The rewarding effects of cocaine have been reported to occur within seconds of administration. Extensive evidence suggests that these actions involve the ability of cocaine to inhibit the dopamine (DA) transporter. We recently showed that 1.5 mg/kg intravenous (i.v.) cocaine inhibits DA uptake within 5 sec. Despite this evidence there remains a lack of consensus regarding how quickly i.v. cocaine and other DA uptake inhibitors elicit DA uptake inhibition. The current studies sought to better characterize the onset of cocaine-induced DA uptake inhibition and to compare these effects to those obtained with the high-affinity, long-acting DA transporter inhibitor, 1-(2-bis(4-fluorphenyl)-methoxy)-ethyl)-4-(3-phenyl-propyl)piperazine (GBR-12909). Using in vivo fast scan cyclic voltammetry, we showed that i.v. cocaine (0.75, 1.5, and 3.0 mg/kg) significantly inhibited DA uptake in the nucleus accumbens of anesthetized rats within 5 sec. DA uptake inhibition peaked at 30 sec and returned to baseline levels in approximately one hour. The effects of cocaine were dosedependent, with the 3.0 mg/kg dose producing greater uptake inhibition at the early time points and exhibiting a longer latency to return to baseline. Further, the blood-brain barrier impermiant cocainemethiodide had no effect on DA uptake or peak height, indicating that the generalized peripheral effects of cocaine do not contribute to the CNS alterations measured here. Finally, we show that GBR-12909 (0.75, 1.5, and 3.0 mg/kg) also significantly inhibited DA uptake within 5 sec postinjection, although the peak effect and return to baseline were markedly delayed compared to cocaine, particularly at the highest dose. Combined, these observations indicate that the central effects of dopamine uptake inhibitors occur extremely rapidly following i.v. drug delivery.Keywords nucleus accumbens; onset; cocaine methiodide; fast scan cyclic voltammetry; ratThe subjective effects of cocaine have been reported to begin within seconds of administration (Seecof and Tennant 1986;Evans et al., 1996;Zernig et al., 2003). Although it is well established that cocaine increases extracellular dopamine (DA) via inhibitory actions on the DA transporter (DAT), it remains unclear whether there is a direct relationship between DAT blockade and the rapid subjective reinforcing affects of cocaine (Koob and Bloom, 1988;Kuhar et al., 1991;Wise et al., 1995;Volkow et al., 1997). Slow and long-acting DAT inhibition has been associated with poor reinforcing effects, while rapid and short-acting DAT inhibition has Correspondence: Sara R. Jones, Department of Physiology and Pharmacology, Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, NC 27157, Office:336-716-8533, Fax: 336-716-8501, E-mail: srjones@wfubmc.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting...