Neurochemistry

Many neurochemistry experiments can be performed using an e-corder with Chart, Scope, EChem or PowerChrom software, or a PowerChrom system.
Monitoring of metabolite concentrations (for example glutamate, glucose, glycerol, ascorbate and acetylcholine) with e-corder can done with a microdialysis electrode connected to an EA362 Dual Picostat

Microdialysis of neural tissue can use e-corder to record and analyse the resulting chromatograms.

The Chart, Scope and EChem software can be used for a wide variety of electrochemistry experiments with the Dual Picostat in order to identify and quantify various neurotransmitter and other metabolites.

The common techniques are:

• Amperometry

  (Sometimes called chronoamperometry, or constant potential recording).
  Typically used with a microdialysis system, or dialysis/biosensor electrode. Can also be done with in vivo microelectrodes. A fixed potential is held at the working electrode and the current flow monitored with time. PowerChrom or Chart software is used. With Chart you can also use the Computed Function Integral to integrate the signal over a fixed time constant to improve the signal-to-noise ratio for very low amplitude signals.

• Differential Pulse Amperomtery

  A fixed potential is held at the working electrode, except for voltage pulses which are applied at regular intervals. The current flow is monitored just prior to, and also during the pulse. The current flow measured immediately prior to the pulse is subtracted from the current measured during the pulse. These current differences versus time are plotted. This has the effect of removing 'baseline drift'. The EChem MultiPulse Amperometry technique is designed for this type of experiment.

• Differential Pulse Voltammetry

  A gradually increasing (or decreasing) potential is applied at the electrode by incrementing the potential in small steps. At the end of each step a voltage pulse is applied. The current flow is measured just before, and again during the pulse. The resulting difference between these two current flows are plotted versus the potential of the step. The occurrence of a signal peak at a particular potential gives an indication of the type of substance present while the peak height (or peak area) gives a quantitative measure of the concentration. Use the EChem Differential Pulse Voltammtery technique for this type of experiment. 

• Cyclic Voltammetry

  A gradually increasing (or decreasing) potential is applied at the electrode by incrementing the potential in small steps. When the maximum (or minimum) desired potential is reached the direction of the 'sweep' is reversed. The current flow is measured at each step (usually at the end of the step). The current flow is plotted versus the potential of the step. The occurrence of a signal peak at a particular potential gives an indication of the type of substance present. While peak height gives an indication of concentration the method is usually not used for accurate quantitative determinations. Use the EChem Cyclic Voltammtery technique (up to about 500 V/s) this type of experiment.

e-corder can also provide timing pulses to activate an external stimulator for evoked response experiments.

In vivo voltammetry experiments are usually performed with carbon fibre electrodes. Many researchers make their own but they are also available from:

• ALA Scientific Instruments

For general information see the article:

• "Detection of Secretion with Electrochemical Methods"
    by S. E. Hochstetler and R. M. Wightman, on the Biophysical Society web site.

Also see the Microdialysis page.

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