Corticospinal output and loss of force during motor fatigue

The objective of this study was to analyze central motor output changes in relation to contraction force during motor fatigue. The triple stimulation technique (TST, Magistris et al. in Brain 121(Pt 3):437-450, 1998) was used to quantify a central conduction index (CCI=amplitude ratio of central conduction response and peripheral nerve response, obtained simultaneously by the TST). The CCI removes effects of peripheral fatigue from the quantification. It allows a quantification of the percentage of the entire target muscle motor unit pool driven to discharge by a transcranial magnetic stimulus. Subjects (n=23) performed repetitive maximal voluntary contractions (MVC) of abductor digiti minimi (duration 1s, frequency 0.5Hz) during 2min. TST recordings were obtained every 15s, using stimulation intensities sufficient to stimulate all cortical motor neurons (MNs) leading to the target muscle, and during voluntary contractions of 20% of the MVC to facilitate the responses. TST was also repetitively recorded during recovery. This basic exercise protocol was modified in a number of experiments to further characterize influences on CCI of motor fatigue (4min exercise at 50% MVC; delayed fatigue recovery during local hemostasis, "stimulated exercise” by 20Hz trains of 1s duration at 0.5Hz during 2min). In addition, the cortical silent period was measured during the basic exercise protocol. Force fatigued to approximately 40% of MVC in all experiments and in all subjects. In all subjects, CCI decreased during exercise, but this decrease varied markedly between subjects. On average, CCI reductions preceded force reductions during exercise, and CCI recovery preceded force recovery. Exercising at 50% for 4min reduced muscle force more markedly than CCI. Hemostasis induced by a cuff delayed muscle force recovery, but not CCI recovery. Stimulated exercise reduced force markedly, but CCI decreased only marginally. Summarized, force reduction and reduction of the CCI related poorly quantitatively and in time, and voluntary drive was particularly critical to reduce the CCI. The fatigue induced reduction of CCI may result from a central inhibitory phenomenon. Voluntary muscle activation is critical for the CCI reduction, suggesting a primarily supraspinal mechanis

Novas ocorrências na formação Rio do Rasto, permiano superior, estado do Paraná

Up to several years ago very little was known on the Late Permian Floras in Brazilian Gondwana. This paper is an account of the recent discoveries of eight news localities having the youngest known Glossopteris assemblages in South America. These localities occur along a band about 10 km long in southern Paraná State, Brazil. The preliminary list of fossils includes Glossopteris augustifolia, G. browniana, ?G. stricta, Sphenophyllum cf. speciosum, Paracalamites australis, PDizeugotheca as well as precopterid remains, stems, seeds and conchostracean shells

Glossopterideas de fluviópolis (permiano superior) no sul do Estado do Parana

This paper describes the Glossopteris species of a compact carbonaceous siltstone of the Upper Permian Serra Alta (or Terezina?) Formation (Paraná Basin), cropping out along the right margin of the Iguacu River, néar Fluviópolis, State of Parana, southern Brazil. The study of over 100 specimens related to the genus Glossopteris showed that they predominantly are of two possibly new species. However, because the small number of specimens with well preserved venation does not constitute an adequate basis for the creation of new species, the specimens are here referred to Glossopteris cf. G. occidentalis and Glossopteris cf. G. angustifoliaO presente trabalho descreveve as glossopterídeas procedentes de um afloramento de siltitos calcíferos compactos, provavelmente pertencentes à Formação Serra Alta, e situado à margem direita do Rio Iguaçu, próximo a Fluviópolis, no Estado do Paraná. Foram coletadas mais de 100 amostras de glossopterídeas que aparecem como finas películas carbonosas, já sem estrutura ou preservação de cutícula. Após a retirada das películas, observam-se impressões corn qualidade variável. São descritas duas formas: uma apresentando uma nervura mediana bastante larga, estriada lon-gitudinalmente e bem marcada. As nervuras secundárias emergem em ângulo bastante agudo, sofrem dicotomias e anastomoses próximo da nervura mediana e se encurvam abruptamente alcançanda a margem em ângulos de cerca de 80º. Apresentam maior semelhança com G. occidentalis da qual diferem, sobretudo, por apresentarem tamanho médio bem menor dos espécimes. Um segundo grupo de formas, representado principalmente pela porção médio-apical do limbo foliar, foi determinado como Glossopteris cf. G. angustifoli

Licófitas paleozóicas do Chile

Impressões caulinares de licófitas da Formação Arrayan, do Neopaleozóico da Cordilheira Chilena são aqui estudadas. Seu caráter fragmentário e sua má preservação não permitem uma identificação genérica segura. Entretanto foram reconhecidos 5 tipos básicos de cicatrizes os quais apresentam relações possíveis com Haplostigma Seward, Cyclostigma pacífica Jongmans, Bergeria Presl e mais distantemente Protolepidodendron e Sigillaria do tipo Eusigillaria. São feitas algumas reflexões em relação a uma possível idade D superior a C inferior

Sedimentological evidence for pronounced glacial‐interglacial climate fluctuations in NE Tibet in the latest Pliocene to early Pleistocene

The intensification of Northern Hemisphere glaciation (iNHG) and uplift of the Tibetan Plateau have been argued to be among the main drivers of climate change in midlatitude Central Asia during the Pliocene/Pleistocene. While most proxy records that support this hypothesis are from regions outside the Tibetan Plateau (such as from the Chinese Loess Plateau), detailed paleoclimatic information for the plateau itself during that time has yet remained elusive. Here we present a temporally highly resolved (~500 years) sedimentological record from the Qaidam Basin situated on the northeastern Tibetan Plateau that shows pronounced glacial‐interglacial climate variability during the interval from 2.7 to 2.1 Ma. Glacial (interglacial) intervals are generally characterized by coarser (finer) grain size, minima (maxima) in organic matter content, and maxima (minima) in carbonate content. Comparison of our results with Earth's orbital parameters and proxy records from the Chinese Loess Plateau suggests that the observed climate fluctuations were mainly driven by changes in the Siberian High/East Asian winter monsoon system as a response to the iNHG. They are further proposed to be enhanced by the topography of the Tibetan Plateau and its impact on the position and intensity of the westerlies

Covert Reorganization of Implicit Task Representations by Slow Wave Sleep

There is evidence that slow wave sleep (SWS) promotes the consolidation of memories that are subserved by mediotemporal- and hippocampo-cortical neural networks. In contrast to implicit memories, explicit memories are accompanied by conscious (attentive and controlled) processing. Awareness at pre-sleep encoding has been recognized as critical for the off-line memory consolidation. The present study elucidated the role of task-dependent cortical activation guided by attentional control at pre-sleep encoding for the consolidation of hippocampus-dependent memories during sleep.A task with a hidden regularity was used (Number Reduction Task, NRT), in which the responses that can be implicitly predicted by the hidden regularity activate hippocampo-cortical networks more strongly than responses that cannot be predicted. Task performance was evaluated before and after early-night sleep, rich in SWS, and late-night sleep, rich in rapid eye movement (REM) sleep. In implicit conditions, slow cortical potentials (SPs) were analyzed to reflect the amount of controlled processing and the localization of activated neural task representations.During implicit learning before sleep, the amount of controlled processing did not differ between unpredictable and predictable responses, nor between early- and late-night sleep groups. A topographic re-distribution of SPs indicating a spatial reorganization occurred only after early, not after late sleep, and only for predictable responses. These SP changes correlated with the amount of SWS and were covert because off-line RT decrease did not differentiate response types or sleep groups.It is concluded that SWS promotes the neural reorganization of task representations that rely on the hippocampal system despite absence of conscious access to these representations.Original neurophysiologic evidence is provided for the role of SWS in the consolidation of memories encoded with hippocampo-cortical interaction before sleep. It is demonstrated that this SWS-mediated mechanism does not depend critically on explicitness at learning nor on the amount of controlled executive processing during pre-sleep encoding

Human Hepatitis B Virus Production in Avian Cells Is Characterized by Enhanced RNA Splicing and the Presence of Capsids Containing Shortened Genomes

Experimental studies on hepatitis B virus (HBV) replication are commonly done with human hepatoma cells to reflect the natural species and tissue tropism of the virus. However, HBV can also replicate, upon transfection of virus coding plasmids, in cells of other species. In such cross-species transfection experiments with chicken LMH hepatoma cells, we previously observed the formation of HBV genomes with aberrant electrophoretic mobility, in addition to the those DNA species commonly seen in human HepG2 hepatoma cells. Here, we report that these aberrant DNA forms are mainly due to excessive splicing of HBV pregenomic RNA and the abundant synthesis of spliced DNA products, equivalent to those also made in human cells, yet at much lower level. Mutation of the common splice acceptor site abolished splicing and in turn enhanced production of DNA from full-length pgRNA in transfected LMH cells. The absence of splicing made other DNA molecules visible, that were shortened due to the lack of sequences in the core protein coding region. Furthermore, there was nearly full-length DNA in the cytoplasm of LMH cells that was not protected in viral capsids. Remarkably, we have previously observed similar shortened genomes and non-protected viral DNA in human HepG2 cells, yet exclusively in the nucleus where uncoating and final release of viral genomes occurs. Hence, two effects reflecting capsid disassembly in the nucleus in human HepG2 cells are seen in the cytoplasm of chicken LMH cells

A retrospective analysis of noise-induced hearing loss in the Dutch construction industry

Purpose Noise exposure is an important and highly prevalent occupational hazard in the construction industry. This study examines hearing threshold levels of a large population of Dutch construction workers and compares their hearing thresholds to those predicted by ISO-1999. Methods In this retrospective study, medical records of periodic occupational health examinations of 29,644 construction workers are analysed. Pure-tone audiometric thresholds of noise-exposed workers are compared to a non-exposed control group and to ISO-1999 predictions. Regression analyses are conducted to explore the relationship between hearing loss and noise intensity, noise exposure time and the use of hearing protection. Results Noise-exposed workers had greater hearing losses compared to their non-noise-exposed colleagues and to the reference population reported in ISO-1999. Noise exposure explained only a small proportion of hearing loss. When the daily noise exposure level rose from 80 dB(A) towards 96 dB(A), only a minor increase in hearing loss is shown. The relation of exposure time and hearing loss found was similar to ISO-1999 predictions when looking at durations of 10 years or more. For the first decade, the population medians show poorer hearing than predicted by ISO-1999. Discussion Duration of noise exposure was a better predictor than noise exposure levels, probably because of the limitations in noise exposure estimations. In this population, noise-induced hearing loss was already present at the beginning of employment and increased at the same rate as is predicted for longer exposure duration