Evaluation of Cow-Side Meters to Determine Somatic Cell Count in Individual Cow Quarter and Bulk-Tank Milk Samples.

Intramammary infections, which cause mastitis, can increase treatment and labor costs, decrease milk production, and affect milk quality. Meters that measure quarter somatic cell count (SCC) could be used to make more informed dry cow therapy decisions. The objective of this study was to compare the RT-10 iPhone adapter (RT-10; Dairy Quality Inc., Newmarket, ON, Canada), DeLaval Cell Counter (DSCC; DeLaval, Gurnee, IL, USA), Porta Check Quick Test (PortaCheck, White City, OR, USA), California Mastitis Test (ImmuCell, Portland, ME USA), pH meter (Hanna Instruments, Smithfield, RI, USA), electrical conductivity meter (OHAUS, Parsippany, NJ, USA), and the dual laser infrared temperature thermometer (Klein Tools, Lincolnshire, IL, USA) for measuring SCC in individual Holstein mammary quarters in comparison to a reference standard, the Fourier Transform Spectrometer 600 Combi System (Combi; Bentley Instruments, Chaska, MN, USA). Meters were evaluated using 658 individual cow quarter samples and 100 bulk-tank samples to measure SCC. Individual quarter milk samples from 160 cows from four commercial dairy herds were collected just before dry off and tested within 4 h of collection. To test bulk-tank SCC, 100 bulk-tank milk samples (25 mL) were collected from UC Davis Veterinary Medicine Teaching and Research Milk Quality Lab. Meter SCC values were regressed on observed Combi SCC. Goodness of fit was then evaluated by partitioning the mean square predicted error (MSPE). For individual quarter SCC, RT-10 had the highest coefficient of determination (R2 = 0.86), lowest MSPE, and highest proportion of MSPE due to random variation (96%). Both the RT-10 and DSCC had the highest sensitivity and specificity for identifying quarter SCC above and below 200,000 cells/mL. For bulk-tank SCC, DSCC had the highest coefficient of determination (R2 = 0.45), lowest MSPE, and highest proportion of MSPE due to random variation (80%). The RT-10 and DSCC could be used to measure individual quarter SCC to determine which cows to treat at dry off potentially reducing antibiotic use.

Efficacy and Safety of Lisdexamfetamine in Preschool Children With Attention-Deficit/Hyperactivity Disorder.

OBJECTIVE: To evaluate the acute efficacy, safety, and tolerability of lisdexamfetamine dimesylate (LDX) vs placebo (PBO) in preschool-aged children with attention-deficit/hyperactivity disorder (ADHD). METHOD: This phase 3, double-blind, fixed-dose study randomly assigned children (aged 4-5 years) with ADHD to 6 weeks of LDX (5, 10, 20, 30 mg) or PBO. The prespecified primary (change from baseline at week 6 in ADHD Rating Scale IV, Preschool version, total score [ADHD-RS-IV-PS-TS]) and key secondary (Clinical Global Impression-Improvement [CGI-I] score at week 6) efficacy endpoints were assessed using linear mixed-effects models for repeated measures. Safety and tolerability assessments included treatment-emergent adverse events (TEAEs) and changes in pulse and blood pressure (BP). RESULTS: The study comprised 199 participants randomly asigned 5:5:5:5:6 to receive 5, 10, 20, 30 mg LDX or PBO, respectively. Least squares (LS) mean (95% CI) treatment difference at week 6 between pooled LDX (10, 20, 30 mg) and PBO was statistically significant for ADHD-RS-IV-PS-TS change (-5.9 [-11.01, -0.78], p = .0242; effect size [ES], -0.43). CGI-I scores improved (ie, 1-2 on CGI-I) in 41.7% for pooled LDX and 24.3% for PBO (p = .0857). The LS mean (95% CI) treatment difference between pooled LDX and PBO for CGI-I score at week 6 was -0.6 (-1.03, -0.16; p = .0074; ES, -0.52). Frequency of TEAEs was 46.6% across all 4 LDX doses vs 42.2% with PBO; the most frequent TEAEs were decreased appetite (13.7% vs 8.9%, respectively) and irritability (9.6% vs 0%). Discontinuations because of TEAEs were 5.5% for all LDX doses and 4.4% for PBO. Mean ± SD pulse/BP changes from baseline at week 6/early termination were numerically greater with LDX vs PBO (pulse beats/min: 2.7 ± 10.79 vs 1.2 ± 9.90; systolic BP, mm Hg: 1.0 ± 7.51 vs 0.3 ± 6.06; diastolic BP, mm Hg: 1.7 ± 5.90 vs 0.0 ± 6.88). CONCLUSION: In children aged 4 to 5 years with ADHD, LDX was more efficacious than PBO in reducing symptoms. The observed ES for change in ADHD-RS-IV-PS-TS appears to be smaller in magnitude than has been reported for studies of LDX conducted in older children and adolescents. LDX was generally well tolerated, and no new safety signals were identified. CLINICAL TRIAL REGISTRATION INFORMATION: Safety and Efficacy Study in Preschool Children Aged 4-5 Years With Attention-Deficit/Hyperactivity Disorder; http://www. CLINICALTRIALS: gov; NCT03260205.

LC-MS/MS assays to quantify sulfatides and lysosulfatide in cerebrospinal fluid of metachromatic leukodystrophy patients.

Aim: Two separate LC-MS/MS assays were developed to quantitate sulfatides and lysosulfatide in human cerebrospinal fluid (CSF). Materials & methods: Lysosulfatide and the 15 most abundant sulfatide species were quantitated by LC-MS/MS using artificial CSF as surrogate matrix to prepare calibration curves. Results: Validation criteria were met (linear range: 0.02-1.00 µg/ml sulfatides [0.02-1.00 ng/ml lysosulfatide]); accuracy/precision were within ±15%. CSF from 21 children with metachromatic leukodystrophy had significantly higher sulfatide and lysosulfatide concentrations than CSF from 60 healthy children (p < 0.0001). Worse motor function correlated with higher CSF sulfatide (p = 0.0087) and lysosulfatide (p = 0.0034) levels. Conclusion: These assays, validated in patients with metachromatic leukodystrophy, may aid the clinical assessment of therapeutic responses.

NaV channel variants in patients with painful and nonpainful peripheral neuropathy.

OBJECTIVE: To examine the incidence of nonsynonymous missense variants in SCN9A (NaV1.7), SCN10A (NaV1.8), and SCN11A (NaV1.9) in patients with painful and nonpainful peripheral neuropathy. METHODS: Next-generation sequencing was performed on 457 patient DNA samples provided by the Peripheral Neuropathy Research Registry (PNRR). The patient diagnosis was as follows: 278 idiopathic peripheral neuropathy (67% painful and 33% nonpainful) and 179 diabetic distal polyneuropathy (77% painful and 23% nonpainful). RESULTS: We identified 36 (SCN9A), 31 (SCN10A), and 15 (SCN11A) nonsynonymous missense variants, with 47.7% of patients carrying a low-frequency (minor allele frequency <5%) missense variant in at least 1 gene. The incidence of previously reported gain-of-function missense variants was low (≤3%), and these were detected in patients with and without pain. There were no significant differences in missense variant allele frequencies of any gene, or SCN9A haplotype frequencies, between PNRR patients with painful or nonpainful peripheral neuropathy. PNRR patient SCN9A and SCN11A missense variant allele frequencies were not significantly different from the Exome Variant Server, European American (EVS-EA) reference population. For SCN10A, there was a significant increase in the alternate allele frequency of the common variant p.V1073A and low-frequency variant pS509P in PNRR patients compared with EVS-EA and the 1000 Genomes European reference populations. CONCLUSIONS: These results suggest that identification of a genetically defined subpopulation for testing of NaV1.7 inhibitors in patients with peripheral neuropathy is unlikely and that additional factors, beyond expression of previously reported disease "mutations," are more important for the development of painful neuropathy than previously discussed.

Dramatic elevation in urinary amino terminal titin fragment excretion quantified by immunoassay in Duchenne muscular dystrophy patients and in dystrophin deficient rodents.

Enzyme-linked and electrochemiluminescence immunoassays were developed for quantification of amino (N-) terminal fragments of the skeletal muscle protein titin (N-ter titin) and qualified for use in detection of urinary N-ter titin excretion. Urine from normal subjects contained a small but measurable level of N-ter titin (1.0 ± 0.4 ng/ml). A 365-fold increase (365.4 ± 65.0, P = 0.0001) in urinary N-ter titin excretion was seen in Duchene muscular dystrophy (DMD) patients. Urinary N-ter titin was also evaluated in dystrophin deficient rodent models. Mdx mice exhibited low urinary N-ter titin levels at 2 weeks of age followed by a robust and sustained elevation starting at 3 weeks of age, coincident with the development of systemic skeletal muscle damage in this model; fold elevation could not be determined because urinary N-ter titin was not detected in age-matched wild type mice. Levels of serum creatine kinase and serum skeletal muscle troponin I (TnI) were also low at 2 weeks, elevated at later time points and were significantly correlated with urinary N-ter titin excretion in mdx mice. Corticosteroid treatment of mdx mice resulted in improved exercise performance and lowering of both urinary N-ter titin and serum skeletal muscle TnI concentrations. Low urinary N-ter titin levels were detected in wild type rats (3.0 ± 0.6 ng/ml), while Dmdmdx rats exhibited a 556-fold increase (1652.5 ± 405.7 ng/ml, P = 0.002) (both at 5 months of age). These results suggest that urinary N-ter titin is present at low basal concentrations in normal urine and increases dramatically coincident with muscle damage produced by dystrophin deficiency. Urinary N-ter titin has potential as a facile, non-invasive and translational biomarker for DMD.

Evaluation of the agonist PET radioligand [¹¹C]GR103545 to image kappa opioid receptor in humans: kinetic model selection, test-retest reproducibility and receptor occupancy by the antagonist PF-04455242.

INTRODUCTION: Kappa opioid receptors (KOR) are implicated in several brain disorders. In this report, a first-in-human positron emission tomography (PET) study was conducted with the potent and selective KOR agonist tracer, [(11)C]GR103545, to determine an appropriate kinetic model for analysis of PET imaging data and assess the test-retest reproducibility of model-derived binding parameters. The non-displaceable distribution volume (V(ND)) was estimated from a blocking study with naltrexone. In addition, KOR occupancy of PF-04455242, a selective KOR antagonist that is active in preclinical models of depression, was also investigated. METHODS: For determination of a kinetic model and evaluation of test-retest reproducibility, 11 subjects were scanned twice with [(11)C]GR103545. Seven subjects were scanned before and 75 min after oral administration of naltrexone (150 mg). For the KOR occupancy study, six subjects were scanned at baseline and 1.5 h and 8 h after an oral dose of PF-04455242 (15 mg, n=1 and 30 mg, n=5). Metabolite-corrected arterial input functions were measured and all scans were 150 min in duration. Regional time-activity curves (TACs) were analyzed with 1- and 2-tissue compartment models (1TC and 2TC) and the multilinear analysis (MA1) method to derive regional volume of distribution (V(T)). Relative test-retest variability (TRV), absolute test-retest variability (aTRV) and intra-class coefficient (ICC) were calculated to assess test-retest reproducibility of regional VT. Occupancy plots were computed for blocking studies to estimate occupancy and V(ND). The half maximal inhibitory concentration (IC50) of PF-04455242 was determined from occupancies and drug concentrations in plasma. [(11)C]GR103545 in vivo K(D) was also estimated. RESULTS: Regional TACs were well described by the 2TC model and MA1. However, 2TC VT was sometimes estimated with high standard error. Thus MA1 was the model of choice. Test-retest variability was ~15%, depending on the outcome measure. The blocking studies with naltrexone and PF-04455242 showed that V(T) was reduced in all regions; thus no suitable reference region is available for the radiotracer. V(ND) was estimated reliably from the occupancy plot of naltrexone blocking (V(ND)=3.4±0.9 mL/cm(3)). The IC50 of PF-04455242 was calculated as 55 ng/mL. [(11)C]GR103545 in vivo K(D) value was estimated as 0.069 nmol/L. CONCLUSIONS: [(11)C]GR103545 PET can be used to image and quantify KOR in humans, although it has slow kinetics and variability of model-derived kinetic parameters is higher than desirable. This tracer should be suitable for use in receptor occupancy studies, particularly those that target high occupancy.

Glutamate and choline levels predict individual differences in reading ability in emergent readers.

Reading disability is a brain-based difficulty in acquiring fluent reading skills that affects significant numbers of children. Although neuroanatomical and neurofunctional networks involved in typical and atypical reading are increasingly well characterized, the underlying neurochemical bases of individual differences in reading development are virtually unknown. The current study is the first to examine neurochemistry in children during the critical period in which the neurocircuits that support skilled reading are still developing. In a longitudinal pediatric sample of emergent readers whose reading indicators range on a continuum from impaired to superior, we examined the relationship between individual differences in reading and reading-related skills and concentrations of neurometabolites measured using magnetic resonance spectroscopy. Both continuous and group analyses revealed that choline and glutamate concentrations were negatively correlated with reading and related linguistic measures in phonology and vocabulary (such that higher concentrations were associated with poorer performance). Correlations with behavioral scores obtained 24 months later reveal stability for the relationship between glutamate and reading performance. Implications for neurodevelopmental models of reading and reading disability are discussed, including possible links of choline and glutamate to white matter anomalies and hyperexcitability. These findings point to new directions for research on gene-brain-behavior pathways in human studies of reading disability.

The COMT Val/Met polymorphism is associated with reading-related skills and consistent patterns of functional neural activation.

In both children and adults there is large variability in reading skill, with approximately 5-10% of individuals characterized as having reading disability; these individuals struggle to learn to read despite adequate intelligence and opportunity. Although it is well established that a substantial portion of this variability is attributed to the genetic differences between individuals, specifics of the connections between reading and the genome are not understood. This article presents data that suggest that variation in the COMT gene, which has previously been associated with variation in higher-order cognition, is associated with reading and reading-related skills, at the level of both brain and behavior. In particular, we found that the COMT Val/Met polymorphism at rs4680, which results in the substitution of the ancestral Valine (Val) by Methionine (Met), was associated with better performance on a number of critical reading measures and with patterns of functional neural activation that have been linked to better readers. We argue that this polymorphism, known for its broad effects on cognition, may modulate (likely through frontal lobe function) reading skill.

Quantitative PK-PD model-based translational pharmacology of a novel kappa opioid receptor antagonist between rats and humans.

Pharmacokinetic-pharmacodynamic (PK-PD) modeling greatly enables quantitative implementation of the "learn and confirm" paradigm across different stages of drug discovery and development. This work describes the successful prospective application of this concept in the discovery and early development of a novel κ-opioid receptor (KOR) antagonist, PF-04455242, where PK-PD understanding from preclinical biomarker responses enabled successful prediction of the clinical response in a proof of mechanism study. Preclinical data obtained in rats included time course measures of the KOR antagonist (PF-04455242), a KOR agonist (spiradoline), and a KOR-mediated biomarker response (prolactin secretion) in plasma. Clinical data included time course measures of PF-04455242 and prolactin in 24 healthy volunteers following a spiradoline challenge and single oral doses of PF-04455242 (18 and 30 mg). In both species, PF-04455242 successfully reversed spiradoline-induced prolactin response. A competitive antagonism model was developed and implemented within NONMEM to describe the effect of PF-04455242 on spiradoline-induced prolactin elevation in rats and humans. The PK-PD model-based estimate of K(i) for PF-04455242 in rats was 414 ng/mL. Accounting for species differences in unbound fraction, in vitro K(i) and brain penetration provided a predicted human K(i) of 44.4 ng/mL. This prediction was in good agreement with that estimated via the application of the proposed PK-PD model to the clinical data (i.e., 39.2 ng/mL). These results illustrate the utility of the proposed PK-PD model in supporting the quantitative translation of preclinical studies into an accurate clinical expectation. As such, the proposed PK-PD model is useful for supporting the design, selection, and early development of novel KOR antagonists.

Early and late talkers: school-age language, literacy and neurolinguistic differences.

Early language development sets the stage for a lifetime of competence in language and literacy. However, the neural mechanisms associated with the relative advantages of early communication success, or the disadvantages of having delayed language development, are not well explored. In this study, 174 elementary school-age children whose parents reported that they started forming sentences 'early', 'on-time' or 'late' were evaluated with standardized measures of language, reading and spelling. All oral and written language measures revealed consistent patterns for 'early' talkers to have the highest level of performance and 'late' talkers to have the lowest level of performance. We report functional magnetic resonance imaging data from a subset of early, on-time and late talkers matched for age, gender and performance intelligence quotient that allows evaluation of neural activation patterns produced while listening to and reading real words and pronounceable non-words. Activation in bilateral thalamus and putamen, and left insula and superior temporal gyrus during these tasks was significantly lower in late talkers, demonstrating that residual effects of being a late talker are found not only in behavioural tests of oral and written language, but also in distributed cortical-subcortical neural circuits underlying speech and print processing. Moreover, these findings suggest that the age of functional language acquisition can have long-reaching effects on reading and language behaviour, and on the corresponding neurocircuitry that supports linguistic function into the school-age years.

Phonological awareness predicts activation patterns for print and speech.

Using fMRI, we explored the relationship between phonological awareness (PA), a measure of metaphonological knowledge of the segmental structure of speech, and brain activation patterns during processing of print and speech in young readers from 6 to 10 years of age. Behavioral measures of PA were positively correlated with activation levels for print relative to speech tokens in superior temporal and occipito-temporal regions. Differences between print-elicited activation levels in superior temporal and inferior frontal sites were also correlated with PA measures with the direction of the correlation depending on stimulus type: positive for pronounceable pseudowords and negative for consonant strings. These results support and extend the many indications in the behavioral and neurocognitive literature that PA is a major component of skill in beginning readers and point to a developmental trajectory by which written language engages areas originally shaped by speech for learners on the path toward successful literacy acquisition.

Allelic variation of calsyntenin 2 (CLSTN2) modulates the impact of developmental tobacco smoke exposure on mnemonic processing in adolescents.

BACKGROUND: Exposure to nicotine in tobacco smoke during development has been linked to subsequent deficits in attention and memory. The present study tested for evidence that genetic variation may contribute to individual differences in vulnerability to the effects of developmental exposure to tobacco smoke on memory and medial temporal lobe function in adolescents. METHODS: Verbal and visuospatial memory were assessed and functional magnetic resonance imaging (fMRI) data were acquired in 101 adolescents systematically characterized for prenatal and adolescent exposure to tobacco smoke, while they performed an encoding and recognition memory task. The impact of allelic variation at loci within CLSTN2 (encoding synaptic protein calsyntenin 2) and KIBRA, shown previously to modulate early and delayed recall of words, on the dependent measures was examined. RESULTS: KIBRA genotype did not exert significant main or interacting effects with prenatal or adolescent exposure to tobacco smoke on verbal or visuospatial memory. Previous observations of a beneficial effect of the CLSTN2 C allele on verbal recall were replicated. Adolescent exposure to tobacco smoke reversed this beneficial effect and was associated with increased activation of parahippocampal gyrus during early and delayed recognition in CLTSN2 C allele carriers. While the CLSTN2 C allele conferred enhanced functional connectivity between brain regions subserving accurate verbal recognition, adolescent exposure to tobacco smoke reversed this effect. CONCLUSIONS: These findings extend previous work demonstrating that calsyntenins play an essential role in learning and indicate that this role is modulated both by CLSTN2 genotype and, during adolescent development, by exposure to tobacco smoke.

Prenatal and adolescent exposure to tobacco smoke modulates the development of white matter microstructure.

Prenatal exposure to maternal smoking has been linked to cognitive and auditory processing deficits in offspring. Preclinical studies have demonstrated that exposure to nicotine disrupts neurodevelopment during gestation and adolescence, possibly by disrupting the trophic effects of acetylcholine. Given recent clinical and preclinical work suggesting that neurocircuits that support auditory processing may be particularly vulnerable to developmental disruption by nicotine, we examined white matter microstructure in 67 adolescent smokers and nonsmokers with and without prenatal exposure to maternal smoking. The groups did not differ in age, educational attainment, IQ, years of parent education, or symptoms of inattention. Diffusion tensor anisotropy and anatomical magnetic resonance images were acquired, and auditory attention was assessed, in all subjects. Both prenatal exposure and adolescent exposure to tobacco smoke was associated with increased fractional anisotropy (FA) in anterior cortical white matter. Adolescent smoking was also associated with increased FA of regions of the internal capsule that contain auditory thalamocortical and corticofugal fibers. FA of the posterior limb of the left internal capsule was positively correlated with reaction time during performance of an auditory attention task in smokers but not in nonsmokers. Development of anterior cortical and internal capsule fibers may be particularly vulnerable to disruption in cholinergic signaling induced by nicotine in tobacco smoke. Nicotine-induced disruption of the development of auditory corticofugal fibers may interfere with the ability of these fibers to modulate ascending auditory signals, leading to greater noise and reduced efficiency of neurocircuitry that supports auditory processing.

Impact of smoking abstinence on working memory neurocircuitry in adolescent daily tobacco smokers.

RATIONALE: Efficient function of neurocircuitry that supports working memory occurs within a narrow range of dopamine neurotransmission. Work in rodents has shown that exposure to nicotine during adolescence leads to nicotine withdrawal emergent alterations in cortical and subcortical dopamine neurotransmission. OBJECTIVES: To test for evidence that the efficiency of neurocircuitry supporting working memory is altered during acute smoking abstinence in adolescent daily tobacco smokers. MATERIALS AND METHODS: Fifty-five adolescent daily tobacco smokers were compared with 38 nonsmokers using functional magnetic resonance imaging while subjects performed a verbal working memory task. Smokers were studied during smoking and after 24 h of abstinence from tobacco use. RESULTS: Performance of a task with high working memory load in the context of smoking abstinence was associated with greater activation of components of the verbal working memory neurocircuit, including left ventrolateral prefrontal cortex and left inferior parietal lobe, among smokers relative to nonsmokers. During smoking abstinence, smokers failed to exhibit increases in functional connectivity between components of the working memory neurocircuit with increasing working memory load observed in nonsmoking adolescents and in prior studies of adults. CONCLUSIONS: Smoking abstinence in adolescent smokers is associated with reductions in the efficiency of working memory neurocircuitry and alterations in the functional coordination between components of the working memory neurocircuit. These alterations may stem from effects of nicotine exposure on catecholaminergic systems during adolescent development.

Gender-specific effects of prenatal and adolescent exposure to tobacco smoke on auditory and visual attention.

Prenatal exposure to active maternal tobacco smoking elevates risk of cognitive and auditory processing deficits, and of smoking in offspring. Recent preclinical work has demonstrated a sex-specific pattern of reduction in cortical cholinergic markers following prenatal, adolescent, or combined prenatal and adolescent exposure to nicotine, the primary psychoactive component of tobacco smoke. Given the importance of cortical cholinergic neurotransmission to attentional function, we examined auditory and visual selective and divided attention in 181 male and female adolescent smokers and nonsmokers with and without prenatal exposure to maternal smoking. Groups did not differ in age, educational attainment, symptoms of inattention, or years of parent education. A subset of 63 subjects also underwent functional magnetic resonance imaging while performing an auditory and visual selective and divided attention task. Among females, exposure to tobacco smoke during prenatal or adolescent development was associated with reductions in auditory and visual attention performance accuracy that were greatest in female smokers with prenatal exposure (combined exposure). Among males, combined exposure was associated with marked deficits in auditory attention, suggesting greater vulnerability of neurocircuitry supporting auditory attention to insult stemming from developmental exposure to tobacco smoke in males. Activation of brain regions that support auditory attention was greater in adolescents with prenatal or adolescent exposure to tobacco smoke relative to adolescents with neither prenatal nor adolescent exposure to tobacco smoke. These findings extend earlier preclinical work and suggest that, in humans, prenatal and adolescent exposure to nicotine exerts gender-specific deleterious effects on auditory and visual attention, with concomitant alterations in the efficiency of neurocircuitry supporting auditory attention.

Abnormal hippocampal neurochemistry in smokers: evidence from proton magnetic resonance spectroscopy at 3 T.

OBJECTIVE: In animals, nicotine, the primary psychoactive constituent of tobacco smoke, reduces neurogenesis and increases cell loss in both hippocampus and cortex. Accordingly, tobacco smoking has been linked to reduced performance on cognitive paradigms requiring attention and working memory in humans. However, few prior studies have tested for evidence of structural brain alterations in human tobacco smokers. In this study, proton magnetic resonance spectroscopy was used to assess the effects of chronic smoking on neuronal integrity of the hippocampus and anterior cingulate cortex (ACC). METHODS: Absolute concentrations of N-acetylaspartate, total choline (tCho), and total creatine were measured in the left hippocampus and ACC in 13 chronic tobacco smokers and 13 nonsmokers matched for age, sex, and education. RESULTS: The N-acetylaspartate concentration was significantly reduced in smokers relative to nonsmokers in the left hippocampus but not in the ACC. There were no group differences in the tCho and total creatine concentrations in either voxel. However, ACC tCho concentration was positively correlated with magnitude of lifetime exposure to tobacco smoke (pack-years). CONCLUSION: The results are consistent with prior observations of hippocampal neuronal damage in rodents receiving nicotine and working memory deficits in human tobacco smokers. The positive relationship between tCho and lifetime tobacco exposure suggests that a component of tobacco smoke, presumably nicotine, may increase cortical membrane turnover or modify cell density. Together, these results add to growing evidence that nicotine exerts neurotoxic effects in human brain, although an a priori nature of the findings cannot be ruled out.

Functional correlates of verbal memory deficits emerging during nicotine withdrawal in abstinent adolescent cannabis users.

BACKGROUND: Cannabis remains the most widely used illicit substance by adolescents and is typically consumed by this population in the context of ongoing tobacco use. Human studies have shown that both cannabis and tobacco exert effects on cognitive function; however, little is known about possible interacting effects of these drugs on brain function and cognition during adolescent development. METHODS: Verbal learning and memory were assessed in 20 adolescent users of tobacco and cannabis and 25 adolescent tobacco users with minimal history of cannabis use. Functional magnetic resonance imaging was used to examine brain function and functional connectivity while a subset of these subjects performed a verbal working memory task. RESULTS: Delayed recall of verbal stimuli deteriorated during nicotine withdrawal among cannabis users but not among comparison subjects. During high verbal working memory load, nicotine withdrawal selectively increased task-related activation of posterior cortical regions and was associated with disruption of frontoparietal connectivity in adolescent cannabis users relative to comparison subjects. CONCLUSIONS: These observations suggest that cannabis use during adolescent development may disrupt neurocircuitry supporting verbal memory formation and that deficits associated with disruption of these neurocircuits are unmasked during nicotine withdrawal.

Smoking and structural brain deficits: a volumetric MR investigation.

Growing evidence from animal studies indicates brain-damaging properties of nicotine exposure. Investigations in humans found a wide range of functional cerebral effects of nicotine and cigarette smoking, but studies focusing on brain damage are sparse. In 22 smokers and 23 never-smokers possible differences of the cerebral structures were investigated using magnetic resonance imaging and voxel-based morphometry. Significantly smaller grey matter volume and lower grey matter density (P = 0.05, corrected) were observed in the frontal regions (anterior cingulate, prefrontal and orbitofrontal cortex), the occipital lobe and the temporal lobe including parahippocampal gyrus, in smokers than in never-smokers. Group differences of either grey matter volume or grey matter density were also found in the thalamus, cerebellum and substantia nigra, among other regions. Smokers did not show greater volumes than never-smokers in any cerebral region. Magnitude of lifetime exposure to tobacco smoke (pack-years) was inversely correlated with volume of frontal and temporal lobes and cerebellum (P = 0.001, uncorrected). The data indicate structural deficits of several cortical and subcortical regions in smokers relative to never-smokers. The topographic profile of the group differences show some similarities to brain networks known to mediate drug reinforcement, attention and working memory processing. The present findings may explain in part the frequently reported cognitive dysfunctions in chronic cigarette consumers.

C957T polymorphism of the dopamine D2 receptor gene modulates the effect of nicotine on working memory performance and cortical processing efficiency.

RATIONALE: In both animals and humans, nicotine produces behavioral effects that vary across individuals. Studies examining the role of genetic variability in modulating individual response to nicotine in humans have increased, with recent work showing that genetic variation at the dopamine D2 receptor (DRD2) predicts response to pharmacotherapy for tobacco dependence. OBJECTIVES: To determine whether a polymorphism of the DRD2 gene, C957T, that alters DRD2 binding availability in humans modifies the effects of nicotine on verbal working memory performance and on processing efficiency of brain regions that support verbal working memory. MATERIALS AND METHODS: Working memory and brain function were assessed in 36 adult subjects (15,957T allele carriers and 21,957C homozygotes), each of whom was studied twice, once after placement of a placebo patch and once after placement of a nicotine patch. Brain function was assessed using functional magnetic resonance imaging while the subjects performed a verbal working memory task. RESULTS: During performance of a task with high verbal working memory load, nicotine administration worsened performance accuracy and reduced the processing efficiency of brain regions that support phonological rehearsal during verbal working memory in carriers of the 957T allele. CONCLUSIONS: These findings are consistent with the notion that genetic variation in DRD2 contributes to individual variation in a range of behavioral and brain responses to nicotine in humans.

Visuospatial memory deficits emerging during nicotine withdrawal in adolescents with prenatal exposure to active maternal smoking.

Active maternal smoking during pregnancy elevates the risk of cognitive deficits and tobacco smoking among offspring. Preclinical work has shown that combined prenatal and adolescent exposure to nicotine produces more pronounced hippocampal changes and greater deficits in cholinergic activity upon nicotine withdrawal than does prenatal or adolescent exposure to nicotine alone. Few prior studies have examined the potential modifying effects of gestational exposure to active maternal smoking on cognitive or brain functional response to tobacco smoking or nicotine withdrawal in adolescents. We examined visuospatial and verbal memory in 35 adolescent tobacco smokers with prenatal exposure to active maternal smoking and 26 adolescent tobacco smokers with no prenatal exposure to maternal smoking who were similar in age, educational attainment, general intelligence, and baseline plasma cotinine. Subjects were studied during ad libitum smoking and after 24 h of abstinence from smoking. A subset of subjects from each group also underwent functional magnetic resonance imaging while performing a visuospatial encoding and recognition task. Adolescent tobacco smokers with prenatal exposure experienced greater nicotine withdrawal-related deficits in immediate and delayed visuospatial memory relative to adolescent smokers with no prenatal exposure. Among adolescent smokers with prenatal exposure, nicotine withdrawal was associated with increased activation of left parahippocampal gyrus during early recognition testing of visuospatial stimuli and increased activation of bilateral hippocampus during delayed recognition testing of visuospatial stimuli. These findings extend prior preclinical work and suggest that, in human adolescent tobacco smokers, prenatal exposure to active maternal smoking is associated with alterations in medial temporal lobe function and concomitant deficits in visuospatial memory.