In vivo monitoring of dopamine overflow in the central nervous system by amperometric techniques combined with carbon fibre electrodes.

Electrochemical techniques are extensively used to investigate in vivo and in vitro events associated with neurotransmission, particularly dopamine (DA) transmission. In vivo amperometric measurements only concern evoked extracellular neurochemical events over short time periods independently of changes in basal release. In this context, DA release is evoked either by brief and low electrical or by chemical stimulation, which, respectively, mimics or elicits the physiological discharge rates of DA neurones. The combination of electrochemically treated carbon fibre electrodes with differential pulse amperometry (DPA) has been extensively used to monitor DA overflow on a 1-s time scale. The more recent in vivo combination of untreated carbon fibre electrodes with continuous amperometry gives better temporal information allowing the precise description of the kinetic parameters of the mechanisms which regulate DA overflow. The results obtained in rats extended by the results obtained in mice lacking a protein involved in DA transmission demonstrate that DA autoregulation and DA uptake: (i) contributes to the operational properties of DA terminals in converting action potentials into DA release as a high pass filter which favours short bursts of action potentials and (ii) inhibits excessive DA release which might result from prolonged and large increases in the impulse flow.