Our results indicated that smokers with the l/l genotype of the 5-HTTLPR gene, compared with smokers carrying the s allele, showed significantly greater acoustic startle response suppression when provided with nicotine vs. placebo nasal spray. This interaction did not differ by race, as it was found for both Caucasian and African-American smokers, and the effect was observed across all types of stimuli (i.e., there was no interaction with valence). In other words, l/l smokers experienced an overall decrease in activation of defensive pathways brought about by the startle probe, when given nicotine compared to smokers without the l allele, regardless of the type of foreground cue. These results suggest that nicotine may activate appetitive mechanisms that suppress the startle response to a greater degree among l/l smokers than smokers with the l/s or s/s alleles. However, this did not result in differential effects across valences; in other words, the effect seems to reduce startle responding irresespective of the valence of the foreground cue and was observed even startle responses in the absence of any emotional cue were included in the analysis.
