Electrophysiological and amperometric evidence that modafinil blocks the dopamine uptake transporter to induce behavioral activation.

Full study

> In spite of this, rather recent electrophysiological results, obtained in dopaminergic mesencephalic neurons, indicated that
modafinil does not block DAT but has a direct agonistic effect on D2 DA receptors (Korotkova et al., 2007).

Hmm, direct D2 agonism. Interesting! If that quote is in the study, why does the title say that it blocks the DAT? It specifically says that it does not block the DAT...

>The inhibition of firing activity caused by the continuous superfusion of DA and modafinil
were counteracted by the co-application of the DA D2 receptor antagonist sulpiride (3 µmol/L; Fig.
1c).

So a D2 receptor antagonist counteracted the observed stimulation. That says to me that the mechanism is D2 agonist related, not DAT inhibition related.

>We also tested the effects of modafinil on the stimulus-evoked DA overflow before and during
the perfusion of the DA-uptake blocker cocaine. In the presence of cocaine (1 µmol/L) the DA
signal was increased in amplitude (67 ± 1 %, p < 0.001 paired t-test) and in half-decay
duration (50 ± 7 %, p < 0.001 paired t-test). Interestingly, under this condition, modafinil (10
µmol/L) did not significantly change the amplitude (72 ± 7 %, p > 0.05 unpaired t-test) or the
half-decay duration (64 ± 6 %, p > 0.05 unpaired t-test) (Fig. 2d-f). A similar effect was also
achieved with higher concentrations of modafinil (30 µmol/L) (data not shown).

So when administered concurrently with cocaine, modafinil did not significantly increase the effects. They stipulate that is due to modafinil binding to the same site as cocaine, but having a lower relative affinity. So now they are back to the DAT as the cause...

>We also studied the effect of modafinil on dopaminergic neurons recorded from DAT-CI mice. In
mesencephalic slices obtained from these animals, bath application of modafinil (30 µmol/L)
neither influenced the firing discharge of the cells, even when co-applied with DA (3 µmol/L) (p >
0.05) (Fig. 3a,b), nor changed the outward responses of these cells to the exogenous application of
DA (3 µmol/L) (p > 0.05) (Fig. 3c).

And mice with reduced DAT expression, the effects were not seen when administering modafinil. They allude to the fact that means modafinil's main action is DAT inhibition, but could it not also be due to down-regulation of D2 receptors in response to elevated DA levels in the DAT-CI mice?

> Noteworthy, the locomotor activity in DAT-CI was already enhanced, supporting
previous results showing that these genetically-modified animals are more active than their wild-
type littermates (Napolitano et al., 2011).

So they admit that the DAT-CI mice are already more active than normal mice. Perhaps that is why they did not see effects, and the mechanism is still D2 agonism related.

>In agreement with our data, modafinil has been shown to bind to DAT (Mignot et al., 1994; Madras
et al., 2006; Zolkowska et al., 2009) and, by blocking DA reuptake, to increase the extracellular DA
concentration in the nucleus accumbens (Loland et al., 2012). Moreover, positron emission
tomography studies in rhesus monkey and in human subjects have also demonstrated that it binds to
DAT at therapeutic doses (Volkow et al., 2009). Noteworthy, we have found that modafinil
activated locomotion in wild-type mice while it was devoid of effects in DAT-CI mice. Therefore,
when the behavioral changes caused by the drug are examined, these are consistent with an
increased extracellular level of DA in the basal ganglia (Murillo-Rodríguez et al., 2007; Zolkowska
et al., 2009). Since we did not observe any effects of modafinil in cocaine-insensitive animals, our
data agree with the earlier observation that the wake-promoting actions of the drug are absent in
DAT-knockout mice (Wisor et al., 2001).

Hmmm. I am not sure.