694 Fig. 2 Effects of pramipexole on startle magnitude (mean ±SEM) (a) and %PPI (mean±SEM) (b) across all trial conditions in groups treated with placebo vs. 0.125 mg pramipexole (n=20) or placebo vs. 0.1875 mg pramipexole (n=20). Open circle Placebo; closed circle active dose. Asterisk Startle-reducing effects of 0.1875 mg pramipex- ole on prepulse+pulse trials at 120-ms prepulse intervals (p<0.003); number sign PPI-enhancing effects of pramipexole at 120-ms prepulse intervals (p<0.05) two-way interactions). However, 0.1875 mg pramipexole did appear to reduce startle magnitude, and this was also confirmed by ANOVA (placebo vs. 0.1875 mg, F = 5.40, df 1,19, p = 0.005; main effect of trial, F = 18.32, df 5,95, p < 0.0001). The interaction of dose × trial type was also significant (F = 2.43, df 5,95, p < 0.045), suggesting differ- ent effects of pramipexole on startle magnitude across the different trial types. Post hoc comparisons revealed that pramipexole did not significantly reduce startle magnitude on pulse-alone trials (F = 2.06, df 1,19, ns), but did significantly reduce startle magnitude on 120-ms prepulse trials (F = 11.97, df 1,19, p < 0.003; Fig. 2a). To examine the independence of pramipexole effects on pulse alone vs. 120-ms prepulse trials, a subgroup of 17 subjects was created by eliminating three subjects whose pulse-alone startle magnitude was most reduced by pramipexole. In Psychopharmacology (2009) 205:689–698 this way, the remaining group (n = 17) exhibited absolutely no startle-reducing effects of pramipexole on pulse-alone trials [F<<1; mean (SEM) startle magnitude placebo vs. 0.1875 mg pramipexole = 117.20 (15.90) vs. 116.04 (17.75)] but nonetheless exhibited significant startle- reducing effects of pramipexole on 120-ms prepulse trials (F = 8.46, df 1,16, p = 0.01; Fig. 3a). Consistent with the selective startle-reducing effects of pramipexole on 120-ms prepulse trials, pramipexole significantly increased PPI at 120-ms intervals (Fig. 2b). Across all subjects, ANOVA revealed no main effect of pramipexole (F < 1) or dose group (F < 1) and no prami- pexole × dose group interaction (F < 1). There was a significant effect of trial type (F = 51.76, df 4,152, p < 0.0001) and a significant interaction of pramipexole × dose group × trial type (F = 2.53, df 4,152, p < 0.05). Post hoc comparisons revealed significant PPI-enhancing effects of pramipexole on 120-ms prepulse trials (main effect of pramipexole, F = 4.12, df 1,38, p < 0.05). This effect did not differ by dose group (F < 1) nor was there an interaction of pramipexole × dose group (F < 1), though Fig. 3 Effects of pramipexole on startle magnitude (mean ±SEM) (a) and %PPI (mean±SEM) (b) across all trial conditions in a subgroup of subjects treated with placebo vs. 0.1875 mg pramipexole (n=17) in whom pramipexole caused no change in pulse alone startle magnitude. Open circle Placebo; closed circle active dose. Asterisk Startle reducing effects of pramipexole on prepulse+pulse trials at 120 ms prepulse intervals (p =0.01); number sign PPI-enhancing effects of pramipexole at 120-ms prepulse intervals (p=0.005)