Large Pleomorphic Vesicles Research Articles

Efferent projections from the striatal patch compartment: anterograde degeneration after selective ablation of neurons expressing μ-opioid receptor in rats

Local injection of μ-opioid receptor specific neurotoxin, dermorphin-saporin, into the striatum resulted in selective degeneration of striatal neurons in the patch compartment. We analyzed subsequent anterograde degeneration of axons and terminals at light and electron microscopic level. Light microscopic examination after silver impregnation method revealed that degenerating axons and terminals arising from the striatal patch compartment were distributed in the globus pallidus, entopeduncular nucleus, and substantia nigra. They were found in both pars reticulata and compacta of the substantia nigra. Electron microscopic examination revealed that the degenerating axon terminals contained large pleomorphic vesicles and formed symmetric synapses on dendrites. The present results suggest that patch neurons expressing μ-opioid receptor send projection fibers to multiple nuclei of the basal ganglia.

Two different types of dynorphin-A-immunoreactive terminals in rat substantia nigra

The opioid peptide dynorphin A (1-17) is the third transmitter identified in the striatonigral projection, the other two being gamma-aminobutyric acid (GABA) and substance P. The ultrastructural features of the dynorphinergic terminals in substantia nigra/pars reticulata were studied using pre-embedding immunocytochemistry with the classical peroxidase-antiperoxidase-diaminobenzidine-method; these features were compared with GABAergic boutons visualized with an immunogold method. Two distinct types of dynorphin-A-immunoreactive boutons could be identified: (1) type A (81%) possessing characteristics similar to the GABAergic nerve endings in this region, i.e., large pleomorphic vesicles and symmetric synaptic contacts; (2) type B (19%) displaying asymmetric synaptic zones and small, mostly round vesicles. These results are in agreement with physiological studies suggesting a dual action of dynorphin A in substantia nigra.

Ultrastructural morphology of dopaminergic nerve terminals and synapses in the striatum of the rat using tyrosine hydroxylase immunocytochemistry: A topographical study

Structures immunoreactive for TH were examined in the rat striatum (including caudateputamen, nucleus accumbens and globus pallidus) by electron microscopy using the indirect peroxidase-labeled antibody method. Axon profiles and nerve terminals were the only structures stained by DAB precipitates in the axoplasm. The reactive boutons frequently contained a population of large pleomorphic vesicles (40–60 nm in diameter) but their interiors remained free of reactions. The synaptic contacts formed belonged principally to the symmetric type 2 of Gray while asymmetric Gray's type 1 synapses were rarely observed. The former were mostly apposed to dendritic trunks (rarely to perikarya) and the latter to dendritic spines. In addition, numerous immunoreactive nerve terminals were often found in close contact with small structures identified as the neck of dendritic spines. The active zone of these presumed synapses was characterized by a prominent thickening of the presynaptic membrane but the post-synaptic thickening was lacking. For similar reasons, it was difficult to assert the existence of one axo-axonic synapse when a positive nerve terminal was closely apposed to another one (generally unreactive). The exact morphology of dopaminergic synapses, or even their existence, have not been firmly established owing to large discrepancies between previous reports. No synapses, or synaptic contacts of either asymmetric or symmetric type were described according to the technique used. Our work was undertaken to elucidate further this problem, and in particular, we thought that regional differences in the synaptic organization might explain the divergent data. However, regional quantitative analysis performed in this study did not show significant differences in the percentage of either kind of synapses in the various striatal regions.

An intracellular HRP study of the rat globus pallidus. II. Fine structural characteristics and synaptic connections of medially located large GP neurons.

In order to classify the presynaptic elements contacting the principle class of globus pallidus neurons, electron microscopic examination of serial sections made from a medially located large globus pallidus neuron, labeled with intracellular horseradish peroxidase, was undertaken. In addition, the use of labeled and light microscopically reconstructed material allowed us to quantitatively determine the distribution of each bouton type along the soma and dendrites. Six types of presynaptic terminals contacting the labeled cell have been recognized. Type 1 endings, the most numerous (84%), make symmetrical contacts on all portions of the cell, except spines, contain large pleomorphic, and a few large dense-core vesicles. Type 2 endings are filled with small spherical-to-ellipsoidal synaptic vesicles. They make asymmetrical contacts only with higher-order dendrites and account for 12% of synaptic contacts onto the labeled neuron. Type 3 endings are large, contain sparsely distributed large pleomorphic vesicles, and make two symmetrical synapses per bouton, one onto a spine head and the other onto the underlying dendritic shaft. They are infrequent (0.2%), being found only in association with dendritic spines. Type 4 endings contain large pleomorphic synaptic vesicles and no dense-core vesicles. They make symmetrical contacts with the short primary dendrites. Type 5 endings contain a mixture of small clear pleomorphic vesicles and numerous large dense-core vesicles. They contact only the cell body and the short primary dendrites, making up 20% of somatic synaptic contacts but less than 1% of contacts onto dendrites. Type 6 boutons contain oval and flattened synaptic vesicles and establish symmetrical contacts with higher-order dendritic branches and the cell body.

The postnatal development of the substantia nigra: a light and electron microscopy study.

The early postnatal development of neurons, dendrites and synaptic connectivity in kitten substantia nigra (SN) was studied by light and electron microscopy. The compact and reticular divisions of the SN are present at birth but boundaries are indistinct. Most nigral neurons stain deeply in routine histological sections and their diameters increase slightly with age. Ultrastructurally, cell bodies are characterized by eccentrically located and often invaginated nuclei surrounded by cytoplasm rich in well-formed organelles. Axosomatic synapses are infrequent and cell surfaces are enveloped by glial processes. Immature dendritic features, including growth cones and filiform processes, are commonly observed during the first 10 days. Gradually the dendritic profiles elongate and thicken and contours become smoother, retaining only scattered spinelike appendages. Clear examples of the three synaptic types described in cat are found in newborn kittens, but immature terminals contain fewer synaptic vesicles and mitochondria. Approximately 90% of synapses present at birth in both nigra subdivisions are Type I, which contain large pleomorphic vesicles and contact dendrites symmetrically. Asymmetrical contacts characterize most of the remaining definable synapses. The postnatal increase in synaptic connectivity, which was estimated from random photographs of pars reticulata neuropil, is twofold during the first 50 days of life. Initially young dendrites are enveloped by glia and then gradually become ensheathed by axon terminals. Synaptogenesis in pars reticulata reflects the postnatal increase of neostriatal inputs to this subdivision and can be correlated with functional changes in strionigral connectivity.

Fine structure and synaptic connections of the common spiny neuron of the rat neostriatum: a study employing intracellular inject of horseradish peroxidase.

Medium-sized spiny neurons of the neostriatum, identified by intracellular injection of horseradish peroxidase, were examined at both light and electron microscopic levels. These neurons were characterized by their heavy investment of dentritic spines, beginning about 20 micron from the soma and continuing to the tips of the dendrites. Their axons arose from the soma or from a large dendritic trunk very near the soma, and tapered rapidly to form a main axonal branch from which arose several smaller initial collaterals. These arborized extensively throughout an area of about the same size as, and highly overlapping with, the dendritic field of the cell, while the main axon could be followed for distances of up to 1 mm in the direction of the globus pallidus. Three major synaptic types were seen in contact with spiny neurons. Boutons containing small round synaptic vesicles formed synapses exclusively with spiny regions of the dendrites, and most of these were axo-spinous. Small, very pleomorphic synaptic vesicles characterized a second bouton type of unknown origin, which made contacts with somata, initial segments, and dendrites, but not dendritic spines. Boutons containing large pleomorphic synaptic vesicles had the most widespread distribution, contacting all regions including dendritic spines. Spines receiving these contacts also were postsynaptic to boutons containing small round vesicles. Axon collaterals of spiny cells formed synapses with large pleomorphic vesicles and made synapses with somata, initial segments of axons, dendrites, and dendritic spines of striatal neurons, including other spiny cells.

The discrimination of nine different types of synaptic boutons in the fundus striati (Nucleus accumbens septi).

An attempt has been made to discriminate additional types of synapses than have been previously described in the nucleus accumbens septi of the cat, which can, according to Brockhaus (1942), justifiably be termed the fundus striati due to the fact that it possesses all of the morphological and some of the neurochemical features of the striatum. This was undertaken in order to correlate at least one type of synapse with each different afferent pathway. Nine distinct types of synapses could be differentiated electron microscopically: Type I: axo-spinous synapses with sparse, small, round vesicles which seemed to be the nigro-striatal endings (35%). Type II: axo-somatic or axo-dendritic en passant synapses containing small, round vesicles (3%). Type III: axo-spinous synapses filled with densely-packed, small, round vesicles displaying strong postsynaptic thickenings which seem to be cortico-striatal (17%). Type IV: large axo-spinous synapses with densely-arranged, small, round vesicles contacting larger spines branching off a pedicle (9%). Type V: axo-somatic or axo-dendritic synapses containing large pleomorphic vesicles, probably axon collaterals (1%). Type VI: axo-somatic or axo-dendritic synapses with elongated small vesicles (20 X 45 nm) (3%). Type VII: large axo-somatic or axo-dendritic synapses filled by densely-packed, small, round vesicles (11%). Type VIII: large axo-somatic or axo-dendritic synapses containing loosely-arranged, small, round vesicles (8%). Type IX: axo-somatic or axo-dendritic synapses containing large, round vesicles in a translucent axoplasm (13%).

An electron microscopic study of degenerative changes in the cat cerebellum after intrinsic and extrinsic lesions.

AbstractDegenerative changes in the cerebellum of the cat have been observed electron microscopically 2 to 30 days after surgical lesions were placed in the inferior or middle cerebellar peduncles or after undercutting or isolating cerebellar folia. The changes were confined to the mossy fibers of the white matter and granular layer except when Purkinje cells were damaged buy undercutting. Mossy fiber terminals in the glomeruli underwent two kinds of change. Either the synaptic vesicles and mitochondria coalesced into dense clumps with loss of mitochondrial outer membranes and proliferation of cristae, or the vesicles and miotochondria disappeared leaving a swollen terminal containing only a few large pleomorphic vesicles and small dense polygonal bodies. Neurofilaments proliferated and filled a few terminals but most of the neurofilamentous hypertrophy and proliferation was confined to myelinated axons. Some phagocytosis of degenerated endings was observed and mild fibrous gliosis occurred in the glomeruli.All of the changes observed in the present study have been reported in degenerating synapses and axons elsewhere in the central and peripheral nervous system, but there appeared to be more pleomorphism and less predictability of changes in the cerebellar cortex than have been noted in other single areas of the central nervous system.