The opioid peptide nociceptin/orphanin FQ mediates prostaglandin E2-induced allodynia, tactile pain associated with nerve injury

Temporal and regulatory dynamics of the inner ear transcriptome during development in mice

The inner ear controls hearing and balance, while the temporal molecular signatures and transcriptional regulatory dynamics underlying its development are still unclear. In this study, we investigated time-series transcriptome in the mouse inner ear from embryonic day 11.5 (E11.5) to postnatal day 7 (P7) using bulk RNA-Seq. A total of 10,822 differentially expressed genes were identified between pairwise stages. We identified nine significant temporal expression profiles using time-series expression analysis. The constantly down-regulated profiles throughout the development are related to DNA activity and neurosensory development, while the constantly upregulated profiles are related to collagen and extracellular matrix. Further co-expression network analysis revealed that several hub genes, such as Pnoc, Cd9, and Krt27, are related to the neurosensory development, cell adhesion, and keratinization. We uncovered three important transcription regulatory paths during mice inner ear development. Transcription factors related to Hippo/TGFβ signaling induced decreased expressions of genes related to the neurosensory and inner ear development, while a series of INF genes activated the expressions of genes in immunoregulation. In addition to deepening our understanding of the temporal and regulatory mechanisms of inner ear development, our transcriptomic data could fuel future multi-species comparative studies and elucidate the evolutionary trajectory of auditory development.

Neuropathic pain promotes adaptive changes in gene expression in brain networks involved in stress and depression

Neuropathic pain is a complex chronic condition characterized by various sensory, cognitive, and affective symptoms. A large percentage of patients with neuropathic pain are also afflicted with depression and anxiety disorders, a pattern that is also seen in animal models. Furthermore, clinical and preclinical studies indicate that chronic pain corresponds with adaptations in several brain networks involved in mood, motivation, and reward. Chronic stress is also a major risk factor for depression. We investigated whether chronic pain and stress affect similar molecular mechanisms and whether chronic pain can affect gene expression patterns that are involved in depression. Using two mouse models of neuropathic pain and depression [spared nerve injury (SNI) and chronic unpredictable stress (CUS)], we performed next-generation RNA sequencing and pathway analysis to monitor changes in gene expression in the nucleus accumbens (NAc), the medial prefrontal cortex (mPFC), and the periaqueductal gray (PAG). In addition to finding unique transcriptome profiles across these regions, we identified a substantial number of signaling pathway-associated genes with similar changes in expression in both SNI and CUS mice. Many of these genes have been implicated in depression, anxiety, and chronic pain in patients. Our study provides a resource of the changes in gene expression induced by long-term neuropathic pain in three distinct brain regions and reveals molecular connections between pain and chronic stress.

Intrathecal administration of low-dose nociceptin/orphanin FQ induces allodynia via c-Jun N-terminal kinase and monocyte chemoattractant protein-1

Pathological chronic pain, which is frequently associated with prolonged tissue damage, inflammation, tumour invasion, and neurodegenerative diseases, gives rise to hyperalgesia and allodynia. We previously reported that intrathecal administration of nociceptin/orphanin FQ (N/OFQ), an endogenous ligand for the orphan opioid receptor-like receptor, in the femtomole range induces touch-evoked allodynia. N/OFQ has been implicated in multiple signalling pathways, such as inhibition of cAMP production and Ca(2+) channels, or activation of K(+) channels and mitogen-activated protein kinase, although the signalling pathways of N/OFQ-induced allodynia remain unclear. To address these issues, we developed an ex vivo mitogen-activated protein kinase assay by using intact slices of mouse spinal cord. N/OFQ markedly increased the phosphorylation of c-Jun N-terminal kinase (JNK) in the superficial dorsal horn of the spinal cord. The N/OFQ-stimulated JNK phosphorylation was significantly inhibited by pertussis toxin, the phospholipase C inhibitor U73122, and the inositol trisphosphate receptor antagonist Xestospongin C. Intrathecal administration of the JNK inhibitor SP600125 inhibited N/OFQ-evoked allodynia. The N/OFQ-induced increase in JNK phosphorylation was observed in astrocytes that expressed glial fibrillary acidic protein. N/OFQ also induced monocyte chemoattractant protein-1 (MCP-1) release via the JNK pathway, and N/OFQ-induced JNK phosphorylation was observed in MCP-1-immunoreactive astrocytes. Intrathecal administration of the MCP-1 receptor antagonist RS504393 inhibited N/OFQ-evoked allodynia. These results suggest that, in the spinal dorsal horn, N/OFQ induces allodynia through activation of JNK via the phospholipase C-inositol trisphosphate pathway, which is coupled to pertussis toxin-sensitive G-protein, and following the release of MCP-1 from astrocytes.

Epigenetic modification of DRG neuronal gene expression subsequent to nerve injury: etiological contribution to complex regional pain syndromes (Part I)

DRG is of importance in relaying painful stimulation to the higher pain centers and therefore could be a crucial target for early intervention aimed at suppressing primary afferent stimulation. Complex regional pain syndrome (CRPS) is a common pain condition with an unknown etiology. Recently added new information enriches our understanding of CRPS pathophysiology. Researches on genetics, biogenic amines, neurotransmitters, and mechanisms of pain modulation, central sensitization, and autonomic functions in CRPS revealed various abnormalities indicating that multiple factors and mechanisms are involved in the pathogenesis of CRPS. Epigenetics refers to mitotically and meiotically heritable changes in gene expression that do not affect the DNA sequence. As epigenetic modifications potentially play an important role in inflammatory cytokine metabolism, neurotransmitter responsiveness, and analgesic sensitivity, they are likely key factors in the development of chronic pain. In this dyad review series, we systematically examine the nerve injury-related changes in the neurological system and their contribution to CRPS. In this part, we first reviewed and summarized the role of neural sensitization in DRG neurons in performing function in the context of pain processing. Particular emphasis is placed on the cellular and molecular changes after nerve injury as well as different models of inflammatory and neuropathic pain. These were considered as the potential molecular bases that underlie nerve injury-associated pathogenesis of CRPS.

Role of nociceptin/orphanin FQ and NOP receptors in the response to acute and repeated restraint stress in rats

Central nociceptin/orphanin FQ (N/OFQ)-expressing neurones are abundantly expressed in the hypothalamus and limbic system and are implicated in the regulation of activity of the hypothalamic-pituitary-adrenal axis (HPA) and stress responses. We investigated the role of the endogenous N/OFQ receptor (NOP) system using the nonpeptidic NOP antagonist, JTC-801 [N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxy-methyl)benzamide monohydrochloride], during the HPA axis response to acute physical/psychological stress (60 min of restraint). Although i.v. JTC-801 (0.05 mg/kg in 100 μl) had no significant effect on restraint-induced plasma corticosterone release at 30 or 60 min post-injection, i.v. JTC-801 (0.05 mg/kg in 100 μl) in quiescent rats significantly increased basal plasma corticosterone at the 30-min time-point compared to i.v. vehicle (1% dimethysulphoxide in sterile saline). Central injection of JTC-801 i.c.v. was associated with increased Fos expression in the parvocellular paraventricular nucleus 90 min after infusion compared to vehicle control. These findings contrast to the effects of i.c.v. UFP-101, a NOP antagonist that we have previously shown to have no effect on HPA activity in quiescent rats. To determine whether restraint stress was associated with compensatory changes in N/OFQ precursor (ppN/OFQ) or NOP receptor mRNAs, in a separate study, we undertook reverse transcriptase-polymerase chain reaction and in situ hybridisation analysis of ppN/OFQ and NOP transcripts in the brains of male Sprague-Dawley rats. In support of an endogenous role for central N/OFQ in psychological stress, we found that acute restraint significantly decreased preproN/OFQ transcript expression in the hippocampus 2 h after stress compared to unstressed controls. PpN/OFQ mRNA was also reduced in the mediodorsal forebrain 4 h after stress. NOP mRNA was reduced in the hypothalamus 2 h after restraint and at 4 h in mediodorsal forebrain and hippocampus. In situ hybridisation analysis showed that acute restraint significantly decreased ppNN/OFQ in the central amygdala, with significantly increased expression in bed nucleus and reticular thalamus associated with repeated restraint. There was a strong trend for reduced NOP mRNA in the bed nucleus of acute and repeated restraint groups, although there were no other significant changes seen. Although the exact mechanisms require elucidation, the findings obtained in the present study provide evidence indicating that the endogenous N/OFQ system is involved in both acute and chronic restraint stress responses. In summary, our findings confirm the significant role of endogenous NOP receptors and tonic N/OFQ function in the response to the psychological stress of restraint.

Opioid-related (ORL1) receptors are enriched in a subpopulation of sensory neurons and prolonged activation produces no functional loss of surface N-type calcium channels

The opioid-related receptor, ORL1, is activated by the neuropeptide nociceptin/orphanin FQ (N/OFQ) and inhibits high-voltage-activated (HVA) calcium channel currents (I(Ca)) via a G-protein-coupled mechanism. Endocytosis of ORL1 receptor during prolonged N/OFQ exposure was proposed to cause N-type voltage-gated calcium channel (VGCC) internalization via physical interaction between ORL1 and the N-type channel. However, there is no direct electrophysiological evidence for this mechanism in dorsal root ganglion (DRG) neurons or their central nerve terminals. The present study tested this using whole-cell patch-clamp recordings of HVA I(Ca) in rat DRG neurons and primary afferent excitatory synaptic currents (eEPSCs) in spinal cord slices. DRG neurons were classified on the basis of diameter, isolectin-B4 (IB4) binding and responses to capsaicin, N/OFQ and a μ-opioid agonist, DAMGO. IB4-negative neurons less than 20 μm diameter were selectively responsive to N/OFQ as well as DAMGO. In these neurons, ORL1 desensitization by a supramaximal concentration of N/OFQ was not followed by a decrease in HVA I(Ca) current density or proportion of whole-cell HVA I(Ca) contributed by N-type VGCC as determined using the N-type channel selective blocker, ω-conotoxin CVID. There was also no decrease in the proportion of N-type I(Ca) when neurons were incubated at 37°C with N/OFQ for 30 min prior to recording. In spinal cord slices, N/OFQ consistently inhibited eEPSCs onto dorsal horn neurons. As observed in DRG neurons, preincubation of slices in N/OFQ for 30 min produced no decrease in the proportion of eEPSCs inhibited by CVID. In conclusion, no internalization of the N-type VGCC occurs in either the soma or central nerve terminals of DRG neurons following prolonged exposure to high, desensitizing concentrations of N/OFQ.

Effects of intraplantar nocistatin and (±)-J 113397 injections on nociceptive behavior in a rat model of inflammation

Nocistatin (NST) and Nociceptin/Orphanin FQ (N/OFQ) are derived from the same precursor protein, pre-proN/OFQ, and exert opposite effects on the modulation of pain signals. However, the role of the peripheral N/OFQ and the NOP receptor, which is located at the endings of sensory nerves, in inflammatory pain was not ascertained. NST administered intrathecally (i.t.) prevented the nociceptive effects induced by i.t. N/OFQ and PGE₂. Moreover an up regulation of N/OFQ was shown in the rat in response to peripheral inflammation. Here, we investigated the effects of intraplantar (i.pl.) administration of functional N/OFQ and NOP receptor antagonists in a rat model of inflammatory pain. Our findings showed that i.pl. injection of (±)-J 113397, a selective antagonist of the NOP receptor, and NST, the functional N/OFQ antagonist, prior to carrageenan significantly reduced the paw allodynic and thermal hyperalgesic threshold induced by the inflammatory agent. The resulting antiallodynic and antihyperalgesic effects by co-administering NST and (±)-J 113397 prior to carrageenan were markedly enhanced, and the basal latencies were restored. Thus, it is likely that the peripheral N/OFQ/NOP receptor system contributes to the abnormal pain sensitivity in an inflammatory state.

Pro-inflammatory and vasoconstricting prostanoid PGF2α causes no headache in man

Background: During two decades of migraine provocation studies with naturally occurring signalling molecules, vasodilators such as prostaglandin E2, prostaglandin I2 (prostacyclin) and prostaglandin D2 were shown to be able to induce headache in man. To elucidate the role of inflammation and vasodilatation in the generation of headache, we investigated whether the pro-inflammatory and vasoconstricting prostanoid prostaglandin F2α (PGF2α) would cause headache in a human model of headache.

Methods: Twelve healthy volunteers were randomly allocated to receive 3.5 µg/kg/min PGF2α or placebo over 20 min in a two-way crossover study. We recorded headache intensity on a verbal rating scale, middle cerebral artery blood flow velocity (VMCA) and the diameters of the superficial temporal artery (STA) and radial artery (RA).

Results: We found no difference in the area under the curve (AUC) for immediate headache (0–90 min) between PGF2α and placebo ( p = 0.144). The McNemar's test showed no difference in the incidence of immediate and delayed headache between verum and placebo ( p = 0.500 and p = 1.000, respectively). There was no difference in VMCA ( p = 0.776) and in the diameter of the STA ( p = 0.460) or RA ( p = 0.780) between PGF2α and placebo.

Conclusion: The present study shows that PGF2α, unlike vasodilating prostaglandins, does not provoke headache. We suggest that the vasodilating abilities of prostaglandins are important for the induction of experimental headache in healthy volunteers.

Signaling pathways of ATP-induced PGE2 release in spinal cord astrocytes are EGFR transactivation-dependent

Traumatic spinal cord injury is characterized by an immediate, irreversible loss of tissue at the lesion site, as well as a secondary expansion of tissue damage over time. Although secondary injury should, in principle, be preventable, no effective treatment options currently exist for patients with acute spinal cord injury (SCI). Excessive release of ATP by the traumatized tissue, triggers the rapid release of arachidonic acid (AA) and prostaglandin E2 (PGE2), and has beenimplicated in acute and chronic neuropathic pain and inflammation. But the intracellular pathways between ATP and PGE2 remain largely unknown. We have explored the signaling events involved in this synthesis by primarily culturing spinal cord astrocytes: (1) we determined significant PGE2 production increased by ATP is mainly via Subtype 1 of P2 purinoceptors (P2Y1) but not P2Y2; (2) we found that ATP strongly increased the level of intracellular Ca(2+) via P2Y1 receptor; (3) we indicated that ATP stimulates the definitely release of AA and PGE2 which involved the transactivation of epidermal growth factor (EGF) receptor, the phosphorylation of extracellular-regulated protein kinases 1 and 2 (ERK(1/2) ) and the activation of cytosolic phospholipase A(2) (cPLA(2) ); (4) we examined ATP could increase the phosphorylation of Akt via P2Y1 receptor which also depend on the transactivation of EGFR, but the activation of Akt has no effect on the downstream of cPLA(2) phosphorylation. ATP induced by SCI could mobilize the release of AA and PGE2. And inhibition of PGE2 release reduces behavioral signs of pain after SCI and peripheral nerve injury.

Characterization of nestin expression in the spinal cord of GFP transgenic mice after peripheral nerve injury

Many studies have shown that activation and increase in the number of astrocytes and microglia in the spinal cord participate in the initiation and maintenance of neuropathic pain, but little attention has been paid to the responses of neural progenitor cells to peripheral nerve injury. Nestin, a class VI intermediate filament protein, is expressed both in neuronal and glial progenitors as well as in their common precursors; and nestin-positive cells appear in the brain and spinal cord following various forms of damage to these regions. To clarify the responses of neural progenitor cells to nerve injury, we applied L5 spinal nerve transection (L5-SNT) to nestin-promoter GFP (pNestin-GFP) transgenic mice to narrow the target to them. While pNestin-GFP expression was strongly retained in the ependyma lining the central canal of the transgenic spinal cord even in adulthood, it was markedly reduced in the dorsal horn during postnatal development by day 7. Increases in pNestin-GFP expression and labeling by the proliferation marker 5-bromodeoxyuridine were broadly found in the dorsal horn of adult mice on day 3 after L5-SNT. On the other hand, the activation and increase in number of microglia and astrocytes are restricted to the superficial layer of the dorsal horn, the central terminal of injured primary afferent fibers. Purinergic P2X agonist α, β-MeATP increased [Ca(2+)]i in nestin-positive cells in the superficial layer ipsilateral to nerve injury and P2 receptor antagonists suramin and pyridoxalphosphate-6-azophenyl-2,4-disulphonic acid (PPADS) blocked the expression and elongation of pNestin-GFP fibers in the slice culture of the spinal cord. These results with pNestin-GFP transgenic mice demonstrate that nestin-positive cells proliferate in the dorsal horn in response to peripheral nerve injury and suggest that ATP may contribute to the expression of nestin and activation of neural progenitor cells after nerve injury.

Models and mechanisms of hyperalgesia and allodynia

Hyperalgesia and allodynia are frequent symptoms of disease and may be useful adaptations to protect vulnerable tissues. Both may, however, also emerge as diseases in their own right. Considerable progress has been made in developing clinically relevant animal models for identifying the most significant underlying mechanisms. This review deals with experimental models that are currently used to measure (sect. II) or to induce (sect. III) hyperalgesia and allodynia in animals. Induction and expression of hyperalgesia and allodynia are context sensitive. This is discussed in section IV. Neuronal and nonneuronal cell populations have been identified that are indispensable for the induction and/or the expression of hyperalgesia and allodynia as summarized in section V. This review focuses on highly topical spinal mechanisms of hyperalgesia and allodynia including intrinsic and synaptic plasticity, the modulation of inhibitory control (sect. VI), and neuroimmune interactions (sect. VII). The scientific use of language improves also in the field of pain research. Refined definitions of some technical terms including the new definitions of hyperalgesia and allodynia by the International Association for the Study of Pain are illustrated and annotated in section I.

Nociceptin/orphanin FQ (N/OFQ)-evoked bradycardia, hypotension, and diuresis are absent in N/OFQ peptide (NOP) receptor knockout mice

Intracerebroventricular administration of the opioid-like peptide nociceptin/orphanin FQ (N/OFQ) produces bradycardia, hypotension, and diuresis in mice. We hypothesized that these responses are solely caused by selective activation of central N/OFQ peptide (NOP) receptors. To test this premise, we first examined whether i.c.v. N/OFQ produced dose-dependent diuretic and cardiovascular depressor responses in commercially available C57BL/6 mice. Next, using doses established in these studies, we examined the renal excretory and cardiovascular responses to i.c.v. N/OFQ in conscious transgenic NOP receptor knockout mice (NOP(-/-)). In metabolic studies, i.c.v. N/OFQ, but not saline vehicle, dose-dependently increased urine output (V) in NOP(+/+); this response was significant at 3 nmol (N/OFQ, V = 0.39 +/- 0.10 ml/2 h; saline, 0.08 +/- 0.05 ml/2 h). The N/OFQ-evoked diuresis was absent in littermate NOP(-/-) (N/OFQ, V = 0.06 +/- 0.06 ml/2 h; saline, 0.03 +/- 0.03 ml/2 h). There were no significant changes in urinary sodium or potassium excretion or free water clearance in either group. In telemetry studies, i.c.v. N/OFQ dose dependently lowered heart rate (HR) and mean arterial pressure (MAP). At 3 nmol N/OFQ, both HR and MAP were reduced in NOP(+/+) (peak DeltaHR = -217 +/- 31 bpm; peak DeltaMAP =-47 +/- 7 mm Hg) compared with saline (peak DeltaHR =-14 +/- 5 bpm; peak DeltaMAP = 2 +/- 3 mm Hg). These N/OFQ-evoked bradycardic and hypotensive responses were absent in NOP(-/-) (peak DeltaHR =-13 +/- 17 bpm; peak DeltaMAP =-2 +/- 4 mm Hg, respectively). Basal 24-h cardiovascular and renal excretory function were not different between NOP(-/-) and NOP(+/+) mice. These results establish that the bradycardia, hypotension and diuresis produced by centrally administered N/OFQ are mediated by selective activation of NOP receptors.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

NOP receptor antagonist, JTC-801, blocks cannabinoid-evoked hypothermia in rats

The present study used the endpoint of hypothermia to investigate cannabinoid and nociceptin/orphanin FQ (N/OFQ) interactions in conscious animals. Prior work has established that cannabinoids produce hypothermia by activating central cannabinoid CB(1) receptors. The administration of N/OFQ into the brain also causes significant hypothermia. Those data suggest a link between cannabinoid CB(1) receptors and N/OFQ peptide (NOP) receptors in the production of hypothermia. Therefore, we determined if NOP receptor activation is required for cannabinoid-evoked hypothermia and if cannabinoid CB(1) receptor activation is necessary for N/OFQ-induced hypothermia. In actual experiments, a cannabinoid agonist, WIN 55212-2 (2.5, 5, and 10 mg/kg, i.p.), caused significant hypothermia in male Sprague-Dawley rats (200-225 g). A NOP receptor antagonist, JTC-801 (1 mg/kg, i.p.), did not affect body temperature. For combined administration, JTC-801 (1 mg/kg, i.p.) blocked a significant proportion of the hypothermia caused by each dose of WIN 55212-2 (2.5, 5, and 10 mg/kg, i.p.). JTC-801 (1 mg/kg, i.p.) also blocked the hypothermia caused by another cannabinoid agonist, CP-55, 940 (1 mg/kg, i.p.). In separate experiments, the direct administration of N/OFQ (9 microg/rat, i.c.v.) into the brain produced significant hypothermia. The hypothermic effect of N/OFQ was blocked by JTC-801 (1 mg/kg, i.p.) but not by a selective cannabinoid CB(1) antagonist, SR 141716A (5 mg/kg, i.m.). The finding that a NOP receptor antagonist abolishes a significant percentage of cannabinoid-induced hypothermia suggests that NOP receptor activation is required for cannabinoids to produce hypothermia. This interaction, quantitated in the present study, is the first evidence that NOP receptors mediate a cannabinoid-induced effect in conscious animals.