Evaluation of Chromatin Clumping and Myelination of the Spinal Cord of Pigs with Congenital Tremor

Transcription

1 Vet. Pathol. 12: 1-5 (1975) Evaluation of Chromatin Clumping and Myelination of the Spinal Cord of Pigs with Congenital Tremor C.H. LAMAR and D.C. VAN SICKLE School of Veterinary Medicine, Purdue University, West Lafayette, Ind. Abstract. Clumps of chromatin in the spinal cord of 2- to 10-day-old pigs with congenital tremor were of no diagnostic value since they were present also in unaffected pigs of the same age. No differences in shape, size, number, location, and staining characteristics of the clumps were found. The clumps were thought to be evidence of cellular necrobiosis. The cords of pigs with tremor had distinctly less myelin than those of normal Pigs. Congenital tremor of swine is characterized by the lack of gross lesions. Microscopically, cerebellar hypoplasia and defective myelination have been associated with the condition [5], but no particular finding has been consistent in all cases. In 1969, it was reported [6] that there was mononuclear cell infiltration of the media of several large vessels in the brain stem of adult swine affected previously with congenital tremor; the brains of newborn myoclonic pigs were found to have peculiar intranuclear structures in the regions of the lateral ventricles, cerebral cortex, and brain stem. These structures were spherical, pm in diameter, and contained DNA-positive, round bodies each 1-6 pm in diameter. This report concerns a study of a similar structure (fig. 1) in the spinal cords of control pigs and pigs with congenital tremor. Materials and Methods Thirty pigs from 2 to 10 days of age were examined. Ten were affected with congenital tremor and were obtained from three unrelated farms in central Indiana. The 20 control pigs were obtained from two separate swine enterprises in central Indiana. A routine blood examination, consisting of a packed cell volume, total leukocyte count, and differential

2 2 LAMARIVAN SICKLE._.i - Fig 1. Clumps of chromatin (arrow) in the spinal cord of a pig with congenital tremor. HE. count, was done on each of the control animals. All animals were killed by electrocution and immediately exsanguinated. The spinal cords were quickly removed and placed in 10% neutral buffered formalin. Sections of liver, spleen, kidney, lung, heart, small intestine, brain, and mesenteric lymph node taken for microscopic examination were similarly fixed. Segments C,, T,, L,, and S, of the spinal cord were processed and embedded in paraplast (Sherwood Medical Industries, Inc., St. Louis, Mo.), as were selected pieces of the visceral organs. Sections of the spinal cord were cut at 10 pm on a rotary microtome and stained with hematoxylin and eosin (HE) [3], by the Kluver-Barrera method for rnyelin [3], the Menzie method for nucleic acids [3], the Feulgen method for DNA [4], and the McManus method for glycogen [3]. Three serial sections from each HE-stained segment were examined at a magnification of 600 with a light microscope. The location of all the structures was recorded on tracings of each segment. They were designated according to their location and relationship to cellular nuclei, cytons, and blood vessels. Diameters of the structures were determined with an ocular micrometer. Results There were no gross lesions in the central nervous system nor evidence of systemic infection in any of the animals. The sections of spleen, heart, lung, liver, kidney, small intestine, brain, and mesenteric lymph node were normal. The control animals were normal with respect to body temperature, body weight, and the various hematologic values. Characterization of chromatin clumping in the spinal cords of the control and pigs with congenital tremor did not produce any significant differences with respect to shape, size, number, or staining characteristics. Clumps of

3 Congenital Tremor of Swine 3 Table I. Distribution and association of chromatin clumps in affected and control pigs Age, days Number of pigs Percentage associated with gray matter glial nuclei cytons blood V~S- - sels CT = Congenital tremor; C = control Days Fig. 2. Mean number of chromatin clumps per section in various regions of the spinal cord. - = Control, = congenital tremor. chromatin occurred mainly in the white matter of the spinal cord but at 4-5 days after birth more particles were found in the gray matter of the pigs affected with congenital tremor (table I). From 60 to 70% of the clumps were closely associated with glial nuclei. The remainder were in the neuropil. The number of particles in both groups increased with age (fig. 2). The predomi-

4 4 LAMARIVAN SICKLE w U _pqa-!zzi! / 1 Fig. 3. The difference in intensity of staining of myelin in spinal cords of a pig affected with congenital tremor (a) and a control pig (b). Kluver-Barrera stain for myelin. nately round chromating clumps were pm in diameter. These data represent a mean value of the three serial sections examined. The staining reactions of the clumps were very similar in both groups of animals. With HE, a typical particle contained intensely basophilic, spherical granules, usually from one to six, surrounded by pink material. The stains for DNA, RNA, and glycogen showed the clumps of both control and affected animals to consist of DNA-positive granules surrounded by nonreactive substance. The spinal cord sections of the affected pigs stained by the Kluver-Barrera method, stained less intensely than those of normal pigs (fig. 3). This difference in staining intensity occurred in both the gray and white matter and was uniformly distributed throughout the tissue sections. Discussion This study shows that differences in location, number, and staining qualities of clumps of chromatin in glial cells and other sites of affected and control pigs are equivocal. These clumps would be of little value as diagnostic criteria for congenital tremor. The nature of these structures is not known, although their appearance is similar to that of the granules in granulocytic white blood cells. Since they may be degenerating cellular material and are similar in both the control and infected animals, necrobiosis could be an explanation for them. Necrobiosis has previously been reported in laboratory animals [l].

5 Congenital Tremor of Swine 5 The reduction of myelin in the spinal cords of affected animals confirms a previous report of this effect [2]. This study shows that clumps of chromatin in glial cells in the spinal cords of pigs 4-7 days old affected with congenital tremor are not of diagnostic value. Acknowledgement Published as Paper No. 5660, Purdue University Agricultural Experiment Station, West Lafayette, Ind. References I CAMMERMEYER, J.: The life history of the microglial cell: a light microscopic study; in EHRENPREIS and SOLNITZKY Neurosciences research, vol. 3, pp (Academic Press, New York 1970). 2 FLETCHER, T. F.: Ablation and histopathologic studies on myoclonic congenita in swine. Am. J. vet. Res. 29: (1968). 3 HUMASON, G.L.: Animal tissue techniques, p. 294 (Freeman, San Francisco 1962). 4 LUNA, L. G. (ed.): Manual of histologic staining methods of the Armed Forces Institute of Pathology; 3rd ed. (McGraw-Hill, New York 1968). 5 STROMBERG, M.W.: Myoclonia congenita; in DUNNE Diseases of swine; 3rd ed., pp (Iowa State University Press, Ames 1970). 6 STROMBERG, M.W. and GUSTAFSON, D.P.: Pathological findings in mature and newborn myoclonic pigs. Proc. Symp. on Factors Producing Embryonic and Fetal Abnormalities, Death, and Abortion in Swine, ARS, 91-73, pp (1969). Dr. C.H. LAMAR, Purdue University School of Veterinary Medicine, Lufuyerte, IN (USA)