Effects of intraperitoneal and intracerebroventricular injections of oxytocin on social and emotional behaviors in pubertal male mice

Oxytocin effects on socially transmitted food preferences are moderated by familiarity between rats

RATIONALE

In the socially transmitted food preference (STFP) paradigm, rats change their preference for food rewards after socially interacting with a conspecific who has been fed with the originally non-preferred food. Here, we asked if oxytocin (OXT), a neuropeptide known for its role in social affiliation and social behavior, plays a role in STFP. Since OXT's influences on social behavior can be familiarity-dependent, we further asked if OXT effects on STFP are moderated by the familiarity between rats.

OBJECTIVES

Does OXT modulate rats' socially transmitted food choices in a familiarity-dependent way.

METHODS

We systemically injected either vehicle, low-dose (0.25 mg/kg) of OXT, or large-dose (1.0 mg/kg) of OXT before social interaction with either a familiar cagemate (in-group) or an unfamiliar conspecific from a different cage (out-group).

RESULTS

We found an intergroup bias in STFP: vehicle-treated rats showed larger socially transmitted changes in food preference in the out-group than the in-group condition. OXT modulated STFP in a familiarity-dependent way: OXT prevented the increase in the consumption of the non-preferred food in the out-group, and decreased the consumption of the preferred food in the in-group. These effects were dose-dependent and observed under acute OXT action, but also on the subsequent day when acute OXT effects dissipated, suggesting long-lasting social learning effects of OXT. Additional analyses suggest that the familiarity and dose-dependent effects of OXT on STFP cannot be attributed to OXT's anorexic actions or differences in the duration of the social interactions.

CONCLUSIONS

OXT modulates STFP in a familiarity-dependent way.

Sympathetic innervation of interscapular brown adipose tissue is not a predominant mediator of OT-elicited reductions of body weight gain and adiposity in male diet-induced obese rats

Recent studies indicate that central administration of oxytocin (OT) reduces body weight (BW) in high fat diet-induced obese (DIO) rodents by reducing energy intake and increasing energy expenditure (EE). Previous studies in our lab have shown that administration of OT into the fourth ventricle (4V; hindbrain) elicits weight loss and stimulates interscapular brown adipose tissue temperature (T IBAT ) in DIO rats. We hypothesized that OT-elicited stimulation of sympathetic nervous system (SNS) activation of IBAT contributes to its ability to activate BAT and reduce BW in DIO rats. To test this, we determined the effect of disrupting SNS activation of IBAT on OT-elicited stimulation of T IBAT and reduction of BW in DIO rats. We first confirmed that bilateral surgical SNS denervation to IBAT was successful based on having achieved ≥ 60% reduction in IBAT norepinephrine (NE) content from DIO rats. NE content was selectively reduced in IBAT by 94.7 ± 2.7, 96.8 ± 1.8 and 85.9 ± 6.1% ( P <0.05) at 1, 6 and 7-weeks post-denervation, respectively, and was unchanged in liver or inguinal white adipose tissue. We then measured the impact of bilateral surgical SNS denervation to IBAT on the ability of acute 4V OT (1, 5 µg) to stimulate T IBAT in DIO rats. We found that the high dose of 4V OT (5 µg) stimulated T IBAT similarly between sham and denervated rats ( P =NS) and that the effects of 4V OT to stimulate T IBAT did not require beta-3 adrenergic receptor signaling. We subsequently measured the effect of bilateral surgical denervation of IBAT on the effect of chronic 4V OT (16 nmol/day) or vehicle infusion to reduce BW, adiposity and energy intake in DIO rats. Chronic 4V OT reduced BW gain by -7.2 ± 9.6 g and -14.1 ± 8.8 g in sham and denervated rats ( P <0.05 vs vehicle treatment), respectively, and this effect was similar between groups ( P =NS). These effects were associated with reductions in adiposity and energy intake ( P <0.05). Collectively, these findings support the hypothesis that sympathetic innervation of IBAT is not required for central OT to increase BAT thermogenesis and reduce BW gain and adiposity in male DIO rats.

Sympathetic innervation of interscapular brown adipose tissue is not a predominant mediator of oxytocin-elicited reductions of body weight and adiposity in male diet-induced obese mice

Previous studies indicate that CNS administration of oxytocin (OT) reduces body weight in high fat diet-induced obese (DIO) rodents by reducing food intake and increasing energy expenditure (EE). We recently demonstrated that hindbrain (fourth ventricular [4V]) administration of OT elicits weight loss and elevates interscapular brown adipose tissue temperature (TIBAT, a surrogate measure of increased EE) in DIO mice. What remains unclear is whether OT-elicited weight loss requires increased sympathetic nervous system (SNS) outflow to IBAT. We hypothesized that OT-induced stimulation of SNS outflow to IBAT contributes to its ability to activate BAT and elicit weight loss in DIO mice. To test this hypothesis, we determined the effect of disrupting SNS activation of IBAT on the ability of 4V OT administration to increase TIBAT and elicit weight loss in DIO mice. We first determined whether bilateral surgical SNS denervation to IBAT was successful as noted by ≥ 60% reduction in IBAT norepinephrine (NE) content in DIO mice. NE content was selectively reduced in IBAT at 1-, 6- and 7-weeks post-denervation by 95.9 ± 2.0, 77.4 ± 12.7 and 93.6 ± 4.6% (P<0.05), respectively and was unchanged in inguinal white adipose tissue, pancreas or liver. We subsequently measured the effects of acute 4V OT (1, 5 µg ≈ 0.99, 4.96 nmol) on TIBAT in DIO mice following sham or bilateral surgical SNS denervation to IBAT. We found that the high dose of 4V OT (5 µg ≈ 4.96 nmol) elevated TIBAT similarly in sham mice as in denervated mice. We subsequently measured the effects of chronic 4V OT (16 nmol/day over 29 days) or vehicle infusions on body weight, adiposity and food intake in DIO mice following sham or bilateral surgical denervation of IBAT. Chronic 4V OT reduced body weight by 5.7 ± 2.23% and 6.6 ± 1.4% in sham and denervated mice (P<0.05), respectively, and this effect was similar between groups (P=NS). OT produced corresponding reductions in whole body fat mass (P<0.05). Together, these findings support the hypothesis that sympathetic innervation of IBAT is not necessary for OT-elicited increases in BAT thermogenesis and reductions of body weight and adiposity in male DIO mice.

Loss of Mitochondrial Tusc2/Fus1 Triggers a Brain Pro-Inflammatory Microenvironment and Early Spatial Memory Impairment

Brain pathological changes impair cognition early in disease etiology. There is an urgent need to understand aging-linked mechanisms of early memory loss to develop therapeutic strategies and prevent the development of cognitive impairment. Tusc2 is a mitochondrial-resident protein regulating Ca2+ fluxes to and from mitochondria impacting overall health. We previously reported that Tusc2-/- female mice develop chronic inflammation and age prematurely, causing age- and sex-dependent spatial memory deficits at 5 months old. Therefore, we investigated Tusc2-dependent mechanisms of memory impairment in 4-month-old mice, comparing changes in resident and brain-infiltrating immune cells. Interestingly, Tusc2-/- female mice demonstrated a pro-inflammatory increase in astrocytes, expression of IFN-γ in CD4+ T cells and Granzyme-B in CD8+T cells. We also found fewer FOXP3+ T-regulatory cells and Ly49G+ NK and Ly49G+ NKT cells in female Tusc2-/- brains, suggesting a dampened anti-inflammatory response. Moreover, Tusc2-/- hippocampi exhibited Tusc2- and sex-specific protein changes associated with brain plasticity, including mTOR activation, and Calbindin and CamKII dysregulation affecting intracellular Ca2+ dynamics. Overall, the data suggest that dysregulation of Ca2+-dependent processes and a heightened pro-inflammatory brain microenvironment in Tusc2-/- mice could underlie cognitive impairment. Thus, strategies to modulate the mitochondrial Tusc2- and Ca2+- signaling pathways in the brain should be explored to improve cognitive health.

Paraventricular nucleus-central amygdala oxytocinergic projection modulates pain-related anxiety-like behaviors in mice

AIMS

Anxiety disorders associated with pain are a common health problem. However, the underlying mechanisms remain poorly understood. We aimed to investigate the role of paraventricular nucleus (PVN)-central nucleus of the amygdala (CeA) oxytocinergic projections in anxiety-like behaviors induced by inflammatory pain.

METHODS

After inflammatory pain induction by complete Freund's adjuvant (CFA), mice underwent elevated plus maze, light-dark transition test, and marble burying test to examine the anxiety-like behaviors. Chemogenetic, optogenetic, and fiber photometry recordings were used to modulate and record the activity of the oxytocinergic projections of the PVN-CeA.

RESULTS

The key results are as follows: inflammatory pain-induced anxiety-like behaviors in mice accompanied by decreased activity of PVN oxytocin neurons. Chemogenetic activation of PVN oxytocin neurons prevented pain-related anxiety-like behaviors, whereas inhibition of PVN oxytocin neurons induced anxiety-like behaviors in naïve mice. PVN oxytocin neurons projected directly to the CeA, and microinjection of oxytocin into the CeA blocked anxiety-like behaviors. Inflammatory pain also decreased the activity of CeA neurons, and optogenetic activation of PVNoxytocin -CeA circuit prevented anxiety-like behavior in response to inflammatory pain.

CONCLUSION

The results of our study suggest that oxytocin has anti-anxiety effects and provide novel insights into the role of PVNoxytocin -CeA projections in the regulation of anxiety-like behaviors induced by inflammatory pain.

Prefrontal cortex is necessary for long-term social recognition memory in mice

The prefrontal cortex (PFC) plays critical roles in social cognition and emotional regulation in humans and rodents; however, its involvement in social recognition memory in mice remains unclear. Here, we examined the roles of the PFC in short-term and long-term social recognition memory, social motivation, and anxiety-related behavior in C57BL/6J male mice. Sham control and PFC-lesioned mice underwent four different behavioral tests. In the social recognition test, composed of three daily trials over 3 consecutive days, the control mice spent less time investigating the juvenile stimulus mouse both within each day and across days. By contrast, while social investigation behavior in PFC-lesioned mice decreased across the three trials within each day, it did not decrease over the 3-day testing period. These results indicate that the PFC has an important role in long-term, but not short-term, social recognition memory. The control and PFC-lesioned mice exhibited similar social motivation in the three-chamber test - both groups preferred the juvenile mouse to the empty cylinder and did not prefer the adult mouse. In addition, the PFC lesion had no impact on anxiety-related behavior or general activity in the light-dark transition test or the open field test. Our findings demonstrate that the PFC is essential for long-term social recognition memory and that it plays a critical role in higher-order social cognition.

Effects of Intranasal Administration of Oxytocin and Vasopressin on Social Cognition and Potential Routes and Mechanisms of Action

Acute and chronic administration of intranasal oxytocin and vasopressin have been extensively utilized in both animal models and human preclinical and clinical studies over the last few decades to modulate various aspects of social cognition and their underlying neural mechanisms, although effects are not always consistent. The use of an intranasal route of administration is largely driven by evidence that it permits neuropeptides to penetrate directly into the brain by circumventing the blood-brain barrier, which has been considered relatively impermeable to them. However, this interpretation has been the subject of considerable debate. In this review, we will focus on research in both animal models and humans, which investigates the different potential routes via which these intranasally administered neuropeptides may be producing their various effects on social cognition. We will also consider the contribution of different methods of intranasal application and additionally the importance of dose magnitude and frequency for influencing G protein-coupled receptor signaling and subsequent functional outcomes. Overall, we conclude that while some functional effects of intranasal oxytocin and vasopressin in the domain of social cognition may result from direct penetration into the brain following intranasal administration, others may be contributed by the neuropeptides either entering the peripheral circulation and crossing the blood-brain barrier and/or producing vagal stimulation via peripheral receptors. Furthermore, to complicate matters, functional effects via these routes may differ, and both dose magnitude and frequency can produce very different functional outcomes and therefore need to be optimized to produce desired effects.

Oxytocin receptor disruption in Avil-expressing cells results in blunted sociability and increased inter-male aggression

Social behaviors are foundational to society and quality of life while social behavior extremes are core symptoms in a variety of psychopathologies and developmental disabilities. Oxytocin (OXT) is a neuroactive hormone that regulates social behaviors through its receptor (OXTR), with all previously identified social behavior effects attributed to the central nervous system, which has developmental origins in the neural tube. However, OXTR are also present in neural crest-derived tissue including sensory ganglia of the peripheral nervous system. Avil encodes for the actin-binding protein ADVILLIN, is expressed in neural crest-derived cells, and was therefore used as a target in this study to knock out OXTR expression in neural-crest derived cells. Here, we tested if OXTRs specifically expressed in Avil positive neural crest-derived cells are necessary for species-typical adult social behaviors using a Cre-LoxP strategy. Genetically modified male and female mice lacking OXTR in Avil expressing cells (OXTRAvil KO) were tested for sociability and preference for social novelty. Males were also tested for resident intruder aggression. OXTRAvil KO males and females had reduced sociability compared to OXTRAvil WT controls. Additionally, OXTRAvil KO males had increased aggressive behaviors compared to controls. These data indicate that OXTRs in cells of neural crest origin are important regulators of typical social behaviors in C57BL/6J adult male and female mice and point to needed directions of future research.

Oxytocin-induced anxiogenic behavior in juvenile male rats

Oxytocin (OT) is considered beneficial to mental health owing to its anxiolytic, prosocial, and anti-stress effects; however, the adverse effects of OT have been controversial, such as its potentially anxiogenic actions. Although OT influences drug abuse and reciprocally affects vulnerability to drug use, the relationship between OT’s anxiogenic working and nicotine preference intake has not been clearly defined. To clarify this issue, the effect of acute peripheral administration of OT on anxiety and nicotine preference was investigated in juvenile male rats. Anxiogenic behaviors were noticeably increased in OT-administrated rats, with an increase in serum corticosterone levels. Moreover, increased anxiety-like behaviors and corticosterone levels were observed in the OT analog carbetocin-injected rats. In the nicotine preference test, the rats’ aversive responses to initial nicotine choice and preference were not significantly different between saline-injected and OT-injected rats. However, when administered with OT, there was a significant negative correlation between anxiety-like behavior and low-dose nicotine consumption. Collectively, these results provide evidence that acute OT exposure could induce anxiogenic behavior with corticosterone augmentation, contributing to the attenuation of nicotine preference. This suggests that both aspects of OT, as well as their benefits and drawbacks, should be considered.

The influence of oxytocin-based interventions on sleep-wake and sleep-related behaviour and neurobiology: A systematic review of preclinical and clinical studies

The oxytocin (OXT) system has garnered considerable interest due to its influence on diverse behaviours. However, scant research has considered the influence of oxytocin on sleep-wake and sleep-related behaviour and neurobiology. Consequently, the objective of this systematic review was to assess the extant preclinical and clinical evidence for the influence of oxytocin-based interventions on sleep-wake outcomes. The primary search was conducted on 22/7/2020 using six electronic databases; 30 studies (19 preclinical, 11 clinical) were included based on inclusion criteria. Studies were evaluated for risk of bias using the SYRCLE tool and the Cochrane risk of bias tools for preclinical and clinical studies, respectively. Results indicated manipulation of the OXT system can influence sleep-wake outcomes. Preclinical evidence suggests a wake-promoting influence of OXT system activation whereas the clinical evidence suggests little or no sleep-promoting influence of OXT. OXT dose was identified as a likely modulatory factor of OXT-induced effects on sleep-wake behaviour. Future studies are necessary to validate and strengthen these tentative conclusions about the influence of OXT on sleep-wake behaviour.

Kamikihito, a traditional Japanese Kampo medicine, increases the secretion of oxytocin in rats with acute stress

ETHNOPHARMACOLOGICAL RELEVANCE

Kamikihito (KKT) is a Kampo medicine that is prescribed in Japan for the treatment of anemia, insomnia and mental anxiety in Japan. However, its precise mechanism of action remains unclear.

AIM OF THE STUDY

This study aimed to evaluate the possible antistress effect of KKT in rats with acute stress and the contribution of oxytocin to the process.

MATERIALS AND METHODS

Acute immobilization stress (AIS; for 90 min) was used to assess the effect of KKT on acute stress. Male Wistar rats were orally treated with KKT. Parameters of stress were evaluated, and concentrations of oxytocin in plasma and cerebrospinal fluid (CSF) were measured.

RESULTS

AIS-induced defecation and fecal weight were significantly decreased because of treatment with KKT. The plasma levels of stress-related hormones following AIS were investigated. The pre-administration of KKT significantly increased adrenocorticotrophic hormone (ACTH) and corticosterone (CORT) levels following AIS. Conversely, there was no significant change in the plasma oxytocin level. Microdialysis and hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) were used to monitor the oxytocin secretion in CSF. Oxytocin level increased during AIS following the treatment of KKT. At 30 min after AIS, the level remained higher than before AIS. Furthermore, using an open field test, the locomotion (exploratory behavior) immediately after AIS was examined. The total traveled distance decreased after AIS; however, the decrease was significantly inhibited by the treatment of KKT. However, the effect of KKT was obstructed by the pre-administration of the oxytocin receptor antagonist.

CONCLUSIONS

These results suggest that KKT has antistress activity and increased oxytocin secretion may be a mechanism underlying this phenomenon.

In the nose or on the tongue? Contrasting motivational effects of oral and intranasal oxytocin on arousal and reward during social processing

Intranasal oxytocin exerts wide-ranging effects on socioemotional behavior and is proposed as a potential therapeutic intervention in psychiatric disorders. However, following intranasal administration, oxytocin could penetrate directly into the brain or influence its activity via increased peripheral concentrations crossing the blood-brain barrier or influencing vagal projections. In the current randomized, placebo-controlled, pharmaco-imaging clinical trial we investigated effects of 24IU oral (lingual) oxytocin spray, restricting it to peripherally mediated blood-borne and vagal effects, on responses to face emotions in 80 male subjects and compared them with 138 subjects treated intranasally with 24IU. Oral, but not intranasal oxytocin administration increased both arousal ratings for faces and associated brain reward responses, the latter being partially mediated by blood concentration changes. Furthermore, while oral oxytocin increased amygdala and arousal responses to face emotions, after intranasal administration they were decreased. Thus, oxytocin can produce markedly contrasting motivational effects in relation to socioemotional cues when it influences brain function via different routes. These findings have important implications for future therapeutic use since administering oxytocin orally may be both easier and have potentially stronger beneficial effects by enhancing responses to emotional cues and increasing their associated reward.

Peripheral oxytocin injection modulates vomeronasal sensory activity and reduces pup-directed aggression in male mice

Behaviors are shaped by hormones, which may act either by changing brain circuits or by modifying sensory detection of relevant cues. Pup-directed behaviors have been previously shown to change via action of hormones at the brain level. Here, we investigated hormonal control of pup-induced activity in the vomeronasal organ, an olfactory sensory structure involved in the detection of non-volatile chemosignals. Vomeronasal activity decreases as males switch from a pup-aggressive state to a non-aggressive parenting state, after they socially contact a female. RNA sequencing, qPCR, and in situ hybridization were used to identify expression, in the vomeronasal sensory epithelium, of candidate GPCR hormone receptors chosen by in silico analyses and educated guesses. After identifying that oxytocin and vasopressin receptors are expressed in the vomeronasal organ, we injected the corresponding hormones in mice and showed that oxytocin administration reduced both pup-induced vomeronasal activity and aggressive behavior. Conversely, injection of an oxytocin receptor antagonist in female-primed male animals, which normally exhibit reduced vomeronasal activity, significantly increased the number of active vomeronasal neurons. These data link oxytocin to the modulation of olfactory sensory activity, providing a possible mechanism for changes in male behavior after social experience with females.

Measuring sociability of mice using a novel three-chamber apparatus and algorithm of the LABORAS™ system

BACKGROUND

The social approach and social novelty tests utilizing the three-chamber apparatus are widely accepted to measure social behavior of rodents. The LABORAS™ system offers a possibility to assess sociability of mice in a reliable and objective manner.

NEW METHOD

We assessed the capability of the LABORAS™ sociability cage and algorithm (2.6.6) to detect social behaviors in mice. Furthermore, we investigated whether the system is able to detect various levels of sociability due to genetic background or after pharmacological treatments.

RESULTS

By comparing manual scoring with various detection zone settings of the automated registration, the most fitting algorithm with a detection zone radius of 90 mm was identified. When different strains were investigated, C57Bl/6 J and NMRI mice proved to be social, while CD1 mice were found asocial. The system was able to detect the sociability increasing effect of R-baclofen (0.5 mg/kg i.p.) and oxytocin (12 ng i.c.v.) in asocial CD1 mice. The negative control PCP impaired social behavior of C57Bl/6 J mice (1 mg/kg i.p.) and increased social avoidance in CD1 mice (0.3 mg/kg i.p.).

COMPARISON WITH EXISTING METHOD(S)

This setup, in contrast to video frame analysis softwares, determines signal changes caused by movements of rodents allowing accurate detection and analysis of trajectories. Parallel automated measurements also allow replacing time and labor intensive, highly subjective human observational work.

CONCLUSIONS

The set-up provides a fast and reliable method to examine social behavior of mice in the three-chamber apparatus. The system is capable of detecting pro or antisocial activity of pharmacological agents.

Intramuscular antagonism of the G-protein coupled estrogen receptor 1 partially affects dimorphic characteristics of the syrinx, but is ineffective within the neural song circuit of zebra finches

Within the zebra finch song system, robust sex differences exist that enable singing behavior in males, but not females. Estradiol is a potent contributor to this process, but how and through which receptor(s) it acts is not clear. Historically, pharmacological manipulations of nuclear estrogen receptors have yielded conflicting results possibly due to method of drug delivery. More recently, the membrane bound G-protein coupled estrogen receptor 1 (GPER1) has also been identified as a potential candidate, but its function has not been fully described. To further investigate the role of GPER1, and the importance of the route of drug administration, a specific antagonist (G-15) was intramuscularly administered to zebra finches for 25 days, starting on the day of hatching. G-15 significantly decreased muscle fiber sizes of ventralis and dorsalis in the syrinx of males only. Dimorphic characteristics of the neural song system were unaffected by this manipulation in either sex. These results contrast with a study in which G-15 was intracranially delivered. In males, select song nuclei were decreased in volume, and in females, syrinx muscle fiber size was increased. Together, these results support the hypothesis that estrogens acting through GPER1 influence dimorphic development of the song system, and that method of drug administration is important in this species.

Impaired sex preference, but not social and social novelty preferences, following systemic blockade of oxytocin receptors in adult male mice

The hypothalamic neuropeptide oxytocin (OT) is a powerful modulator of mammalian social behavior and its administration was shown to affect various types of social interactions. However, systematic examinations of the role of endogenous OT release in social behavior have heretofore been done only using genetically modified animal models in which the genes encoding either OT or the OT receptor (OTR) were mutated. While such genetic manipulations revealed various behavioral deficits, these deficits may involve developmental or long-term processes and do not prove the participation of acute OT release in the impaired behavior. Here we used a battery of social discrimination tasks to evaluate the effects of acute systemic OTR blockade, using a non-peptide, orally active OTR antagonist (L368,899), on social behavior of adult male C57BL/6 J mice. We found no effect of the pharmacological manipulation on the social preference and social novelty preference behaviors. However, the preference of a male mouse for investigating a female conspecific more than a male (sex preference behavior), was lost by administration of the OTR antagonist. Finally, we found that blocking OTR activity before social defeat prevented the consequent loss of social preference, suggesting a role for OT in the acquisition of aversive social memory. Overall, our results suggest that OT plays a role in modulating the salience of social stimuli and facilitating their memory, as predicted by the social salience theory, rather than in regulating the internal motivation of the subject for social interactions.