Transgenesis and the study of expression, cellular targeting and function of oxytocin, vasopressin and their receptors

Oxytocin receptors in the nucleus accumbens shell are necessary for the onset of maternal behavior

In rodents, oxytocin (Oxt) contributes to the onset of maternal care by shifting the perception of pups from aversive to attractive. Both Oxt receptor knockout (Oxtr -/-) and forebrain-specific Oxtr knockout (FB/FB) dams abandon their first litters, likely due to a failure of the brain to 'switch' to a more maternal state. Whether this behavioral shift is neurochemically similar in virgin females, who can display maternal behaviors when repeatedly exposed to pups, or what neuroanatomical substrate is critical for the onset of maternal care remains unknown. To understand similarities and differences in Oxtr signaling in virgin pup-sensitized Oxtr FB/FB as opposed to post-parturient Oxtr -/- and Oxtr FB/FB dams, maternal behavior (pup-sensitized females only) and immediate early gene activation were assessed. Pup-sensitized Oxtr FB/FB females retrieved pups faster on day one of testing and had reduced c-Fos expression in the dorsal lateral septum as compared to virgin pup-sensitized Oxtr +/+ females. This differs from what was observed in post-parturient Oxtr -/- and Oxtr FB/FB dams, where increased c-Fos expression was observed in the nucleus accumbens (NAcc) shell. Based on these data, we then disrupted Oxtr signaling in the NAcc shell or the posterior paraventricular thalamus (pPVT) (control region) of female Oxtr floxed mice using a Cre recombinase expressing adeno-associated virus. Knockout of the Oxtr only in the NAcc shell prevented the onset of maternal care post-parturient females. Our data suggest that a pup-sensitized brain may differ from a post-parturient brain and that Oxtr signaling in the NAcc shell is critical to the onset of maternal behavior.

Therapeutic potential of vasopressin in the treatment of neurological disorders

Vasopressin (VP) is a nonapeptide made of nine amino acids synthesized by the hypothalamus and released by the pituitary gland. VP acts as a neurohormone, neuropeptide and neuromodulator and plays an important role in the regulation of water balance, osmolarity, blood pressure, body temperature, stress response, emotional challenges, etc. Traditionally VP is known to regulate the osmolarity and tonicity. VP and its receptors are widely expressed in the various region of the brain including cortex, hippocampus, basal forebrain, amygdala, etc. VP has been shown to modulate the behavior, stress response, circadian rhythm, cerebral blood flow, learning and memory, etc. The potential role of VP in the regulation of these neurological functions have suggested the therapeutic importance of VP and its analogues in the management of neurological disorders. Further, different VP analogues have been developed across the world with different pharmacotherapeutic potential. In the present work authors highlighted the therapeutic potential of VP and its analogues in the treatment and management of various neurological disorders.

Crustacean cardioactive peptide signaling system in the gastropod mollusk Pacific abalone

Crustacean cardioactive peptide (CCAP) signaling systems have been characterized in a diverse range of protostomes, representatively in arthropods. The cyclic CX5C-type CCAP regulates various biological activities through CCAP receptors (CCAPRs), which are orthologous to neuropeptide S receptors (NPSRs) in deuterostomes. However, the CCAPRs of the lophotrochozoa remain poorly characterized; therefore, the relationship between the CCAP, NPS, and CX4C-type oxytocin/vasopressin (OT/VP) signaling systems is unclear. In this study, we identified a CCAP precursor and two CCAPR isoforms in the Pacific abalone (Haliotis discus hannai; Hdh). The Hdh-CCAP precursor was found to harbor three CX5C-type and one CX4C-type CCAPs. The Hdh-CCAPRs displayed homology with protostome CCAPRs and deuterostome NPSRs, having characteristics of the rhodopsin-type G protein-coupled receptors. Phylogenetic analysis showed that lophotrochozoan CCAPRs, including Hdh-CCAPRs, form a monophyletic group distinct from arthropod CCAPRs. Reporter assays demonstrated that all examined Hdh-CCAPs and insect CCAP-induced intracellular Ca2+ mobilization and cAMP accumulation in Hdh-CCAPR-expressing HEK293 cells, whereas none of the CCAP peptides inhibited the forskolin-stimulated cAMP signaling pathway even at micromolar concentrations. In silico ligand-receptor docking models showed that the N-terminal FCN motifs of Hdh-CCAPs are deeply inserted inside the binding pocket of Hdh-CCAPR, forming extensive hydrophobic interactions. In mature Pacific abalone, the transcripts for Hdh-CCAP precursor and Hdh-CCAPR were highly expressed in the neural ganglia compared to the peripheral tissues. Collectively, this study characterized the first CCAP signaling system linked to both Ca2+/PKC and cAMP/PKA signal transduction pathways in gastropod mollusks and gives insights into the evolutional origins of deuterostomian NPS and OT/VP signaling systems.

Circuits underlying social function and dysfunction

Substantial advances have been made toward understanding the genetic and environmental risk factors for autism, a neurodevelopmental disorder with social impairment as a core feature. In combination with optogenetic and chemogenetic tools to manipulate neural circuits in vivo, it is now possible to use model systems to test how specific neural circuits underlie social function and dysfunction. Here, we review the literature that has identified circuits associated with social interest (sociability), social reward, social memory, dominance, and aggression, and we outline a preliminary roadmap of the neural circuits driving these social behaviors. We highlight the neural circuitry underlying each behavioral domain, as well as develop an interactive map of how these circuits overlap across domains. We find that some of the circuits underlying social behavior are general and are involved in the control of multiple behavioral aspects, whereas other circuits appear to be specialized for specific aspects of social behavior. Our overlapping circuit map therefore helps to delineate the circuits involved in the various domains of social behavior and to identify gaps in knowledge.

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.

Hippocampal oxytocin is involved in spatial memory and synaptic plasticity deficits following acute high-fat diet intake in juvenile rats

The hippocampus undergoes maturation during juvenility, a period of increased vulnerability to environmental challenges. We recently found that acute high-fat diet (HFD) impaired hippocampal long-term potentiation (LTP) and hippocampal-dependent spatial memory. We also recently reported that similar HFD exposure affected prefrontal plasticity and social memory through decreased oxytocin levels in the prefrontal cortex. In the present study, we therefore evaluated whether hippocampal oxytocin levels are also affected by juvenile HFD and could mediate deficits of hippocampal LTP and spatial memory. We found that postweaning HFD decreased oxytocin levels in the CA1 of the dorsal hippocampus. Interestingly, systemic injection of high, but not low, dose of oxytocin rescued HFD-induced LTP impairment in CA1. Moreover, deficits in long-term object location memory (OLM) were prevented by systemic injection of both high and low dose of oxytocin as well as by intra-CA1 infusion of oxytocin receptor agonist. Finally, we found that blocking oxytocin receptors in CA1 impaired long-term OLM in control-fed juvenile rats. These results suggest that acute HFD intake lowers oxytocin levels in the CA1 that lead to CA1 plasticity impairment and spatial memory deficits in juveniles. Further, these results provide the first evidence for the regulatory role of oxytocin in spatial memory.

Anxiety and Depression: What Do We Know of Neuropeptides?

In modern society, there has been a rising trend of depression and anxiety. This trend heavily impacts the population’s mental health and thus contributes significantly to morbidity and, in the worst case, to suicides. Modern medicine, with many antidepressants and anxiolytics at hand, is still unable to achieve remission in many patients. The pathophysiology of depression and anxiety is still only marginally understood, which encouraged researchers to focus on neuropeptides, as they are a vast group of signaling molecules in the nervous system. Neuropeptides are involved in the regulation of many physiological functions. Some act as neuromodulators and are often co-released with neurotransmitters that allow for reciprocal communication between the brain and the body. Most studied in the past were the antidepressant and anxiolytic effects of oxytocin, vasopressin or neuropeptide Y and S, or Substance P. However, in recent years, more and more novel neuropeptides have been added to the list, with implications for the research and development of new targets, diagnostic elements, and even therapies to treat anxiety and depressive disorders. In this review, we take a close look at all currently studied neuropeptides, their related pathways, their roles in stress adaptation, and the etiology of anxiety and depression in humans and animal models. We will focus on the latest research and information regarding these associated neuropeptides and thus picture their potential uses in the future.

The Pan social brain: An evolutionary history of neurochemical receptor genes and their potential impact on sociocognitive differences

Humans have unique cognitive capacities that, compared with apes, are not only simply expressed as a higher level of general intelligence, but also as a quantitative difference in sociocognitive skills. Humans' closest living relatives, bonobos (Pan paniscus), and chimpanzees (Pan troglodytes), show key between-species differences in social cognition despite their close phylogenetic relatedness, with bonobos arguably showing greater similarities to humans. To better understand the evolution of these traits, we investigate the neurochemical mechanisms underlying sociocognitive skills by focusing on variation in genes encoding proteins with well-documented roles in mammalian social cognition: the receptors for vasopressin (AVPR1A), oxytocin (OXTR), serotonin (HTR1A), and dopamine (DRD2). Although these genes have been well studied in humans, little is known about variation in these genes that may underlie differences in social behavior and cognition in apes. We comparatively analyzed sequence data for 33 bonobos and 57 chimpanzees, together with orthologous sequence data for other apes. In all four genes, we describe genetic variants that alter the amino acid sequence of the respective receptors, raising the possibility that ligand binding or signal transduction may be impacted. Overall, bonobos show 57% more fixed substitutions than chimpanzees compared with the ancestral Pan lineage. Chimpanzees, show 31% more polymorphic coding variation, in line with their larger historical effective population size estimates and current wider distribution. An extensive literature review comparing allelic changes in Pan with known human behavioral variants revealed evidence of homologous evolution in bonobos and humans (OXTR rs4686301(T) and rs237897(A)), while humans and chimpanzees shared OXTR rs2228485(A), DRD2 rs6277(A), and DRD2 rs11214613(A) to the exclusion of bonobos. Our results offer the first in-depth comparison of neurochemical receptor gene variation in Pan and put forward new variants for future behavior-genotype association studies in apes, which can increase our understanding of the evolution of social cognition in modern humans.

The inflammatory event of birth: How oxytocin signaling may guide the development of the brain and gastrointestinal system

The role of oxytocin (OT) as a neuropeptide that modulates social behavior has been extensively studied and reviewed, but beyond these functions, OT's adaptive functions at birth are quite numerous, as OT coordinates many physiological processes in the mother and fetus to ensure a successful delivery. In this review we explore in detail the potential adaptive roles of oxytocin as an anti-inflammatory, protective molecule at birth for the developing fetal brain and gastrointestinal system based on evidence that birth is a potent inflammatory/immune event. We discuss data with relevance for a number of neurodevelopmental disorders, as well as the emerging role of the gut-brain axis for health and disease. Finally, we discuss the potential relevance of sex differences in OT signaling present at birth in the increased male vulnerability to neurodevelopmental disabilities.

Oxytocin therapy in hypopituitarism: Challenges and opportunities

Patients with hypopituitarism display impaired quality of life and excess morbidity and mortality, despite apparently optimal pituitary hormone replacement. Oxytocin is a neuropeptide synthesized in the anterior hypothalamus which plays an important role in controlling social and emotional behaviour, body weight and metabolism. Recent studies have suggested that a deficiency of oxytocin may be evident in patients with hypopituitarism and craniopharyngioma, and that this may be associated with deficits in cognitive empathy. Preliminary data hint at potential benefits of oxytocin therapy in improving these deficits and the accompanying metabolic disturbances that are common in these conditions. However, several challenges remain, including an incomplete understanding of the regulation and mechanisms of action of oxytocin, difficulties in accurately measuring oxytocin levels and in establishing a diagnosis of oxytocin deficiency, and a need to determine both the optimal mode of administration for oxytocin therapy and an acceptable safety profile with long-term use. This review considers the data linking oxytocin to the neuropsychological and metabolic disturbances evident in patients with craniopharyngioma and hypopituitarism, and describes the challenges that need to be overcome before replacement therapy can be considered as a therapeutic option in clinical practice.

Mitochondria, Oxytocin, and Vasopressin: Unfolding the Inflammatory Protein Response

Neuroendocrine and immune signaling pathways are activated following insults such as stress, injury, and infection, in a systemic response aimed at restoring homeostasis. Mitochondrial metabolism and function have been implicated in the control of immune responses. Commonly studied along with mitochondrial function, reactive oxygen species (ROS) are closely linked to cellular inflammatory responses. It is also accepted that cells experiencing mitochondrial or endoplasmic reticulum (ER) stress induce response pathways in order to cope with protein-folding dysregulation, in homeostatic responses referred to as the unfolded protein responses (UPRs). Recent reports indicate that the UPRs may play an important role in immune responses. Notably, the homeostasis-regulating hormones oxytocin (OXT) and vasopressin (AVP) are also associated with the regulation of inflammatory responses and immune function. Intriguingly, OXT and AVP have been linked with ER unfolded protein responses (UPR^ER), and can impact ROS production and mitochondrial function. Here, we will review the evidence for interactions between these various factors and how these neuropeptides might influence mitochondrial processes.

Conditional Deletion of Hippocampal CA2/CA3a Oxytocin Receptors Impairs the Persistence of Long-Term Social Recognition Memory in Mice

Oxytocin (OXT) receptors (OXTRs) are prominently expressed in hippocampal CA2 and CA3 pyramidal neurons, but little is known about its physiological function. As the functional necessity of hippocampal CA2 for social memory processing, we tested whether CA2 OXTRs may contribute to long-term social recognition memory (SRM) formation. Here, we found that conditional deletion of Oxtr from forebrain (Oxtr^-/-) or CA2/CA3a-restricted excitatory neurons in adult male mice impaired the persistence of long-term SRM but had no effect on sociability and preference for social novelty. Conditional deletion of CA2/CA3a Oxtr showed no changes in anxiety-like behavior assessed using the open-field, elevated plus maze and novelty-suppressed feeding tests. Application of a highly selective OXTR agonist [Thr⁴,Gly⁷]-OXT to hippocampal slices resulted in an acute and lasting potentiation of excitatory synaptic responses in CA2 pyramidal neurons that relied on N-methyl-d-aspartate receptor activation and calcium/calmodulin-dependent protein kinase II activity. In addition, Oxtr^-/- mice displayed a defect in the induction of long-term potentiation, but not long-term depression, at the synapses between the entorhinal cortex and CA2 pyramidal neurons. Furthermore, Oxtr deletion led to a reduced complexity of basal dendritic arbors of CA2 pyramidal neurons, but caused no alteration in the density of apical dendritic spines. Considering that the methodologies we have used to delete Oxtr do not rule out targeting the neighboring CA3a region, these findings suggest that OXTR signaling in the CA2/CA3a is crucial for the persistence of long-term SRM.SIGNIFICANCE STATEMENT Oxytocin receptors (OXTRs) are abundantly expressed in hippocampal CA2 and CA3 regions, but there are little known about their physiological function. Taking advantage of the conditional Oxtr knock-out mice, the present study highlights the importance of OXTR signaling in the induction of long-term potentiation at the synapses between the entorhinal cortex and CA2 pyramidal neurons and the persistence of long-term social recognition memory. Thus, OXTRs in the CA2/CA3a may provide a new target for therapeutic approaches to the treatment of social cognition deficits, which are often observed in patients with neuropsychiatric disorders.

The effects of adjunctive intranasal oxytocin in patients with schizophrenia

OBJECTIVES

Both human and animal studies have suggested that oxytocin may have therapeutic potential in the treatment of schizophrenia. We evaluated the effects of intranasal oxytocin on cognition and its predictive factors in Japanese patients with schizophrenia.

METHODS

Subjects were 16 chronic schizophrenia patients who underwent intranasal oxytocin treatment for 3 months and were assessed for changes in severity of clinical symptoms and cognitions. Fifteen of the 16 subjects underwent 3-Tesla magnetic resonance imaging.

RESULTS

Oxytocin significantly reduced scores on the positive and negative syndrome scale, especially on the negative symptoms. As for cognition, there was an improvement of the verbal fluency. Furthermore, the change of the negative score in positive and negative syndrome scale showed a negative correlation with the gray matter volumes of the right insula and left cingulate cortex.

CONCLUSIONS

Our results indicate that daily administration of intranasal oxytocin may be effective for ameliorating clinical symptoms and cognitive functions in chronic schizophrenia patients, and this improvement may be related to the gray matter volume of the right insula and left cingulate cortex.

Oxytocin stimulates hippocampal neurogenesis via oxytocin receptor expressed in CA3 pyramidal neurons

In addition to the regulation of social and emotional behaviors, the hypothalamic neuropeptide oxytocin has been shown to stimulate neurogenesis in adult dentate gyrus; however, the mechanisms underlying the action of oxytocin are still unclear. Taking advantage of the conditional knockout mouse model, we show here that endogenous oxytocin signaling functions in a non-cell autonomous manner to regulate survival and maturation of newly generated dentate granule cells in adult mouse hippocampus via oxytocin receptors expressed in CA3 pyramidal neurons. Through bidirectional chemogenetic manipulations, we also uncover a significant role for CA3 pyramidal neuron activity in regulating adult neurogenesis in the dentate gyrus. Retrograde neuronal tracing combined with immunocytochemistry revealed that the oxytocin neurons in the paraventricular nucleus project directly to the CA3 region of the hippocampus. Our findings reveal a critical role for oxytocin signaling in adult neurogenesis.

Oxytocin (OXT) has been implicated in adult neurogenesis. Here the authors show that CA3 pyramidal cells in the adult mouse hippocampus express OXT receptors and receive inputs from hypothalamic OXT neurons; activation of OXT signaling in CA3 pyramidal cells promotes the survival and maturation of newborn neurons in the dentate gyrus in a non-cell autonomous manner.

Oxytocin and behavior: Lessons from knockout mice

It is well established that the nonapeptide oxytocin (Oxt) is important for the neural modulation of behaviors in many mammalian species. Since its discovery in 1906 and synthesis in the early 1950s, elegant pharmacological work has helped identify specific neural substrates on which Oxt exerts its effects. More recently, mice with targeted genetic disruptions of the Oxt system-i.e., both the peptide and its receptor (the Oxtr)-have further defined Oxt's actions and laid some important scientific groundwork for studies in other species. In this article, we highlight the scientific contributions that various mouse knockouts of the Oxt system have made to our understanding of Oxt's modulation of behavior. We specifically focus on how the use of these mice has shed light on our understanding of social recognition memory, maternal behavior, aggression, and several nonsocial behaviors. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 190-201, 2017.

Oxytocin in survivors of childhood-onset craniopharyngioma

Quality of survival of childhood-onset craniopharyngioma patients is frequently impaired by hypothalamic involvement or surgical lesions sequelae such as obesity and neuropsychological deficits. Oxytocin, a peptide hormone produced in the hypothalamus and secreted by posterior pituitary gland, plays a major role in regulation of behavior and body composition. In a cross-sectional study, oxytocin saliva concentrations were analyzed in 34 long-term craniopharyngioma survivors with and without hypothalamic involvement or treatment-related damage, recruited in the German Childhood Craniopharyngioma Registry, and in 73 healthy controls, attending the Craniopharyngioma Support Group Meeting 2014. Oxytocin was measured in saliva of craniopharyngioma patients and controls before and after standardized breakfast and associations with gender, body mass index, hypothalamic involvement, diabetes insipidus, and irradiation were analyzed. Patients with preoperative hypothalamic involvement showed similar oxytocin levels compared to patients without hypothalamic involvement and controls. However, patients with surgical hypothalamic lesions grade 1 (anterior hypothalamic area) presented with lower levels (p = 0.017) of oxytocin under fasting condition compared to patients with surgical lesion of posterior hypothalamic areas (grade 2) and patients without hypothalamic lesions (grade 0). Craniopharyngioma patients' changes in oxytocin levels before and after breakfast correlated (p = 0.02) with their body mass index. Craniopharyngioma patients continue to secrete oxytocin, especially when anterior hypothalamic areas are not involved or damaged, but oxytocin shows less variation due to nutrition. Oxytocin supplementation should be explored as a therapeutic option in craniopharyngioma patients with hypothalamic obesity and/or behavioral pathologies due to lesions of specific anterior hypothalamic areas. Clinical trial number: KRANIOPHARYNGEOM 2000/2007(NCT00258453; NCT01272622).

Neuropeptide diversity and the regulation of social behavior in New World primates

Oxytocin (OT) and vasopressin (AVP) are important hypothalamic neuropeptides that regulate peripheral physiology, and have emerged as important modulators of brain function, particularly in the social realm. OT structure and the genes that ultimately determine structure are highly conserved among diverse eutherian mammals, but recent discoveries have identified surprising variability in OT and peptide structure in New World monkeys (NWM), with five new OT variants identified to date. This review explores these new findings in light of comparative OT/AVP ligand evolution, documents coevolutionary changes in the oxytocin and vasopressin receptors (OTR and V1aR), and highlights the distribution of neuropeptidergic neurons and receptors in the primate brain. Finally, the behavioral consequences of OT and AVP in regulating NWM sociality are summarized, demonstrating important neuromodulatory effects of these compounds and OT ligand-specific influences in certain social domains.

Aquaporins: Multiple Roles in the Central Nervous System

Aquaporins (AQPs) represent a diverse family of membrane proteins found in prokaryotes and eukaryotes. The primary aquaporins expressed in the mammalian brain are AQP1, which is densely packed in choroid plexus cells lining the ventricles, and AQP4, which is abundant in astrocytes and concentrated especially in the end-feet structures that surround capillaries throughout the brain and are present in glia limitans structures, notably in osmosensory areas such the supraoptic nucleus. Water movement in brain tissues is carefully regulated from the micro- to macroscopic levels, with aquaporins serving key roles as multifunctional elements of complex signaling assemblies. Intriguing possibilities suggest links for AQP1 in Alzheimer's disease, AQP4 as a target for therapy in brain edema, and a possible contribution of AQP9 in Parkinson's disease. For all the aquaporins, new contributions to physiological functions are likely to continue to be discovered with ongoing work in this rapidly expanding field of research. NEUROSCIENTIST 13(5):470—485, 2007.

Vasopressin and oxytocin receptor systems in the brain: Sex differences and sex-specific regulation of social behavior

The neuropeptides vasopressin (VP) and oxytocin (OT) and their receptors in the brain are involved in the regulation of various social behaviors and have emerged as drug targets for the treatment of social dysfunction in several sex-biased neuropsychiatric disorders. Sex differences in the VP and OT systems may therefore be implicated in sex-specific regulation of healthy as well as impaired social behaviors. We begin this review by highlighting the sex differences, or lack of sex differences, in VP and OT synthesis in the brain. We then discuss the evidence showing the presence or absence of sex differences in VP and OT receptors in rodents and humans, as well as showing new data of sexually dimorphic V1a receptor binding in the rat brain. Importantly, we find that there is lack of comprehensive analysis of sex differences in these systems in common laboratory species, and we find that, when sex differences are present, they are highly brain region- and species-specific. Interestingly, VP system parameters (VP and V1aR) are typically higher in males, while sex differences in the OT system are not always in the same direction, often showing higher OT expression in females, but higher OT receptor expression in males. Furthermore, VP and OT receptor systems show distinct and largely non-overlapping expression in the rodent brain, which may cause these receptors to have either complementary or opposing functional roles in the sex-specific regulation of social behavior. Though still in need of further research, we close by discussing how manipulations of the VP and OT systems have given important insights into the involvement of these neuropeptide systems in the sex-specific regulation of social behavior in rodents and humans.

The -216- to -100-bp Sequence in the 5'-Flanking Region of the Oxytocin Gene Contains a Cell-Type Specific Regulatory Element for its Selective Expression in Oxytocin Magnocellular Neurones

The oxytocin (OXT) gene is abundantly and highly selectively expressed in magnocellular neurones (MCNs) of the hypothalamic-neurohypophysial system. Previous DNA sequence deletion studies in vivo have shown that the -216- to -100-bp sequence in the 5'-flanking region of the oxytocin gene was required for its cell-type specific expression in the rat supraoptic nucleus. In the present study, we test the coupled hypotheses that this -216- to -100-bp sequence is responsible for (i) the selective expression of the OXT gene in OXT-MNCs and (ii) its selective repression in vasopressin (AVP)-MCNs. We show that, consistent with hypothesis 1, removal of the -216- to -100-bp sequence from the OXT gene completely eliminates its expression in OXT-MCNs in vivo but, in contrast to the prediction of hypothesis 2, there was no appearance of OXT gene expression in AVP-MCNs. Taken together, these and other data demonstrate that the -216- to -100-bp sequence in the 5'-flanking region of the oxytocin gene contains only an activator of transcription operating in the OXT-MCNs.

Chimpanzee sociability is associated with vasopressin (Avpr1a) but not oxytocin receptor gene (OXTR) variation

The importance of genes in regulating phenotypic variation of personality traits in humans and animals is becoming increasingly apparent in recent studies. Here we focus on variation in the vasopressin receptor gene 1a (Avpr1a) and oxytocin receptor gene (OXTR) and their effects on social personality traits in chimpanzees. We combine newly available genetic data on Avpr1a and OXTR allelic variation of 62 captive chimpanzees with individual variation in personality, based on behavioral assessments. Our study provides support for the positive association of the Avpr1a promoter region, in particular the presence of DupB, and sociability in chimpanzees. This complements findings of previous studies on adolescent chimpanzees and studies that assessed personality using questionnaire data. In contrast, no significant associations were found for the single nucleotide polymorphism (SNP) ss1388116472 of the OXTR and any of the personality components. Most importantly, our study provides additional evidence for the regulatory function of the 5' promoter region of Avpr1a on social behavior and its evolutionary stable effect across species, including rodents, chimpanzees and humans. Although it is generally accepted that complex social behavior is regulated by a combination of genes, the environment and their interaction, our findings highlight the importance of candidate genes with large effects on behavioral variation.

G9a-Mediated Regulation of OXT and AVP Expression in the Basolateral Amygdala Mediates Stress-Induced Lasting Behavioral Depression and Its Reversal by Exercise

Chronic stress produces behavioral depression. Conversely, physical exercise is held to be beneficial in the treatment of depression. Although genomic mechanisms are likely involved in these behavioral changes, underlying mechanisms are not clearly understood. In the present study, we investigated whether stress effects and their reversal by exercise occur via genomic mechanisms in the amygdala, a core part of the limbic system important for regulating mood states. Mice treated with chronic restraint showed lasting depression-like behaviors, which were counteracted by treatment with scheduled forceful exercise. Microarray analysis identified a number of genes whose expression in the amygdala was either upregulated or downregulated after repeated stress, and these changes were reversed by exercise. Of these genes, the neuropeptides oxytocin (OXT) and arginine vasopressin (AVP) were selected as representative stress-induced and exercise-responded genes in the BLA. Stereotaxic injection of OXT or AVP receptor agonists within the BLA in normal mice produced depression-like behaviors, whereas small interfering RNA (siRNA)-mediated suppression of the OXT or AVP transcripts in the BLA was sufficient to block stress-induced depressive behaviors. Stress-induced depression-like behaviors were accompanied by a global reduction of G9a histone methyltransferase and H3K9me2 at the OXT and AVP promoters. Conversely, repeated exercise increased the levels of G9a and H3K9me2 at the OXT and AVP promoters in the BLA, which was associated with the suppression of OXT and AVP expressions. These results identify G9a-induced histone methylation at the OXT and AVP promoters in the BLA as a mechanism for mediating stress-induced lasting behavioral depression and its reversal by exercise.

Oxytocin and vasopressin receptor gene variation as a proximate base for inter- and intraspecific behavioral differences in bonobos and chimpanzees

Recent literature has revealed the importance of variation in neuropeptide receptor gene sequences in the regulation of behavioral phenotypic variation. Here we focus on polymorphisms in the oxytocin receptor gene (OXTR) and vasopressin receptor gene 1a (Avpr1a) in chimpanzees and bonobos. In humans, a single nucleotide polymorphism (SNP) in the third intron of OXTR (rs53576 SNP (A/G)) is linked with social behavior, with the risk allele (A) carriers showing reduced levels of empathy and prosociality. Bonobos and chimpanzees differ in these same traits, therefore we hypothesized that these differences might be reflected in variation at the rs53576 position. We sequenced a 320 bp region surrounding rs53576 but found no indications of this SNP in the genus Pan. However, we identified previously unreported SNP variation in the chimpanzee OXTR sequence that differs from both humans and bonobos. Humans and bonobos have previously been shown to have a more similar 5′ promoter region of Avpr1a when compared to chimpanzees, who are polymorphic for the deletion of ∼360 bp in this region (+/− DupB) which includes a microsatellite (RS3). RS3 has been linked with variation in levels of social bonding, potentially explaining part of the interspecies behavioral differences found in bonobos, chimpanzees and humans. To date, results for bonobos have been based on small sample sizes. Our results confirmed that there is no DupB deletion in bonobos with a sample size comprising approximately 90% of the captive founder population, whereas in chimpanzees the deletion of DupB had the highest frequency. Because of the higher frequency of DupB alleles in our bonobo population, we suggest that the presence of this microsatellite may partly reflect documented differences in levels of sociability found in bonobos and chimpanzees.

Efferent pathways in sodium overload-induced renal vasodilation in rats

Hypernatremia stimulates the secretion of oxytocin (OT), but the physiological role of OT remains unclear. The present study sought to determine the involvement of OT and renal nerves in the renal responses to an intravenous infusion of hypertonic saline. Male Wistar rats (280–350 g) were anesthetized with sodium thiopental (40 mg. kg⁻¹, i.v.). A bladder cannula was implanted for collection of urine. Animals were also instrumented for measurement of mean arterial pressure (MAP) and renal blood flow (RBF). Renal vascular conductance (RVC) was calculated as the ratio of RBF by MAP. In anesthetized rats (n = 6), OT infusion (0.03 µg • kg⁻¹, i.v.) induced renal vasodilation. Consistent with this result, exvivo experiments demonstrated that OT caused renal artery relaxation. Blockade of OT receptors (OXTR) reduced these responses to OT, indicating a direct effect of this peptide on OXTR on this artery. Hypertonic saline (3 M NaCl, 1.8 ml • kg⁻¹ b.wt., i.v.) was infused over 60 s. In sham rats (n = 6), hypertonic saline induced renal vasodilation. The OXTR antagonist (AT; atosiban, 40 µg • kg⁻¹ • h⁻¹, i.v.; n = 7) and renal denervation (RX) reduced the renal vasodilation induced by hypernatremia. The combination of atosiban and renal denervation (RX+AT; n = 7) completely abolished the renal vasodilation induced by sodium overload. Intact rats excreted 51% of the injected sodium within 90 min. Natriuresis was slightly blunted by atosiban and renal denervation (42% and 39% of load, respectively), whereas atosiban with renal denervation reduced sodium excretion to 16% of the load. These results suggest that OT and renal nerves are involved in renal vasodilation and natriuresis induced by acute plasma hypernatremia.

Fluorescent visualisation of the hypothalamic oxytocin neurones activated by cholecystokinin-8 in rats expressing c-fos-enhanced green fluorescent protein and oxytocin-monomeric red fluorescent protein 1 fusion transgenes

The up-regulation of c-fos gene expression is widely used as a marker of neuronal activation elicited by various stimuli. Anatomically precise observation of c-fos gene products can be achieved at the RNA level by in situ hybridisation or at the protein level by immunocytochemistry. Both of these methods are time and labour intensive. We have developed a novel transgenic rat system that enables the trivial visualisation of c-fos expression using an enhanced green fluorescent protein (eGFP) tag. These rats express a transgene consisting of c-fos gene regulatory sequences that drive the expression of a c-fos-eGFP fusion protein. In c-fos-eGFP transgenic rats, robust nuclear eGFP fluorescence was observed in osmosensitive brain regions 90 min after i.p. administration of hypertonic saline. Nuclear eGFP fluorescence was also observed in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) 90 min after i.p. administration of cholecystokinin (CCK)-8, which selectively activates oxytocin (OXT)-secreting neurones in the hypothalamus. In double transgenic rats that express c-fos-eGFP and an OXT-monomeric red fluorescent protein 1 (mRFP1) fusion gene, almost all mRFP1-positive neurones in the SON and PVN expressed nuclear eGFP fluorescence 90 min after i.p. administration of CCK-8. It is possible that not only a plane image, but also three-dimensional reconstruction image may identify cytoplasmic vesicles in an activated neurone at the same time.

Sex-specific Esr2 mRNA expression in the rat hypothalamus and amygdala is altered by neonatal bisphenol A exposure

Perinatal life is a critical window for sexually dimorphic brain organization, and profoundly influenced by steroid hormones. Exposure to endocrine-disrupting compounds may disrupt this process, resulting in compromised reproductive physiology and behavior. To test the hypothesis that neonatal bisphenol A (BPA) exposure can alter sex-specific postnatal Esr2 (Erβ) expression in brain regions fundamental to sociosexual behavior, we mapped Esr2 mRNA levels in the principal nucleus of the bed nucleus of the stria terminalis (BNSTp), paraventricular nucleus (PVN), anterior portion of the medial amygdaloid nucleus (MeA), super optic nucleus, suprachiasmatic nucleus, and lateral habenula across postnatal days (PNDs) 0-19. Next, rat pups of both sexes were subcutaneously injected with 10 μg estradiol benzoate (EB), 50 μg/kg BPA (LBPA), or 50 mg/kg BPA (HBPA) over the first 3 days of life and Esr2 levels were quantified in each region of interest (ROI) on PNDs 4 and 10. EB exposure decreased Esr2 signal in most female ROIs and in the male PVN. In the BNSTp, Esr2 expression decreased in LBPA males and HBPA females on PND 10, thereby reversing the sex difference in expression. In the PVN, Esr2 mRNA levels were elevated in LBPA females, also resulting in a reversal of sexually dimorphic expression. In the MeA, BPA decreased Esr2 expression on PND 4. Collectively, these data demonstrate that region- and sex-specific Esr2 expression is vulnerable to neonatal BPA exposure in regions of the developing brain critical to sociosexual behavior in rat.

Expression of arginine vasotocin receptors in the developing zebrafish CNS

Vasotocin/vasopressin is a neuropeptide that regulates social and reproductive behaviors in a variety of animals including fish. Arginine vasotocin (AVT) is expressed by cells in the ventral hypothalamic and preoptic areas in the diencephalon during embryogenesis in zebrafish suggesting that vasotocin might mediate other functions within the CNS prior to the development of social and reproductive behaviors. In order to examine potential early roles for vasotocin we cloned two zebrafish vasotocin receptors homologous to AVPR1a. The receptors are expressed primarily in the CNS in similar but generally non-overlapping patterns. Both receptors are expressed in the forebrain, midbrain and hindbrain by larval stage. Of note, AVTR1a-expressing neurons in the hindbrain appear to be contacted by the axons of preoptic neurons in the forebrain that include avt+ neurons and sensory axons in the lateral longitudinal fasciculus (LLF). Furthermore, AVTR1a-expressing hindbrain neurons extend axons into the medial longitudinal fasciculus (MLF) that contains axons of many neurons thought to be involved in locomotor responses to sensory stimulation. One hypothesis consistent with this anatomy is that AVT signaling mediates or gates sensory input to motor circuits in the hindbrain and spinal cord.

MicroRNA profiling in the mouse hypothalamus reveals oxytocin-regulating microRNA

Oxytocin (Oxt), produced in the hypothalamic paraventricular and supraoptic nuclei for transport to and release from the posterior pituitary, was originally discovered through its role in lactation and parturition. Oxt also plays important roles in the central nervous system by influencing various behaviors. MicroRNAs (miRNAs), endogenous regulators of many genes, are a class of small non-coding RNAs that mediate post-transcriptional gene silencing. We performed miRNA expression profiling of the mouse hypothalamus by deep sequencing. Among the sequenced and cross-mapped small RNAs, expression of known miRNAs and unknown miRNAs candidates were analyzed. We investigated in detail one miRNA, miR-24, and found that it is a novel regulator of Oxt and controls both transcript and peptide levels of Oxt. These results provide insights into potential neurohypophysial hormone regulation mediated by miRNAs.

[The use of genetic modification techniques in the fluorescent visualization of oxytocin neurons]

Oxytocin, a neurohypophyseal hormone, is synthesized in the magnocellular neurosecretory cells located in the paraventricular and supraoptic nuclei of the hypothalamus, and is secreted into the systemic blood flow from the axon terminals. It is well known that plasma oxytocin is involved in contraction of the uterus during parturition and milk ejection reflex during lactation. It has recently come to the attention of researchers that oxytocin receptors are abundant in the brain and oxytocin is involved in higher brain functions such as bonding between parent and child and trust. Since it was difficult to identify neurohypophyseal hormones, oxytocin- and vasopressin-producing neurons in a living cell, we tried to generate transgenic animals that express fluorescent proteins as a tag protein to visualize neurohypophyseal hormones. In this paper we review the use of genetic modification techniques in the fluorescent visualization of oxytocin neurons and its application.

A brief history of oxytocin and its role in modulating psychostimulant effects

Over the past century, the polypeptide oxytocin has played an important role in medicine with major highlights including the identification of its involvement in parturition and the milk let-down reflex. Oxytocin is now implicated in an extensive range of psychological phenomena including reward and memory processes and has been investigated as a treatment for several psychiatric disorders including addiction, anxiety, autism, and schizophrenia. In this review, we first provide an historical overview of oxytocin and describe key aspects of its physiological activity. We then outline some pharmacological limitations in this field of research before highlighting the role of oxytocin in a wide range of behavioral and neuronal processes. Finally, we review evidence for a modulatory role of oxytocin with regard to psychostimulant effects. Key findings suggest that oxytocin attenuates a broad number of cocaine and methamphetamine induced behaviors and associated neuronal activity in rodents. Evidence also outlines a role for oxytocin in the prosocial effects of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) in both rodents and humans. Clinical trials should now investigate the effectiveness of oxytocin as a novel intervention for psychostimulant addiction and should aim to determine its specific role in the therapeutic properties of MDMA that are currently being investigated.

Oxytocin promotes long-term potentiation by enhancing epidermal growth factor receptor-mediated local translation of protein kinase Mζ

In addition to triggering the birthing process and milk release, the hypothalamic neuropeptide oxytocin (OXT) plays an important role in the regulation of complex social cognition and behavior. Previous work has shown that OXT can regulate hippocampal synaptic plasticity and improve hippocampus-dependent cognitive functions in the female mice, but the underlying mechanisms remain largely unclear. Here, we demonstrate that OXT promotes the maintenance of long-term potentiation (LTP) induced by one train of tetanic stimulation (TS) in the CA1 region of hippocampal slices from both nulliparous female and male rats through a previously unknown mechanism involving OXT receptor (OXTR)-dependent and epidermal growth factor receptor (EGFR)-mediated local translation of an atypical protein kinase C isoform, protein kinase Mζ (PKMζ), in dendrites. Using pharmacological and biochemical approaches, we show that both the conventional OXTR-associated signaling pathway (G(q/11)-coupled phospholipase C) and the transactivated EGFR downstream signaling pathways (phosphatidylinositol 3 kinase and extracellular signal-regulated kinase 1/2) are involved in the regulation of OXT. In addition, OXT stimulates local dendritic PKMζ mRNA translation via activation of a mammalian target of rapamycin-regulated mechanism. Furthermore, blockade of OXTR results in a modest decrease in the ability to maintain late-phase LTP induced by three trains of TS. These results reveal a novel OXTR-to-EGFR communication to regulate the new synthesis of PKMζ, which functions to promote the maintenance of LTP at hippocampal CA1 synapses.

Cell-type specific expression of the vasopressin gene analyzed by AAV mediated gene delivery of promoter deletion constructs into the rat SON in vivo

The magnocellular neurons (MCNs) in the supraoptic nucleus (SON) of the hypothalamus selectively express either oxytocin (Oxt) or vasopressin (Avp) neuropeptide genes. In this paper we examine the cis-regulatory domains in the Avp gene promoter that are responsible for its cell-type specific expression. AAV vectors that contain various Avp gene promoter deletion constructs using EGFP as the reporter were stereotaxically injected into the rat SON. Two weeks following the injection immunohistochemical assays of EGFP expression from these constructs were done to determine whether the expressed EGFP reporter co-localizes with either the Oxt- or Avp-immunoreactivity in the MCNs. The results identify three major enhancer domains located at −2.0 to −1.5 kbp, −1.5 to −950 bp, and −950 to −543 bp in the Avp gene promoter that regulate the expression in Avp MCNs. The results also show that cell–type specific expression in Avp MCNs is maintained in constructs containing at least 288 bp of the promoter region upstream of the transcription start site, but this specificity is lost at 116 bp and below. Based on these data, we hypothesize that the −288 bp to −116 bp domain contains an Avp MCN specific activator and a possible repressor that inhibits expression in Oxt-MCNs, thereby leading to the cell-type specific expression of the Avp gene only in the Avp-MCNs.

The hypothalamic-neurohypophyseal system: from genome to physiology

The elucidation of the genomes of a large number of mammalian species has produced a huge amount of data on which to base physiological studies. These endeavours have also produced surprises, not least of which has been the revelation that the number of protein coding genes needed to make a mammal is only 22 333 (give or take). However, this small number belies an unanticipated complexity that has only recently been revealed as a result of genomic studies. This complexity is evident at a number of levels: (i) cis-regulatory sequences; (ii) noncoding and antisense mRNAs, most of which have no known function; (iii) alternative splicing that results in the generation of multiple, subtly different mature mRNAs from the precursor transcript encoded by a single gene; and (iv) post-translational processing and modification. In this review, we examine the steps being taken to decipher genome complexity in the context of gene expression, regulation and function in the hypothalamic-neurohypophyseal system (HNS). Five unique stories explain: (i) the use of transcriptomics to identify genes involved in the response to physiological (dehydration) and pathological (hypertension) cues; (ii) the use of mass spectrometry for single-cell level identification of biological active peptides in the HNS, and to measure in vitro release; (iii) the use of transgenic lines that express fusion transgenes enabling (by cross-breeding) the generation of double transgenic lines that can be used to study vasopressin (AVP) and oxytocin (OXT) neurones in the HNS, as well as their neuroanatomy, electrophysiology and activation upon exposure to any given stimulus; (iv) the use of viral vectors to demonstrate that somato-dendritically released AVP plays an important role in cardiovascular homeostasis by binding to V1a receptors on local somata and dendrites; and (v) the use of virally-mediated optogenetics to dissect the role of OXT and AVP in the modulation of a wide variety of behaviours.

Cell-type specific expression of oxytocin and vasopressin genes: an experimental odyssey

The supraoptic nucleus (SON) is a particularly good model for the study of cell-type specific gene expression because it contains two distinct neuronal phenotypes, the oxytocin (OT) and vasopressin (AVP) synthesising magnocellular neurones (MCNs). The MCNs are found in approximately equal numbers and selectively express either the OT or the AVP gene in approximately 97% of the MCN population in the SON. An unresolved issue has been to determine what mechanisms are responsible for the highly selective regulation of the cell-type specific expression of OT and AVP genes in the MCNs. Previous attempts to address this question have used various bioinformatic and molecular approaches, which included using heterologous cell lines to study the putative cis-elements in the OT and AVP genes, and the use of OT and/or AVP transgenes in transgenic rodents. The data from all of the above studies identified a region < 0.6 kbp upstream of OT exon I and approximately 3 kb upstream of AVP exon I as being sufficient to produce cell-specific expression of the OT and AVP genes, respectively, although they failed to identify the specific cis-domains responsible for the MCN-specific gene expression. An alternative experimental approach to perform promoter deletion analysis in vivo (i.e. to use stereotaxic viral vector gene transfer into the SON to further dissect the cis-elements in the OT and AVP genes) will be described here. This in vivo method uses adeno-associated viral (AAV) vectors expressing OT-promoter deletion constructs and utilises the enhanced green fluorescent protein (EGFP) as the reporter. The AAV constructs are stereotaxically injected into the rat brain above the SON and, 2 weeks post injection, the rats are sacrificed and assayed for EGFP expression. Using this method, it has been possible to identify specific regions upstream of the transcription start site in the OT and AVP gene promoters that are responsible for conferring the cell-type specificity of the OT and AVP gene expression in the SON.

An ouabain-like factor is secreted from immortalized hypothalamic cells in an aldosterone-dependent manner

Ouabain-like factor (OLF) modulates blood pressure via sodium pump inhibition in the central nervous system and in the peripheral circulation. Ouabain-like factor (OLF) is thought to be produced in the adrenal gland and hypothalamus, and it may relate locally to the renin-angiotensin-aldosterone system. However, the evidence for the latter was obtained from in vivo experiments using animals. In the present study, we investigated ouabain production in the immortalized hypothalamic cell line N1. First, cell culture supernatant was collected from the immortalized hypothalamic cell line N1 at 0.5, 4, 8, and 24 h. A newly developed enzyme-linked immunosorbent assay (ELISA) that used anti-ouabain antibody showed that immunoreactivity in the supernatant was increased significantly at 24 vs. 0.5 h (0.01±0.004 vs. 0.16±0.033 pmol/mg protein, p<0.01). A combination of HPLC and ELISA was used to characterize N1 cell-derived OLI, showing that the highest peak of OLI had the same retention time as authentic ouabain. Thereafter, N1 cells were cultured with (1-10 μM) aldosterone, and supernatant was collected after 24 h of culture. In addition, N1 cells were cultured with 5 μM eplerenone, a mineralocorticoid receptor blocker, plus aldosterone. OLI was significantly increased in the supernatant of the cells cultured with 10 μM aldosterone (0.40±0.078 pmol/mg protein), and this increase was abolished by the addition of the aldosterone antagonist eplerenone (0.12±0.030 pmol/mg protein). These data suggest that the immortalized hypothalamic N1 cells secrete OLF and that aldosterone stimulates its secretion via mineralocorticoid receptors.

REVIEW: Oxytocin: Crossing the bridge between basic science and pharmacotherapy

Is oxytocin the hormone of happiness? Probably not. However, this small nine amino acid peptide is involved in a wide variety of physiological and pathological functions such as sexual activity, penile erection, ejaculation, pregnancy, uterus contraction, milk ejection, maternal behavior, osteoporosis, diabetes, cancer, social bonding, and stress, which makes oxytocin and its receptor potential candidates as targets for drug therapy. In this review, we address the issues of drug design and specificity and focus our discussion on recent findings on oxytocin and its heterotrimeric G protein‐coupled receptor OTR. In this regard, we will highlight the following topics: (i) the role of oxytocin in behavior and affectivity, (ii) the relationship between oxytocin and stress with emphasis on the hypothalamo–pituitary–adrenal axis, (iii) the involvement of oxytocin in pain regulation and nociception, (iv) the specific action mechanisms of oxytocin on intracellular Ca²⁺ in the hypothalamo neurohypophysial system (HNS) cell bodies, (v) newly generated transgenic rats tagged by a visible fluorescent protein to study the physiology of vasopressin and oxytocin, and (vi) the action of the neurohypophysial hormone outside the central nervous system, including the myometrium, heart and peripheral nervous system. As a short nine amino acid peptide, closely related to its partner peptide vasopressin, oxytocin appears to be ideal for the design of agonists and antagonists of its receptor. In addition, not only the hormone itself and its binding to OTR, but also its synthesis, storage and release can be endogenously and exogenously regulated to counteract pathophysiological states. Understanding the fundamental physiopharmacology of the effects of oxytocin is an important and necessary approach for developing a potential pharmacotherapy.

Oxytocin and vasopressin immunoreactive staining in the brains of Brandt's voles (Lasiopodomys brandtii) and greater long-tailed hamsters (Tscherskia triton)

Immunoreactive (ir) staining of the neuropeptides oxytocin (OT) and vasopressin (AVP) was performed in the brains of Brandt's voles (Lasiopodomys brandtii) and greater long-tailed hamsters (Tscherskia triton)-two species that differ remarkably in social behaviors. Social Brandt's voles had higher densities of OT-ir cells in the medial preoptic area (MPOA) and medial amygdala (MeA) as well as higher densities of AVP-ir cells in the lateral hypothalamus (LH) compared to solitary greater long-tailed hamsters. In contrast, the hamsters had higher densities of OT-ir cells in the anterior hypothalamus (AH) and LH and higher densities of AVP-ir cells in the MPOA than the voles. OT-ir and AVP-ir fibers were also found in many forebrain areas with subtle species differences. Given the roles of OT and AVP in the regulation of social behaviors in other rodent species, our data support the hypothesis that species-specific patterns of central OT and AVP pathways may underlie species differences in social behaviors. However, despite a higher density of OT-ir cells in the paraventricular nucleus of the hypothalamus (PVN) in females than in males in both species, no other sex differences were found in OT-ir or AVP-ir staining. These data failed to support our prediction that a sexually dimorphic pattern of neuropeptide staining in the brain is more apparent in Brandt's voles than in greater long-tailed hamsters.

Specific expression of an oxytocin-enhanced cyan fluorescent protein fusion transgene in the rat hypothalamus and posterior pituitary

We have generated rats bearing an oxytocin (OXT)-enhanced cyan fluorescent protein (eCFP) fusion transgene designed from a murine construct previously shown to be faithfully expressed in transgenic mice. In situ hybridisation histochemistry revealed that the Oxt-eCfp fusion gene was expressed in the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) in these rats. The fluorescence emanating from eCFP was observed only in the SON, the PVN, the internal layer of the median eminence and the posterior pituitary (PP). In in vitro preparations, freshly dissociated cells from the SON and axon terminals showed clear eCFP fluorescence. Immunohistochemistry for OXT and arginine vasopressin (AVP) revealed that the eCFP fluorescence co-localises with OXT immunofluorescence, but not with AVP immunofluorescence in the SON and the PVN. Although the expression levels of the Oxt-eCfp fusion gene in the SON and the PVN showed a wide range of variations in transgenic rats, eCFP fluorescence was markedly increased in the SON and the PVN, but decreased in the PP after chronic salt loading. The expression of the Oxt gene was significantly increased in the SON and the PVN after chronic salt loading in both non-transgenic and transgenic rats. Compared with wild-type animals, euhydrated and salt-loaded male and female transgenic rats showed no significant differences in plasma osmolality, sodium concentration and OXT and AVP levels, suggesting that the fusion gene expression did not disturb any physiological processes. These results suggest that our new transgenic rats are a valuable new tool to identify OXT-producing neurones and their terminals.

Robust up-regulation of nuclear red fluorescent-tagged fos marks neuronal activation in green fluorescent vasopressin neurons after osmotic stimulation in a double-transgenic rat

The up-regulation in the expression of mRNA or protein encoded by the c-fos gene is widely used as a marker of neuronal activation elicited by various stimuli. To facilitate the detection of activated neurons, we generated transgenic rats expressing a fusion gene consisting of c-fos coding sequences in frame with monomeric red fluorescent protein 1 (mRFP1) under the control of c-fos gene regulatory sequences (c-fos-mRFP1 rats). In c-fos-mRFP1 transgenic rats, 90 min after hypertonic saline ip administration, nuclear mRFP1 fluorescence was observed abundantly in brain regions known to be osmosensitive, namely the median preoptic nucleus, organum vasculosum lamina terminalis, supraoptic nucleus, paraventricular nucleus, and subfornical organ. Immunohistochemistry for Fos protein confirmed that the distribution of Fos-like immunoreactivity in nontransgenic rats was similar to those of mRFP1 fluorescence after ip administration of hypertonic saline in the transgenic rats. Several double-transgenic rats were obtained from matings between transgenic rats expressing an arginine vasopressin-enhanced green fluorescent protein fusion gene (AVP-eGFP rats) and c-fos-mRFP1 rats. In these double-transgenic rats, almost all eGFP neurons in the supraoptic nucleus and PVN expressed nuclear mRFP1 fluorescence 90 min after hypertonic saline administration. The c-fos-mRFP1 rats are a powerful tool that enables the facile identification of activated neurons in the nervous system. Furthermore, when combined with transgenes expressing another fluorophore under the control of cell-specific regulatory sequences, activation of specific neuronal cell types in response to physiological cues can be readily detected.

Oxytocin: the great facilitator of life

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

Characterization of the neurohypophysial hormone gene loci in elephant shark and the Japanese lamprey: origin of the vertebrate neurohypophysial hormone genes

BACKGROUND

Vasopressin and oxytocin are mammalian neurohypophysial hormones with distinct functions. Vasopressin is involved mainly in osmoregulation and oxytocin is involved primarily in parturition and lactation. Jawed vertebrates contain at least one homolog each of vasopressin and oxytocin, whereas only a vasopressin-family hormone, vasotocin, has been identified in jawless vertebrates. The genes encoding vasopressin and oxytocin are closely linked tail-to-tail in eutherian mammals whereas their homologs in chicken, Xenopus and coelacanth (vasotocin and mesotocin) are linked tail-to-head. In contrast, their pufferfish homologs, vasotocin and isotocin, are located on the same strand of DNA with isotocin located upstream of vasotocin and separated by five genes. These differences in the arrangement of the two genes in different bony vertebrate lineages raise questions about their origin and ancestral arrangement. To trace the origin of these genes, we have sequenced BAC clones from the neurohypophysial gene loci in a cartilaginous fish, the elephant shark (Callorhinchus milii), and in a jawless vertebrate, the Japanese lamprey (Lethenteron japonicum). We have also analyzed the neurohypophysial hormone gene locus in an invertebrate chordate, the amphioxus (Branchiostoma floridae).

RESULTS

The elephant shark neurohypophysial hormone genes encode vasotocin and oxytocin, and are linked tail-to-head like their homologs in coelacanth and non-eutherian tetrapods. Besides the hypothalamus, the two genes are also expressed in the ovary. In addition, the vasotocin gene is expressed in the kidney, rectal gland and intestine. These expression profiles indicate a paracrine role for the two hormones. The lamprey locus contains a single neurohypophysial hormone gene, the vasotocin. The synteny of genes in the lamprey locus is conserved in elephant shark, coelacanth and tetrapods but disrupted in teleost fishes. The amphioxus locus encodes a single neurohypophysial hormone, designated as [Ile4]vasotocin.

CONCLUSION

The vasopressin- and oxytocin-family of neurohypophysial hormones evolved in a common ancestor of jawed vertebrates through tandem duplication of the ancestral vasotocin gene. The duplicated genes were linked tail-to-head like their homologs in elephant shark, coelacanth and non-eutherian tetrapods. In contrast to the conserved linkage of the neurohypophysial genes in these vertebrates, the neurohypophysial hormone gene locus has experienced extensive rearrangements in the teleost lineage.

Fluorescent agonists and antagonists for vasopressin/oxytocin G protein-coupled receptors: usefulness in ligand screening assays and receptor studies

Different series of fluorescent agonists and antagonists have been developed and characterized for arginine-vasopressin and oxytocin G protein-coupled receptors. Both cyclic and linear peptide analogs of the neurohypophysial hormones are useful tools for investigating receptor localization and trafficking, analysing receptor structural organization, and developing new receptor-selective high-throughput ligand screening assays.

A conditional knockout mouse line of the oxytocin receptor

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

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

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

Sequence and organization of coelacanth neurohypophysial hormone genes: evolutionary history of the vertebrate neurohypophysial hormone gene locus

BACKGROUND

The mammalian neurohypophysial hormones, vasopressin and oxytocin are involved in osmoregulation and uterine smooth muscle contraction respectively. All jawed vertebrates contain at least one homolog each of vasopressin and oxytocin whereas jawless vertebrates contain a single neurohypophysial hormone called vasotocin. The vasopressin homolog in non-mammalian vertebrates is vasotocin; and the oxytocin homolog is mesotocin in non-eutherian tetrapods, mesotocin and [Phe2]mesotocin in lungfishes, and isotocin in ray-finned fishes. The genes encoding vasopressin and oxytocin genes are closely linked in the human and rodent genomes in a tail-to-tail orientation. In contrast, their pufferfish homologs (vasotocin and isotocin) are located on the same strand of DNA with isotocin gene located upstream of vasotocin gene separated by five genes, suggesting that this locus has experienced rearrangements in either mammalian or ray-finned fish lineage, or in both lineages. The coelacanths occupy a unique phylogenetic position close to the divergence of the mammalian and ray-finned fish lineages.

RESULTS

We have sequenced a coelacanth (Latimeria menadoensis) BAC clone encompassing the neurohypophysial hormone genes and investigated the evolutionary history of the vertebrate neurohypophysial hormone gene locus within a comparative genomics framework. The coelacanth contains vasotocin and mesotocin genes like non-mammalian tetrapods. The coelacanth genes are present on the same strand of DNA with no intervening genes, with the vasotocin gene located upstream of the mesotocin gene. Nucleotide sequences of the second exons of the two genes are under purifying selection implying a regulatory function. We have also analyzed the neurohypophysial hormone gene locus in the genomes of opossum, chicken and Xenopus tropicalis. The opossum contains two tandem copies of vasopressin and mesotocin genes. The vasotocin and mesotocin genes in chicken and Xenopus, and the vasopressin and mesotocin genes in opossum are linked tail-to-head similar to their orthologs in coelacanth and unlike their homologs in human and rodents.

CONCLUSION

Our results indicate that the neurohypophysial hormone gene locus has experienced independent rearrangements in both placental mammals and teleost fishes. The coelacanth genome appears to be more stable than mammalian and teleost fish genomes. As such, it serves as a valuable outgroup for studying the evolution of mammalian and teleost fish genomes.