MDMA enhances empathy-like behaviors in mice via 5-HT release in the nucleus accumbens

Can ketamine and other glutamate receptor modulators be considered entactogens?

Subanesthetic-dose ketamine has recently been reported to improve hedonic pleasures associated with social interactions and altruism in individuals with treatment-resistant depression. However, whether ketamine-among other glutamate receptor modulators-also improves empathy and/or prosocial behavior in humans remains unknown. Under a framework grounded in neurobiology that proposes that prosocial behavior is preceded by empathy, this systematic review sought to: (1) explore the entactogenic effects of glutamate receptor modulators observed in clinical trials (as either primary or secondary outcomes), and (2) synthesize the findings regarding which glutamate receptor modulators produce entactogenic effects. Thirty studies that included self-reported ratings, neuroimaging, and/or behavioral task outcomes met inclusion criteria suggesting potential entactogenic effects associated with ketamine and, to less convincing extent, d-cycloserine (DCS). The findings suggest that ketamine and DCS may modulate self- and other-perception, involving changes in activity in brain regions involved in empathetic concerns and mentalizing, the ability to understand one's own and others' thoughts and feelings. These findings may guide potential therapeutic interventions for neuropsychiatric conditions associated with impaired empathy and prosocial behavior, including mood disorders, neurodevelopmental disorders, psychotic disorders, and personality disorders.

Neuronal and therapeutic perspectives on empathic pain: A rational insight

Empathy is the capacity to experience and understand the feelings of others, thereby playing a key role in a person's mental well-being essentially by promoting kindness and a sense of belongingness to the group. However, too much empathy may result in psychological problems such as empathic distress, compassion fatigue, and burnout, collectively termed empathic pain. Several brain regions are implicated in processing empathic pain perception. Neuroimaging investigations bring in the context of brain structures involved in this emotional exchange, pointing toward the anterior insula (AI) and anterior cingulate cortex (ACC), indicating an overlap between the neural representation of direct and simulative pain. To discern such overlaps, therapeutic techniques for managing empathic pain require understanding different brain regions and their respective neural networks. At the moment, empathic pain is being treated using various methods, including pharmacological treatments such as antidepressants and psychological treatments such as mindfulness or meditation. For instance, researchers have been exploring the modulatory effects of neurotransmitters like serotonin, norepinephrine, and oxytocin on individuals' responses to empathic pain experience. Importantly, this review focuses on the specific brain parts and their unique roles in neurobiological pathways associated with emphatic pain and how shared neural networks play into available treatment options, suggesting possible future health benefits. Such an understanding of empathy can lead to more efficient management of types of care, focusing on enhancing social connections and mental well-being.

The neural basis of affective empathy: What is known from rodents

Empathy is the cornerstone of social interactions between conspecies for human beings and other social animals. Human beings with empathy defects might either suffer unpleasant or failed social interactions as ASD patients, or even display antisocial behaviors. To find efficient cure for empathy defects, first of all, the neural mechanisms underpinning various empathy behaviors should be well studied and understood. And the research in the field of affective empathy thrives fast in recent years. It is necessary to review the important contributions in this field, especially for understanding the delicate neural mechanisms of diverse forms of affective empathy. Here, we have summarized the characteristics of various types of affective empathy. We also discuss the distinctions between empathy for pain and fear, as well as instinctive and experienced empathy. Our analysis further highlights the findings in the complex neural mechanisms and potential brain regions underlying different affective empathy behaviors. Above all, this work is expected to help enhance our comprehension of behavioral dynamics and neural basis of affective empathy along with its role in emotional regulation and social behavior.

Brain circuits that regulate social behavior

Social interactions are essential for the survival of individuals and the reproduction of populations. Social stressors, such as social defeat and isolation, can lead to emotional disorders and cognitive impairments. Furthermore, dysfunctional social behaviors are hallmark symptoms of various neuropsychiatric disorders, including autism spectrum disorder (ASD) and post-traumatic stress disorder (PTSD). Consequently, understanding the neural circuit mechanisms underlying social behaviors has become a major focus in neuroscience. Social behaviors, which encompass a wide range of expressions and phases, are regulated by complex neural networks. In this review, we summarize recent progress in identifying the circuits involved in different types of social behaviors, including general social investigation, social preference, mating, aggression, parenting, prosocial behaviors, and dominance behaviors. We also outline the circuit mechanisms associated with social deficits in neuropsychiatric disorders, such as ASD, schizophrenia, and PTSD. Given the pivotal role of rodents in social behavior research, our review primarily focuses on neural circuits in these animals. Finally, we propose future research directions, including the development of specific behavioral paradigms, the identification of circuits involved in motor output, the integration of activity, transcriptome, and connectome data, the multifunctional roles of neurons with multiple targets, and the interactions among multiple brain regions.

Intercalated Amygdala Dysfunction Drives Avoidance Extinction Deficits in the Sapap3 Mouse Model of Obsessive-Compulsive Disorder

BACKGROUND

The avoidance of aversive stimuli through negative reinforcement learning, which demands dynamic responding to both positive and negative stimuli that often conflict with each other, is critical for survival in real-world environments. Individuals with obsessive-compulsive disorder commonly exhibit impaired negative reinforcement and extinction, perhaps involving deficits in amygdala functioning. The intercalated nuclei of the amygdala (ITC) is an amygdala subregion of particular interest that has been linked to negative reinforcement and extinction, with distinct clusters mediating separate aspects of behavior. This study focuses on the dorsal ITC cluster (ITCd) and its role in negative reinforcement during a complex behavior that models real-world dynamic decision making.

METHODS

We investigated the impact of ITCd function on negative reinforcement and extinction by applying fiber photometry measurement of GCaMP6f signals and optogenetic manipulations during a platform-mediated avoidance task in a mouse model of obsessive-compulsive disorder-like behavior, the Sapap3-null mouse.

RESULTS

We found impaired neural activity in the ITCd of male and female Sapap3-null mice to the encoding of negative stimuli during platform-mediated avoidance. Sapap3-null mice also exhibited deficits in extinction of avoidant behavior, which were modulated by ITCd neural activity.

CONCLUSIONS

Sapap3-null mice failed to extinguish avoidant behavior in platform-mediated avoidance due to heightened ITCd activity. This deficit was rescued by optogenetically inhibiting ITCd during extinction. Together, our results provide insight into the neural mechanisms that underlie negative reinforcement deficits in the context of obsessive-compulsive disorder and emphasize the necessity of ITCd in responding to negative stimuli in complex environments.

A review of the effects of different types of social behaviors on the recruitment of neuropeptides and neurotransmitters in the nucleus accumbens

There is a lack of understanding of the neural mechanisms regulating the rewarding effects of social interactions. A significant contributor to this lack of clarity is the diversity of social behaviors and animal models utilized to investigate mechanisms. Other sources of the lack of clarity are the diversity of brain regions that can regulate social reward and the diversity of signaling pathways that regulate reward. To provide some clarity into the mechanisms of social reward, this review focused on the brain region most implicated in reward for multiple stimuli, the nucleus accumbens, and surveyed (systematically reviewed) studies that investigated the relationship between social interaction and five signaling systems implicated in the regulation of reward and social behavior: oxytocin, vasopressin, serotonin, opioids and endocannabinoids. Moreover, all of these studies were organized by the type of social behavior studied: affiliative interactions, play behavior, aggression, social defeat, sex behavior, pair-bonding, parental behavior and social isolation. From this survey and organization, this review concludes that oxytocin, endocannabinoids and mu-opioid receptors in the nucleus accumbens positively regulate the rewarding social behaviors, and kappa-opioid receptors negatively regulate the rewarding social behaviors. The opposite profile is observed for these signaling systems for the aversive social behaviors. More studies are needed to investigate the directional role of the serotonin system in the nucleus accumbens in the regulation of many types of social behaviors, and vasopressin likely does not act in the nucleus accumbens in the regulation of the valence of social behaviors. Many of these different signaling systems are also interdependent of one another in the regulation of different types of social behaviors. Finally, the interaction of these signaling systems with dopamine in the nucleus accumbens is briefly discussed.

From Efficacy to Effectiveness: Evaluating Psychedelic Randomized Controlled Trials for Trustworthy Evidence-Based Policy and Practice

The recent review of a new drug application for MDMA-assisted therapy for posttraumatic stress disorder by the United States' Food and Drug Administration (FDA) highlighted epistemological and methodological challenges for evidence assessments. Similar challenges will also be faced in reviews of other compounds in early- and late-stage development, like psilocybin for depression. The regulatory demand for two successful phase 3 randomized controlled trials (RCTs) seems problematic, given a current lack of agreement on what constitutes "success", particularly when psychoactive drug administration is concomitant with (psycho)therapy. These complex arrangements challenge the internal validity of estimated average treatment effect through comparison with conventional control conditions. This paper reviews the assumptions behind RCTs' current "gold-standard" status in the hierarchy of evidence-based medicine (EBM). Recapitulating known epistemic limits of randomization and blinding, it emphasizes the urgent need to avoid the extrapolation fallacy. The resulting argument is that the degree of trustworthiness that efficacy-reported in RCTs-will reliably predict effectiveness-in target populations outside RCTs-depends on what type of psychedelic treatments will be regulated. If "stand-alone" drugs for large-scale prescription and consumption, trustworthiness should be graded low. On the other hand, for regulation of drug-assisted (psycho) therapies, the degree of trustworthiness can be considered high. The reason being that these two treatment approaches are based on different causal claims with distinct external validities. Therefore, careful assessment of support factors in each is recommended to prevent detrimental consequences, from potential rejection of effective therapies up to medical reversal of eventually approved drugs.

Neural circuits and therapeutic mechanisms of empathic pain

Empathy is the capacity to understand and share the experiences of others. This ability fosters connections between individuals, enriching the fabric of our shared world. One notable example is empathy for the pain of others. Such experiences facilitate the identification of potential dangers, both for oneself and for others. Neuroimaging studies have helped to pinpoint brain regions that modulate empathic pain. Recently, there has also been a surge in studies exploring the neural mechanisms of empathic pain in rodent models. Neuropsychiatric disorders such as autism, psychosis, and schizophrenia often exhibit empathy deficits. Targeting the modulation of empathic pain holds potential for alleviating core symptoms in these patients. Interestingly, empathy research may also benefit pain management, leading to new approaches for understanding the negative emotions associated with pain. This review summarizes recent advances in neuroimaging for the study of empathic pain, outlines the underlying neurocircuit mechanisms, describes therapeutic strategies, and explores promising avenues for future research. This article is part of the Special Issue on "Empathic Pain".

Uncovering Psychedelics: From Neural Circuits to Therapeutic Applications

Psychedelics, historically celebrated for their cultural and spiritual significance, have emerged as potential breakthrough therapeutic agents due to their profound effects on consciousness, emotional processing, mood, and neural plasticity. This review explores the mechanisms underlying psychedelics' effects, focusing on their ability to modulate brain connectivity and neural circuit activity, including the default mode network (DMN), cortico-striatal thalamo-cortical (CSTC) loops, and the relaxed beliefs under psychedelics (REBUS) model. Advanced neuroimaging techniques reveal psychedelics' capacity to enhance functional connectivity between sensory cerebral areas while reducing the connections between associative brain areas, decreasing the rigidity and rendering the brain more plastic and susceptible to external changings, offering insights into their therapeutic outcome. The most relevant clinical trials of 3,4-methylenedioxymethamphetamine (MDMA), psilocybin, and lysergic acid diethylamide (LSD) demonstrate significant efficacy in treating treatment-resistant psychiatric conditions such as post-traumatic stress disorder (PTSD), depression, and anxiety, with favorable safety profiles. Despite these advancements, critical gaps remain in linking psychedelics' molecular actions to their clinical efficacy. This review highlights the need for further research to integrate mechanistic insights and optimize psychedelics as tools for both therapy and understanding human cognition.

5-HT2C receptors in the nucleus accumbens constrain the rewarding effects of MDMA

MDMA is a promising adjunct to psychotherapy and has well-known abuse liability, although less than other amphetamine analogs. While the reinforcing dopamine (DA)-releasing properties of MDMA are on par with methamphetamine (METH), MDMA is a far more potent serotonin (5-HT) releaser, via the 5-HT transporter (SERT). MDMA-mediated 5-HT release in a major reward center, the nucleus accumbens (NAc), drives prosocial behaviors via 5-HT1BR activation. We hypothesized that this prosocial mechanism contributes to the reduced reinforcing properties of MDMA compared to METH and used a platform of assays to predict the balance of prosocial and abuse-linked effects of (R)-MDMA, a novel entactogen in clinical development. NAc DA release, measured by GRAB-DA photometry in vivo, increased in proportion to MDMA (7.5 and 15 mg/kg, i.p.) and METH (2 mg/kg i.p.)-conditioned place preference (CPP). Using conditional knockouts (cKOs) for DAT and SERT, microdialysis, and photometry, we found that MDMA-released 5-HT limited MDMA-released DA through actions in the NAc, rather than at ventral tegmental area DAergic cell bodies. SERT cKO reduced the MDMA dose required for CPP three-fold. This enhanced MDMA-CPP and increased DA release were replicated by intra-NAc infusion of either a 5-HT reuptake inhibitor (escitalopram) to prevent MDMA interaction with SERT, or a 5-HT2CR antagonist (SB242084), but not by the 5-HT1BR antagonist NAS-181. These data support separate mechanisms for the low abuse potential versus prosocial effect of MDMA. Using this platform of assays, (R)-MDMA is predicted to have prosocial effects and low abuse potential.

The efficacy and safety of MDMA-assisted psychotherapy for treatment of posttraumatic stress disorder: A systematic review and meta-analysis from randomized controlled trials

3,4-methylenedioxymethamphetamine (MDMA), commonly known as ecstasy, is one of the most widely used illicit substances worldwide. MDMA-assisted psychotherapy has become a novel treatment for posttraumatic stress disorder (PTSD), and many randomized controlled trials (RCTs) have been performed over the past decade. Therefore, this study aimed to systematically review and demonstrate the efficacy and safety of MDMA-assisted psychotherapy for the treatment of PTSD. We conducted a systematic search of PubMed, Embase, and Web of Science databases up to October 27, 2023, selected RCTs assessing the efficacy and safety of MDMA-assisted psychotherapy for the treatment of PTSD, and evaluated their quality using the Cochrane risk of bias tool. Seven RCTs were selected from the retrieved references. The results revealed that MDMA-assisted psychotherapy effectively reduced the change from baseline score in the Clinician-Administered PTSD Scale in patients with PTSD compared with either placebo or active controls. However, MDMA causes a series of adverse events, including muscle tightness, nausea, and decreased appetite. To a certain extent, MDMA-assisted psychotherapy may improve symptoms in patients with PTSD. However, side effects and abuse issues still seriously hinder clinical application of MDMA.