AVMA Panel on Euthanasia. American Veterinary Medical Association. 2000 Report of the AVMA Panel on Euthanasia

Effects of dietary selenium supplementation on DNA damage and apoptosis in canine prostate

The trace mineral selenium inhibits cancer development in a variety of experimental animal models. We used an in vivo canine model to evaluate the effects of dietary selenium supplementation on DNA damage in prostate tissue and on apoptosis in prostate epithelial cells. Sexually intact elderly male beagle dogs were randomly assigned to receive an unsupplemented diet (control group) or diets that were supplemented with selenium (treatment group), either as selenomethionine or as high-selenium yeast at 3 micro g/kg or 6 micro g/kg body weight per day for 7 months. The extent of DNA damage in prostate cells and in peripheral blood lymphocytes, as determined by the alkaline comet assay, was lower among the selenium-supplemented dogs than among the control dogs (prostate P<.001; peripheral blood lymphocytes P =.003; analysis of variance) but was not associated with the activity of the antioxidant enzyme glutathione peroxidase in plasma. The median number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive (i.e., apoptotic) prostate epithelial cells was 3.7 (interquartile range = 1.1-7.6) for the selenium-supplemented dogs and 1.7 (interquartile range = 0.2-2.8) for the control dogs ( P =.04, Mann-Whitney U test). These data suggest that dietary selenium supplementation decreases DNA damage and increases epithelial cell apoptosis within the aging canine prostate.

Acute in vivo testing of a respiratory assist catheter: implants in calves versus sheep

A respiratory catheter that is inserted through a peripheral vein and placed within the vena cava is being developed for CO2 removal in patients with acute exacerbations of chronic obstructive pulmonary disease (COPD). The catheter uses a rapidly pulsating balloon to enhance gas exchange. In this study, the CO2 removal performance of our catheter was assessed in acute sheep implants and compared with calf implants, primarily because sheep have cardiac outputs (CO) that are more comparable with human CO and lower than calves. Respiratory catheters (25 mL balloon, 0.17 m2) were inserted acutely in sheep (n = 2) and calves (n = 6) through the jugular vein and placed within the vena cava in two positions: spanning the right atrium (RA) and within the inferior vena cava (IVC). The postinsertion CO in the sheep ranged from 4.1 to 7.2 L/min compared with 6.2 to 15.5 L/min for the calves. The maximum CO2 removal rates (vCO2) were 297 ml/min/m2 (calf) and 282 ml/min/m2 (sheep) in the RA position and 240 ml/min/m2 (calf) and 248 ml/min/m2 (sheep) in the IVC position. The respective removal rates between animal models were not statistically different (p values > 0 .05 for all data sets). The dependence of the vCO2 on balloon pulsation was also not statistically different between the animal models.

Microstructure and mineral content of femora in male turkeys with and without fractures

Microscopic and radiographic observations, as well as ash, calcium, phosphorus, copper, manganese, and zinc concentrations, were evaluated from femora of 32- to 35-wk-old male turkeys from two different farms (A and B). Turkeys from Farm A were divided into birds with femoral fracture (AF) and without femoral fracture (ANF). Turkeys from Farm B did not have femoral fractures (BNF). In the mid-diaphyseal cortex of turkeys without femoral fractures, collagen fibers were evenly distributed parallel to the transverse plane of bone surface. In contrast, collagen fibers were disorganized and the cortex was osteoporotic in turkeys with femoral fractures. Each turkey with femoral fractures also had callus on the mediocaudal region of the femoral middiaphysis. The periosteal callus was interrupted at the insertion of the puboischiofemoralis muscle. Muscle attachment to the bone might have interfered with the formation of periosteal callus. The concentration of calcium was lower in the cortex of turkeys in group AF compared to turkeys in groups ANF and BNF. The focal nature of the callus, along with the low levels of calcium, is indicative of a local repair response with alteration in cortical structure and altered concentrations of minerals in the cortex. These changes in the bone and the routine handling of the birds might have predisposed the turkeys to complete fractures of the femur.

Learning to see the trees before the forest: reversible deactivation of the superior colliculus during learning of local and global visual features

Previous studies have established that deactivation of the superior colliculus severely retards the normally rapid learning of pattern discriminations in the mature cat. The purpose of this study was to test the hypothesis that the midbrain plays an important role in the learning of simple pattern discriminations and that the contribution of this pathway is to the perception of global, rather than local, features of a figure. To answer this question, pattern discrimination learning was studied in three intact cats and in three experimental cats during bilateral reversible deactivation of the superficial layers of the superior colliculus (SC). The animals concurrently learned to discriminate three pairs of compound visual patterns composed of small (local element) Ts or 7s. Congruent and incongruent stimulus pairs were large (global) Ts vs. 7s comprising the same or different local elements, respectively. The random stimulus pair consisted of randomly scattered local elements (Ts vs. 7s). The animals were trained to respond to the large Ts in the congruent and incongruent pairs and the small Ts in the random pair. In the normal cats, learning of the random pair was much slower than the learning of the congruent and incongruent pairs. This finding demonstrated the theory of global precedence, because the animals learned the global features of the congruent and incongruent pairs much more quickly than the local features of the random pair. In contrast, during bilateral deactivation of the superficial layers of the SC, the learning of the incongruent pair was significantly retarded and took longer to learn than the random pair. Congruent and random pair learning rates were unchanged. The specific deficit in learning the incongruent pair indicates that the learning of global, but not local, elements of the visual pattern is impaired during deactivation of the SC. The unimpaired use of local features permitted the animals to learn the congruent and random pairs at normal rates. Therefore, deactivation of the superficial layers of the SC during pattern discrimination learning reverses the precedence for global visual features that is typical of normal learning.