Development of a voltammetric technique for monitoring brain dopamine metabolism: compensation for interference caused by DOPAC electrogenerated during homovanillic acid detection

Abstract

The established stability of carbon-paste electrodes (CPEs) in brain extracellular fluid was exploited to develop a voltammetric technique to monitor the dopamine metabolite, homovanillic acid (HVA), at 10 s intervals. At the scan rates needed for this time resolution, 3,4-dihydroxyphenylacetic acid (DOPAC), electrogenerated as a result of HVA oxidation, was observed in the cyclic staircase voltammograms, and this interfered with the straightforward reliable quantification of HVA. However, correction of the HVA signal, recorded in mixtures, with currents from the DOPAC and ascorbate regions of the voltammogram allowed the reproducible construction of well behaved HVA calibration plots. These showed good linearity, LOD values, selectivity and stability during six days of continuous CPE exposure to a lipid medium, which served as an in-vitro model of CPE implantation in brain tissue for future applications. IntroductionDopamine (DA) is a catecholamine neurotransmitter in a number of brain regions, and is important in the expression of a wide range of behaviours, including motor control, cognitive functions and reinforcement emotions. 1-4 Indeed, many of the common drugs of abuse have specific actions on brain DA reward systems, and this mechanism may be involved in their addictive properties. 5 The ability to monitor a highly temporally resolved index of DA activity in discrete brain areas over extended periods, during well defined behaviours and in response to pharmacological challenges, would provide an important key to understanding more fully the role this molecule plays in brain function.A growing number of in-vivo monitoring (IVM) methodologies are being developed, including sampling, 6,7 spectroscopic 8 and electrochemical, 9-11 to study neurochemical phenomena in the intact brain. One subset of these techniques focuses on the insitu detection of substances in brain extracellular fluid (ECF), using in-vivo voltammetry (IVV) with implanted amperometric electrodes. An important aspect of developing an IVV technique is the choice of target analyte whose concentration can be used as a reliable index of neurotransmitter release. The most obvious candidate for monitoring DA release is the concentration of DA itself in ECF, resulting from its overflow from the synapse, 10 and a number of successful IVV techniques have been devised to monitor DA in neurochemical applications. [10][11][12][13][14][15][16] One problem with the direct detection of DA is its very low baseline concentration in the ECF (<50 nM 17-20 ), due to efficient DA re-uptake mechanisms. Thus, the established IVV technique for monitoring neurotransmitter DA in the ECF with sub-second time resolution, using fast cyclic voltammetry and carbon fibre electrodes, is limited to a time range of minutes, because the small DA signal is overwhelmed by metabolite contamination (mainly 3,4-dihydroxyphenylacetic acid, DOPAC) after this time. 21 DOPAC itself is considered to be more closely coupled to DA synthesis than release, 22-26 and the very high affinity o...

Poly‐(Alizarin Red S)‐Modified Glassy Carbon Electrode for Simultaneous Electrochemical Determination of Levodopa, Homovanillic Acid and Ascorbic Acid

“…On the subsequent scan, the formed DOPAC is oxidized to regenerate 4‐aceto‐ o ‐quinone (step 3) results in peak 3. The suggestion that peaks 2 and 3 correspond to electrogenerated DOPAC is reported in literature 30.…”

Long Term Amperometric Recordings in the Brain Extracellular Fluid of Freely Moving Immunocompromised NOD SCID Mice

“…It is imperative that the sensor demonstrates efficient stability for continuous long term recordings. The potential benefits of pre-treating microelectrodes with lipids [29,38] and proteins [39] has been investigated by research groups to permit more accurate pre-calibration techniques by mitigating this sensitivity decrease observed upon implantation. These studies have established that exposing the electrodes to fouling agents in vitro may serve as a good model of the behaviour of implanted sensors in brain tissue.…”

Identification and structural characterization by LC‐ESI‐IONTRAP and LC‐ESI‐TOF of some metabolic conjugation products of homovanillic acid in urine of neuroblastoma patients

“…For this reason, liquid chromatography with electrochemical detection is the election method for their determination in biological matrices (brain tissues, urine and plasma) . As previously reported, the electrochemical reaction of HVA involves the selective oxidation of the vanillyl nucleus to the corresponding o‐benzoquinone derivative and methanol.…”