Anecdotal descriptions of atypical FeLV infections, wherein standard clinical ELISA or immunofluorescence testing fails to detect active infections, suggest that an unknown proportion of FeLV-infected cats may go undetected. In this study, 127 viremic and nonviremic cats experimentally inoculated with FeLV were evaluated at necropsy for atypical expression of FeLV antigen. Results from viremic cats were in accordance with results of earlier studies on the pathogenesis of FeLV infection in cats, wherein antigen was found in lymphoid and epithelial tissues. Differences in time course or tissue distribution of viral antigen in some cats appeared to be attributable to the challenge virus preparations, consisting of cell-free tumor homogenate or infectious plasma. It was discovered that 5 of 19 of the FeLV challenge-exposed cats that were nonviremic had FeLV-specific antigens in select tissues (bone marrow, spleen, lymph node, and small intestine) 6 to 75 weeks after inoculation. These results indicated an additional category of possible outcomes for cats exposed to FeLV. Localized FeLV infection, as described here, may explain the discordance between clinical disease and laboratory testing for FeLV.

Experiments were carried out on 8 healthy ponies to examine the effects of prolonged submaximal exercise on regional distribution of brain blood flow. Brain blood flow was ascertained by use of 15-microm-diameter radionuclidelabeled microspheres injected into the left ventricle. The reference blood was withdrawn from the thoracic aorta at a constant rate of 21.0 ml/min. Hemodynamic data were obtained with the ponies at rest (control), and at 5, 15, and 26 minutes of exercise performed at a speed setting of 13 mph on a treadmill with a fixed incline of 7%. Exercise lasted for 30 minutes and was carried out at an ambient temperature of 20 degrees C. Heart rate, mean arterial pressure, and core temperature increased significantly with exercise. With the ponies at rest, a marked heterogeneity of perfusion was observed within the brain; the cerebral, as well as cerebellar gray matter, had greater blood flow than in the respective white matter, and a gradually decreasing gradient of blood flow existed from thalamushypothalamus to medulla. This pattern of perfusion heterogeneity was preserved during exercise. Regional brain blood flow at 5 and 15 minutes of exercise remained similar to resting values. However, at 26 minutes of exercise, vasoconstriction resulted in a significant reduction in blood flow to all cerebral and brain-stem regions. In the cerebellum, the gray matter blood flow and vascular resistance remained near control values even at 26 minutes of exercise. Vasoconstriction in various regions of the cerebrum and brainstem at 26 minutes of exertion may have occurred in response to exercise-induced hypocapnia, arterial hypertension, and/or sympathetic neural activation.