An electron microscopic study of the direct spino-olivary projection to the inferior olivary nucleus in the rat

This study examines electrophysiologically the projection of neurons in the mesodiencephalic junction to the inferior rectus subdivision of the oculomotor nucleus, using cats anesthetized with pentobarbital sodium. Many of these neurons projected directly to the ipsilateral inferior rectus subdivision and some to both sides. The neurons appeared to distribute axon branches probably terminating within and near the subdivision. They were located in the medial region of the mesodiencephalic junction between A 6.5 and 8.0 histologically corresponding to the campus prerubralis.     

The development of major projections to the inferior olivary nucleus

Summary We have employed degeneration techniques to study the ontogeny of major projections to the inferior olivary nucleus in the North American opossum, a species which is born 12 days after conception and which enjoys a protracted development in an external pouch. Subsequent to spinal lesions a small amount of axonal degeneration can be produced within the edge of the olive before subnuclei can be distinguished (7 days after birth, 24 mm, snout-rump length). Degenerating axons are present more deeply within the olive in animals operated 12 days after birth (30 mm, snout-rump length) and by at least day 16 (36 mm, snout-rump length), they are found in all of the regions they occupy in the adult animal. Subsequent to lesions which undercut all descending mesencephalic and diencephalic systems, a small amount of axonal degeneration is found at the dorsolateral edge of the olive by day 7 (23 mm, snout-rump length). Degenerating axons fill more of the olive, particularly caudally, after comparable lesions in older animals and by day 17 (38 mm, snout-rump length), degeneration is present in all of the olivary regions innervated by midbrain and thalamic axons in the adult opossum. There is some evidence that spinal, mesencephalic and diencephalic axons follow a caudal to rostral gradient in their intraolivary growth. Lesions which undercut neurites growing out of the cerebellum produce evidence for cerebello-olivary connections by day 17. Axons from the cerebral cortex reach their olivary targets considerably later than those from either the spinal cord, mesencephalon, diencephalon or cerebellum. It is not until approximately postnatal day 30 (55 mm, snout-rump length) that degenerating axons can be traced into the olive after lesions of the cortical mantle. These data indicate that the inferior olive receives major connections early in development and that there is an orderly sequence to their growth.This investigation was supported by U.S.P.H.S. Grants NS-07410 and NS-08798 and The West Virginia University Medical Corporation.     

An electron microscopic study of GABAergic neurons and terminals in the central nucleus of the inferior colliculus of the rat

Summary Neurons and terminals in the ventral lateral portion of the central nucleus of the inferior colliculus (ICCN) of the rat were labelled immunocytochemically with antisera to GABA or to its synthesizing enzyme, glutamic acid decarboxylase. Four types of GABAergic neuron are described: small, medium-sized and large multipolar neurons, as well as medium-sized bipolar neurons. All sizes of GABAergic multipolar neurons are characterized by highly infolded nuclei, many mitochondria and both asymmetric and symmetric axosomatic synapses. A dense plexus of terminals occurs on the proximal dendrites of GABAergic neurons, and most of these terminals form asymmetric axodendritic contacts. Small GABAergic neurons (diameter < 15 m) are multipolar, and have a large nucleus to cytoplasm ratio, prominent nucleoli and usually two to five axosomatic synapses per thin section, with the majority of these contacts being symmetric. Medium-sized GABAergic neurons (15–25 m in diameter) display both multipolar and fusiform shaped somata, have a more abundant cytoplasm than the small neurons and show about ten axosomatic contacts per thin section. Large GABAergic neurons (diameters > 25 m) have eccentrically located, highly infolded nuclei, abundant cytoplasm and a denser plexus of terminals that form axosomatic synapses than the other cell types. These results indicate that four of the six major cell types in the ICCN are probably GABAergic inhibitory neurons.The axon initial segments of GABAergic neurons in the ICCN all have similar features in that they are contacted by only one or two terminals that form symmetric synapses on their proximal portions and are invested by a glial sheath from 3 to 20 m from the cell body. Many immunoreactive myelinated axons (approximately 0.5 m in diameter) are observed and some terminals that arise from these axons form synapses with small neuronal somata. Both these and other labelled terminals are shown to form symmetric synapses. These data suggest a complex circuitry for the GABAergic neurons within the ICCN.     

Descending inputs to the cat dorsal cochlear nucleus: An electron microscopic study

Summary This experimental study provides identification of several types of terminals in the fusiform cell layer (FCL) of the cat dorsal cochlear nucleus (DCN). Eight types of synaptic terminal were defined in control animals. 22 experimental cats were then subjected to unilateral lesions of the superior olivary complex or SOC (Groups I and II), the inferior colliculus or IC (Groups III and IV), or the IC plus the dorsal nucleus of the lateral lemniscus or DNLL (Groups V and VI). After one to 14 days, animals were killed by perfusion-fixation and brain stems prepared for light and electron microscopic study of degeneration. After SOC lesions, theipsilateral FCL showed degeneration of small (type 2a) endings on small dendritic shafts; thecontralateral FCL showed degeneration of larger (type 5) endings mostly on fusiform cell somata and on some primary dendrites. Both sides showed mild degeneration of large, glomerular (type 1a) endings. After small IC lesions, theipsilateral FCL demonstrated degeneratingtype 1a glomerular endings but thecontralateral FCL showed severe degeneration of type 5a terminals (axodendritic to fusiform cells) and mild degeneration of bothglomerular (type 1a) and axosomatic (type 5) endings. Combined IC-DNLL lesions caused extensive degeneration in a pattern similar to that following IC lesions. In addition retrograde degeneration of fusiform cells occurred bilaterally.These studies showed that: (1)type 2a endings originate in the ipsilateral SOC; (2)type 5 endings on fusiform cell bodies originate from the contralateral SOC; (3)type 5a endings on fusiform cell dendrites originate from the contralateral IC; and (4)type 1a glomerular endings probably arise from several sources, including the IC, the SOC and (possibly) the DNLL of both sides.     

The neural connectivity of the inferior olivary nucleus in the human brain: A diffusion tensor tractography study

Objectives

Many animal studies have reported on the neural connectivity of the inferior olivary nucleus (ION). However, the neural connectivity of the ION has not been clearly elucidated in the human brain. In this study, the neural connectivity of the ION in the human brain was investigated by diffusion tensor imaging (DTI).

Methods

Forty healthy subjects were recruited. DTIs were acquired using a sensitivity-encoding head coil at 1.5 T. Connectivity was defined as the incidence of connection between the ION and regions of interest (ROIs) in the brain.

Results

In these subjects, the ION showed higher connectivity to the reticular formation (100%), the posterior limb of internal capsule (100%), the red nucleus (93.75%), the cerebral peduncle of midbrain (91.25%), the primary motor cortex (86.25%), the primary somatosensory cortex (85%), the periaqueductal gray mater (81.25%), the globus pallidus (81.25%), the anterior limb of internal capsule (62.5%), the pontine basis (62.5%), and the posterior parietal cortex (60%).

Conclusions

The ION shows high connectivity with motor function-related areas, such as, the posterior limb of internal capsule, the red nucleus, the cerebral peduncle of midbrain, the primary motor cortex, and the pontine basis. These results indicate that the ION is closely related to motor function in the human brain.     

The development of the extracellular space in neonatal rat inferior colliculus: An electron microscopic study,

Rat inferior colliculi were fixed by intracardiac perfusion of 4% methanol-free formalin in an isotonic phosphate-sucrose buffer, dehydrated in ethanol and studied during the first two weeks of postnatal life. The extracellular space during the first week was made up of intercellular gaps about 100–150 Å wide and large intercellular lakes (1–3 μ long) which diminished in size and number as maturation proceeded. Similar intercellular lakes were found in tissue fixed by immersion in glutaraldehyde containing ruthenium red. In these tissues an intense ruthenium red reaction product, distributed extracellularly, suggested an intercellular substance comparable to that described in adult brain. Intercellular lakes were also found in tissue dehydrated in acetone. Morphometric estimations indicated the extracellular space of neuropil during the first week to be about twice that of the adult, which was approached progressively.     

The neural connectivity of the inferior olivary nucleus in the human brain: a diffusion tensor tractography study

Propofol is a rapidly acting water-insoluble non-barbiturate anesthetic agent that is widely used as an intravenous sedative-hypnotic agent. Anecdotal evidence indicates that propofol may be effective at terminating intractable migraine headache. Cortical spreading depression (CSD) is believed to be the neural correlate of migraine aura and may be a trigger for migraine pain. Agents that block the induction or slow the spread of CSD may be of utility in treating migraine. Here we examined the ability of propofol hemisuccinate (PHS), a water-soluble prodrug of propofol, to affect CSD in mice. For comparison, we examinined dizocilpine, an NMDA receptor antagonist, that is well recognized to inhibit CSD. When administered 15min prior to activation of CSD by KCl application to the cortex, intraperitoneal PHS at doses of 120 and 200mg/kg decreased the number of CSD deflections without an effect on CSD amplitude, and at 200mg/kg caused a 77% reduction in CSD velocity. The minimally-effective dose of PHS (120mg/kg) did not cause sedation or motor impairment and while some animals receiving 200mg/kg did demonstrate motor impariment none exhibited loss-of-righting reflex (anesthesia). Dizocilpine produced comparable inhibition of CSD at doses of 0.5 and 2.5mg/kg. We conclude that acute PHS treatment inhibits CSD. Our results indicate that propofol, or its prodrug PHS, are worthy of further investigation as a treatment for migraine.     

Transsynaptic degeneration in the inferior olivary nucleus associated with pontine glioblastoma

A case of glioblastoma arising in the pons of a 14-year-old boy in whom transsynaptic degeneration was found in the inferior olivary nucleus is reported. The tumor occupied most of the pons including the tegmental tract and invaded into the midbrain, medulla oblongata, cerebellar peduncles, thalamus, basal ganglia, and meninges. The right inferior olivary nucleus was devoid of the tumorous lesion, but many neurons were severely vacuolated. An immunohistochemical study using glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), and S-100 protein was performed. GFAP and S-100 protein were positive in the reactive glia of the nucleus and NSE gave a faint reaction in some degenerated neurons. These degenerative changes found in neurons of the inferior olivary nucleus were considered to be transsynaptic degeneration due to the destruction of the tegmental tract at the pons and of cerebellar peduncles by invasive pontine glioblastoma.     

An electron microscopic study of the developing caudate nucleus in euthyroid and hypothyroid states

Summary Thyroid hormone exerts a powerful influence on CNS growth and maturation. Hypothyroidism early in life has long been known to cause disturbances in innate behavior, motor performance, severe and frequently irreversible mental retardation. In this deficiency, depressed caudate neurogenesis, cell migration and neuropil development during the rapid period of CNS growth may contribute to the clinical picture of perceptual handicaps often seen in cretins. Light microscopic and Golgi studies of the developing caudate nucleus in thyroid deficiency have been carried out to help attain insights into the mechanisms whereby the extrapyramidal system regulates motor function. The ultrastructural study of caudate nuclear cytogenesis and synaptogenesis in normal and hypothyroid states provides more detailed information for further analysis of the problem.Hypothyroidism was induced from birth by adding propylthiouracil to the food and drinking water of lactating dams. Linear development of the caudate nucleus of both normal and hypothyroid rats at ages 8, 14, 20, 30 and 42 days was studied by electron microscopy. Thyroid glands were examined by light microscopy to assess the normal and deficient states.Immature cells, primitive processes and synapses were the characteristic features of the 8-day-old normal caudate nucleus. Distinctively wide cisternae of the rough endoplasmic reticulum, loosely packed Golgi apparatus and chromatin clumps throughout the nuclei of the neurons were significant early morphologic variations. The dramatic cytoarchitectural maturation in the 14- and 20-day normal caudate neuropil points to the rapidity of developmental rate. After the growth spurt of the first three weeks a maturational plateau occurs which is characterized by well-formed neuronal cytoplasmic organelles, myelinated and non-myelinated axons, axon terminals, dendrites and their spines, and synapses.Thyroid deficiency causes a marked maturational delay of approximately 7 days in caudate neuronal proliferation, the elaboration of neuronal networks and the attainment of mature synaptic contents and membranes. This delay is evidenced by comparison of the structural similarities between 8-day-old normal and 14-day-old deficient rats; and additional comparisons between the 14-day-old normal and 20-day-old hypothyroid rats. A rapid catch up process in fine structural morphogenesis takes place in the period between days 14 and 30 in the deficient animals. Repression of thyroid function does not entirely prevent development of the caudate nucleus but allows a fairly extensive, though critically incomplete degree of maturation. This imperfection is manifested by a decrease in the number of synaptic contacts that persists even after the rapid catch up phenomenon of caudate synaptogenesis.Partially supported by USPHS Grant No. HD-05615     

Neonatal muscle: An electron microscopic study

A spaced serial section, electron microscopic study of the extensor digitorum longus of the 2-day-old rat was undertaken to determine whether all cells wedged between the basement membrane and the sarcolemma of a muscle fiber, regardless of their morphology, were true myosatellite cells. The muscle was relatively immature, containing groups of cells enclosed in a common basement membrane (clusters) and exhibiting primitive myoneural junctions. Cells of the muscle line included in the clusters were primary fibers, satellite fibers, myotubes in different stages of development and myosatellite cells. In single ultrathin sections, some early myotubes lacked myofilaments and were difficult to distinguish from myosatellite cells. Spaced serial sections revealed that all myosatellite cells have heterochromatic nuclei and a high nuclear/cytoplasmic ratio, and that all pale staining nuclei were found in cells with a lower nuclear/ cytoplasmic ratio, containing variable quantities of myofilaments. In addition to the cells of the muscle line, mast cells, fibroblast-like cells and other “unclassified” cells were entirely or partially enclosed within the cluster's basement membrane. This study demonstrated that location alone or location and the morphological appearance of cells in a single ultrathin section failed to provide sufficient criteria to properly classify all of the cells found in neonatal muscle clusters.     

A Golgi study on the inferior olivary nucleus in the red sting ray, Dasyatis akajei

The intranuclear organization of the inferior olivary nucleus (ION) was studied in the red sting ray, using the rapid Golgi method. The ION neurons had polygonal, triangular or spindle cell bodies which generated 3-5 primary dendrites. These dendrites were relatively straight, sparsely spinous, and distributed mainly within the ION. The axons of the ION neurons extended medially and joined fiber bundles which ran transversely in the ION. Three groups of olivary afferents were distinguished: fibers derived from the tegmental area travelled ventrally and ended totally in the ION, composing a dense fiber plexus; collaterals of fibers which extended in a longitudinal direction in and around the ION distributed mainly in the lateral portion of the ION; and collaterals of fibers which ran transversely in the ION also ended in the ION. Some fibers from these 3 afferent groups converged to form pericellular baskets. Thus, the fundamental organization of the ION in the red sting ray was similar to that of the ION in mammals.     

An electron microscopic study of the nodose (inferior vagal) ganglion cells in the monkey

Summary The present study described the normal ultrastructure of the monkey nodose ganglion cells. Furthermore, experimental monkeys were subjected to supranodose vagotomy in order to ascertain if the parent cell bodies would undergo degeneration following severance of their central processes. In the normal materials, most of the ganglion cells possessed a single neurite. However, occasional cells bearing more than one process in a sectioned profile were observed. The neurites, ranging between 2–4 m in diameter, displayed a relatively regular contour. Their cytoplasm contained parallel arrays of microtubules, ribosomes, endoplasmic reticulum and slender mitochondria. The electron density of some of these neurites was abnormally high. Embedded in these darkened neurites were a variable number of swollen mitochondria characterized by disrupted cristae. Axon terminals containing round agranular and a few large dense cored vesicles formed synaptic contacts primarily with the neurites of some of the ganglion cells. Three days after supranodose vagotomy, darkened neurites were more commonly observed but their incidence was comparable to that of the normal ganglion in longer survival animals. Another reactive change was the appearance of axon terminals undergoing various degrees of degeneration. There was no evidence of cell death in the duration studied.It was concluded from this study that the occasional darkened neurites from the normal ganglion cells was probably undergoing spontaneous degeneration which appeared to be accentuated when their central process was severed by supranodose vagotomy. The degeneration of axon terminals associated with some of the ganglion cells following the vagotomy suggested that they were derived from vagal descending fibres which were undergoing anterograde degeneration. The presence of synapses on some of the ganglion cells was also discussed and the possibility considered that the latter may represent aberrant or displaced autonomic neurons.     

Primary afferent terminals in the nucleus of the solitary tract of the frog: An electron microscopic study

In the frog solitarius nucleus, primary afferent terminals of the facial and glossopharyngeal-vagal nerves were identified with cobalt labelling and electron microscopy. The labelled terminals were grouped in two main categories, one with small (1-2 micron) and pale terminals, and another with large (3-5 micron) and dark terminals. The small terminals greatly outnumbered the large ones. In addition many terminals intermediate in size and staining reactions were found. All kinds of labelled boutons contained medium-size clear synaptic vesicles, among which dense-core vesicles of the smaller type frequently occurred. The labelled primary afferent terminals established axo-dendritic contacts of the asymmetric type. Close to these contact sites they were themselves very frequently contacted by a profile interpreted as presynaptic in relation to them. Such profiles contained spherical, pleomorphic (including dense-core) or flattened vesicles; a fourth kind was interpreted as presynaptic dendrites. It is concluded that viscerosensory fibres, as opposed to somatosensory fibres, predominantly generate small and lightly stained terminals. It is likely that the effect of synaptic transmission at the solitarius tract terminals is modulated in a very versatile manner by the various presynaptic profiles converging on these terminals.     

Scanning electron microscopic study of spinal arachnoid plaques

Calcified or ossified plaques within the spinal arachnoid membranes are often reported at autopsy and are occasionally incriminated as the cause of neurological symptoms in patients undergoing surgery. Histological studies of plaques have been done, but to our knowledge no studies using the scanning electron microscope (SEM) have been reported. In this study, portions of the spinal cord with plaques were removed from adult human cadavers in the dissecting laboratory and processed for SEM and energy-dispersive x-ray analysis (EDAX). The surfaces of the plaques appeared to be fibrous in some areas, studded with irregularly shaped projections or nodules in others, and smooth in yet other areas. Cells were seen in lacunae-like depressions on the surfaces of some plaques and EDAX revealed the presence of calcium on and near the cells. In some areas calcium and phosphorus were both detected, but not in the ratios seen in bone. No calcium was seen on smooth or fibrous areas. It is suggested that the plaques sampled in this study were composed largely of fibrous tissue encrusted in some areas with calcium salts. There was no evidence that any of the plaques contained bone.     

Rubratoxin B hepatotoxicity: An electron microscopic study

Rubratoxin B, the principal toxin produced by Penicillium rubrum, causes hepatic damage. The present study describes ultrastructural changes in rat livers at intervals of 3, 6, 24, and 72 hr following administration of 0.36 mg/kg rubratoxin B. Three hours after treatment, minimal ultrastructural changes including loss of glycogen and dilatation of rough endoplasmic reticulum (RER) were observed in groups of hepatocytes. These groups of altered cells showed a random, multifocal pattern of distribution throughout the liver by light and electron microscopy. At 6 hr, hepatocytes in the focal areas affected by rubratoxin showed more severe ultrastructural changes. There was increased vesiculation of RER with loss of ribosomes from the membranes and disaggregation of polyribosome complexes. Mitochondria contained inclusions of cytoplasmic material and intramatrix myelin figures. Increased numbers of lipid droplets were observed in some cells. Sinusoids appeared to be slightly congested. At the 24-hr interval, hepatocytes in the affected areas showed progressive degenerative changes. Mitochondria were extremely swollen and showed loss of cristae and increased numbers of myelin figures in their matrix. Accumulation of cytoplasmic lipid was more evident, and autophagic vacuoles were occasionally seen. Nuclear changes in these hepatocytes included clumping and margination of chromatin. Sinusoids at the 24-hr interval were severely congested with blood cells, platelets, and fibrin. Endothelial cells lining the sinusoids were fragmented and, in some areas, completely absent. By 72 hr, most hepatocytes in the focal, involved areas were completely necrotic. Cytoplasmic organelles showed irreversible, degenerative changes and cell membranes were frequently ruptured. Sinusoids showed complete loss of lining endothelium, and the lumens were occluded with blood cells, fibrin, and cellular debris.     

A qualitative and quantitative light microscopic study of the inferior olivary complex in the adult staggerer mutant mouse

In the homozygous staggerer (sg/sg) mutant mouse, most of the Purkinje cells (the primary targets for olivocerebellar climbing fibers) are missing or ectopic. In this study, the organization and cell number of the inferior olivary complex in sg/sg were determined and compared to the inferior olive of the wildtype (+/+) mouse. Our results indicate that there is a marked disorganization and loss of almost 60% of the cells within the inferior olivary complex. This suggests that the inferior olive may be secondarily affected by the staggerer gene due to the defects in its main target cell, the Purkinje cell.     

An electron microscopic study of astroglia and oligodendroglia in the lateral geniculate nucleus of aged rats

The ultrastructural features of glial cells in the lateral geniculate nucleus of aged rats have been studied. Abundant filaments as well as heterogeneous dense bodies are observed in the majority of astrocytes. They frequently surround both axons and nerve terminals showing signs of degeneration. In addition, some degenerating myelinated axons are seen in phase suggestive of engulfment by astrocyte processes. Oligodendrocytes display broad processes containing an organelle-rich cytoplasm and a continuity between their plasma membrane and the outer myelin lamellae which partially ensheath the adjacent axons. Multivesicular bodies and pleomorphic dense inclusions, composed of amorphous material as well as laminated structures, are also present in oligodendrocytes. The significance of these morphological features is discussed in relation to process of normal ageing.