Atypical dopamine transporter inhibitors R-modafinil and JHW 007 differentially affect D2 autoreceptor neurotransmission and the firing rate of midbrain dopamine neurons

Abstract

Abuse of psychostimulants like cocaine that inhibit dopamine (DA) reuptake through the dopamine transporter (DAT) represents a major public health issue, however FDA-approved pharmacotherapies have yet to be developed. Recently a class of ligands termed “atypical DAT inhibitors” has gained attention due to their range of effectiveness in increasing extracellular dopamine (DA) levels without demonstrating significant abuse liability. These compounds not only hold promise as therapeutic agents to treat stimulant use disorders but also as experimental tools to improve our understanding of DAT function. Here we used patch clamp electrophysiology in mouse brain slices to explore the effects of two atypical DAT inhibitors (R-modafinil and JHW 007) on the physiology of single DA neurons in the substantia nigra and ventral tegmental area. Despite their commonalities of being DAT inhibitors that lack cocaine-like behavioral profiles, these compounds exhibited surprisingly divergent cellular effects. Similar to cocaine, R-modafinil slowed DA neuron firing in a D2 receptor-dependent manner and rapidly enhanced the amplitude and duration of D2 receptor-mediated currents in the midbrain. In contrast, JHW 007 exhibited little effect on firing, slow DAT blockade, and an unexpected inhibition of D2 receptor-mediated currents that may be due to direct D2 receptor antagonism. Furthermore, pretreatment with JHW 007 blunted the cellular effects of cocaine, suggesting that it may be valuable to investigate similar DAT inhibitors as potential therapeutic agents. Further exploration of these and other atypical DAT inhibitors may reveal important cellular effects of compounds that will have potential as pharmacotherapies for treating cocaine use disorders.

Translating the atypical dopamine uptake inhibitor hypothesis toward therapeutics for treatment of psychostimulant use disorders

“…Further, blockade of cocaine's enhancement of DA-mediated currents in DA neurons by JJC8-091 is consistent with our previous findings with similar compounds [26]. We previously showed that the benztropine analogue, JHW007, had little effect on its own but was able to blunt the cocaine-induced increase in DA currents, while R-modafinil alone enhanced DA currents and interacted in an additive manner with cocaine [26]. Similar findings were obtained here for JJC8-088, which appeared more cocaine-like, and JJC8-091, which dose-dependently inhibited the acute enhancement produced by cocaine in an even more efficacious manner than JHW007.…”

“…Also, JJC8-088, but not JJC8-091, produced significant cocaine-like effects on stimulus-elicited DA Max further suggesting a potential atypical profile for JJC8-091. Further, blockade of cocaine's enhancement of DA-mediated currents in DA neurons by JJC8-091 is consistent with our previous findings with similar compounds [26]. We previously showed that the benztropine analogue, JHW007, had little effect on its own but was able to blunt the cocaine-induced increase in DA currents, while R-modafinil alone enhanced DA currents and interacted in an additive manner with cocaine [26].…”

“…Patch clamp electrophysiology in mouse brain slices Whole cell patch clamp recordings were conducted as described previously [26]. Briefly, male DBA/2J mice aged 7-13 weeks were sacrificed, and horizontal midbrain slices (200 µm) containing the substantia nigra were cut with a vibrating microtome.…”

“…JJC8-091, but not JJC8-088, blocks cocaine-induced enhancement of D2 receptor currents We next tested the effects of the compounds on D2 receptormediated potassium currents, which we previously showed are enhanced by cocaine [26,35,36]. We used electrophysiological recordings of substantia nigra DA neurons in brain slices from mice to study the effects of cocaine, JJC8-088, and JJC8-091 on currents elicited by DA iontophoresis.…”

Atypical dopamine transporter inhibitors attenuate compulsive-like methamphetamine self-administration in rats

“…The classic atypical DAT inhibitor JHW 007 (benztropine-derived, not modafinil-derived) has been shown to effectively block cocaine and METH self-administration in rats (Hiranita et al , 2014, 2017). The off-target binding profile of both classes of drug are different and likely important for explaining the mechanism of action their effects (see for review, Avelar et al , 2017). One potentially relevant point of overlap is that the sigma-1/DAT binding ratio (0.24) for JJC8-089 (attenuated METH self-administration in LgA rats in the 6 h session) is equivalent to that of JHW 007 (0.20-0.23; Cao et al , 2016; Hiranita et al , 2017).…”