Anxiogenic Effects of Auditory Stimuli As Measured with Acoustic Startle

Increased startle has been associated with increased levels of anxiety. Auditory stimuli facilitate startle suggesting that the auditory stimuli increase levels of anxiety. We have found that presentation of a moderate intensity (60 dB) tone facilitates startle in C57BL/6J mice and the facilitation persists after the offset of the tone. Because auditory stimuli activate neural regions related to anxiety, such as the bed nucleus of the stria terminalis (BNST), we investigated whether the persistent elevation in startle after the offset of a tone is due to a tone-induced anxiety state. In these three experiments, we examined if it was the tone that induced the elevation of inter-trial interval (ITI) startle amplitudes, whether this effect persisted over multiple tone presentations, and the effects of administering the anxiolytic drug buspirone on the ITI startle enhancement. The experimental session used for assessing the nature of the ITI startle elevations consisted of a series of consecutive startle stimuli (pre-tones, 20 msec noise burst) for measuring baseline startle followed by 27 tones (12 kHz, 60 dB, 30 sec) intermixed with 27 startle stimuli (same as pre-tones). Startle amplitude after the offset of tones was significantly higher than startle amplitude to the initial pre-tone stimuli. The elevation in startle after the offset of the tones was reduced by pre-test administration of the anxiolytic buspirone (4mg/kg). These data suggest that in mice, a moderate intensity tone produces a persistent elevation in startle that may be related to a tone-induced anxious state.