Utilization of same- vs. mixed-sex dyads impacts the observation of sex differences in juvenile social play behavior

Psychostimulants and social behaviors

Mounting evidence from animal models and human studies indicates that psychostimulants can significantly affect social behaviors. This is not surprising considering that the neural circuits underlying the regulation and expression of social behaviors are highly overlapped with those targeted by psychostimulants, which in most cases have strong rewarding and, consequently, addictive properties. In the present work, we provide an overview regarding the effects of illicit and prescription psychostimulants, such as cocaine, amphetamine-type stimulants, methylphenidate or modafinil, upon social behaviors such as social play, maternal behavior, aggression, pair bonding and social cognition and how psychostimulants in both animals and humans alter them. Finally, we discuss why these effects can vary depending on numerous variables such as the type of drug considered, acute versus long-term use, clinical versus recreational consumption, or the presence or absence of concomitant risk factors.

The medial preoptic area and its projections to the ventral tegmental area and the periaqueductal gray are activated in response to social play behavior in juvenile rats

The medial preoptic area (MPOA) is well known for its role in sexual and maternal behaviors. This region also plays an important role in affiliative social behaviors outside reproductive contexts. We recently demonstrated that the MPOA is a central nucleus in which opioids govern highly rewarding social play behavior in adolescent rats. However, the neural circuit mechanisms underlying MPOA-mediated social play remain largely unresolved. We hypothesized that the MPOA unites a complementary neural system through which social play induces reward via a projection to the ventral tegmental area (VTA) and reduces a negative affective state through a projection to the periaqueductal gray (PAG). To test whether the two projection pathways are activated in response to social play behavior, we combined retrograde tract tracing with immediate early gene (IEG) expression and immunofluorescent labeling to identify opioid-sensitive projection pathways from the MPOA to VTA and PAG that are activated after performance of social play. Retrograde tracer, fluoro-gold (FG), was microinjected into the VTA or PAG. IEG expression (i.e., Egr1) was assessed and triple immunofluorescent labeling for mu opioid receptor (MOR), Egr1, and FG in the MPOA was performed after social play. We revealed that play animals displayed an increase in neurons double labeled for Egr1 + FG and triple labeled for MOR + Egr1 + FG in the MPOA projecting to both the VTA and PAG when compared to no-play rats. The increased activation of projection neurons that express MORs from MPOA to VTA or PAG after social play suggests that opioids may act through these projection pathways to govern social play. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Lactational exposure to venlafaxine provokes late repercussions on reproductive parameters in male rat offspring

Exposure to selective serotonin reuptake inhibitors can affect hormone-dependent processes, such as the brain sexual differentiation. Because the use of these antidepressants cause concern during lactation, we evaluated the possible effects of venlafaxine on lactational exposure and its late repercussions on reproductive parameters in male rats. Lactating rats were exposed to venlafaxine (3.85, 7.7, or 15.4 mg/kg/body weight; gavage), from lactational day 1 to 20. Venlafaxine and O-desmethylvenlafaxine residues were found in all milk samples of dams treated, demonstrating the lactational transfer of this antidepressant to the offspring. Although the maternal behavior was normal, the dams presented an increase in urea and uric acid levels in the groups treated with 7.7 and 15.4, respectively, as well as a spleen weight increased in the 3.85 and 15.4 groups. The male offspring showed a decrease in play behavior parameters in the intermediate dose group. Sperm analysis indicated a reduction in sperm motility in all treated groups. The androgen receptor expression in the hypothalamus was decreased in the highest dose group, although the sexual behavior had not been affected. In conclusion, venlafaxine was transferred through breast milk and promoted changes in play behavior, sperm quality, and hypothalamic androgen receptor (AR) content, which may indicate an incomplete masculinization of the brain of male offspring.

Systematic Review: microRNAs as Potential Biomarkers in Mild Cognitive Impairment Diagnosis

The rate of progression from Mild Cognitive Impairment (MCI) to Alzheimer's disease (AD) is estimated at >10% per year, reaching up to 80-90% after 6 years. MCI is considered an indicator of early-stage AD. In this context, the diagnostic screening of MCI is crucial for detecting individuals at high risk of AD before they progress and manifest further severe symptoms. Typically, MCI has been determined using neuropsychological assessment tools such as the Montreal Cognitive Assessment (MoCA) or Mini-Mental Status Examination (MMSE). Unfortunately, other diagnostic methods are not available or are unable to identify MCI in its early stages. Therefore, identifying new biomarkers for MCI diagnosis and prognosis is a significant challenge. In this framework, miRNAs in serum, plasma, and other body fluids have emerged as a promising source of biomarkers for MCI and AD-related cognitive impairments. Interestingly, miRNAs can regulate several signaling pathways via multiple and diverse targets in response to pathophysiological stimuli. This systematic review aims to describe the current state of the art regarding AD-related target genes modulated by differentially expressed miRNAs in peripheral fluids samples in MCI subjects to identify potential miRNA biomarkers in the early stages of AD. We found 30 articles that described five miRNA expression profiles from peripheral fluid in MCI subjects, showing possible candidates for miRNA biomarkers that may be followed up as fluid biomarkers or therapeutic targets of early-stage AD. However, additional research is needed to validate these miRNAs and characterize the precise neuropathological mechanisms.

Social behavior in prepubertal neurexin 1α deficient rats: A model of neurodevelopmental disorders

Loss-of-function mutations in the synaptic protein neurexin1α (NRXN1α) are associated with several neurodevelopmental disorders, including autism spectrum disorder (ASD), schizophrenia, and attention-deficit hyperactivity disorder (ADHD), and many of these disorders are defined by core deficits in social cognition. Mouse models of Nrxn1α deficiency are not amenable to studying aspects of social cognition because, in general, mice do not engage in complex social interactions such as social play or prosocial helping behaviors. Rats, on the contrary, engage in these complex, well-characterized social behaviors. Using the Nrxn1tm1Sage Sprague Dawley rat, we tested a range of cognitive and social behaviors in juveniles with haplo- or biallelic Nrxn1α mutation. We found a deficit in ultrasonic vocalizations (USVs) of male and female neonatal rats with Nrxn1α deficiency. A male-specific deficit in social play was observed in Nrxn1α-deficient juveniles, although sociability and social discrimination were unaltered. Nurturing behavior induced by exposure to pups was enhanced in male and female juveniles with biallelic Nrxn1α mutation. Performance in tasks of prosocial helping behavior and food retrieval indicated severe deficits in learning and cognition in juveniles with biallelic Nrxn1α mutation, and a less severe deficit in haploinsufficient rats, although Pavlovian learning was altered only in haploinsufficient males. We also observed a male-specific increase in mobility and object investigation in juveniles with complete Nrxn1α deficiency. Together, these observations more fully characterize the Nrxn1tm1Sage Sprague Dawley rat as a model for Nrxn1α-related neurodevelopmental disorders, and support a rationale for the juvenile rat as a more appropriate model for disorders that involve core deficits in complex social behaviors. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Sex-specific effects of neonatal progestin receptor antagonism on juvenile social play behavior in rats

Developing mammals are exposed to progesterone through several sources; however, the role of progesterone in early development is not well understood. Males express more progestin receptors (PRs) than females within several brain regions during early postnatal life, suggesting that PRs may be important for the organization of the sex differences in the brain and behavior. Indeed, previous studies showed cognitive impairments in male rats treated neonatally with a PR antagonist. In the present study, we examined the role of PRs in organizing juvenile behaviors. Social play behavior and social discrimination were examined in juvenile male and female rats that had been treated with CDB, a PR antagonist, during the first week of postnatal life. Interestingly, neonatal PR antagonism altered different juvenile behaviors in males and females. A transient disruption in PR signaling during development had no effect on social discrimination but increased play initiation and pins in females. These data suggest that PRs play an important role in the organization of sex differences in some social behaviors.

Excessive Laughter-like Vocalizations, Microcephaly, and Translational Outcomes in the Ube3a Deletion Rat Model of Angelman Syndrome

Angelman syndrome (AS) is a rare genetic neurodevelopmental disorder characterized by intellectual disabilities, motor and balance deficits, impaired communication, and a happy, excitable demeanor with frequent laughter. We sought to elucidate a preclinical outcome measure in male and female rats that addressed communication abnormalities of AS and other neurodevelopmental disorders in which communication is atypical and/or lack of speech is a core feature. We discovered, and herein report for the first time, excessive laughter-like 50 kHz ultrasonic emissions in the Ube3a ^mat-/pat+ rat model of AS, which suggests an excitable, playful demeanor and elevated positive affect, similar to the demeanor of individuals with AS. Also in line with the AS phenotype, Ube3a ^mat-/pat+ rats demonstrated aberrant social interactions with a novel partner, distinctive gait abnormalities, impaired cognition, an underlying LTP deficit, and profound reductions in brain volume. These unique, robust phenotypes provide advantages compared with currently available mouse models and will be highly valuable as outcome measures in the evaluation of therapies for AS.SIGNIFICANCE STATEMENT Angelman syndrome (AS) is a severe neurogenetic disorder for which there is no cure, despite decades of research using mouse models. This study used a recently developed rat model of AS to delineate disease-relevant outcome measures to facilitate therapeutic development. We found the rat to be a strong model of AS, offering several advantages over mouse models by exhibiting numerous AS-relevant phenotypes, including overabundant laughter-like vocalizations, reduced hippocampal LTP, and volumetric anomalies across the brain. These findings are unconfounded by detrimental motor abilities and background strain, issues plaguing mouse models. This rat model represents an important advancement in the field of AS, and the outcome metrics reported herein will be central to the therapeutic pipeline.

Maternal allergic inflammation in rats impacts the offspring perinatal neuroimmune milieu and the development of social play, locomotor behavior, and cognitive flexibility

Maternal systemic inflammation increases risk for neurodevelopmental disorders like autism, ADHD, and schizophrenia in offspring. Notably, these disorders are male-biased. Studies have implicated immune system dysfunction in the etiology of these disorders, and rodent models of maternal immune activation provide useful tools to examine mechanisms of sex-dependent effects on brain development, immunity, and behavior. Here, we employed an allergen-induced model of maternal inflammation in rats to characterize levels of mast cells and microglia in the perinatal period in male and female offspring, as well as social, emotional, and cognitive behaviors throughout the lifespan. Adult female rats were sensitized to ovalbumin (OVA), bred, and challenged intranasally on gestational day 15 of pregnancy with OVA or saline. Allergic inflammation upregulated microglia in the fetal brain, increased mast cell number in the hippocampus on the day of birth, and conferred region-, time- and sex- specific changes in microglia measures. Additionally, offspring of OVA-exposed mothers subsequently exhibited abnormal social behavior, hyperlocomotion, and reduced cognitive flexibility. These data demonstrate the long-term effects of maternal allergic challenge on offspring development and provide a basis for understanding neurodevelopmental disorders linked to maternal systemic inflammation in humans.

Developmental origins of sex differences in the neural circuitry of play

Social play consists of reciprocal physical interactions between conspecifics with many features conserved across species, including the propensity for males to engage in play more frequently and with higher physical intensity. Animal models, such as the laboratory rat, reveal that the underlying neural circuitry of play is subject to sexual differentiation during a critical period early in life. In this review, we discuss the developmental processes that produce distinct neural nodes which modulate both shared and sex-specific aspects of play with a focus on the medial amygdala, lateral septum, and prefrontal cortex. While the cellular mechanisms determining sex differences in play are beginning to be uncovered, the ultimate advantages of play continue to be debated.

Developmental social communication deficits in the Shank3 rat model of phelan-mcdermid syndrome and autism spectrum disorder

Mutations in the SHANK3 gene have been discovered in autism spectrum disorder (ASD), and the intellectual disability, Phelan-McDermid Syndrome. This study leveraged a new rat model of Shank3 deficiency to assess complex behavioral phenomena, unique to rats, which display a richer social behavior repertoire than mice. Uniquely detectable emissions of ultrasonic vocalizations (USV) in rats serve as situation-dependent affective signals and accomplish important communicative functions. We report, for the first time, a call and response acoustic playback assay of bidirectional social communication in juvenile Shank3 rats. Interestingly, we found that Shank3-deficient null males did not demonstrate the enhanced social approach behavior typically exhibited following playback of pro-social USV. Concomitantly, we discovered that emission of USV in response to playback was not genotype-dependent and emitted response calls were divergent in meaning. This is the first report of these socially relevant responses using a genetic model of ASD. A comprehensive and empirical analysis of vigorous play during juvenile reciprocal social interactions further revealed fewer bouts and reduced durations of time spent playing by multiple key parameters, including reduced anogenital sniffing and allogrooming. We further discovered that male null Shank3-deficient pups emitted fewer isolation-induced USV than Shank3 wildtype controls. Postnatal whole brain anatomical phenotyping was applied to visualize anatomical substrates that underlie developmental phenotypes. The data presented here lend support for the important role of Shank3 in social communication, the core symptom domain of ASD. By increasing the number of in vivo functional outcome measures, we improved the likelihood for identifying and moving forward with medical interventions. Autism Res 2018, 11: 587-601. © 2018 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Clinically relevant outcomes are required to demonstrate the utility of therapeutics. We introduce findings in a rat model, and assess the impact of mutations in Shank3, an autism risk gene. We found that males with deficient expression of Shank3 did not demonstrate typical responses in a bi-directional social communication test and that social interaction was lower on key parameters. Outcome measures reported herein extend earlier results in mice and capture responses to acoustic calls, which is analogous to measuring receptive and expressive communication.

Activation of Both CB1 and CB2 Endocannabinoid Receptors Is Critical for Masculinization of the Developing Medial Amygdala and Juvenile Social Play Behavior

Juvenile social play behavior is a shared trait across a wide variety of mammalian species. When play is characterized by the frequency or duration of physical contact, males usually display more play relative to females. The endocannabinoid system contributes to the development of the sex difference in social play behavior in rats. Treating newborn pups with a nonspecific endocannabinoid agonist, WIN55,212-2, masculinizes subsequent juvenile rough-and-tumble play behavior by females. Here we use specific drugs to target signaling through either the CB1 or CB2 endocannabinoid receptor (CB1R or CB2R) to determine which modulates the development of sex differences in play. Our data reveal that signaling through both CB1R and CB2R must be altered neonatally to modify development of neural circuitry regulating sex differences in play. Neonatal co-agonism of CB1R and CB2R masculinized play by females, whereas co-antagonism of these receptors feminized rates of male play. Because of a known role for the medial amygdala in the sexual differentiation of play, we reconstructed Golgi-impregnated neurons in the juvenile medial amygdala and used factor analysis to identify morphological parameters that were sexually differentiated and responsive to dual agonism of CB1R and CB2R during the early postnatal period. Our results suggest that sex differences in the medial amygdala are modulated by the endocannabinoid system during early development. Sex differences in play behavior are loosely correlated with differences in neuronal morphology.