Changes in the brain kappa-opioid receptor levels of rats in withdrawal from physical dependence upon butorphanol

A review of the kappa opioid receptor system in opioid use

The kappa opioid receptor (KOR) system is implicated in dysphoria and as an "anti-reward system" during withdrawal from opioids. However, no clear consensus has been made in the field, as mixed findings have been reported regarding the relationship between the KOR system and opioid use. This review summarizes the studies to date on the KOR system and opioids. A systematic scoping review was reported following PRISMA guidelines and conducted based on the published protocol. Comprehensive searches of several databases were done in the following databases: MEDLINE, Embase, PsycINFO, Web of Science, Scopus, and Cochrane. We included preclinical and clinical studies that tested the administration of KOR agonists/antagonists or dynorphin and/or measured dynorphin levels or KOR expression during opioid intoxication or withdrawal from opioids. One hundred studies were included in the final analysis. Preclinical administration of KOR agonists decreased drug-seeking/taking behaviors and opioid withdrawal symptoms. KOR antagonists showed mixed findings, depending on the agent and/or type of withdrawal symptom. Administration of dynorphins attenuated opioid withdrawal symptoms both in preclinical and clinical studies. In the limited number of available studies, dynorphin levels were found to increase in cerebrospinal fluid (CSF) and peripheral blood lymphocytes (PBL) of opioid use disorder subjects (OUD). In animals, dynorphin levels and/or KOR expression showed mixed findings during opioid use. The KOR/dynorphin system appears to have a multifaceted and complex nature rather than simply functioning as an anti-reward system. Future research in well-controlled study settings is necessary to better understand the clinical role of the KOR system in opioid use.

Effect of Packaging Materials and the Leached Iron on the Stability of Butorphanol Tartrate Injection

The aim of this study was to investigate the effect of various parameters on the stability of butorphanol tartrate injection and to screen the optimal packaging material. The effect of the headspace oxygen levels, ampoule color, manufacturer, and size on the stability of butorphanol tartrate formulation were evaluated. The headspace oxygen levels controlled by nitrogen purging were found to be particularly effective in improving stability of the butorphanol formulation, especially below 2%. Although it is a photolabile drug, butorphanol tartrate was getting degraded at much higher extent in amber color ampoules in comparison to clear ampoules. The degradation by oxidation was found to be a free radical-mediated process catalyzed by the presence of iron ions leached from the amber ampoules. The ampoule manufacturers also had a significant effect on the stability of butorphanol. Two-milliliter ampoules provided a better stability of the butorphanol tartrate injection than 1mL ampoules as 2-mL ampoules had the lower headspace oxygen level at the same level of oxygen content. The oxidation mechanism of the butorphanol tartrate injection was investigated under various conditions, which include iron powder spiking, removal of excipients, exposure to oxygen/nitrogen, exposure to stainless steel and at different pH. Iron powder spiking, presence of citric acid, exposure to oxygen, exposure to stainless steel, and high pH accelerated the oxidative degradation. The effect of oxygen, iron ion and citric acid is in agreement with a metal-catalyzed oxidation mechanism called Udenfriend reaction. Based on the formulation test results, limiting headspace oxygen level, ampoule color, manufacturer, size, controlling iron ion contamination, and pH are recommended for formulation development. In conclusion, it can be suggested that this study can lead to a better understanding of the degradation mechanism of butorphanol tartrate; hence, it would contribute to the development of butorphanol tartrate injection with improved stability. Virous packaging materials have different effects on the stability of butorphanol tartrate injection, and the leached iron of packaging ampoules and stainless steel can trigger Udenfriend reaction with butorphanol tartrate and citric acid (CA), which lead to the oxydative degradation of butorphanol tartrate injection.

Global changes in the rat heart proteome induced by prolonged morphine treatment and withdrawal

Morphine belongs among the most commonly used opioids in medical practice due to its strong analgesic effects. However, sustained administration of morphine leads to the development of tolerance and dependence and may cause long-lasting alterations in nervous tissue. Although proteomic approaches enabled to reveal changes in multiple gene expression in the brain as a consequence of morphine treatment, there is lack of information about the effect of this drug on heart tissue. Here we studied the effect of 10-day morphine exposure and subsequent drug withdrawal (3 or 6 days) on the rat heart proteome. Using the iTRAQ technique, we identified 541 proteins in the cytosol, 595 proteins in the plasma membrane-enriched fraction and 538 proteins in the mitochondria-enriched fraction derived from the left ventricles. Altogether, the expression levels of 237 proteins were altered by morphine treatment or withdrawal. The majority of changes (58 proteins) occurred in the cytosol after a 3-day abstinence period. Significant alterations were found in the expression of heat shock proteins (HSP27, α-B crystallin, HSP70, HSP10 and HSP60), whose levels were markedly up-regulated after morphine treatment or withdrawal. Besides that morphine exposure up-regulated MAPK p38 (isoform CRA_b) which is a well-known up-stream mediator of phosphorylation and activation of HSP27 and α-B crystallin. Whereas there were no alterations in the levels of proteins involved in oxidative stress, several changes were determined in the levels of pro- and anti-apoptotic proteins. These data provide a complex view on quantitative changes in the cardiac proteome induced by morphine treatment or withdrawal and demonstrate great sensitivity of this organ to morphine.

Effect of honokiol on activity of GAD(65) and GAD(67) in the cortex and hippocampus of mice

Honokiol, an active agent extracted from magnolia bark, has been reported that induces anxiolytic action in a mouse elevated plus-maze test. However, the mechanism of anxiolytic action induced by honokiol remains unclear. This study was to investigate the change in two forms of glutamic acid decarboxylase (GABA synthesized enzymes) GAD(65) and GAD(67) in the cortex and hippocampus areas while the anxiolytic actions induced by chronic administration of honokiol in mice. Mice treated with 7 daily injection of honokiol (1mg/kg, p.o.) caused anxiolytic action which was similar to that was induced by 7 daily injection of diazepam (2mg/kg, p.o.) in the elevated plus-maze test. In addition, the activity of hippocampal GAD(65) of honokiol treated mice was significantly increased than that of the vehicle or diazepam treated groups. These data suggest that honokiol causes diazepam-like anxiolytic action, which may be mediated by altering the synthesis of GABA in the brain of mice.

Evidence for modulation of opioidergic activity in central vestibular processing: A [(18)F] diprenorphine PET study

Animal and functional imaging studies had identified cortical structures such as the parieto-insular vestibular cortex, the retro-insular cortex, or the anterior cingulate cortex belonging to a vestibular cortical network. Basic animal studies revealed that endorphins might be important transmitters involved in cerebral vestibular processing. The aim of the present study was therefore to analyse whether the opioid system is involved in vestibular neurotransmission of humans or not. Changes in opioid receptor availability during caloric air stimulation of the right ear were studied with [(18)F] Fluoroethyl-diprenorphine ([(18)F]FEDPN) PET scans in 10 right-handed healthy volunteers and compared to a control condition. Decrease in receptor availability to [(18)F]FEDPN during vestibular stimulation in comparison to the control condition was significant at the right posterior insular cortex and the postcentral region indicating more endogenous opioidergic binding in these regions during stimulation. These data give evidence that the opioidergic system plays a role in the right hemispheric dominance of the vestibular cortical system in right-handers.

Imaging of opioid receptors in the central nervous system

In vivo functional imaging by means of positron emission tomography (PET) is the sole method for providing a quantitative measurement of mu-, kappa and delta-opioid receptor-mediated signalling in the central nervous system. During the last two decades, measurements of changes to the regional brain opioidergic neuronal activation--mediated by endogenously produced opioid peptides, or exogenously administered opioid drugs--have been conducted in numerous chronic pain conditions, in epilepsy, as well as by stimulant- and opioidergic drugs. Although several PET-tracers have been used clinically for depiction and quantification of the opioid receptors changes, the underlying mechanisms for regulation of changes to the availability of opioid receptors are still unclear. After a presentation of the general signalling mechanisms of the opioid receptor system relevant for PET, a critical survey of the pharmacological properties of some currently available PET-tracers is presented. Clinical studies performed with different PET ligands are also reviewed and the compound-dependent findings are summarized. An outlook is given concluding with the tailoring of tracer properties, in order to facilitate for a selective addressment of dynamic changes to the availability of a single subclass, in combination with an optimization of the quantification framework are essentials for further progress in the field of in vivo opioid receptor imaging.

Functional interaction between α2-adrenoceptors, μ- and κ-opioid receptors in the guinea pig myenteric plexus: Effect of chronic desipramine treatment

The existence of a functional interplay between alpha(2)-adrenoceptor and opioid receptor inhibitory pathways modulating neurotransmitter release has been demonstrated in the enteric nervous system by development of sensitivity changes to alpha(2)-adrenoceptor, mu- and kappa-opioid receptor agents on enteric cholinergic neurons after chronic sympathetic denervation. In the present study, to further examine this hypothesis we evaluated whether manipulation of alpha(2)-adrenoceptor pathways by chronic treatment with the antidepressant drug, desipramine (10 mg/kg i.p. daily, for 21 days), could entail changes in enteric mu- and kappa-opioid receptor pathways in the myenteric plexus of the guinea pig distal colon. In this region, subsensitivity to the inhibitory effect of both UK14,304 and U69,593, respectively alpha(2A)-adrenoceptor and kappa-opioid receptor agonist, on the peristaltic reflex developed after chronic desipramine treatment. On opposite, in these experimental conditions, supersensitivity developed to the inhibitory effect of [D-Ala, N-Me-Phe4-Gly-ol5]-enkephalin (DAMGO), mu-opioid receptor agonist, on propulsion velocity. Immunoreactive expression levels of alpha(2A)-adrenoceptors, mu- and kappa-opioid receptors significantly decreased in the myenteric plexus of the guinea pig colon after chronic desipramine treatment. In these experimental conditions, mRNA levels of alpha(2A)-adrenoceptors, mu- and kappa-opioid receptors significantly increased, excluding a direct involvement of transcription mechanisms in the regulation of receptor expression. Levels of G protein-coupled receptor kinase 2/3 and of inhibitory G(i/o) proteins were significantly reduced in the myenteric plexus after chronic treatment with desipramine. Such changes might represent possible molecular mechanisms involved in the development of subsensitivity to UK14,304 and U69,593 on the efficiency of peristalsis. Alternative molecular mechanisms, including a higher efficiency in the coupling between receptor activation and downstream intracellular effector systems, possibly independent from inhibitory G(i/o) proteins, may be accounted for the development of supersensitivity to DAMGO. Increased sensitivity to the mu-opioid agonist might compensate for the development of alpha(2A)-adrenoceptor and kappa-opioid receptor subsensitivity. On the whole, the present data further strengthen the concept that, manipulation of alpha(2)-adrenergic inhibitory receptor pathways in the enteric nervous system entails changes in opioid inhibitory receptor pathways, which might be involved in maintaining homeostasis as suggested for mu-opioid, but not for kappa-opioid receptors.

Butorphanol dependence increases hippocampal kappa-opioid receptor gene expression

Butorphanol is a synthetic opioid agonist/antagonist analgesic agent, which exerts its effects mainly via kappa-opioid receptors. Characterizations of the gene expression levels of the mRNA for and protein levels of the kappa-opioid receptor in different brain regions of rats are essential for investigating possible mechanisms in the development of physical dependence on and withdrawal from butorphanol. Animals were rendered dependent by intracerebroventricular (i.c.v.) infusion of butorphanol (26 nmol/microl/hr) via osmotic minipumps for 3 days. Rats were sacrificed immediately (dependent group) or 7 hr after discontinuation of i.c.v. butorphanol infusion (withdrawal group). Expression levels of the mRNA for the kappa-opioid receptor, as detected by reverse transcription-polymerase chain reaction followed by Southern blot analysis, were significantly increased in the cerebral cortex, striatum, and midbrain, including thalamus, hippocampus, and pons, in animals dependent on butorphanol. In both dependent and withdrawal groups, Western blot analysis of kappa-opioid receptor protein levels showed significant increases in the amygdaloid nucleus, paraventricular thalamus, and thalamus. However, in the withdrawal group, there were significant decreases in the hippocampus and cortical regions, including the frontal, parietal, and temporal cortex. Regional changes in the mRNA for and protein levels of the kappa-opioid receptor focus attention on highly special roles for this receptor in the development of physical dependence on and the expression of withdrawal from butorphanol dependence.

Elevated μ-opioid receptor expression in the nucleus of the solitary tract accompanies attenuated withdrawal signs after chronic low dose naltrexone in opiate-dependent rats

We previously described a decrease in withdrawal behaviors in opiate-dependent rats that were chronically treated with very low doses of naltrexone in their drinking water. Attenuated expression of withdrawal behaviors correlated with decreased c-Fos expression and intracellular signal transduction elements [protein kinase A regulatory subunit II (PKA) and phosphorylated cAMP response element binding protein (pCREB)] in brainstem noradrenergic nuclei. In this study, to determine whether similar cellular changes occurred in forebrain nuclei associated with drug reward, expressions of PKA and pCREB were analyzed in the ventral tegmental area, frontal cortex, striatum, and amygdala of opiate-treated rats that received low doses of naltrexone in their drinking water. No significant difference in PKA or pCREB was detected in these regions following drug treatment. To examine further the cellular mechanisms in noradrenergic nuclei that could underlie attenuated withdrawal behaviors following low dose naltrexone administration, the nucleus of the solitary tract (NTS) and locus coeruleus (LC) were examined for opioid receptor (OR) protein expression. Results showed a significant increase in muOR expression in the NTS of morphine-dependent rats that received low doses of naltrexone in their drinking water, and increases in muOR expression were also found to be dose dependent. Protein expression of muOR in the LC and deltaOR in either brain region remained unchanged. In conclusion, our previously reported decreases in c-Fos and PKA expression in the NTS following pretreatment with low doses of naltrexone may be partially explained by a greater inhibition of NTS neurons resulting from increased muOR expression in this region.

Antiexudative Effects of Opioids and Expression of κ- and δ- Opioid Receptors during Intestinal Inflammation in Mice: Involvement of Nitric Oxide

The study evaluates the effects of kappa- (KOR), delta- (DOR), and mu-opioid receptor (MOR) agonists on the inhibition of plasma extravasation during acute and chronic intestinal inflammation in mice. The antiexudative effects of KOR and DOR agonists in animals treated with nitric oxide synthase (NOS) inhibitors and their protein levels in the gut (whole jejunum and mucosa) and spinal cord of mice with chronic intestinal inflammation were also measured. Inflammation was induced by the intragastric administration of one (acute) or two (chronic) doses of croton oil. Plasma extravasation was measured using Evans blue and protein levels by Western blot and immunoprecipitation. Plasma extravasation was significantly increased 2.7 times during chronic inflammation. The potency of the KOR agonist trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolydinyl)cyclohexyl]-benzeneazetamine (U50,488H) inhibiting plasma extravasation was enhanced 26.3 times during chronic compared with acute inflammation. [d-Pen(2),d-Pen(5)]-Enkephalin (DPDPE) (a DOR agonist) was also 11.8 times more potent during chronic inflammation, whereas the antiexudative effects of fentanyl (a MOR agonist) were not significantly altered. Receptor-specific antagonists reversed the effects. Protein levels of KOR and DOR in the whole jejunum and mucosa were significantly increased after chronic inflammation. Treatment with NOS inhibitors N(omega)-nitro-l-arginine methyl ester or l-N(6)-(1-iminoethyl)-lysine hydrochloride diminished plasma extravasation and inhibited the increased antiexudative effects of U50,488H and DPDPE during chronic intestinal inflammation. The data show that the enhanced antiexudative effects of KOR and DOR agonists could be related to an increased expression of KOR and DOR in the gut and that the release of nitric oxide may play a role augmenting the effects of opioids during chronic inflammation.

Conditioned place preference associates with the mRNA expression of diazepam binding inhibitor in brain regions of the addicted rat during withdrawal

The diazepam binding inhibitor (DBI) modulating the functions of the GABAA receptors is involved in the maladaptation of neural system during using opiate, but its role in opiate dependence is not fully understood. Using conditioned place preference (CPP) rat model and in situ hybridization technique, we examined the correlation between opiate dependence and the mRNA expression of DBI. We found that chronic morphine treatment enabled CPP and increased the DBI mRNA expression in crucial brain regions of addiction. Withdrawal for 3 days caused significant physical signs and further increased the DBI mRNA expression. Both the DBI mRNA and CPP expression remained significantly high but physical signs were at control level in the animals withdrawal for 6 days. Remarkably, the DBI mRNA expressions in the CA1 region of the hippocampus (CA1), ventral tagmental area (VTA), nucleus accumbens (NAc) and amygdala (AMG) were positively correlated to CPP during the periods from withdrawal for 3 days to withdrawal for 6 days. These findings suggest that DBI may play a role in both physical and psychological dependence of opiates.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).