[LIPOXYGENASES AND PLANT CELL METABOLISM REGULATION].

Lipoxygenases are widespread plant enzymes that catalyze the peroxidation of polyunsaturated fatty acids. This reaction is pivotal in the enzymatic cascade that leads to production of numerous metabolism regulators named oxylipins. The activity of these biologically active substances is directly associated with defence reactions in conditions of biotic and abiotic stresses as well as with the regulation of plant growth, propagation and senescence. In this review the contemporary notions about lipoxygenases classification, structure and catalytic properties are summarized. The features of enzyme activity regulation by transcriptional and posttranslational mechanisms in addition to the role of lipoxygenase catalysis in plant cell signalling are discussed.

Morphine modifies the cingulate-operculum network underlying painful rectal evoked potentials.

The effect of opioids on brain networks underlying rectal evoked potentials (EPs) has never been investigated. This study utilized brain source connectivity to explore whether morphine induced changes in brain networks underlying painful rectal EPs would reflect changes in pain scores due to morphine. Twenty healthy volunteers were included in this placebo-controlled cross-over study. Sensory and pain thresholds to electrically induced rectal stimulation were taken before (baseline) and 70 min after placebo/morphine (30 mg) administration. The stimulation intensity required to evoke moderate pain at baseline was employed for EPs. The pain score of this stimulation intensity was recorded again 70 min after placebo/morphine administration. 62-channel EPs were recorded for both arms. Amplitudes and latencies were analysed and brain source connectivity analysis was done. Changes in any of the parameters describing EPs were correlated to changes in subjective pain ratings. Morphine increased sensory and pain thresholds by 28.8% and 27.5% (P ≤ 0.02). The pain score corresponding to moderate pain at baseline was attenuated in both placebo and morphine arms by 14.5% and 37.5% (P < 0.05). There was a 33.9% reduction in EP amplitudes due to placebo (P < 0.05), whereas EP amplitudes remained stable due to morphine. A dominating cingulate-operculum network to rectal pain was seen. Cingulate source shifted anteriorly in the morphine arm (P < 0.001) and this shift was positively correlated to the change in the pain score (r = 0.6, P < 0.05). These findings indicate that visceral pain relief due to morphine is associated with reorganization within cingulate cortex, which may be used as a biomarker of opioid effects.

Molecular structure of phospholipase D and regulatory mechanisms of its activity in plant and animal cells.

Phospholipase D (PLD) catalyzes hydrolysis of phospholipids with production of phosphatidic acid, which often acts as secondary messenger of transduction of intracellular signals. This review summarizes data of leading laboratories on specific features of organization and regulation of PLD activity in plant and animal cells. The main structural domains of PLD (C2, PX, PH), the active site, and other functionally important parts of the enzyme are discussed. Regulatory mechanisms of PLD activity are characterized in detail. Studies associated with molecular design, analysis, and synthesis of new nontoxic substances capable of inhibiting different PLD isoenzymes in vivo are shown to be promising for biotechnology and medicine.

Lorentz force velocimetry.

We describe a noncontact technique for velocity measurement in electrically conducting fluids. The technique, which we term Lorentz force velocimetry (LFV), is based on exposing the fluid to a magnetic field and measuring the drag force acting upon the magnetic field lines. Two series of measurements are reported, one in which the force is determined through the angular velocity of a rotary magnet system and one in which the force on a fixed magnet system is measured directly. Both experiments confirm that the measured signal is a linear function of the flow velocity. We then derive the scaling law that relates the force on a localized distribution of magnetized material to the velocity of an electrically conducting fluid. This law shows that LFV, if properly designed, has a wide range of potential applications in metallurgy, semiconductor crystal growth, and glass manufacturing.

Analgesic synergy between topical lidocaine and topical opioids.

Topical drugs avoid many of the problematic side effects of systemic agents. Immersion of the tail of a mouse into a solution of dimethyl sulfoxide (DMSO)-containing morphine produces a dose-dependent, naloxone-sensitive, analgesia (ED(50) 6.1 mM; CL 4.3, 8.4) limited to the portion of the tail exposed to the drug. DMSO alone in this paradigm had no analgesic activity. Like morphine, the opioids levorphanol (ED(50) 5.0 mM; CL 3.8, 7.8) and buprenorphine (ED(50) 1. 1 mM; CL 0.7, 1.5) were effective topical analgesics. Lidocaine also was active in the tail-flick assay (ED(50) 2.5 mM; CL 2.0, 3.4), with a potency greater than morphine. As expected, the free base of lidocaine was more potent than its salt. Combinations of a low dose of lidocaine with a low dose of an opioid yielded significantly greater than additive effects for all opioids tested. Isobolographic analysis confirmed the presence of synergy between lidocaine and morphine, levorphanol and buprenorphine. These studies demonstrate a potent interaction peripherally between opioids and a local anesthetic and offer potential advantages in the clinical management of pain.

Peripheral blockade of topical morphine tolerance by ketamine.

Repeated topical administration of morphine daily produces tolerance within three days. Ketamine alone has little effect in the radiant heat tailflick assay. However, with administered with morphine, topical ketamine prevented the development of morphine tolerance in a dose-dependent manner. Furthermore, topical ketamine also slowly reversed pre-existing morphine tolerance. These observations imply that topical morphine tolerance is mediated, at least in part, through peripheral N-methyl-D-aspartate (NMDA) receptors and raises the possibility of the use of topical NMDA receptor antagonists clinically.

Peripheral orphanin FQ/nociceptin analgesia in the mouse.

Orphanin FQ/Nociceptin (OFQ/N) administered peripherally was an effective analgesic in the tailflick test in mice (ED50 16.3 microg). It had a peak effect at 5 min and lasted up to 30 min. The kappa3 analgesic naloxone benzoylhydrazone was also active peripherally (ED50 3.8 microg). The analgesic actions of both agents were blocked by naloxone. Neither OFQ/N(1-11) nor OFQ/N(1-7) had appreciable peripheral activity. Antisense mapping both compounds against the murine orphan opioid receptor (KOR-3) confirmed the importance of this clone in their actions. Antisense probes targeting the second and third coding exons significantly lowered the analgesic effects of both compounds. However, the antisense targeting the first coding exon blocked only the actions of OFQ/N and not kappa3 analgesia.

Topical opioids in mice: analgesia and reversal of tolerance by a topical N-methyl-D-aspartate antagonist.

In addition to its central actions, morphine has important peripheral effects. To examine peripheral analgesic mechanisms, we developed a topical opioid paradigm in which the tail was immersed in a dimethyl sulfoxide (DMSO) solution containing various drugs. Alone, DMSO was inactive in the tail-flick assay in mice. DMSO solutions containing morphine and peptides such as [D-Ala2,MePhe4, Gly(ol)5]enkephalin (DAMGO) produced a potent, dose-dependent analgesia with the radiant heat tail-flick assay. The actions of the drugs were local. Analgesia was observed only in regions of the tail exposed to the solution and not in more proximal unexposed portions of the tail. Immersion of the tail in a solution containing either 125I-labeled morphine or 125I-labeled DAMGO revealed no detectable uptake of radioactivity into the brain, spinal cord, or blood. In the tail, radioactivity was limited only to the regions actually immersed in the solutions. The topical drugs potentiated systemic agents, similar to the previously established synergy between peripheral and central sites of action. Local tolerance was rapidly produced by repeated daily exposure of the tail to morphine. Topical morphine tolerance was effectively blocked by the N-methyl-D-aspartate (NMDA) antagonist MK801 given either systemically or topically but not intrathecally. The ability of a topical NMDA antagonist to block local morphine tolerance suggests that peripheral NMDA receptors mediate topical morphine tolerance. Morphine was cross-tolerant to DAMGO, but not to morphine-6beta-glucuronide, implying different mechanisms of action. These observations are significant in the design and use of opioids clinically.

Anti-neoplastic properties of human corticotropin releasing factor: involvement of the nitric oxide pathway.

We report a series of the in vivo and in vitro studies that evaluate the anti-neoplastic potential of hCRF in W256 rat mammary carcinoma. Using magnetic resonance imaging (MRI) and direct measurements of tumor and peritumoral brain water content we found that hCRF treatment (100 micrograms/kg subcutaneously twice a day for 3 days) caused significant inhibition of growth and vascular permeability of the i.c. W256 tumors. hCRF also exhibited antiproliferative and differentiation-inducing effects in W256 cells in vitro. The calculated IC50 values were 70 nM and 100 nM of hCRF, as measured by digital videomicroscopic quantitation of tumor cell population growth rate and by [3H]-thymidine incorporation assay, respectively. The observed effects in W256 cells were CRF receptor mediated. This was shown in two ways: by the presence of relatively high levels of CRF1 receptor mRNA in W256 cells, and by the fact that the tumor growth inhibitory and differentiation inducing effects of hCRF in vitro were abolished by the CRF receptor antagonist a-helical CRF (9-41). Antiproliferative and differentiation inducing effects of hCRF in W256 cells involve activation of nitric oxide synthase (NOS) and L-arginine-NO pathway. This was shown by using the inhibitor of NOS, the L-nitro-arginine methyl esther (L-NAME), which prevented the antiproliferative and differentiation inducing effects of hCRF in vitro. The cytotoxicity of NO in W256 cells was assessed by the addition of sodium nitroprusside (SNP) to the media. SPN exhibited dose-dependent cytotoxicity in W256 cells with IC50 of 100 muM SNP as measured by [3H]-thymidine incorporation assay. We conclude, that hCRF has substantial anti-neoplastic effects which include inhibition of proliferation and induction of differentiation of the tumor cells in vitro, and a decrease in tumor vascular permeability (and possibly neo-angiogenesis) in vivo.

Lack of morphine and enkephalin tolerance in 129/SvEv mice: evidence for a NMDA receptor defect.

In contrast to the rapid development of tolerance to morphine in CD-1 mice, tolerance is not seen in 129/SvEv mice implanted with morphine pellets or given daily morphine injections for 5 days. Similarly, the progressive and complete loss of analgesia in CD-1 mice seen with repeated dosing of the delta ligand [D-Pen2, D-Pen5]enkephalin is not observed in 129/SvEv mice. In contrast, tolerance develops normally to both the kappa1 drug U50,488H and the kappa3 agent naloxone benzoylhdrazone. N-methyl-D-aspartate (NMDA) given alone attenuates morphine analgesia in CD-1 mice and accelerates the development of tolerance in CD-1 mice when given daily with morphine. In contrast, NMDA has no significant effect in the 129/SvEv mice in either paradigm. Activation of NMDA receptors can lead to the production of nitric oxide, which also is involved with morphine tolerance. Sodium nitroprusside and L-arginine increase nitric oxide levels and decrease morphine analgesia in both the control CD-1 and 129/SvEv mice. Thus, the defect in the NMDA/nitric oxide cascade responsible for the loss of morphine tolerance in the 129/SvEv mice rests at the level of the NMDA receptor itself or in the steps up to the activation of nitric oxide synthase.

Functionally differentiating two neuronal nitric oxide synthase isoforms through antisense mapping: evidence for opposing NO actions on morphine analgesia and tolerance.

Several isoforms of neuronal nitric oxide synthase (nNOS) have been identified. Antisense approaches have been developed which can selectively down-regulate nNOS-1, which corresponds to the full-length nNOS originally cloned from the brain, and nNOS-2, a truncated form lacking two exons which is generated by alternative splicing, as demonstrated by decreases in mRNA levels. Antisense treatment also lowers nNOS enzymatic activity. Down-regulation of nNOS-1 prevents the development of morphine tolerance. Whereas morphine analgesia is lost in control and mismatch-treated mice given daily morphine injections for 5 days, mice treated with antisense probes targeting nNOS-1 show no decrease in their morphine sensitivity over the same time period. Conversely, an antisense probe selectively targeting nNOS-2 blocks morphine analgesia, shifting the morphine dose-response curve over 2-fold to the right. Both systems are active at the spinal and the supraspinal levels. An antisense targeting inducible NOS is inactive. Studies with NG-nitro-L-arginine, which does not distinguish among NOS isoforms, indicate that the facilitating nNOS-2 system predominates at the spinal level while the inhibitory nNOS-1 system is the major supraspinal nNOS system. Thus, antisense mapping distinguishes at the functional level two isoforms of nNOS with opposing actions on morphine actions. The ability to selectively down-regulate splice variants opens many areas in the study of nNOS and other proteins.

Blockade of morphine-induced hindlimb myoclonic seizures in mice by ketamine.

Morphine administration can lead to a variety of side-effects, including myoclonus. In an animal model, high morphine doses given intrathecally elicit hindlimb myoclonic seizures which are not influenced by traditional opioid receptor antagonists, such as naloxone. Ketamine prevents this seizure-like activity in a dose-dependent manner. The response is stereoselective, with S-ketamine far more potent than R-ketamine. A competitive NMDA antagonist, NPC17742, also prevents the seizures, although less potently than ketamine. Dextromethorphan has limited activity in this model, while haloperidol and pentothal are without any effect.

Peripheral morphine analgesia: synergy with central sites and a target of morphine tolerance.

Morphine injected s.c. in the tail is a potent analgesic in the tail-flick assay when the radiant heat source is focused directly over the injection site (ED50, 4.5 micrograms), but not if the radiant heat source is moved 1 cm proximally or distally to the injection site. Naloxone given systemically reverses this peripheral analgesia. Antisense oligodeoxynucleotides directed against exons 1 and 4 of MOR-1, a cloned mu opioid receptor, administered intrathecally (i.t.) block the local analgesic effect of morphine in the tail, indicating that the local response is mediated through mu receptors located on the terminals of sensory neurons from the dorsal root ganglia. Combinations of morphine given locally in the tail and spinally (i.t.) are synergistic. Spinal morphine also synergizes with systemic morphine in analgesia assays. Supraspinal morphine enhances systemic morphine analgesia, but less dramatically. We also examined tolerance on these analgesic systems by using a daily morphine injection paradigm which shifts the dose-response curve for systemic morphine approximately 2-fold after 5 days. In this paradigm, morphine's analgesic potency after either supraspinal or spinal administration alone does not change. However, the dose-response curve for local morphine in the tail is shifted by over 19-fold. The analgesic activity of the combination of supraspinal and systemic morphine is lowered approximately 2-fold and the combination of i.t. and systemic morphine by 12-fold. These studies confirm the presence of a peripheral mechanism for morphine analgesia mediated by mu receptors located on sensory neurons from the dorsal root ganglia, which is extremely sensitive to chronic morphine dosing.

Peripheral kappa 1-opioid receptor-mediated analgesia in mice.

When injected directly into the tail, U50,488H is a potent analgesic in the tailflick assay (ED50 3.1 micrograms). The analgesic activity is lost if the radiant heat is focused 1 cm away from the site of injection. The kappa 1-opioid receptor antagonist nor-binaltorphimine given systemically reverses the local analgesic response of U50,488H, but the antagonist is 100-fold more potent when injected directly into the tail. Intrathecal antisense treatment with a probe targeting the mRNA encoding the kappa 1-opioid receptor blocks the local analgesic actions of U50,488H in the tail, suggesting that U50,488H is acting on dorsal ganglia neurons.

Modulation of opioid analgesia by agmatine.

Administered alone, agmatine at doses of 0.1 or 10 mg/kg is without effect in the mouse tailflick assay. However, agmatine enhances morphine analgesia in a dose-dependent manner, shifting morphine's ED50 over 5-fold. A far greater effect is observed when morphine is given intrathecally (9-fold shift) than after intracerebroventricular administration (2-fold). In contrast to the potentiation of morphine analgesia, agmatine (10 mg/kg) has no effect on morphine's inhibition of gastrointestinal transit. delta-Opioid receptor-mediated analgesia also is potentiated by agmatine, but kappa1-receptor-mediated (U50,488H; trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeneacetemide) and kappa3-opioid receptor-mediated (naloxone benzoylhydrazone) analgesia is not significantly enhanced by any dose of agmatine tested in this acute model. In chronic studies, agmatine at a low dose (0.1 mg/kg) which does not affect morphine analgesia acutely prevents tolerance following chronic morphine dosing for 10 days. A higher agmatine dose (10 mg/kg) has a similar effect. Agmatine also blocks tolerance to the delta-opioid receptor ligand [D-Pen2,D-Pen5]enkephalin given intrathecally, but not to the kappa3-opioid receptor agonist naloxone benzoylhydrazone. Despite its inactivity on kappa1-opioid analgesia in the acute model, agmatine prevents kappa1-opioid receptor-mediated tolerance. These studies demonstrate the dramatic interactions between agmatine and opioid analgesia and tolerance.

Perspectives on the N-methyl-D-aspartate/nitric oxide cascade and opioid tolerance.

Opioid tolerance can be modulated by the N-methyl-D-aspartate/nitric oxide (NMDA/NO) cascade. Evidence exploring a daily injection paradigm indicates that agents antagonizing NMDA receptors can prevent tolerance to morphine and delta drugs, but not kappa agents. Drugs work regardless of whether they act as competitive or noncompetitive antagonists. Even an agent acting as an antagonist on the glycine site of the NMDA receptor is effective. Blockade of nitric oxide synthase has similar effects on opioid tolerance, preventing morphine and delta tolerance but not that of kappa drugs. Even methylene blue, which can inhibit guanylyl cyclase activity, is effective, presumably by blocking cGMP formation resulting from NO release. These results demonstrate the importance of an intact NMDA/NO cascade in the production of opioid tolerance and open new possibilities in the design of agents acting on opioid tolerance.

Nitric oxide and opioid tolerance.

Under conditions in which NG-nitro-L-arginine (NOArg) treatment prevents morphine tolerance, NOArg induces a slow progressive inhibition of nitric oxide synthase (NOS), starting at approx. 20% after a single treatment and increasing to approx. 65% after 10 days. Studies designed to examine potential changes in NOS levels with chronic morphine administration reveal no change. Total NOS activity in both brainstem and cerebellum homogenates is unchanged, as are levels of NOS mRNA in a variety of brain regions. L-Arginine, the precursor of nitric oxide (NO), accelerates tolerance when coadministered with morphine and when given alone L-arginine decreases morphine's potency. Administration of L-arginine alone for 3-10 days shifts morphine's dose-response curve over 2-fold to the right while D-arginine is without effect, as is daily administration of L-arginine along with the NOS inhibitor NOArg. Thus, chronic L-arginine induces "tolerance" in opioid naive mice through NOS. Together, our data indicate an important role for NO in the modulation of opioid analgesia.

1-Aminocyclopropane carboxylic acid (ACPC) prevents mu and delta opioid tolerance.

1-Aminocyclopropane carboxylic acid (ACPC), a partial agonist of the glycine site on the NMDA receptor, prevents tolerance to the mu opioid morphine and the delta ligand [D-Pen2,D-Pen5]enkephalin (DPDPE) when co-administered with the opioid. In contrast, ACPC does not significantly influence tolerance to the kappa1 opioid U50,488H or the kappa3 ligand naloxone benzoylhydrazone (NalBzoH). The actions of ACPC are restricted to tolerance. When given alone, ACPC has no analgesic actions in the tailflick assay and it does not change morphine's ED50 in naive mice. Chronic administration of ACPC alone for 5 days does not affect the sensitivity of mice to morphine. ACPC also reverses preexisting tolerance. When mice are made tolerant to morphine over 5 days and then receive ACPC along with their morphine, analgesia returns to naive levels within 3 days despite the continued administration of morphine. The actions of ACPC on opioid tolerance correspond closely with those previously described with both competitive and non-competitive NMDA antagonists.

Blockade of tolerance to morphine but not to kappa opioids by a nitric oxide synthase inhibitor.

The nitric oxide synthase inhibitor NG-nitro-L-arginine (NO2Arg) blocks morphine tolerance in mice. After implantation of morphine pellets the analgesic response decreases from 100% on the first day to 0% on the third. Coadministration of NO2Arg along with the pellets markedly retards the development of tolerance; 60% of mice are analgesic after 3 days, and 50% of mice are analgesic after 5 days. In a daily injection paradigm the analgesic response to morphine is reduced from 60% to 0% by 5 days. Concomitant administration of morphine along with NO2Arg at doses of 2 mg/kg per day prevents tolerance for 4 weeks. A single NO2Arg dose retards morphine tolerance for several days, and dosing every 4 days is almost as effective as daily NO2Arg. NO2Arg slowly reverses preexisting tolerance over 5 days despite the continued administration of morphine along with NO2Arg. NO2Arg also reduces dependence and reverses previously established dependence. NO2Arg does not prevent tolerance to analgesia mediated by the kappa 1 agonist trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolindinyl)cyclohexyl]- benzene-acetamide (U50,488H) or the kappa 3 agent naloxone benzoylhydrazone, indicating a selective action of NO in the mechanisms of mu tolerance and dependence.

Blockade of mu and kappa 1 opioid analgesic tolerance by NPC17742, a novel NMDA antagonist.

NPC17742 is a potent competitive NMDA antagonist. Low doses of NPC17742 prevent the development of tolerance to repeated daily injections of the mu agonist morphine and the kappa 1 agonist U50,488H. However, NPC17742 at these same doses is without effect against the kappa 3 analgesic naloxone benzoylhydrazone (NalBzoH). At these doses, NPC17742 does not significantly influence morphine's ED50 value following single or repeated doses of the NMDA antagonist. The ability of NPC17742 to block tolerance to U50488H distinguishes this compound from other NMDA antagonists and raises the possibility of subclasses of NMDA antagonists. Furthermore, these results emphasize the different mechanisms involved with analgesic tolerance among mu, kappa 1 and kappa 3 receptors.