Neuronal enriched endosomal protein of 21 kDa colocalizes with glutamate receptor subunit GLUR2/3 at the postsynaptic membrane.

Functional evidence suggests that neuronal enriched endosomal protein of 21 kDa (NEEP21) takes part in facilitating transport of AMPA receptors (AMPAR) in the synapse. To explore the anatomical basis for a role in this synaptic trafficking, we investigated the ultrastructural localization of NEEP21 in rodent brain. Using immunogold electron microscopy, we show that NEEP21 is colocalized with the AMPAR subunits GluR2/3 in postsynaptic spines. Quantitative analysis of gold particle distribution along an axis perpendicular to the postsynaptic specialization indicated that NEEP21 occurs in the postsynaptic membrane but also in the interior of the spines. NEEP21 positive endosomes/multivesicular bodies were found throughout cell bodies and dendrites. In light microscopical preparations, the NEEP21 antibody produced a labeling pattern in the neocortex, hippocampus and cerebellum that mimicked that of GluR2/3 and not that of GluR1 or 4. Our findings are consistent with a role for NEEP21 in facilitating vesicular transport of GluR2 between intracellular compartments and the postsynaptic plasma membrane.

Protein interacting with C kinase 1 (PICK1) and GluR2 are associated with presynaptic plasma membrane and vesicles in hippocampal excitatory synapses.

AMPA receptors have been identified in different populations of presynaptic terminals and found to be involved in the modulation of neurotransmitter release. The mechanisms that govern the expression of presynaptic AMPA receptors are not known. One possibility is that pre- and postsynaptic AMPA receptors are regulated according to the same principles. To address this hypothesis we investigated whether protein interacting with C kinase 1 (PICK1), known to interact with AMPA receptors postsynaptically, also is expressed presynaptically, together with AMPA receptors. Subfractionation and high-resolution immunogold analyses of the rat hippocampus revealed that GluR2 and PICK1 are enriched postsynaptically, but also in presynaptic membrane compartments, including the active zone and vesicular membranes. PICK1 and GluR2 are associated with the same vesicles, which are immunopositive also for synaptophysin and vesicle-associated membrane protein 2. Based on what is known about the function of PICK1 postsynaptically, the present data suggest that PICK1 is involved in the regulation of presynaptic AMPA receptor trafficking and in determining the size of the AMPA receptor pool that modulates presynaptic glutamate release.

Different modes of expression of AMPA and NMDA receptors in hippocampal synapses.

Postembedding immunogold labeling was used to determine the relationship between AMPA and NMDA receptor density and size of Schaffer collateral-commissural (SCC) synapses of the adult rat. All SCC synapses expressed NMDA receptors. AMPA and NMDA receptors were colocalized in at least 75% of SCC synapses; the ratio of AMPA to NMDA receptors was a linear function of postsynaptic density (PSD) diameter, with AMPA receptor number dropping to zero at a PSD diameter of approximately 180 nm. These findings indicate that 'silent' SCC synapses are smaller than the majority of SCC synapses at which AMPA and NMDA receptors are colocalized. Thus synapse size may determine important properties of SCC synapses.

Presynaptic Ca2+-activated K+ channels in glutamatergic hippocampal terminals and their role in spike repolarization and regulation of transmitter release.

Large-conductance Ca(2+)-activated K(+) channels (BK, also called Maxi-K or Slo channels) are widespread in the vertebrate nervous system, but their functional roles in synaptic transmission in the mammalian brain are largely unknown. By combining electrophysiology and immunogold cytochemistry, we demonstrate the existence of functional BK channels in presynaptic terminals in the hippocampus and compare their functional roles in somata and terminals of CA3 pyramidal cells. Double-labeling immunogold analysis with BK channel and glutamate receptor antibodies indicated that BK channels are targeted to the presynaptic membrane facing the synaptic cleft in terminals of Schaffer collaterals in stratum radiatum. Whole-cell, intracellular, and field-potential recordings from CA1 pyramidal cells showed that the presynaptic BK channels are activated by calcium influx and can contribute to repolarization of the presynaptic action potential (AP) and negative feedback control of Ca(2+) influx and transmitter release. This was observed in the presence of 4-aminopyridine (4-AP, 40-100 microm), which broadened the presynaptic compound action potential. In contrast, the presynaptic BK channels did not contribute significantly to regulation of action potentials or transmitter release under basal experimental conditions, i.e., without 4-AP, even at high stimulation frequencies. This is unlike the situation in the parent cell bodies (CA3 pyramidal cells), where BK channels contribute strongly to action potential repolarization. These results indicate that the functional role of BK channels depends on their subcellular localization.

Dietary fat intake and risk of lung cancer: a prospective study of 51,452 Norwegian men and women.

The relationship between incidence of lung cancer and intake of dietary fats, high-fat foods, fish, and fish products was studied in 25,956 men and 25,496 women aged 16-56 years attending Norwegian health screening between 1977 and 1983. Linkage to the Cancer Registry of Norway and the Central Bureau of Statistics of Norway ensured a complete follow-up until 31 December 1991. Diet was recorded on a semiquantitative food-frequency questionnaire, and 153 cases of lung cancer were identified during follow-up. Mean age at diagnosis was 56 years. After adjusting for smoking status, gender, age at screening, and attained age, significant lower risks were found for cod liver oil supplement (incidence rate ratio (IRR) = 0.5, 95% CI = 0.3-1.0) and for skim milk compared to whole milk (IRR = 0.5, 95% CI = 0.3-0.9)). No association was found with dietary cholesterol and saturated fat. A threshold of increased risk starting at the second quartile was seen for mono- and polyunsaturated fat. The potential protective effect of cod liver oil, a supplement rich in preformed vitamin A, omega-3 fatty acids, and monounsaturated fat, has to our knowledge, not been reported before. Confounding from lifestyle is possible, but the result deserves further investigation.

Supplier inducement. Its effect on dental services in Norway.

In many western countries, supply of dental services exceeds demand, mainly because of the marked reduction in the prevalence of dental diseases during the last 10-15 years. An important issue is whether dentists can counteract this fall in demand by stimulating increased demand and/or utilization for their services. Some evidence that this may be the case was found in the present study, in Norway. The results indicate that demand and utilization for dental services are influenced by supplier inducement.

Reporting data following major trauma and analysing factors associated with outcome using the new Utstein style recommendations.

STUDY OBJECTIVE: To collect and present retrospectively the recommended core data from the Utstein style, analyse factors associated with outcome in major trauma, and discuss the value of the Utstein style definition of major trauma. DESIGN: A retrospective trauma cohort study. SETTING: A Norwegian trauma system with a 1200 bed combined local and referral trauma hospital without a formal trauma registry, covering a population of approximately 2.0 million. PARTICIPANTS: 3391 injured patients admitted 12 months from January 15, 1996. MAIN OUTCOME MEASURES: Recommended core data from the Utstein style, and factors associated with outcome defined as in-hospital death within 30 days. RESULTS: 225 patients had an injury severity score (ISS)>15. In each of the 225 patients, we were able to obtain at least 47% of the recommended core data. Age >70 years, fall as a mechanism of injury, and a Trauma Score (TS)< or =14 were significantly associated with poor outcome. Of 22 with no major trauma (ISS<16), two died in hospital and 20 had an intensive care unit stay of more than 2 days. CONCLUSION: We found it difficult to collect retrospectively the recommended core data of the Utstein style. Age and physiological alterations (TS) were significantly related to outcome. The recommended definition of major trauma (ISS>15) did not cover all life-threatening injuries. The implementation of trauma registries based on the Utstein style recommendations could facilitate system evaluation and comparison, but definitions and categorizations should be further developed. Efforts should be made to reduce the number of core data.

Accessibility of dental services according to family income in a non-insured population.

The aim of this study was to examine the effect of family income on accessibility to dental services among adults in Norway. The analysis was performed on a set of national data collected in 1989, which was representative of the non-institutionalized Norwegian population aged 20 years and above. The sample size was 1200 individuals. The data were analyzed according to a two-part model. The first part determined the probability of whether the consumer had demanded the services or not during the last year according to family income. The second part estimated how the amount of services utilized depended on family income, for those with demand. The elasticity of the odds of having demanded the services with respect to family income was 0.48. Family income had no effect on the amount of services utilized. Additional analyses also showed that there was no effect of family income on the probability of having received a filling or a crown when visiting the dentist. In Norway, almost all costs for dental services are paid by the consumer. It is not possible from the data alone to say whether subsidized dental care is an effective way of reducing the inequalities in demand.

Incidence and risk factors of cancer among men and women in Norwegian agriculture.

OBJECTIVES: The objective of the study was to examine cancer incidence and identify risk factors among subjects born in 1925-1971 and engaged in agricultural activities in Norway. METHODS: A cohort was established through linkage between agricultural censuses in 1969-1989 and the Central Population Register, which identifies farm holders and their spouses. Available census information on the activity of the farm provided the exposure indicators. Incident cancer in 1969-1991 was identified in the Cancer Register. In an analysis for standardized incidence ratios (SIR), the cohort was compared with the total rural population of Norway. Associations with exposure indicators were investigated in a Poisson regression analysis. RESULTS: In the follow-up of 136,463 men for 1.5 million person-years and 109,641 women for 0.6 million person-years, 3333 and 2145 cancer cases were identified, respectively. The subset defined as farmers had an SIR of 77 [95% confidence interval (95% CI) 73-81] for the men and 92 (95% CI 85-99) for the women, with particularly low SIR values for lung cancer and other sites linked to life-style. The several positive associations found confirmed the a priori hypothesis of an association between dairy farming and acute leukemia among men [rate ratio 1.76, 95% CI 1.02-3.05]. Multiple myeloma was associated with pesticide indicators for both genders, mainly for subjects cultivating potatoes. CONCLUSIONS: The results support the hypothesis of a relationship between acute leukemia and animal contact and between multiple myeloma and pesticides in potato cultivation. Other exposure associations, especially for cancer among women, warrant further investigation.

Kiwifruit decreases blood pressure and whole-blood platelet aggregation in male smokers.

Lifestyle modifications to reduce risk factors for cardiovascular diseases such as blood pressure (BP) and smoking have been emphasized. Fruits and vegetables may modify such risk factors. The major aim of this randomized, controlled trial was to investigate the effects of (1) kiwifruits and (2) an antioxidant-rich diet compared with (3) a control group on BP and platelet aggregation (that is, whole-blood platelet aggregation) after 8 weeks in male smokers (age 44-74 years, n=102). The kiwifruit group received 3 kiwifruits per day, whereas the antioxidant-rich diet group received a comprehensive combination of antioxidant-rich foods. In the kiwifruit group, reductions of 10 mm Hg in systolic BP and 9 mm Hg in diastolic BP were observed (P=0.019 and P=0.016 (change from baseline in the kiwifruit group compared with change from baseline in the control group)). In the antioxidant-rich diet group, a reduction of 10 mm Hg in systolic BP was observed among hypertensives (P=0.045). Additionally, a 15% reduction in platelet aggregation and an 11% reduction in angiotensin-converting enzyme activity was observed in the kiwifruit group (P=0.009 and P=0.034). No effects on these parameters were observed in the antioxidant-rich diet group. This study suggest that intake of kiwifruit may have beneficial effects on BP and platelet aggregation in male smokers.

Deletion of the betaine-GABA transporter (BGT1; slc6a12) gene does not affect seizure thresholds of adult mice.

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian brain. Once released, it is removed from the extracellular space by cellular uptake catalyzed by GABA transporter proteins. Four GABA transporters (GAT1, GAT2, GAT3 and BGT1) have been identified. Inhibition of the GAT1 by the clinically available anti-epileptic drug tiagabine has been an effective strategy for the treatment of some patients with partial seizures. Recently, the investigational drug EF1502, which inhibits both GAT1 and BGT1, was found to exert an anti-convulsant action synergistic to that of tiagabine, supposedly due to inhibition of BGT1. The present study addresses the role of BGT1 in seizure control and the effect of EF1502 by developing and exploring a new mouse line lacking exons 3-5 of the BGT1 (slc6a12) gene. The deletion of this sequence abolishes the expression of BGT1 mRNA. However, homozygous BGT1-deficient mice have normal development and show seizure susceptibility indistinguishable from that in wild-type mice in a variety of seizure threshold models including: corneal kindling, the minimal clonic and minimal tonic extension seizure threshold tests, the 6Hz seizure threshold test, and the i.v. pentylenetetrazol threshold test. We confirm that BGT1 mRNA is present in the brain, but find that the levels are several hundred times lower than those of GAT1 mRNA; possibly explaining the apparent lack of phenotype. In conclusion, the present results do not support a role for BGT1 in the control of seizure susceptibility and cannot provide a mechanistic understanding of the synergism that has been previously reported with tiagabine and EF1502.

Choice of test for association in small sample unordered r x c tables.

Pearson's chi-squared, the likelihood-ratio, and Fisher-Freeman-Halton's test statistics are often used to test the association of unordered r x c tables. Asymptotical, exact conditional, or exact conditional with mid-p adjustment methods are commonly used to compute the p-value. We have compared test power and significance level for these test statistics and p-value calculations in small sample r x c tables, mostly 3 x 2 and some with both r and c are greater than 2. After extensive simulations, in general we recommend using an exact conditional mid-p test with Pearson's chi-squared or Fisher-Freeman-Halton's statistic, which usually is the most powerful test yet preserve the approximate significance level. Moreover, we recommend that the asymptotic Pearson's chi-squared or other asymptotic tests not be used for small sample r x c tables.

A simulation study of measurement error correction methods in logistic regression.

Measurement error models in logistic regression have received considerable theoretical interest over the past 10-15 years. In this paper, we present the results of a simulation study that compares four estimation methods: the so-called regression calibration method, probit maximum likelihood as an approximation to the logistic maximum likelihood, the exact maximum likelihood method based on a logistic model, and the naive estimator, which is the result of simply ignoring the fact that some of the explanatory variables are measured with error. We have compared the behavior of these methods in a simple, additive measurement error model. We show that, in this situation, the regression calibration method is a very good alternative to more mathematically sophisticated methods.

Sex-specific trends in mortality for the aging population in Norway: a model with age, period, and cohort effects.

During the last few decades, the citizens of most western countries have experienced an increased expectation of life. The rate of this change differs for males and females. We evaluated reasons for this pattern, using a Poisson model, with age, period, and cohort effects applied to vital statistics data from the Central Bureau of Statistics of Norway. The data comprised the total Norwegian population aged 45 to 104 years who died in the period from 1966 until 1986. Differential changes in life expectancy for the elderly are explained by differences in sex-specific cohort effects. We also observed an extra-Poisson variation, or overdispersion, in the distribution for females.

Trends in diagnosis-specific mortality for the aging population in Norway, 1966-1986.

For the older segment of the Norwegian population, sex, age at time of death, and time-period of death are important factors to consider when describing cause-specific mortality trends. Correspondence analysis was applied to mortality and provided plots which in a conceptually simple way demonstrated the complex relations between sex, age, time-periods and causes of death. Log-linear modelling was used to confirm the findings of the correspondence analyses. During the period of observation, the elderly, regardless of sex, have experienced greater changes in the most important causes of death, than the younger segments of the population. The main intention of this article is to improve the conceptual understanding of how important parameters are associated with trends in mortality rates for the major causes of death in Norway.

Childhood and adult milk consumption and risk of premenopausal breast cancer in a cohort of 48,844 women - the Norwegian women and cancer study.

Analyses of dairy consumption and breast cancer incidence have yielded conflicting results. In this prospective cohort study of 48,844 premenopausal Norwegian women, we examined the relationship between childhood and adult milk consumption and breast cancer incidence. During a mean follow-up time of 6.2 years, 317 incident cases of breast cancer were diagnosed. Information on childhood and adult milk consumption was obtained from frequency questions mailed to the participants in 1991-92. Milk consumption as a child was negatively associated with subsequent breast cancer among the youngest women (34-39 years) (p for trend = 0.001), but not among older ones (40-49 years). Adult milk consumption tended to be negatively related to breast cancer incidence (p for trend = 0.12) after adjustment for age, reproductive and hormonal factors, body mass index, education, physical activity, and alcohol consumption. Women drinking more than 3 glasses of milk per day had an incidence rate ratio of breast cancer of 0.56 (95% confidence interval 0.31-1.01) compared with women not drinking milk. Analyses according to type of milk consumed and milk fat consumption did not reveal any clear associations. A combination of childhood and adult milk consumption produced a clear negative trend in breast cancer incidence rate ratios with increasing milk consumption (p = 0.03).

Exposure misclassification: bias in category specific Poisson regression coefficients.

In epidemiologic studies of the association between exposure and disease, misclassification of exposure is common and known to induce bias in the effect estimates. The nature of the bias is difficult to foretell. For this purpose, we present a simple method to assess the bias in Poisson regression coefficients for a categorical exposure variable subject to misclassification. We derive expressions for the category specific coefficients from the regression on the error-prone exposure (naive coefficients) in terms of the coefficients from the regression on the true exposure (true coefficients). These expressions are similar for crude and adjusted models, if we assume that the covariates are measured without error and that it is independence between the misclassification probabilities and covariate values. We find that the bias in the naive coefficient for one category of the exposure variable depends on all true category specific coefficients weighted by misclassification probabilities. On the other hand, misclassification of an exposure variable does not induce bias in the estimates of the coefficients of the (perfectly measured) covariates. Similarities with linear regression models are pointed out. For selected scenarios of true exposure-disease associations and selected patterns of misclassification, we illustrate the inconsistency in naive Poisson regression coefficients and show that it can be difficult to intuitively characterize the nature of the bias. Both the magnitude and the direction of the bias may vary between categories of an exposure variable.

Body mass index and weight change attempts among adult women. The Norwegian Women and Cancer Study.

BACKGROUND: Based on concern about the widespread increase in being overweight and obesity along with a substantial demand for leanness, we wanted to estimate body mass index (BMI) and the prevalence of weight change attempts in a population-based sample of Norwegian women. Furthermore, we wanted to examine how weight loss attempts are related to BMI and to age, socioeconomic status, reproductive factors, lifestyle and diet. METHODS: A nationwide, cross-sectional study applying a mailed questionnaire was used. Out of a random sample of 20,000 women aged 45-69 years 10,249 women participated. RESULTS: Based on self-reported data, the mean BMI was 24.6 kg m-2 and 40% of the women had a BMI of > or = 25 kg m-2. More than 50% of the women were trying to lose weight and weight loss attempts were very strongly associated with BMI. Age, education, income, smoking status and perception of diet's importance to health were also significant predictors of weight loss attempts. The effect of age, education and income on weight loss attempts was modified by the level of BMI. Women trying to lose weight reported a different diet than those not trying to lose weight, irrespective of BMI. CONCLUSION: A large proportion of middle-aged women are trying to lose weight. BMI is predominant in explaining weight loss attempts. After adjusting for BMI, age, lifestyle and socioeconomic status also contribute to explaining weight loss attempts.

A causal model for physician utilization: analysis of Norwegian data.

This article contains a causal model for physician utilization in Norway. The model relates enabling factors, predisposing factors, and perceived illness to physician utilization in a linear structural equation model. Our aim has been to study the effect of variables other than perceived illness on physician utilization. The results of the analysis indicate that the number of disability days because of illness and psychologic well-being are almost exclusively the only important variables in the explanation of physician utilization in Norway.

On the problem of measuring the distance between distribution functions: analysis of hospitalization versus mortality.

The relationship between hospitalization, as a measure of morbidity, and mortality is examined. The difference between age at hospitalization in a general medical department and age at death in Oslo, Norway, is studied. The problem is transferred to the one of examining the difference between two cumulative distribution functions F and G. For this purpose, a quantile distance function based on the inverses of the distribution functions is applied. We give the natural estimate of the quantile distance function, and some asymptotic properties of the corresponding empirical process. For the particular situation where one of the distribution functions is known, a confidence band for the quantile distance function is derived. Applying these results, we show that there are reasons to believe that age at hospitalization and age at death are equally distributed, apart from a constant shift.