Spinal cord stimulation (SCS)-induced analgesia was characterized, and its underlying mechanisms were examined in a spared nerve injury model of neuropathic pain in rats. The analgesic effect of SCS with moderate mechanical hypersensitivity was increased with increasing stimulation intensity between the 20% and 80% motor thresholds. Various frequencies (2, 15, 50, 100, 10000 Hz, and 2/100 Hz dense-dispersed) of SCS were similarly effective. SCS-induced analgesia was maintained without tolerance within 24 h of continuous stimulation. SCS at 2 Hz significantly increased methionine enkephalin content in the cerebrospinal fluid. The analgesic effect of 2 Hz was abolished by μ or κ opioid receptor antagonist. The effect of 100 Hz was prevented by a κ antagonist, and that of 10 kHz was blocked by any of the μ, δ, or κ receptor antagonists, suggesting that the analgesic effect of SCS at different frequencies is mediated by different endorphins and opioid receptors.
Analgesics ; Animals ; Narcotic Antagonists/pharmacology* ; Neuralgia/therapy* ; Opioid Peptides ; Rats ; Receptors, Opioid/physiology* ; Receptors, Opioid, kappa ; Spinal Cord ; Spinal Cord Stimulation

No abstract available.
Animal ; Cyclic AMP/metabolism ; Cyclic GMP/metabolism ; Neurotransmitters/physiology ; Pharmacology, Clinical/trends* ; Receptors, Adrenergic/physiology ; Receptors, Drug/physiology* ; Receptors, Opioid/physiology

Previous studies have indicated that the thalamic nucleus submedius (Sm) and the anterior pretectal nucleus (APtN) are involved in the descending modulation of nociception. The aim of the present study was to examine whether the opioid receptors in the Sm and APtN mediated the electroacupuncture (EA)-produced analgesia. The latency of tail flick (TF) reflex induced by radiant heat was used as an index of nociceptive response. The effects of microinjection of opioid receptor antagonist naloxone (1.0 microg, 0.5 ml) into Sm or APtN on the inhibition of the TF reflex induced by EA of "Zusanli" point (St. 36) with high- (5.0 mA) and low- (0.5 mA) intensity were examined in the lightly anesthetized rats. Sm microinjection of naloxone blocked the high- but not low-intensity EA-induced inhibition of the TF reflex. In contrast, naloxone applied to APtN blocked the low- but not high-intensity EA-induced inhibition. When naloxone applied to other brain regions adjacent to Sm or APtN, the EA-induced inhibition was not influenced under either high- or low-intensity condition. These results suggest that opioid receptors in Sm are involved in mediating the analgesia by high-intensity EA for exciting small (A-delta and C group) afferent fibers, while opioid receptors in APtN are involved in mediating the analgesia induced by low-intensity EA for only exciting large (A-beta) afferent fibers.
Acupuncture Analgesia ; Animals ; Electroacupuncture ; Naloxone ; pharmacology ; Narcotic Antagonists ; Nociceptors ; physiology ; Pain Measurement ; Rats ; Receptors, Opioid ; physiology ; Thalamic Nuclei ; physiology

G protein-coupled receptors (GPCRs) are the largest superfamily of transmembrane receptors and have vital signaling functions in various organs. Because of their critical roles in physiology and pathology, GPCRs are the most commonly used therapeutic target. It has been suggested that GPCRs undergo massive genetic variations such as genetic polymorphisms and DNA insertions or deletions. Among these genetic variations, non-synonymous natural variations change the amino acid sequence and could thus alter GPCR functions such as expression, localization, signaling, and ligand binding, which may be involved in disease development and altered responses to GPCR-targeting drugs. Despite the clinical importance of GPCRs, studies on the genotype-phenotype relationship of GPCR natural variants have been limited to a few GPCRs such as β-adrenergic receptors and opioid receptors. Comprehensive understanding of non-synonymous natural variations within GPCRs would help to predict the unknown genotype-phenotype relationship and yet-to-be-discovered natural variants. Here, we analyzed the non-synonymous natural variants of all non-olfactory GPCRs available from a public database, UniProt. The results suggest that non-synonymous natural variations occur extensively within the GPCR superfamily especially in the N-terminus and transmembrane domains. Within the transmembrane domains, natural variations observed more frequently in the conserved residues, which leads to disruption of the receptor function. Our analysis also suggests that only few non-synonymous natural variations have been studied in efforts to link the variations with functional consequences.
Amino Acid Sequence ; DNA ; Genetic Variation ; Pathology ; Physiology ; Polymorphism, Genetic ; Receptors, Opioid ; Vital Signs

Animals ; Cytokines ; physiology ; Humans ; Immune System ; drug effects ; physiology ; Melatonin ; pharmacology ; Opioid Peptides ; physiology ; Receptors, Melatonin ; physiology ; Stress, Physiological ; immunology ; T-Lymphocytes ; drug effects ; physiology

BACKGROUNDPreconditioning with repeated electroacupuncture (EA) could mimic ischemic preconditioning to induce cerebral ischemic tolerance in rats. The present study was designed to investigate whether mu (micro)-, delta (delta)- or kappa (kappa)-opioid receptors are involved in the neuroprotection induced by repeated EA preconditioning.

METHODSThe rats were pretreated with naltrindole (NTI), nor-binaltorphimine (nor-BNI) or D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), which is a highly selective delta-, kappa- or micro-opioid receptor antagonist respectively, before each EA preconditioning (30 minutes per day, 5 days). Twenty-four hours after the last EA treatment, the middle cerebral artery occlusion (MCAO) was induced for 120 minutes. The brain infarct volume was determined with 2, 3, 5-triphenyltetrazolium chloride staining at 24 hours after MCAO and compared with that in rats which only received EA preconditioning. In another experiment, the met-enkephalin-like immunoreactivity in rat brain was investigated by immunohistochemistry in both EA preconditioning and control rats.

RESULTSThe EA preconditioning reduced brain infarct volume compared with the control rats (P = 0.000). Administration of both NTI and CTOP attenuated the brain infarct volume reduction induced by EA preconditioning, presenting with larger infarct volume than that in the EA preconditioning rats (P < 0.001). But nor-BNI administration did not block the infarct volume reduction induced by EA preconditioning, presenting with smaller infarct volume than the control group rats (P = 0.000). The number of met-enkephalin-like immunoreactivity positive neurons in the EA preconditioning rats was more than that of the control rats (P = 0.000).

CONCLUSIONRepeated EA preconditioning stimulates the release of enkephalins, which may bind delta- and micro-opioid receptors to induce the tolerance against focal cerebral ischemia.

Animals ; Brain Ischemia ; prevention & control ; Electroacupuncture ; Enkephalin, Methionine ; analysis ; Immunohistochemistry ; Ischemic Preconditioning ; Male ; Naltrexone ; analogs & derivatives ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; physiology ; Receptors, Opioid, mu ; physiology ; Somatostatin ; analogs & derivatives ; pharmacology

OBJECTIVETo investigate the interaction between opioid receptor (OR) stimulation and adrenergic receptor (AR) stimulation in the isolated ischaemia/reperfusion (I-R) rat heart.

METHODSMale Sprague-Dawley rats were used for Langendoff isolated heart perfusion. Myocardial ischemia for 20 min was followed by 30 min of reperfusion, during which the kappa-OR agonist U50488h and beta(1)-AR agonist norepinephrine (NE) were administered.

RESULTS(1) 50488h antagonized the effect of NE in rising left ventricular systolic pressure (LVSP) in the early phase of myocardial ischemia at 10, 20, 30 min of reperfusion. (2) Arrhythmia scores in the I-R+NE+U50488h group were markedly lower than those in the I-R group during the 10 - 20 min reperfusion period. No significant differences in arrhythmia scores were found in either I-R+U50488h or I-R+NE group when compared with I-R group. (3) Compared with the I-R group, U50488h alone or plus NE decreased reperfusion heart rates after myocardial ischemia while NE alone showed no effect.

CONCLUSIONIt is suggested that the interaction in the signaling pathway between kappa-OR and beta(1)-AR occurred during myocardial I-R of rat heart.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer ; pharmacology ; Animals ; Male ; Myocardial Reperfusion ; Norepinephrine ; physiology ; Rats ; Rats, Sprague-Dawley ; Receptors, Adrenergic ; physiology ; Receptors, Opioid, kappa ; physiology ; Signal Transduction ; physiology

In our previous study, we demonstrated that immobilization stress blocked estrogen-induced luteinizing hormone(LH) surge possibly by inhibiting the synthesis and release of gonadotropin-releasing hormone (GnRH) at the hypothalamic level and by blocking estrogen-induced prolactin (PRL) surge by increasing the synthesis of dopamine receptor at the pituitary level in ovariectomized rats. The present study was performed to determine whether immobilization stress affects pituitary LH responsiveness to GnRH, and whether endogenous opioid peptide (EOP) and dopamine systems are involved in blocking LH and PRL surges during immobilization stress. Immobilization stress was found to inhibit basal LH release and to completely abolish LH surge. However, the intravenous application of GnRH agonist completely restored immobilization-blocked LH surge and basal LH release. Treatment with naloxone did not exert any effect on immobilization-blocked LH surge but increased basal LH release during immobilization stress. Pimozide did not affect immobilization-blocked LH surge or basal LH release. Naloxone also decreased immobilization-induced basal PRL release, but had no effect on immobilization-blocked PRL surge. Immobilization-increased basal PRL levels were augmented by pimozide treatment and immobilization-blocked PRL surge was dramatically restored by pimozide. We conclude that immobilization stress does not impair pituitary LH response to GnRH, and that the immobilization stress-induced blockage of LH surge is probably not mediated by either the opioidergic or the dopaminergic system. However, immobilization-blockade of PRL surge may be partly mediated by the dopaminergic system.
Animal ; Estradiol/*pharmacology ; Female ; Gonadorelin/*pharmacology ; Immobilization ; Luteinizing Hormone/*secretion ; Naloxone/pharmacology ; Opioid Peptides/physiology ; Ovariectomy ; Prolactin/*secretion ; Rats ; Rats, Sprague-Dawley ; Receptors, Dopamine/physiology ; Stress/*metabolism

BACKGROUNDMu opioid receptor plays an important role in many physiological functions. Fentanyl is a widely used opioid receptor agonist for analgesia. This study was conducted to test the role of mu-opioid receptor on insulin release by determining whether fentanyl affected insulin release from freshly isolated rat pancreatic islets and if small interfering RNAs (siRNA) targeting mu-opioid receptor in the islets could knock down mu-opioid receptor expression.

METHODSIslets were isolated from ripe SD rats' pancreas by common bile duct intraductal collagenase V digestion and purified by discontinuous Ficoll density gradient centrifugation. The siRNA knock-down of mu-opioid receptor mRNA and protein in islet cells was analyzed by semi-quantitative real time-PCR and Western blotting. After siRNA-transfection for 48 hours, the islets were co-cultured with fentanyl as follows: 0 ng/ml, 3 ng/ml and 30 ng/ml for 48 hours. Then glucose-evoked insulin release was performed. As a control, the insulin release was also analyzed in islets without siRNA-trasfection after being co-cultured with fentanyl for 48 hours.

RESULTSAfter 48 hours of transfections, specific siRNA targeting of mu-opioid receptors produced significant reduction of mu-opioid receptor mRNA and protein (P < 0.01). Fentanyl significantly inhibited glucose-evoked insulin release in islets in a concentration dependent manner (P < 0.01). But after siRNA-transfection for 48 hours, the inhibition on glucose-evoked insulin release was reversed (P < 0.01).

CONCLUSIONSRNA interference specifically reduces mu-opioid receptor mRNA and protein expression, leading to reversal of the fentanyl-induced inhibition on glucose-evoked insulin release of rat islets. The activation of opioid receptor induced by fentanyl functions to inhibit insulin release. The use of RNAi presents a promising tool for future research in diabetic mechanisms and a novel therapy for diabetes.

Analgesics, Opioid ; pharmacology ; Animals ; Cell Survival ; drug effects ; Cells, Cultured ; Fentanyl ; pharmacology ; Glucose ; pharmacology ; Insulin ; secretion ; Islets of Langerhans ; drug effects ; secretion ; Male ; RNA Interference ; RNA, Messenger ; analysis ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, mu ; antagonists & inhibitors ; genetics ; physiology

OBJECTIVETo investigate the cardiac effect of interleukin-2 (IL-2) and to explore the underlying mechanism.

METHODSThe video tracking system and spectrofluorometric method were used to measure the cell contraction and intracellular calcium. Fura-2/AM was used as a calcium fluorescence probe. Langendorff perfusion technique was used to determine the effect of IL-2 on the intact heart.

RESULTSCompared with the control group, IL-2 5 U/ml, 50 U/ml significantly decreased cell contraction amplitude [(74.95+/-4.79) vs (98.09+/-5.02)%, (64.30+/-5.24) vs (97.38+/-4.05)%], peak velocity of cell shortening [(70.23+/-4.85)% vs (98.09+/-5.46)%, (61.15+/-5.20)% vs (97.38+/-6.85)%], peak velocity of cell relengthening [(71.22+/-4.79)% vs (98.32+/-6.08)%, (68.16+/-5.24)% vs (97.55+/-5.00)%] and end- diastolic cell length [(88.28+/-5.84)% vs (97.95+/-5.52)%, (84.18+/-6.52)% vs (98.94+/-6.76)%]. IL-2 (5 U/ml, 50 U/ml) also markedly inhibited intracellular calcium transient [(74.94+/-4.90)% vs (98.09+/-3.74)%,(71.00+/-5.28)% vs (97.38+/-5.52)%], and elevated end-diastolic calcium level of ventricular myocytes [(113.91+/-5.93)% vs (100.10+/-3.02)%, (119.09+/-7.12)% vs (100.52+/-6.00)%], which were attenuated by the opioid receptor antagonist naloxone (Nal,10 nmol/L). In the isolated perfused rat heart,when compared with the control group, IL-2 50 U/ml markedly decreased left ventricular developed pressure [(79.91+/-2.18) vs (93.84+/-2.94)mmHg], maximal rate of rise of left ventricular pressure [(2370.7358.29) vs (2591.50+/-62.81)mmHg] maximal rate of fall of left ventricular [-(1460.95+/-38.6) vs -(1634.24+/-54.05) mmHg/s] and heart rate [(217.35+/-10.56) vs (244.52+/-11.23) beats/min], but increased left ventricular end-diastolic pressure (11.44+/-1.02 vs 9.23+/-0.46). Pretreatment with Nal (10 nmol/L) antagonized the cardiac depression and left ventricular end-diastolic pressure elevation induced by IL-2.

CONCLUSIONThe cardiac effect of IL-2 is mediated by opioid receptors on the membrane of cardiomyocytes.

Animals ; Calcium ; metabolism ; Depression, Chemical ; In Vitro Techniques ; Interleukin-2 ; pharmacology ; Male ; Myocardial Contraction ; drug effects ; Naloxone ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, kappa ; drug effects ; physiology