Substance Abuse in Emerging Adults: The Role of Neuromelanin and Ventral Striatal Response to Social and Monetary Rewards.

Johanna M. Jarcho,Camille R. Johnston,Clifford M. Cassidy,Megan Quarmley,David V. Smith,James B. Wyngaarden

doi:10.3390/brainsci12030352

Johanna M. Jarcho, Camille R. Johnston + Show 4 more

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https://doi.org/10.3390/brainsci12030352

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Abstract

Perturbations in dopamine system function may increase risk of substance use disorder (SUD). We recently demonstrated that neuromelanin (NM) MRI signal in the substantia nigra, a non-invasive index of dopamine system function, is elevated in long term cocaine users (Cassidy et al., 2020). However, it is unclear whether elevated NM-MRI signal is linked to risk of SUD, or is a byproduct of long-term drug use. Our prior work failed to show relations between NM-MRI signal and functional engagement of ventral striatum during a monetary reward task. However, social experiences are commonly linked to drug use and relapse. Given that, NM-MRI signal may be more closely linked to ventral striatal engagement during social, rather than monetary reward processing. Emerging adults (n = 33, 21.88 ± 4.35 years) with varying levels of substance abuse, but without SUD, underwent NM-MRI and fMRI during social and monetary reward processing tasks. Voxelwise analysis within the substantia nigra (SN) demonstrated lower NM-MRI signal was associated with more severe substance abuse. Lower right ventral striatal engagement to social reward was also associated with more severe substance abuse. This relation was moderated by SN NM-MRI signal such that diminished striatal response to reward was associated with greater substance abuse among those with low NM-MRI signal, but lower substance abuse among those with high NM-MRI signal. Unexpectedly, higher right ventral striatal engagement during monetary reward was associated with more severe substance abuse. This relation was moderated by SN NM-MRI signal such that greater striatal response to reward was associated with greater substance abuse among those with low NM-MRI signal. Taken together, we provide preliminary evidence that, in emerging adults, low rather than high dopamine system function may increase risk of substance abuse, and strengthen the association between substance use and the brain’s sensitivity to social and monetary outcomes in different ways.

Highlights

Substance use disorders among late adolescents and emerging adults are common, costly, and on the rise [1,2]
We tested the relation between neuromelanin sensitive-MRI (NM-MRI) signal, substance abuse, and ventral striatal sensitivity to social and monetary reward in emerging adults
Hyper-striatal response to positive monetary feedback coupled with low NM-MRI signal may increase risk of substance abuse behaviors

Summary

Introduction

Substance use disorders among late adolescents and emerging adults are common, costly, and on the rise [1,2]. Since 2016, there has been a 61% increase in substance use among 8th graders [3]. Given the fact that substance use typically peaks between 18−25 years of age [4], we are likely to see a substantial increase in substance abuse and substance use disorders (SUDs) among late adolescents and emerging adults over the several years. Only a minority of those who try drugs of abuse develop a SUD [5]. Attempts have been made to identify risk factors for SUD. Given its role in reward processing, perturbations in dopamine system function has been one target of investigation

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