Systemic and Intra-Habenular Activation of the Orphan G Protein-Coupled Receptor GPR139 Decreases Compulsive-Like Alcohol Drinking and Hyperalgesia in Alcohol-Dependent Rats

Abstract

GPR139 is an orphan G protein-coupled receptor (GPCR) that is expressed mainly in the brain, with the highest expression in the medial habenula. The modulation of GPR139 receptor function has been hypothesized to be beneficial in the treatment of some mental disorders, but behavioral studies have not yet provided causal evidence of the role of GPR139 in brain dysfunction. Because of the high expression of GPR139 in the habenula, a critical brain region in addiction, we hypothesized that GPR139 may play role in alcohol dependence. Thus, we tested the effect of GPR139 receptor activation using the selective, brain-penetrant receptor agonist JNJ-63533054 on addiction-like behaviors in alcohol-dependent male rats. Systemic administration of JNJ-63533054 (30 mg/kg but not 10 mg/kg, p.o.) reversed the escalation of alcohol self-administration in alcohol-dependent rats, without affecting water or saccharin intake in dependent rats or alcohol intake in nondependent rats. Moreover, systemic JNJ-63533054 administration decreased withdrawal-induced hyperalgesia, without affecting somatic signs of alcohol withdrawal. Further analysis demonstrated that JNJ-63533054 was effective only in a subgroup of dependent rats that exhibited compulsive-like alcohol drinking. Finally, site-specific microinjection of JNJ-63533054 in the habenula but not interpeduncular nucleus (IPN) reduced both alcohol self-administration and withdrawal-induced hyperalgesia in dependent rats. These results provide robust preclinical evidence that GPR139 receptor activation reverses key addiction-like behaviors in dependent animals, suggest that GPR139 may be a novel target for the treatment of alcohol use disorder, and demonstrate that GPR139 is functionally relevant in regulating mammalian behavior.

Keywords: alcohol use disorder; compulsivity; habenula; orphan receptor; pain; withdrawal.

Figure 1.

Timeline of the experiment, escalation of alcohol self-administration, and Blood alcohol levels: BALs after exposure to alcohol vapor. A, Timeline of the experiment with systemic JNJ-63533054 administration in alcohol-dependent rats. B, Rats that were exposed to alcohol vapor escalated their alcohol intake after the 6th session of operant self-administration; *p < 0.05, versus pre-vapor baseline. C, BALs significantly increased after eight weeks of alcohol vapor exposure; ****p < 0.0001.

Figure 2.

GPR139 receptor agonist JNJ-63533054 reverses the escalation of alcohol self-administration in alcohol-dependent rats, with no effect in nondependent rats. A, Rats in the alcohol-dependent group were made dependent by chronic intermittent alcohol vapor exposure. Once the animals were made alcohol-dependent and escalated their alcohol intake [****p < 0.0001, pre-vapor baseline (BSL) vs escalated baseline (ESC)], the effect of JNJ-63533054 on alcohol self-administration was evaluated using a within-subjects design (n = 17). One hour before the session, the rats were orally administered a single dose of JNJ-63533054. JNJ-63533054 significantly reduced alcohol self-administration at a dose of 30 mg/kg (**p < 0.05). Water intake was unaffected by JNJ-63533054 treatment. B, The median number of reinforced responses for alcohol in alcohol-dependent rats was 50 after escalation. C, Once a stable baseline of alcohol intake was reached (±10% over the last three sessions), the effect of JNJ-63533054 on alcohol intake was tested in nondependent rats. One hour before the session, the rats were orally administered a single dose of JNJ-63533054 in a within-subjects design (n = 12). JNJ-63533054 did not significantly affect alcohol self-administration in nondependent rats. Water self-administration was unaffected by JNJ-63533054 treatment. D, The effect of JNJ-63533054 (30 mg/kg, p.o.) on 0.04% (w/v) saccharin self-administration was tested in a separate cohort of rats that were made alcohol dependent by chronic intermittent alcohol vapor exposure. Both saccharin and water self-administration was unaffected by vapor exposure or JNJ-63533054.

Figure 3.

GPR139 agonist decreases withdrawal-induced hyperalgesia without affecting somatic signs of withdrawal. A, JNJ-63533054 (30 mg/kg, p.o.) increased paw withdrawal thresholds compared with vehicle-treated rats in the mechanical nociceptive von Frey test (**p < 0.05), indicating an increase in pain thresholds during alcohol withdrawal. B, JNJ-63533054 did not affect the number of somatic signs of alcohol withdrawal; n = 8–9/group. VLR: ventromedial limb retraction, VOC: vocalization, TR: tail rigidity, AG: abnormal gait, and BT: body tremors.

Figure 4.

Dependent rats that exhibit high alcohol drinking exhibit high compulsive-like alcohol drinking. A, Two distinct subgroups of rats in the alcohol-dependent group were identified according to the median of 50 alcohol-reinforced responses during baseline alcohol self-administration after escalation. Baseline alcohol intake was significantly higher in high-compulsive rats compared with low-compulsive rats (***p < 0.001, n = 8–9). B, To further test the compulsivity of alcohol intake, the rats in the low- and high-compulsive subgroups underwent the quinine adulteration test. The rats were subjected to operant alcohol self-administration sessions with increasing concentrations of quinine that were added to the alcohol solution. The data are expressed as the percentage change relative to the escalated baseline (i.e., lever presses for alcohol alone before quinine adulteration). High-compulsive rats maintained their alcohol drinking despite the aversive, bitter taste of quinine in the alcohol solution (i.e., they were high-compulsive alcohol drinkers). Low-compulsive rats decreased their alcohol intake (>20% from baseline) starting with the lowest concentration of quinine (0.005 g/l; i.e., they were low-compulsive), whereas only the highest quinine concentration (0.05 g/l) decreased alcohol intake in high-compulsive rats; #p < 0.05, ##p < 0.01, ###p < 0.001, ####p < 0.0001, significant difference compared with own baseline; *p < 0.05, ***p < 0.001, significant difference between low-compulsive rats and high-compulsive rats. C, The intake of quinine (0.025 g/l)-adulterated water was not different between low-compulsive and high-compulsive rats.

Figure 5.

JNJ-63533054 decreases alcohol intake in high-compulsive alcohol-dependent rats but has no effect on alcohol intake in low-compulsive alcohol-dependent rats. A, Rats in the high-compulsive subgroup of alcohol-dependent rats (n = 9) escalated their alcohol intake [****p < 0.0001, pre-vapor baseline (BSL) vs escalated baseline (ESC)]. JNJ-63533054 (30 mg/kg, p.o.) significantly decreased alcohol intake in high-compulsive rats (**p < 0.01). Rats in the low-compulsive subgroup escalated their alcohol intake after alcohol vapor exposure (*p < 0.05), but JNJ-63533054 had no effect on alcohol intake in low-compulsive rats (n = 8). B, JNJ-63533054 (30 mg/kg) decreased (>30% reduction) alcohol self-administration in high-compulsive rats (***p < 0.0001) but had no effect in low-compulsive rats.

Figure 6.

Intra-habenular but not intra-IPN JNJ-63533054 administration decreases alcohol intake and increases paw withdrawal thresholds in alcohol-dependent rats during withdrawal. A, Timeline of microinfusions of JNJ-63533054 in alcohol-dependent rats. B, Intra-habenular infusion of JNJ-63533054 (0.25 µg/0.5 µl) decreased alcohol self-administration in dependent rats (**p < 0.01), without affecting water self-administration (n = 6). C, Intra-habenular infusion of JNJ-63533054 increased paw withdrawal thresholds during alcohol withdrawal (**p < 0.01). D, Histology of accurate injection sites in the habenula (black circles) and misplaced injection sites (white circles); 5× magnification. E, In situ hybridization of GPR139 receptors in mouse habenula. Modified from Allen Mouse Brain Atlas (AllenMouseBrainAtlas, 2004). F, Intra-IPN infusion of JNJ-63533054 did not affect alcohol or water self-administration in alcohol-dependent rats (n = 7). G, Paw withdrawal thresholds during alcohol withdrawal were unaffected by intra-IPN infusion of JNJ-63533054. H, Histology of accurate injection sites in the IPN (black circles) and misplaced injection sites (white circles); 2.5× magnification. I, In situ hybridization of GPR139 receptors in the mouse IPN. Modified from Allen Mouse Brain Atlas (AllenMouseBrainAtlas, 2004). cp, cerebral peduncle; DG, dentate gyrus; D3V, dorsal third ventricle; LHb, lateral habenula; MHb, medial habenula; ml, medial lemniscus; SN, substantia nigra; VTA, ventral tegmental area.