Neural-hematopoietic-inflammatory axis in nonsmokers, electronic cigarette users, and tobacco smokers

Amygdala activity in context of the splenocardiac model has not been investigated in healthy, young adults and has not been compared between nonsmokers, electronic cigarette users, and smokers. The purpose of the current study was to determine whether fluorodeoxyglucose positron emission tomography/computer tomography (FDG PET/CT) scans would demonstrate positively correlated metabolic activity in the amygdala, bone marrow, spleen, and aorta, elucidating activation of the splenocardiac axis in otherwise healthy young people who use tobacco products compared to nonusers. Moreover, the study was conducted to evaluate whether electronic cigarette users and tobacco smokers have similar levels of inflammation compared to nonusers. In 45 healthy adults (mean age = 25 years), including nonsmoker (n = 15), electronic cigarette user (n = 16), and smoker (n = 14) groups, metabolic activity in the amygdala, spleen, aorta, bone marrow of thoracic vertebrae, and adjacent erector spinae skeletal muscle was quantified through visualization of radioactive glucose (¹⁸ FDG) uptake by FDG-PET/CT. The maximum standardized uptake value for each region was calculated for correlation analyses and comparisons between groups. In correlation analyses, metabolic activity of the amygdala correlated with metabolic activity in the aorta (r = 0.757), bone marrow (r = 0.750), and spleen (r = 0.665), respectively. Metabolic activity in the aorta correlated with ¹⁸ FDG uptake in the thoracic vertebrae (r = 0.703) and spleen (r = 0.594), respectively. Metabolic activity in the spleen also correlated with ¹⁸ FDG uptake in the bone marrow (r = 0.620). Metabolic activity in the adjacent erector spinae skeletal muscle (our control tissue) was not positively correlated with any other region of interest. Finally, there were no statistically significant mean differences in metabolic activity between the three groups: nonsmokers, electronic cigarette users, and smokers in any target tissue. Amygdala metabolic activity, as measured by ¹⁸ FDG uptake in FDG-PET/CT scans, positively correlated with inflammation in the splenocardiac tissues, including: the aorta, bone marrow, and spleen, underscoring the existence of a neural-hematopoietic-inflammatory axis in healthy, young adults.