Neuromodulation of maternal circuits by oxytocin

Acoustic features of and behavioral responses to emotionally intense mouse vocalizations

Social vocalizations contain cues that reflect the motivational state of a vocalizing animal. Once perceived, these cues may in turn affect the internal state and behavioral responses of listening animals. Using the CBA/CAJ mouse model of acoustic communication, this study examined acoustic cues that signal intensity in male-female interactions, then compared behavioral responses to intense mating vocal sequences with those from another intense behavioral context, restraint. Experiment I in this study examined behaviors and vocalizations associated with male-female social interactions. Based on several behaviors, we distinguished more general, courtship-type interactions from mating interactions involving mounting or attempted mounting behaviors. We then compared vocalizations between courtship and mating. The increase in behavioral intensity from courtship to mating was associated with altered syllable composition, more harmonic structure, lower minimum frequency, longer duration, reduced inter-syllable interval, and increased sound intensity. We then used these features to construct highly salient playback stimuli associated with mating. In Experiment II, we compared behavioral responses to playback of these mating sequences with responses to playback of aversive vocal sequences produced by restrained mice, described in previous studies. Subjects were females in estrus and males. We observed a range of behavioral responses. Some (e.g., Attending and Stretch-Attend) showed similar responses across playback type and sex, while others were context dependent (e.g., Flinching, Locomotion). Still other behaviors showed either an effect of sex (e.g., Self-Grooming, Still-and-Alert) or an interaction between playback type and sex (Escape). These results demonstrate both state-dependent features of mouse vocalizations and their effectiveness in evoking a range of behavioral responses, independent of contextual cues provided by other sensory stimuli or behavioral interactions.

The neurobiology of parenting and infant-evoked aggression

Parenting behavior comprises a variety of adult-infant and adult-adult interactions across multiple timescales. The state transition from nonparent to parent requires an extensive reorganization of individual priorities and physiology and is facilitated by combinatorial hormone action on specific cell types that are integrated throughout interconnected and brainwide neuronal circuits. In this review, we take a comprehensive approach to integrate historical and current literature on each of these topics across multiple species, with a focus on rodents. New and emerging molecular, circuit-based, and computational technologies have recently been used to address outstanding gaps in our current framework of knowledge on infant-directed behavior. This work is raising fundamental questions about the interplay between instinctive and learned components of parenting and the mutual regulation of affiliative versus agonistic infant-directed behaviors in health and disease. Whenever possible, we point to how these technologies have helped gain novel insights and opened new avenues of research into the neurobiology of parenting. We hope this review will serve as an introduction for those new to the field, a comprehensive resource for those already studying parenting, and a guidepost for designing future studies.

Parenthood and gene expression of oxytocin receptors and vasopressin receptors in sensory cortices of the male California mouse (Peromyscus californicus)

The onset of parental care is associated with shifts in parents' perception of sensory stimuli from infants, mediated by neural plasticity in sensory systems. In new mothers, changes in auditory and olfactory processing have been linked to plasticity at several points along both sensory pathways, including cortical changes that are modulated, at least in part, by oxytocin. In males of biparental species, vasopressin, in addition to oxytocin, is important for modulating parental behavior; however, little is known about sensory plasticity in new fathers. We examined variation in the mRNA expression of oxytocin and vasopressin receptors (Oxtr and Avpr1a) in sensory cortices of virgin males, paired nonbreeding males, and new fathers in the biparental California mouse (Peromyscus californicus), and variation among cortices using the visual cortex for comparison. Reproductive status did not affect gene expression for either receptor, but compared to the visual cortex, expression of both receptors was higher in the left auditory cortex and lower in the anterior olfactory nucleus. Additionally, expression for both receptors was higher in the left auditory cortex compared to the right auditory cortex. While oxytocin and vasopressin receptor expression may remain stable across reproductive stages in male California mice, our findings provide support for auditory cortex lateralization, with the left auditory cortex possibly displaying higher sensitivity to both oxytocin and vasopressin compared to the right.

Parenthood status and plasma oxytocin levels predict specific emotion perception abilities

Superior recognition of positive emotional facial expressions compared to negative expressions is well established. However, it is unclear whether this superiority effect differs between non-parents and parents, for whom emotion perception (EP) is an indispensable skill. Although EP has been shown to be modulated by the neuropeptide oxytocin, a central factor in the development of parental care, very little research has addressed the relationship between EP skills, the transition to parenthood, and plasma oxytocin levels. In the present study, we assessed EP abilities with a test battery and measured plasma oxytocin in 77 non-parent and 79 parent couples and applied structural equation modelling to the data. The results showed increased happiness perception abilities in both parents and individuals with elevated oxytocin levels. Furthermore, non-parents showed superior abilities to recognise anger expressions. No significant associations were found regarding the perception of other basic emotion categories or with a general EP factor. The findings are consistent with previous research indicating that elevated oxytocin levels are associated with enhanced EP abilities. They also extend the existing literature by demonstrating that mothers and fathers, regardless of their oxytocin levels, exhibit increased EP superiority.

Oxytocin influences parental care in male threespine stickleback across multiple time scales

Oxytocin (OXT) and its homologs are known to regulate parental care in vertebrates, but it is unknown what role these neuropeptides may play in the evolutionary loss of care. Here, we compared two recently diverged ecotypes of threespine stickleback (Gasterosteus aculeatus) that differ in parental care. Males of the common ecotype provide obligate, uniparental care to their offspring, whereas males of the white ecotype abandon their offspring after fertilization. To test if OXT plays a role in the loss of care, we manipulated OXT in males of both ecotypes via intraperitoneal injection of a vehicle control, OXT single- or double-dose, or an OXT antagonist. We observed the behavioral response to injection at two time points for commons (0 and 4 days post-fertilization (dpf)) and one for whites (0 dpf). Our results suggest that, in commons, OXT promotes the onset of care but not its maintenance. Notably, commons that ultimately terminated their clutches did not respond to OXT at 0 dpf, which may have contributed to their failure to transition to a state of care. Whites responded to OXT manipulation in a different manner than commons, suggesting that the loss of care in whites is not due to a loss of sensitivity to OXT, or insufficient levels of OXT ligand, but rather an evolutionary change to the underlying parental circuit that OXT is acting on. These results provide evidence that ancient hormonal systems like OXT can contribute to losses of care over multiple timescales.

Potential role of oxytocin in the regulation of memories and treatment of memory disorders

Oxytocin (OXT) is an "affiliative" hormone or neurohormone or neuropeptide consists of nine amino acids, synthesized in magnocellular neurons of paraventricular (PVN) and supraoptic nuclei (SON) of hypothalamus. OXT receptors are widely distributed in various region of brain and OXT has been shown to regulate various social and nonsocial behavior. Hippocampus is the main region which regulates the learning and memory. Hippocampus particularly regulates the acquisition of new memories and retention of acquired memories. OXT has been shown to regulate the synaptic plasticity, neurogenesis, and consolidation of memories. Further, findings from both preclinical and clinical studies have suggested that the OXT treatment improves performance in memory related task. Various trials have suggested the positive impact of intranasal OXT in the dementia patients. However, these studies are limited in number. In the present study authors have highlighted the role of OXT in the formation and retrieval of memories. Further, the study demonstrated the outcome of OXT treatment in various memory and related disorders.

Methods for the induction of labor: efficacy and safety

This review assessed the efficacy and safety of pharmacologic agents (prostaglandins, oxytocin, mifepristone, hyaluronidase, and nitric oxide donors) and mechanical methods (single- and double-balloon catheters, laminaria, membrane stripping, and amniotomy) and those generally considered under the rubric of complementary medicine (castor oil, nipple stimulation, sexual intercourse, herbal medicine, and acupuncture). A substantial body of published reports, including 2 large network meta-analyses, support the safety and efficacy of misoprostol (PGE1) when used for cervical ripening and labor induction. Misoprostol administered vaginally at doses of 50 μg has the highest probability of achieving vaginal delivery within 24 hours. Regardless of dosing, route, and schedule of administration, when used for cervical ripening and labor induction, prostaglandin E2 seems to have similar efficacy in decreasing cesarean delivery rates. Globally, although oxytocin represents the most widely used pharmacologic agent for labor induction, its effectiveness is highly dependent on parity and cervical status. Oxytocin is more effective than expectant management in inducing labor, and the efficacy of oxytocin is enhanced when combined with amniotomy. However, prostaglandins administered vaginally or intracervically are more effective in inducing labor than oxytocin. A single 200-mg oral tablet of mifepristone seems to represent the lowest effective dose for cervical ripening. The bulk of the literature assessing relaxin suggests this agent has limited benefit when used for this indication. Although intracervical injection of hyaluronidase may cause cervical ripening, the need for intracervical administration has limited the use of this agent. Concerning the vaginal administration of nitric oxide donors, including isosorbide mononitrate, isosorbide, nitroglycerin, and sodium nitroprusside, the higher incidence of side effects with these agents has limited their use. A synthetic hygroscopic cervical dilator has been found to be effective for preinduction cervical ripening. Although a pharmacologic agent may be administered after the use of the synthetic hygroscopic dilator, in an attempt to reduce the interval to vaginal delivery, concomitant use of mechanical and pharmacologic methods is being explored. Combining the use of a single-balloon catheter with dinoprostone, misoprostol, or oxytocin enhances the efficacy of these pharmacologic agents in cervical ripening and labor induction. The efficacy of single- and double-balloon catheters in cervical ripening and labor induction seems similar. To date, the combination of misoprostol with an intracervical catheter seems to be the best approach when balancing delivery times with safety. Although complementary methods are occasionally used by patients, given the lack of data documenting their efficacy and safety, these methods are rarely used in hospital settings.

Long range projections of oxytocin neurons in the marmoset brain

The neurohormone oxytocin (OT) has become a major target for the development of novel therapeutic strategies to treat psychiatric disorders such as autism spectrum disorder because of its integral role in governing many facets of mammalian social behavior. Whereas extensive work in rodents has produced much of our knowledge of OT, we lack basic information about its neurobiology in primates making it difficult to interpret the limited effects that OT manipulations have had in human patients. In fact, previous studies have revealed only limited OT fibers in primate brains. Here, we investigated the OT connectome in marmoset using immunohistochemistry, and mapped OT fibers throughout the brains of adult male and female marmoset monkeys. We found extensive OT projections reaching limbic and cortical areas that are involved in the regulation of social behaviors, such as the amygdala, the medial prefrontal cortex and the basal ganglia. The pattern of OT fibers observed in marmosets is notably similar to the OT connectomes described in rodents. Our findings here contrast with previous results by demonstrating a broad distribution of OT throughout the marmoset brain. Given the prevalence of this neurohormone in the primate brain, methods developed in rodents to manipulate endogenous OT are likely to be applicable in marmosets.

The Role of Central Oxytocin in Autonomic Regulation

Oxytocin (OXT), a neuropeptide originating from the hypothalamus and traditionally associated with peripheral functions in parturition and lactation, has emerged as a pivotal player in the central regulation of the autonomic nervous system (ANS). This comprehensive ANS, comprising sympathetic, parasympathetic, and enteric components, intricately combines sympathetic and parasympathetic influences to provide unified control. The central oversight of sympathetic and parasympathetic outputs involves a network of interconnected regions spanning the neuroaxis, playing a pivotal role in the real-time regulation of visceral function, homeostasis, and adaptation to challenges. This review unveils the significant involvement of the central OXT system in modulating autonomic functions, shedding light on diverse subpopulations of OXT neurons within the paraventricular nucleus of the hypothalamus and their intricate projections. The narrative progresses from the basics of central ANS regulation to a detailed discussion of the central controls of sympathetic and parasympathetic outflows. The subsequent segment focuses specifically on the central OXT system, providing a foundation for exploring the central role of OXT in ANS regulation. This review synthesizes current knowledge, paving the way for future research endeavors to unravel the full scope of autonomic control and understand multifaceted impact of OXT on physiological outcomes.

Neural circuitry for maternal oxytocin release induced by infant cries

Oxytocin is a neuropeptide that is important for maternal physiology and childcare, including parturition and milk ejection during nursing1-6. Suckling triggers the release of oxytocin, but other sensory cues-specifically, infant cries-can increase the levels of oxytocin in new human mothers7, which indicates that cries can activate hypothalamic oxytocin neurons. Here we describe a neural circuit that routes auditory information about infant vocalizations to mouse oxytocin neurons. We performed in vivo electrophysiological recordings and photometry from identified oxytocin neurons in awake maternal mice that were presented with pup calls. We found that oxytocin neurons responded to pup vocalizations, but not to pure tones, through input from the posterior intralaminar thalamus, and that repetitive thalamic stimulation induced lasting disinhibition of oxytocin neurons. This circuit gates central oxytocin release and maternal behaviour in response to calls, providing a mechanism for the integration of sensory cues from the offspring in maternal endocrine networks to ensure modulation of brain state for efficient parenting.

Optopharmacological tools for precise spatiotemporal control of oxytocin signaling in the central nervous system and periphery

Oxytocin is a neuropeptide critical for maternal physiology and social behavior, and is thought to be dysregulated in several neuropsychiatric disorders. Despite the biological and neurocognitive importance of oxytocin signaling, methods are lacking to activate oxytocin receptors with high spatiotemporal precision in the brain and peripheral mammalian tissues. Here we developed and validated caged analogs of oxytocin which are functionally inert until cage release is triggered by ultraviolet light. We examined how focal versus global oxytocin application affected oxytocin-driven Ca2+ wave propagation in mouse mammary tissue. We also validated the application of caged oxytocin in the hippocampus and auditory cortex with electrophysiological recordings in vitro, and demonstrated that oxytocin uncaging can accelerate the onset of mouse maternal behavior in vivo. Together, these results demonstrate that optopharmacological control of caged peptides is a robust tool with spatiotemporal precision for modulating neuropeptide signaling throughout the brain and body.

Multiparity Differentially Affects Specific Aspects of the Acute Neuroinflammatory Response to Traumatic Brain Injury in Female Mice

Pregnancy is associated with profound acute and long-term physiological changes, but the effects of such changes on brain injury outcomes are unclear. Here, we examined the effects of previous pregnancy and maternal experience (parity) on acute neuroinflammatory responses to lateral fluid percussion injury (FPI), a well-defined experimental traumatic brain injury (TBI) paradigm. Multiparous (2-3 pregnancies and motherhood experiences) and age-matched nulliparous (no previous pregnancy or motherhood experience) female mice received either FPI or sham injury and were euthanized 3 days post-injury (DPI). Increased cortical Iba1, GFAP, and CD68 immunolabeling was observed following TBI independent of parity and microglia morphology did not differ between TBI groups. However, multiparous females had fewer CD45⁺ cells near the site of injury compared to nulliparous females, which was associated with preserved aquaporin-4 polarization, suggesting that parity may influence leukocyte recruitment to the site of injury and maintenance of blood brain barrier permeability following TBI. Additionally, relative cortical Il6 gene expression following TBI was dependent on parity such that TBI increased Il6 expression in nulliparous, but not multiparous, mice. Together, this work suggests that reproductive history may influence acute neuroinflammatory outcomes following TBI in females.

Neuromodulatory functions exerted by oxytocin on different populations of hippocampal neurons in rodents

Oxytocin (OT) is a neuropeptide widely known for its peripheral hormonal effects (i.e., parturition and lactation) and central neuromodulatory functions, related especially to social behavior and social, spatial, and episodic memory. The hippocampus is a key structure for these functions, it is innervated by oxytocinergic fibers, and contains OT receptors (OTRs). The hippocampal OTR distribution is not homogeneous among its subregions and types of neuronal cells, reflecting the specificity of oxytocin's modulatory action. In this review, we describe the most recent discoveries in OT/OTR signaling in the hippocampus, focusing primarily on the electrophysiological oxytocinergic modulation of the OTR-expressing hippocampal neurons. We then look at the effect this modulation has on the balance of excitation/inhibition and synaptic plasticity in each hippocampal subregion. Additionally, we review OTR downstream signaling, which underlies the OT effects observed in different types of hippocampal neuron. Overall, this review comprehensively summarizes the advancements in unraveling the neuromodulatory functions exerted by OT on specific hippocampal networks.

Autism Spectrum Disorder: Neurodevelopmental Risk Factors, Biological Mechanism, and Precision Therapy

Autism spectrum disorder (ASD) is a heterogeneous, behaviorally defined neurodevelopmental disorder. Over the past two decades, the prevalence of autism spectrum disorders has progressively increased, however, no clear diagnostic markers and specifically targeted medications for autism have emerged. As a result, neurobehavioral abnormalities, neurobiological alterations in ASD, and the development of novel ASD pharmacological therapy necessitate multidisciplinary collaboration. In this review, we discuss the development of multiple animal models of ASD to contribute to the disease mechanisms of ASD, as well as new studies from multiple disciplines to assess the behavioral pathology of ASD. In addition, we summarize and highlight the mechanistic advances regarding gene transcription, RNA and non-coding RNA translation, abnormal synaptic signaling pathways, epigenetic post-translational modifications, brain-gut axis, immune inflammation and neural loop abnormalities in autism to provide a theoretical basis for the next step of precision therapy. Furthermore, we review existing autism therapy tactics and limits and present challenges and opportunities for translating multidisciplinary knowledge of ASD into clinical practice.

Oxytocin, Vasopressin, and Social Behavior: From Neural Circuits to Clinical Opportunities

Oxytocin and vasopressin are peptide hormones secreted from the pituitary that are well known for their peripheral endocrine effects on childbirth/nursing and blood pressure/urine concentration, respectively. However, both peptides are also released in the brain, where they modulate several aspects of social behaviors. Oxytocin promotes maternal nurturing and bonding, enhances social reward, and increases the salience of social stimuli. Vasopressin modulates social communication, social investigation, territorial behavior, and aggression, predominantly in males. Both peptides facilitate social memory and pair bonding behaviors in monogamous species. Here we review the latest research delineating the neural circuitry of the brain oxytocin and vasopressin systems and summarize recent investigations into the circuit-based mechanisms modulating social behaviors. We highlight research using modern molecular genetic technologies to map, monitor activity of, or manipulate neuropeptide circuits. Species diversity in oxytocin and vasopressin effects on social behaviors are also discussed. We conclude with a discussion of the translational implications of oxytocin and vasopressin for improving social functioning in disorders with social impairments, such as autism spectrum disorder.

Oxytocin: An Old Hormone, A Novel Psychotropic Drug And Possible Use In Treating Psychiatric Disorders

BACKGROUND

Oxytocin is a nonapeptide synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Historically, this molecule has been involved as a key factor in the formation of infant attachment, maternal behavior and pair bonding and, more generally, in linking social signals with cognition, behaviors and reward. In the last decades, the whole oxytocin system has gained a growing interest as it was proposed to be implicated in etiopathogenesis of several neurodevelopmental and neuropsychiatric disorders.

METHODS

With the main goal of an in-depth understanding of the oxytocin role in the regulation of different functions and complex behaviors as well as its intriguing implications in different neuropsychiatric disorders, we performed a critical review of the current state of art. We carried out this work through PubMed database up to June 2021 with the search terms: 1) "oxytocin and neuropsychiatric disorders"; 2) "oxytocin and neurodevelopmental disorders"; 3) "oxytocin and anorexia"; 4) "oxytocin and eating disorders"; 5) "oxytocin and obsessive-compulsive disorder"; 6) "oxytocin and schizophrenia"; 7) "oxytocin and depression"; 8) "oxytocin and bipolar disorder"; 9) "oxytocin and psychosis"; 10) "oxytocin and anxiety"; 11) "oxytocin and personality disorder"; 12) "oxytocin and PTSD".

RESULTS

Biological, genetic, and epigenetic studies highlighted quality and quantity modifications in the expression of oxytocin peptide or in oxytocin receptor isoforms. These alterations would seem to be correlated with a higher risk of presenting several neuropsychiatric disorders belonging to different psychopathological spectra. Collaterally, the exogenous oxytocin administration has shown to ameliorate many neuropsychiatric clinical conditions.

CONCLUSION

Finally, we briefly analyzed the potential pharmacological use of oxytocin in patient with severe symptomatic SARS-CoV-2 infection due to its anti-inflammatory, anti-oxidative and immunoregulatory properties.

Bridging skin, brain, and behavior to understand pleasurable social touch

Social touch-the affiliative skin-to-skin contact between individuals-can rapidly evoke emotions of comfort, pleasure, or calm, and is essential for mental and physical well-being. Physical isolation from social support can be devastating. During the COVID-19 pandemic, we observed a global increase in suicidal ideation, anxiety, domestic violence, and worsening of pre-existing physical conditions, alerting society to our need to understand the neurobiology of social touch and how it promotes normal health. Gaining a mechanistic understanding of how sensory neuron stimulation induces pleasure, calm, and analgesia may reveal untapped therapeutic targets in the periphery for treatment of anxiety and depression, as well as social disorders and traumas in which social touch becomes aversive. Bridging the gap between stimulation in the skin and positive affect in the brain-especially during naturally occurring social touch behaviors-remains a challenge to the field. However, with advances in mouse genetics, behavioral quantification, and brain imaging approaches to measure neuronal firing and neurochemical release, completing this mechanistic picture may be on the horizon. Here, we summarize some exciting new findings about social touch in mammals, emphasizing both the peripheral and central nervous systems, with attempts to bridge the gap between external stimulation and internal representations in the brain.

Experience-Regulated Neuronal Signaling in Maternal Behavior

Maternal behavior is shaped and challenged by the changing developmental needs of offspring and a broad range of environmental factors, with evidence indicating that the maternal brain exhibits a high degree of plasticity. This plasticity is displayed within cellular and molecular systems, including both intra- and intercellular signaling processes as well as transcriptional profiles. This experience-associated plasticity may have significant overlap with the mechanisms controlling memory processes, in particular those that are activity-dependent. While a significant body of work has identified various molecules and intracellular processes regulating maternal care, the role of activity- and experience-dependent processes remains unclear. We discuss recent progress in studying activity-dependent changes occurring at the synapse, in the nucleus, and during the transport between these two structures in relation to maternal behavior. Several pre- and postsynaptic molecules as well as transcription factors have been found to be critical in these processes. This role reflects the principal importance of the molecular and cellular mechanisms of memory formation to maternal and other behavioral adaptations.

The interplay between glutamatergic circuits and oxytocin neurons in the hypothalamus and its relevance to neurodevelopmental disorders

Oxytocin (OXT) neurons of the hypothalamus are at the center of several physiological functions, including milk ejection, uterus contraction, and maternal and social behavior. In lactating females, OXT neurons show a pattern of burst firing and inter-neuron synchronization during suckling that leads to pulsatile release of surges of OXT into the bloodstream to stimulate milk ejection. This pattern of firing and population synchronization may be facilitated in part by hypothalamic glutamatergic circuits, as has been observed in vitro using brain slices obtained from male rats and neonates. However, it remains unknown how hypothalamic glutamatergic circuits influence OXT cell activity outside the context of lactation. In this review, we summarize the in vivo and in vitro studies that describe the synchronized burst firing pattern of OXT neurons and the implication of hypothalamic glutamate in this pattern of firing. We also make note of the few studies that have traced glutamatergic afferents to the hypothalamic paraventricular and supraoptic nuclei. Finally, we discuss the genetic findings implicating several glutamatergic genes in neurodevelopmental disorders, including autism spectrum disorder, thus underscoring the need for future studies to investigate the impact of these mutations on hypothalamic glutamatergic circuits and the OXT system.

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

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

Dendritic osmosensors modulate activity-induced calcium influx in oxytocinergic magnocellular neurons of the mouse PVN

Hypothalamic oxytocinergic magnocellular neurons have a fascinating ability to release peptide from both their axon terminals and from their dendrites. Existing data indicates that the relationship between somatic activity and dendritic release is not constant, but the mechanisms through which this relationship can be modulated are not completely understood. Here, we use a combination of electrical and optical recording techniques to quantify activity-induced calcium influx in proximal vs. distal dendrites of oxytocinergic magnocellular neurons located in the paraventricular nucleus of the hypothalamus (OT-MCNs). Results reveal that the dendrites of OT-MCNs are weak conductors of somatic voltage changes; however, activity-induced dendritic calcium influx can be robustly regulated by both osmosensitive and non-osmosensitive ion channels located along the dendritic membrane. Overall, this study reveals that dendritic conductivity is a dynamic and endogenously regulated feature of OT-MCNs that is likely to have substantial functional impact on central oxytocin release.

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.

Oxytocinergic Feedback Circuitries: An Anatomical Basis for Neuromodulation of Social Behaviors

Oxytocin (OT) is a neuropeptide produced by hypothalamic neurons and is known to modulate social behavior among other functions. Several experiments have shown that OT modulates neuronal activity in many brain areas, including sensory cortices. OT neurons thus project axons to various cortical and subcortical structures and activate neuronal subpopulations to increase the signal-to-noise ratio, and in turn, increases the saliency of social stimuli. Less is known about the origin of inputs to OT neurons, but recent studies show that cells projecting to OT neurons are often located in regions where the OT receptor (OTR) is expressed. Thus, we propose the existence of reciprocal connectivity between OT neurons and extrahypothalamic OTR neurons to tune OT neuron activity depending on the behavioral context. Furthermore, the latest studies have shown that OTR-expressing neurons located in social brain regions also project to other social brain regions containing OTR-expressing neurons. We hypothesize that OTR-expressing neurons across the brain constitute a common network coordinated by OT.

An acute dose of intranasal oxytocin rapidly increases maternal communication and maintains maternal care in primiparous postpartum California mice

Maternal-offspring communication and care are essential for offspring survival. Oxytocin (OXT) is known for its role in initiation of maternal care, but whether OXT can rapidly influence maternal behavior or ultrasonic vocalizations (USVs; above 50 kHz) has not been examined. To test for rapid effects of OXT, California mouse mothers were administered an acute intranasal (IN) dose of OXT (0.8 IU/kg) or saline followed by a separation test with three phases: habituation with pups in a new testing chamber, separation via a wire mesh, and finally reunion with pups. We measured maternal care, maternal USVs, and pup USVs. In mothers, we primarily observed simple sweep USVs, a short downward sweeping call around 50 kHz, and in pups we only observed pup whines, a long call with multiple harmonics ranging from 20 kHz to 50 kHz. We found that IN OXT rapidly and selectively enhanced the normal increase in maternal simple sweep USVs when mothers had physical access to pups (habituation and reunion), but not when mothers were physically separated from pups. Frequency of mothers' and pups' USVs were correlated upon reunion, but IN OXT did not influence this correlation. Finally, mothers given IN OXT showed more efficient pup retrieval/carrying and greater total maternal care upon reunion. Behavioral changes were specific to maternal behaviors (e.g. retrievals) as mothers given IN OXT did not differ from controls in stress-related behaviors (e.g. freezing). Overall, these findings highlight the rapid effects and context-dependent effect a single treatment with IN OXT has on both maternal USV production and offspring care.

Oxytocin, Neural Plasticity, and Social Behavior

Oxytocin regulates parturition, lactation, parental nurturing, and many other social behaviors in both sexes. The circuit mechanisms by which oxytocin modulates social behavior are receiving increasing attention. Here, we review recent studies on oxytocin modulation of neural circuit function and social behavior, largely enabled by new methods of monitoring and manipulating oxytocin or oxytocin receptor neurons in vivo. These studies indicate that oxytocin can enhance the salience of social stimuli and increase signal-to-noise ratios by modulating spiking and synaptic plasticity in the context of circuits and networks. We highlight oxytocin effects on social behavior in nontraditional organisms such as prairie voles and discuss opportunities to enhance the utility of these organisms for studying circuit-level modulation of social behaviors. We then discuss recent insights into oxytocin neuron activity during social interactions. We conclude by discussing some of the major questions and opportunities in the field ahead.

Mother brain is wired for social moments

Reorganization of the maternal brain upon childbirth triggers the species-typical maternal social behavior. These brief social moments carry profound effects on the infant's brain and likely have a distinct signature in the maternal brain. Utilizing a double-blind, within-subject oxytocin/placebo administration crossover design, mothers' brain was imaged twice using fMRI while observing three naturalistic maternal-infant contexts in the home ecology; 'unavailable', 'unresponsive', and 'social', when mothers engaged in synchronous peek-a-boo play. The social condition elicited greater neural response across the human caregiving network, including amygdala, VTA, hippocampus, insula, ACC, and temporal cortex. Oxytocin impacted neural response primarily to the social condition and attenuated differences between social and non-social stimuli. Greater temporal consistency emerged in the 'social' condition across the two imaging sessions, particularly in insula, amygdala, and TP. Findings describe how mother's brain varies by caregiving experiences and gives salience to moments of social synchrony that support infant development and brain maturation.

Receptor for advanced glycation end-products (RAGE) plays a critical role in retrieval behavior of mother mice at early postpartum

Receptor for advanced glycation end-products (RAGE) is a pattern recognition molecule belonging to the immunoglobulin superfamily, and it plays a role in the remodeling of endothelial cells under pathological conditions. Recently, it was shown that RAGE is a binding protein for oxytocin (OT) and a transporter of OT to the brain on neurovascular endothelial cells via blood circulation. Deletion of the mouse RAGE gene, Ager (RAGE KO), induces hyperactivity in male mice. Impairment of pup care by mother RAGE KO mice after stress exposure results in the death of neonates 1-2 days after pup birth. Therefore, to understand the role of RAGE during the postpartum period, this study aims to examine parental behavior in female RAGE KO mice and ultrasonic vocalizations in pups. RAGE KO mothers without stress before delivery raised their pups and displayed hyperactivity at postpartum day (PPD) 3. KO dams showed impaired retrieval or interaction behavior after additional stress, such as body restraint stress or exposure to a novel environment, but such impaired behavior disappeared at PPD 7. Postnatal day 3 pups emitted ultrasonic vocalizations at >60 kHz as a part of the mother-pup relationship, but the number and category of calls by RAGE KO pups were significantly lower than wild-type pups. The results indicate that RAGE is important in the manifestation of normal parental behavior in dams and for receiving maternal care by mouse pups; moreover, brain OT recruited by RAGE plays a role in damping of signals of additional external stress and endogenous stress during the early postpartum period. Thus, RAGE-dependent OT may be critical for initiating and maintaining the normal mother-child relationship.

Oxytocin, eating behavior, and metabolism in humans

The hypothalamic peptide oxytocin has been increasingly recognized as a hormone and neurotransmitter with important effects on energy intake, metabolism, and body weight and is under investigation as a potential novel therapeutic agent for obesity. The main neurons producing oxytocin and expressing the oxytocin receptor are strategically located in brain areas known to be critically involved in homeostatic energy balance as well as hedonic and motivational aspects of eating behavior. In this chapter, we will review the central and peripheral physiology of oxytocin and the interaction of oxytocin with key hormones and neural circuitries that affect food intake and metabolism. Next, we will synthesize the available data on endogenous oxytocin levels related to caloric intake, body weight, and metabolic status. We will then review the effects of exogenous oxytocin administration on eating behavior, body weight, and metabolism in humans, including in healthy individuals as well as specific populations with suspected perturbations involving oxytocin pathways. Finally, we will address the promise and fundamental challenges of translating this line of research to clinical care.

[Clinical, ethologic, endokrinologic, and metabolic aspects of the peripartal period in pigs]

The aim of this review article is to provide an overview of the literature relevant to the peripartal period in swine. As in all other mammals, the farrowing process in pigs is divided into 3 phases (I-III; opening, expulsion, and postnatal stage), during which various essential endocrine and metabolic mechanisms initiate or maintain parturition. These include the hormones progesterone, cortisol, prostaglandin F_2α, oxytocin, estradiol, relaxin as well as electrolytes, enzymes, and metabolites such as calcium, magnesium, inorganic phosphate, glucose, creatine kinase, lactate, non-esterified free fatty acids, and β-hydroxybutyrate. Exogenous or endogenous disruptive factors may result in a delay or even stagnation of labor. For example, the form of husbandry may represent a possible exogenous disruptive factor. Endogenous disruptive factors may arise from insufficient storage and/or distribution of the above-mentioned labor-associated parameters. Subsequent dystocia leads to temporary or permanent consequences for maternal reproductive fitness and impairs piglet vitality at the time of birth, possibly resulting in lower survival rates.

Key Roles of Cyclooxygenase 2-Protein Kinase A-Hyperpolarization-activated Cyclic Nucleotide-gated Channel 3 Pathway in the Regulation of Oxytocin Neuronal Activity in Lactating Rats with Intermittent Pup-Deprivation

Suckling-evoked pulsatile release of oxytocin (OT) from the posterior pituitary plays a key role in breastfeeding, which relies on burst-like discharges of OT neurons. To explore cellular mechanisms regulating OT neuronal activity, using lactating rats with pup-deprivation (PD) during postpartum day 1-5, we observed the involvement of prostaglandin, cyclic AMP/protein kinase A (PKA) and hyperpolarization-activated cyclic nucleotide-gated channel 3 (HCN3) signaling pathway in OT neuronal activity. PD gradually reduced lactation efficiency. Intermittent PD (IPD) was largely reversed by intranasally-applied OT (IAO) but not by hypodermically-applied OT. IPD caused involution-like histological changes in the mammary glands, increased hypothalamic OT release but did not influence plasma OT concentrations. In the supraoptic nucleus, IPD increased OT receptor (OTR) expressions in OT neurons as well as Gαq subunit, Gβ subunit and cyclooxygenase 2 (Cox-2). These effects except that on Gβ subunit were reversed by IAO. Notably, IPD increased the expression of catalytic subunit of PKA in the SON, specifically in vasopressin neurons but not in OT neurons. In addition, IPD increased the expression of HCN3. IAO partially reversed these changes in the SON. Lastly, blocking HCN3 blocked excitation and burst firing in OT neurons-evoked by prostaglandin E₂, a key mediator of OT-evoked burst firing; blocking Cox-2 or PKA reduced the molecular association between OTR and HCN3. Thus, there is a prostaglandin-cAMP/PKA-HCN3 pathway in the regulation of OT neuronal activity. PD disrupts lactation performance through uncoupling OTR and PKA-HCN3 signaling. The reversal effect of IAO highlights its therapeutic potential in PD-evoked hypogalactia.

Innate and plastic mechanisms for maternal behaviour in auditory cortex

Infant cries evoke powerful responses in parents^1–4. To what extent are parental animals intrinsically sensitive to neonatal vocalizations, or might instead learn about vocal cues for parenting responses? In mice, pup-naive virgins do not recognize the meaning of pup distress calls, but retrieve isolated pups to the nest following cohousing with a mother and litter^5–9. Distress calls are variable, requiring co-caring virgins to generalize across calls for reliable retrieval^10,11. Here we show that the onset of maternal behavior in mice results from interactions between intrinsic mechanisms and experience-dependent plasticity in auditory cortex. In maternal females, calls with inter-syllable intervals (ISIs) from 75:375 ms elicited pup retrieval, and cortical responses generalized across these ISIs. In contrast, naive virgins were behaviorally sensitive only to the most common (‘prototypical’) ISIs. Inhibitory and excitatory neural responses were initially mismatched in naive cortex, with untuned inhibition and overly-narrow excitation. During cohousing, excitatory responses broadened to represent a wider range of ISIs, while inhibitory tuning sharpened to form a perceptual boundary. We presented synthetic calls during cohousing and observed that neurobehavioral responses adjusted to match these statistics, a process requiring cortical activity and the hypothalamic oxytocin system. Neuroplastic mechanisms therefore build on an intrinsic sensitivity in mouse auditory cortex, enabling rapid plasticity for reliable parenting behavior.

The role of oxytocin and vasopressin dysfunction in cognitive impairment and mental disorders

Oxytocin (OXT) and arginine-vasopressin (AVP) are structurally homologous peptide hormones synthesized in the hypothalamus. Nowadays, the role of OXT and AVP in the regulation of social behaviour and emotions is generally known. However, recent researches indicate that peptides also participate in cognitive functioning. This review presents the evidence that the OXT/AVP systems are involved in the formation of social, working, spatial and episodic memory, mediated by such brain structures as the hippocampal CA2 and CA3 regions, amygdala and prefrontal cortex. Some data have demonstrated that the OXT receptor's polymorphisms are associated with impaired memory in humans, and OXT knockout in mice is connected with memory deficit. Additionally, OXT and AVP are involved in mental disorders' progression. Stress-induced imbalance of the OXT/AVP systems leads to an increased risk of various mental disorders, including depression, schizophrenia, and autism. At the same time, cognitive deficits are observed in stress and mental disorders, and perhaps peptide hormones play a part in this. The final part of the review describes possible therapeutic strategies for the use of OXT and AVP for treatment of various mental disorders.

The Temporal Association Cortex Plays a Key Role in Auditory-Driven Maternal Plasticity

Mother-infant bonding develops rapidly following parturition and is accompanied by changes in sensory perception and behavior. Here, we study how ultrasonic vocalizations (USVs) are represented in the brain of mothers. Using a mouse line that allows temporally controlled genetic access to active neurons, we find that the temporal association cortex (TeA) in mothers exhibits robust USV responses. Rabies tracing from USV-responsive neurons reveals extensive subcortical and cortical inputs into TeA. A particularly dominant cortical source of inputs is the primary auditory cortex (A1), suggesting strong A1-to-TeA connectivity. Chemogenetic silencing of USV-responsive neurons in TeA impairs auditory-driven maternal preference in a pup-retrieval assay. Furthermore, dense extracellular recordings from awake mice reveal changes of both single-neuron and population responses to USVs in TeA, improving discriminability of pup calls in mothers compared with naive females. These data indicate that TeA plays a key role in encoding and perceiving pup cries during motherhood.

The blockade of oxytocin receptors in the paraventricular thalamus reduces maternal crouching behavior over pups in lactating mice

Oxytocin (OT) systems contribute to the elicitation of stereotypic maternal behaviors. OT peptide-expressing neurons are predominantly localized in the hypothalamus, whereas OT receptor (OTR)-expressing neurons are widely distributed throughout the brain. Among those OTR-expressing regions, the paraventricular thalamus (PVT) consists of heterogeneous neuropeptide-responsive neurons critical for appetitive motivation, food intake control, and social behaviors; however, the precise distribution of OTR-expressing neurons within the PVT and whether these neurons are involved in maternal behaviors in mice are unknown. The distribution of OTR-expressing neurons was examined in an OTR-Venus transgenic line expressing a fluorescent protein controlled by the OTR promoter. The number of Venus expressing neurons was higher in the posterior PVT (pPVT) than in the anterior PVT (aPVT). When OTR-Venus dams were exposed to pups, the number of double-labelled neurons expressing both OTR-Venus and a marker of neuronal activity (c-Fos) was increased in the pPVT compared to non-exposed dams, while the aPVT remained unchanged. To investigate whether OT signaling in the pPVT is essential for maternal behaviors, an OT antagonist (OTA) was transiently or chronically infused into the pPVT of lactating dams during the postpartum period. Although the transient OTR blockade did not affect maternal behaviors, a chronic OTR blockade specifically reduced the duration of crouching behavior over pups. Taken together, these findings suggest that OTR-expressing neurons in the pPVT are involved in maternal crouching behavior.

An insular view of the social decision-making network

Social animals must detect, evaluate and respond to the emotional states of other individuals in their group. A constellation of gestures, vocalizations, and chemosignals enable animals to convey affect and arousal to others in nuanced, multisensory ways. Observers integrate social information with environmental and internal factors to select behavioral responses to others via a process call social decision-making. The Social Decision Making Network (SDMN) is a system of brain structures and neurochemicals that are conserved across species (mammals, reptiles, amphibians, birds) that are the proximal mediators of most social behaviors. However, how sensory information reaches the SDMN to shape behavioral responses during a social encounter is not well known. Here we review the empirical data that demonstrate the necessity of sensory systems in detecting social stimuli, as well as the anatomical connectivity of sensory systems with each node of the SDMN. We conclude that the insular cortex is positioned to link integrated social sensory cues to this network to produce flexible and appropriate behavioral responses to socioemotional cues.

The parental brain and behavior: A target for endocrine disruption

During pregnancy, the sequential release of progesterone, 17β-estradiol, prolactin, oxytocin and placental lactogens reorganize the female brain. Brain structures such as the medial preoptic area, the bed nucleus of the stria terminalis and the motivation network including the ventral tegmental area and the nucleus accumbens are reorganized by this specific hormonal schedule such that the future mother will be ready to provide appropriate care for her offspring right at parturition. Any disruption to this hormone pattern, notably by exposures to endocrine disrupting chemicals (EDC), is therefore likely to affect the maternal brain and result in maladaptive maternal behavior. Development effects of EDCs have been the focus of intense study, but relatively little is known about how the maternal brain and behavior are affected by EDCs. We encourage further research to better understand how the physiological hormone sequence prepares the mother's brain and how EDC exposure could disturb this reorganization.