intermediate doses, intracerebroventricular (i.c.v.) injections of HCRT-1 (0.06 and 0.1 microg) elevated levels of licking and grooming of pups (but not self-grooming) and number of nursing bouts without affecting other behaviours. At the highest dose, HCRT-1 (0.3 microg, i.c.v) delayed latency to nurse, decreased nursing, increased time off nest, and decreased maternal aggression. Intraperitoneal injections of the HCRT-1 receptor antagonist, SB-334867, exhibited a general trend towards increasing time spent low-arched back nursing (P = 0.053) and decreasing licking and grooming of pups while high-arched back nursing (P = 0.052). This suggests that the endogenous release of HCRT, working independently or dependently with other neuromodulators, may be necessary for full maternal behaviour expression. Possible sites of HCRT action in enhancing and impairing maternal care were identified via examinations of c-Fos immunoreactivity in association with i.c.v. HCRT injections. Together, these finding support the idea of HCRT modulating maternal behaviour, with intermediate levels (0.06 and 0.1 microg) supporting (even augmenting) some behaviours, but with levels that are too high (0.3 microg HCRT, i.c.v.), maternal behaviour and aggression are suppressed.

Oxytocin null mice ingest enhanced amounts of sweet solutions during light and dark cycles and during repeated shaker stress

Central oxytocin (OT) pathways appear to limit consumption of sweet solutions. Male and female C57BL/6 mice that lack the gene for oxytocin (OT KO mice) displayed an initial and sustained enhanced intake of sucrose solution over water compared to wild type (WT) mice when the solutions were presented as a two-bottle choice [Amico JA, Vollmer RR, Cai HM, Miedlar JA, Rinaman R. Enhanced initial and sustained intake of sucrose solution in mice with an oxytocin gene deletion. Am J Physiol: Regul Integr Comp Physiol 2005;289:R1798-806]. In this study we examined the ingestion of a non-nutritive sweetener, 0.2% saccharin in sucrose-experienced OT KO and WT mice given a two-bottle choice between saccharin solution and water available ad libitum for 4 days. Compared to WT mice, OT KO mice consumed significantly greater volumes of saccharin solution during the dark and light photoperiods on the first day and subsequent days of the study. The results were replicated when the experiment was repeated in the same animals. In another experiment, we determined that daily exposure to platform shaker stress did not alter the marked sucrose consumption in OT KO mice. OT KO mice drank significantly more sucrose than WT mice during periods of stress and non-stress. We conclude that the avid consumption of sweetened solutions by OT KO mice is not restricted to a single photoperiod, occurs independent of caloric content of the sweetened solution, and is not altered by exposure to the daily stress of platform shaker. The cumulative results from our studies of sucrose and saccharin ingestion in OT KO and WT male and female mice suggest a special role for sweet taste in the recruitment of OT neurons.