Field emission scanning electron microscopy and freeze-fracture transmission electron microscopy of mouse cerebellar synaptic contacts.
Samples of albino mice were processed by the cryofracture method for scanning electron microscopy and examined with the field emission scanning electron microscope (FESEM). Freeze-etching direct replicas of mice cerebellar cortex were also studied with the transmission electron microscope (FFTEM), as a complementary technique for obtaining higher resolution, three-dimensional correlative images of cerebellar synaptic contacts. At the granular, Purkinje cells and molecular layers, the cryofracture method for FESEM selectively removed the neuroglial cell investment, facilitating the visualization of the outer and inner surfaces of cerebellar synaptic contacts. In addition, FFTEM showed the real extension of perisynaptic neuroglial investment. The outer surface of mossy fiber rosettes and their digitiform processes were seen at the granular layer, making flat and invaginated synaptic contacts with the granule cell dendrites. At the molecular layer, the longitudinal traject of parallel fibers or nonsynaptic segments and their synaptic varicosities were characterized. These latter established synaptic contacts with Purkinje dendritic spines. Fractured parallel fiber endings showed the SE-I images of clustered spheroidal synaptic vesicles and mitochondria and the surrounding cotton-like appearance of Bergmann glial cell cytoplasm. Climbing fibers showed a characteristic crossing-over bifurcation pattern in the white matter and in the three-layer structure of cerebellar cortex, formation of tendril collaterals in the granular layer, topographical relationship with Purkinje cell soma and retrograde collaterals in the molecular layer. The climbing fiber synaptic relationship with Purkinje dendritic spines was characterized, by means of FFTEM, by the presence of large synaptic endings and aggregation of intramembrane particles at the P and E faces of presynaptic endings, characteristic of excitatory synapses.
Castejón
O J
OJ
Institute of Biological Investigations Dres. Orlando J. Castejon y Haydee Viloria de Castejón, Faculty of Medicine, University of Zulia, Maracaibo, Venezuela. ocastejo@cantv.net
Apkarian
R P
RP
Castejón
H V
HV
Alvarado
M V
MV
D000818:Animals; D002540:Cerebral Cortex / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D005614:Freeze Fracturing / Q000379:methods; D017629:Gap Junctions / Q000648:ultrastructure*; D051379:Mice; D008855:Microscopy, Electron, Scanning / Q000379:methods; D011689:Purkinje Cells / Q000648:ultrastructure