Apomorphine disrupts the inhibition of acoustic startle induced by weak prepulses in rats

Separate experiments conducted in two different laboratories assessed the importance of the prepulse intensity in the ability of apomorphine to reduce prepulse inhibition of acoustic startle responses. Rats were presented with noise bursts alone or noise bursts 100 ms after presentation of prepulse stimuli ranging from 70 to 85 or 90 dB. Throughout testing, the background noise was maintained at 65 dB. In both laboratories, apomorphine markedly decreased the absolute magnitude of prepulse inhibition when the prepulse stimuli were no more than 10 dB above the background. With more intense prepulse stimuli, apomorphine had no significant effect on prepulse inhibition. Hence, apomorphine does not interfere with the inhibitory process which actually mediates prepulse inhibition, but appears to affect the detectability of the prepulse.