Pathologic changes in otitis externa

Otitic lesions must be evaluated in the context of the whole animal. Accurate historical and clinical assessments are important aids to the pathologist attempting to reach an accurate diagnosis. Primary lesions of the pinna, with or without involvement of the external ear canal, may be an extension of a more generalized dermatologic problem or may specifically involve the ear because of its unique gross and histologic characteristics.     

Alteration of neutrophil function associated with coccidiosis in cattle: influence of decoquinate and dexamethasone

Twenty Holstein steers subclinically infected with coccidia were allotted to 2 groups of 10 steers each. One group received a diet containing 0.5 mg of decoquinate/kg of body weight. After 25 days on the diet, there was no difference between the groups in lymphocyte blastogenic responsiveness to mitogens; however, there were differences in neutrophil function. Lymphocytes from steers of the decoquinate-fed group had decreased random migration under agarose, enhanced cytochrome C reduction, and enhanced iodination activity. Other measures of neutrophil function evaluated (chemotactic index, Staphylococcus aureus ingestion, and antibody-dependent and -independent cell-mediated cytotoxicity) were not affected. After 30 days of decoquinate feeding, half of the cattle in each group received 5 daily IM injections of dexamethasone (0.04 mg/kg of body weight). The dexamethasone-treated steers from the group that did not have decoquinate in the diet developed clinical coccidiosis, whereas the decoquinate-treated steers remained clinically normal. Lymphocyte and neutrophil function were again evaluated for a 3-day period beginning 4 days after dexamethasone treatment was halted. Neutrophils from the steers that developed clinical coccidiosis after dexamethasone administration had significantly (P less than 0.05) inhibited random migration under agarose, cytochrome C reduction, and iodination activity, but significantly (P less than 0.01) enhanced S aureus ingestion. The feeding of decoquinate prevented the inhibition of neutrophil cytochrome C reduction and lessened the inhibition of neutrophil iodination in the dexamethasone-treated group. Dexamethasone treatment was associated with an inhibition of lymphocyte blastogenic responsiveness to phytohemagglutinin in principals as well as controls.     

Scintigraphic diagnosis of primary hepatocellular carcinoma in the woodchuck (Marmota monax)

Hepatic imaging with 99mTc-sulfur colloid was used to diagnose primary hepatocellular carcinoma (PHC) in woodchucks infected with woodchuck hepatitis virus (WHV). Based on imaging results, 6 of 12 WHV-infected woodchucks had space-occupying hepatic lesions, and all 6 had PHC. Of the remaining woodchucks, 2 did not have PHC, 2 had discrete tumors (less than 1 cm diameter), 1 had miliary small tumors, and 1 had tumors located near the great vessels. Hepatic imaging was a valuable technique for diagnosis of PHC in WHV-infected woodchucks.     

Correlations of stomatal conductance with hydraulic, chemical and environmental variables in five urban tree species

Recent findings suggest that stomatal conductance (g_s) may be as closely linked to plant chemical variables as to hydraulic variables. To test this in an urban field setting, we examined seasonal g_s in relation to a number of plant and environmental variables in five temperate, deciduous tree species. Stomatal conductance was generally more closely correlated with abscisic acid concentrations in xylem sap than with shoot water potential, shoot osmotic potential, pH of xylem sap or environmental variables. Seasonal g_s was mostly poorly correlated with shoot water potential and osmotic potential. Among environmental variables, PPFD accounted for most variability in g_s. We tested a model, developed previously in maize, that describes regulation of g_s by abscisic acid concentration of xylem sap with leaf water status acting to modify stomatal sensitivity to the abscisic acid signal. This model explained somewhat more variation in g_s than abscisic acid concentrations alone. Response surface models, especially those incorporating environmental variables, were most successful at explaining g_s. Our findings with urban trees are consistent with the theory of regulation of g_s by root-sourced abscisic acid.     

Effect of levamisole on lymphocyte blastogenesis and neutrophil function in dexamethasone-treated cattle

Levamisole was evaluated at 6 dose levels for its ability to prevent the dexamethasone-induced suppression of in vitro lymphocyte blastogenesis or neutrophil function in cattle. Dexamethasone (0.4 mg/kg of body weight, IM) and levamisole hydrochloride (0.5, 1.0, 2.0, 4.0, or 8.0 mg/kg orally) were administered to groups of 4 cattle daily for 3 days. Another group of 4 cattle were given the 3-day dexamethasone treatment and 6.0 mg/kg of levamisole (the recommended anthelmintic dose) was given only once on the 1st day that dexamethasone was given. Results obtained from the dexamethasone-levamisole-treated cattle were compared with results obtained from cattle that were given only dexamethasone. Levamisole had no apparent consistent ability to enhance lymphocyte blastogenic responsiveness (to the mitogens phytohemagglutinin, concanavalin A, or pokeweed mitogen or in a 1-way mixed lymphocyte reaction) or to enhance neutrophil function (random migration, nitroblue tetrazolium reduction, iodination, or antibody-dependent cell-mediated cytotoxicity) in dexamethasone-treated cattle.     

Alterations in bovine lymphocyte function during the periparturient period

Lymphocytes from 8 Holstein heifers were evaluated during the periparturient period for mitogen-induced lymphocyte blastogenic responses. Phytohemagglutinin P- and concanavalin A-induced lymphocyte blastogenesis increased 2 and 3 weeks before parturition, respectively. However, by the first week after parturition, lymphocyte blastogenesis was markedly impaired.     

Massive increase in splenic germinal centres of chickens experimentally-infected with Trypanosoma brucei brucei

Domestic chickens infected with Trypanosoma brucei brucei developed a latent parasitaemia which lasted for one year. Six distinct variable antigen types were isolated. Spleens from infected birds were studied histologically at different stages of the infection. Trypanosome infection produced a progressive increase in the number of germinal centres during the early stages of the infection. Peak numbers of germinal centres were reached in the spleen at Day 84 after which the numbers were maintained during an active infection. A tenfold increase in the number of germinal centres was found in trypanosome-infected birds compared to controls. No splenomegaly was observed. Lymphoid cells of the caecal tonsil and the thymus remained apparently normal during the course of infection. Chemotherapeutic termination of infection with berenil resulted in an initial increase in the number of germinal centres. A gradual return to normal level was observed on Day 100 post cure. It is suggested that the development of such a large number of germinal centres reflects the bird's response to the elaboration of a succession of trypanosome variable antigens.