Nonhomogeneous distribution of filamentous actin in the presynaptic terminals on the spinal motoneurons.
Although actin is known to play important roles in synapses, immunocytochemical and structural studies on synaptic actin have resulted in conflicting data, and the presence and precise localization of filamentous actin (F-actin) in the synapses have still not been well clarified. We recently described a phalloidin-based antifluorescein isothiocyanate system, which has been successfully developed for ultrastructural investigations of F-actin in the ependymal microvilli. By this technique, the present study has demonstrated the presence of F-actin in both the pre- and the postsynaptic regions in the synapses of spinal motoneurons. In the presynaptic terminal, F-actin was localized predominantly in the active zones and the adjacent synaptic vesicle clusters, including the vesicles docked at the active zones and a population of recycling vesicles. By contrast, the proximally located vesicle pool was much less intensely stained. In the postsynaptic region, F-actin was concentrated at the postsynaptic densities and stretched some way into the surrounding cytoplasm. Insofar as the axonal terminals analyzed in this study touched on either the cell body or the dendritic shaft, where the postsynaptic regions did not form spine-like specializations, our results cannot shed any light on the distribution of F-actin within spines. However, the present study has provided a hitherto unreported ultrastructural view of the subcellular distribution of F-actin in the synapse, which is thought to be helpful for understanding the roles of the synaptic actin cytoskeleton.
Li
Yan-Chao
YC
Department of Histology and Embryology, Norman Bethune College of Medicine, Jilin University, Changchun, Jilin Province 130021, China. ldlyc@yahoo.com
Bai
Wan-Zhu
WZ
Zhou
Li
L
Sun
Lian-Kun
LK
Hashikawa
Tsutomu
T
D000199:Actins / Q000378:metabolism / Q000648:ultrastructure*; D000818:Animals; D005260:Female; D007150:Immunohistochemistry; D009046:Motor Neurons / Q000378:metabolism / Q000648:ultrastructure*; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000166:cytology*; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure*
D000199:Actins