No abstract

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.