Oxytocin transported from the blood across the blood-brain barrier by receptor for advanced glycation end-products (RAGE) affects brain function related to social behavior.

Oxytocin (OT) is a neuropeptide that primarily functions as a hormone controlling female reproductive processes. Since numerous recent studies have shown that single and repetitive administrations of OT increase trust, social interaction, and maternal behaviors in humans and animals, OT is considered a key molecule that regulates social memory and behavior. Furthermore, OT binds to receptors for advanced glycation end-products (RAGE), and it has been demonstrated that loss of RAGE in the brain vascular endothelial cells of mice fails to increase brain OT concentrations following peripheral OT administration. This leads to the hypothesis that RAGE is involved in the direct transport of OT, allowing it access to the brain by transporting it across the blood-brain barrier; however, this hypothesis is only based on limited evidence. Herein, we review the recent results related to this hypothesis, such as the mode of transport of OT in the blood circulation to the brain via different forms of RAGE, including membrane-bound full-length RAGE and soluble RAGE. We further review the modulation of brain function and social behavior, which seem to be mediated by RAGE-dependent OT. Overall, this review mostly confirms that RAGE enables the recruitment of circulating OT to the brain, thereby influencing social behavior. The requirement for further studies considering the physiological aspects of RAGE is also discussed.

Biosynthesis and Function of VIP and Oxytocin: Mechanisms of C-terminal Amidation, Oxytocin Secretion and Transport.

In this review, we provide the status of research on vasoactive intestinal peptide (VIP) and oxytocin, typical C-terminal α-amidated peptide hormones, including their precursor protein structures, processing and C-terminal α-amidation, and the recently identified mechanisms of regulation of oxytocin secretion and its transportation through the blood brain barrier. More than half of neural and endocrine peptides, such as VIP and oxytocin, have the α-amide structure at their C-terminus, which is essential for biological activities. We have studied the synthesis and function of C-terminal α-amidated peptides, including VIP and oxytocin, since the 1980s. Human VIP mRNA encoded not only VIP but also another related C-terminal α-amidated peptide, PHM-27 (peptide having amino-terminal histidine, carboxy-terminal methionine amide, and 27 amino acid residues). The human VIP/PHM-27 gene is composed of 7 exons and regulated synergistically by cyclic AMP and protein kinase C pathways. VIP has an essential role in glycemic control using transgenic mouse technology. The peptide C-terminal α-amidation proceeded through a 2-step mechanism catalyzed by 2 different enzymes encoded in a single mRNA. In the oxytocin secretion from the hypothalamus/the posterior pituitary, the CD38-cyclic ADP-ribose signal system, which was first established in the insulin secretion from pancreatic ß cells of the islets of Langerhans, was found to be essential. A possible mechanism involving RAGE (receptor for advanced glycation end-products) of the oxytocin transportation from the blood stream into the brain through the blood-brain barrier has also been suggested.

Postnatal expression of CD38 in astrocytes regulates synapse formation and adult social memory.

Social behavior is essential for health, survival, and reproduction of animals; however, the role of astrocytes in social behavior remains largely unknown. The transmembrane protein CD38, which acts both as a receptor and ADP-ribosyl cyclase to produce cyclic ADP-ribose (cADPR) regulates social behaviors by promoting oxytocin release from hypothalamic neurons. CD38 is also abundantly expressed in astrocytes in the postnatal brain and is important for astroglial development. Here, we demonstrate that the astroglial-expressed CD38 plays an important role in social behavior during development. Selective deletion of CD38 in postnatal astrocytes, but not in adult astrocytes, impairs social memory without any other behavioral abnormalities. Morphological analysis shows that depletion of astroglial CD38 in the postnatal brain interferes with synapse formation in the medial prefrontal cortex (mPFC) and hippocampus. Moreover, astroglial CD38 expression promotes synaptogenesis of excitatory neurons by increasing the level of extracellular SPARCL1 (also known as Hevin), a synaptogenic protein. The release of SPARCL1 from astrocytes is regulated by CD38/cADPR/calcium signaling. These data demonstrate a novel developmental role of astrocytes in neural circuit formation and regulation of social behavior in adults.

Remission of social behavior impairment by oral administration of a precursor of NAD in CD157, but not in CD38, knockout mice.

Nicotinamide adenine dinucleotide (NAD) is a substrate of adenosine diphosphate (ADP)-ribosyl cyclase and is catalyzed to cyclic ADP-ribose (cADPR) by CD38 and/or CD157. cADPR, a Ca2+ mobilizing second messenger, is critical in releasing oxytocin from the hypothalamus into the brain. Although NAD precursors effectively play a role in neurodegenerative disorders, muscular dystrophy, and senescence, the beneficial effects of elevating NAD by NAD precursor supplementation on brain function, especially social interaction, and whether CD38 is required in this response, has not been intensely studied. Here, we report that oral gavage administration of nicotinamide riboside, a perspective NAD precursor with high bioavailability, for 12 days did not show any suppressive or increasing effects on sociability (mouse's interest in social targets compared to non-social targets) in both CD157KO and CD38KO male mice models in a three-chamber test. CD157KO and CD38KO mice displayed no social preference (that is, more interest towards a novel mouse than a familiar one) behavior. This defect was rescued after oral gavage administration of nicotinamide riboside for 12 days in CD157KO mice, but not in CD38KO mice. Social memory was not observed in CD157KO and CD38KO mice; subsequently, nicotinamide riboside administration had no effect on social memory. Together with the results that nicotinamide riboside had essentially no or little effect on body weight during treatment in CD157KO mice, nicotinamide riboside is less harmful and has beneficial effect on defects in recovery from social behavioral, for which CD38 is required in mice.

Oral Supplementation with Maca Improves Social Recognition Deficits in the Valproic Acid Animal Model of Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a congenital, lifelong neurodevelopmental disorder whose main symptom is impaired social communication and interaction. However, no drug can treat social deficits in patients with ASD, and treatments to alleviate social behavioral deficits are sorely needed. Here, we examined the effect of oral supplementation of maca (Lepidium meyenii) on social deficits of in utero-exposed valproic acid (VPA) mice, widely used as an ASD model. Although maca is widely consumed as a fertility enhancer and aphrodisiac, it possesses multiple beneficial activities. Additionally, it benefits learning and memory in experimental animal models. Therefore, the effect of maca supplementation on the social behavioral deficit of VPA mice was assessed using a social interaction test, a three-stage open field test, and a five-trial social memory test. The oral supplementation of maca attenuated social interaction behavior deficit and social memory impairment. The number of c-Fos-positive cells and the percentage of c-Fos-positive oxytocin neurons increased in supraoptic and paraventricular neurons of maca-treated VPA mice. These results reveal for the first time that maca is beneficial to social memory and that it restores social recognition impairments by augmenting the oxytocinergic neuronal pathways, which play an essential role in diverse social behaviors.

Two oxytocin analogs, N-(p-fluorobenzyl) glycine and N-(3-hydroxypropyl) glycine, induce uterine contractions ex vivo in ways that differ from that of oxytocin.

Contraction of the uterus is critical for parturient processes. Insufficient uterine tone, resulting in atony, can potentiate postpartum hemorrhage; thus, it is a major risk factor and is the main cause of maternity-related deaths worldwide. Oxytocin (OT) is recommended for use in combination with other uterotonics for cases of refractory uterine atony. However, as the effect of OT dose on uterine contraction and control of blood loss during cesarean delivery for labor arrest are highly associated with side effects, small amounts of uterotonics may be used to elicit rapid and superior uterine contraction. We have previously synthesized OT analogs 2 and 5, prolines at the 7th positions of which were replaced with N-(p-fluorobenzyl) glycine [thus, compound 2 is now called fluorobenzyl (FBOT)] or N-(3-hydroxypropyl) glycine [compound 5 is now called hydroxypropyl (HPOT)], which exhibited highly potent binding affinities for human OT receptors in vitro. In this study, we measured the ex vivo effects of FBOT and HPOT on contractions of uteri isolated from human cesarean delivery samples and virgin female mice. We evaluated the potency and efficacy of the analogs on uterine contraction, additivity with OT, and the ability to overcome the effects of atosiban, an OT antagonist. In human samples, the potency rank judged by the calculated EC50 (pM) was as follows: HPOT (189) > FBOT (556) > OT (5,340) > carbetocin (12,090). The calculated Emax was 86% for FBOT and 75% for HPOT (100%). Recovery from atosiban inhibition after HPOT treatment was as potent as that after OT treatment. HPOT showed additivity with OT. FBOT (56 pM) was found to be the strongest agonist in virgin mouse uterus. HPOT and FBOT demonstrated high potency and partial agonist efficacy in the human uterus. These results suggested that HPOT and FBOT are highly uterotonic for the human uterus and performed better than OT, indicating that they may prevent postpartum hemorrhage.

Infant Stimulation Induced a Rapid Increase in Maternal Salivary Oxytocin.

Oxytocin (OT) is a neuropeptide involved in human social behaviors and reproduction. Non-invasive OT levels in saliva have recently roused interest as it does not require a specialized medical setting. Here, we observed one woman's basal serum and saliva OT from pregnancy to 1 year postpartum to track OT concentration changes over this period. We examined the changes in salivary OT levels over time in response to maternal physiological and behavioral responses. The fluctuation of saliva OT levels is well correlated with serum OT during pregnancy and breastfeeding. However, while salivary OT increased rapidly during direct interaction (social interaction tests) with the infant and/or when the mother was watching her own infant's video (video tests), no increase was observed in serum. We used social interaction and video tests on a group of mothers (nine mothers for social interaction and six for the video test) to clarify these single-subject results. In both tests, the mothers had increased OT in their saliva but not serum. Our study may suggest that salivary samples reflect not only the physical but also the emotional state and that saliva samples may be useful for monitoring women's OT levels during pre- and postpartum periods. Further studies with larger sample numbers are necessary to confirm the rapid changes in salivary OT levels in response to maternal physiological and behavioral responses.

Receptor for advanced glycation end-products and child neglect in mice: A possible link to postpartum depression.

The receptor for advanced glycation end-products (RAGE), a pattern recognition molecule, has a role in the remodeling of vascular endothelial cells mainly in lungs, kidney and brain under pathological conditions. We recently discovered that RAGE binds oxytocin (OT) and transports it to the brain from circulation on neurovascular endothelial cells. We produced knockout mice of the mouse homologue of the human RAGE gene, Ager, designated RAGE KO mice. In RAGE KO mice, while hyperactivity has been reported in male mice, maternal behavior was impaired in female mice. After an additional stress, deficits in pup care were observed in RAGE KO mother mice. This resulted in pup death within 1-2 days, suggesting that RAGE plays a critical role during the postpartum period. Thus, RAGE seems to be important in the manifestation of normal maternal behavior in dams. In this review, we summarize the significance of brain OT transport by RAGE and propose that RAGE-dependent OT can dampen stress signals during pregnancy, delivery and early postpartum periods. To the best of our knowledge, there have been no previous articles on these RAGE-dependent results. Based on these results in mice, we discuss a potential critical role of RAGE in emotion swings at the puerperium (peripartum) and postpartum periods in women.

Early-onset of social communication and locomotion activity in F2 pups of a valproic acid-induced mouse model of autism.

Autism spectrum disorder (ASD) is a heterogeneously pervasive developmental disorder that usually occurs before 3 years old. Animal models of psychiatric disorders are essential for elucidating the underlying preclinical neural mechanisms. Mice that are prenatally exposed to valproic acid (VPA, F1) are widely used as an ASD model. Epigenetics has recently been suggested as a contributor to ASD etiology with the hypothesis that epigenetic marks can be transgenerationally inherited. Previous studies have indicated that autism-like behavioral phenotypes detected in F1 VPA mice transgenetically appear in F2 and F3 generations. However, studies on the autism-like behavioral phenotypes during the early postnatal days in subsequent generations are scarce. Here, the behavioral deficit on postnatal day 5 of the F2 generation was examined to assess the onset of ASD symptoms. Communication disorders were examined by analyzing maternal separation-induced ultrasonic vocalizations (USVs). Although the duration and frequency of USVs were not significantly altered, the emission rate was significantly lower in F2 VPA pups. Furthermore, the locomotive activity with or without littermates was altered in F2 VPA pups. The data of the current study suggest that social deficit and impaired locomotion are inherited by the subsequent generation and were apparent on early postnatal day 5.

Oxytocin Dynamics in the Body and Brain Regulated by the Receptor for Advanced Glycation End-Products, CD38, CD157, and Nicotinamide Riboside.

Investigating the neurocircuit and synaptic sites of action of oxytocin (OT) in the brain is critical to the role of OT in social memory and behavior. To the same degree, it is important to understand how OT is transported to the brain from the peripheral circulation. To date, of these, many studies provide evidence that CD38, CD157, and receptor for advanced glycation end-products (RAGE) act as regulators of OT concentrations in the brain and blood. It has been shown that RAGE facilitates the uptake of OT in mother's milk from the digestive tract to the cell surface of intestinal epithelial cells to the body fluid and subsequently into circulation in male mice. RAGE has been shown to recruit circulatory OT into the brain from blood at the endothelial cell surface of neurovascular units. Therefore, it can be said that extracellular OT concentrations in the brain (hypothalamus) could be determined by the transport of OT by RAGE from the circulation and release of OT from oxytocinergic neurons by CD38 and CD157 in mice. In addition, it has recently been found that gavage application of a precursor of nicotinamide adenine dinucleotide, nicotinamide riboside, for 12 days can increase brain OT in mice. Here, we review the evaluation of the new concept that RAGE is involved in the regulation of OT dynamics at the interface between the brain, blood, and intestine in the living body, mainly by summarizing our recent results due to the limited number of publications on related topics. And we also review other possible routes of OT recruitment to the brain.

Mitochondrial LETM1 drives ionic and molecular clock rhythms in circadian pacemaker neurons.

The mechanisms that generate robust ionic oscillation in circadian pacemaker neurons are under investigation. Here, we demonstrate critical functions of the mitochondrial cation antiporter leucine zipper-EF-hand-containing transmembrane protein 1 (LETM1), which exchanges K+/H+ in Drosophila and Ca2+/H+ in mammals, in circadian pacemaker neurons. Letm1 knockdown in Drosophila pacemaker neurons reduced circadian cytosolic H+ rhythms and prolonged nuclear PERIOD/TIMELESS expression rhythms and locomotor activity rhythms. In rat pacemaker neurons in the hypothalamic suprachiasmatic nucleus (SCN), circadian rhythms in cytosolic Ca2+ and Bmal1 transcription were dampened by Letm1 knockdown. Mitochondrial Ca2+ uptake peaks late during the day were also observed in rat SCN neurons following photolytic elevation of cytosolic Ca2+. Since cation transport by LETM1 is coupled to mitochondrial energy synthesis, we propose that LETM1 integrates metabolic, ionic, and molecular clock rhythms in the central clock system in both invertebrates and vertebrates.

Oral Supplementation with L-Carnosine Attenuates Social Recognition Deficits in CD157KO Mice via Oxytocin Release.

The outcomes of supplementation with L-carnosine have been investigated in clinical trials in children with autism spectrum disorder (ASD). However, reports on the effects of L-carnosine in humans have been inconsistent, and the efficacy of L-carnosine supplementation for improving ASD symptoms has yet to be investigated in animal studies. Here, we examined the effects of oral supplementation with L-carnosine on social deficits in CD157KO mice, a murine model of ASD. Social deficits in CD157KO mice were assessed using a three-chamber social approach test. Oral supplementation with L-carnosine attenuated social behavioral deficits. The number of c-Fos-positive oxytocin neurons in the supraoptic nucleus and paraventricular nucleus was increased with L-carnosine supplementation in CD157KO mice after the three-chamber social approach test. We observed an increase in the number of c-Fos-positive neurons in the basolateral amygdala, a brain region involved in social behavior. Although the expression of oxytocin and oxytocin receptors in the hypothalamus was not altered by L-carnosine supplementation, the concentration of oxytocin in cerebrospinal fluid was increased in CD157KO mice by L-carnosine supplementation. These results suggest that L-carnosine supplementation restores social recognition impairments by augmenting the level of released oxytocin. Thus, we could imply the possibility of a safe nutritional intervention for at least some types of ASD in the human population.

Dual Nature of RAGE in Host Reaction and Nurturing the Mother-Infant Bond.

Non-enzymatic glycation is an unavoidable reaction that occurs across biological taxa. The final products of this irreversible reaction are called advanced glycation end-products (AGEs). The endogenously formed AGEs are known to be bioactive and detrimental to human health. Additionally, exogenous food-derived AGEs are debated to contribute to the development of aging and various diseases. Receptor for AGEs (RAGE) is widely known to elicit biological reactions. The binding of RAGE to other ligands (e.g., high mobility group box 1, S100 proteins, lipopolysaccharides, and amyloid-ß) can result in pathological processes via the activation of intracellular RAGE signaling pathways, including inflammation, diabetes, aging, cancer growth, and metastasis. RAGE is now recognized as a pattern-recognition receptor. All mammals have RAGE homologs; however, other vertebrates, such as birds, amphibians, fish, and reptiles, do not have RAGE at the genomic level. This evidence from an evolutionary perspective allows us to understand why mammals require RAGE. In this review, we provide an overview of the scientific knowledge about the role of RAGE in physiological and pathological processes. In particular, we focus on (1) RAGE biology, (2) the role of RAGE in physiological and pathophysiological processes, (3) RAGE isoforms, including full-length membrane-bound RAGE (mRAGE), and the soluble forms of RAGE (sRAGE), which comprise endogenous secretory RAGE (esRAGE) and an ectodomain-shed form of RAGE, and (4) oxytocin transporters in the brain and intestine, which are important for maternal bonding and social behaviors.

Use of Cocultures to Measure the Blood-Brain Barrier Permeability of Oxytocin.

Primary monkey brain capillary endothelial cell cultures, with rat pericytes and astrocytes, provide an assay system for predicting the ability of oxytocin (OT) to cross the blood-brain barrier (BBB), using a commercially available in vitro BBB kit. The integrity of the in vitro "BBB," which has a high transendothelial electrical resistance (TEER), can be established approximately 4 days after preparations for experiments. Dominant endothelial transport of OT is from the upper (luminal blood side) to lower (abluminal brain side) chambers, dose-dependently. OT is transported by the receptor for advanced glycation end-products (RAGE) in endothelial cells, which is evidenced using the RAGE knockdown system with short hairpin RNA (shRNA) treatment. This in vitro assay system is useful for further assessment of OT transport across the BBB.

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.

A huggable device can reduce the stress of calling an unfamiliar person on the phone for individuals with ASD.

Individuals with autism spectrum disorders (ASD) are often not comfortable during mobile-phone conversations with unfamiliar people. "Hugvie" is a pillow with a human-like shape that has been designed to provide users with the tactile sensation of hugging another person during phone conversations to promote feelings of comfort and trust in the speaker toward their conversation partners. Our primary aim was to examine whether physical contact by hugging a Hugvie could reduce the stress of speaking with an unfamiliar person on the phone in individuals with ASD. We enrolled 24 individuals and requested them to carry out phone conversations either using only a mobile phone or using a mobile phone along with the Hugvie. All participants in both groups completed questionnaires designed to evaluate their self-confidence while talking on the phone, and also provided salivary cortisol samples four times each day. Our analysis revealed that the medium of communication was a significant factor, indicating that individuals with ASD who spoke with an unfamiliar person on the phone while hugging a Hugvie had stronger self-confidence and lower stress levels than those who did not use Hugvie. Hence, we recommend that huggable devices be used as adjunctive tools to support individuals with ASD during telephonic conversations with unfamiliar people.

Oxytocin-Trust Link in Oxytocin-Sensitive Participants and Those Without Autistic Traits.

There have been numerous studies in which the biological role of oxytocin in trusting behavior has been investigated. However, a link between oxytocin and trust in humans was discovered only in one early study. We hypothesized that there is a large interindividual variation in oxytocin sensitivity, and that such variation is one reason for the doubt surrounding the role of oxytocin in trusting behavior. Here, in a double-blind, prospective, case-control study, we administered intranasal oxytocin to participants of trust and risk games. We measured salivary oxytocin concentration, relating it to the amount of money transferred among participants (a proxy for trust) and the autism-spectrum quotient (AQ). A one-sided Fisher's exact test was performed to detect differences between the oxytocin and placebo groups in the proportions of investors who transferred the maximum amount of money. We discovered a tendency for participants who received oxytocin to transfer higher amounts of money to co-participants than those who received a placebo (P = 0.04). We also revealed a high degree of interindividual variation in salivary oxytocin concentrations after oxytocin administration. After stratifying the samples with respect to oxytocin sensitivity, oxytocin-sensitive participants in the oxytocin group also transferred higher amounts of money than those in the placebo group (P = 0.03), while such a tendency was not observed for oxytocin-insensitive participants (P = 0.34). Participants with lower AQ scores (less severe autistic traits) exhibited a greater tendency toward trusting behavior after oxytocin administration than did those with higher AQ scores (P = 0.02). A two-sample t-test that was performed to detect significant differences in the mean transfers between the oxytocin and placebo groups indicated no significant between-group difference in the mean transfers (P = 0.08). There are two possible interpretations of these results: First, there is no effect of oxytocin on trust in humans; second, the effects of oxytocin on trust in humans is person-dependent. However, the results should be interpreted with caution as the effect size was not larger than the minimal detectable effect size and the results were not statistically significant (P > 0.05) after Bonferroni corrections.

Oxytocin ameliorates impaired social behavior in a Chd8 haploinsufficiency mouse model of autism.

BACKGROUND: Autism spectrum disorder (ASD) is characterized by the core symptoms of impaired social interactions. Increasing evidence suggests that ASD has a strong genetic link with mutations in chromodomain helicase DNA binding protein 8 (CHD8), a gene encoding a chromatin remodeler. It has previously been shown that Chd8 haplodeficient male mice manifest ASD-like behavioral characteristics such as anxiety and altered social behavior. Along with that, oxytocin (OT) is one of the main neuropeptides involved in social behavior. Administration of OT has shown improvement of social behavior in genetic animal models of ASD. The present study was undertaken to further explore behavioral abnormalities of Chd8 haplodeficient mice of both sexes, their link with OT, and possible effects of OT administration. First, we performed a battery of behavioral tests on wild-type and Chd8+/∆SL female and male mice. Next, we measured plasma OT levels and finally studied the effects of intraperitoneal OT injection on observed behavioral deficits. RESULTS: We showed general anxiety phenotype in Chd8+/∆SL mice regardless of sex, the depressive phenotype in Chd8+/∆SL female mice only and bidirectional social deficit in female and male mice. We observed decreased level of OT in Chd+/∆SL mice, possibly driven by males. Mice injected by OT demonstrated recovery of social behavior, while reduced anxiety was observed only in male mice. CONCLUSIONS: Here, we demonstrated that abnormal social behaviors were observed in both male and female Chd8+/∆SL mice. The ability of peripheral OT administration to affect such behaviors along with altered plasma OT levels indicated a possible link between Chd8 + /∆SL and OT in the pathogenesis of ASD as well as the possible usefulness of OT as a therapeutic tool for ASD patients with CHD8 mutations.

Inhibition of CD38 and supplementation of nicotinamide riboside ameliorate lipopolysaccharide-induced microglial and astrocytic neuroinflammation by increasing NAD.

Neuroinflammation is initiated by activation of the brain's innate immune system in response to an inflammatory challenge. Insufficient control of neuroinflammation leads to enhanced or prolonged pathology in various neurological conditions including multiple sclerosis and Alzheimer's disease. Nicotinamide adenine dinucleotide (NAD+ ) plays critical roles in cellular energy metabolism and calcium homeostasis. Our previous study demonstrated that deletion of CD38, which consumes NAD+ , suppressed cuprizone-induced demyelination, neuroinflammation, and glial activation. However, it is still unknown whether CD38 directly affects neuroinflammation through regulating brain NAD+ level. In this study, we investigated the effect of CD38 deletion and inhibition and supplementation of NAD+ on lipopolysaccharide (LPS)-induced neuroinflammation in mice. Intracerebroventricular injection of LPS significantly increased CD38 expression especially in the hippocampus. Deletion of CD38 decreased LPS-induced inflammatory responses and glial activation. Pre-administration of apigenin, a flavonoid with CD38 inhibitory activity, or nicotinamide riboside (NR), an NAD+ precursor, increased NAD+ level, and significantly suppressed induction of cytokines and chemokines, glial activation and subsequent neurodegeneration after LPS administration. In cell culture, LPS-induced inflammatory responses were suppressed by treatment of primary astrocytes or microglia with apigenin, NAD+ , NR or 78c, the latter a specific CD38 inhibitor. Finally, all these compounds suppressed NF-κB signaling pathway in microglia. These results suggest that CD38-mediated neuroinflammation is linked to NAD+ consumption and that boosting NAD+ by CD38 inhibition and NR supplementation directly suppress neuroinflammation in the brain.

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.