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 (S1) was evaluated as a function of the interstimulus interval (ISI) between 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 CBA/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: Amplitudes were much larger when S1 was present. Prepulse inhibition (PPI) occurred 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 studies of neural plasticity have shown that frequencies of 8-16 kHz become "over-represented" (more neurons responding) in the central auditory system of C57 mice, suggesting a link with prolonged PPI observed here.