In vivo voltammetry with removable carbon fibre electrodes in freely-moving mice: dopamine release during intracranial self-stimulation.

The advantages of in vivo voltammetry at carbon fibre electrodes cannot be fully realised without the registration of neurotransmitter release in freely moving animals. Here we describe an approach to record electrically evoked dopamine release in freely-moving mice. A description of a simple in-house made micromanipulator (0.4 g) and preamplifier (0.6 g) is given. This system was used to record electrochemical signal in the nucleus accumbens four to eight times during 2 weeks following intracranial self-stimulation (ICSS) of the median forebrain bundle. High-speed chronoamperometry was found to be the best choice for recording. The most efficient parameters of electrical stimulation for training and self-stimulation (50 Hz, 0.2 s, 60 microA) were insufficient to induce a measurable voltammetric signal. Increasing the strength of stimulation (0.5 s, 160 microA) significantly decreased the rate of self-stimulation and allowed the registration of separate peaks of dopamine overflow on each stimulation and a tonic increase of electrochemical signal following higher rates of ICSS. Due to exhaustion of the readily releasable dopamine pool, the length of recording the electrochemical signal depended on the rate of self-stimulation. A fixed ratio schedule of ICSS decreased the rate of electrical stimulation and permitted the maintenance of stable peaks of dopamine overflow at a high rate of nose-poking.