Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) of Rocky Mountain elk in North America. Recent studies suggest that tissue and blood mineral levels may be valuable in assessing TSE infection in sheep and cattle. The objectives of this study were to examine baseline levels of copper, manganese, magnesium, zinc, selenium, and molybdenum in the brains of Rocky Mountain elk with differing prion genotypes and to assess the association of mineral levels with CWD infection. Elk with leucine at prion position 132 had significantly lower magnesium levels than elk with 2 copies of methionine. Chronic wasting disease-positive elk had significantly lower magnesium than control elk. The incorporation of manganese levels in addition to magnesium significantly refined explanatory ability, even though manganese alone was not significantly associated with CWD. This study demonstrated that mineral analysis may provide an additional disease correlate for assessing CWD risk, particularly in conjunction with genotype.

Objective-To investigate the feasibility of evoking the nociceptive withdrawal reflex (NWR) from fore- and hind limbs in conscious dogs, score stimulus-associated behavioral responses, and assess the canine NWR response to suprathreshold stimulations. Animals-8 adult Beagles. Procedure-Surface electromyograms evoked by transcutaneous electrical stimulation of ulnaris and digital plantar nerves were recorded from the deltoideus, cleidobrachialis, biceps femoris, and tibialis cranialis muscles. Train-of-five pulses (stimulus(train)) were used; reflex threshold (I(t train)) was determined, and recruitment curves were obtained at 1.2, 1.5, and 2 X I(t train). Additionally, a single pulse (stimulus(single)) was given at 1, 1.2, 1.5, 2, and 3 X I(t train). Latency and amplitude of NWRs were analyzed. Severity of behavioral reactions was subjectively scored. Results-Fore- and hind limb I(t train) values (median; 25% to 75% interquartile range) were 2.5 mA (2.0 to 3.6 mA) and 2.1 mA (1.7 to 2.9 mA), respectively. At I(t train), NWR latencies in the deltoideus, cleidobrachialis, biceps femoris, and cranial tibialis muscles were not significantly different (19.6 milliseconds 17.1 to 20.5 milliseconds, 19.5 milliseconds 18.1 to 20.7 milliseconds, 20.5 milliseconds 14.7 to 26.4 milliseconds, and 24.4 milliseconds 17.1 to 40.5 milliseconds, respectively). Latencies obtained with stimulus(train) and stimulus(single) were similar. With increasing stimulation intensities, NWR amplitude increased and correlated positively with behavioral scores. Conclusions and Clinical Relevance-In dogs, the NWR can be evoked from limbs and correlates with behavioral reactions. Results suggest that NWR evaluation may enable quantification of nociceptive system excitability and efficacy of analgesics in individual dogs.

A series of studies was conducted to identify a practical measure for preventing dental calculus formation in dogs. The studies involved a colony of 27 Beagles that received an initial dental prophylaxis. The dogs were then stratified on the basis of their normal rate of calculus formation and randomly assigned to parallel groups within each strata. During 4-week test periods, a variety of experimental regimens were instituted, followed by clinical assessments of calculus. Major observations were that a crystal growth inhibitor, soluble pyrophosphate, incorporated into a dry dog food modestly reduced calculus formation when used at high concentrations; anticalculus effects attributable to this agent were significant (P < 0.05) only when it was used as a surface coating the coating of dry dog chow or plain biscuits with a calcium sequestrant, sodium hexametaphosphate (HMP), provided the greatest benefit and resulted in significant (P < 0.05) reductions in calculus formation of about 60 to 80%, depending on the dosage regimen; and the feeding of a single daily snack of 2 HMP-coated plain biscuits (0.6% HMP) decreased calculus formation by nearly 80%. We concluded that the coating of dry dog chow or plain dog biscuits with HMP is an effective means of reducing calculus formation in dogs.

Pharmacodynamic variables of enrofloxacin were investigated in a neutropenic mouse Escherichia coli and staphylococcal thigh infection model. Enrofloxacin pharmacokinetics in clinically normal mice and dogs were compared to confirm that doses evaluated in the mouse model would include enrofloxacin doses appropriate for use in dogs. Mice were made neutropenic by treatment with cyclophosphamide and injected in the thigh muscle with approximately 10(6) colony-forming units of E. coli (n = 2) or a staphylococcal (n = 2) clinical isolate. Enrofloxacin dosages tested ranged from 0.78 to 50 mg/kg of body weight and 6.25 to 200 mg/kg in the E. coli and staphylococcal infection trials, respectively. In each 24-hour dosage trial, enrofloxacin was administered SC as a single dose or in divided doses given every 3, 6, or 12 hours. Comparison of log(10) colony-forming units per thigh muscle in untreated control mice and mice treated with enrofloxacin was used as a measure of efficacy. Two-way ANOVA was used to determine that the enrofloxacin total dose, but not the dose frequency, was significant in determining drug efficacy. Pharmacokinetic values analyzed by use of multivariant stepwise linear regression analysis indicated that the area under the concentration-time curve, but not time above minimum inhibitory concentration, was significant in predicting efficacy of enrofloxacin treatment. We conclude that enrofloxacin killing of E. coli and staphylococci is concentration dependent and not time dependent.

Twenty-four horses were randomly allocated to 3 groups. All horses underwent a ventral midline celiotomy, and the large colon was exteriorized and instrumented. Group-1 horses served as sham-operated controls, group-2 horses underwent 6 hours of colonic ischemia, and group-3 horses were subjected to 3 hours of ischemia and 3 hours of reperfusion. Baseline blood samples were collected, then low-flow colonic ischemia was induced in horses of groups 2 and 3 by reducing colonic arterial blood flow to 20% of baseline. All horses were monitored for 6 hours. Citrated systemic venous (SV) blood samples were collected from the main pulmonary artery, and colonic venous (CV) samples were collected from the colonic vein draining the ventral colon. Samples were collected at 0, and 2, 3, 3.25, 4, and 6 hours for determination of one-stage prothrombin time, activated partial thromboplastin time, antithrombin III activity, and fibrinogen concentration. Data were analyzed statistically, using two-way ANOVA for repeated measures, and post-hoc comparisons were made by use of Student Newman Keul's test. Statistical significance was set at P < 0.05. There were significant decreases in all hemostatic variables by 2 hours in SV and SV samples from horses of all 3 groups, but there were no differences among the 3 groups for any of these variables. These hemostatic alterations could have been secondary to a hypercoagulable state or to fluid therapy-induced hemodilution. Colonic ischemia-reperfusion was not the cause of these alterations because these alterations also were observed in the sham-operated control horses. Significant temporal alterations existed even after accounting for the hemodilution. The most plausible explanation for these alterations is that hemostatic activation was incited by the celiotomy and manipulation of the colon during exteriorization and instrumentation. Comparison of paired SV and CV samples for each hemostatic variable revealed significant differences for the absolute values of one-stage prothrombin time and fibrinogen concentration, but not for activated partial thromboplastin time or antithrombin III activity. This indicates that monitoring SV hemostatic variables does not necessarily provide an accurate assessment of hemostatic function in regional vascular beds. Large-colon ischemia with or without reperfusion did not alter hemostatic function.

Starling forces and hemodynamics in the digits of 5 horses were studied during early laminitis induced by oral administration of an aqueous extract of black walnut (Juglans nigra). The black walnut extract was prepared from heartwood shavings and was administered by nasogastric tube. Heart and respiratory rates, rectal temperature, central venous and arterial pressures, digital pulses, and signs of lameness were monitored. Blood samples were collected for determination of WBC count, hemoglobin concentration, and PCV and for endotoxin and tumor necrosis factor assays. Total WBC count and central venous pressure were monitored until they decreased by 30 or 20%, respectively. These decreases in WBC count and central venous pressure were observed 2 to 3 hours after dosing with black walnut extract. Respiratory and heart rates, body temperature, systolic and diastolic blood pressures, PCV, and hemoglobin concentration did not change significantly. Anesthesia was induced, heparin (500 IU/kg of body weight) was administered IV, and a pump-perfused extracorporeal digital preparation was established. Digital arterial and venous pressures were maintained at 100 and 30 mm of Hg, respectively. Blood flow, capillary pressure, lymph and plasma protein concentrations, and weight of the isolated digit during rapid increase in venous pressure were measured. Isogravimetric capillary filtration coefficient, vascular compliance, vascular and tissue oncotic pressures, tissue pressure, osmotic reflection coefficient, and precapillary and postcapillary resistances were calculated. Mean digital blood flow was 14 ml/min/100 g, capillary pressure was 52 mm of Hg, and vascular compliance was 0.06 ml/mm of Hg. The vascular and tissue oncotic pressures were 21.49 and 4.93 mm of Hg, respectively. The osmotic reflection coefficient was 0.71, and tissue pressure was 41 mm of Hg. The precapillary and postcapillary resistances were 7 and 2 mm of Hg/ml, respectively. Capillary permeability to proteins was not significantly different from that previously measured in healthy horses, suggesting that the increased capillary filtration coefficient reflected increased capillary hydrostatic pressure and perfusion of previously nonperfused capillaries. Neither endotoxin nor serum tumor necrosis factor activity was detected in any samples. The hemodynamic and Starling forces observed in this study were similar to those observed after laminitis was induced by administration of a carbohydrate gruel. Significant differences between the 2 models were detected for total vascular resistance, postcapillary resistance, and capillary filtration coefficient. It is likely that these differences were identified because the horses administered the black walnut extract were at an earlier stage in the disease process. The findings of this study suggest that the increase in capillary pressure causes transvascular fluid movement, resulting in increased tissue pressure and edema. We hypothesize that further increases in tissue pressure may collapse capillary beds and lead to tissue ischemia.

Technetium-99m sulfur colloid scintigraphy was used to study alterations of reticuloendothelial function in 7 dogs with experimentally induced biliary cirrhosis and portosystemic shunting. Scintigraphic studies were performed before and 6 weeks after common bile duct ligation. Radiocolloid plasma clearance rate was determined by measuring activity in plasma samples and by analyzing the rate of liver uptake on dynamic scintigraphic image sequences. Percentage of uptake in the liver, spleen, and lungs, as well as the ratio of hepatic-to-extrahepatic uptake, was determined from static equilibrium images. Relative to preoperative values, there were significant decreases in plasma clearance rate, percentage of liver uptake, and ratio of hepatic-to-extrahepatic uptake and significant increases in percentage of spleen and lung uptake on postoperative studies. The mechanism of technetium-99m-labeled sulfur colloid extraction by the liver is different from that of other radiocolloids; it does not require active phagocytosis or pinocytosis. Thus, liver uptake of this tracer principally reflects effective liver blood flow. Portosystemic shunting was documented in these dogs at the time of the postoperative radiocolloid scans, and we believed was responsible for the decrease in liver reticuloendothelial activity. Possible mechanisms for the increased splenic and pulmonary reticuloendothelial activities are discussed.

We examined the electromyographic activity of the costal portion of the diaphragm and the transverse abdominal and external oblique muscles in 6 chronically instrumented awake adult horses during eupneic breathing during 2 levels of hypercapnia (fractional concentration of inspired CO2; FICO2 = 0.4 and 0.6), and during 2 levels of hypocapnic hypoxia (FIO2 = 0.15 and 0.12). Using the inert gas technique, we also measured the end-expiratory lung volumes of the 6 horses during eupnea, 6% CO2 challenge, and 12% O2 breathing. During eupneic breathing, phasic electrical activity of these 3 muscles was always present and was preceded by the onset of mechanical flow. At progressive levels of hypercapnia, the magnitude of inspiratory and expiratory electrical activity increased, and for the expiratory muscles, this recruitment coincided with significant (P < 0.05) increases in peak expiratory gastric pressure. However, during hypocapnic hypoxia, differential recruitment patterns of the respiratory muscles were found. The electrical activity of the diaphragm increased in magnitude and occurred sooner relative to the onset of mechanical flow. The magnitude and onset of abdominal expiratory activity failed to increase significantly during these episodes of hyperpnea and this pattern of activity coincided with decrements in peak expiratory gastric pressure. Despite alterations in muscle recruitment patterns during these hyperpneic episodes, end-expiratory lung volume remained unchanged. Thus, we conclude that adult horses respond similarly to awake dogs during peripheral and central chemoreceptor stimulation.

The effects of mitomycin-C on intraocular pressure (IOP), facility of outflow (C), and Tenon's capsule fibrosis were studied over 60 days in 10 clinically normal dogs. A 1-piece, silicone glaucoma implant was surgically implanted into both eyes; the filtration site of one eye was treated with a single, 5-minute intraoperative application of mitomycin (0.5 mg/ml), and the fellow eye was treated in a similar manner with balanced salt solution. There were no significant differences in preoperative IOP or C-values between treatment groups. Mean IOP in eyes of both groups initially decreased from the preoperative value, but returned to the baseline value by day 21. Mean facility of aqueous outflow (C-value) increased in all eyes during the first 14 days (mitomycin-C-value = 2.26 +/- 0.72; control C-value = 2.38 +/- 0.81), then reached a plateau that was significantly higher than the baseline value in mitomycin (P = 0.039) and control (P = 0.041) eyes. Histologic evaluation revealed all implants surrounded by a connective tissue capsule composed of regular dense collagen and fibroblasts that was significantly (P = 0.003) thinner in the mitomycin-treated (scleral side = 167 +/- 62 micrometer; conjunctival side = 122 +/- 41 micrometer) than the control (scleral side = 261 +/- 92 micrometer; conjunctival side = 180 +/- 48 micrometer) group. There were, however, no significant differences in IOP or C-values between groups at any postoperative time interval. Results of this study indicate that intraoperative treatment with mitomycin suppresses, but does not prevent fibrosis around silicone filtering implants.

In an effort to better understand the role of vasodilators in the management of pulmonary hypertension associated with chronic heartworm disease (HWD), pulmonary hemodynamic measurements were obtained from 7 experimentally infected, anesthetized dogs before and after hydralazine administration (mean dose, 1.96 mg/kg of body weight). Five dogs were maintained on room air, while 2 were maintained on 100% oxygen during the hydralazine study. The hemodynamic effect of hydralazine in dogs with HWD was evaluated, using heart rate, cardiac index, mean pulmonary artery pressure, mean arterial pressure, total pulmonary resistance, total systemic resistance, total systemic resistance/total pulmonary resistance, left ventricular dP/dt(max), left ventricular end diastolic pressure, and left and right ventricular double products ([mean arterial pressure X heart rate] and [mean pulmonary artery pressure X heart rate], respectively). Responders were defined as those in which total pulmonary resistance decreased greater than or equal to 20% without an increase in mean pulmonary arterial pressure and in which heart rate increase was less than or equal to 10%. Comparison was also made between maximal hemodynamic effect of hydralazine with that after 100% oxygen administration for 15 minutes to previously normoxemic dogs (n = 5). Significance was determined if P < 0.05, using the paired t-test. Hydralazine induced significant reductions in mean pulmonary and systemic arterial pressures and total pulmonary resistance, with no significant change in heart rate, cardiac index, total systemic resistance, left ventricular dP/dt(max), left ventricular end diastolic pressure, or right and left ventricular double products. Four (57%) of the 7 dogs studied were considered responders. Pretreatment cardiac index, mean pulmonary artery pressure, and total pulmonary resistance did not allow differentiation of responders from nonresponders. However, pretreatment right ventricular end diastolic pressure was significantly less in responders than in nonresponders. Two dogs sustained hypotension after hydralazine administration, but no dogs had significant tachycardia. In dogs with experimentally induced HWD, treatment with hydralazine had significantly greater effect on cardiac index and mean pulmonary and systemic arterial pressures and resistance than did administration of 100% oxygen. These data indicate that further study of vasodilators for treatment of HWD-induced pulmonary hypertension may be warranted.