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Notes: Abstract: The complex pharmacological profile (excitation/inhibition) of ibotenic acid on single neurons in the mammalian CNS prompted studies on the stability of ibotenic acid and a number of structurally related excitatory amino acids under different in vitro conditions in the presence or absence of enzymes. Ibotenic acid, (RS)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-7-carboxylic acid (7-HPCA), (RS)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and (RS)-α-amino-3-hydroxy-4-bromo-5-isoxazolepropionic acid (4-Br-homoibotenic acid) were all inhibitors of (S)-glutamic acid decarboxylase (GAD) in mouse brain homogenates, but only ibotenic acid was shown to undergo decarboxylation during incubation with brain homogenates. The formation of the decarboxylated product, muscimol, which primarily occurred in a synaptosomal fraction, was dependent on the presence of pyridoxal-5-phosphate (PALP) and was inhibited by (S)-glutamic acid, 3-mercaptopropionic acid (3MPA), aminooxyacetic acid (AOAA), and allylglycine, suggesting that ibotenic acid is a substrate for GAD. The overall decomposition rate for ibotenic acid (8.7 nmol min−1 mg−1 of protein), which apparently embraces other reactions in addition to decarboxylation to muscimol, was higher than the rate of decarboxylation of (S)-glutamic acid (3.2 nmol min−1 mg−1 of protein). At pH 7.4 and 37°C, but in the absence of enzymes, none of the excitatory amino acids under study underwent any detectable decomposition, whereas ibotenic acid and 7-HPCA, but not AMPA and 4-Br-homoibotenic acid, decomposed, partially by decarboxylation, at 100°C in a pH-dependent manner. In the presence of liver homogenates, ibotenic acid was also shown to decompose. Although muscimol was the only detectable reaction product, mechanisms other than decarboxylation may be involved. Under these conditions, the degradation reaction or reactions were partially dependent on PALP and were inhibited by AOAA and 3MPA but not by allylglycine. The present in vitro studies indicate that ibotenic acid is likely to undergo enzyme-catalyzed decomposition to give muscimol in brain tissue and after systemic administration to animals. These aspects must be taken into consideration in the interpretation of the pharmacological or neurotoxic effects of ibotenic acid after direct application near central neurons, after local injections into animal brains, or after systemic administration to animals.

Notes: Ion milling has been used to convert molecular beam epitaxy vacancy-doped CdxHg1−xTe from p- to n-type. Electron beam induced current and remote electron beam induced current (REBIC) measurements have been performed to study the pn junction depth and lateral extension dependence on the milling time, milling current, and vacancy concentration. The conversion depth is linear with the milling time and current and inversely proportional to the vacancy concentration in layers thinner than 10 μm. This shows that filling of Hg vacancies in this region during conversion is limited by the rate of supply of extra Hg from the milling. The lateral extension also increases linearly with the milling time, the ratio of the lateral extension to the depth being ∼0.5. One can therefore use REBIC on the top surface to determine the junction depth, which greatly simplifies the measurement and does not destroy the diodes. © 2002 American Institute of Physics.

Notes: An apparatus is described for measuring the temperature and magnetic field dependencies of the resistance and critical current of high-temperature superconductors. The automated setup together with a set of inserts forms a universal system allowing for fast sample selection as well as for accurate complementary measurements at temperatures from 4.2 to 300 K and in high magnetic fields up to 30 T. Design details and low resistance measuring algorithm are presented and system peformance is discussed.

Notes: Negative differential resistance due to Auger suppression is demonstrated in CdHgTe diodes grown by molecular beam epitaxy (MBE) using silver as acceptor dopant. These devices require growth of relatively complicated heterostructures, and control of n- and p-type doping over a large range. For this reason, the use of silver as an acceptor in CdHgTe devices grown by MBE has been reexamined. The results show that the diffusion of silver at the growth temperature does not necessarily preclude the use of silver doping in devices. For concentrations up to high 1017 cm−3, silver appears to be fully electrically active. © 1996 American Institute of Physics.

Notes: In all of four human germinal centre cell-associated B lymphomas carrying sIgM + sIgD F(ab')2 fragments of rabbit antibodies to human μ-chain were accumulated intracellularly, whereas the accumulation of antibodies to δ-chain was considerably less abundant. The accumulation of antibodies to light chain was intermediate between antibodies to μ- and δ-chain. These results could be explained by the following observations: (i) the difference in the level of reexpression of sIgM and sIgD and (ii) the discovery that antibodies to δ-chain bound to reexpressed sIgD were degraded at a higher rate than those bound to primary sIgD and at a higher rate than antibodies to μ-chain, whether hound to primary or reexpressed sIgM.

Notes: The blastogenesis of human blood lymphocytes has been studied by measuring the distribution of cellular and nuclear volumes in concanavalin A (Con A)-stimulated leucocyte cultures by means of a modified Coulter counter. Agglutinated and adherent cells wan dispersed by 3 h of incubation will α-methyl-mannoside and EDTA. Fresh suspensions contained 5-35% monocytes with an average cellular volume 2-2.5 times that of small lymphocytes. The nuclear volume of monocytes was similar to that of small lymphocytes within 10% and remained constant upon stimulation. In cultures given the optimal dose of Con A, 30 μg/ml. measurable cell growth commenced within 8-12 h, whereas nuclear growth began some 6 h later, which is approximately 6-8 h before increased 3H-thymidine incorporation could he detected. The average volume of responding cells grew by a factor of about 4 until mitosis, which started after around 48 h. whereas the average nuclear volume increased by a factor of about 3. The percentage of cells responding by volume growth increased with mitogen concentration even for hyperoptimal concentrations (150μg/ml) which strongly suppressed 3H-thymidine incorporation. The results exemplify the type of information obtained by volume spectroscopy of leucocyte cultures. This method appears to have several advantages over conventional assays of immune response.

Notes: The effect of anti-Igs in combination with the tumour promoter TPA on DNA and Ig synthesis in a human follicular germinal centre cell lymphoma carrying slgM and slgD was investigated. The lymphoma cells responded to both amiti-μ and anti-γ chains and to anti-δ light chains by DNA synthesis, as measured by mcthy-(3H)-thymidine incorporation. Flow cytofluorometric measurements, however, showed that only anti-μ chains induced marked increase in cytoplasmic Ig content. This result suggests that in certain B-cell subsets the signals elicited via slgM and slgD are different.

Notes: The importance of substrate adhesion and cell aggregation for the Con A-induced blastogenesis of human peripheral lymphocytes was studied by flow cytometric methods. The percentage of lymphocytes responding to the mitogen by growth and DNA synthesis was approximately the same among non-adherent, single cells as among substrate-adherent and aggregated cells. However, the response of the former cells was delayed by about 10 h as compared with that of adherent and aggregated cells. This delay increased to about 20 h in monocyte-depleted cultures. Stimulation with succinyl-Con A, which caused negligible aggregation, produced a significant response. Blast cells appeared to be largely nonadherent. It is concluded that neither substrate adhesion nor cell aggregation are prerequisites for Con A-induced blastogenesis, although substrate adhesion seems to have a significant promotive effect that is probably associated with a direct contact of the lymphocytes with monocytes.

Notes: The effect of various concentrations of rat-liver macrophages on the Con A-induced blastogenesis of syngeneic spleen lymphocytes has been studied by means of flow-cytometric methods and by measurement of the uptake of 3H-thymidine. By measuring the distributions of cellular and nuclear volume and cellular DNA to characterize the progression of responding lymphocytes through the cell cycle, we have distinguished a promotive and an inhibitory effect of macrophages. The promotive effect is on the number of cells initiating blastogenesis and on their rate of progression through the cell cycle. The degree of promotion increased strongly with the concentration of macrophages even for concentrations that suppressed the incorporation of 3H-thymidine almost completely from about 30 h of culture. The inhibition observed for macrophage concentrations ± 10% was a late effect causing stagnation of cell cycle and reduced viability only from about 24 h of culture.