The Role of Time and Nicotine Dose on Anxiety Measured with Light Enhanced Startle

Two experiments using Light-enhanced startle (LES) examined dose-dependent and time- dependent effects of acute nicotine on anxiety. In Experiment 1 rats were exposed to saline, .15 mg/kg, or .40 mg/kg (i.p.) nicotine and 5 minutes later were behaviorally tested in LES. Data suggested that nicotine at both doses was anxiolytic in males but not anxiolytic in females. In females, the higher nicotine dose, .40 mg/kg, was anxiogenic but only during later portions of the test session. In both males and females, within-session variation in LES provided evidence that LES increased in magnitude as time since nicotine administration increased. Therefore, in Experiment 2, longer drug-to-test intervals were applied in order to examine possible time- dependent increases in anxiety produced by nicotine. In Experiment 2, rats were exposed to saline or .40 mg/kg nicotine and were behaviorally tested 15 min or 35 min after nicotine administration in LES. Trends in the available data suggested an anxiogenic profile of nicotine when tested 15 min following drug administration but an anxiolytic profile when tested 35 min following drug administration. At the short 5 min drug-to-test interval used in Experiment 1, findings contradict those in other experiments using the social interaction test of anxiety. Collectively, results suggest Light-enhanced startle is sensitive to dose and time-dependent effects of nicotine on anxiety. Possible differences between reflexive and non-reflexive measures of fear and gonadal influences in anxiety expression are discussed.