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Biomedical subjects

N Petersen

Publications and source records attributed to N Petersen.

At least 19 recordsLinked to original sources
PubMed2002

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.

Adult↗
PubMed2002

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.

Adenocarcinoma↗
PubMed2002

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.

Animals↗
PubMed2001

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.

Adult↗
PubMed2000

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.

Animals↗
PubMed2000

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

Action Potentials↗
PubMed2000

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.

Adult↗
PubMed2000

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.

Adenosine↗
PubMed2000

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.

Adult↗
PubMed2000

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.

Action Potentials↗
PubMed2000

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.

Animals↗
PubMed2000

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.

Administration, Oral↗
PubMed2000

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.

Animals↗
PubMed1999

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.

Adult↗
PubMed1999

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.

Ankle↗
PubMed1999

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.

Action Potentials↗
PubMed1999

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.

Adult↗