ABSTRACT
The startle potentiated startle (SPS) paradigm has been reported to be an effective procedure for studying the conditioned enhancement of acoustic startle in the absence of electric shocks or extinction. This study examines the effects of two anxiolytic treatments, buspirone and alprazolam, on this SPS effect. Subjects were tested in the SPS paradigm 2 days a week (Monday and Thursday) for 10 weeks. Each startle test session consisted of 10 Noise Alone trials (115 dB acoustic noise burst presented for 40 ms) and 10 Light+Noise trials (115 dB acoustic stimuli presented during the latter 40 ms of a 3,540 ms period in which a 15-watt light was illuminated). Although there was no difference in startle amplitude on Noise Alone trials when compared to Light+Noise trials initially, by the end of the first test session and continuing throughout the duration of the experiment, startle amplitude on Light+Noise trials was significantly (approximately 50-75%) greater than on Noise Alone trials. After five control (i.e., no injection) SPS test sessions, once-weekly drug challenges were conducted over the course of 7 weeks. In these weekly drug challenges, subjects received acute treatment with various doses of the benzodiazepine anxiolytic alprazolam (0.25, 0.5, 1.0 mg/kg) or the novel anxiolytic buspirone (1.0, 2.0, 4.0 mg/kg); subjects also received vehicle treatment (0.5% methylcellulose) on one treatment day. All treatments were administered intraperitoneally (i.p.), 15 min before the start of startle testing. Consistent with previous reports, buspirone increased and alprazolam decreased startle amplitude on the Noise Alone trials; these effects were dose-related. Both agents reduced the magnitude of the SPS effect when it was expressed as the Light+Noise startle amplitude minus the Noise Alone startle amplitude. These findings are similar to the effects of these treatments in the traditional shock-based fear-potentiated startle paradigm.
