Changes in the distribution of geniculocortical projections following monocular deprivation in tree shrews

We examined changes in the percentages and distribution of labelled geniculate (LGN) cells following injection of HRP into the striate cortices of normal and monocularly deprived tree shrews. Results show that deprivation does not affect the percentage of labelled cells but does alter the distribution. The projection column of labelled cells is much narrower in deprived than in non-deprived layers suggesting that the axons of non-deprived LGN cells either extend across greater distances in cortex to reach the injection sites or have more peripheral terminal sites available for transport than deprived counterparts. This finding indicates that, although ocular input to tree shrew striate cortex is organized in the form of horizontal strips, not columns, binocular competition still results in alterations in the growth of geniculocortical axons.     

Spatial contrast sensitivity of the tree shrew

Spatial contrast sensitivity functions (CSFs) were measured for 3 tree shrews. Our two-alternative forced-choice discrimination paradigm required the animals to discriminate a vertical sine-wave luminance grating from a homogeneous field of the same size (16 degrees) and mean luminance (35 cd/m2). Spatial frequencies tested ranged from 0.1 to 2.0 c/deg and grating contrast was varied trial-by-trial using a modified staircase technique. Small between-subject variations in the shape of the CSFs appeared to be correlated with our estimates of refractive error for each animal. In general, the CSFs were of the typical band-pass type with peak sensitivity occurring at approximately 0.7 c/deg. Estimates of grating acuity derived from the CSFs ranged from 1.2 to 2.4 c/deg and are within the limitations set by the eye size and retinal anatomy of the tree shrew.     

Oral contraceptive use and early abortion as risk factors for breast cancer in young women.

A case-control study was conducted in Los Angeles County, California, of 163 very young breast-cancer cases (all aged 32 or less at diagnosis) to investigate the role, if any, of oral contraceptives (OC) in the development of the disease. OC use before first full-term pregnancy (FFTP) was associated with an elevated risk, which increased with duration of OC use (relative risk approximately 2.2 at 6 years of use, P < 0.01). This increased risk could not be explained by other risk factors. OC use after FFTP was not associated with any change in risk. A first-trimester abortion before FFTP, whether spontaneous or induced, was associated with a 2.4-fold increase in breast-cancer risk (P < 0.005).     

Effect of caffeine on performances of a perceptual-restructuring task at different stages of practice

Caffeine, a sympathomimetic drug which stimulates the adrenergic nervous system, was hypothesized to exert opposite effects upon performances of a perceptual-restructuring task (the Embedded Figures Task) at different stages of practice. Specifically, caffeine was hypothesized to impair performances of perceptual-restructuring tasks when the task is still novel in early trials; and to facilitate practice induced gains in task performance as the task becomes less novel. Sixty male undergraduates were studies. Each subject was tested on the Embedded Figures Task twice, in one of the following three sequences: caffeine-placebo; placebocaffeine; and placebo-placebo. Both hypotheses received statistically significant support.Eugene Casagrande participated in this study as an undergraduate Honor Student at the College of the Holy Cross.     

Gated MR imaging of left atrial myxomas

Two cases of left atrial myxoma were evaluated with magnetic resonance (MR) imaging. In both cases, the myxoma was clearly defined as to its location, origin, and size. In one case, the myxoma prolapsed through the mitral valve. Our study indicates that MR imaging is valuable in the diagnosis of myxomas.