concanavalin-a and Nerve-Degeneration

We previously reported that the cerebellar fastigial nucleus, output nucleus of the spinocerebellum, modulates lymphocyte function. To further explore the role of the cerebellum in neuroimmunomodulation, we here lesioned bilaterally the cerebellar interposed nuclei (IN) of rats with kainic acid (KA) injections. On days 8, 16 and 32 after IN lesions, lymphocyte percentage in peripheral white blood cells was examined. Furthermore, proliferation of lymphocytes from mesenteric lymph nodes induced by concanavalin A, sheep red blood cell-specific IgM antibody in the serum and cytotoxicity of natural killer cells from spleen against YAC-1 cells were measured by methyl-thiazole-tetrazolium assay, enzyme-linked immunosorbent assay and flow cytometric assay, respectively. On days 8, 16 and 32 after KA injection in the IN, the lymphocyte percentage in the peripheral white blood cells was notably diminished with respect to control rats injected with saline in the IN. Concanavalin A-induced lymphocyte proliferation, serum sheep red blood cell-specific IgM antibody and natural killer cell toxicity of the IN-lesioned rats were significantly attenuated with respect to IN-saline control rats at all the post-lesion time points. The findings reveal that KA-induced neuronal loss in the IN of both sides exerts an inhibitory effect on number and functions of T, B and natural killer lymphocytes, and indicate that the cerebellar IN participates in regulating immune function. Thus, the data suggest that the cerebellum may be an important brain area for neuroimmunomodulation, besides its well-known role in motor control.

Topics: Animals; B-Lymphocytes; Cell Death; Cell Proliferation; Cells, Cultured; Cerebellar Nuclei; Concanavalin A; Denervation; Down-Regulation; Immunoglobulin M; Killer Cells, Natural; Leukocyte Count; Lymphocyte Activation; Lymphocytes; Nerve Degeneration; Neuroimmunomodulation; Neurotoxins; Rats; Rats, Sprague-Dawley; T-Lymphocytes

The loss of neurons by programmed cell death is a normal feature of the nervous system during development and has recently been implicated as a major mechanism of cell death in neurodegenerative diseases. In some cases, programmed cell death is induced by the activation of membrane receptors and is referred to as activation-induced programmed cell death. Activation-induced programmed cell death has been previously described in cells from the immune system, in which the activation of receptors by receptor clustering leads to programmed cell death. To determine whether activation-induced programmed cell death occurs in neurons, Concanavalin A was used to cross-link membrane receptors on cortical neurons. Concanavalin A-induced neuronal death was dose dependent and effective at concentrations previously shown to induce activation-induced programmed cell death in lymphocytes. Programmed cell death was attenuated when Concanavalin A-specific binding to neurons was blocked with methyl alpha-D-mannopyranoside. Succinyl Concanavalin A, which bound to Concanavalin A receptors but was ineffective at cross-linking them, did not induce programmed cell death. Concanavalin A-induced neuronal death exhibited many of the hallmarks associated with programmed cell death, such as membrane blebbing, nuclear condensation and margination, and internucleosomal DNA cleavage. In addition, neurons exposed to Concanavalin A displayed a rapid, robust, and persistent increase in the immediate early gene protein c-Jun. A similar increase in c-Jun precedes programmed cell death induced by beta-amyloid in neurons, and under some conditions an increase in c-Jun has been shown to be required for programmed cell death to occur in neurons. Increased expression of c-jun and other immediate early genes has also been correlated with activation-induced programmed cell death in lymphocytes. These observations suggest that Concanavalin A induces activation-induced programmed cell death in neurons via signals produced from the cross-linking of receptors on neuronal membranes. These results also raise the possibility that beta-amyloid induces programmed cell death in a similar manner, by causing the cross-linking of receptors on neuronal membranes. This mechanism may be relevant to neuronal programmed cell death that occurs during development and neurodegeneration.

Topics: Animals; Apoptosis; Cells, Cultured; Concanavalin A; Cycloheximide; Dactinomycin; Gene Expression Regulation; Genes, jun; Nerve Degeneration; Nerve Tissue Proteins; Neurons; Nucleic Acid Synthesis Inhibitors; Protein Synthesis Inhibitors; Proto-Oncogene Proteins c-jun; Rats; Rats, Sprague-Dawley; Receptor Aggregation; Receptors, Concanavalin A; Signal Transduction

This report describes the partial characterization of 5'-nucleotidase (5'-AMPase) in Schwann-cell plasmalemmae (PM) prepared from degenerated cat sciatic nerve. 5'-AMPase was enriched 3.7-fold in the PM fraction over that of the crude homogenate preparation. The plant lectin concanavalin-A (Con-A) reduced Schwann cell PM 5'-AMPase activity in a concentration-dependent manner (30-600 micrograms/ml). Plasma membrane 5'-AMPase activity was maximally inhibited to 20% of control values by Con-A (400-600 micrograms/ml), and activity returned to control levels by pretreatment with the hapten sugar alpha-methyl-D-mannoside (50 mM). Equimolar concentrations of UDP and ADP (100 microM) reduced the rate of hydrolysis of labeled AMP to labeled adenosine in PM to 45% and 35% of control, respectively. This is the first study to characterize a Schwann-cell PM enzyme and demonstrates that 5'-AMPase may be used as a Schwann-cell PM marker enzyme.

Topics: 5'-Nucleotidase; Adenosine; Adenosine Diphosphate; Adenosine Monophosphate; Animals; Cats; Cell Membrane; Concanavalin A; Female; Male; Methylmannosides; Nerve Degeneration; Nucleotidases; Schwann Cells; Sciatic Nerve; Uridine Diphosphate

The cytotoxicity of glutamate and several analogues was investigated using a well characterized glutamatergic system; the neuromuscular system of the locust leg. In the presence of Con A (10(-6) M) (which blocks glutamate receptor desensitization) bath application on L-glutamate to isolated nerve-muscle preparations induced degeneration of the muscle cells in a dose-dependent manner. The ability of glutamate analogues to cause similar damage corresponded to their pharmacological potency, i.e. L-quisqualate greater than L-glutamate greater than L-cysteine greater than L-aspartate and L-kainate. Glutamate and the more potent agonists initially caused muscle swelling. This was followed by an increase in opacity of the muscle due to vacuolation resulting from disruption of the sarcoplasmic reticulum. Ca2+-free saline slowed the cytotoxic action of these amino acids, whilst saline containing high concentrations of Ca2+ (20 mM; substituted for Na+) accelerated muscle destruction. Denervation induces supersensitivity of locust muscle to L-glutamate; in denervated muscles the cytotoxicity of L-glutamate was enhanced. Muscles swollen by exposure to high-potassium saline (100 mM; substituted for sodium) were not damaged. We conclude that in this insect glutamatergic system, when desensitization is prevented, activated glutamate receptors gate the influx of Ca2+ and Na2+ causing an ionic imbalance which results in cellular damage. This mechanism could also account for at least some of the neurotoxic effects of amino acids in the vertebrate central nervous system. The results of our studies also indicate that other transmitters which gate non-desensitizing cationic channels should, in principle, also be cytotoxic.

Topics: Animals; Aspartic Acid; Concanavalin A; Cysteine; Dose-Response Relationship, Drug; Glutamates; Glutamic Acid; Grasshoppers; Kainic Acid; Nerve Degeneration; Neuromuscular Junction; Neurotransmitter Agents; Oxadiazoles; Quisqualic Acid; Receptors, Cell Surface; Receptors, Glutamate; Synaptic Transmission

The administration of concanavalin A (Con A) (50-200 microgram/egg) to chick embryos between the third and the seventh day of incubation has the following effects on the retina: (1) Con A causes the degeneration of a large number of ganglion cells and consequently the layer that should be formed by these cells is not present or is constituted only by a small number of ganglion cells. (2) The lectin seems to be effective only when it is administered during the postmitotic phase of the ganglion cells. (3) The degenerated cells are phagocytosed by the Müller cells in a manner similar to that occurring during the natural cell death in normal retinal development. (4) The differentiation of other retinal elements (photoreceptors, bipolar, amacrine and Müller cells) is not affected by the lectin administration. (5) The administration of Con A in later stages of development, even at ten times higher dosages (2000 microgram/egg), fails to affect retinal neurogenesis. It is suggested that Con A binding to receptor sites of the cell membrane affects the distribution or mobility of surface components producing an alteration in the mechanism by which the developing cells regulate positional information during retinal neurogenesis.

Topics: Animals; Chick Embryo; Concanavalin A; Microscopy, Electron; Nerve Degeneration; Neurons; Retina; Time Factors

Quantitative analyses of electron micrographs have shown a decrease in the number of synapses in the dentate gyrus of the senescent Fischer-344 rat. The loss of synapses, involving both dendritic spines and shafts and axon terminals of more than one population of presynaptic neurons, did not depend upon the antecedent loss of postsynaptic neurons or their dendrites. These findings suggest that the age-related loss of synapses in the dentate gyrus may depend upon an inability of presynaptic elements to maintain the structural integrity of synapses in senescence. It is proposed that a change in the glycoprotein component of presynaptic plasma membranes resulting from a deficiency in axonal transport mechanisms in the septo-hippocampal pathway may underly this presynaptic malfunction. The resulting partial deafferentation of neurons in the dentate gyrus in senescence appears to be associated with a secondary atrophy of dendrites, which results in a loss of postsynaptic membranes before a loss of postsynaptic neurons can be documented.

Topics: Aging; Animals; Atrophy; Concanavalin A; Fucose; Glycoproteins; Hippocampus; Nerve Degeneration; Rats; Rats, Inbred F344; Septal Nuclei; Synapses