Electrophysiological studies, measurement

Sparteine is a drug with antiarrhythmic properties. It has been deduced from pharmacological and electrophysiological studies that sparteine acts via a reduction of the Na inward current, e.g. during the upstroke of cardiac action potentials. This process was elucidated by the determination of sodium currents, in isolated muscle fibbers, by loose patch clamp measurements [236]. The IC50 value for half-maximal blocking of the sodium current was 168.8 )iM, which is in accordance witli the antiarrhythmic activity of sparteine. The importance of sparteine on Na channels inhibition was further analysed because of its potencial strong interference in neuronal transmission, particularly in herbivores. This emphasizes the role of sparteine as a chemical defence compound for the plants that produce it. 

Two methods were used to study the effect of cannabinoids on presynaptic axon terminals. The more frequently used electrophysiological approach measures neurotransmission. In hrain slices or neuronal cultures, electrical currents in postsynaptic neurons are recorded with patch-clamp or microelectrode techniques. Presynaptic axon terminals are electrically stimulated and the postsynaptic current resulting from stimulation of ligand-gated ion channels of postsynaptic neurons hy the released transmitter is determined. The change in the postsynaptic current amplitude is a measure of the change in synaptic transmission. 

Ventricular fibrillation is electrical anarchy of the ventricle resulting in no cardiac output and cardiovascular collapse. Death wiU ensue rapidly if effective treatment measures are not taken. Patients who die abruptly (within 1 hour of initial symptoms) and unexpectedly (i.e., sudden death) usually have ventricular fibrillation recorded at the time of death. Sudden cardiac death accounts for about 400,000 deaths per year or 1000 deaths per day in the United States. Sudden cardiac death occurs most commonly in patients with ischemic heart disease and primary myocardial disease associated with LV dysfunction, less commonly in those with WPW syndrome and mitral valve prolapse, and occasionally, in those without associated heart disease (e.g., Brugada syndrome). Patients who have sudden cardiac death (not associated with acute MI) but survive because of appropriate CPR often have inducible sustained ventricular tachycardia and/or ventricular fibrillation during electrophysiologic studies. These individuals are at high risk for the recurrence of ventricular tachycardia and/or ventricular fibrillation. 

Studies in rodent models suggested a DA D2 autoreceptor mechanism of action for 85. In electrophysiological studies in anesthetized rats, compound 85 was able to completely block firing of substantia nigra DA neurons, an effect believed to involve activation of presynaptic DA D2 autoreceptors. Inhibition of brain dopamine synthesis in rats as measured by decreases in GBL induced DOPA levels, as well as decreases in striatal DA levels in in vivo microdialysis studies, were also consistent with a DA autoreceptor mechanism of action. Similar results were measured in in vivo microdialysis studies carried out in a squirrel monkey, suggesting that the compound was also acting as a DA partial agonist. Reductions in the DA levels of the caudate putamen of a monkey were observed after ip administration of 85. 

Fig. 10.14 Very long HV interval representing severe disease of the His-Purkinje system. His bnndle recording in a patient with right bundle branch block and syncope. Left ventricular ejection fraction was normal. There was no documentation of seconder third-degree AV block before the electrophysiological study. Note the very long HV interval of 124ms measured from the His bundle potential to the earliest ventricular activation either in the surface or intracardiac leads, (normal = 35-55 ms) responsible for the first-degree AV block. Time fines = 10ms. A = low atrial depolarization, H = His bundle potential, V = Activation of high ventricular septum. Syncope disappeared after implantation of a permanent pacemaker.

Electrophysiological Studies. The arsenal of electrophysiological methods includes measures of brain electrical activity (such as electroencephalography and evoked potentials), electromyography, and nerve conduction studies. Electroencephalograms (EEGs) are noninvasive tests that display the electrical activity of the outer cortical layer neurons... 

The second section concentrates on study results and current knowledge, and attempts to summarize what we know as a result of research in relation to lead and intelligence, educational attainment, behaviour, and other psychometric measures. The contribution of animal studies, and studies with electrophysiological outcome measures, to current knowledge is assessed. The problems in interpreting the existing data are discussed in relation to some of the methodological issues described in the first section. 

Electrophysiological studies are also possible on intact cells, by performing photoelectric measurements in cell suspensions. ... 

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