Optogenetic and chemogenetic approaches reveal differences in neuronal circuits that mediate initiation and maintenance of social interaction

Altered Neural Activity in the Mesoaccumbens Pathway Underlies Impaired Social Reward Processing in Shank3-Deficient Rats

Social behaviors are crucial for human connection and belonging, often impacted by conditions like Autism Spectrum Disorder (ASD). The mesoaccumbens pathway (ventral tegmental area (VTA) to the nucleus accumbense (NAc)) plays a pivotal role in social behavior and is implicated in ASD. However, the impact of ASD-related mutations on social reward processing remains insufficiently explored. This study focuses on the Shank3 mutation, associated with a rare genetic condition and linked to ASD, examining its influence on the mesoaccumbens pathway during behavior, using the Shank3-deficient rat model. Our findings indicate that Shank3-deficient rats exhibit atypical social interactions, associated with altered neuronal activity of VTA dopaminergic and GABAergic neurons and reduced dopamine release in the NAc. Moreover, they demonstrate that manipulating VTA neuronal activity can normalize this behavior, providing insights into the effects of Shank3 mutations on social reward processing  and identifying a potential neural pathway for intervention.

Understanding the neurobiology of social behavior through exploring brain-wide dynamics of neural activity

Social behavior is highly complex and adaptable. It can be divided into multiple temporal stages: detection, approach, and consummatory behavior. Each stage can be further divided into several cognitive and behavioral processes, such as perceiving social cues, evaluating the social and non-social contexts, and recognizing the internal/emotional state of others. Recent studies have identified numerous brain-wide circuits implicated in social behavior and suggested the existence of partially overlapping functional brain networks underlying various types of social and non-social behavior. However, understanding the brain-wide dynamics underlying social behavior remains challenging, and several brain-scale dynamics (macro-, meso-, and micro-scale levels) need to be integrated. Here, we suggest leveraging new tools and concepts to explore social brain networks and integrate those different levels. These include studying the expression of immediate-early genes throughout the entire brain to impartially define the structure of the neuronal networks involved in a given social behavior. Then, network dynamics could be investigated using electrode arrays or multi-channel fiber photometry. Finally, tools like high-density silicon probes and miniscopes can probe neural activity in specific areas and across neuronal populations at the single-cell level.

Activation of NPY Receptors in the BLA Inhibits Projections to the Bed Nucleus of the Stria Terminalis and Buffers Stress-Induced Decreases in Social Interaction in Male Rats

Neuropeptide Y (NPY) increases resilience and buffers behavioral stress responses in male rats in part through decreasing the excitability of principal output neurons in the basolateral amygdala (BLA). Intra-BLA administration of NPY acutely increases social interaction (SI) through activation of either Y1 or Y5 receptors, whereas repeated NPY (rpNPY) injections (once daily for 5 d) produce persistent increases in SI through Y5 receptor-mediated neuroplasticity in the BLA. In this series of studies, we characterized the neural circuits from the BLA that underlie these behavioral responses to NPY. Using neuronal tract tracing, NPY Y1 and Y5 receptor immunoreactivity was identified on subpopulations of BLA neurons projecting to the bed nucleus of the stria terminalis (BNST) and the central nucleus of the amygdala (CeA). Inhibition of BLA→BNST, but not BLA→CeA, neurons using projection-restricted, cre-driven designer receptors exclusively activated by designer drug-Gi expression increased SI and prevented stress-induced decreases in SI produced by a 30 min restraint stress. This behavioral profile was similar to that seen after both acute and rpNPY injections into the BLA. Intracellular recordings of BLA→BNST neurons demonstrated NPY-mediated inhibition via suppression of H currents, as seen previously. Repeated intra-BLA injections of NPY, which are associated with the induction of BLA neuroplasticity, decreased the activity of BLA→BNST neurons and decreased their dendritic complexity. These results demonstrate that NPY modulates the activity of BNST-projecting BLA neurons, suggesting that this pathway contributes to the stress-buffering actions of NPY and provides a novel substrate for the proresilient effects of NPY.

Altered neural activity in the mesoaccumbens pathway underlies impaired social reward processing in Shank3-deficient rats

Social behaviors are crucial for human connection and belonging, often impacted in conditions like Autism Spectrum Disorder (ASD). The mesoaccumbens pathway (VTA and NAc) plays a pivotal role in social behavior and is implicated in ASD. However, the impact of ASD-related mutations on social reward processing remains insufficiently explored. This study focuses on the Shank3 mutation, associated with a rare genetic condition and linked to ASD, examining its influence on the mesoaccumbens pathway during behavior, using the Shank3-deficient rat model. Our findings indicate that Shank3-deficient rats exhibit atypical social interactions and have difficulty adjusting behavior based on reward values, associated with modified neuronal activity of VTA dopaminergic and GABAergic neurons and reduced dopamine release in the NAc. Moreover, we demonstrate that manipulating VTA neuronal activity can normalize this behavior, providing insights into the effects of Shank3 mutations on social reward and behavior, and identify a potential neural pathway for intervention.

2023 at PLOS Biology

2023 saw many important advances in the life sciences. In this editorial, we highlight research from across the breadth of PLOS Biology's scope.

Independent neural circuits encode the dynamics of social interaction in rats

A study in PLOS Biology by Rojek-Sito and colleagues demonstrates a key role of the central amygdala and specific circuits projecting to and from this brain area in the initiation versus maintenance of positive social interactions.