Contrast dependency of VEPs as a function of spatial frequency: the parvocellular and magnocellular contributions to human VEPs

The present study investigated the contrast dependency of visual evoked potentials (VEPs) elicited by phase reversing sine wave gratings of varying spatial frequency. Sixty-five trials were recorded for each of 54 conditions: 6 spatial frequencies (0.8, 1.7, 2.8, 4.0, 8.0 and 16.0 c deg(-1)) each presented at 9 contrast levels (2, 4, 8, 11, 16, 23, 32, 64 and 90%). At the lowest spatial frequency, the waveform contained mainly one peak (P1). For spatial frequencies up to 8 c deg(-1), P1 had a characteristic magnocellular contrast response: it appeared at low contrasts, increased rapidly in amplitude with increasing contrast, and saturated at medium contrasts. With increasing spatial frequency, an additional peak (N1) gradually became the more dominant component of the waveform. N1 had a characteristic parvocellular contrast response: it appeared at medium to high contrasts, increased linearly in amplitude with increasing contrast, and did not appear to saturate. The data suggest the contribution of both magnocellular and parvocellular responses at intermediate spatial frequencies. Only at the lowest and highest spatial frequencies tested did magnocellular and parvocellular responses, respectively, appear to dominate.     

In vitro biomechanical testing of the 3.5 mm LCP in torsion: a comparison of unicortical locking to bicortical nonlocking screws placed nearest the fracture gap

Objective

This biomechanical study compared the torsional strength and stiffness of a locking compression plate with all locking versus nonlocking screws and examined the effect of placing a locking unicortical or nonlocking bicortical screw nearest the fracture gap in a synthetic bone model.

Results

Synthetic bone models simulating a diaphyseal fracture without anatomic reduction were tested using four screw configurations: all bicortical locking (ABL), all bicortical nonlocking (ABN), a hybrid construct with a bicortical nonlocking screw nearest the fracture gap (BN), and a unicortical locking screw placed nearest the fracture gap (UL). Torsional stiffness, rotation and torque at failure were compared via ANOVA and post hoc pairwise comparisons (p < 0.05). ABN and BN had the highest stiffness (p < 0.01) with ABL greater than UL (p < 0.01). Rotation at failure was greatest for ABL (p < 0.01) with UL greater than ABN (p < 0.05). Unicortical locking screws nearest the fracture gap decreased stiffness, without significantly affecting torque or rotation at failure. Construct stiffness was found to exist in a very narrow range of 0.9–1.2 N m/deg with standard deviations of 0.1 N m/deg in all cases. The results of this study support the use of nonlocking screws in a hybrid construct to increase torsional stiffness.

     

Changes in UsnRNA biosynthesis during rat liver regeneration

Partial hepatectomy (P.H.) induces a partially synchronized growth response of liver under normal regulation of growth. In this phase changes in cellular morphology, radial distribution pattern of cells and other biological as well as major biochemical changes are well documented [24]. Here, we have shown that the cellular content of UsnRNAs altered during this proliferative phase as well. The level of spliceosomal UsnRNAs (U1, U2, U4–U6) gradually decreased by 30–50% upto 48 hrs of P.H. followed by gradual increase to reach the normal level within one month of P.H. The U3 snRNA level on the other hand, was nearly equal to that in normal liver at 48 hrs of P.H. but in 24 and 72 hrs of P.H. its level was high (4 fold) in contrast to that in other UsnRNAs. Thus, it is clear from our data that the level of all the six UsnRNAs decreased during 48 hrs of P.H. compared to that after first 24 hrs. This has been correlated in the kinetics of UsnRNAs' synthesis (in terms of labelling) in isolated hepatocytes, where the rate of labelling of all the six UsnRNAs increased 20–30% in 24 hrs regenerating hepatocytes (R.H.) followed by sharp decrease by 30–50% within next 24 hrs, compared to that in the normal hepatocytes. But from 72 hrs onwards in R.H. the rate of labelling of all the six UsnRNAs again increased by 30–50% (compared to that in normal hepatocytes) followed by decrease of their labelling-rate to reach the normal level in R.H. within one month of P.H. Thus, it may be concluded that the changes in UsnRNAs' level during the proliferative phase of liver regeneration may be either due to the alteration in the rate of synthesis (in terms of labelling) or along with it differential turn over rate; this phenomenon may have some consequences with the regenerative process of liver.This paper was published in Molecular and Cellular Biochemistry131:67–73, 1994. Kluwer Academic Publishers regret the publication of the only partly corrected version.     

Six novel genes necessary for pre-mRNA splicing in Saccharomyces cerevisiae.

We have identified six new genes whose products are necessary for the splicing of nuclear pre-mRNA in the yeast Saccharomyces cerevisiae. A collection of 426 temperature-sensitive yeast strains was generated by EMS mutagenesis. These mutants were screened for pre-mRNA splicing defects by an RNA gel blot assay, using the intron- containing CRY1 and ACT1 genes as hybridization probes. We identified 20 temperature-sensitive mutants defective in pre-mRNA splicing. Twelve appear to be allelic to the previously identified prp2, prp3, prp6, prp16/prp23, prp18, prp19 or prp26 mutations that cause defects in spliceosome assembly or the first or second step of splicing. One is allelic to SNR14 encoding U4 snRNA. Six new complementation groups, prp29-prp34, were identified. Each of these mutants accumulates unspliced pre-mRNA at 37 degrees C and thus is blocked in spliceosome assembly or early steps of pre-mRNA splicing before the first cleavage and ligation reaction. The prp29 mutation is suppressed by multicopy PRP2 and displays incomplete patterns of complementation with prp2 alleles, suggesting that the PRP29 gene product may interact with that of PRP2. There are now at least 42 different gene products, including the five spliceosomal snRNAs and 37 different proteins that are necessary for pre-mRNA splicing in Saccharomyces cerevisiae. However, the number of yeast genes identifiable by this approach has not yet been exhausted.     

Organization and nucleotide sequence of the Streptococcus mutans galactose operon

The galactose operon encoding a repressor and genes for the Leloir pathway for galactose metabolism (galactokinase, galactose-1-phosphate-uridyl transferase and UDP glucose-4-epimerase) was located adjacent to the multiple sugar metabolism (msm) operon on the chromosome of Streptococcus mutans Ingbritt (serotype c) and the complete nucleotide sequence of this 5-kilobase region was determined. The Leloir pathway was induced by the presence of galactose in the growth medium or following the release of intracellular galactose after uptake and cleavage of -galactosides by the multiple sugar metabolism system. Analysis of the mechanism of galactose transport confirmed the absence of a galactose-specific phosphotransferase system and suggested the presence of an inducible galactose permease. Evidence is presented that galactose transport is independent of the proton motive force and may be ATP-dependent.     

Sex differences in children’s investment in peers

It is hypothesized from within an evolutionary framework that females should be less invested in peer relations than males. Investment was operationalized as enjoyment in Study 1 and as preference for interaction in Study 2. In the first study, four- and six-year-old children’s enjoyment of peer interaction was observed in 26 groups of same-sex peers. Girls were rated as enjoying their interactions significantly less than boys. In the second study, six- and nine-year-old children were interviewed about the individuals with whom they spend time in their homes and neighborhoods and about the individuals who participate in their favorite activities. The proportion of individuals named by children who were peers was significantly lower for girls than boys both in children’s neighborhoods and in children’s favorite activities. Results strongly support the hypothesis that females and males have evolved differential preferences for interaction with peers.     

Persister control by leveraging dormancy associated reduction of antibiotic efflux

Persistent bacterial infections do not respond to current antibiotic treatments and thus present a great medical challenge. These conditions have been linked to the formation of dormant subpopulations of bacteria, known as persister cells, that are growth-arrested and highly tolerant to conventional antibiotics. Here, we report a new strategy of persister control and demonstrate that minocycline, an amphiphilic antibiotic that does not require active transport to penetrate bacterial membranes, is effective in killing Escherichia coli persister cells [by 70.8 ± 5.9% (0.53 log) at 100 μg/mL], while being ineffective in killing normal cells. Further mechanistic studies revealed that persister cells have reduced drug efflux and accumulate more minocycline than normal cells, leading to effective killing of this dormant subpopulation upon wake-up. Consistently, eravacycline, which also targets the ribosome but has a stronger binding affinity than minocycline, kills persister cells by 3 logs when treated at 100 μg/mL. In summary, the findings of this study reveal that while dormancy is a well-known cause of antibiotic tolerance, it also provides an Achilles’ heel for controlling persister cells by leveraging dormancy associated reduction of drug efflux.