Spreading depression: evidence of five electroencephalogram phases.

Spreading depression (SD), a self-propagating wave of astroglial and neuronal depolarization, is an accompaniment of several neurological disorders including epilepsy. Its well-described features are initial depolarization, followed by EEG flattening. In this in vivo study in awake animals, the relationship of SDs to epileptiform activity was re-examined. We assessed SDs generated by mechanical stimulation and by metabolic inhibition with fluorocitrate. In addition to identifying prolonged EEG depression, we identified two periods, one prior to and another during depression, characterized by increases in power of specific frequencies that were sometimes associated with epileptiform discharges. The first period was characterized by ripple activity close to the induction site (88% of SDs with intracortical electrodes). The second period was characterized by localized low-frequency spikes (100% with dural screw electrodes, 65% with intracortical electrodes). By using fluorocitrate to induce SDs, the initial period was also characterized by runs of spikes (52%). Finally, with SDs induced by both methods, there was a period at the end of depression when additional, unprovoked SDs occurred (20%). Five stages of SD were defined by these phenomena, in the order: excitation, depression, excitation, depression, SD, with metabolic inhibition enhancing the expression of epileptiform spiking.

Implications for glycine receptors and astrocytes in ethanol-induced elevation of dopamine levels in the nucleus accumbens.

Elevated dopamine levels are believed to contribute to the rewarding sensation of ethanol (EtOH), and previous research has shown that strychnine-sensitive glycine receptors in the nucleus accumbens (nAc) are involved in regulating dopamine release and in mediating the reinforcing effects of EtOH. Furthermore, the osmoregulator taurine, which is released from astrocytes treated with EtOH, can act as an endogenous ligand for the glycine receptor, and increase extracellular dopamine levels. The aim of this study was to address if EtOH-induced swelling of astrocytes could contribute to elevated dopamine levels by increasing the extracellular concentration of taurine. Cell swelling was estimated by optical sectioning of fluorescently labeled astrocytes in primary cultures from rat, and showed that EtOH (25-150 mM) increased astrocyte cell volumes in a concentration- and ion-dependent manner. The EtOH-induced cell swelling was inhibited in cultures treated with the Na(+) /K(+) /2Cl⁻ cotransporter blocker furosemide (1 mM), Na(+) /K(+) -ATPase inhibitor ouabain (0.1 mM), potassium channel inhibitor BaCl2 (50 µM) and in cultures containing low extracellular sodium concentration (3 mM). In vivo microdialysis performed in the nAc of awake and freely moving rats showed that local treatment with EtOH enhanced the concentrations of dopamine and taurine in the microdialysate, while glycine and ß-alanine levels were not significantly modulated. EtOH-induced dopamine release was antagonized by local treatment with the glycine receptor antagonist strychnine (20 µM) or furosemide (100 µM or 1 mM). Furosemide also prevented EtOH-induced taurine release in the nAc. In conclusion, our data suggest that extracellular concentrations of dopamine and taurine are interconnected and that swelling of astrocytes contributes to the acute rewarding sensation of EtOH.

Lactate contributes to ammonia-mediated astroglial dysfunction during hyperammonemia.

Even though ammonia is considered to underlie nervous system symptoms of dysfunction during hyperammonemia, lactate, which increases as a metabolic consequence of high ammonia levels, might also be a contributing factor. The data presented here show that NH4Cl (5 mM) mediates astroglial cell swelling, and that treatment with NH4Cl or lactate (25 mM) causes rearrangements of actin filaments and reduces astroglial glutamate uptake capacity. Co-application with BaCl2, which blocks astroglial uptake of NH4+, prevents NH4Cl-mediated cell swelling and rearrangement of actin filaments, but does not reduce NH4Cl-induced glutamate uptake capacity inhibition. Neither NH4Cl nor lactate affected glutamate uptake or protein expression in microglial cultures, indicating that astroglial cells are more susceptible to the neurotoxic affects of ammonia. Our results suggest that ammonium underlies brain edema, but that lactate can contribute to some of the cellular dysfunctions associated with elevated cerebral levels of ammonia.

Cell swelling precedes seizures induced by inhibition of astrocytic metabolism.

It is currently unknown what processes take place at the interface between non-ictal and ictal activity during seizure initiation. In this study, using paralysed awake rats, we focally inhibited astrocytic metabolism with fluorocitrate (FC), causing seizures. We measured changes in electroencephalogram (EEG) (0-300 Hz), and extracellular ion-concentrations during ictal onsets defining possible relationships with impedance-determined cell swelling. In animals showing ictal activity (69%) there were spike-wave discharges, spike-wave discharges followed by spreading depression and spreading depression without any discharges. In a high proportion of spike-wave discharges (>95%), just prior to the first spike-wave discharge, there was a decrease in the volume of the extracellular space. Following the initiation of cell swelling and prior to discharges, there were increases in high-frequency (150-300 Hz) EEG activity, increases in extracellular potassium- and decreases in extracellular calcium-concentrations. We suggest that EEG and ionic changes are not causative of cell swelling. Cell swelling due to metabolic failure in astrocytes at the injected site may release excitatory amino acids. At the same time, our results suggest ion homeostasis is not maintained and increased neuronal excitability and synchronisation occur. These could be the drivers changing normal brain activity into ictal activity.

Spectroscopy study of the dynamics of the transencephalic electrical impedance in the perinatal brain during hypoxia.

Hypoxia/ischaemia is the most common cause of brain damage in neonates. Thousands of newborn children suffer from perinatal asphyxia every year. The cells go through a response mechanism during hypoxia/ischaemia, to maintain the cellular viability and, as a response to the hypoxic/ischaemic insult, the composition and the structure of the cellular environment are altered. The alterations in the ionic concentration of the intra- and extracellular and the consequent cytotoxic oedema, cell swelling, modify the electrical properties of the constituted tissue. The changes produced can be easily measured using electrical impedance instrumentation. In this paper, we report the results from an impedance spectroscopy study on the effects of the hypoxia on the perinatal brain. The transencephalic impedance, both resistance and reactance, was measured in newborn piglets using the four-electrode method in the frequency range from 20 kHz to 750 kHz and the experimental results were compared with numerical results from a simulation of a suspension of cells during cell swelling. The experimental results make clear the frequency dependence of the bioelectrical impedance, confirm that the variation of resistance is more sensitive at low than at high frequencies and show that the reactance changes substantially during hypoxia. The resemblance between the experimental and numerical results proves the validity of modelling tissue as a suspension of cells and confirms the importance of the cellular oedema process in the alterations of the electrical properties of biological tissue. The study of the effects of hypoxia/ischaemia in the bioelectrical properties of tissue may lead to the development of useful clinical tools based on the application of bioelectrical impedance technology.

Ethanol acutely decreases astroglial gap junction permeability in primary cultures from defined brain regions.

The acute effect of hyperosmotic ethanol on gap junction permeability was examined in astroglial cells in primary culture from five different brain regions. Gap junction permeability was analyzed by measuring dye spreading from cell to cell with the low molecular weight dye Lucifer Yellow. Ethanol concentrations 25-300 mM significantly decreased dye spreading in cultures from the cerebral cortex in a dose-dependent but time-independent manner for up to 60 min. Besides cerebral cortex, exposure to 150 mM ethanol decreased dye spreading in astroglial cultures from the hippocampus and from the brain stem, while cultures from the olfactory bulb and from the hypothalamus were not significantly affected. The ethanol-induced decrease in dye spreading in cultures from the cerebral cortex was not mediated through changes in cell volume, osmolarity, protein kinase C (PKC) phosphorylation, intracellular pH, or intracellular calcium concentration ([Ca(2+)](i)). The decrease in dye spreading was abolished upon incubation in sodium-reduced buffer, and after blockage of the Na(+)/K(+)/2Cl(-) cotransporter with furosemide. The results presented here indicate that ethanol-mediated decrease in dye spreading is directly or indirectly dependent on sodium.

IGF-I has a direct proliferative effect in adult hippocampal progenitor cells.

The aim of the present study was to investigate the potential direct effects of insulin-like growth factor-I (IGF-I) on adult rat hippocampal stem/progenitor cells (AHPs). IGF-I-treated cultures showed a dose-dependent increase in thymidine incorporation, total number of cells, and number of cells entering the mitosis phase. Pretreatment with fibroblast growth factor-2 (FGF-2) increased the IGF-I receptor (IGF-IR) expression, and both FGF-2 and IGF-I were required for maximal proliferation. Time-lapse recordings showed that IGF-I at 100 ng/ml decreased differentiation and increased proliferation of single AHPs. Specific inhibition of mitogen-activated protein kinase kinase (MAPKK), phosphatidylinositol 3-kinase (PI3-K), or the downstream effector of the PI3-K pathway, serine/threonine p70 S6 kinase (p70(S6K)), showed that both the MAPK and the PI3-K pathways participate in IGF-I-induced proliferation but that the MAPK activation is obligatory. These results were confirmed with dominant-negative constructs for these pathways. Stimulation of differentiation was found at a low dose (1 ng/ml) of IGF-I, clonal analysis indicating an instructive component of IGF-I signaling.

Manual transport in Parkinson's disease.

We analyze hand dexterity in Parkinson's disease patients (PD) and control subjects using a natural manual transport task (moving an object from one place to another). Eight PD patients and 10 control subjects carried out the task repeatedly at maximum speed both in off and on medicated status. The movement parameters and the grip and load forces were recorded. Using the force and velocity signals, 10 subsequent phases of the transport movement were defined and their durations were measured. The difference between the control group and the test group in off and on was established statistically using non-parametric methods. There was slowed reaching and a striking disturbance of establishing the precision grip in PD. The transport capabilities were impaired differentially. Although acceleration and reaching sufficient height of the lift were disturbed in PD subjects, transport of the object toward the target position was almost normal. A partial disturbance was observed when cancelling the grip. Dopaminergic medication improved only specific hand skills, especially establishment of the precision grip and one of the four transport phases. A long movement path was more sensitive for movement disturbance in Parkinson's disease than a short one.

Grip and load force coordination during a manual transport movement: findings in healthy participants.

During transport of an object using the precision grip with thumb and index finger, a modulation of the grip force is needed in response to the forces evoked by the movement. We measured the grip force (GF) and the load force (LF) in 10 healthy participants moving a 640-g object forward and upward. The task was repeated with various speeds. There were considerable changes with speed of the LF trajectory but not of the GF trajectory. A loss of synergy between GF and LF appeared in fast lifts. This is in contrast to the close coupling between load force and grip force repeatedly demonstrated during simple lifts. We suggest that (a) speed should be considered as an input parameter for movement planning, and (b) regulation of GF and of LF are independent under certain conditions. We discuss whether the grip-load force synergy should be considered a special case rather than a more general principle