The modulation of emotional and social behaviors by oxytocin signaling in limbic network

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

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

Aberrant TSC-Rheb axis in Oxytocin receptor+ cells mediate stress-induced anxiety

Stress is a major risk for the onset of several maladaptive processes including pathological anxiety, a diffuse state of heightened apprehension over anticipated threats1. Pathological anxiety is prevalent in up to 59% of patients with Tuberous Sclerosis complex (TSC)2, a neurodevelopmental disorder (NDD) caused by loss-of-function mutations in genes for Tuberin (Tsc2) and/or Hamartin (Tsc1) that together comprise the eponymous protein complex. Here, we generated cell type-specific heterozygous knockout of Tsc2 in cells expressing oxytocin receptor (OTRCs) to model pathological anxiety-like behaviors observed in TSC patient population. The stress of prolonged social isolation induces a sustained negative affective state that precipitates behavioral avoidance, often by aberrant oxytocin signaling in the limbic forebrain3,4. In response to social isolation, there were striking sex differences in stress susceptibility in conditional heterozygote mice when encountering situations of approach-avoidance conflict. Socially isolated male mutants exhibited behavioral avoidance in anxiogenic environments and sought more social interaction for buffering of stress. In contrast, female mutants developed resilience during social isolation and approached anxiogenic environments, while devaluing social interaction. Systemic and medial prefrontal cortex (mPFC)-specific inhibition of downstream effector of TSC, the integrated stress response (ISR), rescued behavioral approach toward anxiogenic environments and conspecifics in male and female mutant mice respectively. Further, we found that Tsc2 deletion in OTRCs leads to OTR-signaling elicited network suppression, i.e., hypofrontality, in male mPFC, which is relieved by inhibiting the ISR. Our findings present evidence in support of a sexually dimorphic role of prefrontal OTRCs in regulating emotional responses in anxiogenic environments, which goes awry in TSC. Our work has broader implications for developing effective treatments for subtypes of anxiety disorders that are characterized by cell-autonomous ISR and prefrontal network suppression.

Social interaction-induced fear memory reduction: exploring the influence of dopamine and oxytocin receptors on memory updating

It has been well established that a consolidated memory can be updated during the plastic state induced by reactivation. This updating process opens the possibility to modify maladaptive memory. In the present study, we evaluated whether fear memory could be updated to less-aversive level by incorporating hedonic information during reactivation. Thus, male rats were fear conditioned and, during retrieval, a female was presented as a social rewarding stimulus. We found that memory reactivation with a female (but not a male) reduces fear expression within-session and in the test, without presenting reinstatement or spontaneous recovery. Interestingly, this intervention impaired extinction. Finally, we demonstrated that this emotional remodeling to eliminate fear expression requires the activation of dopamine and oxytocin receptors during retrieval. Hence, these results shed new lights on the memory updating process and suggests that the exposure to natural rewarding information such as a female during retrieval reduces a previously consolidated fear memory.

Convergence of oxytocin and dopamine signalling in neuronal circuits: Insights into the neurobiology of social interactions across species

Social behaviour is essential for animal survival, and the hypothalamic neuropeptide oxytocin (OXT) critically impacts bonding, parenting, and decision-making. Dopamine (DA), is released by ventral tegmental area (VTA) dopaminergic neurons, regulating social cues in the mesolimbic system. Despite extensive exploration of OXT and DA roles in social behaviour independently, limited studies investigate their interplay. This narrative review integrates insights from human and animal studies, particularly rodents, emphasising recent research on pharmacological manipulations of OXT or DA systems in social behaviour. Additionally, we review studies correlating social behaviour with blood/cerebral OXT and DA levels. Behavioural facets include sociability, cooperation, pair bonding and parental care. In addition, we provide insights into OXT-DA interplay in animal models of social stress, autism, and schizophrenia. Emphasis is placed on the complex relationship between the OXT and DA systems and their collective influence on social behaviour across physiological and pathological conditions. Understanding OXT and DA imbalance is fundamental for unravelling the neurobiological underpinnings of social interaction and reward processing deficits observed in psychiatric conditions.

Adolescent social isolation disrupts developmental tuning of neuropeptide circuits in the hypothalamus to amygdala regulating social and defensive behavior

Engaging in positive social (i.e., prosocial) interactions during adolescence acts to modulate neural circuits that determine adult adaptive behavior. While accumulating evidence indicates that a strong craving for prosocial behavior contributes to sustaining neural development, the consequences of social deprivation during adolescence on social neural circuits, including those involving oxytocin (OXT) and vasopressin (AVP), are poorly characterized. We evaluated adaptive behaviors in socially isolated mice, including anxiety-like, social, and defensive behaviors, along with OXT and AVP neural profiles in relevant brain regions. Social isolation from postnatal day (P-)22 to P-48 induced enhanced defensive and exploratory behaviors, in nonsocial and social contexts. Unlike OXT neurons, AVP+ cell density in the paraventricular nucleus of the hypothalamus increases with age in males. Social isolation also modulated gene expression in the medial amygdala (MeA), including the upregulation of OXT receptors in males and the downregulation of AVP1a receptors in both sexes. Socially isolated mice showed an enhanced defensive, anogenital approach toward a novel adult female during direct social interactions. Subsequent c-Fos mapping revealed diminished neural activity in restricted brain areas, including the MeA, lateral septum, and posterior intralaminar nucleus of the thalamus, in socially isolated mice. These data indicate that neural signals arising from daily social interactions invoke region-specific modification of neuropeptide expression that coordinates with altered defensiveness and neural responsivities, including OXT- and AVP-projecting regions. The present findings indicate an involvement of OXT and AVP circuits in adolescent neural and behavioral plasticity that is tuned by daily social interaction.

Social anxiety disorder-associated gut microbiota increases social fear

Social anxiety disorder (SAD) is a crippling psychiatric disorder characterized by intense fear or anxiety in social situations and their avoidance. However, the underlying biology of SAD is unclear and better treatments are needed. Recently, the gut microbiota has emerged as a key regulator of both brain and behaviour, especially those related to social function. Moreover, increasing data supports a role for immune function and oxytocin signalling in social responses. To investigate whether the gut microbiota plays a causal role in modulating behaviours relevant to SAD, we transplanted the microbiota from SAD patients, which was identified by 16S rRNA sequencing to be of a differential composition compared to healthy controls, to mice. Although the mice that received the SAD microbiota had normal behaviours across a battery of tests designed to assess depression and general anxiety-like behaviours, they had a specific heightened sensitivity to social fear, a model of SAD. This distinct heightened social fear response was coupled with changes in central and peripheral immune function and oxytocin expression in the bed nucleus of the stria terminalis. This work demonstrates an interkingdom basis for social fear responses and posits the microbiome as a potential therapeutic target for SAD.