Normal postnatal development of medial superior olivary neurons in the albino rat: a Golgi and Nissl study.

Bipolar neurons in the medial superior olivary (MSO) nucleus of albino rats were studied at various ages (0-75 days) during development in order to elucidate normal neuronal growth patterns. Neurons, visualized in celloidin embedded Golgi/Nissl- and frozen Nissl-stained sections, were analyzed quantitatively for cell size and extent of dendritic arborization. These parameters, from both sets of data, showed a consistent developmental trend with the existence of two major stages in the ontogenetic process: a rapid developmental and a stabilization stage. The first stage, encompassing postnatal days 0 through approximately 14, was characterized by a rapidly increasing cell size, as observed in frozen sections. At the peak of this rapid growth, Golgi-stained neurons possessed thick dendrites with many appendages, growth cones, and filopodia. The peak in neuronal development coincided with the initiation of ear opening. Morphological features attained a more mature form in the second, stabilizing stage of development, which began at approximately postnatal day 14. This phase was distinguished by a decrement in cell size and dendritic branching. Also, dendrites possessed more regularly distributed varicosities and fewer appendages, growth cones, and filopodia in this period. It was observed that dendritic branching trends paralleled those of cell diameter growth.