In vivo quantification of lead in bone with a portable x-ray fluorescence system--methodology and feasibility.

This study was conducted to investigate the methodology and feasibility of developing a portable x-ray fluorescence (XRF) technology to quantify lead (Pb) in bone in vivo. A portable XRF device was set up and optimal settings of voltage, current, and filter combination for bone lead quantification were selected to achieve the lowest detection limit. The minimum radiation dose delivered to the subject was calculated by Monte Carlo simulations. An ultrasound device was used to measure soft tissue thickness to account for signal attenuation, and an alternative method to obtain soft tissue thickness from the XRF spectrum was developed and shown to be equivalent to the ultrasound measurements (intraclass correlation coefficient, ICC = 0.82). We tested the correlation of in vivo bone lead concentrations between the standard KXRF technology and the portable XRF technology. There was a significant correlation between the bone lead concentrations obtained from the standard KXRF technology and those obtained from the portable XRF technology (ICC = 0.65). The detection limit for the portable XRF device was about 8.4 ppm with 2 mm soft tissue thickness. The entrance skin dose delivered to the human subject was about 13 mSv and the total body effective dose was about 1.5 µSv and should pose minimal radiation risk. In conclusion, portable XRF technology can be used for in vivo bone lead measurement with sensitivity comparable to the KXRF technology and good correlation with KXRF measurements.

Persistent organochlorine pesticides in serum and risk of Parkinson disease.

BACKGROUND: Pesticides have been implicated as likely environmental risk factors for Parkinson disease (PD), but assessment of past exposure to pesticides can be difficult. No prior studies of pesticide exposure and PD used biomarkers of exposure collected before the onset of PD. Our investigation examined the association between prospective serum biomarkers of organochlorine pesticides and PD. METHODS: We conducted a nested case-control study within the Finnish Mobile Clinic Health Examination Survey, with serum samples collected during 1968-1972, and analyzed in 2005-2007 for organochlorine pesticides. Incident PD cases were identified through the Social Insurance Institution's nationwide registry and were confirmed by review of medical records (n = 101). Controls (n = 349) were matched for age, sex, municipality, and vital status. Adjusted odds ratios (ORs) of PD were estimated using logistic regression. RESULTS: Little association emerged with a summary score of the 5 organochlorine pesticides found at high levels, and only increasing dieldrin concentrations trended toward a higher risk of PD (OR per interquartile range [IQR] 1.28, 95% confidence interval [CI] 0.97-1.69, p = 0.08). Because of possible strong confounding by cigarette smoking among smokers, we ran additional analyses restricted to never smokers (n = 68 cases, 183 controls). In these analyses, increasing dieldrin concentrations were associated with increased odds of PD (OR per IQR 1.95, 95% CI 1.26-3.02, p = 0.003). None of the other organochlorine pesticides were associated with PD in these analyses. CONCLUSIONS: These results provide some support for an increased risk of Parkinson disease with exposure to dieldrin, but chance or exposure correlation with other less persistent pesticides could contribute to our findings.

Prospective study of chemical exposures and amyotrophic lateral sclerosis.

BACKGROUND: Although environmental toxins, including pesticides, are suspected of contributing to the risk of amyotrophic lateral sclerosis (ALS), no data exist from large prospective investigations. This study assessed the association between exposure to chemicals and risk of ALS in a prospective cohort study. METHODS: The relation between self-report of regular exposure to 11 different chemical classes or x rays and ALS mortality among over 1 million participants in the American Cancer Society's Cancer Prevention Study II was prospectively assessed. Follow-up from 1989 through 2004 identified 617 deaths from ALS among men and 539 among women. Adjusted rate ratios (RR) were calculated using Cox proportional hazards. RESULTS: The RR for ALS mortality among individuals exposed to pesticides/herbicides compared with that among unexposed individuals was 1.07 (95% CI 0.79 to 1.44), but somewhat higher after excluding those with missing duration of pesticides exposure (RR 1.44; 95% CI 0.89 to 2.31; p = 0.14). A non-significant increase in ALS mortality was found among individuals who reported exposure to formaldehyde (RR 1.34; 95% CI 0.93 to 1.92). Excluding those with a missing duration of formaldehyde exposure, the RR was 2.47 (95% CI 1.58 to 3.86), and there was a strongly significant dose-response relation with increasing years of exposure (p trend = 0.0004). CONCLUSIONS: There was little evidence for any association between pesticides/herbicide exposure and ALS. In contrast, evidence was found, suggesting an increased risk of ALS with formaldehyde exposure. Because of the longitudinal design, this result is unlikely to be due to bias, but it should nevertheless be interpreted cautiously and needs to be verified independently.

Plasma urate and risk of Parkinson's disease.

Oxidative stress contributes to dopaminergic neuron degeneration in Parkinson's disease. Urate, a potent antioxidant, could be neuroprotective. To determine whether higher plasma concentrations of urate predict a reduced risk of Parkinson's disease, the authors conducted a nested case-control study among participants in the Health Professionals Follow-up Study, a cohort comprising over 18,000 men who provided blood samples in 1993-1995. Eighty-four incident cases of Parkinson's disease were diagnosed through 2000, and each was randomly matched to two controls by year of birth, race, and time of blood collection. Rate ratios of Parkinson's disease according to quartile of uricemia were estimated by use of conditional logistic regression. The mean urate concentration was 5.7 mg/dl among cases and 6.1 mg/dl among controls (p = 0.01). After adjustment for age, smoking, and caffeine, the rate ratio of Parkinson's disease for the highest quartile of uricemia compared with the lowest was 0.43 (95% confidence interval: 0.18, 1.02; p(trend) = 0.017). This association was stronger in analyses excluding cases diagnosed within 4 years (median) from blood collection (rate ratio = 0.17, 95% confidence interval: 0.04, 0.69; p(trend) = 0.010). These results suggest that high plasma urate concentrations may decrease the risk of Parkinson's disease, and they raise the possibility that interventions to increase plasma urate may reduce the risk and delay the progression of Parkinson's disease.

Temporal relationship between cigarette smoking and risk of Parkinson disease.

OBJECTIVE: To characterize further the relationship between smoking history and Parkinson disease (PD) risk by considering temporal and qualitative features of smoking exposure, including duration, average intensity, and recentness, as well as the relative importance of smoking during different periods of life. METHODS: We prospectively assessed incident PD from 1992 to 2001 among 79,977 women and 63,348 men participating in the Cancer Prevention Study II Nutrition Cohort, according to their cigarette smoking status and lifetime smoking histories. RESULTS: During follow-up, 413 participants had definite or probable PD confirmed by their treating neurologists or medical record review. Compared with never smokers, former smokers had a relative risk (RR) of 0.78 (95% CI 0.64 to 0.95) and current smokers had an RR of 0.27 (95% CI 0.13 to 0.56). On average, participants with more years smoked, more cigarettes per day, older age at quitting smoking, and fewer years since quitting smoking had lower PD risk. The relative risks and trends did not vary significantly by sex. The cumulative incidence of PD was lowest among participants who quit smoking at later ages. A 30% to 60% decreased risk of PD was apparent for smoking as early as 15 to 24 years before symptom onset, but not for smoking 25 or more years before onset. CONCLUSIONS: The lower risk of Parkinson disease among current and former smokers varied with smoking duration, intensity, and recentness. The dependence of this association on the timing of smoking during life is consistent with a biologic effect.

Prospective study of occupation and amyotrophic lateral sclerosis mortality.

Occupational exposures are suspected of contributing to the risk of amyotrophic lateral sclerosis (ALS), but results of epidemiologic studies have been inconsistent. The authors prospectively assessed the relation between occupation and ALS mortality among more than 1 million participants in the Cancer Prevention Study II of the American Cancer Society. Follow-up from 1989 through 2002 identified 507 ALS deaths among men and 430 among women. Adjusted rate ratios were calculated by using Mantel-Haenszel weights and Cox proportional hazards. Among men, elevated ALS mortality was found for programmers (rate ratio = 4.55, 95% confidence interval: 1.46, 14.2; p = 0.009) and laboratory technicians (rate ratio = 1.96, 95% confidence interval: 1.04, 3.66; p = 0.04). Occupations previously associated with increased risk of ALS for which no increased risk was found included farmers, electricians, and welders, although the numbers of electricians (eight ALS deaths) and welders (two ALS deaths) were small. Among women, only machine assemblers had significantly increased ALS mortality (rate ratio = 2.81, 95% confidence interval: 1.05, 7.53; p = 0.04). Results, which suggest that male programmers and laboratory technicians and female machine assemblers may be at increased risk of death from ALS, should be interpreted cautiously, however, because they are based on small numbers.

Prospective study of military service and mortality from ALS.

BACKGROUND: Two recent studies suggest that the risk of ALS is increased among Gulf War veterans. It is not known whether military service outside of the Gulf War is associated with increased risk of ALS. METHODS: The authors prospectively assessed the relation between service in the military and ALS mortality among participants in the Cancer Prevention Study II cohort of the American Cancer Society, a cohort that includes over 500,000 men from the 50 states, Washington, DC, and Puerto Rico. Participant follow-up was conducted from 1989 through 1998 for ALS mortality. There were a total of 280 deaths from ALS among 126,414 men who did not serve in the military and 281,874 who did. Adjusted relative risks (RRs) were calculated using Mantel-Haenszel weights and Cox proportional hazards. RESULTS: Men who served in the military had an increased death rate from ALS (RR = 1.53; 95% CI: 1.12 to 2.09; p = 0.007) compared with those who did not serve. The increase in ALS mortality was observed among men who served in the Army or National Guard (RR = 1.54), Navy (RR = 1.87), Air Force (RR = 1.54), and Coast Guard (RR = 2.24); no increase in risk was found in men who served in the Marine Corps, although there were only 13,670 men in this group. The risk of ALS among men who served was elevated in every 5-year birth cohort from 1915 through 1939. CONCLUSIONS: Military personnel have an increased risk of ALS. This increase appeared to be largely independent of the branch of service and the time period served.

Prospective study of cigarette smoking and amyotrophic lateral sclerosis.

Cigarette smoking has been proposed as a risk factor for amyotrophic lateral sclerosis (ALS), but because of the low incidence of ALS this association has been examined only with case-control methods. The authors prospectively assessed the relation between cigarette smoking and ALS mortality among participants in the Cancer Prevention Study II cohort of the American Cancer Society, a cohort of over 1 million people enrolled in 1982 who completed a lifestyle questionnaire including a detailed smoking history at baseline. Causes of deaths were ascertained through death certificates; ALS was not identified separately until 1989. From January 1, 1989, through 1998, 291 women and 330 men died from ALS. The relative risk of ALS among current smokers compared with never smokers was 1.67 (95% confidence interval: 1.24, 2.24; p = 0.002) in women and 0.69 (95% confidence interval: 0.49, 0.99; p = 0.04) in men. The difference in the relative risk estimates between the sexes was statistically significant (p < 0.0003). This large prospective study provides limited evidence that current cigarette smoking may be associated with increased death rates from ALS in women but not in men.

Misidentification of Onchocerca volvulus as guinea worm.

Over the past 10 years, the status of human infection with guinea worm (Dracunculus medinensis) in the Central African Republic (CAR) has been difficult to ascertain. It is unclear if indigenous cases are occurring and whether cases are migrating into the CAR from surrounding countries. A team of investigators visited the CAR in July-August 2000, to attempt to ascertain the presence of indigenous transmission. No cases of true guinea-worm infection (i.e. dracunculiasis) were detected, but three cases of human infection with Onchocerca volvulus, each of which had been misidentified as dracunculiasis, were detected. The unusual presentation of skin blisters and extraction of an intact female O. volvulus are described. As a result of this investigation, and the confusion of onchocerciasis being misidentified as dracunculiasis, the presence of endemic transmission of guinea worm in the CAR remains in question.

Wisconsin, July 1999 heat wave: an epidemiologic assessment.

OBJECTIVE: To assess the characteristics of heat-related deaths in Wisconsin during the summer of 1999. METHODS: Review of death certificates indicating heat as an underlying or contributing cause of death. RESULTS: Heat-related illness led to 21 deaths during the summer of 1999 in Wisconsin. The rate of death was highest in the elderly, particularly those aged 65-84 years (2.2/100,000). Heat was the underlying cause for 12 of the 21 deaths. Cardiovascular conditions were the underlying cause in 8 of the deaths, and a contributing cause for another 7. CONCLUSIONS: The elderly, persons taking psychotropic medications, and persons with chronic diseases, particularly cardiovascular conditions, are at increased risk of death from heat during heat waves. Prevention messages and weather advisories during heat emergencies must target these groups. Care givers and medical personnel must be on heightened awareness for the signs and symptoms of heat exhaustion and heat stroke during these periods.

Hazardous ammonia releases in Wisconsin: trends and risk factors for evacuation and injury.

OBJECTIVE: To assess trends in hazardous ammonia releases and risk factors for subsequent evacuation and injury. METHODS: Analysis of the Wisconsin Hazardous Substances Emergency Events Surveillance system data during 1993 through 1998. RESULTS: Ammonia releases (291) accounted for 13% of all reported chemical releases, but 26% of all releases that led to evacuations. The majority of non-transportation-related ammonia releases are the result of equipment failure or operator error (85.5%). Few ammonia releases are transportation-related (6.5%) or occur during extreme weather (14.4%). Extreme weather is not a risk factor for evacuation or injury following ammonia releases. CONCLUSIONS: Ammonia releases are frequently the result of equipment failure or operator error and thus preventable. The majority of ammonia releases that lead to evacuation and injury are not the result of transportation accidents or weather factors beyond human control. Prevention efforts that focus on preventive maintenance, and worker training and awareness could reduce the burden of hazardous ammonia releases.

L-type voltage-gated calcium channels mediate NMDA-independent associative long-term potentiation at thalamic input synapses to the amygdala.

Long-term potentiation (LTP) in the amygdala is a leading candidate mechanism to explain fear conditioning, a prominent model of emotional memory. LTP occurs in the pathway from the auditory thalamus to the lateral amygdala, and during fear conditioning LTP-like changes occur in the synapses of this pathway. Nevertheless, LTP has not been investigated in the thalamoamygdala pathway using in vitro recordings; hence little is known about the underlying mechanisms. We therefore examined thalamoamygdala LTP in vitro using visualized whole-cell patch recording. LTP at these synapses was dependent on postsynaptic calcium entry, similar to synaptic plasticity in other regions of the brain. However, unlike many forms of synaptic plasticity, thalamoamygdala LTP was independent of NMDA receptors, despite their presence at these synapses, and instead was dependent on L-type voltage-gated calcium channels. This was true when LTP was induced by pairing presynaptic activity with either action potentials or constant depolarization in the postsynaptic cell. In addition, the LTP was associative, in that it required concurrent pre- and postsynaptic activity, and it was synapse specific. Thus, although this LTP is different from that described at other synapses in the brain, it is nonetheless well suited to mediate classical fear conditioning.

Distinct populations of NMDA receptors at subcortical and cortical inputs to principal cells of the lateral amygdala.

Fear conditioning involves the transmission of sensory stimuli to the amygdala from the thalamus and cortex. These input synapses are prime candidates for sites of plasticity critical to the learning in fear conditioning. Because N-methyl-D-aspartate (NMDA)-dependent mechanisms have been implicated in fear learning, we investigated the contribution of NMDA receptors to synaptic transmission at putative cortical and thalamic inputs using visualized whole cell recording in amygdala brain slices. Whereas NMDA receptors are present at both of these pathways, differences were observed. First, the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-receptor-mediated component of the synaptic response, relative to the NMDA component, is smaller at thalamic than cortical input synapses. Second, thalamic NMDA responses are more sensitive to Mg2+. These findings suggest that there are distinct populations of NMDA receptors at cortical and thalamic inputs to the lateral amygdala. Differences such as these might underlie unique contributions of the two pathways to fear conditioning.

Characterizing the site and mode of action of dynorphin at hippocampal mossy fiber synapses in the guinea pig.

Extracellular field potential recordings from the CA3 region in guinea pig hippocampal slices were used to study the release and action of dynorphin at the mossy fiber synapse. Dynorphin A(1-17) or U69593 inhibited mossy fiber synaptic responses in preparations in which the CA3 region was surgically isolated from the rest of the hippocampus. This inhibition was completely reversed by the kappa 1 selective antagonist nor-BNI, thus establishing the presence of functional kappa 1 receptors in CA3. Inhibitory effects of dynorphin on mossy fiber responses were unaltered in the presence of the N- or P-type Ca2+ channel blockers, omega-CgTx or omega-Aga IVA, respectively. This indicates that the action of dynorphin is independent of the particular type of Ca2+ channel that mediates transmitter release at the mossy fiber terminal. Heterosynaptic inhibition of mossy fiber responses was observed in the presence of nifedipine, omega-CgTx, or omega-Aga IVA, indicating that dynorphin release does not depend specifically on L-, N-, or P-type Ca2+ channels. The blockade of heterosynaptic inhibition by the membrane-permeant Ca2+ chelator EGTA-AM suggests the involvement of a slow Ca(2+)-dependent process in dynorphin release. On the basis of a variety of experimental evidence, we propose that the time course of heterosynaptic inhibition is determined primarily by the time course of clearance of dynorphin in the extracellular space.

A comparison of the role of dynorphin in the hippocampal mossy fiber pathway in guinea pig and rat.

Several behavioral studies in rat (Gallagher, 1988) have suggested that opioids in the hippocampus could play an important role in learning and memory. However, in this species, very few reports specifically address the issue of physiological actions of opioids released by the mossy fibers which constitute the principal source of dynorphin and enkephalin in the hippocampus. In the guinea pig high frequency stimulation of mossy fibers causes a transient heterosynaptic inhibition of neighboring mossy fibers (Weisskopf et al., 1993) or perforant path synapses in the dentate (Wagner et al., 1993), which is mediated by the synaptic release of dynorphin that activates presynaptic kappa receptors. We show here that neither exogenous nor endogenous dynorphin affect mossy fiber excitatory postsynaptic potentials in the Sprague-Dawley rat, which is consistent with the finding that kappa receptor binding in the mossy fiber termination zone is dense in the guinea pig and sparse in this rat. More surprisingly, although kappa receptor binding is found in the rat dentate gyrus molecular layer and in the CA3 pyramidal cell layer, dynorphin had no action on perforant path field responses, somatic potassium currents or evoked monosynaptic inhibitory postsynaptic currents in CA3 cells. This lack of action appears to be an exception among rodents as dynorphin significantly inhibited mossy fiber responses in the hamster, mouse, and even another strain of rat, Long-Evans. Unlike the kappa mediated actions, the mu opioid receptor agonist DAMGO inhibited Sprague-Dawley mossy fiber responses, as it does in guinea pig. In contrast to other investigators, however, we found that the opioid receptor antagonist naloxone had no effect on Sprague-Dawley mossy fiber LTP.

Presynaptic changes during mossy fibre LTP revealed by NMDA receptor-mediated synaptic responses.

Activity-dependent changes in synaptic strength are important for learning and memory. Long-term potentiation (LTP) of glutamatergic excitatory synapses following brief repetitive stimulation provides a compelling cellular model for such plasticity. In the CA1 region of the hippocampus, anatomical studies have revealed large numbers of NMDA (N-methyl-D-aspartate) receptor sites at excitatory synapses, which express primarily an NMDA receptor-dependent form of LTP. In contrast, these studies have suggested that mossy fibre synapses activate primarily or exclusively alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and, indeed, these synapses express a form of LTP that is entirely independent of NMDA receptors. Here we present physiological data demonstrating that mossy fibres activate a substantial NMDA receptor synaptic component that expresses LTP. The presence of an NMDA receptor response allowed us to use the open-channel NMDA receptor antagonist MK-801 to establish directly that the probability of transmitter release is enhanced during the expression of mossy fibre LTP.

Mediation of hippocampal mossy fiber long-term potentiation by cyclic AMP.

Repetitive activation of hippocampal mossy fibers evokes a long-term potentiation (LTP) of synaptic responses in pyramidal cells in the CA3 region that is independent of N-methyl-D-aspartate receptor activation. Previous results suggest that the site for both the induction and expression of this form of LTP is presynaptic. Experimental elevation of cyclic adenosine 3',5'-monophosphate (cAMP) both mimics and interferes with tetanus-induced mossy fiber LTP, and blockers of the cAMP cascade block mossy fiber LTP. It is proposed that calcium entry into the presynaptic terminal may activate Ca(2+)-calmodulin-sensitive adenylyl cyclase I which, through protein kinase A, causes a persistent enhancement of evoked glutamate release.