Interactions of Stress and Nicotine on Amplitude, Pre-Pulse Inhibition and Habituation of the Acoustic Startle Reflex
Uniformed Services University Of The Health Sciences Bethesda United States
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Cigarette smokers report that one reason for smoking is that it helps them cope with stress. There is little evidence that nicotine reduces any of the physiological effects of stress, and instead, nicotine and stress have an additive effect on physiological indices of stress. One way that nicotine may enhance stress-coping in humans is through changes in attention because nicotine enhances vigilance and selective attention in smokers and nonsmokers. Attention is reflected in aspects of the acoustic startle response ASR, which can be modulated by both stress and nicotine and studied in animals. These experiments used a chronic nicotine administration paradigm and an acute stressor to test for interactions of stress and nicotine on amplitude , pre-pulse inhibition PPI, and habituation of the ASR during nicotine administration and cessation in rats. ASR amplitude is a measure of sensorimotor reactivity, and PPI is believed to reflect processes of attention involved in sensory gating and selective attention. In Experiment 1, 12 mgkgday, 6 mgkgday nicotine , or saline was administered to rats for 11 days. On day 11, rats were stressed by restraint, observation of conspecifics restraint, or were not stressed for 15-20 minutes prior to startling. Nicotine and stress each increased amplitude and PPI. Nicotine significantly interacted with stress such that nicotine prevented the changes in amplitude and PPI associated with stress or nicotine alone. In Experiment 2, nicotine cessation , nicotine 12 mgkgday or saline was administered for 11 days prior to explantation. On Day 1 of drug cessation , subjects were stressed by restraint or were not stressed for 15-20 minutes prior to startling. Cessation effects were generally in a direction opposite to effects of nicotine administration, but results were not significant .