Clustered field evaporation of metallic glasses in atom probe tomography.

Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different - as yet unknown - physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses.

Crystal-Like Rearrangements of Icosahedra in Simulated Copper-Zirconium Metallic Glasses and their Effect on Mechanical Properties.

Indications of the Cu2Zr Laves phase are observed in MD simulations of amorphous Cu64Zr36 upon isothermal holding just above the glass transition temperature. The structural evolution towards Cu2Zr is accompanied by an increase in the fraction of Cu-centered icosahedra, which demonstrates that a large icosahedral fraction does not just indicate structural relaxation. The crystal-like regions generate an increase in strength and Young's modulus, and a stronger localized shear band. A universal relation between the fraction of full icosahedra and their interconnectivity is found, and both can be modified simultaneously via changes of temperature or strain.

Dopaminergic mediation of long-term behavioral effects of in utero drug exposure.

The influence of external agents on the developing brain has led to the hypothesis that, during critical periods of rapid development, such agents may have long-lasting effects on brain function and behavior. The dopaminergic systems are particularly suitable for examining the hypothesis, since the neural tracts using dopamine have been widely studied; their influence on behavior is, to some extent, understood; the tracts begin development in mice and rats late in gestation; and there are a number of drugs known to have particular effects on these systems. Literature is reviewed that supports the hypothesis that drugs affecting dopamine metabolism, when administered during the early development of the dopaminergic tracts, produce persistent changes both in the metabolism of dopamine and in behavior mediated by neural systems which utilize dopamine as a transmitter.

Pregnancy increases reactivity of mice to phenobarbital.

Compared to nonpregnant controls, pregnant mice injected with phenobarbital had lower concentrations of the drug in the plasma but equivalent concentrations in the brain. In spite of the similar concentrations in the brain, the behavioral response to phenobarbital was greater for pregnant than nonpregnant mice. These results suggest that the concentration of phenobarbital in the plasma, which is commonly used as a basis for adjusting phenobarbital dosage during pregnancy, is not an appropriate indicator of the dynamics of the drug.

Brain concentrations of phenobarbital and behavioral activation or depression.

Brain concentrations of phenobarbital and its effects on locomotor activity and lever responding for food reinforcement were determined at several intervals following injections into C57BL/6J mice. Phenobarbital either elevated or depressed both types of behavior depending on dose and time after injection. Excitation was noted at times and doses when brain concentration was 9 micrograms-11.5 micrograms/g tissue. Depression was initially noted at approximately 20 micrograms/g tissue. Lever responding was altered when brain concentrations of the drug were lower than those associated with corresponding effects on locomotor activity. Excitatory and depressive effects were most extensive when basal response rates were moderate or high respectively. Hence, whether phenobarbital is excitatory or depressive depends on a complex interaction of brain concentration, rate of ongoing behavior and the stimulus conditions maintaining the behavior.

Effects of prenatal maternal injections of phenobarbital on brain neurotransmitters and behavior of young C57 mice.

Offspring of C57BL/6J mice injected daily with phenobarbital (20 or 40 mg/kg) for the last 6 or 7 days of pregnancy were compared with offspring of saline control mice on behavioral and neurochemical measures of brain function at 21 days of age. Activity in an open field arena was elevated in male offspring and reactivity to presentation of a tone-light stimulus was increased for female offspring of drug treated dams. Brain concentration of dopamine and norepinephrine was reduced and the uptake of dopamine, norepinephrine serotonin and gamma-aminobutyric acid into synaptosomal preparations of brain tissue was greater for treated offspring. Both the behavioral and neurochemical indices indicate that the brain is altered by maternal prenatal injections of phenobarbital but the relationship between these changes remains speculative.

Prenatal maternal phenobarbital increases reactivity and retards habituation of mature offspring to environmental stimuli.

Adult female offspring of C57BL/6J mice injected daily with phenobarbital for the last third of pregnancy were more active than control offspring during a 3-min test period in an open field arena, thus confirming previous reports of lasting effects of prenatal exposure to phenobarbital. These offspring habituated less rapidly than control offspring to the open field and were more reactive to sudden changes in environmental stimuli. The behavioral changes were not accompanied by body or brain weight deficits. The maternal drug injections did not alter brain concentrations of dopamine or norepinephrine in the adult offspring or the degree of reduction in these transmitters produced by the synthesis inhibitors alpha-methyltyrosine. Although activity was reduced by the catecholamine synthesis inhibitor, the effect was similar by offspring of both drug-treated and control dams.

Ascorbate blocks amphetamine-induced turning behavior in rats with unilateral nigro-striatal lesions.

Unilateral nigro-striatal lesions were produced in rats using 6-hydroxydopamine. Intraperitoneal injections of amphetamine induced circling behavior in these rats due to release of striatal dopamine contralateral to the lesion. Intraperitoneal injections of 1 g/kg of ascorbic acid elevated brain ascorbate. Ascorbate, like other drugs blocking dopamine receptors, attenuated the amphetamine-induced turning behavior. Thus, ascorbic acid might have a role in regulating dopaminergic transmission and could be of therapeutic value in disorders involving functional dopamine excess.

Effects of methadone on activity and on brain monoamines in two strains of mice.

Two strains of mice (C57BL/6J and DBA/2J) were used to determine the effects of single and multiple injections of methadone on open field activity and on brain monoamines. For the DBA strain, the initial injection of methadone produced an attenuation of locomotor activity. After 7 daily injections, activity increased to that of controls. For the C57 strain, the initial injection produced a slight increase in activity which became more pronounced after further daily injections. Norepinephrine concentration was elevated in brains of DBA mice chronically exposed to methadone. This effect was not observed in C57 mice nor in either strain injected only once with the drug. Serotonin concentration was not altered in animals of either strain whether acutely or chronically exposed to methadone. The results of this study suggest: 1) that activity change following methadone injections is dependent upon genetic factors and previous experience with the drug; 2) that the tolerance develops to the drug produced decreases but not increases in activity; and 3) that chronic exposure to the drug can elevate norepinephrine concentration in the brains of DBA mice.

Neurochemical and behavioral effects of diet related perinatal folic acid restriction.

Some effects of restricting dietary folic acid during the perinatal period on tissue folate and S-adenosyl-L-methionine (SAM) concentrations and on behavior were examined in 35-day-old DBA/2J mice. In one study dams were started on diets containing no folate (FO), 1.1 mg of folic acid/kg diet (F1.1) or 9.9 mg of folic acid/kg diet (F9.9) on the day of parturition. In a second study some mice were started on the FO or F9.9 diets 6-7 days prior to parturition and some remained on lab chow (LC). The dams and their pups remained on their assigned diets until offspring were killed for biochemical assays. The major findings of the 2 studies are: (1) that eliminating folic acid from diets of dams and developing pups from birth or 1 week prior to birth causes a reduction of folate in brain tissue; (2) that reduction in brain tissue is not as severe as that of liver; (3) that initiating the folate free diet 1 week prior to birth caused reductions in body, liver, and brain weights and in activity levels of surviving offspring; and (4) that offspring of dams started on either the FO or F9.9 diet one week prior to parturition are less viable and have lower levels of SAM in brain tissue than animals reared on the LC diets.

Phenobarbital during pregnancy alters operant behavior of offspring in C57BL/6J mice.

Offspring of C57BL/6J injected daily with phenobarbital for the last third of pregnancy responded less than control animals when maintained on various fixed ratio schedules of reinforcement. The response decrement became more pronounced as the schedule demands were increased and was noted in offspring of both sexes. The higest dose (80 mg/kg) was less effective than the 2 lower doses (20 mg and 40 mg/kg) in producing the decrement which may reflect a selection factor due to high neonatal mortality previously reported at this dose. The study provides no evidence of the mechanism mediating the long term behavioral abnormality but does clearly extend the finding of such changes to doses which do not produce increased neonatal mortality or noticeable morphological changes.

Effects of phenobarbital given to pregnant mice on behavior of mature offspring.

Mature offspring of C57BL/6J mice (Mus musculus) injected daily with phenobarbital (40 mg/kg) for the last third of pregnancy differed from saline and untreated control animals on 3 measures of behavior. Offspring of phenobarbital treated animals had higher locomotor scores than controls during an open field activity test at 75 days of age. Male offspring were also tested on a 1-trial passive avoidance task and treated animals were found to be deficient. Finally, female offspring responded less than controls on fixed ratio schedules of reinforcement. The behavioral changes suggest that offspring of mice injected with phenobarbital during pregnancy are less responsive to the stimuli in their environment which maintain behavior.

Some effects of prenatal exposure to d-amphetamine sulfate and phenobarbital on developmental neurochemistry and on behavior.

Amphetamine. Prenatal intraperitoneal injection of d-amphetamine sulfate (5 mg/kg) produces decreases in the levels of catecholamines in the brain the day of birth and increases on day 30. Open-field activity from days 12 to 31 was higher for the group of animals injected with amphetamine or saline if scores were totaled across all test days. At day 75 the offspring of amphetamine-injected mothers exhibited altered open-field behavior. The effects were not observed with subcutaneous injection regardless of the dose used (2.5, 5.0, and 10.0 mg/kg). The lowest subcutaneous dose decreases neonatal viability. Phenobarbital. Prenatal intraperitoneal injection of phenobarbital (80 mg/kg) resulted in decreased litter size, increases mortality, and decreased amounts of nucleic acid and protein in the brains of surviving offspring. Behavioral deficits associated with response perseveration could be demonstrated at 60 days in the mice prenatally exposed to this dosage. Subcutaneous injections of phenobarbital to pregnant mice at 80 and 40 mg/kg, but not 20 mg/kg, doses increased neonatal mortality. Mature animals prenatally exposed to 40 mg/kg phenobarbital have altered open-field behavior and differ from control animals on a passive avoidance task. Mature offspring prenatally exposed to the 20 or 40 mg/kg dose also responded less than controls on an operant task requiring an increasing number of responses per reinforcement. These studies suggest that prenatal exposure to phenobarbital has in some way altered the animals' reactivity to stimualtion.