Effects of water on cortical excitability in humans

Measurement of Active Motor Threshold Using a Dynamometer During Navigated Transcranial Magnetic Stimulation in a Patient with Postoperative Brain Tumor: Technical Note

BACKGROUND

Navigated transcranial magnetic stimulation (nTMS) is being used for different purposes in patients with brain tumors. However, the procedure requires a positive electrophysiological response. For patients with negative response in rest conditions, active motor threshold (AMT) may be used. However, sometimes it is difficult to obtain AMT measures owing to inability of the patient to sustain steady muscle contraction. Herein, we describe a simple method by using a hand dynamometer to obtain AMT measures during nTMS session.

CASE DESCRIPTION

A woman aged 68 years underwent total removal of a right frontal lobe oligodendroglioma World Health Organization grade II 15 years ago. Cranial magnetic resonance imaging during follow-up revealed local recurrence. In the postoperative period, she developed left upper limb paresis. A postoperative nTMS session was performed for motor electrophysiological evaluation. However, using the standard technique for AMT measurement, the patient was unable to perform sustained muscle contraction as required. A hand dynamometer was used. It allowed sustained muscle contraction for AMT measurement. A counter force for the index finger flexion, the hand support to stabilize hand joints, and a numerical screen serving for both the examiner and the patient as a feedback parameter may explain the success obtained with this simple device.

CONCLUSIONS

Although more studies are necessary to validate the method, the hand dynamometer should be considered for patients unable to sustain muscle contraction during AMT measurement.

Clinical Factors Underlying the Inter-individual Variability of the Resting Motor Threshold in Navigated Transcranial Magnetic Stimulation Motor Mapping

Correctly determining individual's resting motor threshold (rMT) is crucial for accurate and reliable mapping by navigated transcranial magnetic stimulation (nTMS), which is especially true for preoperative motor mapping in brain tumor patients. However, systematic data analysis on clinical factors underlying inter-individual rMT variability in neurosurgical motor mapping is sparse. The present study examined 14 preselected clinical factors that may underlie inter-individual rMT variability by performing multiple regression analysis (backward, followed by forward model comparisons) on the nTMS motor mapping data of 100 brain tumor patients. Data were collected from preoperative motor mapping of abductor pollicis brevis (APB), abductor digiti minimi (ADM), and flexor carpi radialis (FCR) muscle representations among these patients. While edema and age at exam in the ADM model only jointly reduced the unexplained variance significantly, the other factors kept in the ADM model (gender, antiepileptic drug intake, and motor deficit) and each of the factors kept in the APB and FCR models independently significantly reduced the unexplained variance. Hence, several clinical parameters contribute to inter-individual rMT variability and should be taken into account during initial and follow-up motor mappings. Thus, the present study adds basic evidence on inter-individual rMT variability, whereby some of the parameters are specific to brain tumor patients.

GABA Not Only a Neurotransmitter: Osmotic Regulation by GABA(A)R Signaling

Mature macroglia and almost all neural progenitor types express γ-aminobutyric (GABA) A receptors (GABA_ARs), whose activation by ambient or synaptic GABA, leads to influx or efflux of chloride (Cl⁻) depending on its electro-chemical gradient (E_Cl). Since the flux of Cl⁻ is indissolubly associated to that of osmotically obliged water, GABA_ARs regulate water movements by modulating ion gradients. In addition, since water movements also occur through specialized water channels and transporters, GABA_AR signaling could affect the movement of water by regulating the function of the channels and transporters involved, thereby affecting not only the direction of the water fluxes but also their dynamics. We will here review recent observations indicating that in neural cells GABA_AR-mediated osmotic regulation affects the cellular volume thereby activating multiple intracellular signaling mechanisms important for cell proliferation, maturation, and survival. In addition, we will discuss evidence that the osmotic regulation exerted by GABA may contribute to brain water homeostasis in physiological and in pathological conditions causing brain edema, in which the GABAergic transmission is often altered.

Hydration-sensitive gene expression in brain

Dehydration has a profound influence on neuroexcitability. The mechanisms remained, however, incompletely understood. The present study addressed the effect of water deprivation on gene expression in the brain. To this end, animals were exposed to a 24 hours deprivation of drinking water and neuronal gene expression was determined by microarray technology with subsequent confirmation by RT-PCR. As a result, water deprivation was followed by significant upregulation of clathrin (light polypeptide Lcb), serum/glucocorticoid-regulated kinase (SGK) 1, and protein kinase A (PRKA) anchor protein 8-like. Water deprivation led to downregulation of janus kinase and microtubule interacting protein 1, neuronal PAS domain protein 4, thrombomodulin, purinergic receptor P2Y - G-protein coupled 13 gene, gap junction protein beta 1, neurotrophin 3, hyaluronan and proteoglycan link protein 1, G protein-coupled receptor 19, CD93 antigen, forkhead box P1, suppressor of cytokine signaling 3, apelin, immunity-related GTPase family M, serine (or cysteine) peptidase inhibitor clade B member 1a, serine (or cysteine) peptidase inhibitor clade H member 1, glutathion peroxidase 8 (putative), discs large (Drosophila) homolog-associated protein 1, zinc finger and BTB domain containing 3, and H2A histone family member V. Western blotting revealed the downregulation of forkhead box P1, serine (or cysteine) peptidase inhibitor clade H member 1, and gap junction protein beta 1 protein abundance paralleling the respective alterations of transcript levels. In conclusion, water deprivation influences the transcription of a wide variety of genes in the brain, which may participate in the orchestration of brain responses to water deprivation.

Cost-effectiveness analysis of an occupational therapy-led lifestyle approach and routine general practitioner's care for panic disorder

OBJECTIVE

To assess the cost-effectiveness of an occupational therapy-led lifestyle approach to treating panic disorder in primary care compared with routine general practitioner's (GP) care. The burden of mental health disorders is considerable. Cost-effective interventions are necessary to alleviate some of these burdens. Habitual lifestyle behaviours influence mood, although to date mainly single lifestyle factor trials have been conducted to examine the effects on anxiety.

METHODS

An economic evaluation was conducted alongside an unblinded pragmatic randomised controlled trial with assessment at 5 and 10 months. Costs and consequences, as measured by the Beck anxiety inventory (BAI) and quality adjusted life years (QALYs), were compared using incremental cost-effectiveness ratios (ICERs).

RESULTS

The occupational therapy-led lifestyle intervention was more costly than routine GP care at both 5 and 10 months. Significant outcome improvements were evident at 5 months when using the BAI, although these were not maintained at 10 months. Small differences in mean QALYs were found. The estimated ICER was 36 pounds per BAI improvement for 5 months and 39 pounds for 10 months, and 18,905 pounds per QALY gained for 5 months and 8,283 pounds for 10 months.

CONCLUSIONS

If the maximum willingness to pay per additional QALY is 30,000 pounds, then there is an 86% chance that a lifestyle intervention may be considered to be value-for-money over 10 months.

Swelling-activated chloride channels in leech Retzius neurons

During periods of high activity neurons are expected to swell due to the uptake of Cl(-). To find out whether leech Retzius neurons possess swelling-activated Cl(-) channels that facilitate Cl(-) efflux and, hence, volume recovery, we exposed the cells to hypotonic solutions. In hypotonic solutions, the cells slowly swelled but did not undergo a regulatory volume decrease. However, the cell volume increased less than predicted for an ideal osmometer, suggesting the action of a compensatory mechanism. The cell swelling was paralleled by a marked decrease in the input resistance as well as by the activation of a membrane current with a reversal potential close to the Cl(-) equilibrium potential. This current was substantially diminished by removing bath Cl(-), by applying the Cl(-) channel blocker DIDS, or by treating the cells with the tubulin polymerization inhibitor colchicine. Furthermore, in the presence of colchicine or vinblastine, the cell swelling was substantially increased. It is concluded that leech Retzius neurons possess swelling-activated Cl(-) channels that require an intact microtubule system for activation. The channels may help to restore cell volume after periods of high neuronal activity.

A pragmatic, unblinded randomised controlled trial comparing an occupational therapy-led lifestyle approach and routine GP care for panic disorder treatment in primary care

BACKGROUND

Treated anxiety increased in the UK by over 30% since 1994. Medication and psychological treatment is most common, but outcomes are sometimes poor, with high relapse rates. Lifestyle has a potential role in treatment, but is not considered in clinical guidelines. Panic disorder is potentially influenced by lifestyle factors.

METHODS

16 week unblinded pragmatic randomised controlled trial in 15 East of England primary care practices (2 Primary Care Trusts). Participants met DSM-IV criteria for panic disorder with/without agoraphobia. Follow-up at 20 weeks and 10 months. Control arm, unrestricted routine GP care. Trial Arm, Occupational therapy-led lifestyle treatment comprising: lifestyle review of fluid intake, diet pattern, exercise, caffeine, alcohol and nicotine; negotiation of positive lifestyle changes; monitoring and review of impact of changes.

PRIMARY OUTCOME MEASURE

Beck Anxiety Inventory.

DATA ANALYSIS

Intention-to-treat analysis provided between-group comparisons using analysis of co-variance. Bonferroni method to adjust p-values.

RESULTS

From 199 referrals, 36 GP care and 31 lifestyle arm patients completed to final follow-up. Significantly lower lifestyle arm BAI scores at 20 weeks (p<0.001), non-significant (p=0.167) at 10 months after Bonferroni correction. 63.6% lifestyle arm, and 40% GP arm patients (p=0.045) panic-free at 20 weeks; 67.7% and 48.5% (p=0.123) respectively at 10 months.

LIMITATIONS

Final study size/power calls for caution in interpreting findings.

CONCLUSIONS

A lifestyle approach may provide a clinically effective intervention at least as effective as routine GP care, with significant improvements in anxiety compared with routine GP care at the end of treatment. Further study is required before suggesting practice changes.

The ‘wet mind’: water and functional neuroimaging

Functional neuroimaging has emerged as an important approach to study the brain and the mind. Surprisingly, although they are based on radically different physical approaches both positron emission tomography (PET) and magnetic resonance imaging (MRI) make brain activation imaging possible through measurements involving water molecules. So far, PET and MRI functional imaging have relied on the principle that neuronal activation and blood flow are coupled through metabolism. However, a new paradigm has emerged to look at brain activity through the observation with MRI of the molecular diffusion of water. In contrast with the former approaches diffusion MRI has the potential to reveal changes in the intrinsic water physical properties during brain activation, which could be more intimately linked to the neuronal activation mechanisms and lead to an improved spatial and temporal resolution. However, this link has yet to be fully confirmed and understood. To shed light on the possible relationship between water and brain activation, this introductory paper reviews the most recent data on the physical properties of water and on the status of water in biological tissues, and evaluates their relevance to brain diffusion MRI. The biophysical mechanisms of brain activation are then reassessed to reveal their intimacy with the physical properties of water, which may come to be regarded as the 'molecule of the mind'.

Direct and fast detection of neuronal activation in the human brain with diffusion MRI

Using MRI, we found that a slowly diffusing water pool was expanding (1.7 +/- 0.3%) upon activation on the human visual cortex at the detriment of a faster diffusing pool. The time course of this water phase transition preceded the activation-triggered vascular response detected by usual functional MRI by several seconds. The observed changes in water diffusion likely reflect early biophysical events that take place in the activated cells, such as cell swelling and membrane expansion. Although the exact mechanisms remain to clarify, access to such an early and direct physiological marker of cortical activation with MRI will provide opportunities for functional neuroimaging of the human brain.

Lithium and inositol: effects on brain water homeostasis in the rat

RATIONALE

Since its earliest use in psychiatry, lithium has been known to alter body water homeostasis. Although lithium is also known to decrease the concentration of inositol, an important brain osmolyte, little is known of the effects of lithium on brain water homeostasis.

OBJECTIVE

To determine whether lithium alters brain water homeostasis, and, if so, whether the mechanism involves changes in inositol concentration.

MATERIALS AND METHODS

Rats were fed regular food or regular food plus lithium chloride for either 11 days or 5 weeks. Brains were dissected and assayed for tissue water by the wet-dry method and for inositol by gas chromatography-mass spectrometry.

RESULTS

We found a statistically significant (p=0.05, corrected) 3.1% mean elevation in frontal cortex tissue water in 5-week lithium-fed rats (86.7+/-3.9%), compared to control rats (83.6+/-2.6%). Inositol concentration correlated inversely with percent tissue water (r=-0.50, p=0.003, corrected) in pooled samples of 5-week lithium-fed rats, and was significantly lower in frontal cortex and hippocampus of 5-week lithium-fed rats, compared to controls. Rats fed lithium for 11 days did not differ significantly from controls on either variable.

CONCLUSIONS

This is the first report of a lithium-induced increase in brain tissue water. Although the mechanism is unclear, it does not appear to result from changes in brain inositol concentration or blood sodium concentration. This finding may have implications for the therapeutic or toxic effects of lithium on brain, because increased tissue water can augment cell excitability.

Volume-sensitive chloride channels in mouse cortical neurons: characterization and role in volume regulation

Because persistent swelling causes cell damage and often results in cell death, volume regulation is an important physiological function in both neuronal and non-neuronal cells. Brain cell swelling has been observed not only in various pathological conditions but also during physiological synaptic transmissions. Volume-sensitive anion channels have been reported to play an important role in the regulatory volume decrease occurring after osmotic swelling in many cell types. In this study, using a two-photon laser scanning microscope and patch-clamp techniques, we found that mouse cortical neurons in primary culture exhibit regulatory volume decrease after transient swelling and activation of Cl- currents during exposure to a hypotonic solution. The regulatory volume decrease was inhibited by Cl- channel blockers or K+ channel blockers. Swelling-activated Cl- currents exhibited outward rectification, time-dependent inactivation at large positive potentials, a low-field anion permeability sequence, an intermediate unitary conductance and sensitivity to known blockers of volume-sensitive Cl- channels. Thus, it is concluded that the activity of the volume-sensitive outwardly rectifying Cl- channel plays a role in the control of cell volume in cortical neurons.

Effects of hydration and hyperventilation on cortical complexity

The effects of hydration and hyperventilation on cortical complexity were investigated in a sample of 19 healthy volunteers in a double-blind placebo design using magnetoencephalographic recordings. The subjects were asked to abstain from the intake of liquids 18 h before the study. Spontaneous magnetoencephalograms (MEG) were recorded before and after drinking 750 ml water (WAT group: nine subjects) or saline solution (SAL group: ten subjects) with eyes closed and open and during hyperventilation (HV) with eyes open. The MEG data were analysed using both linear (spectral power) and non-linear (pointwise dimension and largest Lyapunov exponent) algorithms. The prediction that intake of water, because of induced cell swelling, will lead to an increased synchronization and a decreased complexity of the spontaneous MEG during hyperventilation was confirmed. Hyperventilation following the drinking condition produced an increase in all power spectra with a stronger increase of delta and theta power after drinking of water. This synchronization of spontaneous MEG is accompanied by a general significant decrease of cortical complexity, especially after water drinking. Moreover, cortical complexity was inversely related to delta and theta power and partly also to alpha power. The SAL and WAT groups showed different relations between alpha power and dimensional complexity during HV: whereas in the SAL group the correlations between these measures became more negative during HV, they reversed in the WAT group to become positive. The synchronizing effect of hyperventilation, leading to a decrease of cortical complexity, is related in the SAL group to delta, theta and alpha power, whereas in the WAT group only delta and theta activity contribute to a reduction of cortical complexity.