Elsevier

Brain Research

Volume 715, Issues 1–2, 9 April 1996, Pages 32-43
Brain Research

Research report
Perineuronal microglial reactivity following proximal and distal axotomy of rat rubrospinal neurons

https://doi.org/10.1016/0006-8993(95)01418-7Get rights and content

Abstract

Microglial reactivity in the red nucleus of rats was studied following upper cervical and lower thoracic rubrospinal tractotomy using the lectin binding method. Following axotomy, the contralateral nucleus containing the axotomized neurons was identified using the retrograde tracer Fast blue. It was subdivided into dorsomedial (DM) and ventrolateral (VL) portions known to project to the cervical and lumbar spinal cord, respectively. Lectin-labeled microglial cells and processes on the contralateral as well as in the ipsilateral nucleus were then quantified. An early and a late increase in microglial reactivity was observed in the nucleus at 2–5 days and 2–8 weeks following thoracic and cervical tractotomy with the latter producing a more pronounced reactivity. In rats subjected to thoracic axotomy, a similar microglial increase also occurred in the intact contralateral DM nuclear area suggesting the possible action of diffusible factor(s) that might have triggered the microglial activation from the axotomized VL nuclear area. The uninjured ipsilateral nucleus also exhibited a similar pattern of microglial reactivity irrespective of the number of ipsilaterally projecting neurons following both cervical and thoracic axotomy. This could have been elicited by the retrograde influence from the denervated targets carried by the intact rubrospinal fibers of the opposite side since many of them in fact terminate bilaterally (Antal M. et al., J. Comp. Neurol., 325 (1992) 22–37). In all the axotomized or intact nucleus, microglial processes did not appear to surround neuronal cell bodies. The characteristic responses of microglial cells in the red nucleus may be related to the failure of rubrospinal neurons to regenerate following the severance of their axons.

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      A well-characterized event is the perineuronal microglial and astrocytic activation. Similarly, axotomy of cord-projection central neurons such as rubrospinal neurons also leads to the perineuronal glial activation as shown in our previous studies (Liu et al., 2003; Tseng et al., 1996a,b). After close axotomy at the brain stem level, processes of astrocytes cover approximately 40% (20% in control) surface of individual neuronal cell bodies in the red nucleus (Liu et al., 2003).

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