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Numerous brain regions have been identified as contributing to addiction-like behaviors, but unclear is the way in which these brain regions as a whole lead to addiction. The search for a final common brain pathway that is involved in addiction remains elusive. To address this question, we used male C57BL/6J mice and performed single-cell whole-brain imaging of neural activity during withdrawal from cocaine, methamphetamine, and nicotine. We used hierarchical clustering and graph theory to identify similarities and differences in brain functional architecture. Although methamphetamine and cocaine shared some network similarities, the main common neuroadaptation between these psychostimulant drugs was a dramatic decrease in modularity, with a shift from a cortical- to subcortical-driven network, including a decrease in total hub brain regions. These results demonstrate that psychostimulant withdrawal produces the drug-dependent remodeling of functional architecture of the brain and suggest that the decreased modularity of brain functional networks and not a specific set of brain regions may represent the final common pathway that leads to addiction.Significance StatementA key aspect of treating drug abuse is understanding similarities and differences of how drugs of abuse affect the brain. In the present study we examined how the brain is altered during withdrawal from psychostimulants. We found that each drug produced a unique pattern of activity in the brain, but that brains in withdrawal from cocaine and methamphetamine shared similar features. Interestingly, we found the major common link between withdrawal from all psychostimulants, when compared to controls, was a shift in the broad organization of the brain in the form of reduced modularity. Reduced modularity has been shown in several brain disorders, including traumatic brain injury, and dementia, and may be the common link between drugs of abuse.

BackgroundCocaine addiction is a major public health problem. Despite decades of intense research, no effective treatments are available. Both preclinical and clinical studies of drug addiction strongly suggest that the nucleus accumbens (NAcc) is a viable target for deep brain stimulation (DBS).ObjectiveAlthough previous studies have shown that DBS of the NAcc decreases cocaine seeking and reinstatement, the effects of DBS on cocaine intake in cocaine-dependent animals have not yet been investigated.MethodsRats were made cocaine-dependent by allowing them to self-administer cocaine in long-access sessions (6 h, 0.5 mg/kg/infusion). The effects of high-frequency DBS of the NAcc shell on cocaine intake was then studied. Furthermore, cocaine-induced locomotor activity, irritability-like behavior during cocaine abstinence and the levels of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits 1 and 2 (GluR1/GluA1 and GluR2/GluA2) after DBS were investigated.ResultsContrary to our expectations, DBS of the NAcc shell induced a slight increase in both cocaine self-administration and cocaine-induced locomotor activity. In addition, 18 h into cocaine withdrawal, we found that DBS decreased irritability-like behavior. We also found that DBS-induced a robust increase in both cytosolic and synaptosomal levels of GluR1, but not GluR2, specifically in the central nucleus of the amygdala but not in other brain regions.ConclusionsThese preclinical results with cocaine-dependent animals do not support high-frequency DBS of the NAcc shell as a therapeutic approach for the treatment of cocaine addiction in active cocaine users. However, the decrease in irritability-like behavior during cocaine abstinence, together with previous findings showing that DBS of the NAcc shell reduces the reinstatement of cocaine seeking in abstinent animals, warrants future investigations of DBS as a treatment for negative emotional states and craving during abstinence.HighlightsHigh-frequency DBS of the NAcc shell for the treatment of cocaine addiction is proposedDBS of the NAcc shell does not decrease cocaine intake in cocaine-dependent ratsDBS increases the level of GluR1 specifically in the central nucleus of the amygdala

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.

A nicotine-degrading enzyme termed NicA2 was altered (NicA2-J1) through fusion of an albumin binding domain to increase its half-life. Examination of NicA2-J1 in vivo demonstrated a complete blockade of brain nicotine access, which in turn blunted nicotine's psychoactive effects. These data further support development of pharmacokinetic nicotine cessation therapeutics.

BACKGROUND: Environmental conditioning is a major trigger for relapse in abstinent addicts. We showed that activation of the neuropeptide S (NPS) system exacerbates reinstatement vulnerability to cocaine and alcohol via stimulation of the hypocretin-1/orexin-A (Hcrt-1/Ox-A) system. METHODS: Combining pharmacologic manipulations with immunohistochemistry techniques, we sought to determine how NPS and Hcrt-1/Ox-A systems interact to modulate reinstatement of alcohol seeking in rats. RESULTS: Intrahypothalamic injection of NPS facilitated discriminative cue-induced reinstatement of alcohol seeking. This effect was blocked by the selective Hcrt-1/Ox-A antagonist SB334867 microinjected into the hypothalamic paraventricular nucleus (PVN) or into the bed nucleus of the stria terminalis (BNST) but not into the ventral tegmental area or the locus coeruleus. Combining double labeling and confocal microscopy analyses, we found that NPScontaining axons are in close apposition to hypothalamic Hcrt-1/Ox-A positive neurons, a significant proportion of which express NPS receptors, suggesting a direct interaction between the two systems. Retrograde tracing experiments showed that intra-PVN or intra-BNST red fluorobead unilateral injection labeled bilaterally Hcrt-1/Ox-A somata, suggesting that NPS could recruit two distinct neuronal pathways. Confirming this assumption, intra-BNST or PVN Hcrt-1/Ox-A injection enhanced alcohol seeking similarly to hypothalamic NPS injection but to a lesser degree. CONCLUSIONS: Results suggest that the Hcrt-1/Ox-A neurocircuitry mediating the facilitation of cue-induced reinstatement by NPS involves structures critically involved in stress regulation such as the PVN and the BNST. These findings open to the tempting hypothesis of a role of the NPS system in modulating the interactions between stress and environmental conditioning factors in drug relapse.

The GABAergic system in the central amygdala (CeA) plays a major role in ethanol dependence and the anxiogenic-like response to ethanol withdrawal. A large body of evidence shows that Nociceptin/Orphanin FQ (N/OFQ) regulates ethanol intake and anxiety-like behavior. In the rat, ethanol significantly augments CeA GABA release, whereas N/OFQ diminishes it. Using electrophysiological techniques in an in vitro slice preparation, in this study we investigated the effects of a nonpeptidergic NOP receptor agonist, MT-7716 [(R)-2-3-[1-(Acenaphthen-1-yl)piperidin-4-yl]-2-oxo-2,3-dihydro-1H-benzimidazol-1-yl-N-methylacetamide hydrochloride hydrate], and its interaction with ethanol on GABAergic transmission in CeA slices of naïve rats. We found that MT-7716 dose-dependently (100-1000 nM) diminished evoked GABAA receptor-mediated inhibitory postsynaptic potentials (IPSPs) and increased paired-pulse facilitation (PPF) ratio of these evoked IPSPs, suggesting a presynaptic site of action of the MT-7716 by decreasing GABA release at CeA synapses. The presynaptic action of MT-7716 was also supported by the significant decrease in the frequency of miniature inhibitory postsynaptic currents (mIPSCs) induced by the nociceptin receptor (NOP) agonist. Interestingly, MT-7716 prevented the ethanol-induced augmentation of evoked IPSPs. A putative selective NOP antagonist, [Nphe1]Nociceptin(1-13)NH2, totally prevented the MT-7716-induced inhibition of IPSP amplitudes indicating that MT-7716 exerts its effect through NOPs. These data provide support for an interaction between the nociceptin and GABAergic systems in the CeA and for the anti-alcohol properties of the NOP activation. The development of a synthetic nonpeptidergic NOP receptor agonist such as MT-7716 may represent a useful therapeutic target for alcoholism.

Corticotropin releasing factor (CRF) is the primary mediator of stress responses, and nociceptin/orphanin FQ (N/OFQ) plays an important role in the modulation of these stress responses. Thus, in this multidisciplinary study, we explored the relationship between the N/OFQ and the CRF systems in response to stress. Usingin situhybridization (ISH), we assessed the effect of body restraint stress on the gene expression of CRF and N/OFQ-related genes in various subdivisions of the amygdala, a critical brain structure involved in the modulation of stress response and anxiety-like behaviors. We found a selective upregulation of the NOP and downregulation of the CRF1receptor transcripts in the CeA and in the BLA after body restraint. Thus, we performed intracellular electrophysiological recordings of GABAA-mediated IPSPs in the central nucleus of the amygdala (CeA) to explore functional interactions between CRF and N/OFQ systems in this brain region. Acute application of CRF significantly increased IPSPs in the CeA, and this enhancement was blocked by N/OFQ. Importantly, in stress-restraint rats, baseline CeA GABAergic responses were elevated and N/OFQ exerted a larger inhibition of IPSPs compared with unrestraint rats. The NOP antagonist [Nphe1]-nociceptin(1–13)NH2 increased the IPSP amplitudes in restraint rats but not in unrestraint rats, suggesting a functional recruitment of the N/OFQ system after acute stress. Finally, we evaluated the anxiety-like response in rats subjected to restraint stress and nonrestraint rats after N/OFQ microinjection into the CeA. Intra-CeA injections of N/OFQ significantly and selectively reduced anxiety-like behavior in restraint rats in the elevated plus maze. These combined results demonstrate that acute stress increases N/OFQ systems in the CeA and that N/OFQ has antistress properties.

Background Pioglitazone and rosiglitazone belong to the class of thiazolidinediones (TZDs). They were first developed as antioxidants and then approved for the clinical treatment of insulin resistance and Type 2 diabetes. TZDs bind with high affinity and activate peroxisome proliferator-activated receptor-gamma (PPARγ) receptors, which in the brain are expressed both in neurons and in glia. Methods We evaluated the effect of PPARγ activation by TZDs on alcohol drinking, relapse-like behavior, and withdrawal in the rat. We also tested the effect of TZDs on alcohol and saccharin self-administration. Results We showed that activation of PPARγ receptors by pioglitazone (0, 10, and 30 mg/kg) and rosiglitazone (0, 10 and 30 mg/kg) given orally selectively reduced alcohol drinking. The effect was blocked by pretreatment with the selective PPARγ antagonist GW9662 (5 μg/rat) given into the lateral cerebroventricle, suggesting that this TZD's effect is mediated by PPARγ receptors in the central nervous system. Pioglitazone abolished reinstatement of alcohol seeking, a relapse-like behavior, induced by yohimbine, a pharmacologic stressor, but did not affect cue-induced relapse. In the self-administration experiments, pioglitazone reduced lever pressing for alcohol but not for saccharin. Finally, pioglitazone prevented the expression of somatic signs of alcohol withdrawal. Conclusions These findings provide new information about the role of brain PPARγ receptors and identify pioglitazone as candidate treatments for alcoholism and possibly other addictions.

Pregabalin (Lyrica™) is a structural analogue of γ-aminobutyric acid (GABA) approved by FDA for partial epilepsy, neuropathic pain and recently generalized anxiety disorder. While the exact cellular mechanism of action of pregabalin is still unclear, evidence from several studies suggests that it reduces excitatory neurotransmitter release and postsynaptic excitability. Based on these mechanisms we sought interesting to evaluate the effect of pregabalin on alcohol-abuse-related behaviours. For this purpose, using genetically selected alcohol-preferring Marchigian Sardinian (msP) rats, we evaluated the effect of pregabalin on alcohol drinking and relapse to alcohol seeking elicited by environmental conditioning factors or stress. Our results showed that treatment with pregabalin (0, 10, 30 and 60 mg/kg) given orally selectively reduced home cage alcohol drinking in msP rat. This effect was confirmed in self-administration experiments where pregabalin (0, 10 and 30 mg/kg) significantly reduced operant responding for alcohol but not for food. Using alcohol reinstatement models we also found that pregabalin (0, 10 and 30 mg/kg) abolished seeking behaviour elicited by the pharmacological stressor yohimbine as well as cues predictive of alcohol availability. Results demonstrate that pregabalin may have potential in the treatment of alcohol addiction.

Drug addiction is a chronic relapsing disorder characterized by compulsive drug seeking and use. Environmental conditioning factors are among the major determinants of relapse in abstinent cocaine users. Here we describe a role of the neuropeptide S (NPS) system in regulating relapse. In rats with a history of cocaine self-administration, presentation of stimuli predictive of drug availability reinstates drug seeking, triggering relapse. Intracerebroventricular (ICV) injection of NPS increased conditioned reinstatement of cocaine seeking, whereas peripheral administration of the NPS receptor antagonist SHA 68 reduced it. Manipulation of the NPS receptor system did not modify cocaine self-administration. We also found that ICV NPS administration activates c-Fos expression in hypocretin-1/orexin-A (Hcrt-1/Ox-A) immunoreactive neurons in the lateral hypothalamus (LH) and in the perifornical area (PeF). Of note, intra-LH and intra-PeF administration of NPS increased conditioned reinstatement of cocaine responding, an effect that was selectively blocked with the Hcrt-1/Ox-A receptor selective antagonist SB334867. Finally, results showed that intra-LH injection of the NPS antagonist [D-Cys(tBu) (5)]NPS blocked cue-induced cocaine seeking, indicating a role for this system in the pathophysiology of drug relapse.

Background: Alcoholism is a chronic disease characterized by frequent intoxications followed by withdrawal episodes and relapse to alcohol use. Neuroplastic changes associated with these intoxication and withdrawal cycles are thought to play a key role in disease progression. Recently, it has been shown that neuropeptide S (NPS), a newly deorphanized neuropeptide receptor system, facilitates relapse to alcohol seeking in laboratory animals. Given that a history of ethanol intoxication may increase vulnerability to alcohol addiction, we sought to determine whether NPS receptor (NPSR) gene expression is altered during withdrawal. Methods: Rats were subjected to 1 week of intoxication by oral alcohol administration. NPSR gene expression was analyzed by in situ hybridization in rats 12 hours and 7 days after the last alcohol administration. To investigate the functional significance of NPSR system adaptation following protracted withdrawal 7 days after intoxication, we tested the anxiolytic-like properties of NPS in nondependent and postdependent rats using the shock probe defensive burying test (DB). Results: At both time points, increased NPSR gene expression was observed in several brain areas, including the endopiriform nucleus, the motor cortex, and the medial amygdaloid nucleus. Moderate increases in gene expression were also found in the lateral hypothalamus, paraventricular nucleus, basolateral and central amygdala. Differences from control animals were more pronounced after 7 days of abstinence. The upregulation of the NPSR system at this time point was confirmed by functional data indicating that intracerebroventricular (ICV) NPS administration (0.0, 0.3, and 0.1 nmol/rat) elicits more pronounced anxiolytic effects in postdependent animals than in controls subjected to the electric shock probe DB test. Conclusions: Neuropeptide S receptor mRNA expression is increased in different brain areas of postdependent rats; as shown in the DB test, this expression change is functionally relevant.