Opioid use disorder (OUD) has become a considerable global public health challenge; however, potential medications for the management of OUD that are effective, safe, and nonaddictive are not available. Accumulating preclinical evidence indicates that antagonists of the dopamine D₃ receptor (D₃R) have effects on addiction in different animal models. We have previously reported that YQA14, a D₃R antagonist, exhibits very high affinity and selectivity for D₃Rs over D₂Rs, and is able to inhibit cocaine- or methamphetamine-induced reinforcement and reinstatement in self-administration tests. In the present study, our results illustrated that YQA14 dose-dependently reduced infusions under the fixed-ratio 2 procedure and lowered the breakpoint under the progressive-ratio procedure in heroin self-administered rats, also attenuated heroin-induced reinstatement of drug-seeking behavior. On the other hand, YQA14 not only reduced morphine-induced expression of conditioned place preference but also facilitated the extinguishing process in mice. Moreover, we elucidated that YQA14 attenuated opioid-induced reward or reinforcement mainly by inhibiting morphine-induced up-regulation of dopaminergic neuron activity in the ventral tegmental area and decreasing dopamine release in the nucleus accumbens with a fiber photometry recording system. These findings suggest that D₃R might play a very important role in opioid addiction, and YQA14 may have pharmacotherapeutic potential in attenuating opioid-induced addictive behaviors dependent on the dopamine system.
Rats ; Mice ; Animals ; Analgesics, Opioid ; Dopamine ; Heroin/pharmacology* ; Dopamine Antagonists/pharmacology* ; Receptors, Dopamine D3/metabolism* ; Morphine/pharmacology* ; Behavior, Addictive/drug therapy* ; Self Administration

BACKGROUNDCocaine addiction may involve complex neuroadaptations, including many changes of genes expression. Dopamine D3 receptors play an important role in cocaine addiction; however, its role in cocaine induced gene expression change is poorly understood. To identify the changes in gene expression induced by repeated cocaine exposure through D3 dopamine receptors, we compared the expression of four molecules: Janus kinase 2 (Jak2), g-aminobutanoic acid receptor subunit alpha 1 (GABAAalpha1), glutamate receptor AMPA3 alpha 3 (GluR 3) and stromal cell derived factor 1 (SDF1). These four have been implicated in mediating the actions of cocaine in the nucleus accumbens (NAc) and caudoputamen (CPu) in mice after acute and repeated cocaine exposure.

METHODSFor the acute and repeated injections, the mice were divided into four groups: 30 mg/kg cocaine, nafadotride 0.5 mg/kg + cocaine 30 mg/kg, nafadotride 0.5 mg/kg, and saline as the basal group. The expression of Jak2, GABAAalpha1, GluR 3 and SDF1 were assayed by Western blot, quantitative real-time RT-PCR and immunohistochemistry.

RESULTSTwenty-four hours after seven consecutive days of repeated cocaine exposure, the expression of GABAAalpha1 decreased in cocaine group compared with basal line and further decreased in the cocaine + nafadotride group and remained at basal level in the nafadotride group. Similarly, the Jak2 expression decreased in cocaine group compared with base line. However, the levels of Jak2 increased in cocaine + nafadotride group compared with cocaine group, while remained at basal level in nafadotride group.

CONCLUSIONSGABAAalpha1 and Jak2 may be involved in chronic cocaine induced neuroadaptations. D3 dopamine receptors play an important role in the expression of these genes.

Animals ; Brain ; drug effects ; metabolism ; Cocaine ; pharmacology ; Female ; Gene Expression Regulation ; drug effects ; Immunohistochemistry ; Janus Kinase 2 ; analysis ; genetics ; Male ; Mice ; Receptors, Dopamine D3 ; physiology ; Receptors, GABA-A ; analysis ; genetics ; Reverse Transcriptase Polymerase Chain Reaction