POSTNATAL-DEVELOPMENT OF THE PROJECTION FROM THE MEDIAL SUPERIOR OLIVE TO THE INFERIOR COLLICULUS IN THE RAT

Normal projection development from the medial superior olive (MSG) to the inferior colliculus (IC) was examined by injecting Fluoro-Gold (FG ), a retrograde tracer, into the IC unilaterally at postnatal days 0 ( P0), P3, P7 and maturity. The rats were killed 1 day after FG injectio n. At all ages, labeled neurons in the MSO appeared on the ipsilateral side only, as in adult controls. The total number of MSO neurons coun ted in Nissl-stained sections was constant throughout the postnatal pe riods. The labeled frequency index of MSO neurons was increased stepwi se (from 35% to 90%) with increasing postnatal stages (from PO to adul thood), suggesting differential growth of early- and late-developing a xons.