Short-acting cocaine and long-acting GBR-12909 both elicit rapid dopamine uptake inhibition following intravenous delivery

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 i.v. cocaine inhibits DA uptake within 5 s. 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, GBR-12909 (1-(2-bis(4-fluorphenyl)-methoxy)-ethyl)-4-(3-phenyl-propyl)piperazine). 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 s. DA uptake inhibition peaked at 30 s and returned to baseline levels in approximately 1 h. The effects of cocaine were dose-dependent, 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 impermeant cocaine-methiodide 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 s post-injection, although the peak effect and return to baseline were markedly delayed compared with 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.