The effects of digital nerve stimulation on the firing of motor units in human first dorsal interosseous muscle

1. The effect of cutaneous stimulation on the firing of single motor units has been studied during voluntary contractions in human first dorsal interosseous muscle. 2. Electrical stimulation of the index finger at 3 x threshold for perception reduced the firing rate of most units recruited at voluntary contraction strengths less than 1.5 N and increased the firing rate of all units recruited at contraction strengths greater than 1.5 N. The firing rate of all slow twitch units (contraction time greater than 75 msec) was reduced. The behaviour of fast twitch units was mixed but at this stimulus strength all units recruited at contraction strengths greater than 1.5 N had their firing rate increased. 3. Tested at different stimulus strengths, the stronger the stimulus the more the firing rate of low threshold units was reduced. The firing rate of units recruited at high contraction strength was increased by weak stimuli but reduced by strong stimuli. 4. It is concluded that stimulation of the index finger shifts the weighting of synaptic input associated with a voluntary contraction to favour the activity of the more powerful fast twitch motor units in first dorsal interosseous muscle.

Acyclovir inhibition of Epstein-Barr virus replication

Acyclovir [9-(2-hydroxyethoxymethyl)guanine] triphosphate inhibits Epstein-Barr virus (EBV)-associated DNA polymerase (DNA nucleotidyltransferase; EC 2.7.7.7) to a greater extent than it inhibits host alpha and beta DNA polymerases. The affinity of the compound for viral polymerase is 100-fold higher than for alpha-polymerase. The extent of inhibition is dependent upon the base composition of the template-primer. The inhibition is prevented by increasing concentrations of deoxyguanosine triphosphate. The EBV-associated DNA polymerase reaction in the presence of the inhibitor, although depressed, proceeds at a linear rate over a long period of time. In contrast, the reaction of Escherichia coli DNA polymerase I in the presence of 2',3'-dideoxythymidine 5'-triphosphate, a DNA chain terminator, levels off after initial linearity. Preincubation of acyclovir triphosphate with DNA and enzyme does not increase its inhibitory activity. The virus-producing cell line P3HRF-1 consistently shows reduced viral genome numbers and viral capsid antigen on prolonged exposure to acyclovir. The number of EBV genomes returns to the control level when the cells are grown in drug-free medium. The results suggest that a competitive mechanism is the major mode of acyclovir inhibition of EBV replication.

Induction of Epstein-Barr virus-associated DNA polymerase by 12-O-tetradecanoylphorbol-13-acetate. Purification and characterization

The diterpene ester promoter of mouse skin tumors, 12-O-tetradecanoylphorbol-13-acetate (TPA), efficiently induces Epstein-Barr virus (EBV)-associated DNA polymerase (DNA nucleotidyltransferase) activity in the EBV-producing lymphoblastoid cell line, P3HR-1. With the use of intervent dilution chromatography followed by sequential DEAE-cellulose and phosphocellulose column chromatography, the virus-associated enzyme has been isolated and purified 300-fold. The partially purified EBV DNA polymerase activity could be distinguished from cellular polymerases by its activation with salt and its degree of sensitivity to N-ethylmaleimide and phosphonoacetic acid. The enzyme showed maximum activity for copying activated calf thymus DNA in the presence of 100 mM ammonium sulfate. In the absence of salt, the enzyme utilized with high efficiency deoxyoligomer-homopolymer templates, but failed to copy poly(rA) . oligo(dT)10 and oligo(dT)10, showing that the enzyme had properties distinct from DNA polymerase gamma, reverse transcriptase, and terminal deoxynucleotidyltransferase. The partially purified enzyme is strongly inhibited by acyclovir triphosphate and thus has properties similar to herpes simplex virus DNA polymerase.

Foreign Bodies in Male Urethra

A series of six cases of exogenous foreign bodies of various types in male urethra are reported. Diagnosis was made from history and clinical examination in five cases. Strmaight X-ray was helpful in one. Removal of foreign bodies did not present any difficulty. No complication was observed during follow up.

Venereal Diseases and General Practitioners

In our country, most of the patients with venereal are being tackled by the general practitioners. These practitioners may be of great help in the different aspects of nation-wide venereal disease control programme if their services, are properly oriented and integrated.

Vacuum ultraviolet scintillators: sodium salicylate and p-terphenyl

Some of the characteristic properties of sodium salicylate and p-terphenyl have been studied at a convenient incident wavelength of 253.7 nm. These include the fluorescent spectrum, relative quantum efficiency as a function of scintillator thickness, absolute quantum efficiency, and its possible decline with time. It has been shown that the rotary pump and diffusion pump oil vapors in contact with phosphors affect the stability of fluorescence in a marked but complicated manner. The effect of humidity on relative fluorescent quantum efficiency of the phosphors has also been discussed. p-Terphenyl has been found to be a useful alternative to sodium salicylate.

A novel oligoribonuclease of Escherichia coli. II. Mechanism of action

Detailed studies of the mechanism of action of the novel oligoribonuclease of Escherichia coli described in the previous paper (1) led to the following conclusions. 1. The enzyme prefers a free 3'-hydroxyl group for its action. 2. The enzyme attacks the oligoribonucleotide substrate in a sequential manner from the 3' end producing 5'-ribonucleotides. 3. The mode of attack appears to be processive; the enzyme acts by degrading one oligoribonucleotide chain to completion before proceeding to the hydrolysis of another chain. 4. The reaction rate is inversely proportional to the chain length of the substrate; however, the enzyme has a higher affinity for longer chains. 5. The enzyme activity is markedly inhibited by secondary structure; oligoribonucleotides combined with complementary polyribonucleotides are attacked poorly below the melting temperature of the complex and efficiently above the melting temperature. 6. The enzyme is inhibited by 5'-nucleotides of adenine and guanine; those of cytosine and uracil have a much smaller effect. The enzyme is not inhibited by 3'-nucleotides. 7. Studies with dinucleoside monophosphate show highest reaction rates with pyrimidine sequences in the order: CpCgreater than UpUgreater than CpUgreater than UpC. The presence of guanine at the 3' end is strongly inhibitory, and reaction rates are CpGgreater than UpG=ApGgreater than GpG.

A novel oligoribonuclease of Escherichia coli. I. Isolation and properties

A new ribonuclease has been isolated from Escherichia coli. The enzyme is present in the 100,000 times g supernatant fraction and has been purified over 200-fold. Studies of the enzyme reveal that: 1. The enzyme shows a marked preference for oligoribonucleotides; indeed, the reaction rate is inversely proportional to the chain length of the substrate. The enzyme does not attack polynucleotides even at high concentrations of enzyme and has no detectable DNase activity. 2. The enzyme is stimulated strongly by Mn2+, less strongly by Mg2+, and not at all by Ca2+ and monovalent cations. 3. The enzyme is purified free of RNase I, RNase II, RNase III, polynucleotide phosphorylase, and other known ribonucleases of E. coli. The enzyme displays identical properties when isolated from mutants of E. coli that are deficient in the above ribonucleases. 4. The enzyme has a marked thermostability, a point of further distinction from RNase II.

Numerical study of scattered electromagnetic field inside a hollow dielectric cylinder. 2: Scattering of two phasematched beams

The structure of the scattered field inside a hollow lossless dielectric cylinder in the case of two incident TM waves has been discussed. Results are given for the case of opposite directions of incidence, under positive and negative phase-matched conditions of two beams of equal amplitude. It has been shown that so far as high irradiance over a small region is concerned, the effective gain is less than that of the case of a single incident beam. However, the advantage here is the symmetry of the field distribution.

Numerical study of the scattered electromagnetic field inside a hollow dielectric cylinder. 1:Scattering of a single beam

The field structure and the total energy inside a thin hollow lossless dielectric cylinder have been studied numerically for normal incidence of collimated TM waves. The dependence of these quantities on the optical thickness and the inner radius of the cylinder and on the refractive index of the cylinder material has been discussed. It has been shown that optimization of the various parameters may lead to a localized peak of high relative irradiance and also a high concentration of energy inside the cylinder.