Mediodorsal thalamus-projecting anterior cingulate cortex neurons modulate helping behavior in mice

Inhibitory gamma-aminobutyric acidergic neurons in the anterior cingulate cortex participate in the comorbidity of pain and emotion

Pain is often comorbid with emotional disorders such as anxiety and depression. Hyperexcitability of the anterior cingulate cortex has been implicated in pain and pain-related negative emotions that arise from impairments in inhibitory gamma-aminobutyric acid neurotransmission. This review primarily aims to outline the main circuitry (including the input and output connectivity) of the anterior cingulate cortex and classification and functions of different gamma-aminobutyric acidergic neurons; it also describes the neurotransmitters/neuromodulators affecting these neurons, their intercommunication with other neurons, and their importance in mental comorbidities associated with chronic pain disorders. Improving understanding on their role in pain-related mental comorbidities may facilitate the development of more effective treatments for these conditions. However, the mechanisms that regulate gamma-aminobutyric acidergic systems remain elusive. It is also unclear as to whether the mechanisms are presynaptic or postsynaptic. Further exploration of the complexities of this system may reveal new pathways for research and drug development.

Transient Inhibition of the Mediodorsal Thalamus During Early Adolescence Induces Hypofrontality and Social Memory Deficits in Young Adulthood

Background

Dysconnectivity between the mediodorsal thalamus (MD) and medial prefrontal cortex (mPFC) during adolescence is linked to developmental and psychiatric disorders, as well as social behavioral deficits. However, the precise mechanisms that underlie these impairments remain elusive.

Methods

We transiently inhibited MD activity with inhibitory DREADDs (HM4Di) in adolescent mice. Then, we examined the social behavior performance by a three-chamber social behavioral paradigm and neural excitability in both MD and mPFC neurons in adulthood with multiple approaches.

Results

We revealed that this transient MD inhibition during adolescence led to impaired social memory in adulthood. The neuronal excitability of both MD and mPFC excitatory neurons decreased. Meanwhile, excitatory synaptic transmission in excitatory pyramidal neurons in the mPFC was impaired. In vivo calcium imaging showed a persistent reduction of general calcium activity in the mPFC. Unexpectedly, there were significant alterations in intrinsic excitability and synaptic function changes in somatostatin but not in parvalbumin interneurons.

Conclusions

Our findings provide insights into the role of MD input activity in shaping the circuit and functional maturation of the mPFC that is critical for the normal development of social memory and abnormal deficits in psychiatric disorders.

Persistent Disruptions in Prefrontal Connectivity Despite Behavioral Rescue by Environmental Enrichment in a Mouse Model of Rett Syndrome

Rett Syndrome, a neurodevelopmental disorder caused by loss-of-function mutations in the MECP2 gene, is characterized by severe motor, cognitive and emotional impairments. Some of the deficits may result from changes in cortical connections, especially downstream projections of the prefrontal cortex, which may also be targets of restoration following rearing conditions such as environmental enrichment that alleviate specific symptoms. Here, using a heterozygous Mecp2 +/- female mouse model closely analogous to human Rett Syndrome, we investigated the impact of early environmental enrichment on behavioral deficits and prefrontal cortex connectivity. Behavioral analyses revealed that enriched housing rescued fine motor deficits and reduced anxiety, with enrichment-housed Mecp2 +/- mice performing comparably to wild-type (WT) controls in rotarod and open field assays. Anatomical mapping of top-down anterior cingulate cortex (ACA) projections demonstrated altered prefrontal cortex connectivity in Mecp2 +/- mice, with increased axonal density in the somatosensory cortex and decreased density in the motor cortex compared to WT controls. ACA axons revealed shifts in hemispheric distribution, particularly in the medial network regions, with Mecp2 +/- mice exhibiting reduced ipsilateral dominance. These changes were unaffected by enriched housing, suggesting that structural abnormalities in prefrontal cortex connectivity persist despite behavioral improvements. Enriched housing rescued brain-derived neurotrophic factor (BDNF) levels in the hippocampus but failed to restore BDNF levels in the prefrontal cortex, consistent with the persistent deficits observed in prefrontal axonal projections. These findings highlight the focal nature of changes induced by reduction of MeCP2 and by exposure to environmental enrichment, and suggest that environmental enrichment starting in adolescence can alleviate behavioral deficits without reversing abnormalities in large-scale cortical connectivity.

The regulatory effect of the anterior cingulate cortex on helping behavior in juvenile social isolation model mice

Social isolation during adolescence negatively impacts the development of adult social behaviors. However, the exact link between social experiences during adolescence and social behaviors in adulthood is not fully understood. In the present study, we investigated how isolation during juvenility affects harm avoidance behavior in a mouse model of juvenile social isolation. We found that mice subjected to social isolation as juveniles display atypical harm avoidance behaviors and that neurons in the anterior cingulate cortex are involved in these abnormal behaviors. Furthermore, we discovered that the chemogenetic activation of anterior cingulate cortex pyramidal neurons can rescue impaired harm-avoidance behaviors in these mice. Our findings provide valuable insights into the potential mechanisms underlying the impact of social experiences on behavior and brain function. Understanding how social isolation during crucial developmental periods can lead to alterations in behavior opens up new avenues for exploring therapeutic interventions for neuropsychiatric disorders characterized by impaired prosocial behaviors.

Predictive coding for the actions and emotions of others and its deficits in autism spectrum disorders

Traditionally, the neural basis of social perception has been studied by showing participants brief examples of the actions or emotions of others presented in randomized order to prevent participants from anticipating what others do and feel. This approach is optimal to isolate the importance of information flow from lower to higher cortical areas. The degree to which feedback connections and Bayesian hierarchical predictive coding contribute to how mammals process more complex social stimuli has been less explored, and will be the focus of this review. We illustrate paradigms that start to capture how participants predict the actions and emotions of others under more ecological conditions, and discuss the brain activity measurement methods suitable to reveal the importance of feedback connections in these predictions. Together, these efforts draw a richer picture of social cognition in which predictive coding and feedback connections play significant roles. We further discuss how the notion of predicting coding is influencing how we think of autism spectrum disorder.

Neural Network Excitation/Inhibition: A Key to Empathy and Empathy Impairment

Empathy is an ability to fully understand and feel the mental states of others. We emphasize that empathy is elicited by the transmission of pain, fear, and sensory information. In clinical studies, impaired empathy has been observed in most psychiatric conditions. However, the precise impairment mechanism of the network systems on the pathogenesis of empathy impairment in psychiatric disorders is still unclear. Multiple lines of evidence suggest that disturbances in the excitatory/inhibitory balance in neurologic disorders are key to empathetic impairment in psychiatric disorders. Therefore, we here describe the roles played by the anterior cingulate cortex- and medial prefrontal cortex-dependent neural circuits and their impairments in psychiatric disorders, including anxiety, depression, and autism. In addition, we review recent studies on the role of microglia in neural network excitation/inhibition imbalance, which contributes to a better understanding of the neural network excitation/inhibition imbalance and may open up innovative psychiatric therapies.

Cingulate to septal circuitry facilitates the preference to affiliate with large peer groups

Despite the prevalence of large-group living across the animal kingdom, no studies have examined the neural mechanisms that make group living possible. Spiny mice, Acomys, have evolved to live in large groups and exhibit a preference to affiliate with large over small groups. Here, we determine the neural circuitry that facilitates the drive to affiliate with large groups. We first identify an anterior cingulate cortex (ACC) to lateral septum (LS) circuit that is more responsive to large than small groups of novel same-sex peers. Using chemogenetics, we then demonstrate that this circuit is necessary for both male and female group investigation preferences but only males' preference to affiliate with larger peer groups. Furthermore, inhibition of the ACC-LS circuit specifically impairs social, but not nonsocial, affiliative grouping preferences. These findings reveal a key circuit for the regulation of mammalian peer group affiliation.

Prosocial behaviors in rodents

Prosocial behaviors (i.e., actions that benefit others) are central for social interactions in humans and other animals, by fostering social bonding and cohesion. To study prosociality in rodents, scientists have developed behavioral paradigms where animals can display actions that benefit conspecifics in distress or need. These paradigms have provided insights into the role of social interactions and transfer of emotional states in the expression of prosociality, and increased knowledge of its neural bases. However, prosociality levels are variable: not all tested animals are prosocial. Such variation has been linked to differences in animals' ability to process another's state as well as to contextual factors. Moreover, evidence suggests that prosocial behaviors involve the orchestrated activity of multiple brain regions and neuromodulators. This review aims to synthesize findings across paradigms both at the level of behavior and neural mechanisms. Growing evidence confirms that these processes can be studied in rodents, and intense research in the past years is rapidly advancing our knowledge. We discuss a strong bias in the field towards the study of these processes in negative valence contexts (e.g., pain, fear, stress), which should be taken as an opportunity to open new venues for future research.

How is helping behavior regulated in the brain?

In humans and other animals, individuals can actively respond to the specific needs of others. However, the neural circuits supporting helping behaviors are underspecified. In recent work, Zhang, Wu, and colleagues identified a new role for the anterior cingulate cortex (ACC) in the encoding and regulation of targeted helping behavior (allolicking) in mice.