Methodology for coupling local application of dopamine and other chemicalswith rapid in vivo electrochemical recordings in freely-moving rats

Methodology is presented for constructing and using an electrode/microcannu lae assembly that allows in vivo electrochemical measurements coupled with local application of dopamine (DA) and other chemicals in the unanesthetize d freely-moving rat. Rats were implanted with a voltammetric electrode cons tructed of a carbon fiber sealed in fused silica tubing attached to a pair of stainless steel guide cannulae, into which fused silica injection cannul ae were inserted for local application of DA and other chemicals. Precise d elivery of nanoliter volumes was accomplished using a syringe drive combine d with a fluid swivel to deliver the solutions to the injection cannulae. A newly-designed miniature potentiostat connected to a commutator via a modu lar telephone jack assembly allowed for high-speed chronoamperometric elect rochemical recordings in freely-moving rats. Initial experiments characteri zed the in vitro electrochemical recording characteristics of the voltammet ric electrode. In vivo studies were also carried out to study clearance of locally-applied DA and of potassium-evoked endogenous DA in the striatum an d nucleus accumbens of freely-moving rats. In addition, the effects of chlo ral hydrate anesthesia on DA clearance signals in the nucleus accumbens wer e investigated. Moreover, the stability and reproducibility of this recordi ng technique for measuring exogenous DA clearance was verified over a perio d of 5 days. Finally, the concurrent effects of systemic cocaine injection on DA uptake in nucleus accumbens and locomotor activity were examined. The se studies support the conclusion that the methodology described herein all ows for rapid chronoamperometric electrochemical recordings in freely-movin g rats with precise microapplications of DA and other chemicals combined wi th concurrent measures of animal behavior. (C) 1999 Elsevier Science B.V. A ll rights reserved.