THE ELEVATION OF CEREBRAL HISTAMINE- N -AND CATECHOL- O -METHYL TRANSFERASE ACTIVITIES BY l-METHIONINE-dl- SULFOXIMINE 1

The administration of the convulsant, l-methionine-dl-sulfoximine (MSO), increased histamine N -methyl transferase (E.C. 2.1.1.8) (HMT) activity in rat and mouse brain and, to a lesser extent, catechol- O -methyl transferase (E.C. 2.1.1.6) (COMT) activity in rat brain. The duration of this effect was shortened by co-administration of l-methionine. The increased HMT activity was seen in 5 or 7 rat brain regions tested. l-Methionine administration had no effect on the activity of either enzyme. Partially purified HMT preparations from rat or guinea-pig brain exhibited no alterations in activity after the in vitro addition of MSO or l-methionine over a wide range of histamine and S -adenosyl-l-methionine concentrations. Rat brain COMT was equally unaffected by MSO and l-methionine. The in vitro inhibition of HMT and COMT by S -adenosyl-l-homocysteine was the same whether tested on preparations derived from MSO-treated or control animals. The data are discussed with respect to the possible involvement of aberrant methylation processes in the MSO-induced seizure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65751/1/j.1471-4159.1975.tb07696.x.pd

Decreased Transmethylation of Biogenic Amines After In Vivo Elevation of Brain S -Adenosyl-l-Homocysteine

The ability of S -adenosyl-l-homocysteine (AdoHcy) to inhibit biologic transmethylation reactions in vitro has led us to explore the possibility of pharmacologically manipulating AdoHcy levels in vivo and examining the consequences of these alterations on the transmethylation of some biogenic amines. Swiss-Webster mice were injected intraperitoneally with different doses of adenosine (Ado) and d,l-homocysteine thiolactone (Hcy) and were killed at various times thereafter. S -Adenosyl-l-methionine (AdoMet) and AdoHcy concentrations were determined by using a modified isotope dilution-ion exchange chromatography-high pressure liquid chromatography technique sensitive to less than 10 pmol. Increasing doses of Ado + Hcy (50-1000 mg/kg of each) produced a dose-related increase in blood, liver, and brain AdoHcy levels. At a dose level of 200 mg/kg Ado + Hcy, AdoHcy levels were markedly elevated, with minimal concomitant perturbations of AdoMet. This elevation was maximal 40 min after giving Ado + Hcy, returning to control values within 6 h. Ado + Hcy treatment resulted in decreased activities of catechol- O -methyltransferase, histamine- N -methyltransferase, and AdoHcy hydrolase in vitro. The cerebral catabolism of intraventricularly administered [ 3 H]histamine (HA) was decreased in a dose-related manner by Ado + Hcy treatment as evidenced by higher amounts of nonutilized [ 3 H]HA in brain, concurrent decreases in [ 3 H]methylhistamine formation, and decreases in the transmethylation conversion index. Steady state levels of HA also showed dose-related increases after Ado + Hcy treatment. It is concluded that injections of Ado + Hcy can markedly elevate AdoHcy levels in vivo , which can, in turn, decrease the rate of transmethylation reactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66442/1/j.1471-4159.1981.tb00426.x.pd

RAT AND MOUSE BRAIN HISTAMINE N -METHYLTRANSFERASE: MODULATION BY METHYLATED INDOLEAMINES 1

A purification procedure for rat and mouse brain histamine N -methyltransferase (HMT, EC 2.1.1.8) is described which achieves the preparation of 87-fold purified rat brain and 166-fold purified mouse brain enzyme. The purified HMT (MW 29,000) is inhibited by a number of physiologically and pharmacologically active amines, among them several methylated indoleamines, at concentrations above 5 ± 10 -6 M. At concentrations below 1 ± 10 -7 M, most of the methylated indoleamines stimulate HMT , provided histamine is maintained at, or close to, its optimal concentration as an HMT substrate, namely 1 ± 10 -5 M. A study of the nature of the inhibitory process revealed a non-competitive inhibition of HMT by dopamine as against a competitive inhibition of the enzyme by most methylated indoleamines. Increasing the concentration of histamine beyond the optimal value, i.e. to inhibitory levels, resulted in less stimulation. The findings support the notion that MSO elicits the formation in selected brain cells of supranormal amounts of several methylated indoleamines which are able to stimulate HMT (and possibly other methyltransferases, see Salas et al. , 1977), thereby causing the depletion of the cerebral levels of S-adenosyl-L-methionine, reported previously (Schatz & Sellinger, 1975b).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65930/1/j.1471-4159.1978.tb06548.x.pd

ASTROGLIAL UPTAKE IS MODULATED BY EXTRACELLULAR K +

Primary cultures of rat brain astrocytes were used to examine the uptake of the glucose analogue, 2-deoxy- d -glucose (2-DOG). 2-DOG competes with glucose for uptake, indicating that both are transported by the same carrier system. Extracellular K + at 11.9 mM increased the uptake of 2-DOG at 2-DOG concentrations greater than 100 ΜM. Uptake. appears Na + -dependent only at high concentrations of 2-DOG. This suggests that the extracellular concentrations of Na + and K + may regulate the astrocytic uptake of 2-DOG.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65513/1/j.1471-4159.1979.tb05224.x.pd

Biosynthesis of Polyamines in Mouse Brain: Effects of Methionine Sulfoximine and Adenosylhomocysteine

This study examines the consequences on cerebral polyamine biosynthesis of increases and decreases in cerebral methylation. Increases were elicited by administering the convulsant agent methionine sulfoximine (MSO) and decreases by elevating in vivo the cerebral levels of the methylation inhibitor S -adenosyl-homocysteine. Following the intraventricular (i.vt.) administration of one of the two possible polyamine precursors, [1,4- 14 C]putrescine, the specific radioactivity (sra) of the newly formed [ 14 C]spermidine remained unchanged. Conversely, after i.vt. l-[3,4- 14 C]methionine, the other polyamine precursor, significantly higher sra values for [ 14 C]spermidine and [ 14 C]spermine were recorded in the brains of the MSO-treated animals. [ 14 C] S - adenosylmethionine in the brain of the MSO-treated animals was also more highly labeled following [1- 14 C]-methionine, indicating its accelerated formation relative to controls. We also investigated the effect of the administration of adenosine + homocysteine, a treatment that results in elevated brain adenosylhomocysteine levels, on polyamine biosynthesis from [3,4- 14 C]-methionine. The results of these experiments show both significantly lower sra values for [ 14 C]spermidine and [ 14 C]spermine and significantly higher than control endogenous methionine levels, a clear sign of the existence of a retardation in the conversion of methionine to polyamines under these conditions. In conclusion, the present study demonstrates that while interference with cerebral methylation results in significant alterations of the rate of formation of the methionine moiety of spermidine and spermine, it has no effect on the entry of the putrescine moiety into the two polyamine molecules.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66159/1/j.1471-4159.1983.tb08055.x.pd

Noncontact Laser Ultrasonic Inspection of Ceramic Matrix Composites (CMCs)

Ceramic matrix composites (CMCs) are poised to revolutionize jet engine technology by enabling operation temperatures well beyond those possible with current superalloys, while reducing active cooling requirements and engine weight. Manufacturing of parts formed by silicon-carbide (SiC) fibers in a SiC matrix is now well advanced, with the first non-structural static components entering service in 2017 with the CFM Leap® engine that features SiC/SiC turbine shrouds. In order to expand the scope of application of CMCs to rotating parts, such as turbine blades, much work is being conducted to understand and characterize the modes of failure of these materials at temperatures beyond 1,000 °C. In this context, the ability of nondestructively monitoring the formation and progression of damage in CMCs specimens during high-temperature mechanical testing is critical. However, the elevated temperature precludes the possibility of using sensors placed in direct contact with the specimen and therefore severely restricts the range of available NDE techniques. This paper provides the first experimental assessment of the feasibility of noncontact laser ultrasonic inspection of SiC/SiC flat coupons. An Nd:Yag laser is used to excite ultrasonic waves on one side of the specimen while a Michelson interferometer detects the signals emerging on the other side at the epicenter position. The lasers are mounted on synchronized linear stages to form C-scans as in conventional immersion ultrasonics while ablation damage to the surface of the specimen is prevented by operating the lasers at low power density. Despite the complex microstructure of the SiC/SiC material it is found that the measured waveforms are remarkably similar to those observed when conducting the same tests in aluminum specimens. Moreover, it is shown that it is possible to: a) image interlaminar defects caused by impacts, and b) monitor crack opening under tensile load. Finally, very good signal stability is observed when temperature is increased from 25 to 1,250 °C which confirms the feasibility of laser monitoring at high temperature and is consistent with the excellent thermal stability of CMC mechanical properties

Kinetics of Carboxylmethylation of the Charge Isoforms of Myelin Basic Protein by Protein Methyltransferase II

The charge isoforms (C1-C5) of bovine myelin basic protein (MBP) were used as substrates for the rat brain enzyme protein carboxylmethyltransferase (PM II). The objective of these experiments was to ascertain whether the kinetic behavior of the MBP isoforms reflected differences in the structures of this molecular family. Initial velocity plots as a function of the MBP-isoform concentration showed significnt differences ( p > 0.05) among the assayed isoforms except for isoforms C2 and C4. Under the conditions of our experiment all the curves exhibited a consistent sigmoidicity. The kinetic data were best fitted by a model, previously described for the enzyme D-Β-hydroxybutyrate dehydrogenase, in which two independent sites must be randomly occupied before any catalytic activity can occur. This mechanism is substantially different from that proposed by other investigators for similar PM II enzymes and other substrates. The differences in the rates of isoform carboxylmethylation are largely accounted for by the different apparent dissociation constants K s and is explained on the basis of inherent structural differences among the charge isoforms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65821/1/j.1471-4159.1989.tb09257.x.pd

Doping Strategies for Small Molecule Organic Hole-transport Materials: Impacts on Perovskite Solar Cell Performance and Stability

Hybrid organic/inorganic perovskite solar cells (PSCs) have dramatically changed the landscape of the solar research community over the past decade, but \u3e25 year stability is likely required if they are to make the same impact in commercial photovoltaics and power generation more broadly. While every layer of a PSC has been shown to impact its durability in power output, the hole-transport layer (HTL) is critical for several reasons: (1) it is in direct contact with the perovskite layer, (2) it often contains mobile ions, like Li+ – which in this case are hygroscopic, and (3) it usually has the lowest thermal stability of all layers in the stack. Therefore, HTL engineering is one method with a high return on investment for PSC stability and lifetime. Research has progressed in understanding design rules for small organic molecule hole-transport materials, yet, when implemented into devices, the same dopants, bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III) tri[bis(trifluoromethane)sulfonimide] (FK209), are nearly always required for improved charge-transport properties (e.g., increased hole mobility and conductivity). The dopants are notable because they too have been shown to negatively impact PSC stability and lifetime. In response, new research has targeted alternative dopants to bypass these negative effects and provide greater functionality. In this review, we focus on dopant fundamentals, alternative doping strategies for organic small molecule HTL in PSC, and imminent research needs with regard to dopant development for the realization of reliable, long-lasting electricity generation via PSCs

Boron-Rich Benzene and Pyrene Derivatives for the Detection of Thermal Neutrons

A synthetic methodology is developed to generate boron rich aromatic small molecules based on benzene and pyrene moieties for the detection of thermal neutrons. The prepared aromatic compounds have a relatively high boron content up to 7.4 wt%, which is important for application in neutron detection as 10B (20% of natural abundance boron) has a large neutron induced reaction cross-section. This is demonstrated by preparing blends of the synthesized molecules with fluorescent dopants in poly(vinyltoluene) matrices resulting in comparable scintillation light output and neutron capture as state-of-the art commercial scintillators, but with the advantage of much lower cost. The boron-rich benzene and pyrene derivatives are prepared by Suzuki conditions using both microwave and traditional heating, affording yields of 40-93%. This new procedure is simple and straightforward, and has the potential to be scaled up

A STUDY OF THE NASCENT POLYPEPTIDES SYNTHESIZED ON THE FREE POLYRIBOSOMES OF RAT BRAIN IN VIVO 1

The free polyribosomes of the cerebral cortex of the immature rat (12-14 days old) were exposed to very low concentrations of trypsin at 0°C and for very brief periods of time and the conditions under which their breakdown to smaller aggregates occurs were determined. Trypsin also caused the release of nascent, radioactive polypeptides from polyribosomes prelabelled with [ 14 C]amino acids in vivo. An examination of the kinetics of release of the nascent chains by trypsin revealed that it was dependent on the concentration of trypsin as well as on the duration of incubation in the presence of trypsin. The influence of the nature of the [ 14 C]amino acid used as precursor of the nascent polypeptides and of the duration of the radioactive pulse in vivo was also determined. The radioactivity associated with polyribosomes as a result of the brief radioactive pulses administered (2 to 10 minutes) was incompletely removed even after the ribosomes were dissociated into subunits by EDTA. These findings suggest that the assembly of the cerebral ribosome in vivo must be a very rapid process, particularly in the immature animal. The nature of the nascent, radioactive polypeptides was studied by disc gel and high voltage electrophoresis and by thin-layer and column chromatography. Evidence was obtained that a rather limited number of qualitatively different molecules resides on the polyribosomes at any given moment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65454/1/j.1471-4159.1971.tb00223.x.pd