Spinal mu, delta and kappa opioids alter chemical, mechanical and thermal sensitivities in amphibians

Previously we demonstrated the use of chemical (topical acetic acid), thermal (radiant heat) and mechanical (von Frey filament) stimuli as quantifiable behavioral response assays in the northern grass frog, Rana pipiens. Furthermore, response thresholds in all of these sensory modalities are significantly elevated by systemic morphine injections, which can be antagonized by naltrexone. The present study employed these three sensory assays to assess changes in chemical, mechanical and thermal sensitivities following spinal administration of mu, delta and kappa opioids. Significant elevations were observed across all three sensory modalities in each subtype category and these effects were abolished by prior systemic administration of naltrexone. However, naltrexone antagonism of morphine produced hyperalgesia in both the mechanical and thermal modalities. The results support other recent work demonstrating that the spinal site for opioid analgesia is present in amphibians and that the thermal, mechanical and acetic acid assays are measures of true nociceptive activity in the amphibian.     

Assessment of the kappa agonist and antagonist properties of mixed action opioids, mu opioids, and a delta opioid in pigeons.

The present study examined the kappa agonist and antagonist effects of various opioids in pigeons (Columba liva) trained to discriminate the kappa opioid bremazocine from saline. The mixed action opioids oxilorphan and (–)-cylorphan and the opioid antagonist naltrexone produced a dose-related antagonism of the bremazocine stimulus. With oxilorphan, the doses required to decrease responding were approximately 300 tomes larger than those required to antagonize the bremazocine stimulus, whereas with (–)-cylorphan and naltrexone the separation between these doses was relatively small. The mixed action opioid proxorphan substituted partially for and antagonized partially the bremazocine stimulus. Selected mu and delta opioids failed to substitute for or antagonize the bremazocine stimulus. The present findings suggest that mixed action opioids are active at the kappa receptor and that their effects can be distinguished from those of kappa, mu, and delta opioids. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential contribution of descending controls to the antinociceptive actions of kappa and mu opioids: an analysis of formalin-evoked C-fos expression

In this study, the effect of intracerebroventricular (icv) administration of (5R)-(5 alpha, 7 alpha, 8 beta)-N-methyl-N-[7-(1-pyrrolindinyl)-1- oxaspiro[4,5]dec-8-yl]-4-benzofurnacetamide monohydrochloride (Cl-977) on pain behaviors and on spinal cord fos-like immunoreactivity (FLI) evoked by unilateral formalin injection into the hindpaw of rats was examined. Intracerebroventricular administration of Cl-977 (0.13-13.00 nmol) produced a dose-dependent inhibition of formalin-evoked pain behaviors, with significant inhibition after 1.30, 4.40 and 13.00 nmol. The estimated ED50 for icv Cl-977 inhibition of formalin-evoked behaviors was 0.95 nmol and the Emax was 53%. The inhibitory effect of 4.40 nmol of icv Cl-977 on formalin-evoked behaviors was prevented by either pretreatment with the kappa selective antagonist nor-binaltorphimine (10 or 100 nmol) or coadministration of the opiate receptor antagonist, naloxone (30 nmol). The lowest dose of icv Cl-977 tested (0.13 nmol) produced a 50% reduction in FLI in the superficial laminae but did not inhibit the expression of FLI in any other regions of the spinal cord. The fos-inhibitory effect of low-dose icv Cl-977 in the superficial cord was reversed by coadministration of naloxone (30 nmol). Higher doses of icv Cl-977 that suppressed formalin-evoked behaviors did not inhibit the expression of FLI in any region of the spinal cord. Finally, neither the inhibitory effect of 4.40 nmol Cl-977 on formalin-evoked behaviors nor the formalin-evoked pattern of FLI expression in the spinal cord of rats treated with this dose of Cl-977 was affected by lesions of the dorsolateral funiculus. These results provide the first evidence that supraspinal kappa receptor-mediated antinociception is not dependent on the integrity of the dorsolateral funiculus and may be mediated exclusively at the supraspinal level, suggesting that there are multiple mechanisms through which opioids can evoke antinociceptive effects.     

Cross-tolerance to acute administration of mu and kappa opioid agonists at the spinal cord level in the rat

Development of tolerance and cross-tolerance after acute administration of the mu agonist morphine and the kappa agonist U-50,488H was assessed in rats, through recording of a C-fiber-evoked spinal nociceptive reflex. Rats rendered tolerant to morphine (a single dose of 1 mg/kg i.p.) showed, after a 5-hour period, tolerance to morphine and cross-tolerance to the kappa-opioid receptor agonist U-50,488H, as revealed by depressed C-reflex responsiveness. In contrast, pretreatment with U-50,488H (a single dose of 1 mg/kg i.p.) rendered tolerant the rats to U-50,488H, but the animals did not develop cross-tolerance to morphine. Results indicate that acute administration of mu and kappa ligands leads to development of unidirectional cross-tolerance in rat spinal cord. This points to limitations in using alternated mu and kappa opioid agonists to bypass the problem of development of opioid tolerance in chronic pain complaints.     

Comparative clinical pharmacology of short-acting mu opioids in drug abusers

The clinical pharmacology of fentanyl and alfentanil was examined in opioid-experienced volunteers with agonist and antagonist sensitivity measures. Two studies used within-subject, placebo-controlled, crossover designs. In study 1, fentanyl (0.125, 0.25 mg/70 kg i.v.) was followed at 0, 20, 60 and 180 min by naloxone (10 mg/70 kg i.m.). Agonist effects during 180-min and 0-min (control; simultaneous fentanyl-naloxone i.v. infusion) challenge sessions were compared. Fentanyl rapidly constricted pupils, depressed respiration and produced subjective "high" and opiate symptoms lasting 60 to 120 min, depending on the measure. Naloxone precipitated withdrawal symptoms of comparable intensity at each challenge point. In study 2, fentanyl (0.125, 0.25 mg/70 kg i.v.), alfentanil (1, 2 mg/70 kg i.v.) and saline were followed at 1 and 6 hr by naloxone (10 mg/70 kg i.m.). Agonist effects were examined during 6-hr challenge sessions. The two drugs produced a comparable range of effects with similar peak magnitude for 0.125 mg/70 kg fentanyl and 1 mg/70 kg alfentanil and for 0.25 mg/70 kg fentanyl and 2 mg/70 kg alfentanil. Alfentanil's duration of action was brief ( < 60 min). Withdrawal was precipitated at 6 hr only after 0.25 mg/70 kg fentanyl. These findings support typical mu opioid characteristics (pleasurable subjective effects, physical dependence) for both drugs, differential duration of action (fentanyl > alfentanil) and peak effects consistent with a 1:8 (fentanyl/alfentanil) potency ratio.     

Differential regulation of the cloned kappa and mu opioid receptors

To directly compare the regulation of the cloned kappa and mu opioid receptor, we expressed them in the same cells, the mouse anterior pituitary cell line AtT-20. The coupling of an endogenous somatostatin receptor to adenylyl cyclase and an inward rectifier K+ current has been well characterized in these cells, enabling us to do parallel studies comparing the regulation of both the kappa and the mu receptor to this somatostatin receptor. We show that the kappa receptor readily uncoupled from the K+ current and from adenylyl cyclase after a 1 h pretreatment with agonist, as indicated by the loss in the ability of the agonist to induce a functional response. The desensitization of the kappa receptor was homologous, as the ability of somatostatin to mediate inhibition of adenylyl cyclase or potentiation of the K+ current was not altered by kappa receptor desensitization. The mu receptor uncoupled from the K+ current but not adenylyl cyclase after a 1 h pretreatment with agonist. Somatostatin was no longer able to potentiate the K+ current after mu receptor desensitization, thus this desensitization was heterologous. Interestingly, pretreatment with a somatostatin agonist caused uncoupling of the mu receptor but not the kappa receptor from the K+ current. These results show that in the same cell line, after a 1 h pretreatment with agonist, the kappa receptor displays homologous regulation, whereas the mu receptor undergoes only a heterologous form of desensitization. mu receptor desensitization may lead to the alterations of diverse downstream events, whereas kappa receptor regulation apparently occurs at the level of the receptor itself. Broad alterations of non-opioid systems by the mu receptor could be relevant to the addictive properties of mu agonists. Comparison of kappa and mu receptor regulation may help define the properties of the mu receptor which are important in the development of addiction, tolerance, and withdrawal to opioid drugs. These are the first studies to directly compare the coupling of the kappa and mu receptors to two different effectors in the same mammalian expression system.     

Buprenorphine antagonism of mu opioids in the rhesus monkey tail-withdrawal procedure

The apparent in vivo dissociation constant (KA) and relative efficacy values for alfentanil, etonitazene, morphine, and nalbuphine were determined by comparing the effects of these agonists in the presence of buprenorphine with the effects of these agonists alone in the rhesus monkey tail-withdrawal procedure. Initial time course studies of buprenorphine alone indicated that 3.2 and 10 mg/kg produced increases in tail-withdrawal latencies when studied with 48 degrees C water for 48 hr. No increases in tail-withdrawal latency were found with either dose studied with 55 degrees C water. Buprenorphine produced dose-dependent shifts to the right for the antinociceptive effects of alfentanil, etonitazene, morphine and nalbuphine 72 hr after administration and decreased the maximal effects of morphine in 48 degrees C water and those of alfentanil and etonitazene in 55 degrees C water. Buprenorphine administration decreased the receptors available for agonist interaction to approximately 2%. The average apparent in vivo dissociation constant (KA) values for alfentanil, etonitazene, morphine and nalbuphine were 3.3, 0.073, 60 and 31 mg/kg, respectively. High efficacy estimates were determined for alfentanil (149-203) and etonitazene (174-203), whereas lower efficacy estimates were determined for nalbuphine (57) and morphine (17). The apparent in vivo dissociation constant of a pseudoirreversible antagonist (KB) value for buprenorphine averaged 0.15 mg/kg across agonists, temperatures and buprenorphine doses. These data extend and emphasize the significance of in vivo estimates of affinity and relative efficacy for drug classification.     

Osmolality changes in perilymph after systemic administration of glycerin

Blood osmolality was altered in guinea pigs by intravenous administration of glycerin (glycerol). After glycerin administration, serum osmolality increased rapidly, reaching a plateau within 15 minutes. Perilymph osmolality lagged significantly behind the increase of serum osmolality and equalled serum osmolality only after one hour. While perilymph osmolality responded to changes of serum osmolality, there was some time lag noted in the response of perilymph, suggesting the existence of a blood-labyrinth barrier. It was observed that this barrier is permeably to glycerin and water, suggesting the possibility of transient reduction of hydrostatic pressure in the labyrinth by the injection of an osmotic agent into the systemic circulation.     

Clocinnamox antagonism of the antinociceptive effects of mu opioids in squirrel monkeys

The opioid agonists morphine, etorphine, buprenorphine and U50,488 were examined alone and in combination with the insurmountable opioid antagonist clocinnamox (C-CAM) in squirrel monkeys responding under a schedule of shock titration. In this procedure, shock intensity increased every 15 sec from 0.01 to 2.0 mA in 30 increments. Five lever presses during any given 15-sec shock period produced a 15-sec timeout, after which shock resumed at the next lower intensity. When given alone, each of these agonists increased the median intensity at which the monkeys maintained shock [median shock level (MSL)]. At the highest dose examined alone, each agonist produced maximal increases in MSL and, except buprenorphine, decreased response rates. C-CAM dose-dependently antagonized the effects of morphine, etorphine and buprenorphine on MSL. In the presence of the higher C-CAM doses, etorphine, morphine and buprenorphine did not produce maximal effects on MSL. The effects of U50,488 were not systematically altered when tested in combination with the highest C-CAM dose. In general, C-CAM was more potent and the duration of antagonism was slightly longer against buprenorphine than against morphine and etorphine. Quantitative analysis of these data according to an extended model of yielded the following apparent affinity and efficacy estimates, respectively: etorphine (0. 085 mg/kg, 117); morphine (49 mg/kg, 24) and buprenorphine (0.62 mg/kg, 7.1). Determination of the individual q values over time indicated that the receptor population recovers more quickly after C-CAM antagonism of etorphine than from C-CAM antagonism of either morphine or buprenorphine. These data suggest that C-CAM functions as a long-lasting antagonist of mu opioid agonist actions in a shock titration procedure and yields estimates of relative intrinsic efficacy with the rank order of etorphine > morphine > buprenorphine.     

Epidural administration of opioids in labor: pro

PURPOSE: To present our studies concerning the causes of blindness in age-related macular degeneration, including the relationship with risk factors for this disease. MATERIAL AND METHODS: A total number of 158 eyes with AMD in 99 patients were examined. Among them there were 21 cases with visual acuity 0.1 or less in the better eye. This group of patients underwent a detailed analysis in order to determine the factors responsible for visual impairment in comparison to the patients with better visual function. RESULTS AND CONCLUSIONS: Blindness is connected mostly with exudative AMD. There are no significant differences in prevalence of risk factors for AMD between the group of patients with visual loss and that of patients with visual acuity above 0.1. The majority of patients referred to the ophthalmologist too late and on account of that is should be necessary to perform prophylactic examinations of the people above sixty.     

Deposition and retention of radiolabeled serum constituents in hair after systemic administration

We investigated the relationship between the changes in the pulmonary blood flow and histology during acute rejection following single lung transplantation. In single lung transplantation using adult mongrel dogs, immunosuppression with cyclosporine and azathioprine was discontinued after postoperative day 14 to induce rejection. Doppler flow probes were placed adjacent to the ascending aorta and the left pulmonary artery to measure the blood flow on a daily basis. In addition, chest roentgenograms were also examined daily. The pulmonary pressure was measured using a Swan-Ganz catheter prior to and following the induction of rejection. Open lung biopsies were performed when the left pulmonary artery flow decreased to half of the prerejection value. The pulmonary artery flow decreased to 14.3% of the aortic flow 5 days after the discontinuation of immunosuppression. The graft pulmonary vascular resistance increased significantly compared to the prerejection values (P < 0.001). This was not accompanied by any abnormalities on chest roentgenography. The histology was consistent, with marked perivascular lymphocytic infiltration with little alveolar or interstitial changes. During rejection, the increased pulmonary vascular resistance in the graft was probably the result of perivascular inflammatory cell infiltration, which was seen prior to changes on chest roentgenography. Changes in the left pulmonary artery flow and histology thus appear to be closely correlated in the early stages of acute rejection.     

Intraocular concentrations of chemotherapeutic agents after systemic or local administration

OBJECTIVES: To investigate the concentrations of carboplatin and etoposide achieved in the aqueous and vitreous humors after intravenous infusion in nonhuman primates, and to investigate whether local administration of carboplatin might result in higher concentrations in the vitreous humor. METHODS: Macaca fascicularis primates were treated with 1 of 3 regimens: (1) intravenous carboplatin (18.7 mg/kg), etoposide (5 mg/kg), and vincristine sulfate (0.05 mg/kg), (2) peribulbar carboplatin (10 mg/mL), or (3) episcleral balloon carboplatin (10 mg/mL). Concentrations of chemotherapeutic agents were measured in the plasma and in the aqueous and vitreous humors. RESULTS: No measurable amount of etoposide was detected in the aqueous or vitreous humor after intravenous administration. Mean measured peak vitreous concentration of carboplatin after intravenous administration was 0.31 microg/mL, which was 1% of the peak plasma value. Mean measured peak vitreous concentrations of carboplatin after peribulbar or episcleral balloon administration were 2.38 microg/mL and 2.95 microg/mL, respectively, which represent 7.68- and 9.52-fold increases over the concentration achieved after intravenous administration. No serious toxic effect was observed in any animal. CONCLUSIONS: Peribulbar and episcleral balloon administration of carboplatin seemed to be safe and resulted in higher vitreous concentrations than intravenous administration in this model. These results suggest that these alternate routes of delivery should be explored in children with vitreous seeding of retinoblastoma.     

Lidocaine concentrations in plasma and cerebrospinal fluid after systemic bolus administration in humans

Oscillation of membrane potential across a tri-block copolypeptide membrane composed of (Glu)x-(Leu)y-(Glu)x (x = 0.18 and y = 0.64) was observed under an electrical current, when the membrane was placed between equimolar aqueous salt solutions. The amplitude of the oscillation was influenced by the type of cation and anion in the external salt solution, and the amplitude was in the sequence: K+ > Na+ > Cs+ > Ca2+ and Cl- > Br-. The frequencies of the oscillations were in the range 0.1 to 5 Hz, and were also slightly influenced by the type of cation and anion.     

Anatomical studies of DNA fragmentation in rat brain after systemic kainate administration

Rats treated systemically with kainate develop stereotyped epileptic seizures involving mainly limbic structures that may last for hours. This model of limbic status epilepticus has been widely studied using classical neuropathological techniques. We used in situ nick translation histochemistry to examine patterns of DNA fragmentation in this model. We found a stereotyped and reproducible pattern of neuronal populations that demonstrate evidence of DNA fragmentation from 24 h to one week after kainate treatment. Neither blockade of new protein synthesis nor blockade of the N-methyl-D-aspartate-type glutamate receptors significantly altered this response. Moreover, we saw no evidence of the regular internucleosomal cleavage of DNA that produces a characteristic laddered appearance of 180-200 bp DNA fragments after gel electrophoresis in samples obtained from microdissected affected regions. These studies suggest that DNA fragmentation after systemic kainate-induced seizures is not the result of programmed cell death. This assay may be useful for quantitative testing of both neuroprotective agents and mechanistic hypotheses.     

Immunoglobulin kappa chain receptor editing in systemic lupus erythematosus

Wortmannin (WT) and 17beta-hydroxywortmannin (HWT), which are inhibitors of phosphatidylinositol-3(OH)-kinase (PI3K), have been shown previously to inhibit bone resorption in vitro and in vivo, possibly by interfering with formation of the osteoclast ruffled border. Since migration of osteoclasts also plays an important role in the process of bone resorption, we investigated the effects of these inhibitors on osteoclast morphology and motility. Both HWT and WT caused a sustained decrease in the planar area of osteoclasts in vitro (half maximal effect at 25 and 165 nM, respectively), with the effect of HWT on cell area more readily reversible than WT. These agents also caused accumulation of intracellular vesicles. Time-lapse video microscopy was used to record the migration of osteoclasts in response to macrophage colony-stimulating factor (M-CSF) or vehicle, flowing passively from a micropipette positioned 200-400 microm from the cell. M-CSF caused directed migration of osteoclasts, indicating chemotaxis (over 3 h osteoclasts migrated 96 +/- 14 microm in response to M-CSF vs. 11 +/- 2 microm in control experiments). Both WT (100 or 500 nM) and LY294002 (100 microM), a specific PI3K inhibitor structurally unrelated to WT, significantly inhibited osteoclast chemotaxis in response to M-CSF. Taken together, these effects of WT, HWT, and LY294002 are consistent with an important role for PI3K in regulating cytoskeletal function in osteoclasts. The inhibitory effects of WT and HWT on bone resorption may be due, in part, to impairment of osteoclast motility.     

Biodistribution and gene expression of lipid/plasmid complexes after systemic administration

The objectives of this study were to investigate the influence of physicochemical properties of lipid/plasmid complexes on in vivo gene transfer and biodistribution characteristics. Formulations based on 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA) and novel biodegradable cationic lipids, such as ethyl dioleoyl phosphatidylcholine (EDOPC), ethyl palmitoyl myristyl phosphatidylcholine (EPMPC), myristyl myristoyl carnitine ester (MMCE), and oleyl oleoyl L-carnitine ester (DOLCE), were assessed for gene expression after tail vein injection of lipid/plasmid complexes in mice. Gene expression was influenced by cationic lipid structure, cationic lipid-to-colipid molar ratios, plasmid-to-lipid charge ratios, and precondensation liposome size. Detectable levels of human growth hormone (hGH) in serum, human factor IX (hFIX) in plasma, and chloramphenicol acetyltransferase (CAT) in the lung and liver were observed with positively charged lipid/plasmid complexes prepared from 400-nm extruded liposomes with a cationic lipid-to-colipid ratio of 4:1 (mol/mol). Intravenous administration of lipid/CAT plasmid complexes resulted in distribution of plasmid DNA mainly to the lung at 15 min after injection. Plasmid DNA accumulation in the liver increased with time up to 24 hr postinjection. There was a 10-fold decrease in the amount of plasmid DNA in the lung at 15 min after injection, when the lipid/plasmid complex charge ratio was decreased from 3:1 to 0.5:1 (+/-). Bright fluorescent aggregates were evident in in vivo-transfected lung with the positively charged pCMV-CAT/DOLCE:dioleyl phosphatidylethanolamine (DOPE) (1:1, mol/mol) complexes, while more discrete punctate fluorescence was observed with a 4:1 molar ratio of cationic lipid:colipid formulations. Preinjection of polyanions such as plasmid, dextran sulfate, polycytidic acid, and polyinosinic acid decreased hGH expression, whereas the preinjection of both positively charged and neutral liposomes had no effect on hGH serum levels. Of the cationic lipids tested, DOLCE was found to be the most effective potentially biodegradable cationic lipid. A correlation between gene expression and cationic lipid:colipid ratios and lipid-to-plasmid charge ratio was also observed for DOTMA- and DOLCE-based formulations.     

Redistribution of sufentanil to cerebrospinal fluid and systemic circulation after epidural administration in dogs

Due to its higher lipid solubility, sufentanil may be less likely than morphine to migrate rostrally in the cerebral spinal fluid (CSF) and cause delayed respiratory depression following epidural administration. However, early respiratory depression has been reported in patients after relatively large doses of epidural sufentanil. This has been attributed to systemic drug uptake. We used a dog model to investigate the pharmacokinetics and rostral spread of epidural sufentanil in CSF. Sampling catheters were placed in the lumbar subarachnoid space, the cisterna magna, and femoral arteries of six mongrel dogs. Samples of cisternal CSF, lumbar CSF, and blood were drawn at 0, 1, 5, 15, 30, 60, 90, 120, and 180 min after lumbar epidural sufentanil injection. We measured sufentanil concentrations by gas chromatography-mass spectrometry and used the least squares method to a fit tri-exponential function to each sufentanil concentration versus time data set. Paired t-test was used to test for statistical significance. After epidural sufentanil, lumbar CSF concentrations were significantly higher than plasma or cisternal CSF sufentanil concentrations at all assessment times. Sufentanil concentrations were significantly higher in cisternal CSF than in plasma at 30 and 60 min after injection. Sufentanil appeared rapidly in lumbar CSF, reaching a maximum concentration (Cmax) of 57 ng/mL at 6.5 min. In cisternal CSF, a Cmax of 1.2 ng/mL was reached at 21 min, and Cmax in plasma was 0.35 ng/mL at 6 min. The area under the concentration-time curve (AUC) of sufentanil in cisternal CSF was approximately six times higher than the plasma AUC (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)