The Abnormal Structural Connectivity in Adolescent Smoking

Abstract

Smoking addiction is a chronic mental disorder and is closely related to changes in brain structure. There are few studies on the structural connectivity of the thalamus-cortical circuit in adolescent smokers. Therefore, this study used magnetic resonance imaging techniques and four ethological scales: the Fagerstrom Test for Nicotine Dependence (FTND), Pack-years, Cigarettes per day (CPD), and Duration to explore the effects of smoking on the thalamus-cortical circuit’s structural connections in teenagers.

Diffusion tensor imaging and thalamic probabilistic segmentation were used to study the abnormalities of the structural connectivity between the thalamus and seven brain cortical regions in adolescent smokers and non-smokers.

These regions include the anterior cingulate cortex, dorsal posterior cingulate cortex, subfrontal cortex, dorsolateral prefrontal cortex, medial orbital frontal cortex, posterior cingulate cortex, and ventrolateral prefrontal cortex. The study found that, compared with non-smokers, young smokers have significantly lower white matter structural connectivity between the left thalamus and cortical areas such as the anterior cingulate cortex, inferior frontal gyrus, medial orbital frontal cortex, and ventral prefrontal cortex. However, the four behaviors do not correlate with the abnormal structural connectivities of adolescent smokers in the thalamic-cortical circuit.

In summary, this study demonstrates that abnormal structural connectivities in the thalamic-cortical circuit exist in adolescent smokers. This may contribute to our understanding of the neural mechanisms of adolescents’ smoking addiction.
Keywords:
Adolescent Smoking, Diffusion Tensor Imaging, Thalamic-Cortical Circuit, Structural Connectivity.

Introduction:

Nicotine is an agonist of presynaptic nicotinic acetylcholine receptors (nAChRs), and it promotes the synaptic release of several neurotransmitters, including dopamine and glutamate. Because of these characteristics, nicotine plays significant roles in the highly addictive properties of cigarettes. The critical role of dopaminergic transmission in the reward mechanism makes the nAChRs a conduit for sending out signals and maintaining nicotine addiction [47]. The thalamus has the highest nAChRs density [19,40], meaning nicotine addiction is likely to significantly impact the thalamus [4]. The thalamus may integrate activities by transmitting information to the dopamine regulatory system involving the reward system, which is important for the development and maintenance of addiction. Moreover, the thalamus is a key center of the frontal-striatum-thalamic circuit, and any disorders in this circuit may be involved in the persistent drug-seeking behaviors, crucial for studying the neural mechanisms of smoking addiction. According to prior studies, we can discern findings revealing the reduced RSFC of the thalamus with the dlPFC, the ACC, the insula, and the caudate in smokers.

Materials and Methods:

The Medical Ethics Committee of the First Affiliated Hospital of Inner Mongolia University of Science and Technology approved all research steps for this experiment. We selected 64 adolescent male smokers and 58 adolescent male non-smokers, following set selection rules. Firstly, we acquired diffusion tensor imaging and structural T1-weighted images. We used FSL software to execute data preprocessing and extraction of regions of interest (Fig. 1) and probabilistic fiber tracking. Finally, we extracted the relative strength of structural connectivities based on thalamic probability segmentation and performed statistical and Pearson correlation analysis.

Here are the clinical details of young smokers and nonsmokers. The structural connectivities between the left thalamus and anterior cingulate cortex, inferior epithelial cortex, medial temporal prefrontal cortex, and ventral lateral prefrontal cortex were significantly different in adolescent non-smokers and smoking groups (p<0.05). However, no significant difference was found concerning the right thalamus and these cortical regions. No correlation was found between abnormal structural connections and behavioral scales among adolescent smokers. Figure 2 illustrates the differences in structural connectivity between the left and right lateral thalamus and the seven cortical regions between groups. (a-g) demonstrate the structural connectivity difference between the left thalamus and the seven cortical brain regions; (h-n) depict the structural connectivity difference between the right thalamus and the seven cortical brain regions.

Discussion and Conclusion:

The study found that younger smokers had a lower white matter structure connection from the left thalamus to the anterior cingulate cortex, subfrontal cortex, medial temporal frontal cortex, and ventrolateral prefrontal cortex compared with adolescent non-smokers. Adolescent smoking affects the structural connectivities between the thalamus and cortical brain regions. Previous studies have shown a relationship between the thalamus-cortex connectivities and the neurobiology of substance addiction. These findings have jointly demonstrated that the connections between the thalamus and the cortical regions play an important role in smoking.

Acknowledgements

This work was supported by my tutor, Dr. Huang, and Dr. Wang. I also appreciate the guidance and support from Dr. Karen.

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