Normal startle response and decreased PPI in M
R KO mice. (A) M4R KO mice demonstrated normal acoustic startle response for the 100 and 110 dB startle stimulus. (B) No significant differences in PPI for the 74 and 78 dB prepulse sound level followed by 100 dB startle stimulus were observed between genotypes. (C) M4R KO mice demonstrated a significant decrease in prepulse inhibition for the 74 and 78 dB prepulse sound level followed by 110 dB startle stimulus compared to wild-type mice. M4R KO mice, n = 28; wild-type mice, n = 28.