Humans ; Dynorphins/metabolism* ; Receptors, Opioid, kappa/metabolism* ; Cryoelectron Microscopy

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

Amygdala ; drug effects ; metabolism ; Animals ; Conditioning (Psychology) ; Morphine ; adverse effects ; Rats ; Receptors, Opioid, kappa ; metabolism

BACKGROUND: We investigated the effects of pre-emptive administration of ketamine and norBNI on pain behavior and the expression of DREAM, c-Fos, and prodynorphin proteins on the ipsilateral side of the rat spinal cord at 2 and 4 hours after formalin injection. METHODS: Eighty-four male Sprague Dawley rats were divided into 4 major groups consisting of control rats (C) (n = 12), rats given only formalin injections (F) (n = 24), and rats treated with pre-emptive administration of either ketamine (K+F) (n = 24) or norBNI (N+F) (n = 24). The non-control groups were further divided into subgroups consisting of rats that were sacrificed at 2 and 4 hours (n = 12 for each group) after formalin injection. Pain behavior was recorded for 1 hour. After 2 and 4 hours, the rats were sacrificed and the spinal cords (L4-L5 sections) were removed for immunohistochemistry and Western blot analysis. RESULTS: The pain behavior response was reduced in the K+F group compared to the other groups during the second phase of the formalin pain response. We detected an increase in the nuclear DREAM protein level in the K+F group at 2 and 4 hours and a transient decrease in the N+F group at 2 hours; however, it increased at 4 hours after injection. Fos-like immunoreactivity (FLI) and Prodynorphin-like immunoreactivity (PLI) neurons decreased in the K+F group but increased in the N+F group at 2 hours after injection. While FLI decreased, PLI increased in all groups at 4 hours after injection. CONCLUSIONS: We suggest that NMDA and kappa opioid receptors can modulate DREAM protein expression, which can affect pain behavior and protein transcriptional processes at 2 hours and bring about either harmful or protective effects at 4 hours after formalin injection.
Animals ; Blotting, Western ; Enkephalins ; Formaldehyde ; Humans ; Immunohistochemistry ; Ketamine ; Male ; N-Methylaspartate ; Neurons ; Pain Measurement ; Protein Precursors ; Proteins ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, kappa ; Spinal Cord

This study investigates whether kappa-opioid receptor and ORL1 receptor may interact to form a heterodimer. In immunofluorescence and co-immunoprecipitation experiments, differentially epitope-tagged receptors, colocalization and heterodimerization of kappa-opioid receptor and ORL1 receptor were used and examined in primary culturing rat neurons, Chinese hamster ovary (CHO) or human embryonic kidney 293 (HEK293) cells. The results show that fluorescence of both kappa-opioid receptor and ORL1 receptor were overlapping in primary culturing hippocampal and cortical neurons. Similarly in co-expressing CHO or HEK293 cells, HA-KOR and Myc-ORL1 were almost exclusively confined to the membranes, revealing extensive colocalization. When Flag-KOR and Myc-ORL1 were co-expressing in CHO cells, heterodimerization was identified to have the ability to co-immunoprecipitate ORL1-receptors with kappa-opioid receptor and vice versa. In the current study, further evidence was provided for the direct interaction of two subtypes of opioid receptors, kappa-opioid receptor and ORL1-receptor, to form the heterodimerization. The finding represents the novel pharmacological mechanism for modulation of opioid receptor function as well as diversity of G protein-coupled receptors.
Animals ; CHO Cells ; Cells, Cultured ; Cerebral Cortex ; cytology ; metabolism ; Cricetinae ; Cricetulus ; Dimerization ; Female ; HEK293 Cells ; Hippocampus ; cytology ; metabolism ; Humans ; Immunoprecipitation ; Male ; Neurons ; cytology ; metabolism ; Rats ; Rats, Wistar ; Receptors, Opioid ; metabolism ; Receptors, Opioid, kappa ; metabolism

OBJECTIVETo determine the effect of activation of lambda-opioid receptor with U50, 488H, a selective kappa-opioid receptor agonist, on the changes in electrical coupling during prolonged ischemia and to explore the possible mechanism.

METHODSThe isolated rat heart was perfused in a Langendorff apparatus. The effect of U50, 488H on electrical coupling parameters including onset of uncoupling, plateau time, slope and fold increase in r(t) was observed in isolated perfused rat heart subjected to global no-flow ischemia. The effect of U50, 488H on connexin 43 (Cx43) expression of ventricular muscle during ischemia was determined by immunohistochemistry.

RESULTSIn the prolonged ischemia model, U50, 488H concentration dependently delayed the onset of uncoupling, increased time to plateau, and decreased the maximal rate of uncoupling during ischemia. The effect of U50, 488H on electrical uncoupling parameters during ischemia was abolished by a selective kappa-opioid receptor antagonist nor-BNI or a PKC inhibitor chelerythrine. The amount of Cx43 immunoreactive signal in ventricular muscle was greatly reduced after ischemia. U50, 488H markedly increased Cx43 expression during ischemia and its effect was also attenuated by nor-BNI or chelerythrine.

CONCLUSIONThese results demonstrated that U50, 488H delayed the onset of uncoupling and plateau time, decreased the maximal rate of uncoupling and increased Cx43 expression of ventricular muscle during ischemia, and these effects of U50, 488H were mediated by kappa-opioid receptor, in which activation of PKC was involved. The effect of U50, 488H on electrical coupling during ischemia was probably correlated with preservation of Cx43 in cardiac muscle.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer ; pharmacology ; Animals ; Benzophenanthridines ; pharmacology ; Connexin 43 ; metabolism ; Female ; Heart ; drug effects ; In Vitro Techniques ; Myocardial Ischemia ; metabolism ; physiopathology ; Myocardium ; metabolism ; Naltrexone ; analogs & derivatives ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, kappa ; metabolism ; Signal Transduction ; drug effects

OBJECTIVETo demonstrate the inhibitory effect of kappa-opioid receptor activation by U50488H on hypertrophy induced by NE in cultured neonatal rat cardiac myocytes and compare its effect with that of prazosin and propranolol.

METHODSThe cellular proliferation was determined with crystal violet staining. The protein content was assayed with Lowry's method. The cardiomyocytes volumes were measured by computer photograph analysis system. The protein synthesis was assayed with [3H]-lencine incorporation method.

RESULTS(1) NE significantly induced the increase of protein content, [3H]-leucine incorporation and cell size without a concomitant increase in cell number in low serum medium. OThese responses were partially suppressed by prazosin or propranolol alone and completely abolished by both in combination. U50488H significantly inhibited the NE-induced increase of protein content, [3H]-leucine incorporation and cell size. The inhibitory effects of U50488H on NE-induced cardiac hypertrophy were greater than either prazosin or propranolol, but comparable to combination of both.

CONCLUSIONNE, acting via both alpha1- and beta-adrenergic pathway, stimulates myocyte hypertrophy. Stimulating kappa-opioid receptor significantly inhibits NE-induced cardiac hypertrophy, which may be related with alpha1- and beta1-adrenergic pathway.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer ; pharmacology ; Adrenergic alpha-1 Receptor Antagonists ; pharmacology ; Adrenergic beta-Antagonists ; pharmacology ; Animals ; Animals, Newborn ; Cardiomegaly ; chemically induced ; pathology ; prevention & control ; Cell Enlargement ; drug effects ; Cells, Cultured ; Female ; Male ; Myocytes, Cardiac ; cytology ; Norepinephrine ; Prazosin ; pharmacology ; Propranolol ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, kappa ; agonists

OBJECTIVETo observe the effects of kappa-opioid receptor stimulation on high glucose induced myocardial hypertrophy of neonatal rats.

METHODSUsing cultured myocardial cells as a model, the protein content was assayed with Lowrys method. The cardiomyocytes volumes were measured by computer photograph analysis system. The level of p-ERK44/42 was determined by Western blot.

RESULTSCompared with the control, U50488H significantly inhibited the protein content and volumes of cultured hypertrophic myocardial cells induced by high glucose. Meanwhile the role of ERK was important.

CONCLUSIONThe stimulation of kappa-opioid can inhibit myocardial hypertrophy induced by high glucose, which is possibly via attenuating p-ERK.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer ; pharmacology ; Animals ; Animals, Newborn ; Cardiomegaly ; metabolism ; Cells, Cultured ; Female ; Glucose ; adverse effects ; MAP Kinase Signaling System ; Male ; Myocytes, Cardiac ; drug effects ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, kappa ; metabolism

BACKGROUND: Selective inhibitors of cyclooxygenase (COX)-2 are commonly used analgesics in various pain conditions. Although their actions are largely thought to be mediated by the blockade of prostaglandin (PG) biosynthesis, evidences suggesting endogenous opioid peptide link in spinal antinociception of COX inhibitor have been reported. We investigated the roles of opioid receptor subtypes in the spinal antinociception of selective COX-2 inhibitor. METHODS: To examine the antinociception of a selective COX-2 inhibitor, DUP-697 was delivered through an intrathecal catheter, 10 minutes before the formalin test in male Sprague-Dawley rats. Then, the effect of intrathecal pretreatment with CTOP, naltrindole and GNTI, which are micro, delta and kappa opioid receptor antagonist, respectively, on the analgesia induced by DUP-697 was assessed. RESULTS: Intrathecal DUP-697 reduced the flinching response evoked by formalin injection during phase 1 and 2. Naltrindole and GNTI attenuated the antinociceptive effect of intrathecal DUP-697 during both phases of the formalin test. CTOP reversed the antinociception of DUP-697 during phase 2, but not during phase 1. CONCLUSIONS: Intrathecal DUP-697, a selective COX-2 inhibitor, effectively relieved inflammatory pain in rats. The delta and kappa opioid receptors are involved in the activity of COX-2 inhibitor on the facilitated state as well as acute pain at the spinal level, whereas the micro opioid receptor is related only to facilitated pain.
Acute Pain ; Aluminum Hydroxide ; Analgesia ; Analgesics ; Animals ; Carbonates ; Catheters ; Cyclooxygenase 2 ; Formaldehyde ; Humans ; Male ; Naltrexone ; Opioid Peptides ; Pain Measurement ; Prostaglandin-Endoperoxide Synthases ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid ; Receptors, Opioid, kappa ; Somatostatin ; Thiophenes

AIMTo observe the neuroprotective effect of limb ischemic post-conditioning (LIPC) on local brain ischemia and reperfusion injury in rat, and to investigate whether mitochondrial ATP sensitive potassium channel (mito K(ATP)) and kappa-opioid receptor were involved in the neuroprotection.

METHODSRats were randomly divided into 6 groups that were ischemia/reperfusion group, unilateral hindlimb ischemia group (uLIPC), bilateral hindlimbs ischemia group (bLIPC), bLIPC + antagonist of kappa-opioid receptor nor-binaltorphimine (nor-BNI) group, bLIPC + mito K(ATP) blocker 5-hydroxydecanoate(5-HD) group, bLIPC + extracorporeal circulation of bilateral hindlimbs via femoral arteries (EC) group. Cerebral ischemia was induced by middle cerebral artery occlusion (MCAO), neurological scores, plasma levels of dynorphin and enkephalin, the brain infarct areas were determined after reperfusion.

RESULTSUnilateral LIPC partially improved the neurological score after local brain ischemia and reperfusion injury in rat (P < 0.05), and decreased the infarct area compared with the untreated group undergoing brain ischemia and reperfusion (P < 0.01). Bilateral LIPC significantly improved the neurological score after local brain ischemia and reperfusion injury (P < 0.01), and decreased the infarct area (P < 0.01). The neurological scores of bilateral LIPC group were significant higher than those of unilateral LIPC (P < 0.05). The plasma level of dynorphin was significantly increased (P < 0.01) at 5, 15, 30 min, 1 and 2 h after bilateral LIPC, however, it deceased to the normal level at 12 h after bilateral LIPC. The plasma level of enkephalin showed no obvious change after bilateral LIPC (P > 0.05). nor-BNI (25 nmol/L) and 5-HD (10 mg/kg) abolished the effect of bilateral LIPC (P < 0.01).

CONCLUSIONLIPC protects rat from local brain ischemia and reperfusion injury. Mito K(ATP) may be involved in the neuroprotection, and kappa-opioid receptor may also participate in the protective effect.

Animals ; Brain Ischemia ; physiopathology ; Extremities ; blood supply ; Ischemic Postconditioning ; methods ; Male ; Potassium Channels ; metabolism ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, kappa ; metabolism ; Reperfusion Injury ; prevention & control