The nucleoside-transport inhibitor soluflazine (R 64 719) increases the effects of adenosine in the guinea-pig hippocampal slice and is antagonized by adenosine deaminase

Field EPSP slope and population spike (PS) amplitude were measured in the CA1 pyramidal cell region after double-pulse stimulation of the striatum radiatum in hippocampal slices of guinea-pig. Iontophoresis of adenosine reduced the EPSP slope to 77.9 +/- 5.0% (mean +/- S.E.M.) and PS amplitude to 32.9 +/- 9.7% of the control values. Recovery was 98.7 +/- 3% for the EPSP and 82.9 +/- 7.0% for the PS 1.5 min after iontophoresis was stopped. In the presence of soluflazine 10(-6) M the effects of adenosine iontophoresis on the PS amplitude were significantly increased and the recovery of the EPSP and PS was significantly delayed. Soluflazine perfusion alone gradually decreased EPSP slope and PS amplitude as with adenosine. The reductions in EPSP slope and PS amplitude produced by soluflazine were antagonized by adenosine deaminase. An increase in EPSP slope and PS amplitude was seen when adenosine deaminase was given first. This increase was not reduced by exposure to soluflazine. These results are compatible with the hypothesis that soluflazine acts as a nucleoside transport inhibitor in the CNS, where it may increase the extracellular concentration of adenosine.

Pacing and sensing: how can one electrode fulfill both requirements?

Pacing and sensing are two different functions which can be accomplished by one and the same electrode. Optimal pacing requires a high tissue resistance in order to minimize the stimulation energy, making a small surface electrode highly desirable. For adequate sensing, however, the tissue resistance should be as low as possible which requires a larger electrode surface area. Decreasing the electrode surface area results in an increased polarization impedance. As this latter should be low for both pacing and sensing, an electrode with a large surface area should be used. How can these opposing needs be met by one electrode? The combination of a small geometrical surface and a large porous microstructure along with the choice of low polarizable materials meets both the requirements of pacing and sensing.

Prediction of Wenckebach behavior and block response in DDD pacemakers

At higher atrial rates, the behavior of a DDD pulse generator will depend on the atrial rate or spontaneous atrial interval (SAI) and the settings of the pacemaker: upper rate interval (URI), atrioventricular interval (AVI), and atrial refractory interval (ARI). An algorithm was developed enabling the prediction of the degree of Wenckebach block using the parameters mentioned above. In the absence of the programmed settings of the pacemaker, these parameters can be determined by noninvasive methods. AVI can be measured by application of a magnet over the pulse generator, while URI and ARI can be estimated during chest wall stimulation by progressively increasing the frequency of the external extrastimuli. The use of the formula in combination with chest wall stimulation allows the evaluation of the proper functioning of any DDD pacemaker during exercise and in patients with atrial rhythm disturbances, even when no information about the pacemaker settings is available.

N-methyl-D-aspartate and hypoxia induced Ca2+-changes in the CA1 region of the hippocampal slice

Hypoxic neuronal depolarization was accompanied by a large decrease in extracellular [Ca2+]. After reoxygenation, the time at which [Ca2+] normalized was correlated with the extent of recovery of N-methyl-D-aspartate (NMDA) and synaptic responses. There was no evidence that the NMDA receptor system was more disrupted following hypoxia than the receptors involved in synaptic transmission. The Na+/K+ pump appeared to be better able to recover from hypoxia than the NMDA responses or synaptic transmission.

Monoclonal antibody (WT 1) directed against a T cell surface glycoprotein: characteristics and immunosuppressive activity

WT 1, an IgG2a subclass monoclonal antibody, recognizes a human T lineage specific antigen (mol. wt 40,000). This antigen is strongly expressed on thymic T blasts, and on peripheral T cells activated by phytohaemagglutinin, whereas cortical thymocytes and peripheral T cells are moderately positive for WT 1. In contrast, B lymphocytes, myeloid and erythroid cells, including the progenitor cells of these lineages, and terminal deoxynucleotidyl transferase positive cells in the bone marrow, are all WT 1 negative. Binding of WT 1 to T cells is blocked by a previously described antibody (3A1) suggesting that both antibodies bind to the same antigen present on human T cells. WT 1, however, is also reactive with T lymphocytes from rhesus monkeys whereas 3A1 is not. Therefore, the biological effects of WT 1 could be studied in a monkey model. In a skin allograft model, WT 1 was immunosuppressive and induced a marked prolongation of graft survival.

A pendulum system to deliver reproducible taps on single teeth to elicit silent periods in the electromyograms of human jaw muscles

To deliver taps on single teeth, an easily-constructed pendulum system was designed which delivers mechanical stimuli with a constant intensity and morphology at high tapping rates. By interchanging the tips of the hammer mounted as a pendulum, the characteristics of the mechanical pulses can be modified. An electromagnetic brake makes the system insensitive to inevitable small variations of the head position. As no sound is produced prior to and up to 400 ms after the tap on the tooth, expectation patterns or acoustic reflexes which may influence the silent period are avoided. The system can also be used in animals.

Isolation and anaylsis of (Gp)nXp sequences of rat liver 5S RNA by means of restricted ribonucleas T2 hydrolysis

Essentual difficulties arise when base number in oligoguanylic blocks and location of these blocks along the polynucleotide chain need to be determined in the course of determination of the nucleotide sequences in ribonucleic acids. To overcome this difficulty it is suggested to take advantage of a recently discovered resistance of phosphodiester bond between kethoxalated G and its 3'-neighbour against T(2) RNase hydrolysis 1,2. The approach is illustrated by analysis of 5S RNA from rat liver. Sequences of general formula (Gp)(n)Xp were isolated from T(2) RNase hydrolysate of 5 S RNA rapidly and quantitatively. The information obtained greatly facilitates the whole procedure of sequencing. It is expected that the method proposed would be effective for analysis of 5 S and 4 S RNA and for highmolecular weight fragments of ribosomal and viral RNAs.