Rate of onset of dopamine transporter inhibitors assessed with intracranial self-stimulation and in vivo dopamine photometry in rats.

Drug self-administration and intracranial self-stimulation (ICSS) are two preclinical behavioral procedures used to predict abuse potential of drugs, and abuse-related drug effects in both procedures are thought to depend on increased mesolimbic dopamine (DA) signaling. Drug self-administration and ICSS yield concordant metrics of abuse potential across a diverse range of drug mechanisms of action. The "rate of onset," defined as the velocity with which a drug produces its effect once administered, has also been implicated as a determinant of abuse-related drug effects in self-administration procedures, but this variable has not been systematically examined in ICSS. Accordingly, this study compared ICSS effects produced in rats by three DA transporter inhibitors that have different rates of onset (fastest to slowest: cocaine, WIN-35428, RTI-31) and that produced progressively weaker metrics of abuse potential in a drug self-administration procedure in rhesus monkeys. Additionally, in vivo photometry using the fluorescent DA sensor dLight1.1 targeted to the nucleus accumbens (NAc) was used to assess the time course of extracellular DA levels as a neurochemical correlate of behavioral effects. All three compounds produced ICSS facilitation and increased DA levels assessed by dLight. In both procedures, the rank order of onset rate was cocaine > WIN-35428 > RTI-31; however, in contrast to monkey drug self-administration results, maximum effects did not differ across compounds. These results provide additional evidence that drug-induced increases in DA drive ICSS facilitation in rats and illustrate the utility of both ICSS and photometry to evaluate the time course and magnitude of abuse-related drug effects in rats.