ucn-1028-c and Pain

Repeated morphine treatment results in a decreased analgesic effect or the development of analgesic tolerance. However, we reported that some inflammatory chronic pain may inhibit morphine tolerance via kappa opioid receptor (KOR) activation. In this study, we further investigated the role of KOR in the inhibition of morphine tolerance in a chronic pain condition with a focus on the regulation of protein kinase C (PKC) activity.. Chronic pain was induced by formalin treatment into the dorsal part of the left hind paws of mice. The analgesic effect of morphine was measured by the tail flick method. We analysed the protein expression of PKC and its activity, and G-protein activity of mu opioid receptor (MOR) under repeated morphine treatment with or without formalin treatment.. We found that conventional subtypes of PKC (cPKC) were up-regulated by repeated morphine treatment. Also, antisense oligonucleotide (AS-ODN) targeting cPKC completely suppressed the development of morphine tolerance. The disappearance of the repeated morphine-induced up-regulation of cPKC was completely reversed by treatment with AS-ODN targeting KOR. In addition, AS-ODN targeting KOR significantly reversed the chronic pain-induced down-regulation of PKC activity or up-regulation of MOR [(35)S]GTPgammaS binding activity after repeated morphine treatment.. These results indicate that KOR plays an important role in the inhibition of repeated morphine-induced cPKC up-regulation under chronic pain condition. Furthermore, this may result in the increase of MOR activity and in the inhibition of morphine tolerance under chronic pain condition.

Topics: Analgesics, Opioid; Animals; Brain; Chronic Disease; Disease Models, Animal; Down-Regulation; Drug Tolerance; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enzyme Activation; Formaldehyde; Guanosine 5'-O-(3-Thiotriphosphate); Male; Mice; Morphine; Naphthalenes; Oligonucleotides, Antisense; Pain; Pain Measurement; Pain Threshold; Protein Kinase C; Protein Kinase Inhibitors; Receptors, Opioid, kappa; Receptors, Opioid, mu; Time Factors

Stimulation of delta-opioid receptors has been shown to activate phospholipase C via the activation of G-proteins in vitro. The present study was designed to determine, with the tail-flick method, whether the stimulatory effect of delta-opioid receptor agonists on phospholipase C and inositol lipid turnover participates in the mechanisms of the delta-opioid receptor-mediated antinociception in the mouse spinal cord. Intrathecal pretreatment with the phospholipase C inhibitors neomycin and U73122, which produced no changes in the basal tail-flick latencies when they were injected alone, significantly attenuated the antinociception induced by intrathecal administration of the selective delta-opioid receptor agonist [D-Ala(2)]deltorphin II in mice. The selective phosphatidylinositol-specific phospholipase C inhibitor ET-18-OCH(3) inhibited the antinociception induced by intrathecal administration of [D-Ala(2)]deltorphin II in a dose-dependent manner. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, the antinociception induced by intrathecal administration of [D-Ala(2)]deltorphin II was significantly reduced. Co-administration of D-myo-inositol-1,4,5-trisphosphate restored the [D-Ala(2)]deltorphin II-induced antinociception in LiCl-pretreated mice. On the other hand, intrathecal pretreatment with the selective protein kinase C inhibitor calphostin C, but not the protein kinase A inhibitor KT5720, resulted in a dose-dependent enhancement of the [D-Ala(2)]deltorphin II-induced antinociception. These results indicate a potential role for the phospholipase C-inositol-1,4, 5-trisphosphate pathway in the expression of delta-opioid receptor-mediated antinociception in the mouse spinal cord. Furthermore, activation of protein kinase C by the stimulation of delta-opioid receptors may constitute a significant pathway involved in negative modulation of spinal delta-opioid receptor-mediated antinociception.

Topics: Analgesics; Animals; Carbazoles; Cyclic AMP-Dependent Protein Kinases; Estrenes; Indoles; Inositol 1,4,5-Trisphosphate; Male; Mice; Mice, Inbred ICR; Naphthalenes; Oligopeptides; Pain; Pain Measurement; Phosphatidylinositols; Protein Kinase C; Pyrroles; Pyrrolidinones; Receptors, Opioid, delta; Signal Transduction; Spinal Cord; Type C Phospholipases

We examined the tail-flick response to various heat intensities in diabetic and non-diabetic mice. Heat intensities were set to one of five values by adjusting the source voltage of a 50-W projection bulb to 25, 35, 50, 65 and 80 V. These heat intensities produced surface skin heating rates of 0.1, 0.4, 0.9, 3.0 and 7.3 degrees C/s, respectively. Tail-flick latencies at source voltages of 35 and 50 V in diabetic mice were significantly shorter than those in non-diabetic mice. However, there were no significant differences in tail-flick latencies at 25, 65 and 80 V. In non-diabetic mice, tail-flick latencies were not affected by intrathecal (i.t.) pretreatment with capsaicin 24 h before testing. Tail-flick latencies at 35 and 50 V in diabetic mice were increased by pretreatment with capsaicin. Moreover, although tail-flick latencies in non-diabetic mice were not affected by i.t. pretreatment with calphostin C, a selective protein kinase C inhibitor, those at 35 and 50 V in diabetic mice were increased. However, i.t. pretreatment with (8R, 9S, 11S)-(-)-9-hydroxy-9-n-hexyloxy-carbonyl-8-methyl-2, 3, 9, 10-tetrahydro-8, 11-epoxy-1H, 8H, 11H-2, 7b, 11a-triazadibenzo [a, g]cycloocta[cde]-trinden-1-one (KT5720), a selective protein kinase A inhibitor, did not affect tail-flick latencies in either diabetic or non-diabetic mice. In non-diabetic mice, i.t. pretreatment with phorbol 12,13-dibutyrate (PDB), a protein kinase C activator, decreased tail-flick latencies at 35 and 50 V. Tail-flick latencies in diabetic mice were not affected by i.t. pretreatment with PDB 60 min before testing. Furthermore, the attenuation of tail-flick latencies induced by i.t. pretreatment with PDB in non-diabetic mice was reversed by i.t. pretreatment with capsaicin 24 h before testing. These results indicate that diabetic mice exhibit thermal allodynia and hyperalgesia. Furthermore, this thermal allodynia and hyperalgesia in diabetic mice may be due to the enhanced release of substance P followed by activation of protein kinase C in the spinal cord.

Topics: Analysis of Variance; Animals; Capsaicin; Carbazoles; Carcinogens; Cyclic AMP-Dependent Protein Kinases; Diabetes Mellitus; Enzyme Inhibitors; Hot Temperature; Hyperalgesia; Indoles; Male; Mice; Mice, Inbred ICR; Naphthalenes; Pain; Pain Measurement; Phorbol 12,13-Dibutyrate; Protein Kinase C; Pyrroles; Spinal Cord

There is abundant evidence that opioid receptors are present on peripheral terminals of primary afferent neurons. Experimental and clinical studies have shown that activation of these peripheral opioid receptors produces potent analgesia. In addition to peripheral opioid receptors, cholecystokinin receptors are present in sensory neurons. We examined the hypothesis that cholecystokinin receptors may be present on the same primary afferent neuron and that either exogenous or endogenous cholecystokinin may modulate peripheral antinociceptive effects of mu-opioid receptor agonists. Administration of cholecystokinin into inflamed paws, of the rat, but not intravenously attenuated peripheral antinociceptive effects induced by two mu-opioid receptor agonists, [D-Ala2,N-methyl-Phe4,Gly-ol5]-enkephalin and fentanyl. Only the desulphated form of cholecystokinin produced significant and dose-dependent attenuation. Cholecystokinin alone did not alter nociceptive baseline values in inflamed or non-inflamed paws. The anti-opioid effect of cholecystokinin was dose-dependently antagonized by the cholecystokininB receptor-selective antagonist L-365260, but not by the cholecystokininA receptor-selective antagonist L-364718. Local pretreatment with the protein kinase C specific inhibitor calphostin C abolished cholecystokinin's effect. Peripheral antinociceptive effects of [D-Ala2,N-methyl-Phe4,Gly-ol5]-enkephalin and fentanyl were not altered by intraplantar L-365260 alone. These results indicate that activation of peripheral cholecystokininB but not cholecystokininA receptors attenuates the local antinociceptive effects of mu-opioid receptor agonists in inflamed tissue. This anti-opioid effect may be mediated by protein kinase C in sensory nerve terminals. Endogenous cholecystokinin does not seem to influence the efficacy of peripheral opioids under both normal and inflammatory conditions.

Topics: Analgesics, Opioid; Animals; Cholecystokinin; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Enzyme Inhibitors; Fentanyl; Male; Naphthalenes; Pain; Pain Measurement; Pain Threshold; Peripheral Nervous System Diseases; Protein Kinase C; Rats; Rats, Wistar; Receptors, Cholecystokinin