Interaction of oddball probability and primary task type on P300 in the dual-task paradigm

Using a dual-task paradigm with an oddball secondary task, P300 amplitude and latency were studied as a function of factorially manipulated oddball probability (low = .22, high = .44) and primary task type. In addition to a Baselinecondition (oddball task only), three primary tasks were used: (1) Pure Sensory;watching a movie; (2) Pure Motor (manipulating a flashlight); and (3) Sensory/Motor(using the flashlight to trace the outlines of characters in a movie). The findings included the usual significant effects of probability on amplitude. There was also a significant effect of task type on amplitude, and a significant interaction of oddball probability with task type. In the low but not high probability condition, a pure Sensory task depressed P300 amplitude. In both probability conditions, the Sensory/motortask depressed P300 amplitude. Only task type had a significant effect on P300 latency. The results confirm the ability of other labs (using Sensory/motor primary tasks) to demonstrate P300 depression at high oddball probability, in view of the difficulty in our lab of achieving P300 depression with pure sensory tasks and high oddball probabilities. The results are discussed in terms of partial overlap of processing resource pools. A preliminary report of these data was presented at the 1990 meetings of the Society for Psychophysiological Research.     

Choline derivatives and sodium fluoride protect acetylcholinesterase against irreversible inhibition and aging by DFP and paraoxon

A light addressable potentiometric sensor was used to measure acetylcholinesterase (AChE) activity in order to evaluate the protective effects of quaternary compounds and NaF against enzyme phosphorylation and aging by two organophosphates. The use of the immobilized AChE made possible the quick removal of reagents (i.e., organophosphate, 2-pralidoxime, and protectant), thereby permitting accurate determination of AChE activity before and after phosphorylation and aging. Paraoxon was 15-fold more potent in inhibiting AChE than DFP, while the percent aging following phosphorylation by diiso-propylfluorophosphate (DFP) was much higher. Sodium fluoride (NaF), the most effective protectant against phosphorylation and aging, and the quaternary ammonium compounds reduced significantly AChE inhibition by DFP and paraoxon, to similar degrees. Even though the percent AChE activity that was lost to aging was reduced by these agents, aging as a percent of phosphorylated AChE was not reduced. Thus, their major effect was in reducing the percent AChE phosphorylation, which consequently resulted in reduction of total aged AChE. The finding that quaternary ammonium compounds protect against phosphorylation is consonant with the proposed presence of the active site of AChE in an aromatic gorge.     

Determination of Gardnerella vaginalis Genome Size by Pulsed-Field Gel Electrophoresis

The chromosomal DNA of four strains of Gardnerella vaginaliswere digested with rare cutting restriction enzymes and analyzedby pulsed-field gel electrophoresis (PFGE). The four strainsstudied were two clinical isolates (GVP 004 & GVP 007) andtwo American Type Culture Collection strains (ATCC 14018 &ATCC 14019). The restriction enzyme SfiI generated two DNA fragmentsof about 0.6 Mb and 1.1 Mb in all four strains giving a G. vaginalisgenome size of about 1.7 Mb. A similar genome size was calculatedutilizing two more GC-rich sequence specific restriction endonucleases,NotI and AscI. When digested with AscI, the chromosomal DNAof all four strains gave rise to 11 to 12 DNA fragments rangingbetween 0.01 Mb to 0.43 Mb. DNA from the two clinical isolateswere digested by NotI (yielding 7 to 9 fragments), while theDNA from the two ATCC strains were resistant to NotI digestion.In contrast to the clinical isolates, DNA from the two ATCCstrains gave an identical profile for all restriction endonucleasestested. From double digestion experiments, the two SfiI sitescould be localized on two AscI fragments. From these PFGE studies,it is concluded that the G. vaginalis genome is a circular DNAthat ranges between 1.67 Mb and 1.72 Mb in size.     

Membrane-delimited cell signaling complexes: Direct ion channel regulation by G Proteins

Summary Ion channels are signaling molecules and by them-selves perform no work. In this regard they are un like the usual membrane enzyme effectors for G proteins. The pathways of G protein receptor, G protein and ion channels are, therefore, purely infor mational in function. Because a single G protein may have several ion channels as effectors, the effects should be coordinated and this seems to be the case. Inhibition of Ca²⁺ current and stimulation of K⁺ currents would have a greater impact than either alone. Additional flexibility is provided by spontane ous noise in the complexes of G protein receptor, G protein, and ion channel. By having a non-zero setpoint, the range of control is extended and the responses become bi-directional.     

Whole-cell recording of neuroblastoma x glioma cells during downregulation of a major substrate, 80K/MARCKS,of protein kinase C

Summary Differentiated neuroblastoma cells exhibit both the delayed rectifier potassium current (I _K) and the M-current (I _M). The present study was designed to determine the roles of protein kinase C (PKC) and of the calmodulin-binding protein 80K/MARCKS, a prominent substrate for PKC and possible regulator of these currents. Neuroblastoma x glioma (NG108-15) hybrid cells transfected with m1 muscarinic receptors were grown with 1% fetal bovine serum (FBS) without the prostaglandin E₁ (PGE₁) and isobutylmethylxanthine (IBMX) usually added in preparation for electrophysiological studies. Under these conditions, the usual pleomorphism was largely abolished, leaving two populations of small cells with stellate and spherically symmetrical geometries. Whole-cell patch clamping indicated that the two cell types had identical electrophysiological properties, displaying: I _k, a small current through a T-like Ca²⁺ channel, and no M-current.Stimulation with carbachol shifted the distribution of cells to a more stellate morphology within 24 hr and later (after 48 hr) reduced the PKC substrate 80K/MARCKS by 22±7%. In contrast to the stimulation of I _k observed with cardiac cells, PKC activation produced only a small inhibition of I _k, which was independent of carbachol pretreatment. Thus, PKC and 80K/MARCKS can be dissociated from the regulation of I _k in neuroblastoma cells.Supported in part by research grants from the National Institutes of Health (DK-40145 and EY-08343) and from the U.K. Medical Research Council.We thank Dr. Peter J. Parker for his generous gift of PKC, and Yvonne Vallis for her skillful assistance with the cultures and harvesting of the NG108-15 transfected cells.     

Directional mutation pressure,mutator mutations,and dynamics of molecular evolution

Using a general form of the directional mutation theory, this paper analyzes the effect of mutations in mutator genes on the G + C content of DNA, the frequency of substitution mutations, and evolutionary changes (cumulative mutations) under various degrees of selective constraints. Directional mutation theory predicts that when the mutational bias between A/T and G/C nucleotide pairs is equilibrated with the base composition of a neutral set of DNA nucleotides, the mutation frequency per gene will be much lower than the frequency immediately after the mutator mutation takes place. This prediction explains the wide variation of the DNA G + C content among unicellular organisms and possibly also the wide intragenomic heterogeneity of third codon positions for the genes of multicellular eukaryotes. The present analyses lead to several predictions that are not consistent with a number of the frequently held assumptions in the field of molecular evolution, including belief in a constant rate of evolution, symmetric branching of phylogenetic trees, the generality of higher mutation frequency for neutral sets of nucleotides, the notion that mutator mutations are generally deleterious because of their high mutation rates, and teleological explanations of DNA base composition. Presented at the NATO Advanced Research Workshop onGenome Organization and Evolution, Spetsai, Greece, 16–22 September 1992     

Agonist Regulation of Gene Expression of Adrenergic Receptors and G Proteins

Abstract: Study of transmembrane signaling via G proteins has focused to a large extent upon investigations of individual G protein-linked receptor-effector systems. Agonist-induced desensitization and down-regulation of β-adrenergic receptors, for example, have been studied extensively and adopted as a general model for G protein-linked receptor regulation. This review focuses not only on agonist regulation of adrenergic receptor gene expression, but also on how agonists regulate opposing adrenergic receptor-mediated pathways. This important feature of G protein-mediated pathways, i.e., cross-regulation and integration of information among several pathways, will be discussed in the context of what has been learned in the adrenergic receptor-coupled pathways.