Kappa opioid receptors regulate cocaine effects on nucleus accumbens dopamine through phosphorylation of dopamine transporter at the threonine 53 site
Chronic cocaine exposure leads to tolerance of the dopamine transporter (DAT) to cocaine and heightened kappa opioid receptor (KOR)-induced inhibition of dopamine (DA) release in the nucleus accumbens (NAc). KORs on presynaptic DA terminals inhibit DA release and modulate DAT function, but whether KOR signaling causes DAT tolerance is unknown. We demonstrate that rats self-administering cocaine escalate their intake, and the KOR antagonist norbinaltorphimine (nBNI) blunts this escalation. We employed fast-scan cyclic voltammetry (FSCV) in acute brain slices containing the NAc core from these rats and found that the cocaine exposure paradigm resulted in tolerance of the DAT to cocaine, an effect absent in animals pre-treated with nBNI. In drug-naive mice, either superfusion of the KOR agonist U50,488 or a single in vivo injection of U69,593 inhibited DA release and reduced cocaine-induced inhibition of DA reuptake, reproducing the tolerance phenotype without any drug history. We replicated this finding in the NAc of rats, and with the uptake inhibitor nomifensine in rhesus macaques, indicating conservation across rodents and non-human primates. As KOR activation results in phosphorylation of the threonine-53 site on the DAT, we tested whether this is required for the KOR-mediated DAT tolerance to cocaine. We show that a mouse line with a phosphorylation-insensitive alanine-53 mutation of the DAT has enhanced DA release and uptake. Remarkably, KOR agonism no longer mediated DAT tolerance to cocaine in these mice, demonstrating the dependence of this effect on the threonine-53 site and highlighting a KOR-driven mechanism underlying cocaine tolerance at the DAT.