Hypothalamic vasopressin gene expression increases in both males and females postpartum in a biparental rodent

Modulation of the attentional response to baby schema by testosterone in pedohebephilic men and its relation to the nurturing system

Previous fMRI research found increased brain responses in men with pedophilic interest to non-sexual pictures of child and animal faces. This raised the question of whether an aberrant nurturing system could be linked to pedophilia. To further explore this hypothesis, 20 pedohebephilic and 23 teleiophilic men performed a target detection task with adult versus infant human and animal faces, which measured selective attention towards the baby schema by comparing reaction times to infant versus adult targets that were presented amongst distractors of the other category. Since the response to baby schema can be influenced by steroid hormones, saliva samples were additionally collected to determine endogenous testosterone, progesterone, estradiol and cortisol. Contrary to expectations, all men did not react faster to infant than adult faces. Yet, pedohebephilic men were more distracted by infant's faces than teleiophilic men. Pedohebephilic men with higher testosterone were faster in orienting attention to infant targets in the context of adult distractors. This association was not observed in teleiophilic men. Our results support the idea of an overactive nurturing system in pedophilia, which may be influenced by the endogenous testosterone level.

Conserved and differing functions of the endocrine system across different social systems - oxytocin as a case study

A key goal of the field of endocrinology has been to understand the hormonal mechanisms that drive social behavior and influence reactions to others, such as oxytocin. However, it has sometimes been challenging to understand which aspects and influences of hormonal action are conserved and common among mammalian species, and which effects differ based on features of these species, such as social system. This challenge has been exacerbated by a focus on a relatively small number of traditional model species. In this review, we first demonstrate the benefits of using non-traditional models for the study of hormones, with a focus on oxytocin as a case study in adding species with diverse social systems. We then expand our discussion to explore differing effects of oxytocin (and its response to behavior) within a species, with a particular focus on relationship context and social environment among primate species. Finally, we suggest key areas for future exploration of oxytocin's action centrally and peripherally, and how non-traditional models can be an important resource for understanding the breadth of oxytocin's potential effects.

Parental experience is linked with lower vasopressin receptor 1a binding and decreased postpartum androgens in titi monkeys

Parenting induces many neurological and behavioral changes that enable parents to rear offspring. Vasopressin plays an important role in this process via its effects on cognition, affect, and neuroplasticity, and in some cases, via interactions with decreased parental androgens. Thus far, the role of these hormones has been primarily studied in rodents. To address this gap, we explored vasopressin receptors and androgens in titi monkeys, a pair-bonding and biparental primate species. In Studies 1 and 2, we used receptor autoradiography to correlate arginine vasopressin receptor 1a (AVPR1a) binding in the hippocampus (Study 1, n = 10) and the rest of the forebrain (Study 2, n = 23) with parental status, parental experience, parity, infant carrying, and pair affiliation. We found that parents exhibited lower AVPR1a binding than non-parents throughout most brain regions assessed, with especially strong effects in the hippocampus (β = -.61), superior colliculus (β = -.88), lateral septum (β = -.35), and medial preoptic area (β = -.29). The other measures of parental experience also tended to be negatively associated with AVPR1a binding across different brain regions. In Study 3 (n = 44), we compared pre- and postpartum urinary androgen levels in parents and non-parents and found that mothers exhibited a sustained androgen decrease across 3-4 months postpartum (relative to 3 months prepartum; β ranged from -.72 to -.62 for different comparisons). For males, we found that multiparous fathers exhibited decreased androgen levels at 1-2 weeks postpartum (β = -.25) and at 3-4 months postpartum (β = -.40) compared to the prepartum, indicating both immediate and long-term reductions with subsequent paternal experience. Together, the results of this study suggest that decreases in AVPR1a binding and circulating androgens are associated with parental behavior and physiology in titi monkeys.

Therapeutic modulation of JAK-STAT, mTOR, and PPAR-γ signaling in neurological dysfunctions

The cytokine-activated Janus kinase (JAK)-signal transducer and activator of transcription (STAT) cascade is a pleiotropic pathway that involves receptor subunit multimerization. The mammalian target of rapamycin (mTOR) is a ubiquitously expressed serine-threonine kinase that perceives and integrates a variety of intracellular and environmental stimuli to regulate essential activities such as cell development and metabolism. Peroxisome proliferator-activated receptor-gamma (PPARγ) is a prototypical metabolic nuclear receptor involved in neural differentiation and axon polarity. The JAK-STAT, mTOR, and PPARγ signaling pathways serve as a highly conserved signaling hub that coordinates neuronal activity and brain development. Additionally, overactivation of JAK/STAT, mTOR, and inhibition of PPARγ signaling have been linked to various neurocomplications, including neuroinflammation, apoptosis, and oxidative stress. Emerging research suggests that even minor disruptions in these cellular and molecular processes can have significant consequences manifested as neurological and neuropsychiatric diseases. Of interest, target modulators have been proven to alleviate neuronal complications associated with acute and chronic neurological deficits. This research-based review explores the therapeutic role of JAK-STAT, mTOR, and PPARγ signaling modulators in preventing neuronal dysfunctions in preclinical and clinical investigations.

Plasticity in parental behavior and vasopressin: responses to co-parenting, pup age, and an acute stressor are experience-dependent

Introduction

The impact of variation in parental caregiving has lasting implications for the development of offspring. However, the ways in which parents impact each other in the context of caregiving is comparatively less understood, but can account for much of the variation observed in the postnatal environment. Prairie voles (Microtus ochrogaster) demonstrate a range of postnatal social groups, including pups raised by biparental pairs and by their mothers alone. In addition to the challenges of providing parental care, prairie vole parents often experience acute natural stressors (e.g., predation, foraging demands, and thermoregulation) that could alter the way co-parents interact.

Methods

We investigated how variation in the experience of raising offspring impacts parental behavior and neurobiology by administering an acute handling stressor on prairie vole families of single mothers and biparental parents over the course of offspring postnatal development.

Results

Mothers and fathers exhibited robust behavioral plasticity in response to the age of their pups, but in sex-dependent ways. Pup-directed care from mothers did not vary as a function of their partner's presence, but did covary with the number of hypothalamic vasopressin neurons in experience-dependent ways. The relationship between vasopressin neuron numbers and fathers' behaviors was also contingent upon the stress handling manipulation, suggesting that brain-behavior associations exhibit stress-induced plasticity.

Conclusion

These results demonstrate that the behavioral and neuroendocrine profiles of adults are sensitive to distinct and interacting experiences as a parent, and extend our knowledge of the neural mechanisms that may facilitate parental behavioral plasticity.

Support for the parental practice hypothesis: Subadult prairie voles exhibit similar behavioral and neural profiles when alloparenting kin and non-kin

Parental care is critical for offspring survival in altricial species. Although parents are the most common caregivers, other individuals (e.g., older siblings) can also provide alloparental care. Some have argued that animals engage in alloparental behavior to practice providing care for their eventual offspring, whereas others have argued that alloparental behavior enhances indirect fitness. Proximate measures have the potential to test ultimate functions of behavior. A focus on neural expression of oxytocin and vasopressin (two neuropeptides modulating alloparental care) or neural activation following exposure to related and unrelated individuals could reveal whether practice or investment in indirect fitness explains alloparental behavior. This study examined alloparental behaviors and neural responses in prairie voles (Microtus ochrogaster), a species that engages in alloparental behavior. Subadult (independent, yet sexually immature) male prairie voles were exposed to one of four stimuli: same-age sibling, neonatal sibling, unrelated neonate, or inanimate neonate-sized object. We assessed alloparental behaviors and quantified cFos protein expression in oxytocin and vasopressin neuronal populations of the paraventricular nucleus of the hypothalamus and the supraoptic nucleus of the hypothalamus in response to stimulus exposure. We detected no differences in cFos and nonapeptide co-localization among stimulus groups. Subjects performed similar amounts of alloparental care toward related and unrelated neonates, but not other subadults or inanimate objects. Notably, caregiving did not differ based on kin-status. The lack of difference in alloparenting toward related and non-related neonates suggests that alloparental care in prairie voles primarily serves to provide subadults with parental practice.

Parental Behavior in Rodents

Members of the order Rodentia are among the best-studied mammals for understanding the patterns, outcomes, and biological determinants of maternal and paternal caregiving. This research has provided a wealth of information but has historically focused on just a few rodents, mostly members of the two Myomorpha families that easily breed and can be studied within a laboratory setting (including laboratory rats, mice, hamsters, voles, gerbils). It is unclear how well this small collection of animals represents the over 2000 species of extant rodents. This chapter provides an overview of the hormonal and neurobiological systems involved in parental care in rodents, with a purposeful eye on providing information known or could be gleaned about parenting in various less-traditional members of Rodentia. We conclude from this analysis that the few commonly studied rodents are not necessarily even representative of the highly diverse members of Myomorpha, let alone other rodent suborders, and that additional laboratory and field studies of members of this order more broadly would surely provide invaluable information toward revealing a more representative picture of the rich diversity in rodent parenting.

Brain Environment Interactions: Stress, Posttraumatic Stress Disorder, and the Need for a Postmortem Brain Collection

Stress, especially the extreme stress of traumatic events, can alter both neurobiology and behavior. Such extreme environmental situations provide a useful model for understanding environmental influences on human biology and behavior. This paper will review some of the evidence of brain alterations that occur with exposure to environmental stress. This will include recent studies using neuroimaging and will address the need for histological confirmation of imaging study results. We will review the current scientific approaches to understanding brain environment interactions, and then make the case for the collection and study of postmortem brain tissue for the advancement of our understanding of the effects of environment on the brain.Creating a brain tissue collection specifically for the investigation of the effects of extreme environmental stressors fills a gap in the current research; it will provide another of the important pieces to the puzzle that constitutes the scientific investigation of negative effects of environmental exposures. Such a resource will facilitate new discoveries related to the psychiatric illnesses of acute stress disorder and posttraumatic stress disorder, and can enable scientists to correlate structural and functional imaging findings with tissue abnormalities, which is essential to validate the results of recent imaging studies.

Hypothalamus volume in men: Investigating associations with paternal status, self-reported caregiving beliefs, and adult attachment style

Most studies on mammalian caregiving and attachment focused on the mother-child relationship, particularly in humans. Yet, changing societal roles of male caregivers have highlighted the necessity for research with fathers.We examined the volume of the hypothalamus, an important subcortical brain area for caregiving and attachment, in N = 50 fathering (child age 5-6 years) and N = 45 non-fathering men using a novel technique to identify the hypothalamus in 3T MRI. We furthermore employed three self-report measures to assess interindividual differences in adult attachment style across all men and caregiving beliefs in fathers.While we did not observe any significant difference in hypothalamus volume between fathers and non-fathers or associations between hypothalamus volume and self-reported adult attachment style across all men, self-reported caregiving beliefs were positively related to total hypothalamus volume in fathers. A follow-up analysis showed that fathers' self-reported belief that a father's role is important to child development was specifically related to tuberal hypothalamus volume, while self-reported enjoyment of spending time with the child was not associated with sub-regional hypothalamus volume.Together, these findings suggest that interindividual variability in self-reported caregiving beliefs in fathers is related to brain structure, warranting further research.

PATERNAL AND INFANTICIDAL BEHAVIOR IN THE MONGOLIAN GERBIL (Meriones unguiculatus): AN APPROACH TO NEUROENDOCRINE REGULATION

This study aimed to provide evidence on estrogen and androgen pathways regulating the Mongolian gerbil's paternal and infanticidal behaviors (Meriones unguiculatus). We analyzed estrogen receptor alpha (ERα) and androgen receptor (AR) distribution in the medial preoptic area (mPOA), the bed nucleus of stria terminalis (BNST), as well as the anterior hypothalamic nucleus (AHN), the ventromedial hypothalamus nucleus (VMH), and the periaqueductal gray area (PAG) nuclei activated when males interact paternally or aggressively with the pups, respectively. Twenty aggressive males towards the pups and 10 paternal were selected through a screen paternal behavior test. Three groups of 10 males each were formed: paternal males (PAT), males with testosterone (T)-induced paternal behavior (T-PAT), and aggressive males (AGG). Male gerbils could interact with a pup for a few minutes, and their brains were removed and dissected for ERα and AR immunoreactivity (ir). The results showed that in T-PAT and PAT males, the number of ERα-ir and AR-ir cells in the mPOA/BNST was significantly higher than in AGG males. In AGG males, the number of ERα-ir and AR-ir cells in the AHN/VMH/PAG was significantly higher than PAT and T-PAT males. This difference in the presence of ERα and AR in nuclei activated in paternal interactions in the Mongolian gerbil supports the idea that these receptors participate in regulating paternal behavior. Also, these results suggest, for the first time, that they could be involved in the infanticidal behavior in this rodent.

Plasticity of the paternal brain: Effects of fatherhood on neural structure and function

Care of infants is a hallmark of mammals. Whereas parental care by mothers is obligatory for offspring survival in virtually all mammals, fathers provide care for their offspring in only an estimated 5%-10% of genera. In these species, the transition into fatherhood is often accompanied by pronounced changes in males' behavioral responses to young, including a reduction in aggression toward infants and an increase in nurturant behavior. The onset of fatherhood can also be associated with sensory, affective, and cognitive changes. The neuroplasticity that mediates these changes is not well understood; however, fatherhood can alter the production and survival of new neurons; function and structure of existing neurons; morphology of brain structures; and neuroendocrine signaling systems. Although these changes are thought to promote infant care by fathers, very little evidence exists to support this hypothesis; in most cases, neither the mechanisms underlying neuroplasticity in fathers nor its functional significance is known. In this paper, we review the available data on the neuroplasticity that occurs during the transition into fatherhood. We highlight gaps in our knowledge and future directions that will provide key insights into how and why fatherhood alters the structure and functioning of the male brain.

Inotocin, a potential modulator of reproductive behaviours in a biparental beetle, Lethrus apterus

Several members of the highly conserved oxytocin/vasopressin neuropeptide family are involved in the regulation of reproductive and affiliative behaviours in numerous vertebrate and invertebrate species. Here we investigate gene expression patterns of inotocin, the insect ortholog of this peptide family, and its receptor to decipher their possible role in the control of reproductive behaviour in a beetle, Lethrus apterus, with biparental care. In an experiment performed on individuals of a wild population, we found that inotocin is not related to the control of water balance in this species because expression patterns did not change as a response to drought exposure. The expression levels of inotocin and its receptor, however, increased over the reproductive season i.e., when behaviour shifts from pair formation to parental care, suggesting that inotocin might be involved in the regulation of parental care in this insect. No difference was, however, found between sexes; a finding which might indicate that inotocin plays a similar role in both parents.

Vasopressin and parental expressed emotion in the transition to fatherhood

In the last decades, parenting researchers increasingly focused on the role of fathers in child development. However, it is still largely unknown which factors contribute to fathers' beliefs about their child, which may be crucial in the transition to fatherhood. In the current randomized within-subject experiment, the effect of nasal administration of vasopressin (AVP) on both Five Minute Speech Sample-based (FMSS) expressed emotion and emotional content or prosody was explored in 25 prospectivefathers. Moreover, we explored how the transition to fatherhood affected these FMSS-based parameters, using prenatal and early postnatal measurements. Analyses revealed that FMSS-based expressed emotion and emotional content were correlated, but not affected by prenatal AVP administration. However,child's birth was associated with an increase in positivity and a decrease in emotional prosody, suggesting that the child's birth is more influential with regard to paternal thoughts and feelings than prenatal AVP administration.

The neural mechanisms and consequences of paternal caregiving

In recent decades, human sociocultural changes have increased the numbers of fathers that are involved in direct caregiving in Western societies. This trend has led to a resurgence of interest in understanding the mechanisms and effects of paternal care. Across the animal kingdom, paternal caregiving has been found to be a highly malleable phenomenon, presenting with great variability among and within species. The emergence of paternal behaviour in a male animal has been shown to be accompanied by substantial neural plasticity and to be shaped by previous and current caregiving experiences, maternal and infant stimuli and ecological conditions. Recent research has allowed us to gain a better understanding of the neural basis of mammalian paternal care, the genomic and circuit-level mechanisms underlying paternal behaviour and the ways in which the subcortical structures that support maternal caregiving have evolved into a global network of parental care. In addition, the behavioural, neural and molecular consequences of paternal caregiving for offspring are becoming increasingly apparent. Future cross-species research on the effects of absence of the father and the transmission of paternal influences across generations may allow research on the neuroscience of fatherhood to impact society at large in a number of important ways.

Vasopressin Differentially Affects Handgrip Force of Expectant Fathers in Reaction to Own and Unknown Infant Faces

The underlying mechanisms of paternal responses to infant signals are poorly understood. Vasopressin has previously been proposed to affect these responses. Using a double-blind, placebo-controlled, within-subject design (N = 25 expectant fathers), we examined the effect of vasopressin administration on the use of excessive handgrip force during exposure to infant crying versus matched control sounds, while participants saw morphed images representing their own infant versus an unknown infant. We found that, compared to placebo, AVP administration elicited more excessive force while viewing an unknown infant image compared to viewing the image representing one’s own infant, while the reverse was true under placebo. The results are discussed in light of vasopressin’s role in parenting and parental protection among human fathers.

More than just mothers: The neurobiological and neuroendocrine underpinnings of allomaternal caregiving

In a minority of mammalian species, mothers depend on others to help raise their offspring. New research is investigating the neuroendocrine mechanisms supporting this allomaternal behavior. Several hormones have been implicated in allomaternal caregiving; however, the role of specific hormones is variable across species, perhaps because allomothering independently evolved multiple times. Brain regions involved in maternal behavior in non-human animals, such as the medial preoptic area, are also critically involved in allomaternal behavior. Allomaternal experience modulates hormonal systems, neural plasticity, and behavioral reactivity. In humans, fatherhood-induced decreases in testosterone and increases in oxytocin may support sensitive caregiving. Fathers and mothers activate similar neural systems when exposed to child stimuli, and this can be considered a global "parental caregiving" network. Finally, early work on caregiving by non-kin (e.g., foster parents) suggests reliance on similar mechanisms as biologically-related parents. This article is part of the 'Parental Brain and Behavior' Special Issue.

The Monogamy Paradox: What Do Love and Sex Have to Do With It?

Genetic monogamy is rare-at least at the level of a species-and monogamy can exist in the absence of sexual fidelity. Rather than focusing on mating exclusivity, it has become common to use the term "social monogamy" to describe a cluster of social features, including the capacity for selective and lasting social bonds, central to what humans call "love." Socially monogamous mammals often exhibit selective aggression toward strangers and form extended families. These features of social monogamy in mammals are supported by patterns of hormonal function originating in the neurobiology of maternity, including oxytocin, as well as a more primitive vasopressin pathway. Another key feature of social monogamy is reduced sexual dimorphism. Processes associated with sexual differentiation offer clues to the mysteries surrounding the evolution of monogamy. Although there is consistency in the necessary ingredients, it is likely that there is no single recipe for social monogamy. As reviewed here, genes for steroids and peptides and their receptors are variable and are subject to epigenetic regulation across the lifespan permitting individual, gender and species variations and providing substrates for evolution. Reduced sensitivity to gonadal androgens, and a concurrent increased reliance on vasopressin (for selective defense) and oxytocin (for selective affiliation) may have offered pathways to the emergence of social monogamy.

Effects of vasopressin on neural processing of infant crying in expectant fathers

In a randomized, double blind, placebo-controlled, within-subject magnetic resonance imaging study, we examined the effect of 20 IU intranasal vasopressin on the neural processing of infant crying in 25 fathers-to-be. We explored whether familial background modulates vasopressin effects, and whether vasopressin differentially affects cry processing coupled with neutral or emotional contextual information. Participants listened to cries accompanied by neutral ('this is an infant') or emotional ('this infant is sick/bored') contextual information, and neutral control sounds ('this is a saw'). Additionally, participants reported on their childhood experiences of parental love-withdrawal and abuse. Infant crying (vs control sounds) was associated with increased activation in the bilateral auditory cortex and posterior medial cortex. No effects of vasopressin were found in this 'cry network'. Exploratory whole-brain analyses suggested that effects of vasopressin in the anterior cingulate cortex, paracingulate gyrus and supplemental motor area were stronger in fathers who experienced lower (vs higher) levels of love-withdrawal. No interaction was observed for abuse. Vasopressin increased activation in response to cries accompanied by emotional vs neutral contextual information in several brain regions, e.g. the cerebellum, brainstem (midbrain), posterior medial cortex, hippocampus, putamen, and insula. Our results suggest that the experience of love-withdrawal may modulate the vasopressin system, influencing effects of vasopressin administration on cry processing. Results further suggest a role for vasopressin in the processing of cry sounds with emotional contextual information.

Hypothalamic gene expression changes in F1 California mice (Peromyscus californicus) parents developmentally exposed to bisphenol A or ethinyl estradiol

Bisphenol A (BPA) is a pervasive industrial chemical used in many common household items. To examine how early exposure to BPA and ethinyl estradiol (EE, estrogen in birth control pill) might affect biparental care, effects of these chemicals in male and female California mice (Peromyscus californicus), who are monogamous and biparental, were examined. California mice exposed during pre- and peri-natal life to BPA at an environmentally relevant concentration or EE show later disrupted biparental behaviors. The hypothalamus is an important brain region for regulating parental behaviors. Thus, it was hypothesized compromised biparental care might be partially due to hypothalamic gene alterations. To address this question, brains from F1 parenting female and male California mice from controls, BPA- and EE-exposed groups were collected at postnatal day (PND) 2, and RNA was isolated from hypothalamic micropunches. Gene expression was examined in this brain region for genes affected by BPA exposure and attributed to governing parental care in rodents and humans. BPA-exposed California mice showed increased hypothalamic expression of Kiss1, Esr1 and Esr2 relative to AIN control and EE-exposed parents in the case of Esr2. Notably, current studies represent the first report to show that early exposure to BPA can induce longstanding effects on hypothalamic gene expression in parenting male and female rodents. Absence of such hypothalamic gene expression changes in EE-exposed parents indicates early BPA exposure may induce later transcriptomic effects through estrogen receptor-independent pathways. BPA-driven changes in hypothalamic function of California mice might contribute to decreased biparental investment, which could result in F2 multigenerational effects.

Oxytocin Neurons Exhibit Extensive Functional Plasticity Due To Offspring Age in Mothers and Fathers

The needs of offspring change as they develop. Thus, parents should concomitantly change their investment based on the age-related needs of the offspring as they mature. Due to the high costs of parental care, it is optimal for parents to exhibit a shift from intense caregiving of young offspring to promoting independence in older offspring. Yet, the neural mechanisms that underlie shifts in parental behavior are poorly understood, and little is known about how the parental brain responds to offspring of different ages. To elucidate mechanisms that relate to shifts in parental behavior as offspring develop, we examined behavioral and neural responses of male and female prairie voles (Microtus ochrogaster), a biparental rodent, to interactions with offspring at different stages of development (ranging from neonatal to weaning age). Importantly, in biparental species, males and females may adjust their behavior differentially as offspring develop. Because the nonapeptides, vasopressin (VP) and oxytocin (OT), are well known for modulating aspects of parental care, we focused on functional activity of distinct VP and OT cell groups within the maternal and paternal brain in response to separation from, reunion (after a brief period of separation) with, or no separation from offspring of different ages. We found several differences in the neural responses of individual VP and OT cell groups that varied based on the age of pups and sex of the parent. Hypothalamic VP neurons exhibit similar functional responses in both mothers and fathers. However, hypothalamic and amygdalar OT neurons exhibit differential functional responses to being separated from pups based on the sex of the parent. Our results also reveal that the developmental stage of offspring significantly impacts neural function within OT, but not VP, cell groups of both mothers and fathers. These findings provide insight into the functional plastic capabilities of the nonapeptide system, specifically in relation to parental behavior. Identifying neural mechanisms that exhibit functional plasticity can elucidate one way in which animals are able to shift behavior on relatively short timescales in order to exhibit the most context-appropriate and adaptive behaviors.

Neural Regulation of Paternal Behavior in Mammals: Sensory, Neuroendocrine, and Experiential Influences on the Paternal Brain

Across the animal kingdom, parents in many species devote extraordinary effort toward caring for offspring, often risking their lives and exhausting limited resources. Understanding how the brain orchestrates parental care, biasing effort over the many competing demands, is an important topic in social neuroscience. In mammals, maternal care is necessary for offspring survival and is largely mediated by changes in hormones and neuropeptides that fluctuate massively during pregnancy, parturition, and lactation (e.g., progesterone, estradiol, oxytocin, and prolactin). In the relatively small number of mammalian species in which parental care by fathers enhances offspring survival and development, males also undergo endocrine changes concurrent with birth of their offspring, but on a smaller scale than females. Thus, fathers additionally rely on sensory signals from their mates, environment, and/or offspring to orchestrate paternal behavior. Males can engage in a variety of infant-directed behaviors that range from infanticide to avoidance to care; in many species, males can display all three behaviors in their lifetime. The neural plasticity that underlies such stark changes in behavior is not well understood. In this chapter we summarize current data on the neural circuitry that has been proposed to underlie paternal care in mammals, as well as sensory, neuroendocrine, and experiential influences on paternal behavior and on the underlying circuitry. We highlight some of the gaps in our current knowledge of this system and propose future directions that will enable the development of a more comprehensive understanding of the proximate control of parenting by fathers.

Vasopressin and Oxytocin Reduce Food Sharing Behavior in Male, but Not Female Marmosets in Family Groups

Oxytocin (OT) is critical for lactation and maternal care, but OT and the related nonapeptide vasopressin are important for caregiving behaviors in fathers and alloparents as well. This experiment tested the effects of vasopressin and OT on food sharing in marmoset families. We treated caregivers (parents, siblings) with intranasal vasopressin, OT, or saline, and then paired them with the youngest marmoset in the family. Caregivers were given preferred food, and then observed for food sharing and aggressive behavior with young marmosets. OT reduced food sharing from male alloparents to youngest siblings, and fathers that received vasopressin refused to share food with their youngest offspring more often than when treated with OT. Vasopressin increased aggressive vocalizations directed toward potential food recipients in all classes of caregivers. These results indicate that vasopressin and OT do not always enhance prosocial behavior: modulation of food sharing depends on both sex and parental status.

Place preferences associated with pups or cocaine change the expression of D2R, V1aR and OTR in the NAcc and MeA and the levels of plasma AVP, OT, T and E2 in mandarin vole fathers

Drug abuse often has negative impacts on parenting behavior. The dopamine (DA), arginine vasopressin (AVP) and oxytocin (OT) systems are involved in paternal behavior and drug-induced behaviors. Mandarin voles (Microtus mandarinus) are socially monogamous rodents with high levels of paternal behavior. The aims of this study were to examine the protein expression levels of the DA 2-type receptor (D2R), AVP receptor 1A(V1aR) and OT receptor (OTR) in the nucleus accumbens (NAcc) and medial amygdala (MeA) as well as the plasma hormone responses after mandarin vole fathers were conditioned with their pups or cocaine. Our experimental models are based on the conditioned place preference (CPP) paradigm. We observed CPP in response to either pup- or cocaine-associated cues in the mandarin vole fathers. Fathers that were conditioned to either pups or cocaine had a lower expression of D2R and V1aR in the NAcc than did controls. Fathers that were conditioned to pups had higher levels of OTR expression in the MeA and higher plasma levels of AVP, OT, estradiol (E2), and lower plasma levels of testosterone (T) than did controls. Fathers that were conditioned to cocaine exhibited lower levels of plasma AVP and T. These results indicate that the reward effects of pup and cocaine are both mediated by D2R, V1aR and OTR in the NAcc and MeA and that there are subtle differences between the pup and cocaine reward mechanisms that are associated with altered plasma AVP, OT, T and E2.

The spatial-and-ethological population structure, cooperation, and the evolution of sociality in rodents

There are two types of complex social units — aggregations and family groups — in rodent populations, with an essential difference in their social organization. The impact of ecological factors on the evolution of sociality in rodents (the transition from solitary towards family-group lifestyle) is still unclear. The inter-specific comparative analysis based on quantification of social traits related to the spatial-and-ethological population structure and cooperation allows author to propose a new conceptual approach to the assessment of differences between the species under consideration in terms of the evolution of sociality. A new conceptual model of the evolution of sociality in rodents should incorporate ecological conditions and social factors, including cooperation, operating as a complex of selective forces promoting formation of family groups.

Regulatory role of prolactin in paternal behavior in male parents: A narrative review

In all mammalian species, a combination of neuroendocrine and experiential factors contributes to the emergence of remarkable behavioral changes observed in parental behavior. Yet, our understanding of neuroendocrine bases of paternal behavior in humans is still preliminary and more research is needed in this area. In the present review, the authors summarized hormonal bases of paternal behavior in both human and nonhuman mammalian species and focused on studies on the regulatory role of prolactin in occurrence of paternal behavior. All peer-reviewed journal articles published before 2015 for each area discussed (parental brain, hormonal bases of maternal behavior, hormonal bases of paternal behavior and the role of prolactin in regulation of paternal behavior in nonhuman mammalian species, hormonal bases of paternal behavior and the role of prolactin in regulation of paternal behavior in humans) were searched by PubMed, Medline, and Scopus for original research and review articles. Publications between 1973 and 2015 were included. Similar to female parents, elevated prolactin levels in new fathers most probably contribute to child-caring behavior and facilitate behavioral and emotional states attributed to child care. Moreover, elevated parental prolactin levels after childbirth decrease the parents' libidos so that they invest more in parental care than in fertility behavior. According to the available clinical studies, elevation in the amounts of prolactin levels after childbirth in male parents are probably associated with paternal behavior observed in humans.

Neuropeptide Regulation of Social Attachment: The Prairie Vole Model

Social attachments are ubiquitous among humans and integral to human health. Although great efforts have been made to elucidate the neural underpinnings regulating social attachments, we still know relatively little about the neuronal and neurochemical regulation of social attachments. As a laboratory animal research model, the socially monogamous prairie vole (Microtus ochrogaster) displays behaviors paralleling human social attachments and thus has provided unique insights into the neural regulation of social behaviors. Research in prairie voles has particularly highlighted the significance of neuropeptidergic regulation of social behaviors, especially of the roles of oxytocin (OT) and vasopressin (AVP). This article aims to review these findings. We begin by discussing the role of the OT and AVP systems in regulating social behaviors relevant to social attachments, and thereafter restrict our discussion to studies in prairie voles. Specifically, we discuss the role of OT and AVP in adult mate attachments, biparental care, social isolation, and social buffering as informed by studies utilizing the prairie vole model. Not only do these studies offer insight into social attachments in humans, but they also point to dysregulated mechanisms in several mental disorders. We conclude by discussing these implications for human health. © 2017 American Physiological Society. Compr Physiol 7:81-104, 2017.

Oxytocin mediated behavior in invertebrates: An evolutionary perspective

The molecular and functional conservation of oxytocin-related neuropeptides in behavior is striking. In animals separated by at least 600 million years of evolution, from roundworms to humans, oxytocin homologs play critical roles in the modulation of reproductive behavior and other biological functions. Here, we review the roles of oxytocin in invertebrate behavior from an evolutionary perspective. We begin by tracing the evolution of oxytocin through the invertebrate animal lineages, and then describe common themes in invertebrate behaviors that are mediated by oxytocin-related peptides, including reproductive behavior, learning and memory, food arousal, and predator/prey relationships. Finally, we discuss interesting future directions that have recently become experimentally tractable. Studying oxytocin in invertebrates offers precise insights into the activity of neuropeptides on well-defined neural circuits; the principles that emerge may also be represented in the more complex vertebrate brain. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 128-142, 2017.

Evidence for a Neuroendocrinological Foundation of Human Affiliation

Although research on the neurobiological foundation of social affiliation has implicated the neuropeptide oxytocin in processes of maternal bonding in mammals, there is little evidence to support such links in humans. Plasma oxytocin and cortisol of 62 pregnant women were sampled during the first trimester, last trimester, and first postpartum month. Oxytocin was assayed using enzyme immunoassay, and free cortisol was calculated. After the infants were born, their interactions with their mothers were observed, and the mothers were interviewed regarding their infant-related thoughts and behaviors. Oxytocin was stable across time, and oxytocin levels at early pregnancy and the postpartum period were related to a clearly defined set of maternal bonding behaviors, including gaze, vocalizations, positive affect, and affectionate touch; to attachment-related thoughts; and to frequent checking of the infant. Across pregnancy and the postpartum period, oxytocin may play a role in the emergence of behaviors and mental representations typical of bonding in the human mother.

The ties that bond: neurochemistry of attachment in voles

In socially monogamous prairie voles (Microtus ochrogaster), mating induces three primary types of behavior; namely, partner preference, selective aggression toward conspecific strangers, and bi-parental care, making this rodent an ideal model system to study sociality and underlying neurochemical mechanisms associated with monogamous mating strategies. Here, we highlight species differences in neurochemical receptor distributions associated with mating experience leading to the establishment of stable pair-bonds. Specifically, we illustrate the role of nucleus accumbens dopamine in programming the formation and maintenance of monogamous bonds and describe the role of anterior hypothalamic vasopressin in the regulation of selective aggression. We conclude by discussing recent molecular work in voles and emphasize the importance of this rodent for future research in the behavioral neurobiology field.

Fatherhood contributes to increased hippocampal spine density and anxiety regulation in California mice

INTRODUCTION

Parenting alters the hippocampus, an area of the brain that undergoes significant experience-induced plasticity and contributes to emotional regulation. While the relationship between maternal care and hippocampal neuroplasticity has been characterized, the extent to which fatherhood alters the structure and function of the hippocampus is far less understood.

METHODS

Here, we investigated to what extent fatherhood altered anxiety regulation and dendritic morphology of the hippocampus using the highly paternal California mouse (Peromyscus californicus).

RESULTS

Fathers spent significantly more time on the open arms of the elevated plus maze, compared to non-fathers. Total distance traveled in the EPM was not changed by paternal experience, which suggests that the increased time spent on the open arms of the maze indicates decreased anxiety-like behavior. Fatherhood also increased dendritic spine density of granule cells in the dentate gyrus and basal dendrites of pyramidal cells in area CA1 of the hippocampus.

CONCLUSIONS

These findings parallel those observed in maternal rodents, suggesting that the hippocampus of fathers and mothers respond similarly to offspring.

Fathering in rodents: Neurobiological substrates and consequences for offspring

This article is part of a Special Issue "Parental Care". Paternal care, though rare among mammals, is routinely displayed by several species of rodents. Here we review the neuroanatomical and hormonal bases of paternal behavior, as well as the behavioral and neuroendocrine consequences of paternal behavior for offspring. Fathering behavior is subserved by many of the same neural substrates which are also involved in maternal behavior (for example, the medial preoptic area of the hypothalamus). While gonadal hormones such as testosterone, estrogen, and progesterone, as well as hypothalamic neuropeptides such as oxytocin and vasopressin, and the pituitary hormone prolactin, are implicated in the activation of paternal behavior, there are significant gaps in our knowledge of their actions, as well as pronounced differences between species. Removal of the father in biparental species has long-lasting effects on behavior, as well as on these same neuroendocrine systems, in offspring. Finally, individual differences in paternal behavior can have similarly long-lasting, if more subtle, effects on offspring behavior. Future studies should examine similar outcome measures in multiple species, including both biparental species and closely related uniparental species. Careful phylogenetic analyses of the neuroendocrine systems presumably important to male parenting, as well as their patterns of gene expression, will also be important in establishing the next generation of hypotheses regarding the regulation of male parenting behavior.

Comparative analysis of oxytocin receptor density in the nucleus accumbens: an adaptation for female and male alloparental care?

Parental behavior is commonly displayed by progenitors. However, other individuals, genetically related (e.g. siblings, aunts, uncles) or not with the newborns, also display parental behavior (commonly called alloparental, or adoptive behavior). I hypothesize that species that live in family or social groups where other non-reproductive members (males and females) take care of infants, have brain adaptations to promote or facilitate that behavioral response. The present work revises the evidence supporting the hypothesis that high density of oxytocin receptors (OXTR) in the nucleus accumbens (NA) is one of those adaptations. All species known to have high NA OXTR show not only female, but also male alloparental care. Therefore, I predict that high NA OXTR could be present in all species in which juvenile and adult male alloparental behavior have been observed. Strategies to test this and other alternative working hypothesis and its predictions are presented.

Oxytocin: parallel processing in the social brain?

Early studies attempting to disentangle the network complexity of the brain exploited the accessibility of sensory receptive fields to reveal circuits made up of synapses connected both in series and in parallel. More recently, extension of this organisational principle beyond the sensory systems has been made possible by the advent of modern molecular, viral and optogenetic approaches. Here, evidence supporting parallel processing of social behaviours mediated by oxytocin is reviewed. Understanding oxytocinergic signalling from this perspective has significant implications for the design of oxytocin-based therapeutic interventions aimed at disorders such as autism, where disrupted social function is a core clinical feature. Moreover, identification of opportunities for novel technology development will require a better appreciation of the complexity of the circuit-level organisation of the social brain.

Examining the Role of Vasopressin in the Modulation of Parental and Sexual Behaviors

Vasopressin (VP) and VP-like neuropeptides are evolutionarily stable peptides found in all vertebrate species. In non-mammalian vertebrates, vasotocin (VT) plays a role similar to mammalian VP, whereas mesotocin and isotocin are functionally similar to mammalian oxytocin (OT). Here, we review the involvement of VP in brain circuits, synaptic plasticity, evolution, and function, highlighting the role of VP in social behavior. In all studied species, VP is encoded on chromosome 20p13, and in mammals, VP is produced in specific hypothalamic nuclei and released by the posterior pituitary. The role of VP is mediated by the stimulation of the V1a, V1b, and V2 receptors as well as the oxytocinergic and purinergic receptors. VT and VP functions are usually related to osmotic and cardiovascular homeostasis when acting peripherally. However, these neuropeptides are also critically involved in the central modulation of social behavior displays, such as pairing recognition, pair-bonding, social memory, sexual behavior, parental care, and maternal and aggressive behavior. Evidence suggests that these effects are primarily mediated by V1a receptor in specific brain circuits that provide important information for the onset and control of social behaviors in normal and pathological conditions.

Social functions of individual vasopressin-oxytocin cell groups in vertebrates: what do we really know?

Vasopressin-oxytocin (VP-OT) nonapeptides modulate numerous social and stress-related behaviors, yet these peptides are made in multiple nuclei and brain regions (e.g., >20 in some mammals), and VP-OT cells in these areas often exhibit overlapping axonal projections. Furthermore, the magnocellular cell groups release peptide volumetrically from dendrites and soma, which gives rise to paracrine modulation in distal brain areas. Nonapeptide receptors also tend to be promiscuous. Hence, behavioral effects that are mediated by any given receptor type (e.g., the OT receptor) in a target brain region cannot be conclusively attributed to either VP or OT, nor to a specific cell group. We here review what is actually known about the social behavior functions of nonapeptide cell groups, with a focus on aggression, affiliation, bonding, social stress, and parental behavior, and discuss recent studies that demonstrate a diversity of sex-specific contributions of VP-OT cell groups to gregariousness and pair bonding.

Functional significance of hormonal changes in mammalian fathers

In the 5-10% of mammals in which both parents routinely provide infant care, fathers as well as mothers undergo systematic endocrine changes as they transition into parenthood. Although fatherhood-associated changes in such hormones and neuropeptides as prolactin, testosterone, glucocorticoids, vasopressin and oxytocin have been characterised in only a small number of biparental rodents and primates, they appear to be more variable than corresponding changes in mothers, and experimental studies typically have not provided strong or consistent evidence that these endocrine shifts play causal roles in the activation of paternal care. Consequently, their functional significance remains unclear. We propose that endocrine changes in mammalian fathers may enable males to meet the species-specific demands of fatherhood by influencing diverse aspects of their behaviour and physiology, similar to many effects of hormones and neuropeptides in mothers. We review the evidence for such effects, focusing on recent studies investigating whether mammalian fathers in biparental species undergo systematic changes in (i) energetics and body composition; (ii) neural plasticity, cognition and sensory physiology; and (iii) stress responsiveness and emotionality, all of which may be mediated by endocrine changes. The few published studies, based on a small number of rodent and primate species, suggest that hormonal and neuropeptide alterations in mammalian fathers might mediate shifts in paternal energy balance, body composition and neural plasticity, although they do not appear to have major effects on stress responsiveness or emotionality. Further research is needed on a wider variety of biparental mammals, under more naturalistic conditions, to more fully determine the functional significance of hormone and neuropeptide profiles of mammalian fatherhood and to clarify how fatherhood may trade off with (or perhaps enhance) aspects of organismal function in biparental mammals.

Separation anxiety, attachment and inter-personal representations: disentangling the role of oxytocin in the perinatal period

In this paper, we aimed to assess cross-sectionally and longitudinally associations between disturbances in maternal early attachment experiences, symptoms of separation anxiety and depression and oxytocin plasma levels. We examined a mediational model that tested the hypothesis that anxious attachment style arising from the mothers’ early bonding experiences with her own parents was associated with high levels of separation anxiety which, via its impact on depression, was associated with reduced levels of oxytocin in the postnatal period. Data is reported on a structured sample of 127 women recruited during pregnancy from a general hospital antenatal clinic and an initial follow up cohort of 57 women who were re-assessed at 3-months post-partum. We found an association between lower oxytocin level in the post partum period and symptoms of separation anxiety and depression during pregnancy, as well as maternal negative interpersonal representations, upbringing attributes and anxious attachment style. Further meditational analysis revealed that the unique association between anxious attachment and depression is mediated by separation anxiety and that depressed mood mediated the relationship between separation anxiety and oxytocin. In conjunction with evidence from the literature suggesting that lower oxytocin level is associated with bonding difficulties, our findings have significant implications for understanding the biological processes underpinning adverse attachment experiences, negative affect state, and mother-to-infant bonding difficulties.

The role of oxytocin in male and female reproductive behavior

Oxytocin (OT) is a nonapeptide with an impressive variety of physiological functions. Among them, the 'prosocial' effects have been discussed in several recent reviews, but the direct effects on male and female sexual behavior did receive much less attention so far. As our contribution to honor the lifelong interest of Berend Olivier in the control mechanisms of sexual behavior, we decided to explore the role of OT in the present review. In the successive sections, some physiological mechanisms and the 'pair-bonding' effects of OT will be discussed, followed by sections about desire, female appetitive and copulatory behavior, including lordosis and orgasm. At the male side, the effects on erection and ejaculation are reviewed, followed by a section about 'premature ejaculation' and a possible role of OT in its treatment. In addition to OT, serotonin receives some attention as one of the main mechanisms controlling the effects of OT. In the succeeding sections, the importance of OT for 'the fruits of labor' is discussed, as it plays an important role in both maternal and paternal behavior. Finally, we pay attention to an intriguing brain area, the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), apparently functioning in both sexual and aggressive behavior, which are at first view completely opposite behavioral systems.

Cocaine withdrawal influences paternal behavior and associated central expression of vasopressin, oxytocin and tyrosine hydroxylase in mandarin voles

Although the disruptive effects of cocaine on the maternal care are well known, little is known about paternal care in the context of cocaine abuse. Vasopressin (AVP), oxytocin (OT) and dopamine (DA) have been found to regulate paternal behavior and are also involved in cocaine abuse. Mandarin voles (Microtus mandarinus) are socially monogamous and display high levels of paternal care. Here, we investigated whether paternal behavior and associated central levels of AVP, OT and DA were altered following 24 h of withdrawal from 4 day administration of 20 mg/kg/day cocaine. Our data shows that vole fathers did not experience altered levels of locomotion during an open field test. However, compared to controls, cocaine attenuated licking/grooming and contact behavior and shortened the latency to crouching, contact and pup retrieval. Last, fewer AVP and OT immunoreactive neurons in the paraventricular nucleus and more tyrosine hydroxylase immunoreactive neurons in the ventral tegmental area were observed in cocaine-treated fathers. These results indicate that cocaine withdrawal disturbs the expression of partial paternal behavior by altering central levels of AVP, OT and DA.

Oxytocin gene polymorphisms influence human dopaminergic function in a sex-dependent manner

BACKGROUND

Oxytocin, classically involved in social and reproductive activities, is increasingly recognized as an antinociceptive and anxiolytic agent, effects which may be mediated via oxytocin's interactions with the dopamine system. Thus, genetic variation within the oxytocin gene (OXT) is likely to explain variability in dopamine-related stress responses. As such, we examined how OXT variation is associated with stress-induced dopaminergic neurotransmission in a healthy human sample.

METHODS

Fifty-five young healthy volunteers were scanned using [¹¹C]raclopride positron emission tomography while they underwent a standardized physical and emotional stressor that consisted of moderate levels of experimental sustained deep muscle pain, and a baseline, control state. Four haplotype tagging single nucleotide polymorphisms located in regions near OXT were genotyped. Measures of pain, affect, anxiety, well-being and interpersonal attachment were also assessed.

RESULTS

Female rs4813625 C allele carriers demonstrated greater stress-induced dopamine release, measured as reductions in receptor availability from baseline to the pain-stress condition relative to female GG homozygotes. No significant differences were detected among males. We also observed that female rs4813625 C allele carriers exhibited higher attachment anxiety, higher trait anxiety and lower emotional well-being scores. In addition, greater stress-induced dopamine release was associated with lower emotional well-being scores in female rs4813625 C allele carriers.

CONCLUSIONS

Our results suggest that variability within the oxytocin gene appear to explain interindividual differences in dopaminergic responses to stress, which are shown to be associated with anxiety traits, including those linked to attachment style, as well as emotional well-being in women.

Isotocin regulates paternal care in a monogamous cichlid fish

While the survival value of paternal care is well understood, little is known about its physiological basis. Here we investigate the neuroendocrine contributions to paternal care in the monogamous cichlid, Amatitlania nigrofasciata. We first explored the dynamic range of paternal care in three experimental groups: biparental males (control fathers housed with their mate), single fathers (mate removed), or lone males (mate and offspring removed). We found that control males gradually increase paternal care over time, whereas single fathers increased care immediately after mate removal. Males with offspring present had lower levels of circulating 11-ketotestosterone (11-KT) yet still maintained aggressive displays toward brood predators. To determine what brain regions may contribute to paternal care, we quantified induction of the immediate early gene c-Fos, and found that single fathers have more c-Fos induction in the forebrain area Vv (putative lateral septum homologue), but not in the central pallium (area Dc). While overall preoptic area c-Fos induction was similar between groups, we found that parvocellular preoptic isotocin (IST) neurons in single fathers showed increased c-Fos induction, suggesting IST may facilitate the increase of paternal care after mate removal. To functionally test the role of IST in regulating paternal care, we treated biparental males with an IST receptor antagonist, which blocked paternal care. Our results indicate that isotocin plays a significant role in promoting paternal care, and more broadly suggest that the convergent evolution of paternal care across vertebrates may have recruited similar neuroendocrine mechanisms.

Oxytocin and social affiliation in humans

A conceptual model detailing the process of bio-behavioral synchrony between the online physiological and behavioral responses of attachment partners during social contact is presented as a theoretical and empirical framework for the study of affiliative bonds. Guided by an ethological behavior-based approach, we suggest that micro-level social behaviors in the gaze, vocal, affective, and touch modalities are dynamically integrated with online physiological processes and hormonal response to create dyad-specific affiliations. Studies across multiple attachments throughout life are presented and demonstrate that the extended oxytocin (OT) system provides the neurohormonal substrate for parental, romantic, and filial attachment in humans; that the three prototypes of affiliation are expressed in similar constellations of social behavior; and that OT is stable over time within individuals, is mutually-influencing among partners, and that mechanisms of cross-generation and inter-couple transmission relate to coordinated social behavior. Research showing links between peripheral and genetic markers of OT with concurrent parenting and memories of parental care; between administration of OT to parent and infant's physiological readiness for social engagement; and between neuropeptides and the online synchrony of maternal and paternal brain response in social-cognitive and empathy networks support the hypothesis that human attachment develops within the matrix of biological attunement and close behavioral synchrony. The findings have conceptual implications for the study of inter-subjectivity as well as translational implications for the treatment of social disorders originating in early childhood, such as autism spectrum disorders, or those associated with disruptions to early bonding, such as postpartum depression or child abuse and neglect. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Who, what, where, when (and maybe even why)? How the experience of sexual reward connects sexual desire, preference, and performance

Although sexual behavior is controlled by hormonal and neurochemical actions in the brain, sexual experience induces a degree of plasticity that allows animals to form instrumental and Pavlovian associations that predict sexual outcomes, thereby directing the strength of sexual responding. This review describes how experience with sexual reward strengthens the development of sexual behavior and induces sexually-conditioned place and partner preferences in rats. In both male and female rats, early sexual experience with partners scented with a neutral or even noxious odor induces a preference for scented partners in subsequent choice tests. Those preferences can also be induced by injections of morphine or oxytocin paired with a male rat's first exposure to scented females, indicating that pharmacological activation of opioid or oxytocin receptors can "stand in" for the sexual reward-related neurochemical processes normally activated by sexual stimulation. Conversely, conditioned place or partner preferences can be blocked by the opioid receptor antagonist naloxone. A somatosensory cue (a rodent jacket) paired with sexual reward comes to elicit sexual arousal in male rats, such that paired rats with the jacket off show dramatic copulatory deficits. We propose that endogenous opioid activation forms the basis of sexual reward, which also sensitizes hypothalamic and mesolimbic dopamine systems in the presence of cues that predict sexual reward. Those systems act to focus attention on, and activate goal-directed behavior toward, reward-related stimuli. Thus, a critical period exists during an individual's early sexual experience that creates a "love map" or Gestalt of features, movements, feelings, and interpersonal interactions associated with sexual reward.

Oxytocin in the medial preoptic area facilitates male sexual behavior in the rat

Oxytocin (OT) is a versatile neuropeptide that is involved in a variety of mammalian behaviors, and its role in reproductive function and behavior has been well established. The majority of pharmacological studies of the effects of OT on male sexual behavior have focused on the paraventricular nucleus (PVN), ventral tegmental area (VTA), hippocampus, and amygdala. Less attention has been given to the medial preoptic area (MPOA), a major integrative site for male sexual behavior. The present study investigated the effects of intra-MPOA administration of OT and (d(CH2)51, Tyr(Me)2, Thr4, Orn8, Tyr-NH29)-vasotocin, an OT antagonist (OTA), on copulation in the male rat. The relationship between OT receptor (OTR) binding levels in the MPOA and sexual efficiency was also explored. Microinjection of OT into the MPOA facilitated copulation in sexually experienced male rats, whereas similar injections of an OTA inhibited certain aspects of copulation but had no significant effect on locomotor activity in an open field. Contrary to expectation, sexually efficient males had lower levels of OTR binding in the rostral MPOA compared to inefficient animals. The present data suggest that OT activity in the MPOA is not necessary for the expression of male sexual behavior but is sufficient to facilitate copulatory behaviors and improve sexual efficiency in sexually experienced male rats. These data also suggest that OTR activity in the MPOA stimulates anogenital investigation, facilitates the initiation of copulation, and plays a role in the sensitization effect of the first ejaculation on subsequent ejaculations.

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.