Sequence of tissue responses in the early stages of experimental allergic encephalomyelitis (EAE): immunohistochemical, light microscopic, and ultrastructural observations in the spinal cord.

Experimental allergic encephalomyelitis (EAE) was induced in adult Lewis rats with purified guinea pig CNS myelin and Freund's adjuvant. As soon as the very earliest clinical signs appeared the animals were perfused with fixatives and the spinal cord analyzed by electron microscopy, silver methods, and immunocytochemistry. Our findings suggest that in the early stages of EAE a sequence of events can be traced, although these events frequently overlap. The earliest morphological change appears to be astrocytic edema in both the cell body and processes. Increased amounts of glycogen particles and dispersion of glial filaments are prominent. These changes seem to occur just prior to the time when inflammatory cells begin to penetrate the capillary walls. Invasion of the neuropil mainly by macrophages and lymphocytes closely follows. Both macrophages and microglia seem to participate in phagocytosis of oligodendrocytes and myelin. Demyelination, however, is not a prominent feature at this early stage.

Dissociation of GFAP intermediate filaments in EAE: observations in the lumbar spinal cord.

Acute experimental allergic encephalomyelitis (EAE) in the Lewis rat is a cell-mediated autoimmune disease of central nervous system myelin. The lesion has been characterized by breakdown of the blood-brain barrier, edema, and periventricular infiltration of macrophages and lymphocytes. At the early stage of the disease, the astrocytes show a marked increase in immunostaining for glial fibrillary acidic protein (GFAP). A corresponding increase in GFAP content, however, cannot be demonstrated. Electron microscopic examination of the early lesion shows a typical reactive astrocytic response expressed by an enlarged watery cytoplasm, particularly at the level of the processes surrounding neurons and blood vessels and in the neuropil itself. The astroglial processes contain numerous glycogen particles (aggregates and single particles). Glial filaments are also conspicuous and are arranged in small bundles or loose thin filaments adjacent to the bundles. The glial filaments that normally appear as tight bundles have expanded and appear less dense. We suggest that the increase in GFAP immunostaining of the astrocytes in the early lesion is due in part to edema, which causes dissociation of the filaments and thereby exposes more antigenic sites to the antibodies.

Immunocytochemical localization of glutamic acid decarboxylase (GAD) and glutamine synthetase (GS) in the area postrema of the cat. Light and electron microscopy.

The present study was designed to investigate the existence of two key enzymes involved in the metabolism of gamma-aminobutyric acid, glutamic acid decarboxylase (GAD) and glutamine synthetase (GS), in the area postrema (AP) of the cat. The results showed that punctuate structures of variable size corresponding to axon terminals, exhibited GAD-immunoreactivity and were distributed in varying densities. The greatest accumulation was present in the caudal and middle segment of the AP and particularly in the area subpostrema, where the aggregation of terminals was extremely dense. The population of the GAD-labelled axon profiles gradually decreased toward the solitary complex. No neuronal bodies were labelled in our preparations. The electron microscopic studies revealed a large variety of contacts between labelled terminals and unlabelled dendrites, axons or neurons. The possibility that the GAD-immunoreactive terminals might correspond to vagal afferent projections was discussed on the basis of our observations and of other studies that employed horseradish peroxidase or degeneration methods. GS-immunoreactivity was seen in ependymoglial cells of the AP, particularly toward the caudal region, and in astrocytes and their processes of the AP proper. The latter were frequently observed around capillaries. The presence of both GAD-immunoreactive profiles and GS-immunostained ependymoglial cells and astrocytes in the AP, provided further immunocytochemical evidence of the functional correlation between the two enzymes.

Axoglial contacts in the area postrema of the cat: an ultrastructural study.

Axoglial contacts were observed in an ultrastructural study of the area postrema of the cat. According to the disposition of the electron-dense projections attached to the adjoining membranes these contacts were classified as symmetrical or asymmetrical. The axon profiles contained aggregations of clear vesicles randomly distributed or grouped in cluster adjacent to the electron-dense projections. Dense core vesicles were occasionally seen. The neuroglial profiles were either astrocytic or ependymoglial in nature. The astrocytes showed a clear cytoplasm, polymorphous vesicles, mitochondria, glycogen granules, and bundles of filaments. The ependymal cells, in contrast, had a more electron-dense and granular appearance, tubular structures, irregular vesicular formations, profiles of smooth reticuloendoplasm, and filaments grouped in bundles or isolated in the cytoplasm. The possibility that these contacts might play a role in the chemical transfer from neurons to glial cells is discussed on the basis of existing biochemical data.

Immunocytochemical localization of glial fibrillary acidic protein (GFAP) in the area postrema of the cat. Light and electron microscopic study.

Glial fibrillary acidic protein (GFAP) was demonstrated in the cytoplasm and processes of ependymal cells and astroglial components of the area postrema of the cat. These observations differ from the findings in the ependyma of the ventricular cavities which are consistently negative for the protein. Since some studies have suggested sensory functions of the glial cells in this emetic chemoreceptor trigger zone, a careful consideration of morphological and biochemical attributes of these cells seems appropriate.

The Golgi-Hortega-Lavilla technique, with a useful additional step for application to brain tissue after prolonged fixation.

The Golgi-Hortega-Lavilla silver impregnation technique was successfully applied to brain slices of various species that had been fixed for six to 24 months in a glutaraldehyde-paraformaldehyde fixative. The procedure is described in detail. Aside from being able to use material after prolonged fixation, the technique has the following advantages: 1) the impregnation is stable and yields constant results at all levels of the central nervous system, and 2) contrast is enhanced because any background precipitate that forms during staining is cleared with potassium cyanide. The possibility of using this method on material held in fixative for even longer periods is suggested.

Synaptic plasticity in the cerebral cortex of mice: effects of radiation and anesthesia.

In the neuropil of layers II and III of the frontal cortex of adult mice, as seen in the electron microscope, sodium pentobarbital anesthesia alone results in a significant decrease in synaptic profile length at 1 day after anesthetization, followed by a return to normal or above normal levels after 2-28 days, while the number of synaptic profiles per unit cross section (profile incidence) is not altered; irradiation with 5-500 rad plateau argon particles significantly inhibits the profile shortening effect of anesthesia at 1 day after exposure, but this inhibition is not dose related; an inverse dose relationship in profile incidence appears at 2 days following irradiation with argon particles; at 1 to 2 hours after 150 or 220 rad x-irradiation, profile incidence is significantly reduced while the length is increased, effects that appear to be dose related and unaffected by adrenalectomy.

An electron-microscopic study of the brain of the fruit fly, Drosophila melanogaster, exposed to high-LET krypton (84Kr) particle radiation.

Fruit flies (Drosophila melanogaster) were exposed to high-LET krypton (84Kr) ions at low (4.2 rad) and high (1,584 rad) doses and killed to assess acute (36 h post-exposure) and late (35 days post-exposure) effects in the brain by means of electron microscopy. The main findings were: (a) glycogen granules appeared in the neuroglial compartment 36 h after exposure to either dose and were no longer present in flies killed 35 days later, (b) neuronal alterations (swelling and membrane disruption) were observed 35 days after exposure to both doses, (c) changes in the neuroglia (electron-dense masses of concentrically arranged membranous structures) were seen 35 days after exposure. The data are discussed in relation to previous research in the fruit fly using argon (40Ar) charged particles and to other radiation studies performed in the mammalian brain with the view of using the insect brain as a model for detailed study of radiation effects on neurons, neuroglia, and the neuron-neuroglia unit.