IMPAIRMENT OF AXONAL DEVELOPMENT AND OF SYNAPTOGENESIS IN HIPPOCAMPAL-NEURONS OF SYNAPSIN I-DEFICIENT MICE

Synapsin I, the most abundant of all neuronal phosphoproteins, is enri ched in synaptic vesicles, It has been hypothesized to regulate synapt ogenesis and neurotransmitter release from adult nerve terminals. The evidence for such roles has been highly suggestive but not compelling. To evaluate the possible involvement of synapsin I in synaptogenesis and in the function of adult synapses, we have generated synapsin I-de ficient mice by homologous recombination. We report herein that outgro wth of predendritic neurites and of axons was severely retarded in the hippocampal neurons of embryonic synapsin I mutant mice, Furthermore, synapse formation was significantly delayed in these mutant neurons. These results indicate that synapsin I plays a role in regulation of a xonogenesis and synaptogenesis.