An in vivo microdialysis characterization of extracellular dopamine and GABA in dorsolateral striatum of awake freely moving and halothane anaesthetised rats

This study describes the results of a systematic characterization of extracellular dopamine (DA) and γ-aminobutyric acid (GABA) recovered from dorsolateral striatum using in vivo microdialysis in rats following acute (2.5 h) and chronic (1 day, 2 day and 4 day) implantation of the probe. The voltage and calcium dependence of DA and GABA overflow was characterised by perfusion with the sodium channel blocker tetrodotoxin (TTX 10-6M) and with Ca²⁺-free Ringers perfusion medium. In addition, the effect of halothane anaesthesia on the responsiveness of these neurotransmitter substances to TTX and Ca²⁺-free perfusion medium was investigated. Perfusion with TTX decreased basal DA levels by at least 60% in all groups. The TTX-induced decrease was most profound in halothane-anaesthetised rats, 24 h after implantation of the probe. Responsiveness of GABA to TTX infusion was different between the groups. In acutely implanted halothane-anaesthetised rats basal GABA levels were unaltered by perfusion with TTX while in the remaining groups at least a 35% reduction was observed. In awake rats 2 days following implantation of the probe removal and replacement of the Ca²⁺ from the perfusion medium resulted in a reversible reduction of basal DA by 87%. In addition, basal GABA levels were decreased by 52%. This decrease was delayed and was not reversed 1.5 h after the Ca²⁺-free perfusion medium was replaced with normal perfusion medium although basal GABA levels returned to pre-experimental levels by the following day. The present study demonstrates that the responsiveness of striatal DA and GABA to manipulations of both voltage-dependent (TTX) and vesicular release (Ca²⁺-free perfusion) is influenced by the length of time elapsed after the implantation of the dialysis fiber and the conscious state of the animal.