DARPP-32: regulator of the efficacy of dopaminergic neurotransmission

Dopaminergic neurons exert a major modulatory effect on the forebrain. Dopamine and adenosine 3',5'-monophosphate-regulated phosphoprotein (32 kilodaltons) (DARPP-32), which is enriched in all neurons that receive a dopaminergic input, is converted in response to dopamine into a potent protein phosphatase inhibitor. Mice generated to contain a targeted disruption of the DARPP-32 gene showed profound deficits in their molecular, electrophysiological, and behavioral responses to dopamine, drugs of abuse, and antipsychotic medication. The results show that DARPP-32 plays a central role in regulating the efficacy of dopaminergic neurotransmission.

A single ascending dose study of epigallocatechin gallate in healthy volunteers

This randomized, double-blind, placebo-controlled study assessed the safety, tolerability and plasma kinetic behaviour of single oral doses of 94% pure crystalline bulk epigallocatechin gallate (EGCG) under fasting conditions in 60 healthy male volunteers. In each group of 10 subjects, eight received oral EGCG in single doses of 50 mg, 100 mg, 200 mg, 400 mg, 800 mg or 1600 mg, and two received placebo. Blood samples were taken at intervals until 26 h later. The area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)), the maximum plasma concentration (Cmax) of EGCG, the time taken to reach the maximum concentration (Tmax), and the terminal elimination half-life (t1/2z) of EGCG were determined. Safety and tolerability were assessed. In each dosage group, the kinetic profile revealed rapid absorption with a one-peak plasma concentration versus time course, followed by a multiphasic decrease consisting of a distribution phase and an elimination phase. The mean AUC(0-infinity) of total EGCG varied between 442 and 10,368 ng.h/ml. The according mean Cmax values ranged from 130 to 3392 ng/ml and were observed after 1.3-2.2 h. The mean t1/2z values were seen between 1.9 and 4.6 h. Single oral doses of EGCG up to 1600 mg were safe and very well tolerated.

Multiple-dose pharmacokinetics of ritonavir in human immunodeficiency virus-infected subjects

The multiple-dose pharmacokinetics of ritonavir were investigated in four groups of human immunodeficiency virus-positive male subjects (with 16 subjects per group) under nonfasting conditions; a 3:1 ritonavir:placebo ratio was used. Ritonavir was given at 200 (group I), 300 (group II), 400 (group III), or 500 (group IV) mg every 12 h for 2 weeks. The multiple-dose pharmacokinetics of ritonavir were moderately dose dependent, with the clearance for group IV (6.8 +/- 2.7 liters/h) being an average of 32% lower than that for group I (10.0 +/- 3.2 liters/h). First-pass metabolism should be minimal for ritonavir. The functional half-life, estimated from peak and trough concentrations, were similar among the dosage groups, averaging 3.1 and 5.7 h after the morning and evening doses, respectively. The area under the concentration-time curve at 24 h (AUC24) and apparent terminal-phase elimination rate constant remained relatively time invariant, but predose concentrations decreased 30 to 70% over time. Concentration-dependent autoinduction is the most likely mechanism for the time-dependent pharmacokinetics. The Km and initial maximum rate of metabolism (Vmax) values estimated from population pharmacokinetic modeling (nonlinear mixed-effects models) were 3.43 microg/ml and 46.9 mg/h, respectively. The group IV Vmax increased to 68 mg/h after 2 weeks. The maximum concentration of ritonavir in serum (Cmax) and AUC after the evening doses were an average of 30 to 40% lower than the values after the morning doses, while the concentration at 12 h was an average of 32% lower than the predose concentration, probably due to protracted absorption. Less than 2% of the dose was eliminated unchanged in the urine. Triglyceride levels increased from the levels at the baseline, and the levels were correlated with baseline triglyceride levels and AUC, Cmax, or predose concentrations.

Bioavailability of melatonin in humans after day-time administration of D(7) melatonin

Absolute bioavailability of the neurohormone melatonin (MLT) was studied in 12 young healthy volunteers (six males, six females) after administration at midday, on two separate occasions, of 23 microg by intravenous (i.v.) infusion and 250 microg by oral solution of D(7) MLT, a molecule in which seven deuterium atoms replace seven hydrogen atoms. Exogenous (D(7)) and endogenous (D(0)) MLT were quantified simultaneously but separately by a highly specific assay: gas chromatography/negative ion chemical ionization mass spectrometry, developed in our laboratory, which enabled us to go down to 0.5 pg/mL in plasma samples. After i.v. administration, the maximum plasma concentration (C(max)) and the area under the plasma concentration-time curve (AUC) values were significantly different in male and female subjects, but there was no significant gender difference in total body clearance normalized to body weight: 1.27+/-0.20 L/h/kg and 1.18+/-0.22 L/h/kg for males and females, respectively. The apparent terminal half-life (t(1/2(z))) values were 36+/-2 and 41+/-10 min, respectively. After oral administration, pharmacokinetic parameters used to quantify bioavailability were near three-fold greater in female subjects than in males, with large inter-individual variations. The maximum plasma MLT concentration C(max)+/-S.D. was found at 243.7+/-124.6 pg/mL and 623.6+/-575.1 pg/mL for male and female subjects respectively, while the mean values for AUCs were 236+/-107 pg.h/mL and 701+/-645 pg.h/mL. The absolute bioavailability of MLT was from 1 to 37%: mean=8.6+/-3.9% and 16.8+/-12.7% for male and female subjects, respectively.

Organization of point contacts in neuronal growth cones

Growth cones from rat dorsal root ganglia plated on laminin contain integrin clusters over the entire growth cone surface, and growth cones make transient adhesions at sites called point contacts. We examined, by immunocytochemistry and confocal microscopy, the composition and distribution of point contacts in neuronal growth cones. Vinculin was concentrated in the central domain of growth cones and at the tips of filopodia. Vinculin was specifically associated with integrin clusters at the membrane-substrate interface and thus marked point contacts. The cytoskeletal proteins paxillin and talin colocalized with beta1 integrin in a subpopulation of clusters restricted to the central domain of the growth cone and to the tips of filopodia. The neuron-specific kinase, FAK+ also distributed with the vinculin-positive clusters. The Rho family proteins RhoA, RhoB, and Cdc42 were present in growth cones, and a few Rho clusters were colocalized with vinculin. Examination of proteins resistant to detergent extraction in PC12 cells confirmed the retention of beta1 integrin, paxillin, talin, and vinculin with the cytoskeleton. Moreover, we detected FAK+ and RhoA in the detergent-resistant cytoskeleton, supporting their distribution to point contacts. Our observations indicate that two types of integrin clusters are present in growth cones: those associated with vinculin at the cell substratum interface, and those not associated with vinculin. Point contacts are mature adhesion sites defined by the presence of both beta1 integrin and vinculin, and they are associated with signaling proteins.

Plasma-kinetic characteristics of purified and isolated green tea catechin epigallocatechin gallate (EGCG) after 10 days repeated dosing in healthy volunteers

This randomized, double-blind, placebo-controlled study assessed the safety, tolerability, and plasma-kinetic behavior of 94% pure crystalline epigallocatechin gallate (EGCG) after ten days' repeated dosing in 36 healthy male volunteers. Each of the three treatment groups consisted of 12 subjects; nine of them received oral EGCG in one dose of 200, 400, or 800 mg daily, and three received a placebo. Blood samples for plasma-kinetic EGCG characterization were taken on day 1 and day 10. Kinetic parameters for rate and extent, elimination half-lives, and accumulation factor (R) were determined and compared between day 1 and day 10 for each dosage group. Orally administered EGCG is rapidly absorbed from the gut. Dose linearity was applied for single-dose application (day 1). After repeated dosing (day 10) dose linearity was applied between the 200 mg and 400 mg group. Dose escalation to 800 mg was more than dose-proportional in rate and extent, and statistically different from the 200 mg and 400 mg group. An increase in elimination half-life (t1/2.z) and in the accumulation factor (R) in the 800 mg dosage group indicates dose-dependent saturation of capacity-limited excretion routes or an increase of hepato-duodenal re-circulation. Ten days' repeated administration of oral doses of EGCG of up to 800 mg per day were found to be safe and very well tolerated.

Environmental Influences on Infant Cortical Thickness and Surface Area

Cortical thickness (CT) and surface area (SA) vary widely between individuals and are associated with intellectual ability and risk for various psychiatric and neurodevelopmental conditions. Factors influencing this variability remain poorly understood, but the radial unit hypothesis, as well as the more recent supragranular cortex expansion hypothesis, suggests that prenatal and perinatal influences may be particularly important. In this report, we examine the impact of 17 major demographic and obstetric history variables on interindividual variation in CT and SA in a unique sample of 805 neonates who received MRI scans of the brain around 2 weeks of age. Birth weight, postnatal age at MRI, gestational age at birth, and sex emerged as important predictors of SA. Postnatal age at MRI, paternal education, and maternal ethnicity emerged as important predictors of CT. These findings suggest that individual variation in infant CT and SA is explained by different sets of environmental factors with neonatal SA more strongly influenced by sex and obstetric history and CT more strongly influenced by socioeconomic and ethnic disparities. Findings raise the possibility that interventions aimed at reducing disparities and improving obstetric outcomes may alter prenatal/perinatal cortical development.

Melatonin secretion occurs at a constant rate in both young and older men and women

The magnitude and duration of melatonin (MLT) secretion were measured over a period of 25 h with pharmacokinetic studies employing administration of D(7) MLT at midday and at midnight in two separate studies and two groups of subjects, 12 young and 11 older men and women. Plasma levels of endogenous MLT and D(7) MLT were quantified separately by use of a specific and sensitive method (gas chromatography-mass spectrometry) previously developed in our laboratory, enabling us to measure endogenous and exogenous MLT levels down to 0.5 pg/ml in plasma. In the two groups of subjects, MLT secretion occurred only at night: onset time of secretion was from 1915 to 2205 (Greenwich mean time), and offset was from 0305 to 0545. No MLT peak was observed in individual nocturnal MLT profiles that were similar to curves obtained for a rate-constant infusion. Modelization demonstrated the superimposition of observed data and simulated curves. MLT concentrations decreasing from the offset of secretion might correspond to the elimination of MLT present in the body at the end of nocturnal secretion. By use of the MLT clearance given by pharmacokinetics, the amount of secreted MLT was found to be 35.7 and 21.6 microg for men and women, respectively, and the rate of secretion was 4.6 and 2.8 microg/h, respectively. No significant gender difference was observed for these two parameters when normalized to body weight. No significant gender difference was observed for onset times of secretion or duration of secretion (7.6-8.6 h) within the two groups, or between young and older subjects.

A highly sensitive assay of melatonin at the femotogram level in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry

A highly sensitive and specific assay was developed for routine analysis of melatonin at the femotogram level in human plasma. Melatonin and the deuterated internal standard [(2H4)melatonin] were measured by gas chromatography/negative ion chemical ionization mass spectrometry with methane as the reagent gas. A simple liquid-liquid extraction procedure was used to isolate the two compounds of interest from the complex biological matrix. Melatonin was converted to the fluorinated derivative with pentafluoropropionic anhydride. The mass spectrometer was tuned to monitor the very intense and stable ions at m/z 320 and 323 which were generated into the ion source by a dissociative capture process. This assay was conducted with 1 ml of plasma and the quantification limit of the method was statistically calculated as 0.5 pg ml-1. The very low relative standard deviations and mean percentages of error calculated during the within-day or between-day repeatability assays have clearly demonstrated the ruggedness of the technique for the routine quantitative measurement of melatonin in plasma. Some results on the melatonin circadian rhythm are presented to illustrate the applicability of this powerful gas chromatographic/mass spectrometric method.

White matter connectomes at birth accurately predict cognitive abilities at age 2

Cognitive ability is an important predictor of mental health outcomes that is influenced by neurodevelopment. Evidence suggests that the foundational wiring of the human brain is in place by birth, and that the white matter (WM) connectome supports developing brain function. It is unknown, however, how the WM connectome at birth supports emergent cognition. In this study, a deep learning model was trained using cross-validation to classify full-term infants (n = 75) as scoring above or below the median at age 2 using WM connectomes generated from diffusion weighted magnetic resonance images at birth. Results from this model were used to predict individual cognitive scores. We additionally identified WM connections important for classification. The model was also evaluated in a separate set of preterm infants (n = 37) scanned at term-age equivalent. Findings revealed that WM connectomes at birth predicted 2-year cognitive score group with high accuracy in both full-term (89.5%) and preterm (83.8%) infants. Scores predicted by the model were strongly correlated with actual scores (r = 0.98 for full-term and r = 0.96 for preterm). Connections within the frontal lobe, and between the frontal lobe and other brain areas were found to be important for classification. This work suggests that WM connectomes at birth can accurately predict a child's 2-year cognitive group and individual score in full-term and preterm infants. The WM connectome at birth appears to be a useful neuroimaging biomarker of subsequent cognitive development that deserves further study.

White matter microstructural development and cognitive ability in the first 2 years of life

White matter (WM) integrity has been related to cognitive ability in adults and children, but it remains largely unknown how WM maturation in early life supports emergent cognition. The associations between tract-based measures of fractional anisotropy (FA) and axial and radial diffusivity (AD, RD) shortly after birth, at age 1, and at age 2 and cognitive measures at 1 and 2 years were investigated in 447 healthy infants. We found that generally higher FA and lower AD and RD across many WM tracts in the first year of life were associated with better performance on measures of general cognitive ability, motor, language, and visual reception skills at ages 1 and 2, suggesting an important role for the overall organization, myelination, and microstructural properties of fiber pathways in emergent cognition. RD in particular was consistently related to ability, and protracted development of RD from ages 1 to 2 years in several tracts was associated with higher cognitive scores and better language performance, suggesting prolonged plasticity may confer cognitive benefits during the second year of life. However, we also found that cognition at age 2 was weakly associated with WM properties across infancy in comparison to child and demographic factors including gestational age and maternal education. Our findings suggest that early postnatal WM integrity across the brain is important for infant cognition, though its role in cognitive development should be considered alongside child and demographic factors.

Subcortical Brain Development in Autism and Fragile X Syndrome: Evidence for Dynamic, Age- and Disorder-Specific Trajectories in Infancy

OBJECTIVE

Previous research has demonstrated that the amygdala is enlarged in children with autism spectrum disorder (ASD). However, the precise onset of this enlargement during infancy, how it relates to later diagnostic behaviors, whether the timing of enlargement in infancy is specific to the amygdala, and whether it is specific to ASD (or present in other neurodevelopmental disorders, such as fragile X syndrome) are all unknown.

METHODS

Longitudinal MRIs were acquired at 6-24 months of age in 29 infants with fragile X syndrome, 58 infants at high likelihood for ASD who were later diagnosed with ASD, 212 high-likelihood infants not diagnosed with ASD, and 109 control infants (1,099 total scans).

RESULTS

Infants who developed ASD had typically sized amygdala volumes at 6 months, but exhibited significantly faster amygdala growth between 6 and 24 months, such that by 12 months the ASD group had significantly larger amygdala volume (Cohen's d=0.56) compared with all other groups. Amygdala growth rate between 6 and 12 months was significantly associated with greater social deficits at 24 months when the infants were diagnosed with ASD. Infants with fragile X syndrome had a persistent and significantly enlarged caudate volume at all ages between 6 and 24 months (d=2.12), compared with all other groups, which was significantly associated with greater repetitive behaviors.

CONCLUSIONS

This is the first MRI study comparing fragile X syndrome and ASD in infancy, demonstrating strikingly different patterns of brain and behavior development. Fragile X syndrome-related changes were present from 6 months of age, whereas ASD-related changes unfolded over the first 2 years of life, starting with no detectable group differences at 6 months. Increased amygdala growth rate between 6 and 12 months occurs prior to social deficits and well before diagnosis. This gradual onset of brain and behavior changes in ASD, but not fragile X syndrome, suggests an age- and disorder-specific pattern of cascading brain changes preceding autism diagnosis.

Quantitative measurement of clenbuterol at the femtomole level in plasma and urine by combined gas chromatography/negative ion chemical ionization mass spectrometry

A highly sensitive and specific assay was developed for the quantitative measurement of clenbuterol at the femtomole level in human plasma and urine. Clenbuterol and the internal standard (2H9)clenbuterol were measured by gas chromatography/negative ion chemical ionization mass spectrometry with methane as the reagent gas. The two compounds of interest were extracted from the biological samples at pH 13 using ethyl acetate. After two subsequent purification steps, the cleaned-up organic extract was derivatized with pentafluoropropionic anhydride. The mass spectrometer was set to monitor the abundant [M-HCl]- ions of the perfluoroacyl derivatives (m/z 368 and 377), which were generated in the ion source by an electron capture process. This assay required 1 ml of plasma or 0.5 ml of urine and the detection limit of the method was 5 pg ml-1 with a 12.8% relative standard deviation. The accuracy of the clenbuterol assay was also tested day to day with quality control specimens spiked blind to the analyst. The mean difference between the theoretical and actual values was lower than 4.1%.

Phase I study of percutaneous 4-hydroxy-tamoxifen with analyses of 4-hydroxy-tamoxifen concentrations in breast cancer and normal breast tissue

4-OH-tamoxifen is an active metabolite of tamoxifen that is detectable in the serum and tumour tissue of patients treated by oral tamoxifen. As this metabolite penetrates through the skin, it is possible to compare percutaneous 4-OH-tamoxifen (4-OH-TAM) and oral tamoxifen treatments. We report herein a randomized study of percutaneous 4-OH-TAM versus oral tamoxifen in women with breast cancer. This pharmacology study was designed to compare the 4-OH-TAM concentration in breast cancer and normal breast tissue according to the route and dose used for administration of tamoxifen after a 3-week period prior to surgery and tissue sampling. Women were randomized into one of the five following groups: group I, oral tamoxifen given at 10 mg twice a day; group II, 4-OH-TAM delivered percutaneously at 0.5 mg day to both breast areas; group III, 4-OH-TAM applied percutaneously at 1 mg/day to both breast areas; group IV, 4-OH-TAM delivered percutaneously at 1 mg/day to a large cutaneous area excluding the breasts; and group V, 4-OH-TAM applied percutaneously at 2 mg/day to a large skin area excluding the breasts. 4-OH-TAM plasma and tissue concentrations were significantly higher in the oral tamoxifen group as compared with either the high- or the low-dose percutaneous 4-OH-TAM group. In group II, percutaneous 4-OH-TAM treatment resulted in tissue concentrations of 1,446 and 352 pg/g in tumour tissue and normal breast tissue, respectively. In group I these concentrations were as follows: tumour tissue, 12, 453 pg/g; and normal tissue, 10,214 pg/g. 4-OH-TAM concentrations in tumour tissue and normal breast tissue did not significantly differ in any group. In the oral group we observed classic effects on coagulation and lipid metabolism when pre- and post-treatment values of these biological variables were compared, whereas no difference was observed in the percutaneous group. Although percutaneous administration of 4-OH-TAM led to a low plasmatic concentration of this active metabolite, the breast tissue concentration remained lower than those observed after oral tamoxifen treatment. Therefore, at the doses described in this study, percutaneous 4-OH-TAM cannot be proposed as an alternative tamoxifen treatment.

Carbamazepine-nefazodone interaction in healthy subjects

The pharmacokinetic interaction between nefazodone and carbamazepine was investigated in 12 healthy male volunteers. Subjects received nefazodone 200 mg twice daily for 5 days, and blood sample collection was performed on day 5 for 0- to 48-hour pharmacokinetic analysis. A 4-day wash-out phase then followed from days 6 to 9. Carbamazepine 200 mg was administered once daily from days 10 to 12, and then 200 mg was given twice daily from days 13 to 44. A 0- to 48-hour pharmacokinetic analysis was performed on day 38. Nefazodone 200 mg twice daily was added to the dosing regimen from days 40 to 44, and a subsequent 0- to 48-hour pharmacokinetic analysis was performed on day 44. Coadministration of nefazodone increased steady-state plasma area under the concentration-time curve (AUC) of carbamazepine from 60.77 (+/-8.44) to 74.98 (+/-12.88) microg x hr/mL (p < 0.001) and decreased the active carbamazepine-10,11-epoxide metabolite AUC concentration from 7.10 (+/-1.16) to 5.71 (+/-0.52) microg x hr/mL (p < 0.005). During the combination, the steady-state AUC of nefazodone decreased from 7,326 (+/-3,768) to 542 (+/-191) ng x hr/mL, and the AUCs of its metabolites (hydroxynefazodone, meta-chlorophenylpiperazine, and triazoledione) decreased significantly as well (p < 0.001). Coadministration of nefazodone 200 mg twice daily and carbamazepine 200 mg twice daily was found to be safe and well tolerated; however, the increased plasma exposure to carbamazepine may warrant monitoring of plasma carbamazepine concentrations with the combination. However, higher doses (>400 mg/day) of carbamazepine could yield more extensive induction, affecting tolerability of the combination. No change in the initial nefazodone dose is necessary, and subsequent dose adjustments should be made on the basis of clinical effects; however, the repercussion of carbamazepine induction of nefazodone metabolism on the antidepressant efficacy has yet to be studied.

Genetic influences on neonatal cortical thickness and surface area

Genetic and environmental influences on cortical thickness (CT) and surface area (SA) are thought to vary in a complex and dynamic way across the lifespan. It has been established that CT and SA are genetically distinct in older children, adolescents, and adults, and that heritability varies across cortical regions. Very little, however, is known about how genetic and environmental factors influence infant CT and SA. Using structural MRI, we performed the first assessment of genetic and environmental influences on normal variation of SA and CT in 360 twin neonates. We observed strong and significant additive genetic influences on total SA (a²  = 0.78) and small and nonsignificant genetic influences on average CT (a²  = 0.29). Moreover, we found significant genetic overlap (genetic correlation = 0.65) between these global cortical measures. Regionally, there were minimal genetic influences across the cortex for both CT and SA measures and no distinct patterns of genetic regionalization. Overall, outcomes from this study suggest a dynamic relationship between CT and SA during the neonatal period and provide novel insights into how genetic influences shape cortical structure during early development.

The activity of clarithromycin and its 14-hydroxy metabolite against Haemophilus influenzae, determined by in-vitro and serum bactericidal tests

The in-vitro activity of clarithromycin and its main metabolite 14-hydroxy clarithromycin against Haemophilus influenzae was evaluated by determining minimum inhibitory and minimum bactericidal concentrations. The 14-hydroxy metabolite was more active than the parent compound against H. influenzae. The activity of the parent compound/metabolite combination was evaluated against 20 strains of H. influenzae by the chequerboard technique. The combination was synergistic against seven isolates in terms of fractional bactericidal concentration index and against five isolates in terms of fractional inhibitory concentration index; the combination demonstrated additive activity against the remaining strains. Serum bactericidal activity against H. influenzae was measured in sera from six healthy volunteers who had received 250 mg clarithromycin by mouth. The area under the serum bactericidal activity curve correlated with the area under the curves for clarithromycin and 14-hydroxy clarithromycin, and with the in-vitro susceptibility of the strains tested. Serum bactericidal activity was detected at 30 min after dosing and lasted for 5-6 h.

The Neurodevelopment of Autism from Infancy Through Toddlerhood

Autism spectrum disorder (ASD) emerges during early childhood and is marked by a relatively narrow window in which infants transition from exhibiting normative behavioral profiles to displaying the defining features of the ASD phenotype in toddlerhood. Prospective brain imaging studies in infants at high familial risk for autism have revealed important insights into the neurobiology and developmental unfolding of ASD. In this article, we review neuroimaging studies of brain development in ASD from birth through toddlerhood, relate these findings to candidate neurobiological mechanisms, and discuss implications for future research and translation to clinical practice.

Effect of moderate or severe hepatic impairment on clarithromycin pharmacokinetics

The pharmacokinetic and safety profiles of clarithromycin (C) and its 14-hydroxy-clarithromycin (HC) metabolite were determined after a multiple-dose oral clarithromycin regimen (250 mg twice daily for five doses) in six healthy subjects and seven patients with moderate or severe hepatic impairment (Pugh grades B and C). Plasma and urine C and HC concentrations were determined using high-performance liquid chromatography. Hepatic impairment resulted in increased harmonic mean C terminal disposition half-life and mean +/- SD C renal clearance (CLR) compared with normal volunteers (5.0 vs. 3.3 hr and 170 +/- 69 vs. 111 +/- 17 mL/min, respectively). Hepatic impairment also resulted in decreased metabolite peak plasma concentration and area under the plasma concentration-versus-time curve and decreased metabolite/parent concentration ratios compared with normal volunteers. These data suggest that 14-hydroxylation of C was reduced by moderate to severe hepatic impairment. No adverse events were noted in either study group and there were no study-related clinically significant changes in laboratory parameters. The decrease in C metabolic clearance appears to be partially offset by an increase in C CLR, resulting in comparable steady-state concentrations of parent drug. In those indications in which the metabolite may be a necessary element of the antimicrobial activity of C, it would seem prudent to be cautious in using C in patients with moderate to severe hepatic impairment due to reduced production of HC. Otherwise, no dosage adjustment for C appears necessary for subjects with moderate or severe hepatic impairment provided that renal function is not impaired.

Cortical Structure and Cognition in Infants and Toddlers

Cortical structure has been consistently related to cognitive abilities in children and adults, yet we know little about how the cortex develops to support emergent cognition in infancy and toddlerhood when cortical thickness (CT) and surface area (SA) are maturing rapidly. In this report, we assessed how regional and global measures of CT and SA in a sample (N = 487) of healthy neonates, 1-year-olds, and 2-year-olds related to motor, language, visual reception, and general cognitive ability. We report novel findings that thicker cortices at ages 1 and 2 and larger SA at birth, age 1, and age 2 confer a cognitive advantage in infancy and toddlerhood. While several expected brain-cognition relationships were observed, overlapping cortical regions were also implicated across cognitive domains, suggesting that infancy marks a period of plasticity and refinement in cortical structure to support burgeoning motor, language, and cognitive abilities. CT may be a particularly important morphological indicator of ability, but its impact on cognition is relatively weak when compared with gestational age and maternal education. Findings suggest that prenatal and early postnatal cortical developments are important for cognition in infants and toddlers but should be considered in relation to other child and demographic factors.

Quantitative measurement of clonidine in human plasma by combined gas chromatography/electron capture negative ion chemical ionization mass spectrometry

A new quantitative and selective assay was developed for the measurement of low levels of clonidine in human plasma. The drug and the deuterated internal standard (2H4)clonidine are quantified by gas chromatography/negative ion chemical ionization mass spectrometry with methane as the reagent gas. After a three-step extraction procedure, the two compounds of interest are converted to their fluorinated derivatives using 3,5-bis(trifluoromethyl)benzoyl chloride. The mass spectrometer is focused to monitor abundant and stable characteristic high-mass ions (m/z 673 and 709) which are generated in the ion source by a resonance electron capture process. This assay requires only 1 ml of plasma sample and the limit of detection of the method is 5 pg ml-1 with a relative standard deviation of less than 7%.

White Matter Development from Birth to 6 Years of Age: A Longitudinal Study

Human white matter development in the first years of life is rapid, setting the foundation for later development. Microstructural properties of white matter are linked to many behavioral and psychiatric outcomes; however, little is known about when in development individual differences in white matter microstructure are established. The aim of the current study is to characterize longitudinal development of white matter microstructure from birth through 6 years to determine when in development individual differences are established. Two hundred and twenty-four children underwent diffusion-weighted imaging after birth and at 1, 2, 4, and 6 years. Diffusion tensor imaging data were computed for 20 white matter tracts (9 left-right corresponding tracts and 2 commissural tracts), with tract-based measures of fractional anisotropy and axial and radial diffusivity. Microstructural maturation between birth and 1 year are much greater than subsequent changes. Further, by 1 year, individual differences in tract average values are consistently predictive of the respective 6-year values, explaining, on average, 40% of the variance in 6-year microstructure. Results provide further evidence of the importance of the first year of life with regard to white matter development, with potential implications for informing early intervention efforts that target specific sensitive periods.

Determination of sodium cromoglycate in human plasma by liquid chromatography-mass spectrometry in the turbo ion spray mode

A highly sensitivity liquid chromatography-tandem mass spectrometry method has been developed for the quantitation of sodium cromoglycate (SCG) in human plasma. The method was validated over a linear range of 0.100-50.0 ng/ml, using 13C4 sodium cromoglycate as the internal standard. Compounds were extracted from 1.0 ml of lithium heparin plasma by methanol elution of C18 solid-phase extraction cartridges. The dried residue was reconstituted with 100 microl of 0.01 N HCl. and 30 microl was injected onto the LC-MS-MS system. Chromatographic separation was achieved on a C8 (3.5 microm) column with an isocratic mobile phase of methanol-water-0.5 M ammonium acetate (35:64.8:0.2, v/v/v). The analytes were detected with a PE Sciex API 3000 mass spectrometer using turbo ion spray with positive ionization. Ions monitored in the multiple reaction monitoring (MRM) mode were m/z 469.2 (precursor ion) to m/z 245.1 (product ion) for SCG and m/z 473.2 (precursor ion) to m/z 247.1 (product ion) for 13C4 SCG (I.S.). The average recoveries of SCG and the I.S. from human plasma were 91 and 87%, respectively. The low limit of quantitation was 0.100 ng/ml. Results from a 4-day validation study demonstrated excellent precision (C.V.% values were between 1.9 and 6.5%) and accuracy (-5.4 to - 1.2%) across the calibration range of 0.100-50.0 ng/ml.

Quantitative measurement of 4-hydroxy tamoxifen in human plasma and mammary tumours by combined gas chromatography/negative chemical ionization mass spectrometry

A highly sensitive and specific assay was developed for the quantitative measurement of 4-hydroxy tamoxifen (4-OH Tam) at the femtomole level in human plasma and mammary tumours. The drug and deuterated internal standard (4-OH Tam D4) were measured by gas chromatography/negative chemical ionization mass spectrometry with methane as the reactant gas. The two compounds of interest were isolated from the complex biological matrices using a solid-phase extraction procedure with Extrelut 1 columns. Soft operating conditions were required to convert 4-OH Tam to the fluorinated derivatives with pentafluorobenzyl chloride. The mass spectrometer was tuned to monitor the abundant and stable molecular ions at m/z 581 and 585 which were generated in the ion source by an electron capture process. This assay required only 0.5 ml of plasma or 0.5 g of mammary tissue, and the quantification limits of the method were 20 pg ml-1 for the body fluids or 100 pg g-1 for the tissue samples. The very low relative standard deviation and mean percentage error calculated during the different within-day or day-to-day repeatability assays have clearly demonstrated the ruggedness of the technique for routine analysis of 4-OH Tam.

Determination of clenbuterol in bovine plasma and tissues by gas chromatography-negative-ion chemical ionization mass spectrometry

A highly sensitive and specific assay was developed for the determination of clenbuterol in bovine plasma and tissues. Clenbuterol and the internal standard [2H9]clenbuterol were measured by gas chromatography-negative-ion chemical ionization mass spectrometry with methane as the reagent gas. Bovine tissues including muscle, liver, heart, kidney, lung, suet, brain, spinal cord and thymus were ground in a buffer of pH 7 and then extracted using ethyl acetate. After two subsequent purification steps, the cleaned-up organic extract was derivatized with pentafluoropropionic anhydride. The mass spectrometer was set to monitor the abundant ions m/z 368 and 377 of the perfluoroacyl derivatives. This assay was performed with 1 ml of plasma or 0.2 g of tissue. The feasibility of this method was demonstrated by the determination of clenbuterol residues as the femtomole level in a variety of tissues.