Electron Microscopic Investigation of Monoaminergic Terminals to α-Motoneurons in the Anterior Horn of the Cat Spinal Cord

In the anterior horn of the cat thoracic cord, networks of the monoaminergic fibers surrounding the alpha-motoneurons were investigated by fluorescent microscopy and submicroscopically. Monoaminergic terminals were recognized by the administration of 5-OHDA electron microscopically. These terminals could be classified morphologically into three types. The physiological significance of monoaminergic control of alpha-motoneurons was discussed. Type I of the labeled terminals did not show any typical synaptic specialization, such as aggregation of synaptic vesicles or thickening of the pre- and postsynaptic membranes. This type did not have synaptic contact with the alpha-motoneurons. Type II showed typical synaptic contact and asymmetrical synaptic type membranous thickening. A large number of small dense-cored vesicles were accumulated in the vicinity of the presynaptic membranes. Type III contained a large number of small and large dense-cored vesicles and a few flattened small vesicles. This type had synaptic contact with the presynaptic nerve ending in which a large number of agranular vesicles were contained. This study demonstrated that alpha-motoneurons in the anterior horn receive supraspinal monoaminergic control in three ways: modulator control through Type I, monosynaptic direct control through Type II, and inhibitory control through Type III.</p

Serotonin-containing nerve fibers in the rat spinal cord: electron microscopic immunohistochemistry.

The ultrastructure of the serotonin (5HT) system in the spinal cord of rats was studied by an immunohistochemical peroxidase-antiperoxidase (PAP) method. Under the light microscope, 5HT immunoreactive staining was observed as brown-colored dots in the anterior horn, lateral horn, posterior horn and pericentral canal region. These positively staining dots were probably indicative of 5HT immunoreactive varicosities and nerve terminals. At the ultrastructural level, 5HT immunoreactive nerve fibers appeared as darkly stained varicosities with PAP positive large electron dense vesicles (80-100 nm), as well as small clear vesicles (30-40 nm) finely coated with PAP immunoreactive products. In the anterior horn, some of the 5HT immunoreactive structures were clearly nerve terminals forming asymmetric synaptic contact with soma or dendrites of the anterior horn cells. In the lateral horn, posterior horn and pericentral canal region, however, only 5HT positive varicosities were detected.</p

Ultrastructure of monoaminergic terminals in the intermediolateral nucleus of the cat spinal cord.

Monoaminergic innervation of the intermediolateral nucleus of the cat spinal cord was investigated by fluorescence histochemistry and electron microscopy. Large numbers of monoaminergic terminals were labeled by prior administration of the false neurotransmitter 5-hydroxydopamine (5-OHDA). Ultrastructurally, 5-OHDA-labeled terminals fell into three types. Type I, which made up 55% of the labeled terminals, contained abundant, large and densely labeled vesicles and only a few small and unlabeled vesicles. This type was &#34;bouton de passage&#34;. Type II, which made up 40% of the terminals, made asymmetrical synaptic contacts with typical postsynaptic structures. This type contained many small vesicles, some of which were labeled, and a few large dense-core vesicles. Type III, which made up 5% of the terminals, made close contact with presynaptic nerve endings containing abundant small unlabeled clear vesicles. The type III terminals contained many large and densely labeled vesicles and a few small flattened vesicles, most of which were unlabeled.</p

Electron microscopic study of mossy fiber endings of the hippocampal formation in El mice.

The effects of seizure activity on the mossy fiber endings of El mice were studied by electron microscopy. During epileptic seizures of El mice, the number of clear round vesicles (50 nm) in the mossy fiber endings of the hippocampal formation decreased, while the number of large densecore vesicles (100 nm) increased. In these endings, the large dense-core vesicles were scattered during the resting state, but after seizure activity they tended to accumulate together and attach to the presynaptic membrane. Omega-shaped profiles, which seemed to be due to exocytosis of the large dense-core vesicles, were seen in the presynaptic membrane.</p

Changes in cellular ultrastructure induced by gamma-interferon in K562 cells may be prerequisite for apoptosis.

We report here the time-course of electron microscopic changes induced by gamma-interferon (IFN-gamma) in the human erythromyeloid leukemia cell line K562. In K562 cells treated with IFN-gamma for 6h, the nuclei were polygonal in shape and microvilli were far more abundant on cell membranes compared with control K562 cells, and invaginations were often seen in the cell membranes. There was a reduction in the number of cell-membrane microvilli and an increase in the number of lysosomal bodies in the cytoplasm of K562 cells treated with IFN-gamma for 12h. After treatment with IFN-gamma for 24h, the cell membrane microvilli disappeared, large numbers of cellular organelles were observed, such as mitochondria and lysosomes, and the cytoplasm became electron-dense. Cytoplasmic vesicles and vacuoles were also observed. These vesicles may correspond to an intermediate step in the ultimate cellular disintegration associated with apoptosis caused by IFN-gamma.</p

Detection of metastatic neuroblastoma cells in bone marrow aspirates by formaldehyde induced fluorescence histochemistry.

Metastatic neuroblastoma cells in bone marrow aspirates were examined by the formaldehyde induced fluorescence histochemical method. With this method we could easily identify abnormal cells as metastatic neuroblastoma cells by observing catecholamine green colored fluorescence in their cytoplasma. This formaldehyde induced fluorescence histochemical method is significantly useful for the diagnosis of metastatic neuroblastoma of the bone marrow.</p

Exocytotic features of rat specific atrial granules.

To clarify the mode of secretion of specific atrial granules, rat atrial muscle cells were examined by transmission electron microscopy. Atrial granule formation and exocytotic features of granules were clearly seen. Abrupt breaks in the unit membrane structure of mature granules were observed in thin sections, but these breaks were not detected in freeze-fracture replicas. These findings support the concept that the granule contents are released to the extracellular space by exocytosis.</p