Brain electrochemistry

Bioelectrochemistry is hardly a new area—it led to a Nobel prize in the 1950s—but its theory has hitherto been based on older Nernstian principles, and this type of thinking in electrophysiology involves a conservation that slows the introduction of interfacial electrode kinetics in newer treatments. Metabolism, nerve conduction, brain electrochemistry—these areas are where the mechanism of the processes, as yet poorly understood, certainly involve electric currents and are most probably electrochemical. 

Major areas of electrochemical measurements with CPEs (in order of appearance) (1) Electrode reaction pathways and mechanisms of electroactive organic compounds (see also Figure 11.3a-d) (II) Pharmaceutical and clinical analysis (III) Solid-phase voltammetry with electroactive CPEs (IV) Analysis of (i) inorganic ions and molecules, (ii) organic compounds -i- environmental pollutants, and (iii) analysis of biologically important compounds (BICs) (V) Voltammetry in vivo (also known as brain electrochemistry). 

These early observations have evolved into the branch of chemistry called electrochemistry. This subject deals not only with the use of spontaneous chemical reactions to produce electricity but also with the use of electricity to drive non-spontaneous reactions forward. Electrochemistry also provides techniques for monitoring chemical reactions and measuring properties of solutions such as the pK, of an acid. Electrochemistry even allows us to monitor the activity of our brain and heart (perhaps while we are trying to master chemistry), the pH of our blood, and the presence of pollutants in our water supply. 

Another caution centers on studies combining in-vivo voltammetric electrochemistry with self-administered electrical brain stimulation reward in laboratory animals (Wightman and Garris 1996 Kruk et al. 

Practical Applications of Enzymes on Electrodes. There is a growing field of biosensors, in which electrochemistry is used in biological situations. For example, ultramicroelectiodes (Section 7.5.4.4) can be used to monitor electroencephalogmphic activity in the brain. 

Our second section enters deep into electrophysiology. The electrochemistry is here a tool, but a remarkable one in which use is made of electrodes so thin that they can be inserted into the brain without damage. Here, they provide information on one of the neurotransmitters, dopamine, and what happens to it once it has been produced in a pulse from a neuron. 

R. N. Adams, Anal. Chem.48 1126A (1976). Investigation of the electrochemistry of the brain. 

Refs. [i] Kissinger PT, Hart JB, Adams RN (1973) Brain Res 55 209 [ii] Adams RN (1969) Electrochemistry at solid electrodes (Monographs in Electroanalytical Chemistry and Electrochemistry). Marcel Dekker, New York... 

Gerhardt GA, Oke AF, Nagy G, Moghaddam B, Adams RN (1984) Nafion-coated electrodes with high selectivity for CNS electrochemistry. Brain Res 290(2) 390-395. 

Sasso S V, Pierce R J, Walla R and Yacynych A M 1990 Electropolymerized 1,2-diaminobenzene as a means to prevent interferences and fouling and to stabilize immobilized enzyme in electrochemical biosensors A aA Chem. 62 1111-7 Gerhardt G A, Oke A F, Nagy G, Moghaddam B and Adams R N 1984 Naflon-coated electrodes with high selectivity for CNS electrochemistry Brain Res. 290 390-5... 

Amato, Ivan. New Chemical Lows in Brain Surveillance. Chemical if Engineering News 84 (February 20, 2006) 12-17. This is a brief survey of the future role of electrochemistry in probing the brain. 

Electrochemical techniques have been used in analytical chemistry for more than 50 yr, but there was little interest in or understanding of them by biologists until the 1970s. A breakthrough occurred in 1973 when Ralph Adams and his colleagues (1) showed that it was possible to implant a working electrode in a rat brain and detect electroactive materials in vivo. This heralded a new chapter in electrochemistry because it now appeared to be possible to study the release of neurotransmitters in intact animals without the use of complicated radioactive labeling techniques. 

The electrochemical methods that have evolved for neurochemical applications have several advantages that make them ideally suited to the task for which they are intended the methods are selective, sensitive, and rapid. Nevertheless, the key advantages that will be highlighted in this chapter are derived from the micrometer physical dimensions of the microelectrodes themselves (Fig. 1). Today, the majority of in vivo electrochemistry is conducted in the brain with microelectrodes constructed with individual, or a... 

It is well known that the resting and dynamic electrical activity of the brain is a consequence of electrochemical potentials across membranes. Many other aspects of electrochemistry are also familiar in the neurosciences. Hence it may seem paradoxical to have suggested that the electro-analytical techniques are far afield of the mainstream of neurobiology. However, neuronal membrane potentials depend on ionic charge distributions and fluxes insofar as is known, electron current plays no role. Just the opposite is true for electroanalytical techniques—ionic conductance is of minimal importance but electron flow (current) is the essence of the measurement. The electrodes employed do not sense membrane potentials or respond to sodium or potassium fluxes rather, they pass small but finite currents because molecules close to their surface undergo oxidation or reduction. Such electrochemical measurements are called faradaic (because the amount of material converted at the electrode surface can be calculated from Faraday s law). 

Cheng, H.-Y., Schenk, J., Huff, R., and Adams, R. N., 19796, In vivo Electrochemistry Behavior of microelectrodes in brain tissue, y. Electroanal. Chem. 100 23-31. 

---