CAUDAL PONTINE RETICULAR-FORMATION OF C57BL 6J MICE - RESPONSES TO STARTLE STIMULI, INHIBITION BY TONES, AND PLASTICITY/

C57BL/6J (C57) mice were used to examine relationships between the beh avioral acoustic startle response (ASR) and the responses of neurons i n the caudal pontine reticular formation (PnC) in three contexts: I)re sponses evoked by basic startle stimuli; 2) the prepulse inhibition (P PI) paradigm; and 3) the effects of high-frequency hearing loss and co ncomitant neural plasticity that occurs in middle-aged C57 mice. 1) Re sponses (evoked action potentials) of PnC neurons closely paralleled t he ASR with respect to latency, threshold, and responses to rapidly pr esented stimuli. 2) ''Neural PPI'' (inhibition of responses evoked by a startle stimulus when preceded by a tone prepulse) was observed in a ll PnC neurons studied. 3) In PnC neurons of 6-mo-old mice with high-f requency (>20 kHz) hearing loss, neural PPI was enhanced with 12- and 4-kHz prepulses, as it is behaviorally. These are frequencies that hav e become ''overrepresented'' in the central auditory system of 6-mo-ol d C57 mice. Thus neural plasticity in the auditory system, induced by high-frequency hearing loss, is correlated with increased salience of the inhibiting tones in both behavioral and neural PPI paradigms.