A separate set of rats (N = 48) that were either socially isolated or group reared and either concomitantly handled or non-handled (n = 12/group) were tested on postnatal day 70 in the acoustic startle and prepulse inhibition (PPI) test, as previously described (Bortolato et al., 2005). Rats were placed in a startle reflex apparatus (Med Associates, St Albans, VT, USA) for a 5 min-acclimation period with a 70 dB background noise that continued during the entire session. Each rat was exposed to a session consisting of 3 consecutive trial sequences. In sequence 1 and 3, five pulse-alone trials of 115 dB were presented. During sequence 2, 12 pulse-alone trials, 30 trials of pulse preceded by 73, 76, or 82 dB prepulse tones (10 for each level of prepulse intensity), and 8 no-stimulus trials (only background noise) were delivered in pseudo-random order. Pulse and prepulse tone duration was 80 and 40 ms, respectively. The prepulse-pulse delay was 100 ms. Inter-trial-intervals were randomly selected to occur within a 10 to 15 s range. Percent PPI was calculated with the following formula:
