Histone methylation-mediated microRNA-32-5p down-regulation in sensory neurons regulates pain behaviors via targeting Cav3.2 channels.

microRNA (miRNA)­mediated gene regulation has been studied as a therapeutic approach, but its functional regulatory mechanism in neuropathic pain is not well understood. Here, we identify that miRNA-32-5p (miR-32-5p) is a functional RNA in regulating trigeminal-mediated neuropathic pain. High-throughput sequencing and qPCR analysis showed that miR-32-5p was the most down-regulated miRNA in the injured trigeminal ganglion (TG) of rats. Intra-TG injection of miR-32-5p agomir or overexpression of miR-32-5p by lentiviral delivery in neurons of the injured TG attenuated established trigeminal neuropathic pain. miR-32-5p overexpression did not affect acute physiological pain, while miR-32-5p down-regulation in intact rats was sufficient to cause pain-related behaviors. Nerve injury increased the methylated histone occupancy of binding sites for the transcription factor glucocorticoid receptor in the miR-32-5p promoter region. Inhibition of the enzymes that catalyze H3K9me2 and H3K27me3 restored the expression of miR-32-5p and markedly attenuated pain behaviors. Further, miR-32-5p­targeted Cav3.2 T-type Ca2+ channels and decreased miR-32-5p associated with neuropathic pain caused an increase in Cav3.2 protein expression and T-type channel currents. Conversely, miR-32-5p overexpression in injured TG suppressed the increased expression of Cav3.2 and reversed mechanical allodynia. Together, we conclude that histone methylation-mediated miR-32-5p down-regulation in TG neurons regulates trigeminal neuropathic pain by targeting Cav3.2 channels.

Downregulation of GRK6 in arcuate nucleus promotes chronic visceral hypersensitivity via NF-κB upregulation in adult rats with neonatal maternal deprivation.

AIMS: The arcuate nucleus is a vital brain region for coursing of pain command. G protein-coupled kinase 6 (GRK6) accommodates signaling through G protein-coupled receptors. Studies have demonstrated that GRK6 is involved in inflammatory pain and neuropathic pain. The present study was designed to explore the role and the underlying mechanism of GRK6 in arcuate nucleus of chronic visceral pain. METHODS: Chronic visceral pain of rats was induced by neonatal maternal deprivation and evaluated by monitoring the threshold of colorectal distension. Western blotting, immunofluorescence, real-time quantitative polymerase chain reaction techniques, and Nissl staining were employed to determine the expression and mutual effect of GRK6 with nuclear factor κB (NF-κB). RESULTS: Expression of GRK6 in arcuate nucleus was significantly reduced in neonatal maternal deprivation rats when compared with control rats. GRK6 was mainly expressed in arcuate nucleus neurons, but not in astrocytes, and a little in microglial cells. Neonatal maternal deprivation reduced the percentage of GRK6-positive neurons of arcuate nucleus. Overexpression of GRK6 by Lentiviral injection into arcuate nucleus reversed chronic visceral pain in neonatal maternal deprivation rats. Furthermore, the expression of NF-κB in arcuate nucleus was markedly upregulated in neonatal maternal deprivation rats. NF-κB selective inhibitor pyrrolidine dithiocarbamate suppressed chronic visceral pain in neonatal maternal deprivation rats. GRK6 and NF-κB were expressed in the arcuate nucleus neurons. Importantly, overexpression of GRK6 reversed NF-κB expression at the protein level. In contrast, injection of pyrrolidine dithiocarbamate once daily for seven consecutive days did not alter GRK6 expression in arcuate nucleus of neonatal maternal deprivation rats. CONCLUSIONS: Present data suggest that GRK6 might be a pivotal molecule participated in the central mechanisms of chronic visceral pain, which might be mediated by inhibiting NF-κB signal pathway. Overexpression of GRK6 possibly represents a potential strategy for therapy of chronic visceral pain.

Epigenetic upregulation of acid-sensing ion channel 1 contributes to gastric hypersensitivity in adult offspring rats with prenatal maternal stress.

Functional dyspepsia is a common functional gastrointestinal disorder. Gastric hypersensitivity (GHS) is a hallmark of this disorder, but the cellular mechanisms remain largely unknown. Stressors during gestational period could have effects on the offspring's tissue structure and function, which may predispose to gastrointestinal diseases. The aim of this study was to test whether prenatal maternal stress (PMS) induces GHS and to investigate role of acid-sensing ion channel (ASIC)/nuclear factor-κB (NF-κB) signaling by examining Asic1 methylation status in adult offspring rats. Gastric hypersensitivity in response to gastric distension was examined by electromyography recordings. Changes in neuronal excitability were determined by whole-cell patch-clamp recording techniques. Demethylation of CpG islands of Asic1 was determined by methylation-specific PCR and bisulfite sequencing assay. Prenatal maternal stress produced GHS in adult offspring rats. Treatment with amiloride, an inhibitor of ASICs, significantly attenuated GHS and reversed hyperexcitability of gastric-specific dorsal root ganglion (DRG) neurons labeled by the dye DiI. Expression of ASIC1 and NF-κBp65 was markedly enhanced in T7 to T10 DRGs. Furthermore, PMS led to a significant demethylation of CpG islands in the Asic1 promoter. A chromatin immunoprecipitation assay showed that PMS also enhanced the ability of NF-κBp65 to bind the promoter of Asic1 gene. Blockade of NF-κB using lentiviral-p65shRNA reversed upregulation of ASIC1 expression, GHS, and the hyperexcitability of DRG neurons. These data suggest that upregulation of ASIC1 expression is attributed to Asic1 promoter DNA demethylation and NF-κB activation, and that the enhanced interaction of the Asic1 and NF-κBp65 contributes to GHS induced by PMS.

Hippocampal protein kinase D1 is necessary for DHPG-induced learning and memory impairments in rats.

BACKGROUND: Understanding molecular mechanisms underlying the induction of learning and memory impairments remains a challenge. Recent investigations have shown that the activation of group I mGluRs (mGluR1 and mGluR5) in cultured hippocampal neurons by application of (S)-3,5-Dihydroxyphenylglycine (DHPG) causes the regulated internalization of N-methyl-D-aspartate receptors (NMDARs), which subsequently activates protein kinase D1 (PKD1). Through phosphorylating the C-terminals of the NMDAR GluN2 subunits, PKD1 down-regulates the activity of remaining (non-internalized) surface NMDARs. The knockdown of PKD1 does not affect the DHPG-induced inhibition of AMPA receptor-mediated miniature excitatory post-synaptic currents (mEPSCs) but prevents the DHPG-induced inhibition of NMDAR-mediated mEPSCs in vitro. Thus, we investigated the in vivo effects of bilateral infusions of DHPG into the hippocampal CA1 area of rats in the Morris water maze (MWM) and the novel object discrimination (NOD) tests. METHODS: A total of 300 adult male Sprague Dawley rats (250-280 g) were used for behavioral tests. One hundred ninety four were used in MWM test and the other 106 rats in the NOD test. Following one week of habituation to the vivarium, rats were bilaterally implanted under deep anesthesia with cannulas aimed at the CA1 area of the hippocampus (CA1 coordinates in mm from Bregma: AP -3.14; lateral +/-2; DV -3.0). Through implanted cannulas artificial cerebrospinal fluid (ACSF), the group1 mGluR antagonist 6-Methyl-2-(phenylethynyl)pyridine (MPEP), the dynamin-dependent internalization inhibitor Dynasore, or the PKD1 inhibitor CID755673 were infused into the bilateral hippocampal CA1 areas (2 µL per side, over 5 min). The effects of these infusions and the effects of PKD1 knockdown were examined in MWM or NOD test. RESULTS: DHPG infusion increased the latency to reach the platform in the MWM test and reduced the preference for the novel object in the NOD task. We found that the DHPG effects were dose-dependent and could be maintained for up to 2 days. Notably, these effects could be prevented by pre-infusion of the group1 mGluR antagonist MPEP, the dynamin-dependent internalization inhibitor Dynasore, the PKD1 inhibitor CID755673, or by PKD1 knockdown in the hippocampal CA1 area. CONCLUSION: Altogether, these findings provide direct evidence that PKD1-mediated signaling may play a critical role in the induction of learning and memory impairments by DHPG infusion into the hippocampal CA1 area.

Upregulation of cystathionine ß-synthetase in the arcuate nucleus produces pain hypersensitivity via PKC upregulation and GluN2B phosphorylation in rats with chronic pancreatitis.

Hydrogen sulfide (H2S) contributes to visceral hyperalgesia in primary sensory neurons, but its role in central nervous system remains largely unknown. This study was to investigate the roles and underlying mechanisms of H2S and its endogenous synthesis enzymes in the arcuate nucleus (ARC) in rat pancreatic hyperalgesia. Chronic pancreatitis (CP) was induced in male adult Sprague-Dawley rats by intra-pancreatic ductal injection of trinitrobenzene sulfonic acid (TNBS). Abdominal hyperalgesia was assessed by referred somatic behaviors to mechanical stimulation of rat abdomen. Western blot analysis was performed to detect protein expression in the ARC. CP markedly upregulated cystathionine ß-synthetase (CBS) expression but did not alter cystathionine-γ-lyase level in the ARC at 4 weeks after TNBS injection. Although the expression of total GluN2B was not altered, CP greatly enhanced the phosphorylation level of GluN2B in the ARC when compared with age- and sex-matched control rats. CP also significantly increased expression of protein kinase Cγ (PKCγ) in the ARC. Arcuate microinjection of O-(Carboxymethyl) hydroxylamine hemihydrochloride (AOAA, an inhibitor of CBS) significantly attenuated abdominal pain in CP rats in a dose-dependent manner and reversed the CP-induced upregulation of p-GluN2B and PKCγ in the ARC. Furthermore, the GluN2B inhibitor or specific PKC inhibitor chelerythrine significantly attenuated abdominal hyperalgesia in CP rats. The p-GluN2B expression was also suppressed by PKC inhibitor. Taken together, our results suggest that the upregulation of CBS in the ARC leads to an activation of GluN2B via PKCγ, which may play an important role in generation of pain hypersensitivity of CP.

Development of regional specificity of spinal and medullary dorsal horn neurons.

Extensive studies have focused on the development and regionalization of neurons in the central nervous system (CNS). Many genes, which play crucial roles in the development of CNS neurons, have been identified. By using the technique "direct reprogramming", neurons can be produced from multiple cell sources such as fibroblasts. However, understanding the region-specific regulation of neurons in the CNS is still one of the biggest challenges in the research field of neuroscience. Neurons located in the trigeminal subnucleus caudalis (Vc) and in the spinal dorsal horn (SDH) play crucial roles in pain and sensorimotor functions in the orofacial and other somatic body regions, respectively. Anatomically, Vc represents the most caudal component of the trigeminal system, and is contiguous with SDH. This review is focused on recent data dealing with the regional specificity involved in the development of neurons in Vc and SDH.

Regulated internalization of NMDA receptors drives PKD1-mediated suppression of the activity of residual cell-surface NMDA receptors.

BACKGROUND: Constitutive and regulated internalization of cell surface proteins has been extensively investigated. The regulated internalization has been characterized as a principal mechanism for removing cell-surface receptors from the plasma membrane, and signaling to downstream targets of receptors. However, so far it is still not known whether the functional properties of remaining (non-internalized) receptor/channels may be regulated by internalization of the same class of receptor/channels. The N-methyl-D-aspartate receptor (NMDAR) is a principal subtype of glutamate-gated ion channel and plays key roles in neuronal plasticity and memory functions. NMDARs are well-known to undergo two types of regulated internalization - homologous and heterologous, which can be induced by high NMDA/glycine and DHPG, respectively. In the present work, we investigated effects of regulated NMDAR internalization on the activity of residual cell-surface NMDARs and neuronal functions. RESULTS: In electrophysiological experiments we discovered that the regulated internalization of NMDARs not only reduced the number of cell surface NMDARs but also caused an inhibition of the activity of remaining (non-internalized) surface NMDARs. In biochemical experiments we identified that this functional inhibition of remaining surface NMDARs was mediated by increased serine phosphorylation of surface NMDARs, resulting from the activation of protein kinase D1 (PKD1). Knockdown of PKD1 did not affect NMDAR internalization but prevented the phosphorylation and inhibition of remaining surface NMDARs and NMDAR-mediated synaptic functions. CONCLUSION: These data demonstrate a novel concept that regulated internalization of cell surface NMDARs not only reduces the number of NMDARs on the cell surface but also causes an inhibition of the activity of remaining surface NMDARs through intracellular signaling pathway(s). Furthermore, modulating the activity of remaining surface receptors may be an effective approach for treating receptor internalization-induced changes in neuronal functions of the CNS.

Monoclonal antibodies for diagnosis of enterovirus 71.

Enterovirus 71 (EV71), one of the major causative agents of hand, foot, and mouth disease (HFMD), is now recognized as an emerging neurotropic virus in Asia and may cause severe neurologic complications and mortalities. Laboratory diagnosis of EV71 infection must be efficient and accurate, which could be accomplished by various immunoassays. In this study we use a live EV71 isolate, Tainan/4643/98, with genotype C2 as an immunogen to sensitize BALB/c (H-2(d)) mice and then generate the EV71-specific murine monoclonal antibodies. Five hybridoma clones were established and their monoclonal antibodies were characterized. All five clones are applicable in immunofluorescence staining but with different sensitivities-that is, MAbs 22, 24, and 27 were sensitive in IFA detection, and MAbs 22 and 24 were also confirmed in flow cytometry. None of these cross-reacted with coxsackievirus A16 (CVA16) or Echovirus type 6 (ECHO6), but each varied in binding to different EV71 subgenogroups (B1, B4, B5, C2, and C4). Western blot analysis revealed that all of these MAbs reacted with EV71 VP1 capsid proteins, and in addition MAbs 22 and 24 exhibited potent neutralizing activities against EV71 and protected cells from infection. Further, mapping the epitopes for each MAb revealed that only MAb 27 showed positive for the linear epitope DVIESSIGDSVSRAL, which was located at the N-terminus (a.a. 6-20) of EV71 VP1 and highly conserved among all EV71 subgenotypes. Thus, these MAbs may provide valuable tools for the laboratory diagnosis of EV71 infection and for vaccine development.

Modulation of A-type K+ channels by the short-chain cobrotoxin through the protein kinase C-delta isoform decreases membrane excitability in dorsal root ganglion neurons.

A-type K(+) channels are crucial in controlling neuronal excitability, and their regulation in sensory neurons may alter pain sensation. In this study, we identified the functional role of cobrotoxin, the short-chain α-neurotoxin isolated from Naja atra venom, which acts in the regulation of the transient A-type K(+) currents (IA) and membrane excitability in dorsal root ganglion (DRG) neurons via the activation of the muscarinic M3 receptor (M3R). Our results showed that cobrotoxin increased IA in a concentration-dependent manner, whereas the sustained delayed rectifier K(+) currents (IDR) were not affected. Cobrotoxin did not affect the activation of IA markedly, however, it shifted the inactivation curve significantly in the depolarizing direction. The cobrotoxin-induced IA response was blocked by the M3R-selective antagonists DAU-5884 and 4-DAMP. An siRNA targeting the M3R in small DRG neurons abolished the cobrotoxin-induced IA increase. In addition, dialysis of the cells with the novel protein kinase C-delta isoform (PKC-δ) inhibitor δv1-1 or an siRNA targeting PKC-δ abolished the cobrotoxin-induced IA response, whereas inhibition of PKA or classic PKC activity elicited no such effects. Moreover, we observed a significant decrease in the firing rate of the neuronal action potential induced by M3R activation. Pretreatment of the cells with 4-aminopyridine, a selective blocker of IA, abolished this effect. Taken together, these results suggest that the short-chain cobrotoxin selectively enhances IA via a novel PKC-δ-dependent pathway. This effect occurred via the activation of M3R and might contribute to its neuronal hypoexcitability in small DRG neurons.

Purinergic P2X receptors and diabetic neuropathic pain.

Diabetic peripheral neuropathy (DPN), one of the most common chronic complications of diabetes, is characterized by allodynia, hyperalgesia and spontaneous pain. Chinese epidemiological studies have shown that at least 25% diabetic patients suffered from painful DPN, which compromises patients' daily functioning and becomes a major health care problem. Although the pathogenesis of painful DPN is not fully understood and current treatment options are very limited, research in the field has advanced our understanding on the mechanism of painful DPN in the past Decade of Pain Research and Control. This review will mainly focus on evaluation of current diabetic animal models, possible molecular pathways and available therapies, with an emphasis on roles of purinergic receptor and its signaling transduction pathways. Common therapies address one or two DPN symptoms, while others offer wider symptom control, presumably by targeting pathophysiological mechanisms of DPN. Purinergic receptor signaling transduction pathways might become potential targets for treatment for painful DPN.

Electroacupuncture alleviates stress-induced visceral hypersensitivity through an opioid system in rats.

AIM: To investigate whether stress-induced visceral hypersensitivity could be alleviated by electroacupuncture (EA) and whether EA effect was mediated by endogenous opiates. METHODS: Six to nine week-old male Sprague-Dawley rats were used in this study. Visceral hypersensitivity was induced by a 9-d heterotypic intermittent stress (HIS) protocol composed of 3 randomly stressors, which included cold restraint stress at 4°C for 45 min, water avoidance stress for 60 min, and forced swimming stress for 20 min, in adult male rats. The extent of visceral hypersensitivity was quantified by electromyography or by abdominal withdrawal reflex (AWR) scores of colorectal distension at different distention pressures (20 mmHg, 40 mmHg, 60 mmHg and 80 mmHg). AWR scores either 0, 1, 2, 3 or 4 were obtained by a blinded observer. EA or sham EA was performed at classical acupoint ST-36 (Zu-San-Li) or BL-43 (Gao-Huang) in both hindlimbs of rats for 30 min. Naloxone (NLX) or NLX methiodide (m-NLX) was administered intraperitoneally to HIS rats in some experiments. RESULTS: HIS rats displayed an increased sensitivity to colorectal distention, which started from 6 h (the first measurement), maintained for 24 h, and AWR scores returned to basal levels at 48 h and 7 d after HIS compared to pre-HIS baseline at different distention pressures. The AWR scores before HIS were 0.6 ± 0.2, 1.3 ± 0.2, 1.9 ± 0.2 and 2.3 ± 0.2 for 20 mmHg, 40 mmHg, 60 mmHg and 80 mmHg distention pressures, respectively. Six hours after termination of the last stressor, the AWR scores were 2.0 ± 0.1, 2.5 ± 0.1, 2.8 ± 0.2 and 3.5 ± 0.2 for 20 mmHg, 40 mmHg, 60 mmHg and 80 mmHg distention pressures, respectively. EA given at classical acupoint ST-36 in both hindlimbs for 30 min significantly attenuated the hypersensitive responses to colorectal distention in HIS rats compared with sham EA treatment [AWRs at 20 mmHg: 2.0 ± 0.2 vs 0.7 ± 0.1, P = 4.23,711 E-4; AWRs at 40 mmHg: 2.6 ± 0.2 vs 1.5 ± 0.2, P = 0.00,163; AWRs at 60 mmHg: 3.1 ± 0.2 vs 1.9 ± 0.1, P = 0.003; AWRs at 80 mmHg: 3.6 ± 0.1 vs 2.4 ± 0.2, P = 0.0023; electromyographic (EMG) at 20 mmHg: 24 ± 4.7 vs 13.8 ± 3.5; EMG at 40 mmHg: 60.2 ± 6.6 vs 30 ± 4.9, P = 0.00,523; EMG at 60 mmHg: 83 ± 10 vs 39.8 ± 5.9, P = 0.00,029; EMG at 80 mmHg: 94.3 ± 10.8 vs 49.6 ± 5.9, P = 0.00,021]. In addition, EA at the acupuncture point BL-43 with same parameters did not alleviate visceral hypersensitivity in HIS rats. EA in healthy rats also did not have any effect on AWR scores to colorectal distention at distention pressures of 20 and 40 mmHg. The EA-mediated analgesic effect was blocked by pretreatment with NLX in HIS rats [AWR scores pretreated with NLX vs normal saline (NS) were 2.0 vs 0.70 ± 0.20, 2.80 ± 0.12 vs 1.50 ± 0.27, 3 vs 2.00 ± 0.15 and 3.60 ± 0.18 vs 2.60 ± 0.18 for 20 mmHg, 40 mmHg, 60 mmHg and 80 mmHg; P = 0.0087, 0.0104, 0.0117 and 0.0188 for 20, 40, 60 and 80 mmHg, respectively]. Furthermore, EA-mediated analgesic effect was completely reversed by administration of m-NLX, a peripherally restricted opioid antagonist (EMG pretreated with m-NLX vs NS were 30.84 ± 4.39 vs 13.33 ± 3.88, 74.16 ± 9.04 vs 36.28 ± 8.01, 96.45 ± 11.80 vs 50.19 ± 8.28, and 111.59 ± 13.79 vs 56.42 ± 8.43 for 20 mmHg, 40 mmHg, 60 mmHg and 80 mmHg; P = 0.05,026, 0.00,034, 0.00,005, 0.000,007 for 20 mmHg, 40 mmHg, 60 mmHg and 80 mmHg, respectively). CONCLUSION: EA given at classical acupoint ST-36 alleviates stress-induced visceral pain, which is most likely mediated by opioid pathways in the periphery.

Enhanced NMDA receptor NR1 phosphorylation and neuronal activity in the arcuate nucleus of hypothalamus following peripheral inflammation.

UNLABELLED: AbstractAim:To investigate the role of glutamate and N-methyl-D-aspartate (NMDA) receptors in central sensitization following peripheral inflammation in the arcuate nucleus (ARC) of the mediobasal hypothalamus. METHODS: Mediobasal hypothalamic slices were prepared from rats undergoing peripheral inflammation, which was induced by a unilateral injection of complete Freund's adjuvant (CFA) into hind paw. Neuronal activation levels in the ARC were monitored by recording extracellular unit discharges. The NMDA receptor NR1 subunit (NR1) was measured using Western blot analysis. RESULTS: Enhanced NR1 phosphorylation was observed in the ARC of CFA-inflamed rats. Compared with the control rats, the firing rate of spontaneous discharges in ARC neurons of inflamed rats was significantly higher, and it was significantly reduced both by an NMDA receptor antagonist (MK-801, 300 µmol/L) and by a non-NMDA receptor antagonist (CNQX, 30 µmol/L). Application of exogenous glutamate (200 µmol/L) or NMDA (25 µmol/L) resulted in increased neuronal discharges for ARC neurons, which was enhanced to a greater extent in inflamed rats than in control rats. CONCLUSION: Glutamate receptor activation in the hypothalamic ARC plays a crucial role in central sensitization associated with peripheral inflammation.

[Nitric oxide promotes the differentiation of neural stem cells in vitro derived from the subventricular zone of neonatal rats].

OBJECTIVE: To observe the effect of nitric oxide (NO) on the differentiation of neural stem cells (NSCs) derived from subventricular zone (SVZ) of neonatal rats in vitro. METHODS: Conventional method was used to isolate and culture the NSCs from SVZ. Diethylenetriamine/NO(DETA/NO) was used as NO donor and Nitro-L-arginine methylester (L-NAME) was used as inhibitor of nitric oxide synthase (NOS). The immunofluorescence was used to identify the expression of nestin (a marker of NSCs), beta-III-tubulin (Tuj-1, a marker of neurons), glial fibrillary acidic protein (GFAP, a marker of astrocytes) and nNOS. The concentration of NO in medium was measured by Greiss assay. RESULTS: Cultured neurospheres were nestin-, BrdU- and nNOS-positive. After treatment with 40 micromol/L, 50 micromol/L and 60 micromol/L of DETA/NO for 5 days, the concentration of NO released was increased significantly (P < 0.01) as compared with that of the control group. The percentage of both differentiated neurons and astrocytes was increased significantly (P < 0.01 and P < 0.05) as compared with that of the control group. After treatment with 100 micromol/L, 150 micromol/L and 200 micromol/L of L-NAME for 5 days, the concentration of NO released was decreased as compared with that of the control group (P < 0.05). The percentage of both differentiated neurons and astrocytes were decreased as compared with that of the control group (P < 0.05). CONCLUSION: NO could directly promote the differentiation of NSCs derived from rat subventricular zone in vitro.

Cobratoxin inhibits pain-evoked discharge of neurons in thalamic parafascicular nucleus in rats: involvement of cholinergic and serotonergic systems.

The present study investigated the inhibitory effect of cobratoxin (CTX) on pain-evoked discharge of neurons in thalamic parafascicular nucleus (Pf) of rats and analyzed some of the mechanisms involved in this effect. Intracerebroventricular injection (icv) of CTX at 0.56, 1.12 and 4.50 microg/kg resulted in a dose-dependent inhibitory effect on the pain-evoked discharges of Pf neurons. The inhibition of pain-evoked discharges of Pf neurons by CTX at high dose (4.50 microg/kg) persisted at least for 2h, while the inhibitory effect of morphine (40 microg) persisted no longer than 30 min. The inhibitory effect of CTX was reversed by pretreatment with atropine (icv, 5 microg). In contrast, icv injection of naloxone (4 microg) had no effect on CTX-induced inhibition. Furthermore, pretreatment with parachlorophenylalanine, a specific inhibitor of tryptophan hydroxylase, also significantly attenuated the inhibitory effect of CTX. The results suggested that: (a) CTX has a dose-dependent inhibitory effect on pain-evoked discharges of Pf neurons, confirming electrophysiologically the antinociceptive action of CTX; (b) the inhibitory effect of CTX has a longer duration compared to that of morphine; (c) central cholinergic and serotonergic systems, but not opioidergic system, are involved in the inhibitory effect of CTX.

Inducible expression of functional mu opioid receptors in murine dendritic cells.

Opioids are known to exert direct effects on the immune system, and the expression of functional opioid receptors has been reported on several immune cell types. Dendritic cells (DCs) are important inducers and regulators of immune responses. In this study, we investigated whether murine dendritic cells express functional mu opioid receptors (MOR). RT-PCR analysis and double immunofluorescence staining revealed the expression of MOR in activated murine dendritic cells. We also studied the dynamic expression of MOR messenger RNA in murine dendritic cells in response to different Toll-like receptor ligands. Functionally, treatment of DCs with endomorphin 1 (EM1), a specific agonist of MOR, can inhibit the forskolin-induced formation of cyclic adenosine monophosphate level in activated DCs. Moreover, EM1 treatment resulted in less activation of p38 MAPK and more activation of ERK signaling in lipopolysaccharide-stimulated DCs. Consistently, treatment of DCs with EM1 altered cytokine production by increasing IL-10 and decreasing IL-12 and IL-23. Our results suggest that MOR is inducibly expressed on activated DCs and functionally mediates EM1-induced effects on DCs. Thus, dendritic cells might be involved in crosstalk between the neuroendocrine and the immune system.

Inhibitory effect of crotoxin on the pain-evoked discharge of neurons in thalamic parafascicular nucleus in rats.

Crotoxin (Cro), the principal neurotoxic component of Crotalus durissus terrificus, has been previously reported to have a behavioral analgesic effect in rats and mice. The present study investigated electrophysiologically the effect of Cro on pain-evoked unit discharge of neurons in thalamic parafascicular nucleus (Pf) and underlying mechanisms of its effect. The electrical discharge of Pf neurons was recorded with the microelectrode technique in rats. Intracerebroventricular (i.c.v.) injection of Cro at 0.25, 0.45 and 0.65 microg/kg resulted in a dose-dependent inhibitory effect on the pain-evoked discharge of Pf neurons. The discharge frequency and the discharge duration significantly (P<0.05) decreased after Cro administration. This inhibitory effect was significantly (P<0.05) attenuated after pretreatment with para-chlorophenylalanine (pCPA), or electrolytic lesion of dorsal raphe (DR) nucleus. In contrast, i.c.v. injection of atropine (muscarinic receptor antagonist, 5 microg) or naloxone (opioid receptor antagonist, 4 microg) had no effect on Cro-induced inhibition of discharge of Pf neurons. The results suggested that Cro has an analgesic effect, which is mediated, at least partially, by the central serotonergic system.

An individual variation study of electroacupuncture analgesia in rats using microarray.

The aim of the present study is to probe candidate genes which were involved in the electroacupuncture (EA) analgesia and to understand the molecular basis of the individual difference of EA analgesia in rats. We compared hypothalamus transcriptional profiles of responders with those of non-responders after 1 Hz EA treatment at ST36 acupoint for 1 hour by using oligonucleotide microarray. Responders and non-responders were determined by tail flick latency (TFL). A real-time quantitative RT-PCR was applied to validate the differential expressed genes. Our study provided a global hypothalamus transcriptional profile of EA analgesia in rats. We found that 63 and 3 genes were up- and down-regulated in the responder group, respectively. Half of the differentially expressed genes were classified into 9 functional groups which were ion transport, sensory perception, synaptogenesis and synaptic transmission, signal transduction, inflammatory response, apoptosis, transcription, protein amino acid phosphorylation and G-protein signaling. Glutamatergic receptors, ghrelin precursor, melanocortin 4 receptor (MC4-R) and neuroligin 1 were found to be up-regulated in the responder group which may become new targets for nociceptive study and deserve further investigation for developing new acupuncture therapy and intervention of pain modulation.

Possible involvement of integrin signaling pathway in the process of recovery from restraint stress in rats.

OBJECTIVE: To search novel genes or pathways involved in the recovery process after restraint stress in rats. METHODS: We compared the hypothalamus transcriptional profiles of two different recovery patterns (fast recovery vs slow recovery) from restraint stress in rats using oligonucleotide microarray, the recovery pattern was determined by the decrement of plasma adrenocorticotropic-hormone (ACTH) and corticosterone levels during one hour recovery period after stress. A real-time quantitative RT-PCR was applied to validate the differential expressed genes. RESULTS: Analysis of the microarray data showed that most of genes were not differentially expressed between fast recovery group and slow recovery group. Among the differentially expressed genes we found that talin, together with serine/threonine protein phosphatase PP1-beta catalytic subunit (PP-1B) and integrin alpha-6 precursor (VLA-6) genes, were at least 1.5 fold up-regulated in the fast recovery group, while junctional adhesion molecule 1 (F11r) was 1.5 fold down-regulated in the fast recovery group. CONCLUSION: The results implied that integrin signaling pathway may be involved in the recovery from restraint stress in rats. The present study provided a global overview of hypothalamus transcriptional profiles during the process of recovery from the restraint stress in rats. The integrin signaling pathway seems to be involved in the recovery process, which deserves further study to clarify the integrin-mediated recovery mechanism after restraint stress.

Forced running enhances neurogenesis in the hippocampal dentate gyrus of adult rats and improves learning ability.

To investigate the effect of forced running in motor-driven wheel on neurogenesis in the hippocampal dentate gyrus (DG) of adult rats, 5-bromo-2-deoxyuridine (BrdU), a thymidine analog was applied to mark cell proliferation. Neuroepthelial stem cell protein (nestin) expression was used to identify neural stem/precursor cells. The BrdU- and nestin-positive cells were examined by immunohistochemical technique. The ability of learning was evaluated by Y-maze test to explore the functional role of the newborn cells in the DG after forced running. It was found that the number of BrdU- and nestin-positive cells in the DG in running groups was significantly increased compared to that in the control group (P<0.05). The effect of forced running on neurogenesis was intensity-dependent. In addition, an improvement of learning ability in Y-maze test was observed after forced running. These findings suggest that forced running in motor-driven wheel could enhance neurogenesis in the hippocampal DG of adult rats and improve learning ability.

Establishment of model of visceral pain due to colorectal distension and its behavioral assessment in rats.

AIM: To establish a visceral pain model via colorectal distension (CRD) and to evaluate the efficiency of behavioral responses of CRD by measuring the score of abdominal withdrawal reflex (AWR) in rats. METHODS: Thirty-eight male SD rats weighing 180-240 g were used to establish the visceral pain model. The rat was inserted intra-anally with a 7 cm long flexible latex balloon under ether anesthesia, and colorectal distensions by inflating the balloon with air were made 30 min after recovering from the anesthesia. Five AWR scores (AWR0 to AWR4) were used to assess the intensity of noxious visceral stimuli. It was regarded as the threshold of the minimal pressure (kPa). For abdominal flatting was induced by colorectal distension. RESULTS: A vigorous AWR to distension of the descending colon and rectum was found in 100% of the awake rats tested. The higher the pressure of distension, the higher the score of AWR. The distension pressures of 0, 2.00, 3.33, 5.33 and 8.00 kPa produced different AWR scores (P<0.05). The pain threshold of AWR was constant for up to 80 min after the initial windup (first 1-3 distensions), the mean threshold was 3.69+/-0.35 kPa. Systemic administration of morphine sulfate elevated the threshold of visceral pain in a dose-dependent and naloxone reversible manner. CONCLUSION: Scoring the AWR during colorectal distensions can assess the intensity of noxious visceral stimulus. Flatting of abdomen (AWR 3) to CRD as the visceral pain threshold is clear, constant and reliable. This pain model and its behavioral assessment are good for research on visceral pain and analgesics.