MODIFICATION OF THE ACOUSTIC STARTLE RESPONSE IN HEARING-IMPAIRED C57BL 6J MICE - PREPULSE AUGMENTATION AND PROLONGATION OF PREPULSE INHIBITION/

Modification of acoustic startle amplitude by a 10-ms tone prepulse (S 1) was evaluated as a function of the interstimulus interval (ISI) bet ween the onset of S1 and the onset of the startle-evoking stimulus (S2 ). Subjects were normal-hearing 1-month-old C57BL/6J (C57) mice and CB A/CaJ mice and 5-month-old C57 mice with high-frequency hearing loss. With a 2-ms ISI, 5-month-old C57 mice (but not the normal-hearing mice ) exhibited pronounced prepulse augmentation (PPA) of startle: Amplitu des were much larger when S1 was present. Prepulse inhibition (PPI) oc curred with ISIs of 10-100 ms in all subject groups. With long ISIs of 200 and 500 ms, however, PPI was strong only in 5-month-old C57 mice and only with S1 frequencies of 8, 12, and 16 kHz. Physiological studi es of neural plasticity have shown that frequencies of 8-16 kHz become ''over-represented'' (more neurons responding) in the central auditor y system of C57 mice, suggesting a link with prolonged PPI observed he re.