Solar Elastosis Associated with Neoplasia in Two Dalmations

Abstract

Schwann cells from a variety of nerves in two adult horses and one adult pony contained perinuclear in- tracytoplasmic inclusion complexes consisting of lipid drop- lets, variably electron-dense rounded to elongated bodies and rod-shaped multilamellar structures. The latter were char- acteristic of pi granules of Reich. There were no significant axonal or myelin alterations associated with these inclusions. It was concluded that the inclusions are a component of normal equine Schwann cells. Pi (a) granules of Reich are perinuclear metachromatic, lamellar intracytoplasmic inclusions of Schwann cells which are not infrequent in human peripheral nerve.1.7JoJ2J5 Similar granules have been found, but not described in detail, in Schwann cells of the ape, sheep, tiger, mouse, rat, rabbit, dog, goat, and h o r ~ e . ~ J ~ J ~ , ~ ~ We describe pi granules and related inclusions in peripheral nerve of two horses and a pony and call attention to what may be their relatively high incidence in adult Equidae. Necropsies were performed from 30 to 120 minutes after euthanasia in the following: a 7-year-old Quarter horse geld- ing with dysphagia and guttural pouch inflammation, and a clinically suspected vagal neuropathy (case l), a 1 0-year-old Tennessee Walking stallion with a gunshot wound of the lee. but without clinical neurological disease (case 2), and a -6-year-old grade pony gelding with no clinical disease (case 3). Segments of the proximal portion of the vagus nerve (cases 1 and 3), its pharyngeal (cases 1 and 3) and left cranial la- ryngeal (cases 1 and 2) branches, and medial palmar nerves (case 3) were taken. All nerve segments were gently straight- ened on a strip of index card and fixed by immersion in 2% glutaraldehyde and 2% paraformaldehyde in 0.1 M phos- phate buffer (pH 7.4) for 48 hours at 4 C. The tissue was subsequently rinsed in buffer, post-fixed in phosphate buff- ered 2% osmium tetroxide for 2 hours, dehydrated and embedded in epoxy resin. One pm thick sections were cut and stained with toluidine blue and safranin for light mi- croscopy. Eighty nm thick sections were cut from selected blocks, stained with uranyl acetate and lead citrate, and ex- amined in a JEOL 100 CX-I1 electron microscope at 80 kV. Light microscopic examination of all peripheral nerve specimens revealed the presence of prominent intracyto- plasmic inclusion complexes in Schwann cells of myelinated nerve fibers. These consisted of closely related lipid droplets, clear (unstained) vacuoles, and deep staining, often meta- chromatic oval-to-elongate bodies (Fig. l). Staining of the lipid droplets mimicked that of adipose (fat) cell cytoplasm. Metachromatic bodies frequently were straight or curved, rod-shaped structures. Some Schwann cells only demonstrat- ed the rod-shaped bodies or lipid droplets and/or vacuoles. Fig. 1. Cross-section of cranial laryngeal branch of the vagus nerve from case l . Schwann cells of two myelinated nerve fibers contain dark-staining elongated cytoplasmic bodies (arrows). In the upper cell these bodies are adjacent to a pole of the nucleus. No nerve fiber degeneration is ev- ident. Toluidine blue-safranin stain. Bar = 10 pm.