EARLY SOCIAL ISOLATION STRESS POTENTIATES HEROIN SEEKING BY AGGRAVATING THE DYSFUNCTION OF PRELIMBIC CORTEX TO VENTRAL TEGMENTAL AREA PROJECTION
Authors: Wang *Zijun , Wang Yunwanbin , Yue Shuwen , Yang Fengwei , Singh Archana 
Published: February 2025

Abstract

Background
Opioid use disorder (OUD) is a chronic life-long disease characterized by compulsive drug taking and persistent vulnerability to relapse. Stress has been reported to induce vulnerability to opioid relapse by affecting the gene expression in key brain regions within the reward pathway. However, the specific brain circuits contributing to stress-induced relapse vulnerability, as well as the associated molecular changes within key brain circuits, remain unclear.

Aims & Objectives
Adolescence is a critical period when behavioral and brain circuitry maturation occurs. Stress during this key period results in higher rates of psychiatric disorders, including drug addiction.
Social interaction during early life plays an essential role in cognitive development. Preclinical studies have reported that adolescent social isolation is associated with increased drug taking and seeking.
Concomitantly, our lab previously reported that early social isolation (ESI) stress potentiates heroin- seeking behavior after forced abstinence. Yet, the underlying mechanisms remain elusive.
Stress and substance abuse are associated with neuroplasticity in the mesocorticolimbic pathway. For example, the maladaptation of glutamatergic projecting neurons from the prefrontal cortex (PFC) and its projecting subcortical regions (e.g., ventral tegmental area [VTA]) are implicated in both stress and addiction. Therefore, we hypothesized that ESI stress may increase addiction vulnerability via exerting pathological impairments in these key brain regions.

Method and Results
To test our hypothesis, we used a mouse heroin self-administration model to examine how chronic ESI stress affects the behavioral and neural responses to heroin during adulthood.
We found that ESI stress aggravates heroin abstinence-induced neuronal dysfunction in PFC-&gt;VTA projecting neurons. Additionally, using DREADDs strategy to selectively activate PFC-&gt;VTA projections, we found that activation of PFC-&gt;VTA projections attenuated ESI-potentiated heroin seeking, which is accompanied by the recovery of neuronal firing and excitatory synaptic transmission in these neurons.
Furthermore, using translating ribosome affinity purification (TRAP) coupled sequencing method, we found that ESI stress and heroin abstinence convergently affect the expression of genes regulating morphogenesis, cell communication, and metabolic processes. ESI stress and heroin abstinence interactively affect the expression of genes enriched in signaling pathways related to cell cycle and DNA damage repair. Furthermore, we showed that antioxidant treatment with N-acetylcysteine (NAC), which ameliorates DNA damage, significantly attenuated ESI-potentiated heroin seeking.

Discussion & Conclusion
Together, our study showed that ESI stress-induced susceptibility to heroin relapse is associated with the ESI-potentiated neuronal dysfunction in PFC-VTA projections; and that this neuronal dysfunction is accompanied by gene transcriptional changes within PFC-VTA circuits. Our studies provide novel insight into the