QUANTITATIVE STUDY OF CELLULAR AND VOLUMETRIC GROWTH OF MAGNOCELLULARAND LAMINAR AUDITORY NUCLEI IN DEVELOPING CHICK BRAIN-STEM

Development of the second and third order auditory nuclei-nucleus magn ocellularis (NM) and nucleus laminaris (NL) respectively-was stidied u sing Nissl stained serial sections from brain specimens between 8 day of incubation and posthatch day 1, at every two day interval. Reconstr uction of these nuclei from three incubation ages showed progressive g rowth of both nuclei in a rostrocaudal direction. The volume, total ne uron, dead cell and glial cell numbers were estimated using stereologi cal quantitation methods. Both nuclei, while undergoing an overall gra dual increase in volume up to 20 days registered a transient drop in v olume; earlier for NM at 10 days and later for NL at 18 days. From day 20 the two nuclei showed accelerated growth in volume. The total neur on count rapidly declined up to 12 days with 43% loss of neurons in NM followed by a rise and later stabilization within a certain range. Th e NL, however, showed a continuous fall in neuron numbers throughout t he incubation period with 20% cell loss by day 12 and an overall loss of 52%. Cell death in both nuclei was maximal at 16 days and spanned t he entire period of incubation. Glia showed a biphasic increase with p eak at 14 days for both NM and NL followed by a subsequent rise at day 20 for both nuclei. These data would help in planning further experim ental studies of auditory manipulation.