Effects of intensity and type of prepulse stimulus on prepulse inhibition in scopolamine treated rats

Prepulse inhibition (PPI) of the auditory startle response (ASR) is a behavioral test that has been used to measure auditory thresholds, to assess sensory-motor integration functions, and its use has been recommended in the United States Environmental Protection Agency Developmental Neurotoxicity Guideline (OPPTS 870.6300). The purpose of the present study was to determine to what extent the intensity and/or type of prepulse stimuli modulate PPI in scopolamine-treated rats. The PPI of the ASR peak amplitude was measured when the intensity of a 10-kHz prepulse tone was varied (69-, 80-, and 90 dB[A]; Experiment 1) and when both the intensity and type of auditory prepulse (a 10-kHz tone vs. a white noise burst) were varied (Experiment 2). Scopolamine treatment attenuated PPI in both experiments and interacted significantly with the prepulse stimulus intensity in Experiment 1. In Experiment 2, the percent of PPI was linearly related to prepulse stimulus intensity for trials using a tone, but was biphasic on trials using a white-noise prepulse stimulus. Prepulse stimuli of certain intensities elicited a response, and this response was greater when the prepulse stimulus was a white noise burst versus a tone of the same intensity. Further, the response to the prepulse altered the amount of inhibition and, therefore, confounded the overall measure of PPI at the higher prepulse stimulus intensity levels. Overall, these results indicate that careful consideration of the intensity and type of prepulse stimuli be taken in the context of their potential to induce a prepulse-elicited response, as well as providing the appropriate measures of such a response, when designing and interpreting PPI experiments.