POSTNATAL-DEVELOPMENT OF GAP-43 IMMUNOREACTIVITY IN THE AUDITORY BRAIN-STEM OF THE RAT

Extensive data link the growth associated protein GAP-43 to axonal elo ngation and synapse formation during development and in plastic respon ses of nervous tissue. We have studied the changing levels of GAP-43 e xpression in the auditory brainstem nuclei of the developing rat by ap plying immunocytochemical techniques. By the first postnatal day (P1), GAP-43 was expressed at high concentrations in all subdivisions of th e cochlear nuclear complex and the superior olivary complex. At this s tage, neuropil structures recognized by the antibody did not show any varicosities on cellular processes in all these regions. By P8, the te xture of the stain has turned markedly more granular, a pattern likely to reflect the formation of presynaptic endings. A predominantly gran ular distribution of GAP-43 has developed by P12. At that time, the st aining intensity is markedly reduced compared to the levels of the new born. By P16, the auditory brainstem nuclei have lost most of their GA P-43 immunoreactivity, but a distinct level of staining persisted into adulthood in all of them. This staining was restricted to boutons, wh ich are thought to be presynaptic terminals. We conclude that a modera te but apparently relevant potential for plasticity is retained in the se auditory structures. Should the patterns of neural signals, mediate d by the inner ear, change during adulthood, the central structures ap pear to be able to respond with the formation of altered synaptic conn ectivity. (C) 1997 Wiley-Liss. Inc.