Multichannel-recordings and real-time current source density (CSD) analysis in the central-nervous system of insects

The real-time three-dimensial CSD-analysis was modified for application to the acoustic synaptic regions (acoustic neuropiles) in the migratory locust,Locusta migratoria. The advantages compared with single cell recordings and field potential analysis are discussed. An appropriate conductivity measurement and processing is adapted to this problem. Influences of errors are estimated. Application to the frontal acoustic neuropile of the metathoracic ganglion ofLocusta migratoria leads to first results. A tonotopic distribution of the projection areas of the acoustic receptor groups could be separated.Supported by the Deutsche Forschungsgemeinschaft as part of the program Neurale Mechanismen des Verhaltens (Ka 498/2)     

Mechanics of the transduction of sound in the tympanal organ of adults and larvae of locusts

Summary The mechanical transmission of sound in the tympanal organ of adults and 5th instar larvae ofLocusta migratoria andSchistocerca gregaria has been investigated by means of stroboscopic measurements within a frequency range from 1–20 kHz.Frequency dependent spatial distributions of amplitudes and phases of oscillation on the tympanal membrane and the Müller's organ could be demonstrated. Cuticular structures on the membrane may act as a lever arm (e.g. elevated process) and cause a transformation of the (unidimensional) membrane motion into components of displacements in the Müller's organ perpendicular, as well as even parallel, to the membrane.Sites of maximum relative displacements at distinct frequencies are found to be correlated to the course of the dendrites of the acoustic receptor cells. Differences in morphology of the tympanal organ between the two species as well as between adults and larvae always correspond to differences in the mechanical properties (resonances etc.). Consequently, differences or changes in the neurophysiological response characteristics of the different receptor cells have been found.Based upon these findings a correlation between the anatomical and physiological classification of the receptor cell groups is presented.Abbreviations T1, T2, T3, T6, T7 reference points on the tympanal membrane - M1, M4 reference points on the ganglion of the Müller's organ - K1, K2 reference points on the elevated process     

Linear-no-threshold is a radiation-protection standard rather than a mechanistic effect model

The linear-no-threshold (LNT) controversy covers much more than the mere discussion whether or not “the LNT hypothesis is valid”. It is shown that one cannot expect to find only one or even the only one dose–effect relationship. Each element within the biological reaction chain that is affected by ionizing radiation contributes in a specific way to the final biological endpoint of interest. The resulting dose–response relationship represents the superposition of all these effects. Till now there is neither a closed and clear picture of the entirety of radiation action for doses below some 10 mSv, nor does clear epidemiological evidence exist for an increase of risk for stochastic effects, in this dose range. On the other hand, radiation protection demands for quantitative risk estimates as well as for practicable dose concepts. In this respect, the LNT concept is preferred against any alternative concept. However, the LNT concept does not necessarily mean that the mechanism of cancer induction is intrinsically linear. It could hold even if the underlying multi-step mechanisms act in a non-linear way. In this case it would express a certain “attenuation” of non-linearities. Favouring LNT against threshold-, hyper-, or sub-linear models for radiation-protection purposes on the one hand, but preferring one of these models (e.g. for a specific effect) because of biological considerations for scientific purposes on the other hand, does not mean a contradiction.     

Dose limits for occupational exposure to ionising radiation and genotoxic carcinogens: a German perspective

This paper summarises the view of the German Commission on Radiological Protection (“Strahlenschutzkommission”, SSK) on the rationale behind the currently valid dose limits and dose constraints for workers recommended by the International Commission on Radiological Protection (ICRP). The paper includes a discussion of the reasoning behind current dose limits followed by a discussion of the detriment used by ICRP as a measure for stochastic health effects. Studies on radiation-induced cancer are reviewed because this endpoint represents the most important contribution to detriment. Recent findings on radiation-induced circulatory disease that are currently not included in detriment calculation are also reviewed. It appeared that for detriment calculations the contribution of circulatory diseases plays only a secondary role, although the uncertainties involved in their risk estimates are considerable. These discussions are complemented by a review of the procedures currently in use in Germany, or in discussion elsewhere, to define limits for genotoxic carcinogens. To put these concepts in perspective, actual occupational radiation exposures are exemplified with data from Germany, for the year 2012, and regulations in Germany are compared to the recommendations issued by ICRP. Conclusions include, among others, considerations on radiation protection concepts currently in use and recommendations of the SSK on the limitation of annual effective dose and effective dose cumulated over a whole working life.     

Do we really need the “detriment” for radiation protection?

The purpose of the ICRP detriment concept is to enable a quantitative comparison of stochastic radiation damage for the various organs. For this purpose, the organ-specific nominal risk coefficients are weighted with a function that is intended to express the amount of damage or, respectively, the severity of a disease. This function incorporates a variety of variables that do not depend on radiation parameters, but on characteristics of the disease itself. The question is raised as to whether the rather subtle way of defining the amount of damage is necessary for radiation protection purposes and whether a much simpler relationship can serve for this purpose as well or even better.

     

Non-linear analysis of the transmission of signals in the auditory system of the migratory locust Locusta migratorta

Investigations on the auditory system of the migratory locust using the system theory (i.e. the white-noise method) to determine the transfer characteristics of single auditory neurons are presented for the first time. The transfer characteristics of receptor cells and ascending ventral-cord neurons are evaluated with respect to a special test signal (modulation signal). The test signal determines the temporal course of the actual sound pressure of the stimulus. The use of the white-noise method has the advantage of applying only one particular test signal instead of a very large number of stimuli with varying amplitude and duration. The computational burden is within a reasonable range. The receptor cells in general show a good linear and quadratic coupling between the test signal and their responses whereas the ascending ventral-cord neurons normally do not. The responses of the receptors in contrast to the central auditory neurons depend only on the difference between the actual threshold and the sound-pressure level of the stimulus and not on the carrier frequency of the stimulus signal.Supported by the Deutsche Forschungsgenmeinschaft as part of the program Codierungsleistung der Insektenhörbahn Ka 498/3-1     

Temporal and regional trends of cancer mortality in West Germany

Age-specific and cumulative mortality rates are presented for different cancer sites from 1970 until 1988 for the 11 individual federal states of West Germany (FRG). Sex- and age-specific evaluations are performed and tempora and regional trends in mortality from different cancer sites are revealed. In the FRG there is no comprehensive cancer registry with national coverage for recording cancer patients of all ages (nationwide incidence rates are available only for childhood cancers). Therefore, in view of the lack of a nationwide cancer registry the importance of long-term cancer mortality studies for health policy is emphasized. Methodological aspects of certification regulations and classification of cancer sites are discussed.     

The variance-covariance method: Microdosimetry in time-varying low dose-rate radiation fields

Summary The variance-covariance method is employed at low doses and in radiation fields of low dose rates from an²⁴¹Am (4 nGy/s) and a⁹⁰Sr (300 nGy/s) source. The preliminary applications and results illustrate some of the potential of the method, and show that the dose average of lineal energy or energy imparted can be determined over a wide range of doses and dose rates. The dose averages obtained with the variance-covariance method in time-varying fields, for which the conventional variance method is not suitable, agree well with results obtained under the condition of constant dose rate. The results are compared to data obtained in terms of the conventional single-event measurements. The method has evident advantages, such as facility and speed of measurement.