Effect of feeding patterns on performance of a visuospatial memory task in the beagle dog: a novel cognitive-based protocol for assessing satiety.

The assessment of appetite suppressing effects, or satiating effects, of drugs or other treatments is typically based on the measurement of food consumption and body weight. The present study describes a novel cognitive-based protocol for assessing satiety in the dog based on response latency and performance accuracy on a canine test of spatial working memory, the three-component delayed-non-matching-to-position task (3cDNMP). We hypothesized that satiety, produced by providing food prior to testing, would reduce motivation to respond quickly and accurately on this food-reinforced task. Dogs were first over-trained on a variable-delay version of the 3cDNMP task. They were then pre-fed with either a single or a double portion of food prior to being tested on the same task. Pre-feeding slowed response latency, but had no effect on performance accuracy. A more pronounced increase in response latency was observed in young dogs than in old dogs when offered double portions of food. These results suggest, first, that spatial working memory capability is independent of motivation; second, that satiety is age sensitive; and third, that a cognitive protocol can provide a reliable method for evaluating the satiating effects of various foods and other compounds in the dog.

Histological and magnetic resonance analysis of sciatic nerves in the tellurium model of neuropathy.

Ingestion of tellurium (Te), a toxic element, produces paralysis of the hind limbs in weanling rats that is due to temporary, segmental demyelination of the sciatic nerves bilaterally. Weanling rats were fed a 1.1% elemental Te diet and sacrificed at various time points for histological and magnetic resonance (MR) analysis of the sciatic nerves. No controls exhibited impairments of the hind limbs, whereas Te-treated animals became progressively impaired with increased Te exposure. Toluidine blue-stained nerve sections of Te-treated animals showed widened endoneurial spaces, disrupted myelin sheaths, swollen Schwann cells, and a few instances of axonal degeneration. Te decreased healthy myelin by 68% and increased percent extracellular matrix by 45% on day 7. MR experiments showed a decrease in the area of the short T2 component, an increase in average T1, and an increase in the position of the intermediate T2 component in Te-treated nerves. The correlation coefficient for healthy myelin and average T1 was 0.88 and that for healthy myelin and the area underneath the short T2 component was 0.77. The area of the short T2 component has been postulated as the best measure of the process of demyelination.