Activation of Hypocretin-1/Orexin-A Neurons Projecting to the Bed Nucleus of the Stria Terminalis and Paraventricular Nucleus Is Critical for Reinstatement of Alcohol Seeking by Neuropeptide S.

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 NPS-containing 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.

Activation of PPARγ by pioglitazone potentiates the effects of naltrexone on alcohol drinking and relapse in msP rats.

BACKGROUND: Pioglitazone is a selective peroxisome proliferator-activated receptor γ (PPARγ) agonist used for the treatment of insulin resistance and type 2 diabetes. Previous studies conducted in our laboratory showed that activation of PPARγ by pioglitazone reduces alcohol drinking, stress-induced relapse, and alcohol withdrawal syndrome in rats. Pioglitazone was not able to prevent relapse elicited by alcohol cues. Conversely, the nonselective opioid antagonist naltrexone has been shown to reduce alcohol drinking and cue- but not stress-induced relapse in rodents. METHODS: Based on these findings, this study was sought to determine the efficacy of pioglitazone and naltrexone combination on alcohol intake and relapse behavior. Genetically selected alcohol-preferring Marchigian Sardinian (msP) rats were used for the study. RESULTS: Pioglitazone (10 and 30 mg/kg) and naltrexone (0.25 and 1.0 mg/kg) each individually reduced alcohol drinking in msP rats. The combination of the 2 drugs resulted in a more potent alcohol drinking reduction than single agents. Confirming previous studies, pioglitazone (10 and 30 mg/kg) significantly reduced relapse induced by the pharmacological stressor yohimbine (1.25 mg/kg) but not by cues predictive of alcohol availability. Conversely, naltrexone reduced reinstatement of drug seeking elicited by alcohol cues but not by yohimbine. CONCLUSIONS: The drug combination was effective in reducing both relapse behaviors. These findings open new vistas in the use pioglitazone in combination with naltrexone for the treatment of alcoholism.

Hypothalamic neuropeptide S receptor blockade decreases discriminative cue-induced reinstatement of cocaine seeking in the rat.

RATIONALE: Previous studies have shown that activation of brain neuropeptide S receptor (NPSR) facilitates reinstatement of cocaine seeking elicited by environmental cues predictive of drug availability. This finding suggests the possibility that blockade of NPSR receptors may be of therapeutic benefit in cocaine addiction. To evaluate this hypothesis, we investigated the effect of two newly synthetized NPSR antagonists, namely the quinolinone-amide derivative NPSR-QA1 and the NPS peptidic analogue [D-Cys(tBu)5]NPS on cocaine self-administration and on discriminative cue-induced relapse to cocaine seeking in the rat. METHODS: Separate groups of rats self-administered food and cocaine 0.25 mg/kg/inf in FR1 and FR5 (fixed ratio reinforcement schedules) for 30-min and 2-h sessions per day. After food and cocaine intake reached baseline levels, the effect of NPSR-QA1 was tested on cocaine and food self-administration. The NPSR-QA1 was injected intraperitoneally and its effect on discriminative cue-induced reinstatement was evaluated, while [D-Cys(tBut)5]NPS was injected intracranially, intra-lateral hypothalamus, intra-perifornical area of the hypothalamus, and intra-central amygdala. The effect of the NPSR-QA1 on extinction of cocaine seeking was also assessed. RESULTS: Intraperitoneal administration of NPSR-QA1 (15-30 mg/kg) did not affect cocaine self-administration. Conversely, NPSR-QA1 (15-30 mg/kg) decreased discriminative cue-induced cocaine relapse. At the lowest dose, this effect was specific, while at the highest dose, NPSR-QA1 also reduced food self-administration. The efficacy of NPSR antagonism on cocaine seeking was confirmed with [D-Cys(tBu)5]NPS (10-30 nmol/rat) as it markedly inhibited relapse behavior following site-specific injection into the lateral hypothalamus and the perifornical area of the hypothalamus but not into the central amygdala. CONCLUSIONS: The identification of the NPS/NPSR system as an important new element involved in the physiopathology of cocaine addiction and the discovery of the anti-addictive properties of NPSR antagonists opens the possibility of exploring a new mechanism for cocaine addiction treatment.

Neuropeptide S facilitates cue-induced relapse to cocaine seeking through activation of the hypothalamic hypocretin system.

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.

Persistent increase of alcohol-seeking evoked by neuropeptide S: an effect mediated by the hypothalamic hypocretin system.

The association of ethanol's reinforcing effects with specific environmental stimuli is thought to be a critical factor for relapse risk in alcoholism. This study examined in rats the effects of a newly deorphanized neuropeptide receptor and its cognate ligand, Neuropeptide S (NPS), on ethanol consumption and reinstatement of ethanol-seeking by environmental cues previously associated with ethanol availability. In the self-administration experiments, the stable response rates observed for ethanol reinforcement were not modified by intracerebroventricular (ICV) injection of NPS (1.0 and 2.0 nmol per rat). In the reinstatement experiments, ethanol-associated cues induced robust rates of ethanol seeking, which were highly resistant to extinction over repeated sessions of reinstatement testing. ICV NPS treatment (1.0, 2.0 and 4.0 nmol per rat) resulted in a significant increase of ethanol seeking elicited by ethanol-associated cues. In contrast, NPS did not affect the reinstatement of responding to water-paired stimuli. Site-specific NPS injection (0.1 and 0.5 nmol per rat) into the lateral hypothalamus also reinstated extinguished responding to ethanol. This effect was selectively blocked by pre-treatment with the hypocretin-1/orexin-A antagonist SB-334867 (10 mg/kg, i.p.). At the dose tested, SB-334867 did not modify alcohol reinstatement per se. These results provide the first demonstration that activation of NPS receptors in the LH intensifies relapse to ethanol-seeking elicited by environmental conditioning factors. This effect is selective, and is mediated by activation of LH hypocretin neurones. Based on the present findings, we also predict that antagonism at NPS receptors could represent a novel pharmacological approach to alcohol relapse treatment.