Long-term Continuous Recordings Research Articles

EPILAB: A software package for studies on the prediction of epileptic seizures

Abstract A Matlab ® -based software package, EPILAB, was developed for supporting researchers in performing studies on the prediction of epileptic seizures. It provides an intuitive and convenient graphical user interface. Fundamental concepts that are crucial for epileptic seizure prediction studies were implemented. This includes, for example, the development and statistical validation of prediction methodologies in long-term continuous recordings. Seizure prediction is usually based on electroencephalography (EEG) and electrocardiography (ECG) signals. EPILAB is able to process both EEG and ECG data stored in different formats. More than 35 time and frequency domain measures (features) can be extracted based on univariate and multivariate data analysis. These features can be post-processed and used for prediction purposes. The predictions may be conducted based on optimized thresholds or by applying classifications methods such as artificial neural networks, cellular neuronal networks, and support vector machines. EPILAB proved to be an efficient tool for seizure prediction, and aims to be a way to communicate, evaluate, and compare results and data among the seizure prediction community.

Watershed Sulfur Biogeochemistry: Shift from Atmospheric Deposition Dominance to Climatic Regulation

North American atmospheric S emissions peaked in the early 1970s followed by a dramatic decrease that resulted in marked declines in sulfate (SO₄²⁻)) concentrations in precipitation and many surface waters. These changes in S biogeochemistry have important implications with respect to the mobilization of toxic (Al(n⁺), H⁺) and nutrient (Ca²⁺, Mg²⁺, K⁺) cations and the acidification of watersheds. We used the continuous long-term record for watersheds 1, 3, 5, and 6 (37-44 years from 1965 through 2008) of SO₄²⁻ concentrations and fluxes at Hubbard Brook Experimental Forest in New Hampshire (U.S.) for evaluating S budgets. Analysis revealed that the annual discrepancies in the watershed S budgets (SO₄²⁻ flux in drainage waters minus total atmospheric S deposition) have become significantly (p < 0.001) more negative, indicating the increasing importance of the release of S from internal sources with time. Watershed wetness, as a function of log₁₀ annual water flux, was highly significant (p < 0.001) and explained 57% (n = 157) of the annual variation for the combined results from watersheds 1, 3, 5, and 6. The biogeochemical control of annual SO₄²⁻ export in streamwater of forested watersheds has shifted from atmospheric S deposition to climatic factors by affecting soil moisture.

Elaboration of equipment and methods of continuous recording of electric activity of clariid catfish (Clariidae, Siluriformes) in social and reproductive behavior

Equipment and methods of simultaneous continuous long-term recording of electric activity of clariid catfish (Clariidae) is elaborated. All electric organ discharges (EOD) in any position and orientation of free swimming fish are fixed by simultaneous recording of electric voltage with two mutually perpendicular pairs of electrodes. Light-emitting diodes controlled by a microprocessor allow for the possibility to observe the moments of discharge emission both in real time and during scanning of videorecords. According to its parameters, the created equipment corresponds to characteristics of EOD of clariid catfish, performs primary treatment of signals, and stores in its inner flash memory all discharges recorded in a prolonged experiment (duration up to several days, number of EOD up to several tens of thousands). Various examples of EOD are presented recorded by means of the elaborated methods in clariid catfish (C. macrocephalus, C. batrachus, C. fuscus, and hybrids C. gariepinus × C. macrocephalus) when they manifested aggressive-defensive and spawning behavior. The procedure of treatment of EOD is suggested, including that of special bursts of EODs generated by females in pairing.

The circadian rhythms of valve movements in the mussel Mytilus galloprovincialis

The long-term (10–30 day) continuous recording of valve movements in the mussel Mytilus galloprovincialis was carried out in the laboratory under nearly natural conditions. Fourier analysis revealed the circadian (close to the diurnal) rhythm of the valve activity, the phase of which is readily shifted by a shift in the beginning of the daytime, since the light regime is one of the main factors determining the circadian rhythm. The circadian rhythm was manifested in the daily dynamics of mussel valve activity: in the daytime, mussels hold their valves closed more often than at night. This behavior may be a protective response, namely the “shadow reflex”: mussels close their valves upon a sudden decrease in illumination, thus protecting themselves from possible predators. Circadian activity can mask a mussel’s response to environmental pollution; therefore, regular valve closure should be taken into account in early warning systems such as “MusselMonitor®” with a correction for the season of the year, time of day, and other factors.

Long-range underwater vocalizations of the crabeater seal (Lobodon carcinophaga)

This study provides a comprehensive description of the acoustic characteristics of the predominant long-range underwater vocalizations of the crabeater seal, Lobodon carcinophaga, derived from stationary and continuous long-term recordings obtained in the Southern Ocean in 2007. Visual screening of data recorded between 1 October and 15 December 2007 indicates that the principal period of vocal activity of the crabeater seal is the latter part of October and all of November, coinciding with the breeding season of this species. Two call types were identified during this period: the low moan call, which has been described in previous studies and the high moan call, a call type newly described here. Out of 17 052 manually extracted crabeater seal calls, high-quality recordings of 152 low moans and 86 high moans with a signal-to-noise ratio exceeding 15 dB were selected and call-specific acoustic features were determined. While the mean duration of the two call types was comparable ( approximately 2.5 s), the high moan occurred at notably higher frequencies (1000-4900 Hz) than the low moan (260-2500 Hz). This study provides baseline information necessary to develop automated detection algorithms to facilitate systematic screening of extended data sets for crabeater seal vocalizations.

Application of data mining on partial discharge part I: predictive modelling classification

Innovations in computer technology have made possible continuous on-line monitoring of partial discharge (PD) activities. The power industry aims to assess the condition of power system equipment through on-line monitoring of PD activities. This involves long-term continuous data recording and it is very difficult to extract useful information from such a large amount of raw data, particularly if it is done manually. Instead, data mining can be applied in solving this problem. Data mining can be categorized into predictive modelling and descriptive modelling. In this paper, work was mainly focused on predictive data mining, which is classification of PD. The back propagation neural network (BPN), self-organizing map (SOM) and support vector machine (SVM) were used for classification and compared. Results indicate SVM is the best method in terms of classification accuracy and processing speed.

Visualization and modelling of STLmax topographic brain activity maps

This paper evaluates the descriptive power of brain topography based on a dynamical parameter, the Short-Term Maximum Lyapunov Exponent (STLmax), estimated from EEG, for finding out a relationship of STLmax spatial distribution with the onset zone and with the mechanisms leading to epileptic seizures. Our preliminary work showed that visual assessment of STLmax topography exhibited a link with the location of seizure onset zone. The objective of the present work is to model the spatial distribution of STLmax in order to automatically extract these features from the maps. One-hour preictal segments from four long-term continuous EEG recordings (two scalp and two intracranial) were processed and the corresponding STLmax profiles were estimated. The spatial STLmax maps were modelled by a combination of two Gaussians functions. The parameters of the fitted model allow automatic extraction of quantitative information about the spatial distribution of STLmax: the EEG signal recorded from the brain region where seizures originate exhibited low-STLmax levels, long before the seizure onset, in 3 out of 4 patients (1 out of 2 of scalp patients and 2 out of 2 in intracranial patients). Topographic maps extracted directly from the EEG power did not provide useful information about the location, therefore we conclude that the analysis so far carried out suggests the possibility of using a model of STLmax topography as a tool for monitoring the evolution of epileptic brain dynamics. In the future, a more elaborate approach will be investigated in order to improve the specificity of the method.

Modeling the spontaneous activity in suprachiasmatic nucleus neurons: Role of cation single channels

A population of interconnected neurons of the mammalian suprachiasmatic nuclei (SCN) controls circadian rhythms in physiological functions. In turn, a circadian rhythm of individual neurons is driven by intracellular processes, which via activation of specific membrane channels, produce circadian modulation of electrical firing rate. Yet the membrane target(s) of the cellular clock have remained enigmatic. Previously, subthreshold voltage-dependent cation (SVC) channels have been proposed as the membrane target of the cellular clock responsible for circadian modulation of the firing rate in SCN neurons. We tested this hypothesis with computational modeling based on experimental results from on-cell recording of SVC channel openings in acutely isolated SCN neurons and long-term continuous recording of activity from dispersed SCN neurons in a multielectrode array dish (MED). The model reproduced the circadian behavior if the number of SVC channels or their kinetics were modulated in accordance with protein concentration in a model of the intracellular clock (Scheper et al., 1999. J. Neurosci. 19, 40–47). Such modulation changed the average firing rate of the model neuron from zero (“subjective-night” silence) up to 18 Hz (“subjective-day” peak). Furthermore, the variability of interspike intervals (ISI) and the circadian pattern of firing rate (i.e. silence-to-activity ratio and shape of circadian peaks) are in reasonable agreement with experimental data obtained in dispersed SCN neurons in MED. These results suggest that the variability of ISI in intact SCN neurons is mostly due to stochastic single-channel openings, and that the circadian pattern of the firing rate is specified by threshold properties of dependence of the spontaneous firing rate on the number of single channels ( R– N relationship). This plausible mathematical modeling supports the hypothesis that SVC channels could be a critical element in circadian modulation of firing rate in SCN neurons.

The daily habitual in vivo strain history of a non-weight-bearing bone

Daily mechanical loading strongly influences the architecture and composition of bone tissue. Throughout the day, the amplitudes, rates, frequencies, and the dispersion over time of these loads vary. Nevertheless, most experimental and descriptive studies on the aforementioned relationship consider only cyclic loading and, in addition, focus on weight-bearing bones. A more complete assessment of the daily loading of bone might lead to a better understanding of the natural everyday stimulus for bone maintenance or adaptive responses. In the present study, we measured the daily habitual strain history of the non-weight-bearing mandible bone in the rabbit. Long-term continuous strain recordings were made using an implantable telemetry device able to read out bone-bonded strain gauges. The lateral surface of the rabbit mandibular corpus was chosen as the bone surface of interest. During the recordings, which lasted up to 33 h, the rabbits ( N = 7) were able to move unrestrictedly in their cages, performing their habitual behaviours. Analysis of the recordings revealed that the measured bone surface was subjected to 2.9 (± 1.4) × 10 3 strain events per hour of which 1.8 (± 1.0) × 10 3 had amplitudes ≤ 10 microstrains (μɛ). Larger strain amplitudes occurred less often and principal strains fell within the range of −517 (± 118) μɛ to 298 (± 81) μɛ. Strain rates never exceeded 10,000 μɛ/s and only 8.9% (± 7.2%) of the habitual strain rates were higher than 1000 μɛ/s. Strain frequency spectra displayed clear peaks at 4–5 and 9 Hz. The wirelessly recorded daily strain history of the rabbit mandible featured peak strain amplitudes resembling those of other mammalian mandibles, but much smaller than those found in many long-bone strain measurements.

Decline in whale shark size and abundance at Ningaloo Reef over the past decade: The world’s largest fish is getting smaller

Over-exploitation of whale sharks threatens the future of these wide-ranging pelagic fish. A long-term continuous record (4436 sightings) from a large aggregation (300–500 resident individuals) of whale sharks at Ningaloo Reef, Western Australia shows that mean shark length declined linearly by nearly 2.0 m and relative abundance measured from ecotourism sightings (corrected for variation in search effort and environmental stochasticity) has fallen by approximately 40% over the last decade. This population-level result confirms previous predictions of population decline based on projection models parameterised using mark-recapture estimates of survival. The majority of these changes are driven by reductions in the number of large individuals in the population. Phenomenological time series models support a deterministic (extrinsic) decline in large females, although there was some evidence for density dependence in large males. These reductions have occurred despite the total protection of whale sharks in Australian waters. As this species is highly migratory, the rapid change in population composition over a decade (<1 whale shark generation) supports the hypothesis of unsustainable mortality in other parts of their range (e.g., overfishing), rather than the alternative of long-term abiotic or biotic shifts in the environment. As such, effective conservation of whale sharks will require international protection, and collaborative tagging studies to identify and monitor migratory pathways.

On the role of calcium and potassium currents in circadian modulation of firing rate in rat suprachiasmatic nucleus neurons: Multielectrode dish analysis

The master circadian clock of mammals in the suprachiasmatic nucleus (SCN) of the hypothalamus entrains to a 24-h daily light–dark cycle and regulates circadian rhythms. The SCN is composed of multiple neurons with cell autonomous clocks exhibiting robust firing rhythms with a high firing rate during the subjective day. The membrane target(s) of the cellular clock responsible for circadian modulation of the firing rate in SCN neurons still remain unclear. Previously, L-type Ca 2+ currents and fast delayed rectifier (FDR) K + currents have been suggested to contribute directly to circadian modulation of electrical activity. Using long-term continuous recording of activity from dispersed rat SCN neurons in multielectrode dish and ionic channel blockers, we tested these hypotheses. Neither an L-type Ca 2+ current blocker (20 μM of nifedipine for 2 days) nor an FDR current blocker (500 μM of 4-aminopyridine (4-AP) for 4 days) suppressed the circadian modulation of firing rate. A specific blocker of Na + persistent current (5 μM of riluzole for 1 day followed by 10 μM during the next day) reversibly suppressed firing activity in a dose-dependent manner. These data indicate that neither nifedipine-sensitive Ca 2+ current(s) nor 4-AP-sensitive K + current(s) are key membrane targets for circadian modulation of electrical firing rate in SCN neurons.

Prediction of epileptic seizures and validation of prediction performances as part of the European "EPILEPSIAE" project

Event Abstract Back to Event Prediction of epileptic seizures and validation of prediction performances as part of the European "EPILEPSIAE" project Hinnerk Feldwisch1*, Matthias Ihle2, Michael Jachan1, Jens Timmer1, Andreas Schulze-Bonhage2 and Björn Schelter1 1 University of Freiburg, Germany 2 University Hospital, Germany In recent years, several methods for the prediction of epileptic seizures have been proposed, which are based on recordings of surface and invasive electroencephalogram (EEG). By application of linear or nonlinear measures, pre-seizure changes have been reported. Here, we present a prediction scheme which is based on the mean phase coherence and the dynamical similarity index. Additionally, we compare different approaches for statistical validation of prediction performances. Concerning the development and assessment of the predictability of epileptic seizures, the evaluation of continuous and long-term neurophysiological recordings of epilepsy patients is necessary. The project “EPILEPSIAE” funded by the European Union was set up to compile an extensive database of EEG recordings of 250 epileptic patients in total within the project duration of three years. Based on software infrastructure for both raw data and metadata containing information about the recordings and patients, seizure prediction methods will be developed and assessed. We applied and evaluated two predictive measures to the data of eight patients with invasive EEG recordings. The univariate dynamical similarity index measures the similarity of the dynamics of a reference window of EEG to the dynamics of a sliding window of EEG, whereas the bivariate mean phase coherence is a measure for phase synchronization of two channels of the EEG. For two/one of the patients, significant prediction performances can be observed by the dynamical similarity index/mean phase coherence. As a means to increase seizure prediction performance we tested whether or not two different kinds of combination of seizure prediction methods yield superior prediction results, which is the case for about half of the patients. On average for all patients, prediction sensitivities of 52.8 % can be observed for a maximum false prediction rate of 3.6 false alarms per day. Conclusions: The presented prediction methods are applied to a database of continuous long-term recordings of the invasive EEG of epilepsy patients. For two different measures, significant predictive performances can be observed for a part of the patients, which can be improved by a combination of both measures. Further necessary studies of seizure predictability will be enabled by the currently evolving, extensive database “EPILEPSIAE” of neurophysiological recordings and associated meta-information. Acknowledgements: This work was supported by the European Union (Grant 211713), the German Federal Ministry of Education and Research (BMBF grant 01GQ0420) and the German Science Foundation (Ti 315/2-2; Sonderforschungsbereich-TR3; He1949/1-1). Conference: Neuroinformatics 2008, Stockholm, Sweden, 7 Sep - 9 Sep, 2008. Presentation Type: Poster Presentation Topic: Clinical Neuroinformatics Citation: Feldwisch H, Ihle M, Jachan M, Timmer J, Schulze-Bonhage A and Schelter B (2008). Prediction of epileptic seizures and validation of prediction performances as part of the European "EPILEPSIAE" project. Front. Neuroinform. Conference Abstract: Neuroinformatics 2008. doi: 10.3389/conf.neuro.11.2008.01.113 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 28 Jul 2008; Published Online: 28 Jul 2008. * Correspondence: Hinnerk Feldwisch, University of Freiburg, Freiburg, Germany, hinnerk.feldwisch@bccn.uni-freiburg.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Hinnerk Feldwisch Matthias Ihle Michael Jachan Jens Timmer Andreas Schulze-Bonhage Björn Schelter Google Hinnerk Feldwisch Matthias Ihle Michael Jachan Jens Timmer Andreas Schulze-Bonhage Björn Schelter Google Scholar Hinnerk Feldwisch Matthias Ihle Michael Jachan Jens Timmer Andreas Schulze-Bonhage Björn Schelter PubMed Hinnerk Feldwisch Matthias Ihle Michael Jachan Jens Timmer Andreas Schulze-Bonhage Björn Schelter Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Spontaneous stellate ganglion nerve activity and ventricular arrhythmia in a canine model of sudden death

Little information is available on the temporal relationship between instantaneous sympathetic nerve activity and ventricular arrhythmia in ambulatory animals. The purpose of this study was to determine if increased sympathetic nerve activity precedes the onset of ventricular arrhythmia. Simultaneous continuous long-term recording of left stellate ganglion (LSG) nerve activity and electrocardiography was performed in eight dogs with nerve growth factor infusion to the LSG, atrioventricular block, and myocardial infarction (experimental group) and in six normal dogs (control group). LSG nerve activity included low-amplitude burst discharge activity (LABDA) and high-amplitude spike discharge activity (HASDA). Both LABDA and HASDA accelerated heart rate. In the experimental group, most ventricular tachycardia (86.3%) and sudden cardiac death were preceded within 15 seconds by either LABDA or HASDA. The closer to onset of ventricular tachycardia, the higher the nerve activity. The majority of HASDA was followed immediately by either ventricular arrhythmia (21%) or QRS morphology changes (65%). HASDA occurred in a circadian pattern. HASDA occurred twice as often in the experimental group than in the control group. Electrical stimulation of LSG increased transmural heterogeneity of repolarization (Tpeak-end intervals) and induced either ventricular tachycardia or fibrillation in the experimental group but not in the control group. Immunohistochemical studies revealed increased synaptogenesis and nerve sprouting in the LSG in the experimental group. Two distinct types of LSG nerve activity (HASDA and LABDA) are present in the LSG of ambulatory dogs. The majority of malignant ventricular arrhythmias are preceded by either HASDA or LABDA, with HASDA particularly arrhythmogenic.

Variability of internally generated turbulence in an estuary, from 100 days of continuous observations

We present detailed observations of internally generated turbulence in a sheared, stratified natural flow, as well as an analysis of the external factors leading to its generation and temporal variability. Multi-month time series of vertical profiles of velocity, acoustic backscatter (0.5 Hz), and turbulence parameters were collected with two moored acoustic Doppler current profilers (ADCPs) in the Hudson River estuary, and estuary-long transects of water density were collected 30 times. ADCP backscatter is used for visualization of coherent turbulent structures and evaluation of surface wave biases to the turbulence measurements. Benefits of the continuous long-term turbulence record include our capturing: (1) the seasonality of turbulence due to changing riverflow, (2) hysteresis in stratification and turbulence over the fortnightly cycle of tidal range, and (3) intermittent events such as breaking internal waves. Internal mixing layers (IMLs) are defined as turbulent regions above the logarithmic velocity layer, and the bottom boundary layer (BBL) is defined as the continuously turbulent range of heights above the bed. A cross-correlation analysis reveals how IML and BBL turbulence vary with stratification and external forcing from tidal range, river flow, and winds. Turbulence in both layers is maximal at spring tide and minimal when most stratified, with one exception—IML turbulence at a site with changing channel depth and width is maximal at times of maximum stratification and freshwater input.

Developmental Exposure to Methylmercury Alters Learning and Induces Depression-like Behavior in Male Mice

To investigate the long-term effects of developmental exposure to methylmercury (MeHg), pregnant mice were exposed to at 0.5 mg MeHg/kg/day via drinking water from gestational day 7 until day 7 after delivery. The behavior of offspring was monitored at 5-15 and 26-36 weeks of age using an automated system (IntelliCage) designed for continuous long-term recording of the home cage behavior in social groups and complex analysis of basic activities and learning. In addition, spontaneous locomotion, motor coordination on the accelerating rotarod, spatial learning in Morris water maze, and depression-like behavior in forced swimming test were also studied. The analysis of behavior performed in the IntelliCage without social deprivation occurred to be more sensitive in detecting alterations in activity and learning paradigms. We found normal motor function but decreased exploratory activity in MeHg-exposed male mice, especially at young age. Learning disturbances observed in MeHg-exposed male animals suggest reference memory impairment. Interestingly, the forced swimming test revealed a predisposition to depressive-like behavior in the MeHg-exposed male offspring. This study provides novel evidence that the developmental exposure to MeHg can affect not only cognitive functions but also motivation-driven behaviors.

Autonomic nerve activity and atrial fibrillation

This review focuses on the importance of autonomic nervous system (ANS) activity in the induction of paroxysmal atrial fibrillation (PAF). Clinical studies suggest that both sympathetic and parasympathetic nervous systems are important in mediating PAF. Consistent with that hypothesis, heart rate variability analyses showed that sympathovagal imbalance is present before the onset of PAF episodes. The importance of the ANS in PAF is further supported by animal experiments and recent clinical studies showing that vagal denervation enhances the efficacy of circumferential pulmonary vein ablation in preventing AF recurrence. In vitro studies show that ANS activation facilitates early afterdepolarization and triggered activity by simultaneously prolonging the intracellular calcium (Ca(i)) transient (sympathetic effect) and shortening the action potential duration (parasympathetic effect). By simultaneously mapping the membrane potential and Ca(i) transient in canine pulmonary vein during sympathetic stimulation, we demonstrated that spontaneous (voltage-independent) sarcoplasmic reticulum calcium release underlies the mechanisms of focal discharges. We developed and studied canine models of PAF induced by electrical, structural, and neural remodeling. We also have developed methods for long-term continuous recording of sympathetic and vagal nerve activity in ambulatory dogs. Preliminary results show that simultaneous sympathovagal discharges precede the onset of PAF in these dogs. ANS activity and Ca(i) transient dynamics are important in the development of PAF. These studies suggest that new methods or drugs aimed at modification of cardiac ANS activity may lead to new opportunities for AF control.

YI1-3: Spontaneous stellate ganglion nerve activity and ventricular arrhythmia in a canine model of sudden death

The relationships between sympathetic nerve activity and the initiation of spontaneous paroxysmal ventricular tachycardia (VT) and sudden cardiac death (SCD) have not been tested with direct sympathetic nerve recording. Using implanted radiotransmitters, we performed long-term simultaneous continuous recording of left stellate ganglion nerve activity (SGNA) and surface ECG in 14 ambulatory dogs, including 8 dogs (SCD model group) with myocardial infarction, atrioventricular block and cardiac sympathetic hyperinnervation induced by nerve growth factor infusion to left stellate ganglion (SG) and 6 normal controls.

The use of radiotelemetry to evaluate electrographic seizures in rats with kainate-induced epilepsy

Temporal lobe epilepsy in humans is a chronic condition with a highly variable temporal evolution. Animal models of this disorder have been developed to recapitulate many of the characteristics seen in humans with temporal lobe epilepsy. These animal models generate chronic spontaneous electrographic and motor seizures with a progressive increase in frequency over many months. In order to understand the underlying cellular and molecular mechanisms driving epileptogenesis, a practical means for accurately assessing seizure progression over this extended time period must be devised. In this report, we describe the use of a three-channel radiotelemetry system to record spontaneous electrographic interictal “spikes” and seizure activity from the cortical surface and the two hippocampi. This approach has allowed continuous recording before, during, and several months after kainate-induced status epilepticus. The important advantages of this approach are the potential for long-term continuous electrographic recording with comparatively unrestricted behavior; the disadvantages include increased cost, surgical difficulty and lower frequency-response in the recordings.

High‐precision, automated stable isotope analysis of atmospheric methane and carbon dioxide using continuous‐flow isotope‐ratio mass spectrometry

Small-scale developments have been made to an off-the-shelf continuous-flow gas chromatography/isotope-ratio mass spectrometry (CF-GC/IRMS) system to allow high-precision isotopic analysis of methane (CH(4)) and carbon dioxide (CO(2)) at ambient concentrations. The repeatability (1sigma) obtainable with this system is 0.05 per thousand for delta(13)C of CH(4), 0.03 per thousand for delta(13)C of CO(2), and 0.05 per thousand for delta(18)O of CO(2) for ten consecutive analyses of a standard tank. An automated inlet system, which allows diurnal studies of CO(2) and CH(4) isotopes, is also described. The improved precision for CH(4) analysis was achieved with the use of a palladium powder on quartz wool catalyst in the combustion furnace, which increased the efficiency of oxidation of CH(4) to CO(2). The automated inlet further improved the precision for both CH(4) and CO(2) analysis by keeping the routine constant. The method described provides a fast turn-around in samples, with accurate, reproducible results, and would allow a long-term continuous record of CH(4) or CO(2) isotopes at a site to be made, providing information about changing sources of the gases both seasonally and interannually.

Long-term spinal reflex studies in awake behaving mice

The increasing availability of genetic variants of mice has facilitated studies of the roles of specific molecules in specific behaviors. The contributions of such studies could be strengthened and extended by correlation with detailed information on the patterns of motor commands throughout the course of specific behaviors in freely moving animals. Previously reported methodologies for long-term recording of electromyographic activity (EMG) in mice using implanted electrodes were designed for intermittent, but not continuous operation. This report describes the fabrication, implantation, and utilization of fine wire electrodes for continuous long-term recordings of spontaneous and nerve-evoked EMG in mice. Six mice were implanted with a tibial nerve cuff electrode and EMG electrodes in soleus and gastrocnemius muscles. Wires exited through a skin button and traveled through an armored cable to an electrical commutator. In mice implanted for 59–144 days, ongoing EMG was monitored continuously (i.e., 24 h/day, 7 days/week) by computer for 18–92 days (total intermittent recording for 25–130 days). When the ongoing EMG criteria were met, the computer applied the nerve stimulus, recorded the evoked EMG response, and determined the size of the M-response (MR) and the H-reflex (HR). It continually adjusted stimulation intensity to maintain a stable MR size. Stable recordings of ongoing EMG, MR, and HR were obtained typically 3 weeks after implantation. This study demonstrates the feasibility of long-term continuous EMG recordings in mice for addressing a variety of neurophysiological and behavioral issues.