Optimizing the Aging Brain: The BEAD Study on the Ethics of Dementia Prevention

Dementia has lately undergone a profound reconceptualization. Long conceived of as an unpreventable process of mental deterioration, current evidence shows that it can be prevented in at least one in three cases intervening on a specified set of factors. Issues of justice and equity loom large on the implementation of dementia prevention, from a global health perspective. Our project thus embraces emerging evidence about dementia risk factors and their uneven distribution nationally and globally by specifically focusing on the situated aspects of dementia prevention. The aim of the BEAD study (Optimizing the Aging Brain? Situating Ethical Aspects in Dementia Prevention) is to dissect the ethical and clinical assumptions of this novel understanding of dementia, and to analyze how such new discourse on dementia prevention plays out in three countries: Canada, Germany and Switzerland. This study adopts a multi-perspective, comparative, qualitative approach, combining stakeholder interviews with different kinds of focused ethnographies, elaborating on conceptual, ethical, and social aspects of what we would like to call the "new dementia". By situating the paradigmatic shifts in Alzheimer's and dementia research within current aging cultures and contemporary social policies, we aim to initiate a debate about the often implicit unresolved social, ethical, and political implications and preconditions of the medical understanding and handling of cognitive disorders.

[Traumatology-an interdisciplinary task: exclusively for educational purposes?]

BACKGROUND

Traumatology of the head and neck region is not only a part of otorhinolaryngology, but also has a large overlap with neighboring disciplines of the head and neck region. In Freiburg, an interdisciplinary lecture on "ENT emergencies" was implemented in the 21/22 winter semester. The aim was to provide an even more realistic view on interdisciplinary patient care and to make evident the areas of intersection of four of the major head disciplines (otorhinolaryngology, neurosurgery, ophthalmology, and maxillofacial surgery).

MATERIALS AND METHODS

A new, special lecture in otorhinolaryngology was implemented as part of the regular online lecture series accompanying the semester. With reference to the clinical care of ENT emergencies, possible overlaps with neighboring disciplines were identified and explained by the discipline representatives or discussed in front of and with the auditorium. At the end of the semester, all participating students (n = 173) were invited to evaluate the seminar using the survey tool "EvaSys" (EvaSys GmbH, Lüneburg, Germany). In total, 78 students participated in the evaluation process.

RESULTS

The new lecture concept was very well accepted and immediately ranked top among the interdisciplinary lecture titles within the ENT lecture series. The clear communication of the term "interdisciplinarity" in the sense of a complementary clinical cooperation was also very successful and was appreciated accordingly by students during the evaluation process.

CONCLUSION

Pragmatic presentation of ideal clinical patient care using an interdisciplinary approach is possible within the regular ENT lecture series. This realistic portrayal, beyond any technical and/or professional differences, is of great interest to students and is considered clinically relevant. Thus, interdisciplinary lectures provide a valuable tool to teach the fundamental values of clinical interdisciplinary management for the best possible patient care.

The Role of Long-Term Head-Down Bed Rest in Understanding Inter-Individual Variation in Response to the Spaceflight Environment: A Perspective Review

Exposure to the spaceflight environment results in profound multi-system physiological adaptations in which there appears to be substantial inter-individual variability (IV) between crewmembers. However, performance of countermeasure exercise renders it impossible to separate the effects of the spaceflight environment alone from those associated with exercise, whilst differences in exercise programs, spaceflight operations constraints, and environmental factors further complicate the interpretation of IV. In contrast, long-term head-down bed rest (HDBR) studies isolate (by means of a control group) the effects of mechanical unloading from those associated with countermeasures and control many of the factors that may contribute to IV. In this perspective, we review the available evidence of IV in response to the spaceflight environment and discuss factors that complicate its interpretation. We present individual data from two 60-d HDBR studies that demonstrate that, despite the highly standardized experimental conditions, marked quantitative differences still exist in the response of the cardiorespiratory and musculoskeletal systems between individuals. We also discuss the statistical concept of “true” and “false” individual differences and its potential application to HDBR data. We contend that it is currently not possible to evaluate IV in response to the spaceflight environment and countermeasure exercise. However, with highly standardized experimental conditions and the presence of a control group, HDBR is suitable for the investigation of IV in the physiological responses to gravitational unloading and countermeasures. Such investigations may provide valuable insights into the potential role of IV in adaptations to the spaceflight environment and the effectiveness of current and future countermeasures.

Arthroscopic Minimal Invasive Treatment of Posterolateral Tibial Plateau Impression Fractures

Posterolateral fractures of the tibial plateau are difficult to address. Malunion can lead to early posttraumatic arthritis of the knee due to instability and elevated joint reaction forces. Arthroscopically assisted percutaneous reduction facilitates visualization and avoids open approaches either directly from posterolateral or from lateral with optional extension via a lateral epicondylus osteotomy. We describe and illustrate a minimal invasive technique using an arthroscopic posterolateral viewing portal. Using this technique, we demonstrated very good clinical outcome with excellent patient satisfaction. Key words: Schatzker, tibia head fracture, knee arthroscopy, multiligamentary injury.

Prevalence of impaired renal function in virologically suppressed people living with HIV compared with controls: the Copenhagen Comorbidity in HIV Infection (COCOMO) study

OBJECTIVES

While renal impairment is reported more frequently in people living with HIV (PLWH) than in the general population, the PLWH samples in previous studies have generally been dominated by those at high renal risk.

METHODS

Caucasian PLWH who were virologically suppressed on antiretroviral treatment and did not have injecting drug use or hepatitis C were recruited from the Copenhagen Comorbidity in HIV Infection (COCOMO) study. Sex- and age-matched controls were recruited 1:4 from the Copenhagen General Population Study up to November 2016. We defined renal impairment as one measurement of estimated glomerular filtration rate ≤ 60 mL/min/1.73 m² , and assessed associated factors using adjusted logistic regression models. The impact of HIV-related factors was explored in a subanalysis.

RESULTS

Among 598 PLWH and 2598 controls, the prevalence of renal impairment was 3.7% [95% confidence interval (CI) 2.3-5.5%] and 1.7% (95% CI 1.2-2.2%; P = 0.0014), respectively. After adjustment, HIV status was independently associated with renal impairment [odds ratio (OR) 3.4; 95% CI 1.8-6.3]. In addition, older age [OR 5.4 (95% CI 3.9-7.5) per 10 years], female sex [OR 5.0 (95% CI 2.6-9.8)] and diabetes [OR 2.9 (95% CI 1.3-6.7)] were strongly associated with renal impairment. The association between HIV status and renal impairment became stronger with older age (P = 0.02 for interaction). Current and nadir CD4 counts, duration of HIV infection and previous AIDS-defining diagnosis were not associated with renal impairment among virologically suppressed PLWH.

CONCLUSIONS

The prevalence of renal impairment is low among low-risk virologically suppressed Caucasian PLWH, but remains significantly higher than in controls. Renal impairment therefore remains a concern in all PLWH and requires ongoing attention.

Optimization of Exercise Countermeasures for Human Space Flight: Operational Considerations for Concurrent Strength and Aerobic Training

The physiological challenges presented by space flight and in microgravity (μG) environments are well documented. μG environments can result in declines muscle mass, contractile strength, and functional capabilities. Previous work has focused on exercise countermeasures designed to attenuate the negative effects of μG on skeletal muscle structure, function, and contractile strength and aerobic fitness parameters. Exposure to μG environments influences both strength and aerobic type physical qualities. As such, the current exercise recommendations for those experiencing μG involve a combination of strength and aerobic training or “concurrent training.” Concurrent training strategies can result in development and maintenance of both strength and aerobic capabilities. However, terrestrial research has indicated that if concurrent training strategies are implemented inappropriately, strength development can be inhibited. Previous work has also demonstrated that the aforementioned inhibition of strength development is dependent on the frequency of aerobic training, modality of aerobic training, the relief period between strength and aerobic training, and the intra-session sequencing of strength and aerobic training. While time constraints and feasibility are important considerations for exercise strategies in μG, certain considerations could be made when prescribing concurrent strength and aerobic training to those experiencing human space flight. If strength and aerobic exercise must be performed in close proximity, strength should precede aerobic stimulus. Eccentric strength training methods should be considered to increase mechanical load and reduce metabolic cost. For aerobic capacity, maintenance cycle and/or rowing-based high-intensity intermittent training (HIIT) should be considered and cycle ergometry and/or rowing may be preferable to treadmill running.

Transitional health care for patients with Hirschsprung disease and anorectal malformations

Background

Hirschsprung disease (HD) and anorectal malformations (ARM) are congenital disorders with potentially lifelong consequences. Although follow-up is performed in most pediatric patients, transfer to adult health care is often problematic. This study assesses transitional care with the help of questionnaires in consultation with adult patients.

Methods

This study was conducted in an outpatient clinic of a pediatric surgical center in the Netherlands. All patients born and treated for ARM or HD before 1992 were invited to visit our clinic. Patients completed questionnaires concerning disease-specific functioning and quality of life at an initial visit to in response to which individual treatment plans were modified. Patients were reviewed 1 year later.

Results

Twenty-seven patients (17 ARM and 10 HD), mean age 27.9 years (range 17–64 years) of the 168 invited visited the transitional clinic (17%). Passive fecal incontinence was reported by 7/27, other defecatory problems, including urge incontinence and incomplete evacuation in 17/27 and anal or abdominal pain reported by 9/27. Quality of life was lower than a matched population. Only 13/27 returned for repeat assessment at 1 year; however, a further 8 reported that that their problems had resolved. In those attending follow-up, negative thoughts and feelings about their condition had decreased and one more patient was fully continent. There was no change in quality of life, bowel function or pain recorded. Twelve out of thirteen patients reported that they had found the transitional clinic satisfactory.

Conclusions

The transitional outpatient clinic provides care adapted to the needs and wishes of adult HD and ARM patients. It is a novel addition to quality of care of patients with complex congenital disorders.

Postflight reconditioning for European Astronauts - A case report of recovery after six months in space

BACKGROUND

Postflight reconditioning of astronauts is understudied. Despite a rigorous, daily inflight exercise countermeasures programme during six months in microgravity (μG) on-board the International Space Station (ISS), physiological impairments occur and postflight reconditioning is still required on return to Earth. Such postflight programmes are implemented by space agency reconditioning specialists. Case Description and Assessments: A 38 year old male European Space Agency (ESA) crewmember's pre- and postflight (at six and 21 days after landing) physical performance from a six-month mission to ISS are described.

ASSESSMENTS

muscle strength (squat and bench press 1 Repetition Maximum) and power (vertical jump), core muscle endurance and hip flexibility (Sit and Reach, Thomas Test).

INTERVENTIONS

In-flight, the astronaut undertook a rigorous daily (2-h) exercise programme. The 21 day postflight reconditioning exercise concept focused on motor control and functional training, and was delivered in close co-ordination by the ESA physiotherapist and exercise specialist to provide the crewmember with comprehensive reconditioning support.

OUTCOMES

Despite an intensive inflight exercise programme for this highly motivated crewmember, postflight performance showed impairments at R+6 for most parameters, all of which recovered by R+21 except muscular power (jump tests).

CONCLUSIONS

Regardless of intense inflight exercise countermeasures and excellent compliance to postflight reconditioning, postflight performance showed impairments at R+6 for most parameters. Complex powerful performance tasks took longer to return to preflight values. Research is needed to develop optimal inflight and postflight exercise programmes to overcome the negative effects of microgravity and return the astronaut to preflight status as rapidly as possible.

The role of physiotherapy in the European Space Agency strategy for preparation and reconditioning of astronauts before and after long duration space flight

Spaceflight and exposure to microgravity have wide-ranging effects on many systems of the human body. At the European Space Agency (ESA), a physiotherapist plays a key role in the multidisciplinary ESA team responsible for astronaut health, with a focus on the neuro-musculoskeletal system. In conjunction with a sports scientist, the physiotherapist prepares the astronaut for spaceflight, monitors their exercise performance whilst on the International Space Station (ISS), and reconditions the astronaut when they return to Earth. This clinical commentary outlines the physiotherapy programme, which was developed over nine long-duration missions. Principles of physiotherapy assessment, clinical reasoning, treatment programme design (tailored to the individual) and progression of the programme are outlined. Implications for rehabilitation of terrestrial populations are discussed. Evaluation of the reconditioning programme has begun and challenges anticipated after longer missions, e.g. to Mars, are considered.

Exercise in space: the European Space Agency approach to in-flight exercise countermeasures for long-duration missions on ISS

Background

To counteract microgravity (µG)-induced adaptation, European Space Agency (ESA) astronauts on long-duration missions (LDMs) to the International Space Station (ISS) perform a daily physical exercise countermeasure program. Since the first ESA crewmember completed an LDM in 2006, the ESA countermeasure program has strived to provide efficient protection against decreases in body mass, muscle strength, bone mass, and aerobic capacity within the operational constraints of the ISS environment and the changing availability of on-board exercise devices. The purpose of this paper is to provide a description of ESA’s individualised approach to in-flight exercise countermeasures and an up-to-date picture of how exercise is used to counteract physiological changes resulting from µG-induced adaptation. Changes in the absolute workload for resistive exercise, treadmill running and cycle ergometry throughout ESA’s eight LDMs are also presented, and aspects of pre-flight physical preparation and post-flight reconditioning outlined.

Results

With the introduction of the advanced resistive exercise device (ARED) in 2009, the relative contribution of resistance exercise to total in-flight exercise increased (33–46 %), whilst treadmill running (42–33 %) and cycle ergometry (26–20 %) decreased. All eight ESA crewmembers increased their in-flight absolute workload during their LDMs for resistance exercise and treadmill running (running speed and vertical loading through the harness), while cycle ergometer workload was unchanged across missions.

Conclusion

Increased or unchanged absolute exercise workloads in-flight would appear contradictory to typical post-flight reductions in muscle mass and strength, and cardiovascular capacity following LDMs. However, increased absolute in-flight workloads are not directly linked to changes in exercise capacity as they likely also reflect the planned, conservative loading early in the mission to allow adaption to µG exercise, including personal comfort issues with novel exercise hardware (e.g. the treadmill harness). Inconsistency in hardware and individualised support concepts across time limit the comparability of results from different crewmembers, and questions regarding the difference between cycling and running in µG versus identical exercise here on Earth, and other factors that might influence in-flight exercise performance, still require further investigation.

Physical Training for Long-Duration Spaceflight

INTRODUCTION

Physical training has been conducted on the International Space Station (ISS) for the past 10 yr as a countermeasure to physiological deconditioning during spaceflight. Each member space agency has developed its own approach to creating and implementing physical training protocols for their astronauts. We have divided physical training into three distinct phases (preflight, in-flight, and postflight) and provided a description of each phase with its constraints and limitations. We also discuss how each member agency (NASA, ESA, CSA, and JAXA) prescribed physical training for their crewmembers during the first 10 yr of ISS operations. It is important to understand the operational environment, the agency responsible for the physical training program, and the constraints and limitations associated with spaceflight to accurately design and implement exercise training or interpret the exercise data collected on ISS. As exploration missions move forward, resolving agency differences in physical training programs will become important to maximizing the effectiveness of exercise as a countermeasure and minimizing any mission impacts.

Reliability of a new test battery for fitness assessment of the European Astronaut corps

BACKGROUND

To optimise health for space missions, European astronauts follow specific conditioning programs before, during and after their flights. To evaluate the effectiveness of these programs, the European Space Agency conducts an Astronaut Fitness Assessment (AFA), but the test-retest reliability of elements within it remains unexamined. The reliability study described here presents a scientific basis for implementing the AFA, but also highlights challenges faced by operational teams supporting humans in such unique environments, especially with respect to health and fitness monitoring of crew members travelling not only into space, but also across the world. The AFA tests assessed parameters known to be affected by prolonged exposure to microgravity: aerobic capacity (VO2max), muscular strength (one repetition max, 1 RM) and power (vertical jumps), core stability, flexibility and balance. Intraclass correlation coefficients (ICC3.1), standard error of measurement and coefficient of variation were used to assess relative and absolute test-retest reliability.

RESULTS

Squat and bench 1 RM (ICC3.1 = 0.94-0.99), hip flexion (ICC3.1 = 0.99) and left and right handgrip strength (ICC3.1 = 0.95 and 0.97), showed the highest test-retest reliability, followed by VO2max (ICC3.1 = 0.91), core strength (ICC3.1 = 0.78-0.89), hip extension (ICC3.1 = 0.63), the countermeasure (ICC3.1 = 0.76) and squat (ICC3.1 = 0.63) jumps, and single right- and left-leg jump height (ICC3.1 = 0.51 and 0.14). For balance, relative reliability ranged from ICC3.1 = 0.78 for path length (two legs, head tilted back, eyes open) to ICC3.1 = 0.04 for average rotation velocity (one leg, eyes closed).

CONCLUSIONS

In a small sample (n = 8) of young, healthy individuals, the AFA battery of tests demonstrated acceptable test-retest reliability for most parameters except some balance and single-leg jump tasks. These findings suggest that, for the application with astronauts, most AFA tests appear appropriate to be maintained in the test battery, but that some elements may be unreliable, and require either modification (duration, selection of task) or removal (single-leg jump, balance test on sphere) from the battery. The test battery is mobile and universally applicable for occupational and general fitness assessment by its comprehensive composition of tests covering many systems involved in whole body movement.

Post space mission lumbo-pelvic neuromuscular reconditioning: a European perspective

Long-duration exposure to the space environment causes physical adaptations that are deleterious to optimal functioning on Earth. Post-mission rehabilitation traditionally concentrates on regaining general muscle strength, neuromuscular control, and lumbo-pelvic stability. A particular problem is muscle imbalance caused by the hypertrophy of the flexor and atrophy of the extensor and local lumbo-pelvic muscles, increasing the risk of post-mission injury. A method currently used in European human spaceflight to aid post-mission recovery involves a motor control approach, focusing initially on teaching voluntary contraction of specific lumbo-pelvic muscles and optimizing spinal position, progressing to functional retraining in weight bearing positions. An alternative approach would be to use a Functional Readaptive Exercise Device to appropriately recruit this musculature, thus complementing current rehabilitation programs. Advances in post-mission recovery of this nature may both improve astronaut healthcare and aid terrestrial healthcare through more effective treatment of low back pain and accelerated post bed rest rehabilitation.

Clozapine directly increases insulin and glucagon secretion from islets: implications for impairment of glucose tolerance

Second generation antipsychotics cause derangements in glucose metabolism that are often interpreted as insulin resistance. In previous studies we have shown that this is not classical insulin resistance but the drugs were actually inducing a hyperglycaemic state associated with elevated hepatic glucose output (HGO) and increased levels of glucagon and insulin. However, it remains unclear whether these effects are directly elicited by drug actions in the liver and pancreas, or whether they are indirectly mediated. Here we investigated if clozapine is capable of inducing insulin resistance in the liver or enhancing insulin and glucagon secretion from the pancreas. It was observed that insulin signalling was elevated in livers from animals treated with clozapine indicating there was no insulin resistance in the early steps of insulin signalling. To explore whether the defects arise at later stages of insulin action we used an isolated perfused liver system. In this model, clozapine had no direct effect on insulin's counter regulatory effect on epinephrine-induced HGO. In isolated mouse islets clozapine significantly increased glucose-stimulated insulin secretion while simultaneously blocking glucose-induced reductions in glucagon secretion. We also show that the non-peptidic glucagon receptor like peptide-1 (GLP-1) receptor agonist Boc5 was able to overcome the inhibitory effects of clozapine on glucose metabolism. Taken together these results suggest that clozapine does not have any direct effect on glucose metabolism in the liver but it simultaneously stimulates insulin and glucagon secretion, a situation that would allow for the concurrent presence of high glucose and high insulin levels in treated animals.

Mass mortality and its environmental and evolutionary consequences

The latest Mesozoic and earliest Tertiary sediments at Deep Sea Drilling Project site 524 provide an amplified record of environmental and biostratographic changes at the end of Cretaceous. Closely spaced samples, representing time intervals as short as 10(2) or 10(3) years, were analyzed for their bulk carbonate and trace-metal compositions, and for oxygen and carbon isotopic compositions. The data indicate that at the end of Cretaceous, when a high proportion of the ocean's planktic organisms were eliminated, an associated reduction in productivity led to a partial transfer of dissolved carbon dioxide from the oceans to the atmosphere. This resulted in a large increase of the atmospheric carbon dioxide during the next 50,000 years, which is believed to have caused a temperature rise revealed by the oxygen-isotope data. The lowermost Tertiary sediments at site 524 include fossils with Cretaceous affinities, which may include both reworked individuals and some forms that survived for a while after the catastrophe. Our data indicate that many of the Cretaceous pelagic organisms became extinct over a period of a few tens of thousands of years, and do not contradict the scenario of cometary impact as a cause of mass mortality in the oceans, as suggested by an iridium anomaly at the Cretaceous-Tertiary boundary.

Dominating role of an unusual magnetotactic bacterium in the microaerobic zone of a freshwater sediment

A combination of polymerase chain reaction-assisted rRNA sequence retrieval and fluorescent oligonucleotide probing was used to identify in situ a hitherto unculturable, big, magnetotactic, rod-shaped organism in freshwater sediment samples collected from Lake Chiemsee. Tentatively named "Magnetobacterium bavaricum," this bacterium is evolutionarily distant from all other phylogenetically characterized magnetotactic bacteria and contains unusually high numbers of magnetosomes (up to 1,000 magnetosomes per cell). The spatial distribution in the sediment was studied, and up to 7 x 10 active cells per cm were found in the microaerobic zone. Considering its average volume (25.8 +/- 4.1 mum) and relative abundance (0.64 +/- 0.17%), "M. bavaricum" may account for approximately 30% of the microbial biovolume and may therefore be a dominant fraction of the microbial community in this layer. Its microhabitat and its high content of sulfur globules and magnetosomes suggest that this organism has an iron-dependent way of energy conservation which depends on balanced gradients of oxygen and sulfide.

Sulforhodamine 101 induces long-term potentiation of intrinsic excitability and synaptic efficacy in hippocampal CA1 pyramidal neurons

Sulforhodamine 101 (SR101) has been extensively used for investigation as a specific marker for astroglia in vivo and activity-dependent dye for monitoring regulated exocytosis. Here, we report that SR101 has bioactive effects on neuronal activity. Perfusion of slices with SR101 (1 microM) for 10 min induced long-term potentiation of intrinsic neuronal excitability (LTP-IE) and a long-lasting increase in evoked EPSCs (eEPSCs) in CA1 pyramidal neurons in hippocampal slices. The increase in intrinsic neuronal excitability was a result of negative shifts in the action potential (AP) threshold. The N-methyl D-aspartate receptor (NMDAR) antagonist, AP-5 (50 microM), blocked SR101-induced LTP-IE, but glutamate receptor blockers, AP-5 (50 microM), MCPG (200 microM), and MSOP (100 microM), only partially blocked SR101-induced potentiation of eEPSCs. SR101 induced an enhancement of evoked synaptic NMDAR currents, suggesting that SR101 enhances activation of synaptic NMDARs. SR101-induced LTP-IE and potentiation of synaptic transmission triggered spontaneous neuronal firing in slices and in vivo epileptic seizures. Our results suggest that SR101 is an epileptogenic agent that long-lastingly lowers the AP threshold to increase intrinsic neuronal excitability and enhances the synaptic efficacy to increase synaptic inputs. As such, SR101 can be used as an experimental tool to induce epileptic seizures.

Interaction between peripheral afferent activity and presynaptic inhibition of ia afferents in the cat

It has been demonstrated in man that the H-reflex is more depressed by presynaptic inhibition than the stretch reflex. Here we investigated this finding further in the alpha-chloralose-anesthetized cat. Soleus monosynaptic reflexes were evoked by electrical stimulation of the tibial nerve or by stretch of the triceps surae muscle. Conditioning stimulation of the posterior biceps and semitendinosus nerve (PBSt) produced a significantly stronger depression of the electrically than the mechanically evoked reflexes. The depression of the reflexes has been shown to be caused by presynaptic inhibition of triceps surae Ia afferents. We investigated the hypothesis that repetitive activation of peripheral afferents may reduce their sensitivity to presynaptic inhibition. In triceps surae motoneurones, we measured the effect of presynaptic inhibition on excitatory postsynaptic potentials (EPSPs) produced by repetitive activation of the peripheral afferents or by fast and slow muscle stretch. EPSPs evoked by single electrical stimulation of the tibial nerve or by fast muscle stretch were significantly depressed by PBSt stimulation. However, the last EPSP in a series of EPSPs evoked by a train of electrical stimuli (5-6 shocks, 150-200 Hz) was significantly less depressed by the conditioning stimulation than the first EPSP. In addition, the last part of the long-lasting EPSPs evoked by a slow muscle stretch was also less depressed than the first part. A single EPSP evoked by stimulation of the medial gastrocnemius nerve was less depressed when preceded by a train of stimuli applied to the same nerve than when the same train of stimuli was applied to a synergistic nerve. The decreased sensitivity of the test EPSP to presynaptic inhibition was maximal when it was evoked within 20 ms after the train of EPSPs. It was not observed at intervals longer than 30 ms. These findings suggest that afferent activity may decrease the efficiency of presynaptic inhibition. We propose that the described interaction between afferent nerve activity and presynaptic inhibition may partly explain why electrically and mechanically evoked reflexes are differently sensitive to presynaptic inhibition.

Epidemiological differences between adenocarcinoma of the oesophagus and adenocarcinoma of the gastric cardia in the USA

BACKGROUND AND AIMS

It has been suggested that gastric cardia adenocarcinoma (GCA) is a distinct entity from oesophageal adenocarcinoma (OA). We examined several epidemiological features of GCA and OA in the USA to elucidate differences/similarities between these malignancies.

METHODS

Using the database of Surveillance, Epidemiology, and End Results (SEER) program, we examined incidence rates for temporal changes, and ethnic and age distributions, and performed birth cohort analyses for cases with morphologically and histologically confirmed OA or GCA.

RESULTS

The age adjusted incidence rates of OA rose progressively, reaching 1.8 per 100 000 (95% confidence interval 1.7-1.9) during 1987-1991 and 2.5 per 100 000 (2.3-2.6) during 1992-1996. In 1992-1996, Whites were affected five times more than Blacks, and men eight times more than women. A significant increase in incidence occurred among younger persons aged 45-65 years. Irrespective of age, OA was characterised by higher incidence rates among more recent birth cohorts: a 40% increase in incidence for each five year increase in the date of birth--a "birth cohort effect". On the other hand, the incidence rates of GCA reached their highest level of 3.3 per 100 000 (3.2-3.4) in 1987-1991 and subsequently declined during 1992-1996 to 3.1 per 100 000 (3.0-3.3). Whites were affected twice more than blacks and men five times more than women. Most patients with GCA were older than 60 years with no increase among younger persons and no birth cohort effect (p=0.99).

CONCLUSION

Several significant epidemiological differences exist between OA and GCA. These differences suggest that these two malignancies are separate entities with different risk factors.

Recent experience with human immunodeficiency virus transmission by cellular blood products in Germany: antibody screening is not sufficient to prevent transmission

BACKGROUND AND OBJECTIVES

A case of transfusion-related human immunodeficiency virus-1 (HIV-1) transmission was not detected by standard HIV antibody screening.

MATERIALS AND METHODS

In a look-back procedure, the preceding donations were extensively analyzed by nucleic acid amplification technology (NAT) screening and alternative serological tests.

RESULTS

The chain of infection could be demonstrated by the analysis of HIV-specific amplicon sequences from the donor and the recipient.

CONCLUSION

This case report clearly indicates that the remaining risk of transfusion-related transmission of HIV could be severely reduced, not only by the use of NAT screening but even by HIV antigen screening or more sensitive HIV antibody assays.

Patients with the major and minor form of hyperekplexia differ with regards to disynaptic reciprocal inhibition between ankle flexor and extensor muscles

The aim of the present study was to investigate the contribution of reciprocal inhibition to muscle tone by examining the transmission in the reciprocal inhibitory pathway in patients with a known defect in the glycine receptor. The study was performed in eight patients with hereditary hyperekplexia, six with the major form and two with the minor form of the disease. A mutation in the alpha1-subunit of the glycine receptor had been demonstrated in the patients with the major form, whereas no mutation was seen in the patients with the minor form. Disynaptic reciprocal inhibition, which is presumed to be mediated by glycine, was not seen in the patients with the major form of the disease, while it could be evoked in the patients with the minor form of the disease. Presynaptic inhibition, which is presumed to be mediated by GABA, was seen in both types of patients. It is concluded that the major form of hereditary hyperekplexia is associated with impaired transmission in glycinergic reciprocal inhibitory pathways. The findings demonstrate the importance of reciprocal inhibition for the muscle tone in man, and it is suggested that the impaired reciprocal inhibition seen in patients with a defect in the glycine receptor may contribute to the increased muscle stiffness that is observed in these patients.

Ultraviolet transparent silicon oxynitride waveguides for biochemical microsystems

The UV wavelength region is of great interest in absorption spectroscopy, which is employed for chemical analysis, since many organic compounds absorb in only this region. Germanium-doped silica, which is often preferred as the waveguide core material in optical devices for telecommunication, cannot accommodate guidance below 400 nm, owing to the presence of UV-absorbing centers. We show that silicon oxynitride (SiO(x) N(y)) waveguides exhibit very good UV performance. The propagation loss for 24-microm -wide SiO(x)N (y) waveguides was found to be ~1.0dB/cm in the wavelength range 220-550 nm. The applicability of these waveguides was demonstrated in a biochemical microsystem consisting of multimode buried-channel SiO(x)N (y) waveguides that were monolithically integrated with microfluidic channels. Absorption measurements of a beta -blocking agent, propranolol, at 212-215 nm were performed. The detection limit was reached at a concentration of 13microM , with an optical path length of 500microm (signal/noise ratio, 2).

Induction of interleukin-6 by depolarization of neurons

Interleukin-6 (IL-6) has neuromodulatory and neuroprotective effects in vivo. It is expressed in glial cells and neurons both under physiological conditions and in various neurological diseases. Although the expression of IL-6 in glia has been intensely investigated, little is known about the regulation of IL-6 production by neurons. Therefore, we investigated the regulation of IL-6 expression in neurons. Membrane depolarization raised IL-6 mRNA accumulation in primary cortical cells and the PC-12 cell line. In vivo, IL-6 mRNA in the brain increased significantly after epileptic seizures. To investigate IL-6 gene transcription, PC-12 cells were transfected with reporter gene constructs containing the human IL-6 promoter. Membrane depolarization raised IL-6 transcription twofold to fourfold. This increase could be blocked by lowering extracellular Ca(2+) levels or by inhibiting L-type Ca(2+) channels or Ca(2+)/calmodulin-dependent protein kinases. Internal mutations in various elements of the IL-6 promoter revealed the glucocorticoid response element (GRE) 2 to be a depolarization-responsive element. Although the GRE2 bound the glucocorticoid receptor (GR) and was stimulated by dexamethasone, the GR was not responsible for the effect of membrane depolarization because a consensus GRE did not mediate stimulation by membrane depolarization. Instead, another yet undefined factor that binds to the IL-6 GRE2 may mediate the response to membrane depolarization. These data demonstrate that the expression of IL-6 in neurons is regulated by membrane depolarization and suggest a novel Ca(2+)-responsive promoter element. Through this mechanism, IL-6 may function as a neuromodulator induced by neuronal activity.

Superparamagnetic magnetite in the upper beak tissue of homing pigeons

Homing pigeons have been subject of various studies trying to detect magnetic material which might be involved in magnetic field perception. Here we focus on the upper-beak skin of homing pigeons, a region that has previously been shown to contain nerves sensitive to changes of the ambient magnetic field. We localized Fe3+ concentrations in the subcutis and identified the material by transmission electronmicroscopy (TEM) as aggregates of magnetite nanocrystals (with grain sizes between 1 and 5 nm). The particles form clusters of 1-3 microm diameter, which are arranged in distinct coherent elongated structures, associated with nervous tissue and located between fat cells. Complementary low-temperature magnetic measurements confirm the microscopic observations of fine-grained superparamagnetic particles in the tissue. Neither electron-microscopic nor magnetic measurements revealed any single-domain magnetite in the upper-beak skin tissue.

Cerebral activation during bicycle movements in man

The cerebral activation during bicycle movements was investigated by oxygen-15-labelled H2O positron emission tomography (PET) in seven healthy human subjects. Compared to rest active bicycling significantly activated sites bilaterally in the primary sensory cortex, primary motor cortex (M1) and supplementary motor cortex (SMA) as well as the anterior part of cerebellum. Comparing passive bicycling movements with rest, an almost equal activation was observed. Subtracting passive from active bicycle movements, significant activation was only observed in the leg area of the primary motor cortex and the precuneus, but not in the primary sensory cortex (S1). The M1 activation was positively correlated (alpha=0.75-0.85, t=6.4, P<10(-5)) with the rate of the active bicycle movements. Imagination of bicycle movements compared to rest activated bilaterally sites in the SMA. It is suggested that the higher motor centres, including the primary and supplementary motor cortices as well as the cerebellum, take an active part in the generation and control of rhythmic motor tasks such as bicycling.

Evidence for transcortical reflex pathways in the lower limb of man

The existence of transcortical reflex pathways in the control of distal arm and hand muscles in man is now widely accepted. Much more controversy exists regarding a possible contribution of such reflexes to the control of leg muscles. It is often assumed that transcortical reflex pathways play no, or only a minor, role in the control of leg muscles. Transcortical reflex pathways according to this view are reserved for the control of the distal upper limb and are seen in close relation to the evolution of the primate hand. Here we review data, which provide evidence that transcortical reflexes do exist for lower limb muscles and may play a significant role in the control of at least some of these muscles. This evidence is based on animal research, recent experiments combining transcranial magnetic stimulation with peripheral electrical and mechanical stimulation in healthy subjects and neurological patients. We propose that afferent activity from muscle and skin may play a role in the regulation of bipedal gait through transcortical pathways.

Distribution of non-monosynaptic excitation to early and late recruited units in human forearm muscles

The distribution of monosynaptic and nonmonosynaptic excitation was investigated within flexor carpi radialis (FCR) and extensor carpi radialis (ECR) motoneurone (MN) pools. FCR H reflexes of different size were conditioned by various conditioning stimuli eliciting different effects: (1) musculocutaneous-induced non-monosynaptic excitation of FCR MNs at the onset of biceps contraction, (2) heteronymous monosynaptic Ia facilitation, (3) reciprocal Ia inhibition, and (4) presynaptic inhibition of Ia terminals. Musculocutaneous-induced non-monosynaptic excitation increased continuously with the size of the unconditioned reflex. In contrast, heteronymous monosynaptic Ia excitation first increased and then decreased, with increases in the unconditioned reflex size, reciprocal inhibition and presynaptic inhibition showing an approximately similar tendency. This suggests that the non-monosynaptic excitation is distributed more evenly to early and late recruited MNs than monosynaptic Ia excitation, reciprocal inhibition and presynaptic inhibition. A different pattern of homonymous radial-induced monosynaptic and non-monosynaptic excitation was also found for individual ECR MNs investigated with the poststimulus time histogram (PSTH) method. Whereas the monosynaptic Ia excitation tended to be most marked in lower threshold MUs, the nonmonosynaptic excitation was evenly distributed to lower and higher threshold MUs. We propose that the even distribution of the non-monosynaptic excitation in the motoneuronal pool may be of significance when it is necessary to activate a wide range of MNs more or less simultaneously.

The effect of baclofen on the transmission in spinal pathways in spastic multiple sclerosis patients

OBJECTIVES

To measure the effect of baclofen on the transmission in different spinal pathways to soleus motoneurones in spastic multiple sclerosis patients.

METHODS

Baclofen was administered orally in 14 and intrathecally in 8 patients. H(max)/M(max), presynaptic inhibition by biceps femoris tendon tap of femoral nerve stimulation, depression of the soleus H-reflex following previous activation of the Ia afferents from the soleus muscle (i.e. postactivation depression), disynaptic reciprocal Ia inhibition of the soleus H-reflex and the number of backpropagating action potentials in primary afferents, which may be a sign of presynaptic inhibition, were examined.

RESULTS

Baclofen depressed the soleus H(max)/M(max) ratio significantly following oral and intrathecal baclofen. None of the two tests of presynaptic inhibition, or the postactivation depression or the disynaptic reciprocal Ia inhibition of the soleus H-reflex were affected by baclofen administration. Also the action potentials of the primary afferents were unchanged during baclofen administration.

CONCLUSIONS

The antispastic effect of baclofen is not caused by an effect on the transmitter release from Ia afferents or on disynaptic reciprocal Ia inhibition. One possible explanation of the depression of the H-reflex by baclofen is suggested to be a direct depression of motoneuronal excitability.

Presynaptic control of transmission along the pathway mediating disynaptic reciprocal inhibition in the cat

In cat lumbar motoneurones, disynaptic inhibitory postsynaptic potentials (IPSPs) evoked by stimulation of antagonist motor nerves were depressed for at least 150 ms following conditioning stimulation of flexor (1.7-2 times threshold (T)) and ankle extensor (5T) nerves. The aim of the present study was to investigate the possibility that this depression is caused by presynaptic inhibitory mechanisms acting at the terminals of group I afferent fibres projecting to the Ia inhibitory interneurones and/or the terminals of these interneurones to the target motoneurones. Conditioning stimulation of flexor, but not ankle extensor, nerves evoked a depression of the monosynaptic Ia excitatory postsynaptic potentials (EPSPs) recorded intracellularly in Ia inhibitory interneurones. This depression lasted between 200 and 700 ms and was not accompanied by a depression of the monosynaptic EPSPs evoked by stimulation of descending pathways. These results suggest that flexor, but not ankle extensor, group I afferent fibres can modulate sensory transmission at the synapse between Ia afferent fibres and Ia inhibitory interneurones. Conditioning stimulation of flexor muscle nerves, extensor muscle nerves and cutaneous nerves produced a long-lasting increase in excitability of the terminals of the Ia inhibitory interneurones. The increase in the excitability of the terminals was not secondary to an electrotonic spread of synaptic excitation at the soma. Indeed, concomitant with the excitability increase of the terminals there were signs of synaptic inhibition in the soma. The unitary IPSPs induced in target motoneurones following the spike activity of single Ia inhibitory interneurones were depressed by conditioning stimulation of muscle and cutaneous nerves. Since the conditioning stimulation also evoked compound IPSPs in those motoneurones, a firm conclusion as to whether unitary IPSP depression involved presynaptic inhibitory mechanism of the terminals of the interneurones could not be reached. The possibility that the changes in excitability of the Ia interneuronal terminals reflect the presence of a presynaptic inhibitory mechanism similar to that operating at the terminals of the afferent fibres (presynaptic inhibition) is discussed.1. In cat lumbar motoneurones, disynaptic inhibitory postsynaptic potentials (IPSPs) evoked by stimulation of antagonist motor nerves were depressed for at least 150 ms following conditioning stimulation of flexor (1.7-2 times threshold (T)) and ankle extensor (5T) nerves. The aim of the present study was to investigate the possibility that this depression is caused by presynaptic inhibitory mechanisms acting at the terminals of group I afferent fibres projecting to the Ia inhibitory interneurones and/or the terminals of these interneurones to the target motoneurones. Conditioning stimulation of flexor, but not ankle extensor, nerves evoked a depression of the monosynaptic Ia excitatory postsynaptic potentials (EPSPs) recorded intracellularly in Ia inhibitory interneurones. This depression lasted between 200 and 700 ms and was not accompanied by a depression of the monosynaptic EPSPs evoked by stimulation of descending pathways. These results suggest that flexor, but not ankle extensor, group I afferent fibres can modulate sensory transmission at the synapse between Ia afferent fibres and Ia inhibitory interneurones. Conditioning stimulation of flexor muscle nerves, extensor muscle nerves and cutaneous nerves produced a long-lasting increase in excitability of the terminals of the Ia inhibitory interneurones. The increase in the excitability of the terminals was not secondary to an electrotonic spread of synaptic excitation at the soma. Indeed, concomitant with the excitability increase of the terminals there were signs of synaptic inhibition in the soma. The unitary IPSPs induced in target motoneurones following the spike activity of single Ia inhibitory interneurones were depressed by conditioning stimulation

Adenosine-induced expression of interleukin-6 in astrocytes through protein kinase A and NF-IL-6

In various neurologic diseases, astrocytes express interleukin-6 (IL-6), which is an endogenous pyrogen, a neuroprotective factor, and a regulator of the blood-brain barrier. The expression of IL-6 in astrocytes is stimulated by extracellular adenosine through A(2B) receptors. To investigate the signaling cascade that induces IL-6 gene transcription further, we transfected primary mouse astrocytes with a reporter gene construct, in which luciferase expression is directed by the human IL-6 promoter. Expression of PKI, an inhibitor of protein kinase A (PKA), interfered with IL-6 transcription indicating that PKA mediates the effect of adenosine. The CAAT box of the IL-6 promoter is necessary for the stimulation by adenosine as a mutation in this element reduced the stimulation by adenosine. Indeed, the cAMP agonist forskolin increased the binding of the transcription factors NF-IL-6 and C/EBPdelta to the CAAT box of the IL-6 promoter in nuclear extracts of astrocytes. Inhibition of the de novo synthesis of NF-IL-6 by cycloheximide or an antisense oligonucleotide reduced the enhancement of NF-IL-6 binding to the CAAT box and inhibited stimulation of IL-6 transcription by forskolin. In addition, overexpression of NF-IL-6 induced IL-6 transcription. This suggests that adenosine induces the de novo synthesis of NF-IL-6 through activation of PKA and thereby stimulates transcription of IL-6 in astrocytes.

Ischaemia after exercise does not reduce responses of human motoneurones to cortical or corticospinal tract stimulation

Motor unit firing rates and voluntary activation of muscle decline during sustained isometric contractions. After exercise, the responses to motor cortical and corticospinal stimulation are reduced. These changes may reflect motoneuronal inhibition mediated by group III and IV muscle afferents. To determine whether the post-contraction depression of the responses to corticospinal or motor cortical stimulation could be maintained by continued firing of ischaemically sensitive group III and IV muscle afferents, we examined responses in muscles that were held ischaemic after exercise. Following a sustained maximal voluntary contraction (MVC) of the elbow flexors lasting 2 min, the response to stimulation of the corticospinal tract was reduced but the usual recovery (over approximately 2 min) was not delayed when the muscles were maintained ischaemic for 2 min after the contraction. Following a sustained MVC, the time course of the reduction in the response to motor cortical stimulation (a gradual decrease over approximately 2 min, maintained for > 10 min) was also not altered if the muscle was held ischaemic. Mean arterial blood pressure rose to 155 +/- 12 mmHg during the 2 min MVC, declined to 125 +/- 9 mmHg immediately after it, but remained at this level without returning to pre-exercise levels (102 +/- 10 mmHg) until circulation to the arm was restored. This confirms that the sustained MVC activated a reflex dependent on group III and IV muscle afferents. This study shows that ischaemically sensitive group III and IV muscle afferents do not mediate depression of responses to motor cortical or corticospinal stimulation after fatiguing exercise. It also suggests that firing of such afferents does not directly inhibit motoneurones or motor cortical output cells.

Impaired response of human motoneurones to corticospinal stimulation after voluntary exercise

1. Activation of descending corticospinal tracts with transmastoid electrical stimuli has been used to assess changes in the behaviour of motoneurones after voluntary contractions. Stimuli were delivered before and after maximal voluntary isometric contractions (MVCs) of the elbow flexor muscles. 2. Following a sustained MVC of the elbow flexors lasting 5-120 s there was an immediate reduction of the response to transmastoid stimulation to about half of the control value. The response recovered to control levels after about 2 min. This was evident even when the size of the responses was adjusted to accommodate changes in the maximal muscle action potential (assessed with supramaximal stimuli at the brachial plexus). 3. To determine whether the post-contraction depression required activity in descending motor paths, motoneurones were activated by supramaximal tetanic stimulation of the musculocutaneous nerve for 10 s. This did not depress the response to transmastoid stimulation. 4. Following a sustained MVC of 120 s duration, the response to transcranial magnetic stimulation of the motor cortex gradually declined to a minimal level by about 2 min and remained depressed for more than 10 min. 5. Additional studies were performed to check that the activation of descending tracts by transmastoid stimulation was likely to involve excitation of direct corticospinal paths. When magnetic cortical stimuli and transmastoid stimuli were timed appropriately, the response to magnetic cortical stimulation could be largely occluded. 6. This study describes a novel depression of effectiveness of corticospinal actions on human motoneurones. This depression may involve the corticomotoneuronal synapse.

Modulation of reciprocal inhibition between ankle extensors and flexors during walking in man

1. The modulation of disynaptic reciprocal inhibition between antagonistic ankle muscles during walking was investigated in 17 healthy human subjects. Inhibition from ankle dorsiflexors to ankle plantar flexors was evoked by stimulation of the common peroneal nerve (CPN) and evaluated as the stimulus-induced depression of rectified soleus EMG activity (latency approx. 40 ms) or the short-latency depression of the soleus H-reflex (conditioning-test intervals around 2-3 ms). In some experiments the inhibition from ankle plantar flexors to ankle dorsiflexors was investigated. In these experiments the tibial nerve was stimulated and the amount of inhibition was evaluated from the short-latency depression of the voluntary rectified tibialis anterior (TA) EMG. 2. The short-latency inhibition of the soleus H-reflex following the CPN stimulation (1.1 x motor threshold; MT) was strongly modulated during walking, being large in the swing phase and absent in the stance phase. 3. A smaller amount of EMG depression following the CPN stimulation (1. 1-1.2 x MT) was observed in the stance phase of walking as compared to tonic or dynamic plantar flexion at a similar background EMG activity level in standing or sitting subjects. 4. In four subjects a depression of the TA EMG activity was produced by stimulation of the tibial nerve (1.1-1.2 x MT). In all subjects a smaller amount of inhibition was observed in the swing phase of walking as compared to tonic dorsiflexion at a comparable EMG activity level. 5. It is concluded that the transmission in the disynaptic Ia reciprocal pathway between ankle plantar flexors and dorsiflexors is modulated during walking. Inhibition from dorsiflexors to plantar flexors seems to be large in swing and small in stance, whereas inhibition from plantar flexors to dorsiflexors seems to be small in swing.

Recruitment of extensor-carpi-radialis motor units by transcranial magnetic stimulation and radial-nerve stimulation in human subjects

The responses of 34 extensor-carpi-radialis motor units to graded transcranial magnetic stimulation (TMS) and electrical stimulation of the radial nerve were investigated in six human subjects. Simultaneously with the recording of the single motor-unit discharges, motor-evoked potentials (MEPs) and H-reflexes evoked by the two types of stimulation were recorded by surface electrodes and expressed as a percentage of the maximal motor response (Mmax). Ten motor units were activated in the H-reflex when it was less than 5% of Mmax, but not in the MEP even when it was 15% of Mmax. The opposite was observed for three motor units. Eleven motor units were recruited by both stimuli, but with significantly different recruitment thresholds. Only ten motor units had a threshold similar to TMS and radial nerve stimulation. From these observations, we suggest that caution should be taken when making conclusions regarding motor cortical excitability based on changes in the size of MEPs, even when it is ensured that there are no similar changes in background EMG-activity or H-reflexes.

Bradykinin induces interleukin-6 expression in astrocytes through activation of nuclear factor-kappaB

Bradykinin, a mediator of inflammation, is produced in the brain during trauma and stroke. It is thought to open the blood-brain barrier, although the mechanism is unclear. We have investigated, therefore, the effect of bradykinin on the expression of interleukin-6 (IL-6), a putative modulator of the blood-brain barrier, in astrocytes. IL-6 gene transcription was evaluated by transient transfection of the human IL-6 promoter linked to the luciferase gene. In murine astrocytes, bradykinin stimulated IL-6 secretion and gene transcription. The effect of bradykinin was blocked by KN-93, an inhibitor of Ca2+/calmodulin-dependent protein kinases, and by bisindolylmaleimide I, an inhibitor of protein kinase C, suggesting the involvement of these protein kinases. Mutations in the multiple response element and the binding site for nuclear factor-kappaB (NF-kappaB), but not in other known elements of the IL-6 promoter, interfered with induction of IL-6 transcription. The involvement of NF-kappaB was supported further by the finding that overexpression of nmIkappaB alpha, a stable inhibitor of NF-kappaB, inhibited the induction of IL-6 by bradykinin. Bradykinin activated NF-kappaB in primary astrocytes as shown by increased DNA binding of NF-kappaB. These data demonstrate that bradykinin stimulates IL-6 expression through activation of NF-kappaB, which may explain several inflammatory effects of bradykinin.

Evidence suggesting that a transcortical reflex pathway contributes to cutaneous reflexes in the tibialis anterior muscle during walking in man

Stimulation of cutaneous foot afferents has been shown to evoke a facilitation of the tibialis anterior (TA) EMG-activity at a latency of 70-95 ms in the early and middle swing phase of human walking. The present study investigated the underlying mechanism for this facilitation. In those subjects in whom it was possible to elicit a reflex during tonic dorsiflexion while seated (6 out of 17 tested), the facilitation in the TA EMG evoked by stimulation of the sural nerve (3 shocks, 3-ms interval, 2.0-2.5x perception threshold) was found to have the same latency in the swing phase of walking. The facilitation observed during tonic dorsiflexion has been suggested to be -- at least partly -- mediated by a transcortical pathway. To investigate whether a similar mechanism contributes to the facilitation observed during walking, magnetic stimulation of the motor cortex (1.2x motor threshold) was applied in the early swing phase at different intervals in relation to the cutaneous stimulation in 17 subjects. In 13 of the subjects, the motor potentials evoked by the magnetic stimulation (MEPs) were more facilitated by prior sural-nerve stimulation (conditioning-test intervals of 50-80 ms) than the algebraic sum of the control MEP and the cutaneous facilitation in the EMG when evoked separately. In four of these subjects, a tibialis anterior H-reflex could also be evoked during walking. In none of the subjects was an increase of the H-reflex similar to that for the MEP observed. In five experiments on four subjects, MEPs evoked by magnetic and electrical cortical stimulation were compared. In four of these experiments, only the magnetically induced MEPs were facilitated by prior stimulation of the sural nerve. We suggest that a transcortical pathway may also contribute to late cutaneous reflexes during walking.

The effect of transcranial magnetic stimulation on the soleus H reflex during human walking

1. The effect of transcranial magnetic stimulation (TMS) on the soleus H reflex was investigated in the stance phase of walking in seventeen human subjects. For comparison, measurements were also made during quiet standing, matched tonic plantar flexion and matched dynamic plantar flexion. 2. During walking and dynamic plantar flexion subliminal (0.95 times threshold for a motor response in the soleus muscle) TMS evoked a large short-latency facilitation (onset at conditioning-test interval: -5 to -1 ms) of the H reflex followed by a later (onset at conditioning-test interval: 3-16 ms) long-lasting inhibition. In contrast, during standing and tonic plantar flexion the short-latency facilitation was either absent or small and the late inhibition was replaced by a long-lasting facilitation. 3. When grading the intensity of TMS it was found that the short-latency facilitation had a lower threshold during walking than during standing and tonic plantar flexion. Regardless of the stimulus intensity the late facilitation was never seen during walking and dynamic plantar flexion and the late inhibition was not seen, except for one subject, during standing and tonic plantar flexion. 4. A similar difference in the threshold of the short-latency facilitation between walking and standing was not observed when the magnetic stimulation was replaced by transcranial electrical stimulation. 5. The lower threshold of the short-latency facilitation evoked by magnetic but not electrical transcranial stimulation during walking compared with standing suggests that cortical cells with direct motoneuronal connections increase their excitability in relation to human walking. The significance of the differences in the late facilitatory and inhibitory effects during the different tasks is unclear.

Pharmacologically evoked fictive motor patterns in the acutely spinalized marmoset monkey (Callithrix jacchus)

The existence of a spinal network capable of generating rhythmic alternating activity resembling locomotion still has not been firmly established in primates, including man, although evidence for one is accumulating. The present study investigated whether it is possible to activate such a network by administration of a variety of pharmacological agents to acutely spinalized marmoset monkeys (Callithrix jacchus) in the absence of phasic afferent input to the spinal cord. Fourteen marmoset monkeys were decerebrated, spinalized, and paralyzed. The nerves supplying both hindlimbs were cut and recorded from. In 5 monkeys the effect of electrical stimulation of the brainstem was investigated before spinalization. In 3 of these monkeys, rhythmic activity alternating between extensors and flexor nerves was seen. In the 2 other monkeys only synchronized activity was elicited. In acutely spinalized monkeys, administration of L-3,4-dihydroxyphenylalanine (L-dopa; 3-4 h after treatment with nialamide) failed to evoke any rhythmic alternating activity. In contrast, administration of clonidine elicited alternating activity in all of 8 monkeys tested. In 4 of these monkeys, the activity was restricted to alternation between ipsilateral and contralateral flexor nerves, whereas alternating activity between ipsilateral flexors and extensors was also seen in the other 4 monkeys. Administration of excitatory amino acids (NMDA or NMA) also elicited rhythmic alternating activity in 7 of 10 spinalized monkeys. In 4, rhythmic alternating activity was seen between extensors and flexors on one limb as well as between ipsilateral and contralateral flexors. In 3 monkeys NMDA/NMA produced alternation between extensors and flexors of one limb without alternation between the ipsilateral and contralateral sides. Administration of noradrenaline failed to elicit any rhythmic activity, but rather completely depressed already existing activity. Administration of serotonin (5-HT) was ineffective in facilitating alternating activity in 6 of 8 monkeys and was facilitatory to rhythmic activity in the other 2. We suggest that these data provide further evidence of a network capable of eliciting rhythmic alternating activity resembling locomotion in the primate spinal cord. The network, however, seems to be more difficult to activate pharmacologically in those conditions than in other mammals. This may especially be the case in higher primates, including man.