Isometric agonist and antagonist muscle activation interacts differently with 140-Hz transcranial alternating current stimulation aftereffects at different intensities.

During transcranial electric stimulation, increasing intracellular Ca2+ levels beyond those needed for inducing long term potentiation (LTP) may collapse aftereffects. State-dependent plastic aftereffects are reduced when applied during muscle activation as compared with rest. Cortical surround inhibition by antagonistic muscle activation inhibits the center-innervated agonist. The objective of this study is to determine the interaction of state dependency of transcranial alternating current stimulation (tACS) aftereffects at rest and under activation of agonist and antagonist muscles during stimulation with different intensities. In 13 healthy participants, we measured motor-evoked potential (MEP) amplitudes before and after applying tACS at 140 Hz over the motor cortex in nine single-blinded sessions using sham, 1 mA, and 2 mA stimulation intensities during rest and activation of agonist and antagonist muscles. During rest, only 1 mA tACS produced a significant MEP increase, whereas the 2 mA stimulation produced no significant MEP size shift. During agonist activation 1 mA did not induce MEP changes; after 2 mA, first a decrease and later an increase of MEPs were observed. Antagonist activation under sham tACS led to an inhibition, which was restored to baseline by 1 and 2 mA tACS. Increasing stimulation intensity beyond 1 mA does not increase excitability, compatible with too strong intracellular Ca2+ increase. Antagonist innervation leads to MEP inhibition, supporting the concept of surround inhibition, which can be overcome by tACS at both intensities. During agonist innervation, a tACS dose-dependent relationship exists. Our results integrate concepts of "leaky membranes" under activation, surround inhibition, intracellular Ca2+ increase, and their role in the aftereffects of tACS.NEW & NOTEWORTHY Stimulation intensity and activation of center versus surround muscles affect cortical excitability alterations generated by 140-Hz tACS. At rest, excitatory aftereffects were induced by tACS with 1 mA, but not 2 mA stimulation intensity. With agonistic muscle activation, excitability first decreases, and then increases with 2 mA. For antagonist activation, the MEP amplitude reduction observed in the sham condition is counteracted upon by 1 and 2 mA tACS. This reflects the relation of LTP-like aftereffects to Ca2+ concentration alterations.

Seizures, CSF neurofilament light and tau in patients with subarachnoid haemorrhage.

OBJECTIVES: Patients with severe subarachnoid haemorrhage (SAH) often suffer from complications with delayed cerebral ischaemia (DCI) due to vasospasm that is difficult to identify by clinical examination. The purpose of this study was to monitor seizures and to measure cerebrospinal fluid (CSF) concentrations of neurofilament light (NFL) and tau, and to see whether they could be used for predicting preclinical DCI. METHODS: We prospectively studied 19 patients with aneurysmal SAH who underwent treatment with endovascular coiling. The patients were monitored with continuous EEG (cEEG) and received external ventricular drainage (EVD). CSF samples of neurofilament light (NLF) and total tau (T-tau) protein were collected at day 4 and day 10. Cox regression analysis was applied to evaluate whether seizures and protein biomarkers were associated with DCI and poor outcome. RESULTS: Seven patients developed DCI (37%), and 4 patients (21%) died within the first 2 months. Six patients (32%) had clinical seizures, and electrographic seizures were noted in one additional patient (4.5%). Increased tau ratio (proportion tau10/tau4) was significantly associated with DCI and hazard ratio [HR=1.33, 95% confidence interval (CI) 1.055-1.680. P = .016]. CONCLUSION: Acute symptomatic seizures are common in SAH, but their presence is not predictive of DCI. High values of the tau ratio in the CSF may be associated with development of DCI.

Neuronal tuning: Selective targeting of neuronal populations via manipulation of pulse width and directionality.

INTRODUCTION: Motor evoked potentials (MEP) in response to anteroposterior transcranial (AP) magnetic stimulation (TMS) are sensitive to the TMS pulse shape. We are now able to isolate distinct pulse properties, such as pulse width and directionality and evaluate them individually. Different pulse shapes induce different effects, likely by stimulating different populations of neurons. This implies that not all neurons respond in the same manner to stimulation, possibly, because individual segments of neurons differ in their membrane properties. OBJECTIVES: To investigate the effect of different pulse widths and directionalities of TMS on MEP latencies, motor thresholds and plastic aftereffects of rTMS. METHODS: Using a controllable pulse stimulator TMS (cTMS), we stimulated fifteen subjects with quasi-unidirectional TMS pulses of different pulse durations (40 µs, 80 µs and 120 µs) and determined thresholds and MEP AP latencies. We then compared the effects of 80 µs quasi-unidirectional pulses to those of 80 µs pulses with different pulse directionality characteristics (0.6 and 1.0 M ratios). We applied 900 pulses of the selected pulse shapes at 1 Hz. RESULTS: The aftereffects of 1 Hz rTMS depended on pulse shape and duration. 40 and 80 µs wide unidirectional pulses induced inhibition, 120 µs wide pulses caused excitation. Bidirectional pulses induced inhibition during the stimulation but had facilitatory aftereffects. Narrower pulse shapes caused longer latencies and higher resting motor thresholds (RMT) as compared to wider pulse shapes. CONCLUSIONS: We can tune the aftereffects of rTMS by manipulating pulse width and directionality; this may be due to the different membrane properties of the various neuronal segments such as dendrites. SIGNIFICANCE: To date, rTMS frequency has been the main determinant of the plastic aftereffects. However, we showed that pulse width also plays a major role, probably by recruiting novel neuronal targets.

Terminal component of complement C9 in CSF and plasma of patients with MS and aseptic meningitis.

A sensitive sandwich ELISA was applied to the measurement of the terminal component of complement C9 in CSF and plasma from 40 tension headache patients (reference group), 33 affected by clinically definite MS and 10 by aseptic meningitis. The levels of C9 in plasma were increased in aseptic meningitis. The determinations of CSF/plasma C9 ratio and C9 index, equal to (CSF C9/plasma C9): (CSF albumin/plasma albumin), thus accounting for changes of plasma C9 levels as well as damaged blood brain barrier, documented the existence of local consumption of C9 in aseptic meningitis. In contrast, only borderline alterations were evident in MS. The results indicate that local consumption of total C9 in CSF is an additional variable reflecting an acute inflammation within the CNS, but not demonstrable in MS, a chronic inflammatory CNS disorder.

Intrathecal synthesis of IgG, IgA, IgM and IgD in untreated multiple sclerosis and controls.

The intrathecal production (ITP) of the immunoglobulins (Ig) G, A, M and D was examined in untreated patients with multiple sclerosis (MS) and controls. Sensitive sandwich enzyme-linked immunosorbent assay systems were applied to the determination of IgA, IgM and IgD levels in the cerebrospinal fluid and plasma from a group of 61 consecutive MS patients (41 relapsing-remitting and 20 secondary chronic progressive MS). Age-related reference limits for all Ig variables were defined in a group of 57 patients with tension headache. ITP of IgG was demonstrated in 85% of the MS patients, ITP of IgA in 41%, of IgM in 44% and of IgD in 18%. Among 9 MS patients with normal IgG index, 3 displayed ITP of IgA, 3 of IgM and 1 of IgD. Plasma IgA was elevated in 20% and plasma IgM in 24% of the MS cases. No significant variation of Ig ITP was demonstrated in a different group of 27 untreated MS patients examined during exacerbation and remission. Among control patients with other inflammatory nervous system diseases, ITP of IgA, IgM and IgD was found more frequently, and of IgG in a smaller percentage compared with MS patients.

High performance liquid chromatography as a tool in the definition of abnormalities in monoamine and tryptophan metabolites in cerebrospinal fluid from patients with neurological disorders.

In this study we report the levels of 3-methoxy-4-hydroxyphenylglycol, 3,4-dihydroxyphenylacetic acid, homovallinic acid, tryptophan, 5-hydroxyindole-3-acetic acid and serotonin in lumbar cerebrospinal fluid (CSF) from patients with multiple sclerosis, cerebrovascular disease and muscular tension headache the later, as healthy controls. The separation of these substances was performed on a reversed phase column by ion pair high performance liquid chromatography and detection was made by a glassy carbon electrode set at +900 mV vs Ag+/AgCl. The whole separation was achieved within 25 min. Concentrations of all substances (10-1000 pmole/L) were linearly proportional to areas obtained. The system is sensitive, stable and reproducible. The significance of CSF levels of these metabolites from patients groups compared with healthy controls are discussed.

Use of high performance liquid chromatography in defining the abnormalities in the free amino acid patterns in the cerebrospinal fluid of patients with aseptic meningitis.

Free amino acids were quantitatively determined in cerebrospinal fluid (CSF) and plasma samples from patients with aseptic meningitis by a newly developed high performance liquid chromatographic (HPLC) method. The method of analysis was based on precolumn derivatization of orthophthaladehyde in the presence of 2-mercaptoethanol and detection was made at Eex = 340 nm and Eem = 450 nm. The method was sensitive and the limit for detection was less than 1 pmol for most of the amino acids. It took 45 min to separate 26 amino acids with highly reproducible results, giving a coefficient of variance for retention times and integrated areas less than 0.4% and 2%, respectively, after five replicate runs. The results accumulated in 10 patients were compared statistically with 11 age-matched healthy controls. Among the amino acids almost all the neurotransmitter candidates, such as aspartic acid, glutamic acid, glutamine, glycine, tyrosine, phenylalanine and gamma-aminobutyric acid (GABA), were significantly increased in the patients' CSF, whereas arginine and threonine were low. No change was observed in plasma amino acids in patients as compared to healthy controls. The higher levels of most of the neurotransmitters, especially GABA, aspartic acid and glutamic acid, could be used diagnostically in assessing the progression and remission in aseptic meningitis.