Abstract
Excitotoxins are thought to kill neurons while sparing afferent fibers and axons of passage. The validity of this classical conclusion has recently been questioned by the demonstration of axonal demyelination. In addition, axons are submitted to a profound alteration of their glial environment. This work was, therefore, undertaken to reassess axonoglial interactions over time after an excitotoxic lesion in the rat. Ultrastructural studies were carried out in the ventrobasal thalamus two days to 18 months after neuronal depletion by in situ injections of kainic acid. In some cases, lemniscal afferents were identified by using anterograde transport of wheatgerm agglutinin conjugated to horseradish peroxidase from the dorsal column nuclei.
Two and four days after kainate injection, numerous dying axons displaying typical signs of Wallerian degeneration were observed in a neuropile characterized by the loss of neuronal somata and dendrites, an increase in number of microglia/macrophages and the disappearance of astrocytes. Ten and 12 days after kainate injection, degenerating axons were no longer observed although myelin degeneration of otherwise unaltered axons was ongoing with an accumulation of myelin remnants in the neuropile. At 16 and 20 days, the demyelination process was apparently complete and axons of different diameters were sometimes packed together. One and two months after kainate injection, the axonal environment changed again: remyelination of large-caliber axons occurred at the same time as reactive astrocytes, oligodendrocytes and numerous Schwann cells appeared in the tissue. Schwann cell processes surrounded aggregates of axons of diverse calibers, ensheathed small ones and myelinated larger ones. Axons were also remyelinated by oligodendrocytes. Horseradish peroxidase-labeled lemniscal afferents could be myelinated by either of the two cell types. After three months, the neuropile exhibited an increase in number of hypertrophied astrocytes and the progressive loss of any other cellular or axonal element. At this stage, remaining Schwann cells were surrounded by a glia limitans formed by astrocytic processes.
These data indicate that although excitotoxins are sparing the axons, they are having a profound and complex effect on the axonal environment. Demyelination occurs over the first weeks, accompanying the loss of astrocytes and oligodendrocytes. Axonal ensheathment and remyelination takes place in a second period, associated with the reappearance of oligodendrocytes and recruitment of numerous Schwann cells, while reactive astrocytes appear in the tissue at a slightly later time.
Over the following months, astrocytes occupy a greater proportion of the neuron-depleted territory and other elements decrease in number. These successive stages in alteration of axonoglial interactions seem to evolve in parallel to the changes in density and terminal morphology that we described earlier for myelinated afferent fibers to the excitotoxic lesion.
Abbreviations: BDHC, benzidine di-hydrochloride; HRP, horseradish peroxidase; PNS, peripheral nervous system
References
- 1.Aguayo A.J., Charron L., Bray G.M. Potential of Schwann cells from unmyelinated nerves to produce myelin: a quantitative ultrastructural and autoradiographic study. J. Neurocytol. 1976;5:565–573. doi: 10.1007/BF01175570. [DOI] [PubMed] [Google Scholar]
- 2.Assouline J.G., Bosch P., Lim R., Kim I.S., Jensen R., Pantazis N.J. Rat astrocytes and Schwann cells in culture synthesize nerve growth factor-like neurite-promoting factors. Devl Brain Res. 1987;31:103–118. doi: 10.1016/0165-3806(87)90087-3. [DOI] [PubMed] [Google Scholar]
- 3.Assouline J.G., Pantazis N.J. Localization of the nerve growth factor receptor on fetal human Schwann cells in culture. Expl Cell Res. 1989;182:499–512. doi: 10.1016/0014-4827(89)90253-x. [DOI] [PubMed] [Google Scholar]
- 4.Blakemore W.F. Observations on remyelination in the rabbit spinal cord following demyelination induced by lysolecithin. Neuropath. appl. Neurobiol. 1979;4:47–59. doi: 10.1111/j.1365-2990.1978.tb00528.x. [DOI] [PubMed] [Google Scholar]
- 5.Blakemore W.F. Remyelination of demyelinated spinal cord axons by Schwann cells. In: Kao C.C., Bunge R.P., Reier P.J., editors. Spinal Cord Reconstruction. Raven Press; New York: 1983. pp. 281–291. [Google Scholar]
- 6.Blakemore W.F. Limited remyelination of CNS axons by Schwann cells transplanted into the sub-arachnoid space. J. neurol. Sci. 1984;64:265–276. doi: 10.1016/0022-510x(84)90175-8. [DOI] [PubMed] [Google Scholar]
- 7.Blakemore W.F., Crang A.J., Curtis R. The interaction of Schwann cells with CNS axons in regions containing normal astrocytes. Acta neuropathol., Berlin. 1986;71:295–300. doi: 10.1007/BF00688052. [DOI] [PubMed] [Google Scholar]
- 8.Blakemore W.F., Patterson R.C. Observations on the interactions of Schwann cells and astrocytes following X-irradiation of neonatal rat spinal cord. J. Neurocytol. 1975;4:573–585. doi: 10.1007/BF01351538. [DOI] [PubMed] [Google Scholar]
- 9.Bosch E.P., Zhong W., Lim R. Axonal signals regulate expression of glia Maturation Factor-Beta in Schwann cells: an immunohistochemical study of injured sciatic nerves and cultured Schwann cells. J. Neurosci. 1989;9:3690–3698. doi: 10.1523/JNEUROSCI.09-10-03690.1989. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Büssow H. Schwann cell myelin ensheathing CNS axons in the nerve fibre layer of the rat retina. J. Neurocytol. 1978;7:207–214. doi: 10.1007/BF01217919. [DOI] [PubMed] [Google Scholar]
- 11.Cammer W., Bloom B.R., Norton W.T., Gordon S. Vol. 75. 1978. Degradation of basic protein in myelin by neutral proteases secreted by stimulated macrophages: a possible mechanism of inflammatory demyelination; pp. 1554–1558. (Proc. natn. Acad. Sci. U.S.A.). [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Coffey P.J., Perry V.H., Allen Y., Sinden J., Rawlins J.N.P. Ibotenic acid induced demyelination in the central nervous system: a consequence of a local inflammatory response. Neurosci. Lett. 1988;84:178–184. doi: 10.1016/0304-3940(88)90404-1. [DOI] [PubMed] [Google Scholar]
- 13.Coffey P.J., Perry V.H., Rawlins J.N.P. An investigation into the early stages of the inflammatory response following ibotenic acid-induced neuronal degeneration. Neuroscience. 1990;35:121–132. doi: 10.1016/0306-4522(90)90126-o. [DOI] [PubMed] [Google Scholar]
- 14.Collins G.H., West N.R., Parmely J.D. The histopathology of freezing injury to the rat spinal cord. A light and electron microscope study. II. Repair and regeneration. J. Neuropath. exp. Neurol. 1986;45:742–757. doi: 10.1097/00005072-198611000-00010. [DOI] [PubMed] [Google Scholar]
- 15.Coyle J.T., Molliver M.E., Kuhar M.J. In situ injection of kainic acid: a new method for selectively lesioning neuronal cell bodies while sparing axons of passage. J. comp. Neurol. 1978;180:301–324. doi: 10.1002/cne.901800208. [DOI] [PubMed] [Google Scholar]
- 16.Coyle J.T., Schwarcz R. The use of excitatory ammo acids as selective neurotoxins. In: Björklund A., Hökfelt T., editors. Vol. 1. Elsevier; Amsterdam: 1983. pp. 508–527. (Handbook of Chemical Neuroanatomy). [Google Scholar]
- 17.Divac I., Markowitsch H.J., Pritzel M. Behavioral and anatomical consequences of small intrastriatal injections of kainic acid in the rat. Brain Res. 1978;151:523–532. doi: 10.1016/0006-8993(78)91084-3. [DOI] [PubMed] [Google Scholar]
- 18.Dusart L., Isacson O., Nothias F., Gumpel M., Peschanski M. Presence of Schwann cells in neurodegenerative lesions of the central nervous system. Neurosci. Lett. 1989;105:246–250. doi: 10.1016/0304-3940(89)90628-9. [DOI] [PubMed] [Google Scholar]
- 19.Dusart L., Nothias F., Roudier F., Besson J.M., Peschanski M. Vascularization of fetal cell suspension grafts in the excitotoxically lesioned adult rat thalamus. Devl Brain Res. 1989;48:215–228. doi: 10.1016/0165-3806(89)90077-1. [DOI] [PubMed] [Google Scholar]
- 20.Dusart I., Marty S., Peschanski M. Glial changes following an excitotoxic lesion in the CNS II. Astrocytes. Neuroscience. 1991;45:541–549. doi: 10.1016/0306-4522(91)90269-t. [DOI] [PubMed] [Google Scholar]
- 21.Fishman P.S., Nilaver G., Kelly J.P. Astrogliosis limits the integration of the peripheral nerve grafts into the spinal cord. Brain Res. 1983;277:175–180. doi: 10.1016/0006-8993(83)90922-8. [DOI] [PubMed] [Google Scholar]
- 22.Feigin I., Popoff N. Regeneration of myelin in multiple sclerosis: the role of mesenchymal cells in such regeneration and in myelin formation in the peripheral nervous system. Neurology. 1966;16:364–372. doi: 10.1212/wnl.16.4.364. [DOI] [PubMed] [Google Scholar]
- 23.Gabella G. Chapman and Hall; London: 1976. Structure of the Autonomic Nervous System. [Google Scholar]
- 24.Gilmore S.A., Duncan D. On the presence of peripheral-like nervous and connective tissue within irradiated spinal cord. Anat. Rec. 1968;160:675–690. doi: 10.1002/ar.1091600403. [DOI] [PubMed] [Google Scholar]
- 25.Gilmore S.A., Sims T.J., Heard J.K. Autoradiographic and ultrastructural studies of areas of spinal cord occupied by Schwann cells and Schwann cell myelin. Brain Res. 1982;239:365–375. doi: 10.1016/0006-8993(82)90515-7. [DOI] [PubMed] [Google Scholar]
- 26.Gledhill R.F., McDonald W.I. Morphological characteristics of central demyelination and remyelination. Ann. Neurol. 1977;1:552–560. doi: 10.1002/ana.410010607. [DOI] [PubMed] [Google Scholar]
- 27.Harrison B.M., Pollard J.D. Pattern of Schwann cell remyelination in a spinal cord lesion. Neurosci. Lett. 1984;52:275–280. doi: 10.1016/0304-3940(84)90174-5. [DOI] [PubMed] [Google Scholar]
- 28.Harrison B.M. Schwann cells divide in a demyelinating lesion of the central nervous system. Brain Res. 1987;409:163–168. doi: 10.1016/0006-8993(87)90754-2. [DOI] [PubMed] [Google Scholar]
- 29.Herndon R.M., Addick E., Coyle J.T. Ultrastructural analysis of kainic acid lesions to the cerebellar cortex. Neuroscience. 1980;5:1015–1026. doi: 10.1016/0306-4522(80)90182-7. [DOI] [PubMed] [Google Scholar]
- 30.Hirano A., Zimmerman H.M., Levine S. Electron microscopic observations of peripheral myelin in a central nervous system lesion. Acta neuropath., Berlin. 1969;12:348–365. doi: 10.1007/BF00809131. [DOI] [PubMed] [Google Scholar]
- 31.Kettenmann H., Blankerfeld G.V., Trotter J. Physiological properties of oligodendrocytes during development. Ann. N.Y. Acad. Sci. 1991;633:64–77. doi: 10.1111/j.1749-6632.1991.tb15596.x. [DOI] [PubMed] [Google Scholar]
- 32.Katzman R., Broida R., Raine C.S. Reinnervation, myelination and organization of iris tissue implanted into the rat midbrain—an ultrastructural study. Brain Res. 1977;138:423–443. doi: 10.1016/0006-8993(77)90682-5. [DOI] [PubMed] [Google Scholar]
- 33.Krammer E.B., Lischka M.F., Karobath M., Schonbeck G. Is there a selectivity of neuronal degeneration induced by intrastriatal injection of kainic acid? Brain Res. 1979;177:577–582. doi: 10.1016/0006-8993(79)90476-1. [DOI] [PubMed] [Google Scholar]
- 34.Manthorpe M., Nieto-Sampedro M., Skaper S.D., Lewis E.R., Barbin G., Longo F.M., Cotman C.W., Varon S. Neuronotrophic activity in brain wounds of the developing rat. Correlation with implant survival in the wound cavity. Brain Res. 1983;267:47–56. doi: 10.1016/0006-8993(83)91038-7. [DOI] [PubMed] [Google Scholar]
- 35.Marty S., Dusart I., Peschanski M. Glial changes following an excitotoxic lesion in the CNS. I. Microglia/macrophages. Neuroscience. 1991;45:529–539. doi: 10.1016/0306-4522(91)90268-s. [DOI] [PubMed] [Google Scholar]
- 36.Murabe Y., Ibata Y., Sano Y. Morphological studies on neuroglia. III. Macrophage response and “microgliocytosis” in kainic acid-induced lesions. Cell Tiss. Res. 1981;218:75–86. doi: 10.1007/BF00210092. [DOI] [PubMed] [Google Scholar]
- 37.Nadler J.W., Perry B.W., Gentry W., Cotman C.W. Fate of the hippocampal mossy fibres projection after destruction of its postsynaptic targets with intraventricular kainic acid. J. comp. Neurol. 1981;196:549–569. doi: 10.1002/cne.901960404. [DOI] [PubMed] [Google Scholar]
- 38.Nagashima K., Wege H., Meyermann R., Meulen ter V. Demyelinating encephalomyelitis induced by a long-term Corona virus infection in rats. Acta neuropath., Berlin. 1979;45:205–213. doi: 10.1007/BF00702672. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39.Nothias F., Wictorin K., Isacson O., Bjöklund A., Peschanski M. Morphological alteration of thalamic afferents in the excitotoxically lesioned striatum. Brain Res. 1988;461:349–354. doi: 10.1016/0006-8993(88)90266-1. [DOI] [PubMed] [Google Scholar]
- 40.Nothias F., Cadusseau J., Dusart I., Peschanski M. Fetal neural transplants into an area of neurodegeneration in the spinal cord of the adult rat. Restor. Neurol. Neurosci. 1991;2:183–188. doi: 10.3233/RNN-1991-245617. [DOI] [PubMed] [Google Scholar]
- 41.Périer O., Grégoire A. Electron microscopic features of multiple sclerosis lesions. Brain. 1965;88:937–952. doi: 10.1093/brain/88.5.937. [DOI] [PubMed] [Google Scholar]
- 42.Perry V.H., Hayes L. Lesion-induced myelin formation in the retina. J. Neurocytol. 1985;14:297–307. doi: 10.1007/BF01258454. [DOI] [PubMed] [Google Scholar]
- 43.Peschanski M., Besson J.M. Structural alteration and possible growth of afferents after kainate lesion in the adult thalamus. J. comp. Neurol. 1987;258:185–203. doi: 10.1002/cne.902580203. [DOI] [PubMed] [Google Scholar]
- 44.Peschanski M., Besson J.M. Effects of Injury on Trigeminal and Spinal Somatosensory Systems. Alan R. Liss; New York: 1987. Kainic acid induced neurodegeneration in ventrobasal complex of the rat thalamus: growth cone-like endings of functional afferent fibers; pp. 331–338. [Google Scholar]
- 45.Peschanski M., Roudier F., Ralston H.J., III, Besson J.M. Ultrastructural analysis of the terminals of various somatosensory pathways in the ventrobasal complex of the rat thalamus: an electron-microscopic study using wheatgerm agglutinin conjugated to horseradish peroxidase as an axonal tracer. Somatosensory Res. 1985;3:75–87. doi: 10.3109/07367228509144578. [DOI] [PubMed] [Google Scholar]
- 46.Peters A., Palay S.L., Webster H.de F. Oxford Univ. Press; New York: 1991. The Fine Structure of the Nervous System. [Google Scholar]
- 47.Peterson G.M., Moore R.Y. Selective effects of kainic acid on diencephalic neurons. Brain Res. 1980;202:165–182. [PubMed] [Google Scholar]
- 48.Prineas J.W., Connell F. Remyelination in multiple sclerosis. Ann. Neurol. 1979;5:22–31. doi: 10.1002/ana.410050105. [DOI] [PubMed] [Google Scholar]
- 49.Prineas J.W. The neuropathology of multiple sclerosis. In: Koestsier J.C., editor. Elsevier; Amsterdam: 1985. pp. 213–257. (Handbook of Clinical Neurology: Demyelinating Diseases). [Google Scholar]
- 50.Richardson P.M., McGuinness U.M., Aguayo A.J. Peripheral nerve autografts to the rat spinal cord: studies with axonal tracing methods. Brain Res. 1982;237:147–162. doi: 10.1016/0006-8993(82)90563-7. [DOI] [PubMed] [Google Scholar]
- 51.Scolding N.J., Morgan B.P., Houston W.A.J., Linington C., Campell A.K., Compston D.A.S. Vesicular removal by oligodendrocytes of membrane attack complexes formed by activated complement. Nature. 1989;339:620–622. doi: 10.1038/339620a0. [DOI] [PubMed] [Google Scholar]
- 52.Selmaj K.W., Raine C.S. Tumor necrosis factor mediates myelin and oligodendrocyte damage in vitro. Ann. Neurol. 1988;23:339–346. doi: 10.1002/ana.410230405. [DOI] [PubMed] [Google Scholar]
- 53.Sims T.J., Gilmore S.A. Interactions between intraspinal Schwann cells and the cellular constituents normally occurring in the spinal cord: an ultrastructural study in the irradiated rat. Brain Res. 1983;276:17–30. doi: 10.1016/0006-8993(83)90544-9. [DOI] [PubMed] [Google Scholar]
- 54.Sims T.J., Gilmore S.A., Waxman S.G., Klinge E. Dorsal-ventral differences in the glial limitans of the spinal cord: an ultrastructural study in developing normal and irradiated rats. J. Neuropath. exp. Neurol. 1985;44:415–429. doi: 10.1097/00005072-198507000-00005. [DOI] [PubMed] [Google Scholar]
- 55.Snyder D.H., Valsamis M.P., Stone S.H., Raine C.S. Progressive demyelination and reparative phenomena in chronic experimental allergic encephalomyelitis. J. Neuropath. exp. Neurol. 1975;3:209–221. doi: 10.1097/00005072-197505000-00001. [DOI] [PubMed] [Google Scholar]
- 56.Taniuchi M., Clark B., Schweitzer J.B., Johnson E.M. Expression of nerve growth factor receptors by Schwann cells of axotomized peripheral nerves: ultrastructural location, suppression by axonal contact and binding properties. J. Neurosci. 1988;8:664–681. doi: 10.1523/JNEUROSCI.08-02-00664.1988. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 57.Weinberg E.L., Raine C.S. Reinnervation of peripheral nerve segments implanted into the rat central nervous system. Brain Res. 1980;198:1–11. doi: 10.1016/0006-8993(80)90339-x. [DOI] [PubMed] [Google Scholar]
- 58.Wren D.R., Noble M. Vol. 86. 1989. Oligodendrocytes and oligodendrocyte/type-2 astrocyte progenitor cells of the adult rats are specifically susceptible to the lytic effects of complement in absence of antibody; pp. 9025–9029. (Proc. natn. Acad. Sci. U.S.A.). [DOI] [PMC free article] [PubMed] [Google Scholar]
- 59.Wuerthele S.M., Lovell K.M., Jones M.Z., Moore K.E. A histological study of kainic acid induced lesions in the rat brain. Brain Res. 1978;147:489–497. doi: 10.1016/0006-8993(78)90491-2. [DOI] [PubMed] [Google Scholar]
- 60.Zaczeck R., Schwarcz R., Coyle J.T. Long-term sequelae of striatal kainate lesion. Brain Res. 1978;152:626–632. doi: 10.1016/0006-8993(78)91121-6. [DOI] [PubMed] [Google Scholar]