CHARACTERIZATION AND ONTOGENY OF SYNAPSE-ASSOCIATED PROTEINS IN THE DEVELOPING FACIAL AND HYPOGLOSSAL MOTOR NUCLEI OF THE BRAZILIAN OPOSSUM

The characterization and ontogeny of synapse-associated proteins in th e developing facial and hypoglossal motor nuclei were examined in the Brazilian opossum (Monodelphis domestica). Immunohistochemical markers utilized in this study were the synaptic vesicle-associated proteins synaptophysin and synaptotagmin; a synaptic membrane protein, plasma m embrane-associated protein of 25 kDa (SNAP-25); a growth cone protein, growth-associated phosphoprotein-43 (GAP-43); and the microtubule-ass ociated proteins axonal marker tau and dendritic marker microtubule-as sociated protein-2 (MAP-S). In this study, we have found that, during the first 10 postnatal days (1-10 PN), the facial motor nucleus lacked immunoreactivity for synaptophysin, synaptotagmin, GAP-43, tau, and S NAP-25. After 10 PN, immunoreactivity increased in the facial motor nu cleus for synaptophysin, synaptotagmin, GAP-43, and tau, whereas immun oreactivity for SNAP-25 was not evident until between 15 and 25 PN. Co nversely, immunoreactivity for MAP-2, was present in the facial motor nucleus from the day of birth. In contrast, the hypoglossal motor nucl eus displayed immunoreactivity from 1 PN for synaptophysin, synaptotag min, SNAP-25, GAP-43, tau, and MAP-2. These results suggest that the f acial motor nucleus of the opossum may not receive afferent innervatio n as defined by classical synaptic markers until 15 PN and, further, t hat characteristic mature synapses are not present until between 15 an d 25 PN. These results indicate that there may be a delay in synaptoge nesis in the facial motor nucleus compared to synaptogenetic events in the hypoglossal motor nucleus. Because the facial motor nucleus is ac tive prior to completion of synaptogenesis, we suggest that the facial motoneurons are regulated in a novel or distinct manner during this t ime period. (C) 1996 Wiley-Liss, Inc.