Rotating disk electrode (RDE) voltammetry is applied to the measurement of the transport of the catecholamine neurotransmitters norepinephrine (4-(2-amino-1-hydroxyethyl)-1,2-benzenediol, NE) and dopamine (3,4-dihydroxyphenethylamine, DA) in suspensions of LLC-NET cells, a line of porcine kidney cells expressing the human norepinephrine transporter (hNET). Initial rate of transport was assessed by following the initial decrease in neurotransmitter after its addition to the cell suspension, as measured by the decrease in oxidation current at +0.45 V vs Ag/AgCl. The initial rate of norepinephrine uptake was saturable, with Vmax and KM of 197 +/- 17 amol min-1 cell-1 and 1.64 +/- 0.46 microM, respectively. The RDE method also allows observation of outward transport (efflux) of the DA or NE previously taken up by the cells. Outward transport was induced by the addition of either d-amphetamine (d-AMPH) or p-tyramine (4-hydroxyphenethylamine, p-TYR), which are also substrates for the NE transporter. The technique was also used to monitor accelerated NE uptake by cells preloaded with p-TYR, a phenomenon distinguishing carriers from channels. Together, these findings document the utility of RDE for the nonisotopic measurement of neurotransmitter influx and efflux from transfected mammalian cells.

The results validate the use of microdialysis in awake primates using repeated sampling of the same anatomical site and demonstrate orderly changes in extracellular dopamine following administration of dopamine uptake inhibitors.

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In the first experiment, the conditioned place preference (CPP) paradigm was used to examine the rewarding properties of bilateral microinfusions of cocaine HCl into the nucleus accumbens (0, 12.5, 25, 50, or 100 micrograms). No dose of intra-accumbens cocaine induced a significant CPP. However, bilateral intra-accumbens infusions of d-amphetamine sulfate (10 micrograms) or intraperitoneal administration of cocaine HCl (5 or 10 mg/kg) both produced a significant preference for the drug-paired compartment. In the second experiment, the ability of bilateral intra-accumbens infusions of cocaine HCl (50 micrograms) to elicit conditioned locomotor activity (CLA) was examined. During the conditioning trials, intra-accumbens cocaine significantly increased locomotor activity. On the test day, when no drug was administered, the group that had previously received cocaine in the activity chamber showed significantly greater locomotor activity than the vehicle control group. This demonstration of CLA indicates that rats are able to associate the effects of intra-accumbens infusions of cocaine with environmental stimuli; however, these infusions are not rewarding as measured by the CPP paradigm. In addition, these results may indicate important differences between the neural substrates for cocaine and amphetamine reward and reveal a dissociation between CPP and CLA.