Alzheimer-like visual deficits in Down syndrome.

Patients with Alzheimer disease (AD) show visual impairments in color discrimination (blue hues), stereoacuity, and contrast sensitivity. We asked whether the AD-type visual profile occurs in Down syndrome (DS) in light of the fact that AD neuropathology is present in DS by age 40. We tested 22 adults with DS and 18 adults with mental retardation of non-DS etiology (MR). DS subjects made more tritanomalous errors on the test of color vision than predicated by chance (p < 0.05), indicating a deficiency in the discrimination of short wavelengths (blue hues) but not more of other types of hue discrimination errors. DS subjects had higher stereoacuity thresholds than MR subjects (p < 0.01) and reduced contrast sensitivity across the frequency range (p < 0.01). Taken together, the results point to AD-like visual deficits in DS. Like classic AD, DS may be associated with pathological changes in the parastriate and peristriate visual cortex. DS performance was not correlated with age, suggesting that in individual subjects, the AD-like visual deficits may present prior to and independent of age-associated dementia.

Prenatal protein malnutrition alters response to reward in adult rats.

Developing rats were either malnourished or adequately nourished during the prenatal period by feeding their dams diets of 6% (low) or 25% (adequate) casein content 5 weeks prior to mating and throughout pregnancy. All pups received adequate nutrition from the day of birth onwards. In Experiment 1, male offspring aged 125 days were tested in a food-rewarded variable interval 2-min (VI 2') operant paradigm under three levels of body weight reduction (90%, 85% and 80% of their ad lib feeding weight). Previously malnourished rats showed significantly higher response rates than well-nourished controls at the 90% and 85% levels but not at the 80% level. In Experiment 2, behaviorally native male littermates aged 225 days were tested in a saccharin-solution-rewarded VI 2' operant task. The rate of receipt of reward within each daily session was found to differ in the two nutritional groups. Previously malnourished rats maintained a stable rate of reward throughout the session while the controls showed a rapid decline over the first 15-20 min. The higher rate of reward late in the session in Experiment 2 and the elevated response rate in the first two phases of Experiment 1 suggests that prenatal protein malnutrition increases subsequent responsiveness to reward.