Variability of the pattern electroretinogram

Conflicting results have been obtained concerning the parametric properties of the pattern electroretinogram. These discrepancies may be due to the large amount of variability inherent in recording amplitudes. We have found the variability within a single stimulus condition to be so large (ranging from 30% to 67% of the mean value) that it could mask any underlying spatial frequency tuning. Changing the stimulus conditions failed to significantly reduce the observed variability, although changing recording conditions produced some reduction. The use of a narrower rejection band, a greater number of sweeps, and placement of the reference electrode on the ipsilateral ear (as opposed to the ipsilateral temple) combined to decrease variability of the pattern electroretinogram within a single recording session; however, intersession variability remained high. Therefore one must be careful in evaluating data from this technique, and caution is advised in its clinical use.     

Decreasing the level of translation initiation factor 4E with antisense rna causes reversal of ras-mediated transformation and tumorigenesis of cloned rat embryo fibroblasts

Transformation of cloned rat embryo fibroblasts (CREF) with the T24-ras oncogene results in loss of contact inhibition, growth in soft agar and tumor formation in nude mice. Previously we showed that in such cells (CREF T24), the phosphorylation rate of protein synthesis initiation factor 4E (elF-4E) is increased, correlating with an increase in the general rate of protein synthesis. In the present study, we have expressed antisense RNA complementary to elF-4E mRNA in CREF T24 cells using a stably integrated vector. Cells expressing antisense RNA (CREF T24/AS) contained 30-50% of the normal level of elF-4E and exhibited many of the properties of untransformed cells. CREF T24 had a spindle-shaped, refractile appearance, whereas CREF T24/AS grew in ordered, parallel patterns and exhibited contact inhibition similar to untransformed CREF. The rates of growth and protein synthesis in CREF T24/AS were decreased compared to CREF T24 but were not as low as in CREF. The efficiency of growth in soft agar was 11-fold lower for CREF T24/AS compared with CREF T24. The latency period for tumor formation in nude mice was increased from 8 days for CREF T24 to 17-27 days for CREF T24/AS and various clonal lines derived from them. Cell lines established from these CREF T24/AS-derived tumors were shown to have partially regained the elF-4E levels characteristic of CREF T24. These results demonstrate that many of the phenotypic alterations associated with ras-induced malignant transformation can be reversed by a moderate reduction of the translational initiation capacity and therefore may be mediated through a translational mechanism.     

Statistical analysis of data on airborne asbestos levels collected in an EPA survey of public buildings

Data from a recent EPA study of airborne asbestos levels in 49 buildings occupied by the General Services Administration (GSA) are statistically analyzed. The study focuses on differences between indoor and outdoor levels, and on differences among buildings with no asbestos-containing material (ACM) (6 buildings), buildings with ACM generally in good condition (6 buildings), and buildings containing damaged ACM (37 buildings). Seven indoor samples and a single outdoor sample were collected from most buildings and analyzed by TEM (transmission electron microscopy) using a direct preparation method. No statistically significant differences were detected in asbestos levels between indoors and outdoors or among the three categories of buildings. The average indoor concentration of asbestos was 0.00073 fibers/cc (f/cc) for all fibers and 0.00007 f/cc for fibers 5 microns or longer. The current OSHA occupational standard is 0.2 f/cc for fibers 5 microns or longer as measured by phase-contrast microscopy.     

Early Postnatal Changes in the Somatodendritic Morphology of Ankle Flexor Motoneurons in the Rat

The development of locomotor function in the rat spans the first 3 postnatal weeks. We have studied morphological features of the soma and dendrites of motoneurons innervating the physiological flexor muscles of the ankle, tibialis anterior and extensor digitorum longus, by intracellular injection in vitro between the first and ninth postnatal days. We obtained serial optical sections of 96 adequately filled motoneurons in whole-mounted hemisected spinal cords by confocal microscopy, projected them onto a single plane and analysed them morphometrically. On the day after birth, the somatodendritic surfaces of most such motoneurons were covered in growth-associated spiny, thorny or hair-like appendages. These had disappeared from the soma by the fourth postnatal day and from most proximal dendrites by day 7, but were still common distally on day 9. During this period there was little or no net growth of either the soma (which was still much smaller than in the adult) or the dendritic tree. A dorsal dendritic bias was present and 'sprays' of long, loosely bundled dorsal dendrites were often seen. The mean number of primary dendrites remained constant at about eight, and their combined diameter was already significantly correlated with mean soma diameter, as in the adult cat. Thus, the critical neonatal period during which these ankle flexor motoneurons are known to change their electrophysiological properties and to be particularly sensitive to interference with neuromuscular interaction is characterized by major changes in the neuronal surface, presumably linked to synaptogenesis.