NACL Sensors
Dopamine Metabolites (HVA)

Legend. Schematic representation of an implantable CPE constructed from Teflon-coated wire. After soldering a gold clip to facilitate later connection to the potentiostat, a small cavity (~0.5 mm long) is made by drawing the insulation over the metal wire (usually Ag or Pt-Ir). The carbon paste should be packed carefully into a cavity using a sleeved plunger of the same wire. If the paste is too loose or the cavity too short, the extracellular fluid may penetrate to the metal producing large background currents after a few days. If packed too tightly, the Teflon may crack, again allowing electrolyte into the cavity. These CPEs have been used in voltammetric experiments to monitor brain ascorbate, urate, 5HIAA and HVA, and to monitor ascorbate  amperometrically at low applied potentials.

References:

  • O'Neill R.D., Grunewald R.A., Fillenz M. and Albery W.J. (1982) Linear sweep voltammetry with carbon paste electrodes in the rat striatum. Neuroscience, 7, 1945-1954.
  • Lyne P.D. and O'Neill R.D. (1990) Stearate-modified carbon paste electrodes for detecting dopamine in vivo: decrease in selectivity caused by lipids and other surface-active agents. Anal. Chem., 62, 2347-2351.
  • Kane D.A. and O'Neill R.D. (1998) Major differences in the behaviour of carbon paste and carbon fibre electrodes in a protein-lipid matrix: implications for voltammetry in vivo. Analyst, 123, 2899-2903.

Legend.  Staircase voltammogram (background subtracted) recorded at 5 mV/s with a 160-mm diameter CPE in the striatum of a freely-moving rat several weeks after implantation. Peak 1 is essentially due to AA, peak 2 to 5HIAA, and peak 3 to the DA metabolite HVA.  Increases in the extracellular concentration of catechols, DA and DOPAC, increase the current between peaks 1 and 2, considerably changing the potential of these peaks for large increases. Changes in the height, h, of peak 1, when there is no significant change in its peak potential, reflect variations in the concentration of AA in the ECF. When 320-mm diameter CPEs are used under the same conditions peak 2 is due to about 90% UA and 10% 5HIAA.

Inset: Close-up of peaks 2 and 3 recorded with a 160-mm diameter CPE showing that, although these signals are of the order of 10-10 amps, they are measurable. Changes in the height of peak 3 (h3) can be used to monitor HVA in the ECF; a time course at 12-min intervals for this signal over a 3-day period is shown below.
References:
  • O'Neill R.D., Gonzalez-Mora J.L., Boutelle M.G., Ormonde D.E., Lowry J.P., Duff A., Fumero B., Fillenz M. and Mas M. (1991) Anomalously high concentrations of brain extracellular uric acid detected with chronically implanted probes: implications for in vivo sampling techniques. J. Neurochem., 57, 22-29.
  • Duff A. and O'Neill R.D. (1994) Effect of probe size on the concentration of brain extracellular uric acid monitored with carbon paste electrodes. J. Neurochem., 62, 1496-1502.

Legend: Time-course of the effect of haloperidol (0.5 mg/kg i.p.) on the HVA signal  recorded at 12-min intervals in the dorsal striatum of a freely moving rat over a 24-h period.
Reference:
  • O'Neill R.D. and Fillenz M. (1985) Detection of homovanillic acid in vivo using microcomputer-controlled voltammetry: simultaneous monitoring of rat motor activity and striatal dopamine release. Neuroscience, 14, 753-763.

Legend:  Time course over 3 days of changes in the HVA signal recorded with a CPE in the striatum of a freely-moving rat at 12-min intervals (blue) and simultaneously monitored motor activity (red). Each day's recording started at 12.00 h, with lights off from 20.00 h to 08.00 h as indicated by the light/dark band (center). The period shown corresponds to days 3 to 6 of a longer recording period, and is a demonstration of the stability of CPEs in brain tissue. These results reveal the tight correlation that normally exists between the diurnal pattern of spontaneous locomotion observed behaviorally and the activity of DA terminals in the striatum (both dorsal and ventral).
Reference:
  • O'Neill R.D. and Lowry J.P. (2000) Voltammetry in vivo for chemical analysis of the living brain. In Encyclopedia of Analytical Chemistry (edited by Meyers R.), John Wiley & Sons Ltd., Chichester, pp. 676-709.