The effect of peripheral nerve transection on the size of the microglial cell population in cytoarchitecturally distinct regions of the spinal cord dorsal horn of rats was evaluated at selected intervals 2 through 35 days after unilateral brachial plexotomy. The identification of cells was verified by electron microscopic examination of a representative random sample of cells included in the counts. Microglial cell numbers were increased in laminae I, II as well as the arbitrarily defined deeper laminae 3.5 days after surgery. Although microglial cell numbers in laminae I were within normal range 35 days after axotomy, those of the more ventrally located laminae remained significantly greater than control values for the duration of the experimental period. These findings demonstrate that: 1) microglial cell proliferation in the dorsal horn is an early event in the central changes that are attendant to peripheral nerve injury 2) the time course of the response varies in cytoarchitecturally different regions.
Microspectrophotometric estimates of RNA content and morphometric measurements of cytoplasmic, nuclear and nucleolar areas were made on 30 to 60 motoneurons (somal areas greater than 1000 microns2) ipsilateral and contralateral to brachial plexotomy performed unilaterally on adult cats 2-90 days before sacrifice. Nerve cells of unoperated animals were also assayed. Somal and cytoplasmic areas of axotomized motoneurons were larger than those of the corresponding, contralateral motor nerve cells 4, 6 and 75 days postoperatively. Because of between animal variability, it could not be determined, however, whether this difference was due to an increase in the area of the axotomized motoneurons or to a decrease in the area of the contralateral nerve cells. Nucleolar sizes did not change. In contrast, nuclei of axotomized motoneurons showed a temporary but unequivocal areal decrease. The cytoplasmic RNA content of axotomized motoneurons fell 14-28 days postoperatively but rose thereafter, being increased slightly but significantly 75-90 days after operation. At no postoperative interval, however, did the nucleolar RNA content of the axotomized cells deviate unequivocally from the unoperated or zero day condition. The following points may be emphasized: 1. these results differ from similar measurements of axotomized motoneurons of rodents and lagomorphs; 2. the data do not provide certain evidence of change in either morphometric parameters or RNA content of motoneurons on the side contralateral to surgery, although the possibility of a decrease in the size of these uninjured neurons should be considered; 3. morphometric and RNA measurements on axotomized peripheral (extrinsic) neurons of spinal anterior horn of cat contrast with similar measurements on axotomized central (intrinsic) neurons of cat red nucleus.
Cells laden with pigment granules are described in the leptomeningeal tissues of the cat and kitten. These cells can be identified consistently by gross observation following vascular perfusion. The fusiform or stellate pigmented cells are most often found in association with the outermost layers of the arteries of the subarachnoid space. They are typically separated from the cerebrospinal fluid by an attenuated layer of pial cells. Vessels that are described as having pigmented cells along their course are the anterior and posterior cerebellar; the anterior, middle, and posterior cerebral; and the basilar. Electron microscopic studies confirm the presence of abundant pigment granules. The pigment granules are the predominant component of the cytoplasm. Few organelles are demonstrable except for a large central nucleus. The data provide support for the concept of neural crest contribution to leptomeningeal structures. Identification of this isolated, easily defined population of melanocytes may provide a model for further studies of neural crest distribution as well as experimental approaches to melanogenesis and melanoma production and control.
The cat hypoglossal nerve and nucleus have been used as a model for the study of the occurrence and time course of modifications in the size and composition of the perineuronal glial cell population as they relate to cytological changes in the nerve cell body and the initiation and progress of axon regeneration. Animals were killed at 2, 5, 10, 20, 35, 65, and 115 days after crush injury to the hypoglossal nerve. At 5 days after surgery, growth cones and regenerating unmyelinated axons were present at the lesion site, but no conspicuous changes were apparent in the nerve cell bodies. At 10 days after surgery, the granular endoplasmic reticulum was disaggregated and depleted. The elongation phase appeared to be completed at 20 days, as judged by the bilateral retrograde labeling of the hypoglossal nuclei with horseradish peroxidase. By 35 days, the cytoarchitecture of the nerve cell bodies and maturation of axons, as determined by a comparison of the relative frequency distribution of cross sectional areas proximal and distal to the lesion, were completely restored. Comparative quantitative light microscopic examination of the hypoglossal nuclei of intact and experimental animals failed to reveal any statistically significant differences in the total number of glial cells, number of glial cells/unit area of neuropil, or relative proportions of glial cell types at any of the postoperative time intervals. Moreover, electron microscopic quantitation of the microglial cell population did not reveal any significant alterations in the number, density, location, or morphology of these cells.(ABSTRACT TRUNCATED AT 250 WORDS)
The effect of axotomy on the numbers and density of perineuronal cell populations was evaluated in rats, cats and kittens. Cats were sacrificed at different postoperative time intervals two through 90 days after unilateral plexotomy. Kittens (6-10 weeks of age) were subjected to the same surgical procedure and sacrificed one through 28 days after surgery. Rats were sacrificed 10 and 15 days after unilateral section of the brachial plexus or at 7 or 10 days after section of the left hypoglossal nerve. A marked increase in the total number and density of perineuronal cells occurred in the rat ventral horn 10 and 15 days after axotomy. A similar response was noted in the rat hypoglossal nucleus 7 and 10 days after neurotomy. In contrast, no significant change in these parameters was observed in the ventral horns of cats and kittens at any of the postoperative time intervals. Although quantitatively demonstrable increases in the perineuronal cell populations occur in the ventral horns and hypoglossal nuclei of rats, similar modifications do not occur in the cat following axon injury. These findings suggest that evolutionary modifications may have occurred in how perineuronal glia respond to peripheral axon injury.
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