Methodological Issues and the Impact of Age Stratification on the Proportion of Participants with Low Appendicular Lean Mass When Adjusting for Height and Fat Mass Using Linear Regression: Results from the Canadian Longitudinal Study on Aging.

BACKGROUND: Using residual values calculated from models regressing appendicular lean mass on fat mass and height is one of several suggested strategies for adjusting appendicular lean mass for body size when measuring sarcopenia. However, special consideration is required when using this technique in different subgroups in order to capture the correct individuals as sarcopenic. OBJECTIVES: To provide guidance about how to conduct stratified analyses for the regression adjustment technique using age groups as an example. DESIGN: Cross-sectional study. SETTING: Data collected at baseline (2012-2015) for the Canadian Longitudinal Study on Aging. PARTICIPANTS: Community dwelling participants of European descent aged 45 to 85 years (n=25,399). MEASUREMENTS: Appendicular lean mass, height, and weight were measured. Sex-specific residuals were calculated in participants before and after stratifying participants by age group (45-54, 55-64, 65-74, 75-85 years). Cut offs corresponding to the sex-specific 20th percentile residual values in participants ≥65 years were determined first in the residuals calculated in all participants and residuals calculated in only those aged ≥65 years. For each set of cut offs, the percentage of age and sex-stratified participants with low appendicular lean mass were compared for the residuals calculated in all participants and the residuals calculated after stratifying by age. RESULTS: In 12,622 males and 12,737 females, regardless of the cut off used, the percentage of participants with low appendicular lean mass decreased with age when residuals were calculated after age stratification. When the residuals were calculated in all participants, the percentage of participants with sarcopenia increased from the youngest to the oldest age groups. CONCLUSIONS: Sex-specific residuals in all participants should be calculated prior to stratifying the sample by age group, or other stratification variables, for the purposes of developing appendicular lean mass cut offs or subgroup analyses.

Does conventional early life academic excellence predict later life scientific discovery? An assessment of the lives of great medical innovators.

BACKGROUND: Perhaps, as never before, we need innovators. With our growing population numbers, and with increasing pressures on our education systems, are we in danger of becoming more rigid and formulaic and increasingly inhibiting innovation? When young can we predict who will become the great innovators? For example, in medicine, who will change clinical practice? AIMS: We therefore determined to assess whether the current academic excellence approach to medical school entrance would have captured previous great innovators in medicine, assuming that they should all have well fulfilled current entrance requirements. METHODS: The authors assembled a list of 100 great medical innovators which was then approved, rejected or added to by a jury of 12 MD fellows of the Royal Society of Canada. Two reviewers, who had taken both the past and present Medical College Admission Test as part of North American medical school entrance requirements, independently assessed each innovator's early life educational history in order to predict the innovator's likely success at medical school entry, assuming excellence in all entrance requirements. RESULTS: Thirty-one percent of the great medical innovators possessed no medical degree and 24% would likely be denied entry to medical school by today's standards (e.g. had a history of poor performance, failure, dropout or expulsion) with only 24% being guaranteed entry. Even if excellence in only one topic was required, the figure would only rise to 41% certain of medical school entry. CONCLUSION: These data show that today's medical school entry standards would have barred many great innovators and raise questions about whether we are losing medical innovators as a consequence. Our findings have important implications for promoting flexibility and innovation for medical education, and for promoting an environment for innovation in general.

The influence of maternal and infant nutrition on cardiometabolic traits: novel findings and future research directions from four Canadian birth cohort studies.

A mother's nutritional choices while pregnant may have a great influence on her baby's development in the womb and during infancy. There is evidence that what a mother eats during pregnancy interacts with her genes to affect her child's susceptibility to poor health outcomes including childhood obesity, pre-diabetes, allergy and asthma. Furthermore, after what an infant eats can change his or her intestinal bacteria, which can further influence the development of these poor outcomes. In the present paper, we review the importance of birth cohorts, the formation and early findings from a multi-ethnic birth cohort alliance in Canada and summarise our future research directions for this birth cohort alliance. We summarise a method for harmonising collection and analysis of self-reported dietary data across multiple cohorts and provide examples of how this birth cohort alliance has contributed to our understanding of gestational diabetes risk; ethnic and diet-influences differences in the healthy infant microbiome; and the interplay between diet, ethnicity and birth weight. Ongoing work in this birth cohort alliance will focus on the use of metabolomic profiling to measure dietary intake, discovery of unique diet-gene and diet-epigenome interactions, and qualitative interviews with families of children at risk of metabolic syndrome. Our findings to-date and future areas of research will advance the evidence base that informs dietary guidelines in pregnancy, infancy and childhood, and will be relevant to diverse and high-risk populations of Canada and other high-income countries.

The prevalence of sarcopenia in community-dwelling older adults, an exploration of differences between studies and within definitions: a systematic review and meta-analyses.

Background: sarcopenia in ageing is a progressive decrease in muscle mass, strength and/or physical function. This review aims to summarise the definitions of sarcopenia in community-dwelling older adults and explore similarities and differences in prevalence estimates by definition. Methods: a systematic review was conducted to identify articles which estimated sarcopenia prevalence in older populations using search terms for sarcopenia and muscle mass. Overall prevalence for each sarcopenia definition was estimated stratified by sex and ethnicity. Secondary analyses explored differences between studies and within definitions, including participant age, muscle mass measurement techniques and thresholds for muscle mass and gait speed. Results: in 109 included articles, eight definitions of sarcopenia were identified. The lowest pooled prevalence estimates came from the European Working Group on Sarcopenia/Asian Working Group on Sarcopenia (12.9%, 95% confidence interval: 9.9-15.9%), International Working Group on Sarcopenia (9.9%, 3.2-16.6%) and Foundation for the National Institutes of Health (18.6%, 11.8-25.5%) definitions. The highest prevalence estimates were for the appendicular lean mass (ALM)/weight (40.4%, 19.5-61.2%), ALM/height (30.4%, 20.4-40.3%), ALM regressed on height and weight (30.4%, 20.4-40.3%) and ALM / body mass index (24.2%, 18.3-30.1%) definitions. Within definitions, the age of study participants and the muscle mass cut points used were substantive sources of between-study differences. Conclusion: estimates of sarcopenia prevalence vary from 9.9 to 40.4%, depending on the definition used. Significant differences in prevalence exist within definitions across populations. This lack of agreement between definitions needs to be better understood before sarcopenia can be appropriately used in a clinical context.

Overweight, obesity and adiposity in survivors of childhood brain tumours: a systematic review and meta-analysis.

Survivors of childhood brain tumours (SCBT) have increased cardiometabolic risks, but the determinants of these risks are unclear. This systematic review aims to compare the prevalence of overweight and obesity as well as adiposity measures between SCBT and non-cancer controls. The PubMed, EMBASE, MEDLINE, CINAHL and the Cochrane Library databases were searched. The primary outcomes were the prevalence of overweight and obesity based on body mass index. The secondary outcomes were adiposity measures including percent fat mass, waist-to-hip and waist-to-height ratios. Forty-one studies were included in the meta-analysis. The prevalence of overweight and obesity combined was similar between overall SCBT, SCBT excluding craniopharyngioma and non-cancer controls (42.6%, 95% CI 30.1-55.1 vs. 31.7%, 95% CI 20.4-43.0 vs. 40.4%, 95% CI 34.0-46.8). We also found that SCBT have higher percent fat mass (mean difference 4.1%, 95% CI 2.0-6.1), waist-to-hip ratio (mean difference 0.07, 95% CI 0.02-0.13) and waist-to-height ratio (mean difference 0.06, 95% CI 0.01-0.10) than non-cancer controls. We conclude that SCBT have similar overweight and obesity distribution but higher adiposity than non-cancer controls. More studies were needed to explore the determinants of adiposity and its contribution to cardiometabolic outcomes in SCBT.

On the origin of obesity: identifying the biological, environmental and cultural drivers of genetic risk among human populations.

Genetic predisposition to obesity presents a paradox: how do genetic variants with a detrimental impact on human health persist through evolutionary time? Numerous hypotheses, such as the thrifty genotype hypothesis, attempt to explain this phenomenon yet fail to provide a justification for the modern obesity epidemic. In this critical review, we appraise existing theories explaining the evolutionary origins of obesity and explore novel biological and sociocultural agents of evolutionary change to help explain the modern-day distribution of obesity-predisposing variants. Genetic drift, acting as a form of 'blind justice,' may randomly affect allele frequencies across generations while gene pleiotropy and adaptations to diverse environments may explain the rise and subsequent selection of obesity risk alleles. As an adaptive response, epigenetic regulation of gene expression may impact the manifestation of genetic predisposition to obesity. Finally, exposure to malnutrition and disease epidemics in the wake of oppressive social systems, culturally mediated notions of attractiveness and desirability, and diverse mating systems may play a role in shaping the human genome. As an important first step towards the identification of important drivers of obesity gene evolution, this review may inform empirical research focused on testing evolutionary theories by way of population genetics and mathematical modelling.

The effectiveness of interventions to treat hypothalamic obesity in survivors of childhood brain tumours: a systematic review.

BACKGROUND: Survivors of childhood brain tumours (SCBT) are at risk of type 2 diabetes and cardiovascular diseases. Obesity is a major driver of cardiometabolic diseases in the general population, and interventions that tackle obesity may lower the risk of these chronic diseases. The goal of this systematic review was to summarize current evidence for the presence of interventions to manage obesity, including hypothalamic obesity, in SCBT. METHODS: The primary outcome of this review was the body mass index z-score change from baseline to the end of the intervention and/or follow-up. Literature searches were conducted in PsycINFO, CINAHL, the Cochrane Library, Medline, SPORTDiscus, EMBASE and PubMed. Two reviewers completed study evaluations independently. RESULTS: Eleven publications were included in this systematic review (lifestyle intervention n = 2, pharmacotherapy n = 6 and bariatric surgery n = 3). While some studies demonstrated effectiveness of interventions to manage obesity in SCBT and alter markers of obesity and cardiometabolic risk, the evidence base was limited and of low quality, and studies focused on hypothalamic obesity. We conclude that there is urgent need to conduct adequately powered trials of sufficient duration, using existing and novel therapies to manage obesity, reduce the burden of cardiometabolic disorders and improve outcomes in SCBT.

A systematic review of genetic syndromes with obesity.

Syndromic monogenic obesity typically follows Mendelian patterns of inheritance and involves the co-presentation of other characteristics, such as mental retardation, dysmorphic features and organ-specific abnormalities. Previous reviews on obesity have reported 20 to 30 syndromes but no systematic review has yet been conducted on syndromic obesity. We searched seven databases using terms such as 'obesity', 'syndrome' and 'gene' to conduct a systematic review of literature on syndromic obesity. Our literature search identified 13,719 references. After abstract and full-text review, 119 relevant papers were eligible, and 42 papers were identified through additional searches. Our analysis of these 161 papers found that 79 obesity syndromes have been reported in literature. Of the 79 syndromes, 19 have been fully genetically elucidated, 11 have been partially elucidated, 27 have been mapped to a chromosomal region and for the remaining 22, neither the gene(s) nor the chromosomal location(s) have yet been identified. Interestingly, 54.4% of the syndromes have not been assigned a name, whereas 13.9% have more than one name. We report on organizational inconsistencies (e.g. naming discrepancies and syndrome classification) and provide suggestions for improvements. Overall, this review illustrates the need for increased clinical and genetic research on syndromes with obesity.

Empirical evaluation of the Q-Genie tool: a protocol for assessment of effectiveness.

INTRODUCTION: Meta-analyses of genetic association studies are affected by biases and quality shortcomings of the individual studies. We previously developed and validated a risk of bias tool for use in systematic reviews of genetic association studies. The present study describes a larger empirical evaluation of the Q-Genie tool. METHODS AND ANALYSIS: MEDLINE, Embase, Global Health and the Human Genome Epidemiology Network will be searched for published meta-analyses of genetic association studies. Twelve reviewers in pairs will apply the Q-Genie tool to all studies in included meta-analyses. The Q-Genie will then be evaluated on its ability to (i) increase precision after exclusion of low quality studies, (ii) decrease heterogeneity after exclusion of low quality studies and (iii) good agreement with experts on quality rating by Q-Genie. A qualitative assessment of the tool will also be conducted using structured questionnaires. DISCUSSION: This systematic review will quantitatively and qualitatively assess the Q-Genie's ability to identify poor quality genetic association studies. This information will inform the selection of studies for inclusion in meta-analyses, conduct sensitivity analyses and perform metaregression. Results of this study will strengthen our confidence in estimates of the effect of a gene on an outcome from meta-analyses, ultimately bringing us closer to deliver on the promise of personalised medicine. ETHICS AND DISSEMINATION: An updated Q-Genie tool will be made available from the Population Genomics Program website and the results will be submitted for a peer-reviewed publication.

The effect of ginseng (genus Panax) on blood pressure: a systematic review and meta-analysis of randomized controlled clinical trials.

Pre-clinical evidence indicates the potential for ginseng to reduce cardiovascular disease risk and acutely aid in blood pressure (BP) control. Clinical evidence evaluating repeated ginseng exposure, however, is controversial, triggering consumer and clinician concern. A systematic review and meta-analysis were conducted to assess whether ginseng has an effect on BP. MEDLINE, EMBASE, Cochrane and CINAHL were searched for relevant randomized controlled trials ⩾4 weeks that compared the effect of ginseng on systolic (SBP), diastolic (DBP) and/or mean arterial (MAP) BPs to control. Two independent reviewers extracted data and assessed methodological quality and risk of bias. Data were pooled using random-effects models and expressed as mean differences (MD) with 95% confidence intervals (CIs). Heterogeneity was assessed and quantified. Seventeen studies satisfied eligibility criteria (n=1381). No significant effect of ginseng on SBP, DBP and MAP was found. Stratified analysis, although not significant, appears to favour systolic BP improvement in diabetes, metabolic syndrome and obesity (MD=-2.76 mm Hg (95% CI=-6.40, 0.87); P=0.14). A priori subgroup analyses revealed significant association between body mass index and treatment differences (ß=-0.95 mm Hg (95% CI=-1.56, -0.34); P=0.007). Ginseng appears to have neutral vascular affects; therefore, should not be discouraged for concern of increased BP. More high-quality, randomized, controlled trials assessing BP as a primary end point, and use of standardized ginseng root or extracts are warranted to limit evidence of heterogeneity in ginseng research and to better understand its cardiovascular health potential.

The effect of a dietary portfolio compared to a DASH-type diet on blood pressure.

BACKGROUND AND AIM: Compared to a DASH-type diet, an intensively applied dietary portfolio reduced diastolic blood pressure at 24 weeks as a secondary outcome in a previous study. Due to the importance of strategies to reduce blood pressure, we performed an exploratory analysis pooling data from intensively and routinely applied portfolio treatments from the same study to assess the effect over time on systolic, diastolic and mean arterial pressure (MAP), and the relation to sodium (Na(+)), potassium (K(+)), and portfolio components. METHODS AND RESULTS: 241 participants with hyperlipidemia, from four academic centers across Canada were randomized and completed either a DASH-type diet (control n = 82) or a dietary portfolio that included, soy protein, viscous fibers and nuts (n = 159) for 24 weeks. Fasting measures and 7-day food records were obtained at weeks 0, 12 and 24, with 24-h urines at weeks 0 and 24. The dietary portfolio reduced systolic, diastolic and mean arterial blood pressure compared to the control by 2.1 mm Hg (95% CI, 4.2 to -0.1 mm Hg) (p = 0.056), 1.8 mm Hg (CI, 3.2 to 0.4 mm Hg) (p = 0.013) and 1.9 mm Hg (CI, 3.4 to 0.4 mm Hg) (p = 0.015), respectively. Blood pressure reductions were small at 12 weeks and only reached significance at 24 weeks. Nuts, soy and viscous fiber all related negatively to change in mean arterial pressure (ρ = -0.15 to -0.17, p ≤ 0.016) as did urinary potassium (ρ = -0.25, p = 0.001), while the Na(+)/K(+) ratio was positively associated (ρ = 0.20, p = 0.010). CONCLUSIONS: Consumption of a cholesterol-lowering dietary portfolio also decreased blood pressure by comparison with a healthy DASH-type diet. CLINICAL TRIAL REG. NO.: NCT00438425, clinicaltrials.gov.

Effect of fructose on markers of non-alcoholic fatty liver disease (NAFLD): a systematic review and meta-analysis of controlled feeding trials.

BACKGROUND/OBJECTIVES: In the absence of consistent clinical evidence, there are concerns that fructose contributes to non-alcoholic fatty liver disease (NAFLD). To determine the effect of fructose on markers of NAFLD, we conducted a systematic review and meta-analysis of controlled feeding trials. SUBJECTS/METHODS: We searched MEDLINE, EMBASE, CINAHL and the Cochrane Library (through 3 September 2013). We included relevant trials that involved a follow-up of ≥ 7 days. Two reviewers independently extracted relevant data. Data were pooled by the generic inverse variance method using random effects models and expressed as standardized mean difference (SMD) for intrahepatocellular lipids (IHCL) and mean difference (MD) for alanine aminotransferase (ALT). Inter-study heterogeneity was assessed (Cochran Q statistic) and quantified (I(2) statistic). RESULTS: Eligibility criteria were met by eight reports containing 13 trials in 260 healthy participants: seven isocaloric trials, in which fructose was exchanged isocalorically for other carbohydrates, and six hypercaloric trials, in which the diet was supplemented with excess energy (+21-35% energy) from high-dose fructose (+104-220 g/day). Although there was no effect of fructose in isocaloric trials, fructose in hypercaloric trials increased both IHCL (SMD=0.45 (95% confidence interval (CI): 0.18, 0.72)) and ALT (MD=4.94 U/l (95% CI: 0.03, 9.85)). LIMITATIONS: Few trials were available for inclusion, most of which were small, short (≤ 4 weeks), and of poor quality. CONCLUSIONS: Isocaloric exchange of fructose for other carbohydrates does not induce NAFLD changes in healthy participants. Fructose providing excess energy at extreme doses, however, does raise IHCL and ALT, an effect that may be more attributable to excess energy than fructose. Larger, longer and higher-quality trials of the effect of fructose on histopathological NAFLD changes are required.

A comparative study in rats of the in vitro and in vivo pharmacology of the acetylcholinesterase inhibitors tacrine, donepezil and NXX-066.

The in vitro and in vivo effects of the novel acetylcholinesterase inhibitors donepezil and NXX-066 have been compared to tacrine. Using purified acetylcholinesterase from electric eel both tacrine and donepezil were shown to be reversible mixed type inhibitors, binding to a similar site on the enzyme. In contrast, NXX-066 was an irreversible non-competitive inhibitor. All three compounds were potent inhibitors of rat brain acetylcholinesterase (IC50 [nM]; tacrine: 125 +/- 23; NXX-066: 148 +/- 15; donepezil: 33 +/- 12). Tacrine was also a potent butyrylcholinesterase inhibitor. Donepezil and tacrine displaced [3H]pirenzepine binding in rat brain homogenates (IC50 values [microM]; tacrine: 0.7; donepezil: 0.5) but NXX-066 was around 80 times less potent at this M1-muscarinic site. Studies of carbachol stimulated increases in [Ca2+]i in neuroblastoma cells demonstrated that both donepezil and tacrine were M1 antagonists. Ligand binding suggested little activity of likely pharmacological significance with any of the drugs at other neurotransmitter sites. Intraperitoneal administration of the compounds to rats produced dose dependent increases in salivation and tremor (ED50 [micromol/kg]; tacrine: 15, NXX-066: 35, donepezil: 6) with NXX-066 having the most sustained effect on tremor. Following oral administration, NXX-066 had the slowest onset but the greatest duration of action. The relative potency also changed, tacrine having low potency (ED50 [micromol/kg]; tacrine: 200, NXX-066: 30, donepezil: 50). Salivation was severe only in tacrine treated animals. Using in vivo microdialysis in cerebral cortex, both NXX-066 and tacrine were found to produce a marked (at least 30-fold) increase in extracellular acetylcholine which remained elevated for more than 2 h after tacrine and 4 h after NXX-066.

Identification of the GABAA receptor alpha 3 subunit in the IMR-32 neuroblastoma cell line.

A previous report has described the presence of t-[35S]-butylbicyclophosphorothionate binding sites and GABA-gated Cl- flux in the human neuroblastoma IMR-32 cell line. We now report the further characterisation of this binding site and, even more important, the identification of the GABAA receptor alpha 3 sub-unit expressed in these cells. Cell membranes prepared from IMR-32 cells were screened by immunoblotting for reactivity with various GABAA receptor alpha subunit-specific antibodies. Of these, only anti-Cys alpha 3 454-467 antibodies recognised specifically and in a dose-dependent manner an immunoreactive band. This M(r) 58,000 immunoreactive species and the N-deglycosylated derivatives were both coincident with the respective homologues found in both calf cerebral cortex membranes and purified receptor preparations. This is the first report of the identification of a specific GABAA receptor subunit expressed in a human cell line, and it therefore provides a convenient model for the study of receptor structure and regulation.

The human neuroblastoma cell line, IMR-32 possesses a GABAA receptor lacking the benzodiazepine modulatory site.

GABAA receptors were identified in IMR-32 cell membranes by the binding of [35S]t-butyl-bicyclophosphorothionate ([35S]TBPS) to the chloride channel. GABA (IC50 2.2 microM), muscimol (IC50 0.8 microM), picrotoxin (IC50 1.7 microM), pentobarbitone (IC50 108 microM), etomidate (IC50 53 microM), chlormethiazole (IC50 98 microM) and Ro 5-3663 (IC50 280 microM) all inhibited [35S]TBPS binding. The potency of these drugs at the [35S]TBPS binding site in IMR-32 cell membranes did not correlate with their potency on [35S]TBPS binding to rat cortical membranes (linear correlation of pIC50 values, r = 0.75, NS). No specific binding of the benzodiazepine ligands [3H]flunitrazepam or [3H]Ro 15-4513 to IMR-32 cell membranes was observed. Chloride efflux from IMR-32 cells was studied using the fluorescent dye 6-methoxy-N-(3-sulphopropyl) quinolinium. Chloride efflux was stimulated by GABA and muscimol (0.1-100 microM) but not by the GABAB agonist baclofen (100 microM). In the absence of exogenous GABA chloride efflux was stimulated by chlormethiazole (1-100 microM) in a picrotoxin-sensitive manner. Flurazepam (1-100 microM) both alone and in the presence of GABA had no effect on chloride efflux. It is concluded that IMR-32 cells contain a functional GABAA receptor which differs from that in rat cortex both in its general pharmacology and specifically in the absence of the allosteric modulatory site sensitive to benzodiazepines.

Striatal dopamine release in vivo following neurotoxic doses of methamphetamine and effect of the neuroprotective drugs, chlormethiazole and dizocilpine.

1. Administration to rats of methamphetamine (15 mg kg-1, i.p.) every 2 h to a total of 4 doses resulted in a neurotoxic loss of striatal dopamine of 36% and of 5-hydroxytryptamine (5-HT) in the cortex (43%) and hippocampus (47%) 3 days later. 2. Administration of chlormethiazole (50 mg kg-1, i.p.) 15 min before each dose of methamphetamine provided complete protection against the neurotoxic loss of monoamines while administration of dizocilpine (1 mg kg-1, i.p.) using the same dose schedule provided substantial protection. 3. Measurement of dopamine release in the striatum by in vivo microdialysis revealed that methamphetamine produced an approximate 7000% increase in dopamine release after the first injection. The enhanced release response was somewhat diminished after the third injection but still around 4000% above baseline. Dizocilpine (1 mg kg-1, i.p.) did not alter this response but chlormethiazole (50 mg kg-1, i.p.) attenuated the methamphetamine-induced release by approximately 40%. 4. Dizocilpine pretreatment did not influence the decrease in the dialysate concentration of the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) produced by administration of methamphetamine while chlormethiazole pretreatment decreased the dialysate concentration of these metabolites still further. 5. The concentration of dopamine in the dialysate during basal conditions increased modestly during the course of the experiment. This increase did not occur in chlormethiazole-treated rats. HVA concentrations were unaltered by chlormethiazole administration. 6. Chlormethiazole (100-1000 microM) did not alter methamphetamine (100 microM) or K+ (35 mM)-evoked release of endogenous dopamine from striatal prisms in vitro. 7. Several NMDA antagonists prevent methamphetamine-induced neurotoxicity; however chlormethiazole is not an NMDA antagonist. Inhibition of striatal dopamine function prevents methamphetamine-induced toxicity of both dopamine and 5-HT pathways. Therefore the attenuation of the enhanced dopamine release which occurs in animals given chlormethiazole may be associated with the protective action of this drug against methamphetamine-induced neurotoxicity.

The immediate consequences of middle cerebral artery occlusion on GABA synthesis in mouse cortex and cerebellum.

The effect on gamma-aminobutyric acid (GABA) synthesis of focal ischaemia in the right cortex of the mouse was investigated by performing a right middle cerebral artery (MCA) occlusion. Synthesis of GABA was determined by measurement of the rate of GABA accumulation in tissue following injection of amino oxyacetic acid (AOAA; 30 mg/kg, i.p.). Five min following the MCA occlusion, the rate of GABA synthesis in the right (ischaemic) cortex was decreased by approximately 70% compared to either the left cortex or the right cortex of untreated controls. The basal GABA concentration was however unaffected. Four hours after the occlusion the rate of GABA synthesis was similar in the right and left cortex. The rate of GABA accumulation in the cerebellum was unchanged at both times after the right MCA occlusion compared with untreated control mice. The data suggest that there is a rapid but short lasting decrease in GABA synthesis following an ischaemic insult and it is suggested that this might be associated with the EEG spiking activity that occurs at this time.

The neurotoxic effects of methamphetamine on 5-hydroxytryptamine and dopamine in brain: evidence for the protective effect of chlormethiazole.

Studies were undertaken in mice and rats on the neurotoxic effects of methamphetamine on dopaminergic and 5-hydroxytryptaminergic neurones in the brain and the neuroprotective action of chlormethiazole. In initial studies, mice were injected with methamphetamine (5 mg/kg, i.p.) at 2 hr intervals, to a total of 4 times. This procedure produced a 66% loss of striatal dopamine and a 50% loss of tyrosine hydroxylase activity 3 days later. Chlormethiazole (50 mg/kg, i.p.), given 15 min before each dose of methamphetamine, totally prevented the methamphetamine-induced loss of tyrosine hydroxylase activity and partly prevented the loss of dopamine. Phencyclidine (20 mg/kg, i.p.), given in place of chlormethiazole, also prevented the loss of tyrosine hydroxylase. Administration to rats of 4 doses of methamphetamine (15 mg/kg, i.p.) at 3 hr intervals resulted in a 75% loss of striatal dopamine 3 days later and a similar loss of 5-HT and 5-HIAA in cortex and hippocampus. Chlormethiazole (50 mg/kg, i.p.), given 15 min before each injection of methamphetamine, protected against the loss of dopamine and indoleamine content, in the respective regions. Pentobarbital (25 mg/kg, i.p.) also provided substantial protection but diazepam (2.5 mg/kg, i.p.) was without effect. Confirming earlier studies, dizocilpine (1 mg/kg) also provided substantial protection against the methamphetamine-induced neurotoxicity. Preliminary data indicated that chlormethiazole was not neuroprotective because of a hypothermic action. These data therefore demonstrate that chlormethiazole is an effective neuroprotective agent against methamphetamine-induced neurotoxicity and extend the evidence for the possible value of this drug in preventing neurodegeneration.

Studies on the enhancement of 5-hydroxytryptamine-mediated behaviour by chlormethiazole and phenytoin.

Pre-treatment of rats with chlormethiazole (35 mg/kg) or diphenylhydantoin (phenytoin: 40 mg/kg) markedly enhanced the behavioural syndrome which is induced by injection of tranylcypromine (10 mg/kg) followed by L-tryptophan (50 mg/kg). Phenobarbitone (35 mg/kg) pre-treatment was without effect on the syndrome. This enhancement apparently involved a pre-synaptic mechanism since pre-treatment with chlormethiazole or phenytoin did not result in enhancement of the behavioural syndrome when it was induced by injection of the 5-HT(1A) agonist 8-OH-DPAT (0.75 mg/kg). Pre-treatment of rats with chlormethiazole did not alter the rate of 5-HT synthesis as measured by the accumulation of 5-HT following tranylcypromine. The K(+)-evoked release of endogenous 5-HT from brain slices was unaltered by addition of chlormethiazole (100 µM) to the medium while addition of phenytoin (100 µM) caused a small decrease. Administration of chlormethiazole or phenytoin failed to alter either the 5-HT(2) receptor-mediated head twitch behaviour in mice induced by 5-hydroxytryptophan or the hypothermic response induced in mice by injection of 8-OH-DPAT (0.5 mg/kg s.c.). These data extend the original observation of enhancement of the 5-HT(1A) receptor-mediated behavioural syndrome by phenytoin, using a lower dose of the drug, and show that chlormethiazole has a similar effect, apparently through a pre synaptic mechanism. Some similarities to the effect of administration of Ca(2+) antagonists and lithium are noted but no clear mechanism involving changes in ion flux have been identified to explain the mechanisms involved.