DNA polymerase of Dictyostelium discoideum

Only one molecular weight species of DNA polymerase was found in different developmental stages of the eukaryotic microorganism Dictyostelium discoideum. The molecular weight of this DNA polymerase is estimated to be about 127 000 by sucrose gradient centrifugation. The enzyme is present in all stages of growth and development, including dormant spores. All DNA polymerase activity is lost upon incubation of the crude extract with N-ethylmaleimide. The reaction properties, molecular weight and N-ethylmaleimide sensitivity of the D. discoideum DNA polymerase are similar to those of the DNA polymerase-alpha from mammalian sources.     

Effects of the antiestrogenic environmental pollutant 3,3',4,4', 5-pentachlorobiphenyl (PCB #126) in rat bone and uterus: diverging effects in ovariectomized and intact animals

The purpose of this study was to compare effects on rat bone and uterus of estrogen depletion and exposure to the coplanar PCB-congener 3,3',4,4',5-pentachlorobiphenyl (PCB #126) which exhibits anti-estrogenic properties. Half of the rats were ovariectomized (n = 20) and the other half were sham-operated. Ten of the ovariectomized rats and ten of the sham operated were exposed to PCB #126 (ip injections) for 3 months (total dose: 384 microgram/kg body wt). The remaining control rats were injected with corn oil (vehicle). The rats were killed and the tibiae and uteri were dissected. The left tibia was used for measurements of weight, length, and bone mineral density and the right for histomorphometrical analysis. The uteri were analyzed with respect to estrogen receptor content. PCB #126 exposure did not affect bone mineral density or trabecular bone volume of tibia in sham-operated rats. In ovariectomized rats PCB #126 exposure resulted in a decreased length and an increased bone mineral density of tibia. An obvious PCB #126 induced increase in osteoid surface was observed in sham-operated rats. The cortical thickness and the organic content of the tibia were also increased in these rats. In estrogen deprived tissue like the uteri of ovariectomized rats, PCB #126 showed weak estrogen agonistic activity. The observed effects of PCB #126 on bone and uterine tissues differed between ovariectomized and sham-operated rats.     

Polysilicon TFT structures for kink-effect suppression

Experimental results and numerical simulations of asymmetric fingered polysilicon thin-film transistors (AF-TFTs) are analyzed in detail. In the AF-TFTs, the transistor channel region is split into two zones with different lengths separated by a floating n/sup +/ region. This structure allows an effective reduction of the kink effect depending on the relative length of the two subchannels, without introducing any additional series resistance. In addition, an appreciable reduction of the leakage current is also observed. The AF-TFTs characteristics have been analyzed by two-dimensional numerical simulation and by modeling the device with two transistors in series. This model clarifies the mechanisms of kink effect suppression in AF-TFT. On the basis of this analysis, two new modified device structures for kink-effect suppression are also proposed and discussed.     

EEG evidence of stimulus-directed response dynamics in human somatosensory cortex

Dense multichannel recordings of scalp electroencephalogram (EEG) were obtained in the vicinity of primary somatosensory cortex, time-locked to repetitive vibrotactile stimulation of sites on the right index finger of a single human subject. Frequency-domain analysis of cross-trial averages revealed prominent 'driving' responses in the EEG at the frequency of stimulation, which under specific stimulus conditions displayed pronounced changes in amplitude and topographic organization over brief (4 s) durations of stimulus exposure. The changes were systematic and physiologically coherent, evolving toward driving-response topographies observed in the same subject in conjunction with periodic microstimulation of single mechanoreceptive afferents whose receptive fields occupied corresponding positions on the digit. This dynamic process was orderly and reproducible, and could be controlled by manipulating factors such as the amplitude, frequency, and temporal spacing of the stimuli. The results are tentatively interpreted in light of a previously proposed neurophysiological model of stimulus-driven response plasticity in mammalian somatosensory cortex.