Development of the acoustic startle response in rats and its change after early acoustic trauma.
Even brief acoustic trauma during the critical period of development that results in no permanent hearing threshold shift may lead to altered auditory processing in adulthood. By monitoring the acoustic startle response (ASR), we examined the development of auditory function in control rats and in rats exposed to intense noise at the 14th postnatal day (P14). First ASRs appeared on P10-P11 to intense low-frequency tones. By P14, the range of sound intensities and frequencies eliciting ASRs extended considerably, the ASR reactivity being similar at all frequencies (4-32 kHz). During the subsequent two weeks, ASR amplitudes to low-frequency stimuli (4-8 kHz) increased, whereas the ASRs to high-frequency tones were maintained (16 kHz) or even decreased (32 kHz). Compared to controls, noise exposure on P14 (125 dB SPL for 8, 12, or 25 min) produced transient hyper-reactivity to startle stimuli, manifested by a decrease of ASR thresholds and an increase of ASR amplitudes. ASR enhancement occurred regardless of permanent hearing loss and was more pronounced at high frequencies. The hyper-reactivity of ASRs declined by P30; the ASR amplitudes in adult exposed rats were lower than in controls. The histological control did not reveal loss of hair cells in adult exposed rats, however, the number of inner hair cell ribbon synapses was significantly decreased, especially in the high-frequency part of the cochlea. The results indicate that early acoustic trauma may result in complex changes of ASRs during development.
Department of Auditory Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague, Czech Republic. Electronic address: rybalko@biomed.cas.cz.
Natalia
N
Rybalko
Department of Auditory Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague, Czech Republic.
Tetyana
T
Chumak
Department of Auditory Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague, Czech Republic; Department of Electrical Engineering and Computer Science, College of Polytechnics, Jihlava, Czech Republic.
Zbyněk
Z
Bureš
Department of Auditory Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague, Czech Republic.
Jiří
J
Popelář
Department of Auditory Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague, Czech Republic; Department of Medical Biophysics and Informatics, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
Daniel
D
Šuta
Department of Auditory Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague, Czech Republic.
Josef
J
Syka
D000161:Acoustic Stimulation / Q000009:adverse effects*; D000818:Animals; D001307:Auditory Perception / Q000502:physiology*; D003051:Cochlea / Q000166:cytology / Q000254:growth & development*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005260:Female; D006320:Hearing Tests; D020318:Rats, Long-Evans; D013216:Reflex, Startle / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D013569:Synapses / Q000502:physiology
Acoustic startle reflex; Auditory system; Critical period; Development; Noise exposure; Rat