Abiotic stress does not magnify the deleterious effects of spontaneous mutations.

Although the effects of deleterious alleles often are predicted to be greater in stressful environments, there is no theoretical basis for this prediction and the empirical evidence is mixed. Here we characterized the effects of three types of abiotic stress (thermal, oxidative and hyperosmotic) on two sets of nematode (Caenorhabditis elegans) mutation accumulation (MA) lines that differ by threefold in fitness. We compared the survival and egg-to-adult viability between environments (benign and stressful) and between fitness categories (high-fitness MA, low-fitness MA). If the environment and mutation load have synergistic effects on trait means, then the difference between the high and low-fitness MA lines should be larger in stressful environments. Although the stress treatments consistently decreased survival and/or viability, we did not detect significant interactions between fitness categories and environment types. In contrast, we did find consistent evidence for synergistic effects on (micro)environmental variation. The lack of signal in trait means likely reflects the very low starting fitness of some low-fitness MA lines, the potential for cross-stress responses and the context dependence of mutational effects. In addition, the large increases in the environmental variance in the stressful environments may have masked small changes in trait means. These results do not provide evidence for synergism between mutation and stress.

Study of brain uptake and biodistribution of [11C]toluene in non-human primates and mice.

Inhalant abuse is a rapidly growing health problem particularly among adolescents. Yet we know little about the neural mechanisms underlying the abuse liability of inhalants, particularly when compared to other addictive drugs. Specifically, our understanding of the relationship between the regional brain phamacokinetics and features classically associated with drug reinforcement is lacking. Under the hypothesis that the abuse liability of toluene can be related to its pharmacokinetic properties and the pattern of regional brain uptake, we developed the methodology for radiolabeling and purifying [11C]toluene for use in PET studies. Here we report the regional brain distribution and kinetics of the widely abused solvent toluene in non-human primates and the whole body biodistribution in mice. To our knowledge, this is the first reported study of the in vivo brain pharmacokinetics of labeled toluene in non-human primates. Rapid uptake of radioactivity into striatal and frontal regions was followed by rapid clearance from the brain. Concurrent findings in rodents indicate similar radio-tracer kinetics, with excretion through kidneys and liver. Taken together, our data provides insight into pharmacokinetic features possibly associated with the abuse liability of toluene.

Species differences in [11C]clorgyline binding in brain.

[11C]Clorgyline selectively binds to MAO A in the human brain. This contrasts with a recent report that [11C]clorgyline (in contrast to other labeled MAO A inhibitors) is not retained in the rhesus monkey brain [4]. To explore this difference, we compared [11C]clorgyline in the baboon brain before and after clorgyline pretreatment and we also synthesized deuterium substituted [11C]clorgyline (and its nor-precursor) for comparison. [11C]Clorgyline was not retained in the baboon brain nor was it influenced by clorgyline pretreatment or by deuterium substitution, contrasting to results in humans. This suggests a species difference in the susceptibility of MAO A to inhibition by clorgyline and represents an unusual example of where the behavior of a radiotracer in the baboon brain does not predict its behavior in the human brain.

Evidence that L-deprenyl treatment for one week does not inhibit MAO A or the dopamine transporter in the human brain.

In this study, we investigated whether treatment with L-deprenyl, a selective monoamine oxidase B (MAO B) inhibitor, also inhibits MAO A or the dopamine transporter in the human brain. Six normal volunteers (age 46+/-6 yrs) had two PET sessions, one at baseline and one following L-deprenyl (10 mg/day) for 1 week. Each session included one scan with [11C]clorgyline (to assess MAO A) and one scan 2 hours later with [11C]cocaine (to assess dopamine transporter availability). A 3-compartment model was used to compare the plasma-to-brain transfer constant, K1 (a function of blood flow) and lambdak3 (a kinetic term proportional to brain MAO A) before and after treatment. Dopamine transporter availability was measured as the ratio of distribution volumes of the striatum to cerebellum (DVR) which is equal to Bmax/KD +1. L-Deprenyl treatment for 1 week did not affect either brain MAO A activity or dopamine transporter availability. There was a non-significant trend for an increase in K1 after L-deprenyl. These results confirm that L-deprenyl after one week of treatment at doses typically used clinically is selective for MAO B and that it does not produce a measurable affect on the dopamine transporter, suggesting that MAO A inhibition and dopamine transporter blockade do not contribute to its pharmacological effects.

Maintenance of brain monoamine oxidase B inhibition in smokers after overnight cigarette abstinence.

OBJECTIVE: The authors' goal was to replicate a previous finding that smokers have lower brain monoamine oxidase B (MAO-B) levels than comparison nonsmoking subjects and to determine if levels recover after overnight cigarette abstinence. METHOD: Brain MAO-B levels were measured by means of positron emission tomography in six smokers who were scanned twice: 11.3 hours (baseline) and 10 minutes after smoking one cigarette. RESULTS: Average MAO-B levels in smokers in the present study were similar to those found in the previous study and averaged 39% (SD=17) lower than those found in a comparison group of nonsmokers. Brain MAO-B levels did not differ between baseline levels and 10 minutes after smoking. CONCLUSIONS: This study reinforces the need to investigate whether MAO-B inhibition may account for some of the behavioral and epidemiological features of smoking.

Synthesis and evaluation of 6-[(18)F]fluoro-3-(2(S)-azetidinylmethoxy)pyridine as a PET tracer for nicotinic acetylcholine receptors.

Both ABT-594 ((R)-2-chloro-5-(2-azetidinylmethoxy)pyridine) and A-85380 (3-[2(S)-2-azetidinylmethoxy]pyridine), novel nicotinic agonists that possess potent non-opioid analgesic properties, have high affinity for neuronal nicotinic acetylcholine receptors (nAChR) but do not elicit the pronounced toxicity of epibatidine. 6-[(18)F]Fluoro-3-(2(S)-azetidinylmethoxy)pyridine (6-[(18)F]fluoro-A-85380), a F-18 labeled analogue of these two compounds, is therefore a promising radioligand for positron emission tomography (PET) studies in humans. The use of trimethylammonium as a leaving group in nucleophilic aromatic substitution reactions has proven to be a versatile and efficient strategy, and offers several advantages over other leaving groups. Here, we report the synthetic strategy for the preparation of a precursor, as a trimethylammonium iodide salt, and its use in the radiosynthesis to 6-[(18)F]fluoro-A-85380. Preliminary compartative PET studies of 6-[(18)F]fluoro-A-85380 and 2-[(18)F]fluoro-A-85380 were carried out in baboon to examine their suitability as tracers for studying nAChR system.

Dopamine receptor-mediated regulation of striatal cholinergic activity: positron emission tomography studies with norchloro[18F]fluoroepibatidine.

Large numbers of in vitro studies and microdialysis studies suggest that dopaminergic regulation of striatal acetylcholine (ACh) output is via inhibitory dopamine D2 receptors and stimulatory dopamine D1 receptors. Questions remain as to the relative predominance of dopamine D2 versus D1 receptor modulation of striatal ACh output under physiological conditions. Using positron emission tomography, we first demonstrate that norchloro[18F]fluoroepibatidine ([18F]NFEP), a selective nicotinic ACh receptor (nAChR) ligand, was sensitive to changes of striatal ACh concentration. We then examined the effect of quinpirole (D2 agonist), raclopride (D2 antagonist), SKF38393 (D1 agonist), and SCH23390 (D1 antagonist) on striatal binding of [18F]NFEP in the baboon. Pretreatment with quinpirole increased the striatum (ST) to cerebellum (CB) ratio by 26+/-6%, whereas pretreatment with raclopride decreased the ST/CB ratio by 22+/-2%. The ratio of the distribution volume of [18F]NFEP in striatum to that in cerebellum, which corresponds to (Bmax/K(D)) + 1 (index for nAChR availability), also showed a significant increase (29 and 20%; n = 2) and decrease (20+/-3%; n = 3) after pretreatment with quinpirole and raclopride, respectively. However, both the D1 agonist and antagonist had no significant effect. This suggests that under physiological conditions the predominant influence of endogenous dopamine on striatal ACh output is dopamine D2, not D1, receptor-mediated.

Evidence that gingko biloba extract does not inhibit MAO A and B in living human brain.

Extracts of Ginkgo biloba have been reported to reversibly inhibit both monoamine oxidase (MAO) A and B in rat brain in vitro leading to speculation that MAO inhibition may contribute to some of its central nervous system effects. Here we have used positron emission tomography (PET) to measure the effects of Ginkgo biloba on human brain MAO A and B in 10 subjects treated for 1 month with 120 mg/day of the Ginkgo biloba extract EGb 761, using [11C]clorgyline and [11C]L-deprenyl-D2 to measure MAO A and B respectively. A three-compartment model was used to calculate the plasma to brain transfer constant K1 which is related to blood flow, and lambdak3, a model term which is a function of the concentration of catalytically active MAO molecules. Ginkgo biloba administration did not produce significant changes in brain MAO A or MAO B suggesting that mechanisms other than MAO inhibition need to be considered as mediating some of its CNS effects.

Parasite diversity and anthelmintic resistance in two herds of horses.

Diversity of parasite populations was compared between two herds of horses, one a regularly treated herd the other a feral herd which has bad no anthelmintic treatment for at least 25 years. Eggs obtained from fecal samples of both herds were tested for anthelmintic resistance by use of an in-vitro larval hatch/development assay (LDA), DrenchRite. A fecal egg reduction test was also performed with the domesticated herd using fenbendazole, pyrantel pamoate and ivermectin. Cyathostomes were the predominant group of worms present in both herds. Trichostrongylus axei was seen in both herds, but Strongylus equinus, Strongylus vulgaris, Gyalocephalus capitatus, Poteriostomum spp. and Strongyloides westeri were only found in the feral horses. Larvae of Strongylus edentatus were found in a single domesticated horse. Fecal egg reduction tests with the domesticated herd showed a 32% egg count reduction for fenbendazole, a 93% reduction with pyrantel, and a 99% reduction with ivermectin. From the LDA, anthelmintic resistance was evaluated by determining the resistance ratio of the domesticated herd compared with the feral herd. For benzimidazoles in the domesticated herd, 45% of the cyathostome population was 9.4 times more tolerant than the feral herd's parasite population. The parasite population in the domesticated herd was 1.5 times more tolerant to Levamisole, and 1.7 times more tolerant to the benzimidazole/levamisole combination than the parasite population within the feral herd. 9% of the parasite population in the domesticated herd was 90 times more tolerant to avermectins than the feral herd's parasite population, even though a subpopulation of worms in the feral herd were tolerant to low concentrations of avermectins despite never being previously exposed to this class of anthelmintic.

Smoking a single cigarette does not produce a measurable reduction in brain MAO B in non-smokers.

Positron emission tomography (PET) studies with [11C]L-deprenyl-D2 have shown that brain monoamine oxidase (MAO) B is 40% lower in smokers than in non-smokers. Here we investigated whether MAO B inhibition can be detected after smoking a single cigarette. Eight normal healthy non-smokers (35 +/- 11 years) received two PET studies 2 h apart with [11C]L-deprenyl-D2, one at baseline and the second 5-10 min after the subject had smoked a single cigarette. Plasma nicotine and expired carbon monoxide (CO) were measured prior to smoking and 10 min after smoking completion as an index of tobacco smoke exposure. A three-compartment model was used to calculate lambda k3, a model term which is proportional to MAO B activity and which is derived from the time course of carbon-11 in the brain and the time course of the radiotracer in the plasma and K1, the plasma-to-brain transfer constant (for [11C]L-deprenyl-D2) which is related to brain blood flow. Subjects experienced difficulty inhaling and became dizzy and/or nauseous after smoking. Plasma nicotine averaged 11.6 +/- 5.5 ng/ml and expired CO averaged 8 +/- 10 ppm after smoking. The average lambda k3 and K1 for 11 different brain regions did not differ significantly between baseline and smoking. These results indicate that the reduction in MAO B in smokers probably occurs gradually and requires chronic tobacco smoke exposure.

An acute dose of nicotine does not inhibit MAO B in baboon brain in vivo.

Tobacco smoke exposure has been shown to inhibit brain and platelet MAO B in animals and in humans. Though the mechanism(s) responsible for MAO B inhibition are not known, studies in rodents have shown that nicotine administration does not inhibit brain MAO B. In this study we investigated whether brain MAO B is also unaffected by nicotine in the living primate. Brain MAO B was measured with positron emission tomography (PET) and deuterium substituted [11C]L-deprenyl ([11C]L-deprenyl-D2) in three baboons at baseline and 5 minutes after the injection of (-)-nicotine (0.3 mg administered intravenously). A three-compartment model was used to calculate the plasma to brain transfer constant K1 which is related to blood flow, and lambda k3, which is a function of the concentration of catalytically active MAO B molecules. Nicotine administration did not produce significant changes in either of these parameters. This study in living baboons confirms previous studies in rodents and solidifies the notion that other mechanisms for MAO B inhibition observed in smokers need to be considered.

Chronic disease prevention in Laredo, Texas.

The Laredo-Webb County Health Department began planning a health promotion program for the prevention of chronic diseases during the late 1970s. After receiving a 4-year grant from the W.K. Kellogg Foundation, the Department initiated the program in 1983 by conducting an epidemiologic survey in Laredo, Texas, to determine the major risk factors for chronic disease. A comprehensive health education program was then initiated to reduce the prevalence of these factors in targeted low-income neighborhoods. Health information was disseminated among the population in small neighborhood groups using a variety of techniques to promote favorable changes in health behavior. An evaluation of the program in one neighborhood 1 year later showed an overall reduction in health risk practices of approximately 10%.

Cardiovascular risk factors in Mexican Americans in Laredo, Texas. I. Prevalence of overweight and diabetes and distributions of serum lipids.

An epidemiologic survey of cardiovascular risk factors was carried out on a random sample of Mexican Americans living in two low income census tracts in Laredo, Texas. The prevalence of overweight was found to be intermediate between US national estimates and the rates recorded for Pima Indians. Similarly, the prevalence of fasting hyperglycemia was intermediate between the rates observed in a sample or predominantly Caucasian individuals and those observed in Pima Indians. Excess hyperglycemia in the Laredo Mexican American population compared to predominantly Caucasian populations does not appear to be due to a lower level of medical control of diabetes in the former. Rather, it probably reflects a true excess in the prevalence of diabetes. Serum cholesterol and triglyceride concentrations were also higher in Laredo Mexican Americans than in a Caucasian comparison population. Mexican Americans are of mixed European and native American ancestry. Native Americans have high rates of diabetes which could be on a genetic basis. The intermediate rates of hyperglycemia in Mexican Americans could thus have a genetic explanation. On the other hand, sociocultural determinants could be important since these are known to influence obesity which is a major precursor of diabetes.

Cardiovascular risk factors in Mexican Americans in Laredo, Texas. II. Prevalence and control of hypertension.

In recent years there has been a marked improvement in the level of hypertension control nationally in both blacks and whites. Information is still lacking, however, on the level of hypertension control in Mexican Americans. The authors carried out a cardiovascular risk factor survey on a random sample of Mexican Americans living in two low income census tracts in Laredo, Texas. The percentages of hypertensive women who had been previously diagnosed, were under treatment, and were "under control" compared favorably with national figures for blacks and whites. Corresponding percentages for men indicated that their level of diagnosis, treatment and "control" still lagged behind the national figures. The prevalence of hypertension in Laredo Project participants was intermediate between those observed in national studies for blacks and whites. This finding did not clearly emerge when comparisons were based on either blood pressure distributions or prevalence of elevated diastolic pressures. These results indicate that, because of the increasing number of "controlled" hypertensives in the population, comparisons between populations and across time can no longer be based exclusively on blood pressure measurements, but must include cases of "controlled" hypertension.