Background: Syntaxins 1 through 4 are SNAP receptor (SNARE) proteins that mediate vesicular trafficking to the plasma membrane. In retina, syntaxins 1 and 3 are expressed at conventional and ribbon synapses, respectively, suggesting that synaptic trafficking functions differ among syntaxin isoforms. To better understand syntaxins in synaptic signaling and trafficking, we further examined the cell-and synapse-specific expression of syntaxins 1 through 4 in the mouse retina by immunolabeling and confocal microscopy.

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Central morphine analgesia is significantly greater in male than in female rats. Since mu and delta opioid receptor subtypes have been implicated in supraspinal analgesia, the present study evaluated whether gender or adult gonadectomy altered (a) analgesia on the tail-flick and jump tests following central administration of the mu-selective agonist, [D-Ala2, Me-Phe4, Gly(ol)5] enkephalin (DAMGO) and the delta-selective agonist, [D-Ser2,Leu5] enkephalin-Thr6 (DSLET) and (b) mu1, mu2 and delta opioid receptor binding. Sham-operated male rats displayed significantly greater magnitudes of peak and total analgesia than sham-operated females on the tail-flick test following DAMGO, but not DSLET. Gender differences were not observed for DAMGO and DSLET analgesia on the jump test. Gonadectomy failed to consistently affect either DAMGO or DSLET analgesia. Regression analyses failed to reflect significant shifts in the dose-response functions for either agonist on either measure. Gender differences were not observed for mu1, mu2, or delta binding in hypothalamus or cortex. These data are compared with analgesic responses sensitive to gender differences.

BackgroundClinical studies indicate that post-traumatic stress disorder (PTSD) frequently shares co-morbidity with chronic pain. Although in animals acute stress-induced antinociception is well documented, the effect of PTSD-like stress on nociceptive sensitivity is unclear. Though a few studies measured nociceptive responses at a single time point, no studies have examined changes in nociceptive sensitivity over time following exposure to PTSD-like stress. Nociceptin/orphanin FQ (N/OFQ), an endogenous ligand for the N/OFQ peptide (NOP) receptor, modulates various biological functions in the central nervous system that are affected by PTSD, including nociceptive sensitivity, stress and anxiety, learning and memory.ResultsThe present study examined thermal and mechanical nociceptive sensitivity in male Sprague Dawley rats between 7 and 28 days after single-prolonged stress (SPS), an established animal model for PTSD. Rat paw withdrawal thresholds (PWT) to von Frey and paw withdrawal latencies (PWL) to radiant heat stimuli, respectively, dramatically decreased as early as 7 days after initiation of SPS and lasted the length of the study, 28 days. In addition, N/OFQ levels increased in cerebrospinal fluid (CSF; on days 9, 14 and 28) and serum (day 28), while levels of circulating corticosterone (CORT) decreased 28 days after initiation of SPS. SPS exposure induced anxiety-like behavior and enhanced inhibition of the hypothalamo-pituitary-adrenal (HPA) axis, as previously reported for this model.ConclusionsOur results demonstrate that SPS induces the development of persistent mechanical allodynia and thermal hyperalgesia that is accompanied by increased N/OFQ content in the CSF, and eventually, in serum. These findings suggest a link between N/OFQ and the development of hyperalgesia and allodynia in a rat model of PTSD.

Morphine tolerance in vivo is reduced following blockade of the orphanin FQ/nociceptin (OFQ/N)/opioid receptor-like 1 (ORL1) receptor system, suggesting that OFQ/N contributes to the development of morphine tolerance. We previously reported that a 60-min activation of ORL1 receptors natively expressed in BE(2)-C cells desensitized both and ORL1 receptor-mediated inhibition of cAMP. Investigating the mechanism(s) of OFQ/N-mediated and ORL1 receptor cross-talk, we found that pretreatment with the protein kinase C inhibitor, chelerythrine chloride (1 M), blocked OFQ/N-mediated homologous desensitization of ORL1 and heterologous desensitization of opioid receptors. Furthermore, depletion of PKC by 12-O-tetradecanoylphorbol-13-acetate exposure (48 h, 1 M) also prevented OFQ/N-mediated and ORL1 desensitization. OFQ/N pretreatment resulted in translocation of PKC-␣, G proteincoupled receptor kinase 2 (GRK2) and GRK3 from the cytosol to the membrane, and this translocation was also blocked by chelerythrine. Reduction of GRK2 and GRK3 levels by antisense, but not sense DNA treatment blocks ORL1 and receptor desensitization. This suggests that PKC-␣ is required for GRK2 and GRK3 translocation to the membrane, where GRK can inactivate ORL1 and opioid receptors upon rechallenge with the appropriate agonist. Our results demonstrate for the first time the involvement of conventional PKC isozymes in OFQ/N-induced -ORL1 cross-talk, and represent a possible mechanism for OFQ/N-induced anti-opioid actions.Orphanin FQ/nociceptin (OFQ/N), an exquisitely selective agonist at the opioid receptor-like 1 (ORL1) receptor, modulates both behavioral (nociception, anxiety, learning, reward) and immune (cell proliferation) responses (Harrison and Grandy, 2000;Peluso et al., 2001). Although ORL1 and OFQ/N share greater than 40% homology with other opioid receptors and endogenous opioid peptides, many of their actions are anti-opioid in nature (Harrison and Grandy, 2000). One cellular mechanism for their anti-opioid effect is attributed, at least partially, to actions of OFQ/N on different populations of neurons in the brainstem (Pan et al., 2000). The molecular basis of their anti-opioid effects still remains to be determined, but heterologous cross-talk is a possibility since and ORL1 receptors are colocalized on several cell populations within the descending analgesic pathway (Connor et al

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BACKGROUND AND PURPOSESingle-prolonged stress (SPS), a rat model of post-traumatic stress disorder (PTSD), also induces long-lasting hyperalgesia associated with hypocortisolism and elevated nociceptin/orphanin FQ (N/OFQ) levels in serum and CSF. Here, we determined the effect of JTC-801 (N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl) benzamide monohydrochloride), a nociceptin/orphanin FQ peptide (NOP) receptor antagonist, on symptoms of pain and anxiety in rats after SPS exposure, and examined N/OFQ-NOP receptor system changes. EXPERIMENTAL APPROACHMale Sprague Dawley rats received JTC-801 (6 mg kg −1 i.p., once daily) during days 7-21 of SPS. The ability of JTC-801 to inhibit N/OFQ-stimulated [ 35 S]-GTPγS binding was confirmed in rat brain membranes. Anxiety-like behaviour and pain sensitivity were monitored by changes in elevated plus maze performance and withdrawal responses to thermal and mechanical stimuli. Serum corticosterone and N/OFQ content in CSF, serum and brain tissues were determined by radioimmunoassay; NOP receptor protein and gene expression in amygdala, hippocampus and periaqueductal grey (PAG) were examined by immunoblotting and real-time PCR respectively. KEY RESULTSJTC-801 treatment reversed SPS-induced mechanical allodynia, thermal hyperalgesia, anxiety-like behaviour and hypocortisolism. Elevated N/OFQ levels in serum, CSF, PAG and hippocampus at day 21 of SPS were blocked by JTC-801; daily JTC-801 treatment also reversed NOP receptor protein and mRNA up-regulation in amygdala and PAG. CONCLUSION AND IMPLICATIONSJTC-801 reversed SPS-induced anxiety-and pain-like behaviours, and NOP receptor system up-regulation. These findings suggest that N/OFQ plays an important role in hyperalgesia and allodynia maintenance after SPS. NOP receptor antagonists may provide effective treatment for co-morbid PTSD and pain. LINKED ARTICLESThis article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx