Maintenance of acute morphine tolerance in mice by selective blockage of kappa opioid receptors with norbinaltorphimine

American Society of Regional Anesthesia and Pain Medicine 2021 John J. Bonica Award Lecture

I am as deeply inspired and humbled to receive this prestigious award, as I am profoundly indebted to the Bonica Award selection committee and the American Society of Regional Anesthesia and Pain Medicine Board of Directors for recognizing my contributions to the development, teaching, and practice of pain medicine in the tradition of Dr John J Bonica. I would also like to recognize my parents, Aura and Tito for providing me with the support and the environment to fulfill my professional goals. Moreover, the support that I have gotten from my team at the hospital, and the Chair of my Department, Dr Mark Lema needs to be underscored.

Long-term antagonism of κ opioid receptors prevents escalation of and increased motivation for heroin intake

The abuse of opioid drugs, both illicit and prescription, is a persistent problem in the United States, accounting for >1.2 million users who require treatment each year. Current treatments rely on suppressing immediate withdrawal symptoms and replacing illicit drug use with long-acting opiate drugs. However, the mechanisms that lead to preventing opiate dependence are still poorly understood. We hypothesized that κ opioid receptor (KOR) activation during chronic opioid intake contributes to negative affective states associated with withdrawal and the motivation to take increasing amounts of heroin. Using a 12 h long-access model of heroin self-administration, rats showed escalation of heroin intake over several weeks. This was prevented by a single high dose (30 mg/kg) of the long-acting KOR antagonist norbinaltorphimine (nor-BNI), paralleled by reduced motivation to respond for heroin on a progressive-ratio schedule of reinforcement, a measure of compulsive-like responding. Systemic nor-BNI also significantly decreased heroin withdrawal-associated anxiety-like behavior. Immunohistochemical analysis showed prodynorphin content increased in the nucleus accumbens core in all heroin-exposed rats, but selectively increased in the nucleus accumbens shell in long-access rats. Local infusion of nor-BNI (4 μg/side) into accumbens core altered the initial intake of heroin but not the rate of escalation, while local injection into accumbens shell selectively suppressed increases in heroin intake over time without altering initial intake. These data suggest that dynorphin activity in the nucleus accumbens mediates the increasing motivation for heroin taking and compulsive-like responding for heroin, suggesting that KOR antagonists may be promising targets for the treatment of opioid addiction.

Endogenous kappa-opioid receptor systems inhibit hyperalgesia associated with localized peripheral inflammation

Peripheral inflammation evokes functional and biochemical changes in the periphery and spinal cord which result in central sensitization and hypersensitivity. Inhibitory control systems from the rostral ventromedial medulla (RVM) are also activated. The present study investigates whether endogenous kappa-opioid receptor (KOPr) systems contribute to these neuroadaptations. Inflammation was induced by intraplantar injection of complete Freund's adjuvant (CFA) into one hindpaw. Mechanical and thermal thresholds were determined using the Von Frey and radiant heat tests, respectively. KOPr gene deletion in mice or systemic administration of the long-acting KOPr antagonist, norbinaltorphimine (norBNI) significantly exacerbated mechanical and thermal hypersensitivity of the ipsilateral, inflamed paw. Thermal and mechanical thresholds of the non-inflamed, contralateral hindpaw were unaffected by CFA treatment. However, gene deletion as well as norBNI treatment resulted in mechanical, but not thermal hypersensitivity of the non-inflamed paw. Similar results were obtained when norBNI was administered intrathecally or into the RVM in rats. These data demonstrate a previously unrecognized role of endogenous KOPr systems in inhibiting hyperalgesia during inflammation. Furthermore, they demonstrate that decreased KOPr activity in either the spinal cord or RVM not only enhances mechanical and thermal hyperalgesia of the inflamed limb but also leads to an unmasking of mechanical hyperalgesia at a site remote from inflammation. The differential effects of KOPr antagonism on mechanical versus thermal thresholds for the non-inflamed paw support the notion that distinct neuroanatomical or neurochemical mechanisms modulate the processing of thermal versus mechanical stimuli.

Attenuation of morphine tolerance and withdrawal syndrome by coadministration of nalbuphine

Morphine has been used widely on the treatment of many types of chronic pain. However the development of tolerance to and dependence on morphine by repeat application is a major problem in pain therapy. The purpose of the present study was to investigate whether combined administration of nalbuphine with morphine affects the development of tolerance to and dependence on morphine. We hypothesize that the use of nalbuphine, kappa-agonist may prove to be useful adjunct therapy to prevent morphine-induced undesirable effects in the management of some forms of chronic pain. Morphine (10 mg/kg) was injected to rats intraperitoneally for 5 day. The variable dose of nalbuphine (0.1, 1.0 and 5.0 mg/kg) was administered (i.p.) in combination with morphine injection. The development of morphine tolerance was assessed by measuring the antinociceptive effect with the Randall-Selitto apparatus. The development of dependence on morphine was determined by the scoring the precipitated withdrawal signs for 30 min after injection of naloxone (10 mg/kg, i.p.). Nalbuphine did not attenuate antinociceptive effect of morphine in rats. Interestingly, combined administration of morphine with nalbuphine (10:1) significantly attenuated the development of dependence on morphine. The elevation of [3H]MK-801 binding in frontal cortex, dentate gyrus, and cerebellum after chronic morphine infusion was suppressed by the coadministration of nalbuphine. In addition, the elevation of NR1 expression by morphine was decreased by the coadministration of nalbuphine in rat cortex. These results suggest that the coadministration of nalbuphine with morphine in chronic pain treatment can be one of therapies to reduce the development of tolerance to and dependence on morphine.

Prolonged antagonism of morphine-induced locomotor stimulation by kappa opioid agonists: enhancement by prior morphine exposure

The selective kappa agonists U50488 (10 mg/kg, i.p.) and spiradoline (1 mg/kg, i.p.) attenuated the locomotor activating effects of a morphine challenge (5 mg/kg, i.p.) administered 19 h later in rats. This antagonism of morphine by a kappa agonist was reversed by the selective kappa antagonist, norbinaltorphimine (10 mg/kg, s.c.). Furthermore, the kappa opioid antagonism of morphine was enhanced by prior morphine exposure (2 doses of 30 mg/kg, i.p. administered once a day for 2 days). The present data suggest that kappa-micro opioid interactions may occur over time periods that exceed the acute durations of drug actions.

Mu and kappa opioid system interactions in the expression of acute opioid dependence in isolated guinea-pig ileum

In vivo studies have suggested that the kappa opioid system can partially inhibit the development of physical dependence to mu agonists. Vice versa, activation of mu receptors may inhibit the expression of physical dependence to kappa agonists. We studied mu-kappa interactions in the isolated guinea-pig ileum (GPI). In the isolated GPI briefly exposed to mu or kappa agonists the addition of the respective antagonists precipitated a withdrawal contracture. After a first withdrawal response, however, some tissues failed to exhibit subsequent mu or kappa withdrawal contractures. A withdrawal contracture to the selective mu antagonist, cyprodime, after repeated exposures to a selective mu agonist, dermorphin, was restored by nor-binaltorphimine (BNI), a selective kappa antagonist. Vice versa, after repeated exposures to the kappa agonist, U-50,488H, cyprodime restored tissue responsiveness to BNI. Tissues repeatedly exposed to dermorphin and washed after each exposure contracted to the addition of BNI. Tissues repeatedly exposed to U-50,488H contracted on the addition of cyprodime. These findings strongly suggest that exogenous agonist-elicited stimulation of the mu (or kappa) opioid system indirectly activates the endogenous kappa (or mu) system. The indirectly-activated endogenous system inhibits the withdrawal response to the exogenously-stimulated opioid system. In isolated GPI the mu and kappa opioid systems thus appear to interact, regulating each other.

Modulation of drug-induced sensitization processes by endogenous opioid systems

Behavioural sensitization involves progressive increases in behavioural responses to repeated intermittent administration of drugs of abuse. Behavioural sensitization is observed to the locomotor stimulant, rewarding and discriminative effects of a drug. These are effects which seem to be essential in the initiation, expression and maintenance of a drug-seeking behaviour. Therefore the phenomenon of behavioural sensitization may have important implications for the understanding of addictive processes. Findings given in this review demonstrate the involvement of endogenous opioid systems in the initiation of sensitized responses on the neurochemical level, i.e., within the mesolimbic dopaminergic system, as well as on the behavioural level. Specifically, it is shown that behavioural sensitization to morphine and cocaine is modulated by endogenous kappa-opioid systems.

Opiate withdrawal intensity correlates with the presence of DSLET high-affinity binding

The goal of this study was to compare the characteristics of mu- and delta-opioid receptors in the cortex of DBA/2 and C57BL/6 mice, which differ in sensitivity to the long- and short-term effects of morphine. The characteristics of mu-opiate receptors were not different in the cortex of both strains. Both high- and low-affinity binding sites of DSLET, a specific ligand of delta-opiate receptors, were present in the cortex of C57BL/6 mice, whereas the high-affinity binding sites were not found in the cortex of DBA/2 mice. The absence of high-affinity DSLET binding sites, which are similar to the delta 2 type of opioid receptors, may explain the less intensive naloxone-precipitated withdrawal reaction of DBA/2 as compared with C57BL/6 mice.

Involvement of mesolimbic kappa-opioid systems in the discriminative stimulus effects of morphine

The neuroanatomical basis of opiate addiction has been studied using a variety of behavioural techniques. The aim of the present study was to investigate the role of mesolimbic opioid systems, in particular kappa-opioid systems, in the expression of the discriminative stimulus effects of abused drugs. Rats were trained to discriminate morphine (3.0 mg/kg s.c.) from saline under a fixed ratio schedule of food reinforcement. Once rats had acquired the discrimination, a randomized sequence of different doses of the highly selective kappa-opioid receptor agonist U69593 (0.02-0.16 mg/kg s.c.) was given 20 min prior to a systemic morphine injection. U69593 dose-dependently blocked the morphine discrimination. It is important to note that U69593 at these doses failed to generalize to the systemic morphine cue. The site of action by U69593 (0.02-0.16 microgram) was examined by microinjecting discrete amounts into target brain regions. Intra-nucleus accumbens injections of U69593 dose-dependently blocked the systemic morphine cue, whereas, U69593 failed to generalize to the discriminative stimulus. The same doses did not affect morphine discrimination after intra-ventral tegmental area or striatum injections. Besides the rewarding effects of drugs of abuse, the discriminative stimulus properties of these agents are seen as a major factor in drug seeking behaviours. The present study shows that the discriminative effects of morphine, a measure of the subjective effects of this drug can be blocked by the activation of kappa-opioid receptors located in the nucleus accumbens. In view of these findings which show that the activity of endogenous potassium-opioid systems (dynorphin) may serve as physiological antagonists to counteract the effects of morphine, potassium-agonists therefore may be useful in the treatment of opioid addictions.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.

Involvement of delta-opioid receptors in physical dependence on butorphanol

Butorphanol, a synthetic agonist/antagonist, has been shown to act on mu-, delta- and kappa-opioid receptors. However, the relative involvement of opioid receptor subtypes in mediating butorphanol dependence is not known. In the present study, naltrindole, a delta-selective non-peptide antagonist, was administered intracerebroventricularly (i.c.v.) to mask supraspinal delta-opioid receptors before and during the induction of butorphanol dependence. Treatment with naltrindole (0.1, 1, or 10 nmol/5 microliters per rat) significantly blocked naloxone-, a nonspecific antagonist, precipitated butorphanol withdrawal behaviors (escape behavior, teeth-chattering, wet shakes, forepaw tremors, ptosis, diarrhea, body weight loss, and hypothermia) at all doses tested, and decreased ejaculation at 0.1 nmol in butorphanol-infused rats. In contrast, naltrindole treatment had no effect on yawning, nor urination. These results indicate that central delta-opioid receptors are involved in mediating butorphanol dependence in rats.