Multiple-channel models of human vision: Bandwidth considerations

Physiological constraints and mathematical properties of the Fourier transform imply that frequency-selective channels in the visual system must have nonzero bandwidth. Existing experimental results for aperiodic patterns, interpreted in light of a multiple-channel model, indicate not only that nonzero bandwidths must be used in such a model, but also that bandwidths vary with the characteristic frequency of the channels.     

Elimination of X-ray-induced chromosomal aberrations in the progeny of female mice

Female NMRI mice were irradiated with various doses of X-rays and induced chromosome aberrations were scored in MII oocytes (Dosage: 0.222, 0.666, 2 and 6 Gy). After irradiation with 2 Gy, early zygotes were examined in the 2-cell stage; additional dominant lethals were counted and surviving embryos were examined after 13.5 days of pregnancy. 87.2% of the MII oocytes showed structural chromosomal aberrations after irradiation with 2 Gy. Surviving embryos, however, failed to show any increase in the aberration rate. This result points to (almost) complete elimination of genetically damaged oocytes and zygotes already before birth. In addition to the structural aberrations, aneuploidies were induced. Most of them, however, were hypoploidies. Hence, the study confirmed the well-known susceptibility of oocytes around the time of fertilization for induced chromosome loss. Induced hyperploidies, however, were very rare. Evidence for induction of meiotic non-disjunction was weak. In surviving embryos, no increase in numerical aberrations, either hypoploid or hyperploid was discovered. The significance of these data for the prediction of chromosomal damage due to to ionizing radiation in humans is discussed. Recent risk estimates of UNSCEAR and other agencies represent very cautious upper levels.     

Acute phase proteins and pesticide exposure

Gamma mobility C-reactive protein (CRP) level was determined in the sera of persons occupationally exposed to pesticides and controls in conjunction with serum protein analysis and other biochemical and enzymologic tests. Workers chronically exposed to dieldrin and pentachlorophenol showed significantly higher prevalence of CRP than the unexposed persons. In addition, the pentachlorophenol-exposed subjects revealed significantly elevated levels of total bilirubin and creatine phosphokinase, although the levels were within normal limits. The results suggest that chronic exposure to pentachlorophenol may have been responsible for the difference in the prevalence of CRP between the pentachlorophenol and control groups.     

Round and amoeboid microglial cells in the neonatal rabbit brain

Summary Round and amoeboid microglial cells in brains of neonatal rabbits have been studied with light and electron microscopy. They are present mainly in the white matter where there are large extracellular spaces, but a few occur in the vicinity of blood vessels in the basal ganglia. They are easily recognized by the shape of their processes. Both round and amoeboid cells are highly differentiated cells whose size and cytoplasmic vacuoles are similar to phagocytes. They lack the fibrils and microtubules of young nerve and glial cells and contain a rich complement of cytoplasmic organelles. Large numbers of lipid bodies and vacuoles are their most characteristic features. Small vacuoles are concentrated near the cell surface and contain material identical to that filling the extracellular space. They appear to arise as invaginations at the cell surface, to unite to form large vacuoles, and to increase in density as their contents are degraded. The role of these cells in the embryonic development of the brain is not clear and further work is in progress to establish their origin and fate.This work was supported by Program Project Grant NS 07938. Walter H. Reichert was supported on a student summer fellowship from the National Institutes of Health general research support grant.We are grateful for the excellent technical assistance provided by Barbara Gilson.