[Acoustic stimulation and adaptation to noise of the developing mouse auditory system]

To assess the effects of an acoustically enriched environment during the auditory system development, groups of mouse pups, from two strains (Swiss Albinos Rb-3 and deafness, the latter carrying a recessive gene [dn] making homozygous dn/dn totally deaf), were exposed to pulsed pure-tone stimulation (2 500 Hz; 85 +/- 5 dB SPL) at different periods of development from conception to weaning. Growth curve, weight at 40 days, eye opening and behaviour at 24 days to the same stimulus were analyzed as a function of the mother's audition (hearing or deaf) and of the period of acoustic exposure: exposed since conception, since birth or from 9 days (date of onset of audition). Eye opening is more precocious in all three experimental groups than in controls. Contrary to mouse pups exposed from 9 days, those (also from deaf mothers) treated before onset of hearing show normal growth and behavioural indifference to the stimulus at 24 days. The significant lack of physiological and behavioural effect of the sound stimulus in the groups treated before electrophysiological maturation of hearing has a certain lasting effect, at least up to age 40 days. As electrophysiological studies show no alteration of auditory thresholds in these groups, the hypothesis of a possible process of habituation, stemming from a very early effect of sound stimulation during the non-functional phase of development of the auditory system (from birth to 9 days), is discussed.