Morphine-dependent Monkeys Research Articles

Cross-tolerance to cannabinoids in morphine-tolerant rhesus monkeys.

Opioids remain the drugs of choice for treating moderatetosevere pain, although adverse effects limit their use. Therapeutic utility might be improved by combining opioids with other drugs to enhance analgesic effects, but only if adverse effects are not similarly changed. Cannabinoids have been shown to enhance the antinociceptive potency of opioids without increasing other effects; this study examined whether the effectiveness of cannabinoids is altered in morphine-dependent monkeys. Four monkeys received up to 10mg/kg morphine twice daily. Changes in the antinociceptive effects of opioid receptor agonists (morphine, U50,488) and cannabinoid receptor agonists (WIN 55,212, CP 55,940, and Δ(9)-tetrahydrocannabinol [THC]) were determined by measuring the latency for monkeys to remove their tails from 40, 50, 54, and 58°C water. Before treatment, all drugs increased tail withdrawal latency from warm (54°C) water. Chronic morphine treatment decreased the potency of each drug; the magnitude of rightward shift in dose-effect curves was greatest for morphine, WIN 55,212 and CP 55,940 with at least sixfold shifts for each drug during treatment. Discontinuation of morphine treatment resulted in signs that are indicative of withdrawal, including increased heart rate, decreased daytime activity, and tongue movement. Tolerance developed to the antinociceptive effects of morphine and cross-tolerance developed to cannabinoids under conditions that produced modest physical dependence. Compared with the doses examined in this study, much smaller doses of opioids have antinociceptive effects when given with cannabinoids; it is possible that tolerance will not develop to chronic treatment with opioid/cannabinoid mixtures.

1H‐nuclear magnetic resonance‐based metabonomic analysis of brain in rhesus monkeys with morphine treatment and withdrawal intervention

Comprehensive cerebral metabolites involved in morphine dependence have not been well explored. To gain a better understanding of morphine dependence and withdrawal therapy in a model highly related to humans, metabolic changes in brain hippocampus and prefrontal cortex (PFC) of rhesus monkeys were measured by (1) H-nuclear magnetic resonance spectroscopy, coupled with partial least squares and orthogonal signal correction analysis. The results showed that concentrations of myoinositol (M-Ins) and taurine were significantly reduced, whereas lactic acid was increased in hippocampus and PFC of morphine-dependent monkeys. Phosphocholine and creatine increased in PFC but decreased in hippocampus after chronic treatment of morphine. Moreover, N-acetyl aspartate (NAA), γ-aminobutyric acid, glutamate, glutathione, methionine, and homocysteic acid also changed in these brain regions. These results suggest that chronic morphine exposure causes profound disturbances of neurotransmitters, membrane, and energy metabolism in the brain. Notably, morphine-induced dysregulations in NAA, creatine, lactic acid, taurine, M-Ins, and phosphocholine were clearly reversed after intervention with methadone or clonidine. Our study highlights the potential of metabolic profiling to enhance our understanding of metabolite alteration and neurobiological actions associated with morphine addiction and withdrawal therapy in primates.

MDAN-21: A Bivalent Opioid Ligand Containing mu-Agonist and Delta-Antagonist Pharmacophores and Its Effects in Rhesus Monkeys.

MDAN-21, 7′-{2-[(7-{2-[({(5α, 6α)-4,5-Epoxy-3,14-dihydroxy-17-methylmorphin-6-yl}-aminocarbonyl)metoxy]-acetylamino}-heptylaminocarbonyl)-methoxy]-acetylamino}-naltrindole, a bivalent opioid ligand containing a mu-opioid receptor agonist (derived from oxymorphone) linked to the delta-opioid receptor antagonist (related to naltrindole) by a spacer of 21 atoms, was reported to have potent analgesic properties in mice. Tolerance, physical dependence, and conditioned place preference were not evident in that species. The finding that bivalent ligands in this series, with spacers 19 atoms or greater, were devoid of tolerance and dependence led to the proposal that MDAN-21 targets heteromeric mu-delta-opioid receptors. The present study focused on its effects in nonhuman primates (Macaca mulatta), a species with a physiology and behavioral repertoire not unlike humans. With regard to opioids, this species usually better predicts clinical outcomes. MDAN-21 substituted for morphine in morphine-dependent monkeys in the remarkably low dose range 0.006–0.032 mg/kg, subcutaneously. Although MDAN-21 failed to produce reliable thermal analgesia in the dose range 0.0032–0.032 mg/kg, intramuscularly, it was active in the same dose range and by the same route of administration, in the capsaicin-induced thermal allodynia assay. The results suggest that MDAN-21 may be useful in the treatment of opioid dependence and allodynia. The data provide additional evidence that opioid withdrawal is associated with sensitized pain.

Use of the mouse jumping test for estimating antagonistic potencies of morphine antagonists.

The potencies of 19 reference morphine antagonists have been compared in a modified version of the mouse jumping test. Mice were each implanted subcutaneously with one 75 mg pellet of morphine. Antagonist challenge took place 72 h later and the incidence of repetitive vertical-jumping was monitored over 1 h. A high Pearson correlation coefficient (r = 0.997) was found between quantitative assays based on the total number of jumps per mouse and quantal assays based on mice jumping at least 6 times. A comparison of relative potencies obtained with the mouse test and with non-withdrawn morphine-dependent monkeys gave a Spearman rank order coefficient of 0.91 while a similar comparison with values obtained with the guinea-pig isolated ileum preparation also gave a high correlation coefficient (r= 0.92). Whereas it is difficult to assess the antagonistic component of buprenorphine and cyclorphan with the ileum preparation, both compounds can be satisfactorily assayed in the mouse jumping test. The reported antagonistic properties of ketocyclazocine and profadol could not be confirmed in the mouse model.

Comparison of naltrexone, 6α-naltrexol, and 6β-naltrexol in morphine-dependent and in nondependent rhesus monkeys

Some opioid receptor ligands that appear to be neutral antagonists can have inverse agonist activity under conditions of increased constitutive activity (e.g., agonist treatment). This study compared the opioid receptor antagonist naltrexone and its metabolites 6alpha-naltrexol and 6beta-naltrexol in nondependent and morphine-dependent monkeys to see whether their potencies varied according to drug treatment and, presumably, to differences in constitutive activity of mu opioid receptors. In monkeys (n = 4) receiving 3.2 mg/kg per day of morphine and discriminating 0.0178 mg/kg naltrexone, naltrexone and each metabolite increased responding on the naltrexone lever in a dose-related manner with naltrexone being 8- and 71-fold more potent than 6alpha- and 6beta-naltrexol, respectively. After 27 h of no-morphine treatment, monkeys responded on the naltrexone lever, and this effect was reversed by morphine. Naltrexone and each metabolite prevented morphine reversal of naltrexone-lever responding, and their rank order potency was the same as their substitution for naltrexone; however, the potency between naltrexone and each metabolite was slightly greater in morphine-dependent as compared to morphine-deprived monkeys. In a separate group (n = 3) of nondependent monkeys discriminating 1.78 mg/kg of morphine, all three compounds antagonized morphine with the same potency as in the reversal study (morphine-dependent monkeys), with Schild analyses showing no difference in apparent affinities (pA (2)) between nondependent and morphine-dependent monkeys. Naltrexone and 6alpha- and 6beta-naltrexol have qualitatively similar effects, and their potencies do not vary markedly with opioid treatment, suggesting that under these conditions, they do not vary with regard to inverse agonism.

SIV Vpr evolution is inversely related to disease progression in a morphine-dependent rhesus macaque model of AIDS

Three of six morphine-dependent monkeys progressed rapidly to AIDS and died by 20 weeks in our SIV/SHIV non-human primate model of drug addiction and AIDS. We studied the evolution of the SIV vpr gene in both cerebrospinal fluid (CSF) and plasma in these rapid progressors, in their normal progressor counterparts and in infected, drug-free controls at 12 and 20 weeks post infection. Viral RNA was amplified, cloned, and sequenced to permit phylogenetic analyses of diversity and divergence of the vpr locus. As we found for SIV tat and env, the vpr gene evolves inversely to the rate of disease progression. Further, we found evidence that compartmentalization of the virus in plasma and CSF is significantly greater in the normal progressors than in the morphine-dependent, rapid progressors. Interestingly, although our previous work with the accessory gene nef indicated no association between disease progression and evolution, the accessory factor, vpr, behaves similarly to the essential lentiviral genes tat and env.

Differential in Vivo Potencies of Naltrexone and 6β-Naltrexol in the Monkey

6beta-Naltrexol is the major metabolite of the opioid receptor antagonist, naltrexone, in humans. However, there are no functional studies of 6beta-naltrexol in primates. The aim of this study was to compare the in vitro and in vivo potencies of naltrexone and 6beta-naltrexol in rhesus monkeys. Affinity and potency were determined using radioligand displacement and stimulation of 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding in monkey brain membranes. In vivo apparent pA(2) analysis was applied to compare the mu-opioid receptor (MOR) antagonist potency of both compounds in nondependent monkeys. In addition, the potencies of both compounds were determined in precipitating withdrawal manifested by increased respiratory parameters in acute morphine-dependent monkeys. In vitro assays revealed that naltrexone displayed 2-fold higher affinity and potency than 6beta-naltrexol for the MOR binding site and for MOR agonist-stimulated [(35)S]GTPgammaS binding, respectively. 6beta-Naltrexol (0.32-3.2 mg/kg) dose-dependently produced parallel rightward shifts of the dose-response curve of alfentanil-induced antinociception. Nevertheless, the apparent pA(2) value of 6beta-naltrexol (6.5) was 100-fold less potent than that of naltrexone (8.5) determined previously. 6beta-Naltrexol was also less potent than naltrexone in antagonizing other MOR-mediated effects including respiratory depression and itch/scratching. Naltrexone (0.0032-0.032 mg/kg) and 6beta-naltrexol (0.32-3.2 mg/kg) retained the same potency difference in precipitating withdrawal to a similar degree. Furthermore, 6beta-naltrexol failed to block naltrexone-precipitated withdrawal in morphine-dependent monkeys. These results indicate that naltrexone and 6beta-naltrexol display similar pharmacological actions with a large in vivo potency difference in monkeys such that 6beta-naltrexol may play a minimal role in the therapeutic or antagonist effects of naltrexone in primates.

Morphine promotes simian acquired immunodeficiency syndrome virus replication in monkey peripheral mononuclear cells: induction of CC chemokine receptor 5 expression for virus entry.

Rhesus monkeys (Macaca mulatta) chronically administered opioids were more susceptible to simian immunodeficiency virus (SIV) strain mac239 (SIVmac239) infection than those without prior exposure to opioids. Increased plasma viremia in morphine-dependent monkeys allowed SIV to be detected in the animals' peripheral blood mononuclear cells (PBMC) without cocultivation with a tissue culture cell line. In contrast, virus titers from the PBMC of morphine-naive SIVmac239-infected animals were undetectable in the absence of cocultivation. PBMC isolated from noninfected animals and treated with morphine sulfate in vitro produced an increase in the expression of beta-chemokine receptor 5 (CCR5). Because both SIVmac239 and human immunodeficiency virus (HIV) require CCR5 for cell entry, the unique role of morphine in promoting SIV infection may provide a mechanism to account for the high incidence of HIV disease among drug-using populations.

Quadazocine decreases responding reinforced by ethanol, sucrose, and phencyclidine fluid deliveries in rhesus monkeys: comparison to naltrexone's effects

The endogenous opioid system may mediate the reinforcing effects of ethanol as well as sweet-tasting solutions. For example, opioid antagonists, such as naltrexone, reduce ethanol- and sucrose-reinforced responding in rhesus monkeys. If these effects are due to blockade of the mu-receptor, then an opioid antagonist such as quadazocine with a receptor selectivity profile similar to that of naltrexone should reduce responding at doses correlated with its mu-selectivity. To determine whether quadazocine would reduce responding for ethanol and sucrose at mu-selective doses, and whether quadazocine and naltrexone would reduce responding for a bitter-tasting drug solution such as phencyclidine. Rhesus monkeys were given access to ethanol, sucrose, or phencyclidine concurrently with water. Prior to the drinking sessions, quadazocine (0.032-3.2 mg/kg) or saline was injected intramuscularly. During the phencyclidine experiment, naltrexone (0.1 and 0.32 mg/kg) was also tested. The highest quadazocine doses (1 and 3.2 mg/kg) reduced ethanol and sucrose fluid deliveries without affecting the concurrently available water. Quadazocine reduced the fluid deliveries of both phencyclidine and water when concurrently available. Naltrexone reduced only phencyclidine fluid deliveries. The opioid antagonist effect on oral-reinforced responding is not selective for ethanol or sweet-tasting solutions; responding for phencyclidine was reduced as well. Quadazocine and NTX may reduce responding by blocking the mu-receptor because the relative potency of these antagonists to reduce oral self-administration was similar to their relative potency to produce withdrawal in morphine-dependent monkeys. However, water responding was low in these experiments, and thus we cannot rule out rate-dependent effects of the antagonists.

3-Alkyl ethers of clocinnamox: delayed long-term mu-antagonists with variable mu efficacy.

In recent years there has been considerable interest in the relationship between clocinnamox (C-CAM) and its methyl ether methoclocinnamox (MC-CAM). While C-CAM appears to be an insurmountable mu-antagonist, MC-CAM has been shown to be a potent partial agonist at mu-opioid receptors. To further investigate this relationship we prepared other ethers of C-CAM and evaluated these in opioid receptor binding assays and in vivo in mouse antinociceptive assays and in morphine-dependent monkeys. In opioid binding assays, the ethers were generally mu-selective with affinity equivalent to that of C-CAM itself. Although they displayed little or no efficacy in vitro, some of the ethers showed substantial agonist activity in the in vivo antinociceptive tests. Two of the ethers, the propargyl ether 7 and the cyclopropylmethyl ether 5, were chosen for more detailed analysis in vivo. 7 was shown to have significant mu-agonist character and was able to substitute for morphine in morphine-dependent monkeys. Interestingly, when this agonist effect abated, 7 displayed long-lasting mu-antagonism. In contrast, 5 displayed little agonist activity in vivo and was characterized as a potent, long-acting mu antagonist. Although further work is needed to determine whether metabolism is a crucial factor in determining the pharmacological profile of these ethers, it is clear that 3-O-alkylation is a useful means of varying the mu efficacy displayed by this class of acyl-substituted 14-aminomorphinones. MC-CAM itself has generated considerable interest as a potential pharmacotherapy for opiate abuse. These analogues with differing mu efficacy but retaining the long-lasting mu-antagonist effects provide further opportunities for the development of treatment drugs.

Effects of morphine, naloxone, buprenorphine, butorphanol, haloperidol and imipramine on morphine withdrawal signs in cynomolgus monkeys

This study was conducted to characterize the opiate dependence potential of a number of opiate and non-opiate psychoactive drugs in morphine-dependent cynomolgus monkeys (Macaca fascicularis). In addition, the agonist/antagonist profiles of buprenorphine and butorphanol were directly compared. Six male cynomolgus monkeys were maintained on morphine (3.0 mg/kg, q.i.d.) for 6 months. On evaluation days, monkeys were scored for opiate withdrawal signs 18 h after the last dose of morphine. Single dose suppression studies were conducted by giving subcutaneous injections of morphine (3 or 6 mg/kg), naloxone (0.01, 0.05 or 0.1 mg/kg), buprenorphine (1, 3, 10, 30 or 100 micrograms/kg), butorphanol (0.01, 0.1, 1.0 or 3.2 mg/kg), haloperidol (0.01, 0.05 or 0.1 mg/kg), imipramine (2, 5 or 10 mg/kg) or saline and measuring the number and frequency of withdrawal signs that appeared over a 2-h period. In a separate precipitation experiment either saline or 0.01 or 0.1 mg/kg butorphanol was administered 2 h after the last maintenance dose of morphine. In the single dose suppression test, morphine completely suppressed most withdrawal signs while naloxone increased the severity of withdrawal. All doses of buprenorphine increased many withdrawal signs such as backward gait, rearing, chafing face, chain biting, vomiting, masturbation, and vocalizations after intimidation. Only a few signs were reduced, but the overall withdrawal scores were not significantly increased. Low doses of butorphanol suppressed some signs while the highest dose almost completely eliminated all withdrawal signs. Butorphanol also failed to precipitate opiate withdrawal, and actually reversed the signs present in the saline-treated monkeys. Imipramine and haloperidol had little effect on the morphine withdrawal syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Dihydroetorphine, a potent opioid with low dependent potential

The antinociceptive effects of dihydroetorphine (DHE), 7α-[1-(R)-hydroxyl-1-methylbutyl] 6,14-endoethanotetrahydro-oripavine, could be achieved by injection or sublingual (sl) administrations. ED 50 or minimal effective doses (MED) of DHE against heat, mechanical or chemical stimuli were 0.10–0.50 μg/kg by sc or im in monkeys, rats, mice, rabbits and dogs, and 20 ng/kg in rats and 45 ng/kg in mice by iv, and 2.54 μg/kg in rats and 3.94 μg/kg in mice by sl, respectively. Oral administration was poor effective. In chronic morphine-, and DHE-treated monkeys, the the scores of abstinence syndrome of those of DHE-treated were obviously lower than those of morphine-treated. DHE could substitute abstinence induced by withdrawal in morphine-dependent monkeys. It was implicated that DHE possesses qualitatively opioid-like dependent potential, but markedly lower than that of morphine. The results indicated that DHE would has potentially values as an analgesics and detoxicant of opioid addicts for clinical applications.

Assessment of the abuse potential of acetorphan, an enkephalinase inhibitor

The discriminative stimulus properties, reinforcing effects and physical dependence potential of acetorphan, a parenterally-active enkephalinase (E.G. 3.4.21.11) inhibitor, were assessed in the present studies. Rats trained to discriminate 2 mg/kg morphine from saline did not generalize to acetorphan at any dose tested (5–50 mg/kg). Acetorphan also had minimal reinforcing effects in rhesus monkeys. When acetorphan was substituted for cocaine, one dose (300 μ/kg per inj.) maintained responding somewhat above the range of vehicle values in only two of the four monkeys tested. In physical dependence studies, acetorphan also failed to produce opioid-like effects. In morphine-dependent monkeys and rats, acetorphan failed to suppress withdrawal. Additionally, there were no overt withdrawal signs observed following the termination of chronic acetorphan infusion in the rat. Together, these results indicate that acetorphan appears to have minimal abuse potential.

Kappa receptor mediated opioid dependence in rhesus monkeys

The kappa receptor-selective agonist U-50, 488 was administered chronically to rhesus monkeys. Tolerance developed to the overt behavioral effects of U-50, 488 without cross-tolerance to morphine. Withdrawal behaviors produced by deprivation, naloxone or quadazocine administration in U-50, 488-dependent monkeys consisted of hyperactivity, excessive grooming, and yawning. The syndrome was suppressed in a dose-related manner by a kappa agonist, ethylketazocine, but not by doses of morphine that suppressed its own withdrawal. The mu-selective antagonist, beta-funaltrexamine, at doses which are active in morphine-dependent monkeys, did not precipitate withdrawal in U50, 488-dependent monkeys. Dependence, which is the result of activity at the kappa receptor, was distinct from morphine dependence.

β-Endorphin suppression of acute morphine abstinence in morphine dependent monkeys: Effective given intraventricularly but ineffective given intravenously

Six female adult Macaca mulatta monkeys were made dependent upon morphine sulfate and were implanted with a chronic indwelling needle in the lateral ventricle of the brain for sterile intraventricular injections. Both β-endorphin and morphine, in a dose dependent manner given intraventricularly suppressed the signs of 14 hour acute morphine abstinence. On a molar basis, β-endorphin was more active than morphine in suppressing the signs of morphine abstinence. When given intravenously in much larger doses, β-endorphin was ineffective in contrast to morphine which was effective in suppressing abstinence.

Substitution and primary dependence studies in animals.

The mixed agonist-antagonist analgesics buprenorphine, butorphanol, nalbuphine, pentazocine and picenadol were compared to the prototype mu and kappa agonists morphine and Mr 2033, respectively, in the following tests in rhesus monkeys: overt behavioral effects upon acute administration in drug-naive animals; discriminative stimulus properties in monkeys trained to respond to either etorphine or ethylketazocine; self-administration of the test agent relative to codeine; single dose suppression and precipitation in withdrawn and non-withdrawn morphine-dependent monkeys, respectively; and primary addiction studies in drug-naive animals. Whereas both buprenorphine and nalbuphine precipitate withdrawal in morphine-dependent monkeys, withdrawal following chronic administration of buprenorphine resulted in no observable signs of abstinence, while nalbuphine withdrawal was similar to that seen in morphine-dependent monkeys. Butorphanol, pentazocine and picenadol all produced mild dependence of the kappa-type; that is, natural withdrawal behavior similar to that seen following chronic Mr 2033 administration.

9α- and 9β-Hydroxyphenylmorphans

Platinum-oxide hydrogenation of 5-m-methoxyphenyl-2-methyl-9-oxomorphan (I) gave the 9α-hydroxy racemate (II) whose phenolic analogue (III) is a strong antinociceptive agent, fully supportive of morphine dependence in rhesus monkeys. The di-O-acetyl derivative (VI) of III was similar to III in its profile of activity. The diastereoisomer of III (VII), obtained by hydrogenation of the methobromide of I (IV), extrusion of methyl bromide, and O-demethylation of the resultant free base (VIII), was almost inactive antinociceptively and did not suppress withdrawal symptoms in morphine-dependent monkeys. The orientation of the C-9 hydroxyl groups was deduced from spectral data and by analogy.

Dynorphin-(1-13): effects in nontolerant and morphine-dependent rhesus monkeys.

Abstract Dynorphin-(1–13) (Dyn) substitutes for morphine in morphine-dependent monkeys. At doses which substitute for morphine, this peptide did not produce morphine-like overt effects in nontolerant monkeys. In vivo, Dyn does not behave as a typical κ-agonist. These results are consistent with the suggestion that Dyn's role may be that of a regulatory peptide.

ChemInform Abstract: ANALGESIC NARCOTIC ANTAGONISTS. 2. 8‐ALKYLMORPHINAN‐6‐ONES

AbstractDer aus Thebain leicht zugängliche Enolether (I) wird salzsauer zum Keton (II) gespalten, das mit Lithiumdialkylcupraten zu den substituierten Ketonen (III) reagiert.

An investigation of the negative-reinforcing properties of naloxone and cyclazocine in squirrel monkeys.

Monkeys were trained to emit 10 responses to terminate a schedule complex consisting of a light and masking noise in the presence of which brief, intravenous injections of naloxone (0.01 mg/kg per injection), dl-cyclazocine (0.003, 0.01 mg/kg per injection), or saline were scheduled to occur over blocks of consecutive daily sessions. Completion of the fixed ratio (FR 10) response requirement terminated the schedule complex, producing a time-out of 60 s in which responses were without consequence and injections did not occur. Sessions lasted for 100 min or ended after 100 injections, whichever came first. When monkeys received an intramuscular injection of morphine (10 mg/kg) 60 min preceding each session, responding to avoid injections of naloxone or cyclazocine was well maintained, though morphine-dependent monkeys tolerated injections of saline or the vehicle in which cyclazocine was dissolved. When the morphine pretreatment regimen was discontinued, monkeys tolerated injections of naloxone and cyclazocine though, at the larger cyclazocine dose (0.01 mg/kg per injection), responding was maintained for at least 30 consecutive sessions in two postdependent animals, but not in two other monkeys treated identically. The capacity of these morphine-antagonist drugs to support responding that avoids their injection depends evidently upon whether monkeys are rendered morphine dependent or not; in the case of cyclazocine, however, an increased sensitivity to the negative-reinforcing effects of the drug appears to persist in some "postdependent" monkeys.