# Cigarette smoking is associated with levels of the serotonin transporter in the brain: a [11C]DASB PET Study

## TL;DR

This study shows that current cigarette smoking is linked to higher serotonin transporter levels in the hippocampus, which may indicate lower serotonin levels, and these changes may reverse after quitting.

## Contribution

First in vivo evidence linking current smoking to elevated hippocampal serotonin transporter binding in humans.

## Key findings

- Current smokers had higher hippocampal SERT binding compared to non-smokers and ex-smokers.
- Ex-smokers showed SERT levels similar to non-smokers, suggesting normalization after quitting.
- No significant differences in SERT levels were found in the midbrain or neocortex.

## Abstract

Preclinical work suggests that chronic nicotine/tobacco use is associated with reductions in serotonin within the hippocampus, yet no research has yet shown an association of smoking behaviors and alterations in brain serotonin in humans in vivo.

We therefore analyzed existing [11C]DASB PET data from the Cimbi Database to compare the availability of the serotonin transporter (SERT) in the hippocampus, midbrain (including the raphe), and neocortex of 60 healthy non-smokers, 15 ex-smokers, and 11 current smokers who also provided blood samples for determination of plasma tryptophan load. Because SERT availability is considered to be negatively associated with extracellular serotonin levels, we hypothesized that current smokers would exhibit greater SERT availability than ex-smokers and non-smokers.

There was a significant main effect of group on SERT binding (DASB BPND) values in the bilateral and left hippocampus, and a trend toward such in the right hippocampus. Post hoc ANOVAs revealed that current smokers exhibited greater hippocampal DASB BPND than both non-smokers and ex-smokers, while the latter 2 groups did not differ. There were no group effects on DASB BPND within the midbrain or global neocortex. Finally, there was no significant group effect on plasma tryptophan load.

This study provides the first in vivo evidence that current smoking may be associated with elevated hippocampal SERT binding—possibly reflecting lower synaptic serotonin concentrations, and that this change may normalize following smoking cessation.