Effects of smoking on acoustic startle and prepulse inhibition in humans

Rationale: Prepulse inhibition of the acoustic startle response (PPI) is a paradigm in which a startle response to an auditory stimulus is reduced when that stimulus is preceded by a lower intensity, non-startling stimulus (prepulse). PPI is used as an operational measure of sensorimotor gating in both humans and other mammals. Acute administration of nicotine enhances PPI in rats, an effect that has been recently demonstrated in humans. Objectives: We compared PPI in 12 male smokers and 14 male non-smokers tested in four repeat startle sessions across 2 test days in order to examine further the effects of smoking and smoking withdrawal on acoustic startle and PPI. Methods: In a crossover design, the smokers smoked ad lib or abstained from smoking overnight prior to 9 a.m. testing. These 2 test days were in randomized order. On both days, smokers were immediately retested after smoking three cigarettes. Non-smokers were tested twice on each of 2 separate days. Results: Across sessions, the smokers had reduced startle to pulse alone stimuli in the first block of each session when compared to the non-smokers. The non-smokers had no change in gating across their four test sessions. For the smokers, the abstinence condition produced a non-significant reduction in PPI compared to that of the ad lib smoking day. During the smoking abstinence session, smokers had comparable gating to non-smokers. Smoking immediately after washout produced a significant improvement in PPI such that gating in the smokers exceeded that of the non-smokers. Conclusion: Smoking after overnight washout from cigarettes enhanced sensorimotor gating compared to pre-smoking values and compared to gating in non-smokers.