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Micropipettes and electrodes

• Carbostar-1
• Carbostar-3
• Carbostar-4
• Carbostar-6
• Carbostar-7S
• Sample recording
• Marking recording site with Pontamine Sky Blue

Combination electrodes in microiontophoresis

Microiontophoresis is most often used in conjunction with extracellular recording of neuronal firing. Extracellular 'spikes' are tipically few hundred microvolts in amplitude and are generated by action potentials across the membranes of neurons. They can be recorded through the center barrel of a multibarrel pipette if filled with a suitable electrolyte solution such as sodium chloride. However, electrolyte-filled glass micropipettes in a multibarrel assembly are electrically very noisy. The solid-conductor microelectrodes such as the tungsten or carbon fiber electrodes, in contrast, show significantly less noise in extracellular recordings. Because of this, many attempts have been made to combine a tungsten electrode with a set of iontophoresis barrels. The usual technique has been to glue the two types of electrodes together (piggyback configuration) or to insert a presharpened tungsten wire into one of the barrels (metal-in-glass configuration). Either method is technically very difficult and time consuming procedure. The coaxial, carbon fiber containing recording/microiontophoresis combination electrodes are considerably easier and cheaper to make than tungsten electrodes. Carbon fibers are 5-8 micrometer in diameter and they provide excellent signal-to-noise ratio recordings (see example below). Carbon fiber electrodes can also be used for voltammetric analysis of transmitters in vivo (Millar 1991). This page aims to introduce our CARBOSTAR series carbon fiber electrodes which are used for iontophoresis and extracellular recording/electrochemical analyses with great success.

Our Carbostar electrodes are made by a unique dry fabrication method so their shipping over great distances is safe. Iontophoresis barrels are self filling which make their usage easy with plug and play simplicity. For purchase, see Kation Scientific's Order and Price list page.

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View of the Carbostar-series microelectrodes. The base, single-barrel type (A, Carbostar-1) recording microelectrode can be completed with a varying number of micropipette barrels (B-E, Carbosar-3, 4, 6, 7S) used for drug delivery by means of iontophoresis or pressure or for reference/auxiliary electrodes. Tip ultrastructures are shown below. To read more on properties and uses of carbon fiber microelectrodes click here.

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Carbostar-1 Catalog #: E1011

Scanning electron micrograph of the tip of a Carbostar-1 electrode (left). Photograph of Carbostar-1 electrodes (above).

Single barrel carbon fiber electrodes for extracellular recording and/or in vivo voltammetry. Price information Related item: ExAmp-20KB extracellular amplifier

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Carbostar-3 Catalog #: E1031

The three barrel Carbostar-3 carbon fiber combination electrodes are for extracellular recording and microiontophoresis. One barrel contains the carbon fiber as the recording element, the other two barrels are for microiontophoresis. Recommended when only recording site is to be marked with iontophoresed tracer material or when one or two substances are to be tested on neuronal firing. Note the internal glass filaments within the iontophoresis barrels (arrows) which allow self filling of aqueous solutions. Price information Related items: ExAmp-20KB extracellular amplifier Union-40 nanoampere iontophoresis pump BAB-501 microampere iontophoresis pump

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Carbostar-4 Catalog #: E1041

The four barrel Carbostar-4 carbon fiber combination electrodes are for extracellular recording and microiontophoresis. Recommended when two or three substances are to be tested on neuronal firing. Price information Related items: ExAmp-20KB extracellular amplifier Union-40 nanoampere iontophoresis pump BAB-501 microampere iontophoresis pump

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Carbostar-6 Catalog #: E1061

The six barrel Carbostar-6 carbon fiber combination electrodes are for extracellular recording and microiontophoresis. Recommended when up to five substances are to be tested on neuronal firing. Price information Related items: ExAmp-20KB extracellular amplifier Union-40 nanoampere iontophoresis pump BAB-501 microampere iontophoresis pump

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Carbostar-7S Catalog #: E1073

Light microscopic image of the CARBOSTAR-7 electrode showing the carbon fiber tip protruding from the glass shank of 6 fused-together iontophoresis barrels. The correct tip length was reached by spark etching of the excessive length of carbon fiber according to the method of Williams et al. (1992). The stiffness of the carbon fiber provides good mechanical stability to the electrode and the sharp tip allows easy tissue penetration. Impedances at 1 kHz: Carbon fiber: 300-500 kOhm Iontophoresis barrels: 8-10 mOhm (when filled with 200 mM NaCl) Ultrastructure of the CARBOSTAR-7S electrode as revealed by scanning electron microscopy. The fused-together glass micropipettes form a seal around the protruding carbon fiber. Microiontophoresis can be achieved through the microscopic orifices of the pipettes. Price information Related items: ExAmp-20KB extracellular amplifier Union-40 nanoampere iontophoresis pump BAB-501 microampere iontophoresis pump

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Sample recording

Recording was taken from a brainstem neuron using an ExAmp-20KB in combination with a Carbostar-3 carbon fiber electrode. Cell firing was evoked by iontophoresed NMDA. Currents for the NMDA iontophoresis were delivered by a Union-40 iontophoresis pump. The amplified signals were sampled and digitized at 20 KHz frequency by a National Instruments PCI-1200 data acquisition board.

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Marking recording site with Pontamine Sky Blue

Site of extracellular recording from the hippocampus of the rat was marked by Pontamine Sky Blue (PSB) ejection from an iontophoresis barrel of a Carbostar-4 electrodes. Four % (w/v) PSB solution was made in 0.1 M sodium-acetate solution and was filtered through a 0.1 mm syringe filter just before use. The filtered solution was filled in an iontophoresis barrel of a Carbostar-4 electrode using a PE-10 tubing after extracellular recording and was left equilibrate there for 15 minutes. Iontophoretic ejection was accomplished by a BAB-500 iontophoresis pump using -5 mA for 15 minutes. Tissue was sliced by a vibratome to 50 mm slices. Slices were then counterstained by simple neutral red procedure.

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To place an order see Kation Scientific's Order and Price list page.

References:

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Armstrong-James, M. and J. Millar (1979) Carbon fibre microelectrodes. Journal of Neuroscience Methods, 1: 279-287.

Armstrong-James, M., K. Fox and J. Millar (1980) A method for etching the tips of carbon fibre microelectrodes. Journal of Neuroscience Methods, 2: p.431-432.

Armstrong-James, M., K. Fox, Z.L. Kruk and J. Millar (1981) Quantitative iontophoresis of cathecolamines using multibarrel carbon fiber microelectrodes. Journal of Neuroscience Methods, 4: p.385-406.

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Budai, D. and Zs. Molnár (2001) Novel carbon fiber microeletrodes for extracellular electrophysiology. Acta Biologica Szegediensis, 45:65-73.  Full length article in PDF

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