Modification of anxiety-like behaviors by nociceptin/orphanin FQ (N/OFQ) and time-dependent changes in N/OFQ-NOP gene expression following ethanol withdrawal.

Anxiety is a key consequence of ethanol withdrawal and important risk factor for relapse. The neuropeptide nociceptin/orphanin FQ (N/OFQ) or agonists at this peptide's receptor (NOP) exert anxiolytic-like and antistress actions. N/OFQ dysfunction has been linked to both a high-anxiety behavioral phenotype and excessive ethanol intake. Recent studies suggest a possible link between genetic polymorphisms of the NOP transcript and alcoholism. Thus, in the present study, the effects of intracerebroventricularly administered N/OFQ were tested for modification of anxiety-like behaviors, using the shock-probe defensive burying and elevated plus-maze tests, in ethanol-dependent versus non-dependent rats, 1 and 3 weeks following termination of ethanol exposure. Additionally, prepro-N/OFQ (ppN/OFQ) and NOP receptor gene expression was measured in the central nucleus of the amygdala, in the bed nucleus of the stria terminalis and in the lateral hypothalamus at the same timepoints in separate subjects. One week post-ethanol, N/OFQ dose-dependently attenuated elevated anxiety-like behavior in ethanol-dependent rats and produced anxiolytic-like effects in non-dependent controls in both behavioral tests. However, 3 weeks post-ethanol, N/OFQ altered behavior consistent with anxiogenic-like actions in ethanol-dependent rats but continued to exert anxiolytic-like actions in non-dependent controls. These findings were paralleled by ethanol history-dependent changes of ppN/OFQ and NOP gene expression that showed a distinctive time course in the examined brain structures. The results demonstrate that ethanol dependence and withdrawal are associated with neuroadaptive changes in the N/OFQ-NOP system, suggesting a role of this neuropeptidergic pathway as a therapeutic target for the treatment of alcohol abuse.

∆(9)-Tetrahydrocannabinol decreases NOP receptor density and mRNA levels in human SH-SY5Y cells.

Several studies demonstrated a cross-talk between the opioid and cannabinoid system. The NOP receptor and its endogenous ligand nociceptin/orphanin FQ represent an opioid-related functional entity that mediates some non-classical opioid effects. The relationship between cannabinoid and nociceptin/NOP system is yet poorly explored. In this study, we used the neuroblastoma SH-SY5Y cell line to investigate the effect of delta-9-tetrahydrocannabinol (∆(9)-THC) on nociceptin/NOP system. Results revealed that the exposure to ∆(9)-THC (100, 150, and 200 nM) for 24 h produces a dose-dependent NOP receptor B (max) down-regulation. Moreover, ∆(9)-THC caused a dose-dependent decrease in NOP mRNA levels. The selective cannabinoid receptor CB1 antagonist AM251 (1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide) reduces both effects, suggesting that ∆(9)-THC activation of CB1 receptor is involved in the observed effects. These data show evidence of a cross-talk between NOP and CB1 receptors, thus suggesting a possible interplay between cannabinoid and nociceptin/NOP system.

Kainic acid down-regulates NOP receptor density and gene expression in human neuroblastoma SH-SY5Y cells.

Nociceptin (N/OFQ) is involved in neuronal excitability and in certain types of seizures. Kainate-induced seizures are associated with increased N/OFQ release in the rat thalamus and hippocampus, causing down-regulation of the N/OFQ receptor (NOP). In this study, we used the neuroblastoma SH-SY5Y cell line as a model to investigate the effects of kainate on NOP receptor density and gene expression. Exposure to kainate (10-50 microM) for 3 h did not affect NOP receptor density. In contrast, a NOP Bmax down-regulation was detected in cells exposed to 10 microM kainate for both 6 and 24 h. Moreover, our data show that kainate causes a decrease in NOP mRNA levels after 3, 6, and 24 h, an effect blocked by the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). These findings show that kainate is able to affect the NOP system, both at biosynthesis and receptor density levels in SH-SY5Y cells, and that the kainate ionotropic receptor can contribute to the regulation of the NOP receptor. These data are in agreement with data obtained in vivo and provide new evidence concerning the existence of a cross-talk between NOP and kainate receptors, leading to an interplay between glutamate and N/OFQ circuits.

Effects of prolonged treatment with the opiate tramadol on prodynorphin gene expression in rat CNS.

A low abuse liability is reported for tramadol, an analgesic drug centrally acting through either opioid or nonopioid mechanisms. In this paper, we evaluated the effects of the repeated administration (7 d) of different doses of tramadol (10, 20, and 80 mg/kg, intraperitoneally) on the opioid precursor prodynorphin biosynthesis, in comparison with morphine (10 mg/kg, intraperitoneally), in the rat central nervous system (CNS). Northern analysis showed that morphine and tramadol produced different effects. While morphine caused a downregulation of prodynorphin mRNA levels in all investigated areas (hypothalamus, hippocampus, and striatum), tramadol did not cause any significant change in the striatum, and did not decrease prodynorphin biosynthesis in the hypothalamus and in the hippocampus, at nontoxic doses (10 and 20 mg/kg). The highest dose of tramadol (80 mg/kg) decreased prodynorphin mRNA levels in the hypothalamus and the hippocampus but not in the striatum. These data give some information on tramadol effects at molecular level in the CNS. They indicate that the alterations of prodynorphin gene expression caused by tramadol and morphine show a different pattern that may be related to the different abuse potential of the two analgesic drugs.