Factors affecting visibility of a target tissue in histologic sections.

The objective of histologic techniques is to stain the subject with high specificity and high visibility. Visibility depends on the microscope's resolution and contrast and on the microscopist's skill at optimizing the microscope's image. It also depends on histotechnological factors, which include specificity and differentiation of the stain, density of background staining (particularly in silver stains), innate color, and grayscale contrasts of the dyes in the stains and color and density of the counterstain. If contrast is not optimal, the image should be evaluated on the basis of 2 types of contrast-color and grayscale. Complementary colors have maximum color contrast, and the color triangle is useful in the selection of a suitable counterstain. Grayscale contrast is a function of the density of a stain. If dyes capable of staining the target and backgrounds tissue do not have optimal color contrast, the only method of increasing contrast is to change the grayscale value of one of the stains, usually the counterstain. Colors can have a subconscious effect on a viewer. Depending on whether they are aesthetically pleasing, they may influence the rigor of and time spent on the histopathologic examination. Maximizing the specificity of stains such as hematoxylin, eosin, trichrome, and Luxol fast blue (LFB) depends on optimal differentiation. In differentiation of counterstains such as methylene blue in the Ziehl-Neelsen stain, its recommended density is conveniently expressed as a grayscale value. Independent evaluation of color and grayscale contrasts is very helpful in determining the cause of low contrast in an image. This review discusses aspects of the histotechnique affecting the visibility of tissue components.

Concurrent infection with Toxoplasma gondii and feline leukemia virus. Antibody response and oocyst production.

Four adult cats (two testing positive and two negative for feline leukemia virus FeLV) were fed Toxoplasma gondii tissue cysts collected from the brains of mice. Two control cats (1 FeLV+, 1 FeLV-) were not fed cysts. The cats infected with T. gondii shed thousands of oocysts but remained clinically and physically normal, with hemograms and clinical chemistry values essentially unchanged irrespective of their FeLV status. Infection with FeLV did not increase the duration of oocyst shedding. At necropsy no significant lesions were found. T. gondii antibodies were detected by three serologic tests in the cats fed tissue cysts. The time necessary for an antibody response to T. gondii was not altered by the FeLV infection. Indirect hemagglutination (IHA) was the least reliable of the serologic tests studied; it detected antibodies later in the infection, and titers were less than in the other tests. Latex agglutination (LA) detected antibodies a few days before IHA, but titers were less than in modified direct agglutination (MAT). MAT detected antibodies earliest in the infection and also measured antibodies in aqueous humor and cerebrospinal fluid.

Scanning electron microscopy of ruminal papillae in calves fed various amounts and forms of roughage.

Twenty neonatal calves were fed milk plus 1 of 4 rations ad libitum: pelleted concentrates plus alfalfa hay, pelleted concentrates plus ground alfalfa hay, pelleted concentrates alone, or pelleted concentrates containing whey. Eight calves were killed at 4 weeks of age, and 12 calves at 6 weeks. The ruminal mucosa was examined grossly, by light microscopy, and by scanning electron microscopy. Well-developed differences among groups were evident in calves at 6 weeks of age; changes at 4 weeks were similar, but less developed. In 6-week-old calves fed concentrates plus alfalfa hay ad libitum, papillae were flattened and tongue shaped on the ventral floor of the atrium ruminis (cranial sac). Calves fed concentrates plus ground alfalfa had tongue shaped, rounded, and finger-like papillae. Calves fed concentrates alone or concentrates plus whey developed small, nodular, branched papillae which were cauliflower shaped and severly parakeratotic and were arranged on transverse folds on the floor of the atrium ruminis and on zigzag folds elsewhere in the rumen, except on the dorsal wall in contact with the gas bubble. The transition from tongue-shaped to nodular-shaped papillae under the influence of ration occurred last on the floor of the atrium ruminis. At least in 6-week-old calves, that site generally is not typical of changes in most ruminal papillae.

Age-related changes in percentage of fiber types and mean fiber diameters of the ovine quadriceps muscles.

Mean fiber diameters and percentages of each fiber type of the vastus lateralis, vastus medialis, rectus femoris, and vastus intermedius muscles from 15 sheep, ranging from 1 day to 5 years of age, were determined. Myosin adenosine triphosphatase and nicotinamide adenine dinucleotide-tetrazolium reductase stained sections were used. The vastus lateralis, vastus medialis, and rectus femoris contained 3 fiber types (I, IIA, and IIB). The vastus intermedius was composed almost entirely of type I fibers. From birth to 5 years of age, mean fiber diameters of type I fibers increased from 15.8 to 47.0 micron in the vastus lateralis, 15.6 to 50.7 micron in the vastus medialis, 17.5 to 46.5 micron in the rectus femoris, and 26.7 to 51.8 micron in the vastus intermedius. Means of fiber diameters of type II fibers increased from 16.1 to 44.6 micron in the vastus lateralis, 19.8 to 44.0 micron in the vastus medialis, and 17.0 to 44.5 micron in the rectus femoris. The percentage of type II fibers in the vastus lateralis, vastus medialis, and rectus femoris decreased from 85% to 90% at birth to approximately 72% at 5 years of age. The vastus intermedius consisted of only type I fibers in sheep 2 years and older.

Lesions and tuberculin sensitivity in calves inoculated with group III mycobacterial isolates from swine, pen soil, and cattle feed.

FIFTEEN calves, 7 to 11 months of age, were inoculated intradermally with group III mycobacteria ---6 isolates from swine, 1 isolate from cattle feed, and 2 isolates from soil of swine farrowing pens. Calves were tuberculin tested at 50 days and killed approximately 60 days after inoculation. Only 1 of the cultures, that of porcine origin (93c-0), produced any lesions. There were a caseo-calcareous granuloma 3mm in diameter in the regional lymph node (left prescapular) and a granuloma at the skin inoculation site. None of the 5 calves inoculated with soil- or feed-origin mycobacteria had any lesions. Three of the calves inoculated with porcine origin group III mycobacteria had suspicious or positive caudal fold reactions. Two of these had granulomas at the skin-inoculation sites and one had no lesions. The calf having lymph node and skin-inoculation site granulomas was negative. The 5 calves inoculated with feed- or soil-origin mycobacteria had negative caudal fold tuberculin tests.

Perianal adenoma of apocrine origin in a dog.

At necropsy, a 15-year-old male Standard Poodle had a 6-cm diameter mass in the perianal region. Histologic examination revealed an adenoma of apocrine tubular gland origin, rather than the more common type of perianal gland adenoma derived from modified sebaceous glands. The diameter of the mass had increased from 3 to 6 cm in 12 months and it had failed to respond to treatment with repository stilbestrol.

Projectile expectoration associated with an esophageal diverticulum in a cow.

An adult Milking Shorthorn cow developed a pulsion diverticulum of the esophagus, close to the esophageal hiatus. Clinical signs were loss of condition and projectile expectoration of chewed ingesta, as far as 2 m, accomplished by forceful expiration clearing the regurgitated ingesta from the pharynx. The lesion was detected by digital palpation through the cardia, via a rumenotomy incision.

X-ray computed tomography-aided diagnosis of nasal adenocarcinoma, with extension to the skull and central nervous system, in a dog.

A dog with tonoclonic seizures, disorientation, and tetraparesis was evaluated by use of skull radiography. An advanced, highly aggressive process was centered within the caudal portion of the right nasal cavity. X-ray computed tomography further defined the mass to be occupying the caudal portion of the nasal cavity and frontal sinuses, with concurrent involvement of the adjacent turbinates and frontal, maxillary, and palatine bones. Despite the aggressive nature of the process, no alteration to the external contour of the cranium or nose was observed. Histologic examination revealed well-differentiated adenocarcinoma.

Death of an African elephant from probable toxemia attributed to chronic pulpitis.

A 31-year-old captive male African elephant (Loxodonta africana) of 5,000-kg body weight died suddenly in ventral recumbency. Lesions seen at necropsy were bilateral purulent pulpitis and periodontitis of both tusks, serous atrophy of coronary groove fat, Grammocephalus cholangitis, myocardial and skeletal lipofuscinosis, and scattered segmental necrosis in the pectoral muscles. Nonhemolytic streptococci, Corynebacterium sp, Peptostreptococcus anaerobius, Fusobacterium nucleatum, and Bacteroides sp, were recovered from the exudate around one or both tusks. We postulated that the elephant died of hypoxia from prolonged ventral recumbency because of weakness and inability to rise secondary to toxemia from bilateral pulpitis and periodontitis.

Bacterial epididymitis in two stallions.

Two stallions had unilateral bacterial epididymitis attributable to S zooepidemicus infection. Diagnosis was based on bacterial isolation, WBC in the semen, higher than normal blood fibrinogen concentration, and leukocytosis with regenerative left shift. One horse had high seminal pH. Ultrasonography of the involved epididymides revealed changes consistent with the appearance of abnormal accumulation of exudate in the tail of the epididymis. Treatment included unilateral orchiectomy and antibiotic administration. In stallion 1, the infection persisted despite treatment. Treatment result was not available for stallion 2.