title: Noise exposure during early development impairs the processing of sound intensity in adult rats.
abstract: During the early postnatal development of rats, the structural and functional maturation of the central auditory nuclei strongly relies on the natural character of the incoming neural activity. Even a temporary deprivation in the critical period results in a deterioration of neuronal responsiveness in adult animals. We demonstrate that besides the poorer frequency selectivity of neurons in the impaired animals reported previously [Grecova et al. (2009)Eur. J. Neurosci. 29, 1921-1930], the neuronal representation of sound intensity is significantly affected. Rate-intensity functions of inferior colliculus neurons were recorded in anaesthetized adult rats that were exposed to intense noise at postnatal day 14, and compared with those obtained in age-matched controls. Although the response thresholds were similar in the exposed and control rats, the neurons in the exposed animals had a longer first-spike latency, a narrower dynamic range, lower maximum response magnitudes and a steeper slope of the rate-intensity functions. The percentage of monotonic neurons was significantly lower in the exposed animals. The observed anomalies were confined to the mid- and high-frequency regions, whereas no significant changes were found in the low-frequency neurons. The altered parameters of the individual rate-intensity functions led also to differences in the cumulative responses. We conclude that a brief noise exposure during the critical period leads to a frequency-dependent alteration of the sound intensity representation in the inferior colliculus of adult rats. The results suggest that such impairments may appear in individuals with normal hearing thresholds, but with a history of noise exposure very early in childhood.
authors.affiliation: Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic. buresz@biomed.cas.cz
authors.forename: Zbynek
authors.initials: Z
authors.lastname: Bures
authors.forename: Jolana
authors.initials: J
authors.lastname: Grécová
authors.forename: Jirí
authors.initials: J
authors.lastname: Popelár
authors.forename: Josef
authors.initials: J
authors.lastname: Syka
mesh_terms: D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D003423:Critical Period, Psychological; D005260:Female; D034381:Hearing Loss / Q000209:etiology / Q000503:physiopathology; D007245:Inferior Colliculi / Q000166:cytology / Q000254:growth & development*; D009474:Neurons / Q000502:physiology*; D009622:Noise / Q000009:adverse effects*; D051381:Rats; D020318:Rats, Long-Evans; D011930:Reaction Time; D013016:Sound