Quantitative study of plasticity in the auditory nuclei of chick under conditions of prenatal sound attenuation and overstimulation with species specific and music sound stimuli

Morphological effects of prenatal sound attenuation and sound overstimulati on by species specific and music sounds on the brainstem auditory nuclei of chick have been evaluated quantitatively. Changes in length, volume, neuro n number, size of neuronal nuclei and glial numbers of second and third ord er auditory nuclei, n. magnocellularis (NM) and n. laminaris (NL), were det ermined from thionine-stained serial sections of control and experimental g roups on posthatch day 1 using stereological methods. Significant increase in volume of both auditory nuclei attributable to incr ease in length of nucleus, number and size of neurons, number of glia as we ll as neuropil was observed in response to both species specific and music overstimulation given during the critical period of development. The enhanc ed development of auditory nuclei in response to enriched environment prena tally indicates a positive effect of activity on neurons which may have cli nical implications in addition to providing explanation for preference to a uditory cues in the postnatal life. Reduction in neuron number with a small increase in proportion of cell nucl ei of large size as well as an increase in glial numbers was seen in both N M and NI, of the prenatally sound attenuated chicks. The increase in size o f some neuronal nuclei may probably be evidence of enhanced synthesis of pr oteins involved in cell death or an attempt at recovery. The dissociated response of neurons and glia under sound attenuated and aud itory stimulated conditions suggests that they are independently regulated by activity-dependent signals with glia also being under influence of other signals for a role in removal of dead cell debris. (C) 1999 Published by E lsevier Science Ltd on behalf of ISDN. All rights reserved.