A CRITICAL-ASSESSMENT OF ELECTROCHEMICAL PROCEDURES APPLIED TO THE MEASUREMENT OF DOPAMINE AND ITS METABOLITES DURING DRUG-INDUCED AND SPECIES-TYPICAL BEHAVIORS

Monoamine neurotransmitters and their metabolites are electro-oxidizab le at the surface of electrodes implanted in brain, and this has raise d the expectation that in-vivo electrochemical procedures may be used routinely to monitor dynamic changes in dopamine (DA), noradrenaline a nd serotonin during species-typical and drug-induced behaviours. This expectation is slowly becoming a reality as various laboratories refin e electrochemical procedures and design recording electrodes that are selective for specific neurotransmitters. The most important step is t o conduct rigorous assessments of these procedures in-vivo to confirm that they are indeed valid and reliable bioprobes for a given neuroche mical species, The present review describes the different electrochemi cal procedures and recording electrode designs currently used to measu re monoamines in freely moving animals, Emphasis is placed on recordin g electrodes used to monitor DA in the extracellular compartment of th e brain, In-vitro and in-vivo validation studies, demonstrating the se lectivity and stability of these electrodes, are discussed in detail w ith respect to five criteria: (a) voltammograms recorded in-vivo are i dentical to those recorded in-vitro; (b) independent confirmation of t he species detected and agreement of concentration estimates with othe r neurochemical methods; (c) sufficient electrode sensitivity to measu re impulse-how dependent transmitter efflux; (d) the dependency of the electrochemical signal on the presence of an intact neuronal system; and (e) predictable and reproducible effects of drugs or other manipul ations on the electrochemical signal, The final section discusses rece nt applications of in-vivo electrochemical procedures for the monitori ng of DA neurotransmission in terminal regions of the mesotelencephali c DA system during: (a) operant behaviour reinforced by brain-stimulat ion reward or drugs of abuse; (b) species-typical motivated behaviours , as exemplified by feeding and sexual behaviour, and (c) in response to environmental stressors.