Morphine Withdrawal In Mice Research Articles

N-palmitoylethanolamide attenuates negative emotions induced by morphine withdrawal in mice

Depression and anxiety are prominent symptoms of withdrawal syndrome, often caused by the abuse of addictive drugs like morphine. N-palmitoylethanolamide (PEA), a biologically active lipid, is utilized as an anti-inflammatory and analgesic medication. Recent studies have highlighted PEA’s role in mitigating cognitive decline and easing depression resulting from chronic pain. However, it remains unknown whether PEA can influence negative emotions triggered by morphine withdrawal. This study seeks to explore the impact of PEA on such emotions and investigate the underlying mechanisms. Mice subjected to morphine treatment underwent a 10-day withdrawal period, followed by assessments of the effect of PEA on anxiety- and depression-like behaviors using various tests. Enzyme-linked immunosorbent assay was conducted to measure levels of monoamine neurotransmitters in specific brain regions. The findings indicate that PEA mitigated anxiety and depression symptoms and reduced 5-hydroxytryptamine, noradrenaline, and dopamine levels in the hippocampus and prefrontal cortex. In summary, PEA demonstrates a significant positive effect on negative emotions associated with morphine withdrawal, accompanied with the reduction in levels of monoamine neurotransmitters in key brain regions. These insights could be valuable for managing negative emotions arising from morphine withdrawal.

Teneurin C-terminal associated peptide (TCAP)-1 attenuates the development and expression of naloxone-precipitated morphine withdrawal in male Swiss Webster mice.

Corticotropin-releasing factor (CRF), the apical stress-inducing hormone, exacerbates stress and addictive behaviors. TCAP-1 is a peptide that directly inhibits both CRF-mediated stress and addiction-related behaviors; however, the direct action of TCAP-1 on morphine withdrawal-associated behaviors has not previously been examined. To determine whether TCAP-1 administration attenuates behavioral and physiological consequences of morphine withdrawal in mice. Mice were administered via subcutaneous route TCAP-1 either before or after initial morphine exposure, after which jumping behavior was quantified to assess the effects of TCAP-1 on naloxone-precipitated morphine withdrawal. As a comparison, mice were treated with nonpeptide CRF1 receptor antagonist CP-154,526. In one experiment, plasma corticosterone (CORT) was also measured as a physiological stress indicator. Pretreatment with TCAP-1 (10-250 nmol/kg) before morphine treatment significantly inhibited the development of naloxone-precipitated withdrawal. TCAP-1 (250-500 nmol/kg) treatment administered after morphine treatment attenuated the behavioral expression of naloxone-precipitated withdrawal. TCAP-1 (250 nmol/kg) treatment during morphine treatment was more effective than the optimal dosing of CP-154,526 (20mg/kg) at suppressing the behavioral expression of naloxone-precipitated withdrawal, despite similar reduction of withdrawal-induced plasma CORT level increases. These findings establish TCAP-1 as a potential therapeutic candidate for the prevention and treatment of morphine withdrawal.

Kappa opioid receptor in nucleus accumbens regulates depressive-like behaviors following prolonged morphine withdrawal in mice

Prolonged withdrawal from opioids leads to negative emotions. Kappa opioid receptor (KOR) plays an important role in opioid addiction and affective disorders. However, the underlying mechanism of KOR in withdrawal-related depression is still lacking. We found that escitalopram treatment had a limited effect in improving depression symptoms in heroin-dependent patients. In mice, we demonstrated prolonged (4weeks) but not acute (24 h) withdrawal from morphine induced depressive-like behaviors. The number of c-Fos positive cells and the expression of KOR in the nucleus accumbens (NAc), were significantly increased in the prolonged morphine withdrawal mice. Conditional KOR knockdown in NAc significantly improved depressive-like behaviors. Repeated but not acute treatment with the KOR antagonist norBNI improved depressive-like behaviors and reversed PSD95, synaptophysin, p-ERK, p-CREB, and BDNF in NAc. This study demonstrated the important role of striatal KOR in morphine withdrawal-related depressive-like behaviors and offered therapeutic potential for the treatment of withdrawal-related depression.

Loss of Astrocytic µ Opioid Receptors Exacerbates Aversion Associated with Morphine Withdrawal in Mice: Role of Mitochondrial Respiration.

Astrocytes express mu/µ opioid receptors, but the function of these receptors remains poorly understood. We evaluated the effects of astrocyte-restricted knockout of µ opioid receptors on reward- and aversion-associated behaviors in mice chronically exposed to morphine. Specifically, one of the floxed alleles of the Oprm1 gene encoding µ opioid receptor 1 was selectively deleted from brain astrocytes in Oprm1 inducible conditional knockout (icKO) mice. These mice did not exhibit changes in locomotor activity, anxiety, or novel object recognition, or in their responses to the acute analgesic effects of morphine. Oprm1 icKO mice displayed increased locomotor activity in response to acute morphine administration but unaltered locomotor sensitization. Oprm1 icKO mice showed normal morphine-induced conditioned place preference but exhibited stronger conditioned place aversion associated with naloxone-precipitated morphine withdrawal. Notably, elevated conditioned place aversion lasted up to 6 weeks in Oprm1 icKO mice. Astrocytes isolated from the brains of Oprm1 icKO mice had unchanged levels of glycolysis but had elevated oxidative phosphorylation. The basal augmentation of oxidative phosphorylation in Oprm1 icKO mice was further exacerbated by naloxone-precipitated withdrawal from morphine and, similar to that for conditioned place aversion, was still present 6 weeks later. Our findings suggest that µ opioid receptors in astrocytes are linked to oxidative phosphorylation and they contribute to long-term changes associated with opioid withdrawal.

Sintocalmy, a Passiflora incarnata Based Herbal, Attenuates Morphine Withdrawal in Mice.

Chronic opioid use changes brain chemistry in areas related to reward processes, memory, decision-making, and addiction. Both neurons and astrocytes are affected, ultimately leading to dependence. Passiflora incarnata L. (Passifloraceae) is the basis of frequently used herbals to manage anxiety and insomnia, with proven central nervous system depressant effects. Anti-addiction properties of P. incarnata have been reported. The aim of this study was to investigate the effect of a commercial extract of Passiflora incarnata (Sintocalmy®, Aché Laboratory) in the naloxone-induced jumping mice model of morphine withdrawal. In addition, glial fibrillary acidic protein (GFAP) and S100 calcium-binding protein B (S100B) levels were assessed in the frontal cortex and hippocampus, and DNA damage was verified on blood cells. In order to improve solubilization a Sintocalmy methanol extract (SME) was used. SME is mainly composed by flavonoids isovitexin and vitexin. The effects of SME 50, 100 and 200mg/kg (i.p.) were evaluated in the naloxone-induced withdrawal syndrome in mice. SME 50 and SME 100mg/kg decreased naloxone-induced jumping in morphine-dependent mice without reducing locomotor activity. No alterations were found in GFAP levels, however SME 50mg/kg prevented the S100B increase in the frontal cortex and DNA damage. This study shows anti-addiction effects for a commercial standardized extract of P. incarnata and suggests the relevance of proper clinical assessment.

Sphingosine-1-phosphate receptor subtype 1 activation in the central nervous system contributes to morphine withdrawal in rodents

Opioid therapies for chronic pain are undermined by many adverse side effects that reduce their efficacy and lead to dependence, abuse, reduced quality of life, and even death. We have recently reported that sphingosine-1-phosphate (S1P) 1 receptor (S1PR1) antagonists block the development of morphine-induced hyperalgesia and analgesic tolerance. However, the impact of S1PR1 antagonists on other undesirable side effects of opioids, such as opioid-induced dependence, remains unknown. Here, we demonstrate that naloxone-precipitated morphine withdrawal in mice altered de novo sphingolipid metabolism in the dorsal horn of the spinal cord and increased S1P that accompanied the manifestation of several withdrawal behaviors. Blocking de novo sphingolipid metabolism with intrathecal administration of myriocin, an inhibitor of serine palmitoyltransferase, blocked naloxone-precipitated withdrawal. Noteworthy, we found that competitive (NIBR-15) and functional (FTY720) S1PR1 antagonists attenuated withdrawal behaviors in mice. Mechanistically, at the level of the spinal cord, naloxone-precipitated withdrawal was associated with increased glial activity and formation of the potent inflammatory/neuroexcitatory cytokine interleukin-1β (IL-1β); these events were attenuated by S1PR1 antagonists. These results provide the first molecular insight for the role of the S1P/S1PR1 axis during opioid withdrawal. Our data identify S1PR1 antagonists as potential therapeutics to mitigate opioid-induced dependence and support repurposing the S1PR1 functional antagonist FTY720, which is FDA-approved for multiple sclerosis, as an opioid adjunct.

Efficacy and safety of Sophora alopecuroides var. alopecuroides seed extract for opioid detoxification: A randomized, double-blind, and placebo-controlled clinical trial.

The seeds of Sophora alopecuroides L. var. alopecuroides (S. alopecuroides) have alleviated morphine withdrawal in mice. Therefore, in this study, the alkaloid composition of S. alopecuroides extract was determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analysis. Moreover, 50 abstinent opium addicts consumed three 400 mg extract capsules once daily and 50 other patients took placebo for 8 days. At the baseline and days 3 and 8, the clinical opiate withdrawal scale (COWS) was used to assess withdrawal symptoms. At the baseline and Day 8, the patients' blood levels of serum glutamate oxaloacetate transferase; serum glutamate pyruvate transferase; alkaline phosphatase; total, direct, and indirect bilirubins; creatinine and blood urea nitrogen; complete blood count; and prothrombine time were measured. The groups' parameter values were also compared. Sophocarpine, matrine, and sophoramine were the major alkaloids constituting, respectively, 32.85, 26.55, and 6.91% of the extract. The extract decreased the COWS score at Days 3 and 8 significantly compared with the placebo (p < .001). The extract did not significantly affect the blood parameters' values compared with the placebo (p > .05). There was no adverse drug effect. In conclusion, the extract reduces the acute opioid withdrawal symptoms and seems to have good safety and tolerability.

M-Trifluoromethyl-diphenyl diselenide (m-CF3-PhSe)2 modulates the hippocampal neurotoxic adaptations and abolishes a depressive-like phenotype in a short-term morphine withdrawal in mice

The opioid withdrawal syndrome is defined as a complex phenomenon involving multiple cellular adaptations, which leads to the emergence of aversive physical and affective signs. The m-trifluoromethyl-diphenyl diselenide (m-CF3-PhSe)2 elicits an antidepressant-like effect by modulating the opioid system in different animal models of mood disorders. Notably, repeated exposure to (m-CF3-PhSe)2 developed neither tolerance nor withdrawal signs in mice. The aim of the present study was to investigate whether (m-CF3-PhSe)2 attenuates the physical signs and the depressive-like phenotype during morphine withdrawal through its neuroprotective effects on oxidative stress, the NMDA receptor and the proBDNF/mBDNF signaling in the hippocampus of mice. Adult Swiss mice received saline solution or escalating doses (20–100 mg/kg, sc) of morphine for six days. For the next three days, the animals were treated with canola oil, (m-CF3-PhSe)2 (5 and 10 mg/kg, ig) or methadone (5 mg/kg, sc) whereas morphine injections were discontinued. On day 9, physical withdrawal signs and depressive-like behavior were assessed 30 min after the last administration of (m-CF3-PhSe)2. Although short-term treatment with (m-CF3-PhSe)2 at both doses suppressed the aversive physical and affective signs in morphine withdrawn-mice, the highest dose of (m-CF3-PhSe)2 per se increased the teeth chattering manifestation. The intrinsic antioxidant property of (m-CF3-PhSe)2 modulated oxidative stress, it also restored the NMDA receptor levels in the hippocampus of morphine withdrawn-mice. Besides, (m-CF3-PhSe)2 downregulated the proBDNF/p-75NTR/JNK pro-apoptotic pathway without affecting the mBDNF/TrkB/ERK/CREB pro-survival signaling in the hippocampus of morphine withdrawn-mice. The results show that (m-CF3-PhSe)2 treatment modulated the hippocampal neurotoxic adaptations and abolished the depressive-like phenotype following morphine withdrawal in mice.

Morphine withdrawal recruits lateral habenula cytokine signaling to reduce synaptic excitation and sociability.

The lateral habenula encodes aversive stimuli contributing to negative emotional states during drug withdrawal. Here we report that morphine withdrawal in mice leads to microglia adaptations and diminishes glutamatergic transmission onto raphe-projecting lateral habenula neurons. Chemogenetic inhibition of this circuit promotes morphine withdrawal-like social deficits. Morphine withdrawal-driven synaptic plasticity and reduced sociability require tumor necrosis factor-α (TNF-α) release and neuronal TNF receptor 1 activation. Hence, habenular cytokines control synaptic and behavioral adaptations during drug withdrawal.

Noradrenergic and corticosteroid receptors regulate somatic and motivational symptoms of morphine withdrawal

Somatic and motivational symptoms accompanying opiate withdrawal are considered one of the major reasons for relapse to opiate-seeking and opiate-taking behaviors. These symptoms are accompanied by the activation of stress-related processes including hypothalamic-pituitary-adrenal axis activity and noradrenergic (NA) signaling. In particular, the NA system plays an important role in the expression of somatic signs of opiate withdrawal, whereas glucocorticoid (GR) and mineralocorticoid receptors (MR) are activated during opiate abstinence.The purpose of our study was to examine the roles of α1-, α2-, and β-adrenoceptors (ARs) as well as GR and MR, in the formation and expression of physiological and motivational symptoms of morphine withdrawal. We showed that systemic pretreatment with the selective α1-AR antagonist prazosin (0–1 mg/kg), the selective α2-AR antagonist RX821002 (0–2 mg/kg), the selective β-adrenergic antagonist, propranolol (0–10 mg/kg), or the selective MR antagonist spironolactone (0–50 mg/kg), but not the selective GR antagonist mifepristone (0–40 mg/kg), decreased somatic symptoms of naloxone-precipitated morphine withdrawal in mice chronically treated with morphine. In contrast, only propranolol pretreatment attenuated the dysphoric affective state accompanying naloxone-precipitated morphine withdrawal as assessed in the conditioned place aversion (N-CPA) paradigm.Together, our results demonstrate the important roles of noradrenergic receptors in the modulation of somatic, but not motivational/affective, symptoms of morphine withdrawal. In addition MR but not GR regulates the expression of only somatic symptoms of morphine withdrawal.

Synthesis and Evaluation of a Novel Bivalent Selective Antagonist for the Mu-Delta Opioid Receptor Heterodimer that Reduces Morphine Withdrawal in Mice.

A major limitation in the study of the mu-delta opioid receptor heterodimer (MDOR) is that few selective pharmacological tools exist and no heteromer-selective antagonists. We thus designed a series of variable-length (15-41 atoms) bivalent linked peptides with selective but moderate/low-affinity pharmacophores for the mu and delta opioid receptors. We observed a U-shaped MDOR potency/affinity profile in vitro, with the 24-atom spacer length (D24M) producing the highest MDOR potency/affinity (<1 nM) and selectivity (≥89-fold). We further evaluated D24M in mice and observed that D24M dose-dependently antagonized tail flick antinociception produced by the MDOR agonists CYM51010 and Deltorphin-II, without antagonizing the monomer agonists DAMGO and DSLET. We also observed that D24M sharply reduced withdrawal behavior in models of acute and chronic morphine dependence. These findings suggest that D24M is a first-in-class high-potency MDOR-selective antagonist both in vitro and in vivo.

Geraniin attenuates naloxone-precipitated morphine withdrawal and morphine-induced tolerance in mice.

Potentially life-threatening and unpleasant side effects associated with some analgesics have fueled the drive for the search for more analgesics with better side effect profiles. Geraniin, the most dominant secondary metabolite in the aqueous extract of the aerial parts of Phyllanthus muellerianus, has been shown to possess antinociceptive properties mediated partly by opioidergic mechanisms. The purpose of this study is to determine whether geraniin exhibits tolerance and if it is able to ameliorate withdrawal signs in naloxone-precipitated morphine withdrawal. After chronic treatment of mice with geraniin orally, the formalin test was used to ascertain whether tolerance will develop to its antinociceptive effects and if there is morphine-induced tolerance cross-generalization with geraniin. The effect of geraniin on naloxone-precipitated morphine withdrawal signs in morphine-dependent mice was also investigated. Geraniin (3-30 mg/kg) did not produce any tolerant effects after chronic administration and there was also no cross-generalization with the tolerant effects of morphine. Geraniin did not induce withdrawal signs but significantly reduced the number of jumps in morphine-dependent mice. Geraniin does not produce any tolerant effects like morphine and also reduced the signs associated with naloxone-precipitated morphine withdrawal in mice.

Pioglitazone attenuates the opioid withdrawal and vulnerability to relapse to heroin seeking in rodents.

Relapse to opioids is often driven by the avoidance of the aversive states of opioid withdrawal. We recently demonstrated that activation of peroxisome proliferator-activated receptor gamma (PPARγ) by pioglitazone reduces the motivation for heroin and attenuates its rewarding properties. However, the role of PPARγ in withdrawal and other forms of relapse to heroin is unknown. To further address this issue, we investigated the role of PPARγ on the development and expression of morphine withdrawal in mice and the effect of pioglitazone on several forms of heroin relapse in rats. We induced physical dependence to morphine in mice by injecting morphine twice daily for 6days. Withdrawal syndrome was precipitated on day 6 with an injection of naloxone. In addition, different groups of rats were trained to self-administer heroin and, after the extinction, the relapse was elicited by cues, priming, or stress. The effect of different doses of pioglitazone was tested on these different paradigms. Data show that chronic and acute administration of pioglitazone attenuates morphine withdrawal symptoms, and these effects are mediated by activation of PPARγ receptors. Activation of PPARγ by pioglitazone also abolishes yohimbine-induced reinstatement of heroin seeking and reduces heroin-induced reinstatement, while it does not affect cue-induced relapse. These findings provide new insights on the role of PPARγ on opioid dependence and suggest that pioglitazone may be useful for the treatment of opioid withdrawal in opioid-addicted individuals.

Baclofen prevents the elevated plus maze behavior and BDNF expression during naloxone precipitated morphine withdrawal in male and female mice

In previous studies we have shown that baclofen, a selective GABAB receptor agonist, prevents the somatic expression and reestablishes the dopamine and μ-opioid receptors levels, modified during naloxone-precipitated morphine withdrawal syndrome in male and female mice. There are no previous reports regarding sex differences in the elevated plus maze (EPM) and the expression of BDNF in morphine-withdrawn mice. The present study analyses the behavioral and biochemical variations during morphine withdrawal in mice of both sexes, and whether these variations are prevented with baclofen. Swiss-Webster albino prepubertal mice received morphine (2 mg/kg, i.p.) twice daily, for 9 consecutive days. On the 10th day, one group of morphine-treated mice received naloxone (opioid receptor antagonist; 6 mg/kg, i.p.) 1 h after the last dose of morphine to precipitate withdrawal. A second group received baclofen (2 mg/kg, i.p.) before naloxone administration. The EPM behavior was measured during 15 min after naloxone injection. The expression of BDNF-positive cells was determined by immunohistochemistry. Withdrawn male mice showed a higher percentage of time spent and number of entries to the open arms compared to withdrawn female mice. Baclofen prevented this behavior in both sexes. BDNF expression decreased in the AcbC, BNST, CeC, and CA3 of the hippocampus while increased in the BLA of morphine withdrawn male. Baclofen pretreatment prevented the BDNF expression observed in morphine withdrawn male mice in all the brain areas studied except in the CeC. Baclofen prevention of the EPM behavior associated to morphine withdrawal could be partially related to changes in BDNF expression.

Differential effects of endocannabinoid catabolic inhibitors on morphine withdrawal in mice

BackgroundInhibition of endocannabinoid catabolic enzymes fatty acid amide hydrolase (FAAH) and/or monoacylglycerol lipase (MAGL) reduces somatic morphine withdrawal signs, but its effects on aversive aspects of withdrawal are unknown. The present study investigated whether Δ9-tetrahydrocannabinol (THC), the MAGL inhibitor JZL184, the FAAH inhibitor PF-3845, or the dual FAAH/MAGL inhibitor SA-57 would reduce acquisition of morphine withdrawal-induced conditioned place avoidance (CPA) and jumping. MethodsMice were implanted with placebo or 75mg morphine pellets, 48h later injected with naloxone or saline and placed in the conditioning apparatus, and assessed for CPA at 72h. Subjects were also observed for jumping behavior following naloxone challenge. ResultsNaloxone (0.056mg/kg) produced robust CPA in morphine-pelleted, but not placebo-pelleted, mice. Morphine pretreatment prevented the occurrence of withdrawal CPA and withdrawal jumping, while clonidine (an α2 adrenergic receptor agonist) only blocked withdrawal CPA. THC, JZL184, and SA-57 significantly reduced the percentage of mice that jumped during the conditioning session, but did not affect acquisition of withdrawal CPA. PF-3845 did not reduce morphine withdrawal CPA or jumping. Finally, neither THC nor the endocannabinoid catabolic enzyme inhibitors in non-dependent mice elicited a conditioned place preference or aversion. ConclusionsThese findings suggest that inhibiting endocannabinoid catabolic enzymes reduces somatic morphine withdrawal signs, but not aversive aspects as inferred in the CPA paradigm. The observation that non-dependent mice administered inhibitors of endocannabinoid degradation did not display place preferences is consistent with the idea that that endocannabinoid catabolic enzymes might be targeted therapeutically, with reduced risk of abuse.

Possible Involvement of Endogenous Opioid System Located Downstream of α7 Nicotinic Acetylcholine Receptor in Mice With Physical Dependence on Nicotine

We previously reported that nicotine (NIC)-induced analgesia was elicited in part by activation of the endogenous opioid system. Moreover, it is well known that NIC has physical-dependence liability, but its mechanism is unclear. Therefore, we examined whether physical dependence on NIC was mediated by activation of the endogenous opioid system in ICR mice. We evaluated increased serum corticosterone (SCS) as an indicator of NIC withdrawal, as it is a quantitative indicator of naloxone (opioid receptor antagonist, NLX)-precipitated morphine withdrawal in mice. In this study, NLX precipitated an SCS increase in mice receiving repeated NIC, by a dose-dependent mechanism, and correlated with the dose and number of days of repeated NIC administration. When an opioid receptor antagonist (naltrexone) was concomitantly administered with repeated NIC, the NLX-precipitated SCS increase was not elicited. Concomitant administration of the α7 nicotinic acetylcholine receptor (nAChR) antagonist (methyllycaconitine) with repeated NIC, but not the α4β2 nAChR antagonist (dihydro-β-erythroidine), did not elicit an SCS increase by NLX. Thus, a physical dependence on NIC was in part mediated by the activation of the endogenous opioid system, located downstream of α7 nAChR.

Obestatin prevents analgesic tolerance to morphine and reverses the effects of mild morphine withdrawal in mice

Obestatin is a 23-amino acid gut-derived neuropeptide, encoded by the same gene with ghrelin. The goal of this study was to examine the effects of obestatin on the acute and chronic analgesic actions of morphine and on mild morphine withdrawal. Open-field (OF) and elevated plus maze (EPM) tests were used to assess mild morphine withdrawal-induced behavior changes and the heat-radiant tail-flick assay was used to investigate analgesic actions of morphine. CFLP male mice were treated twice a day with graded doses of morphine in EPM and OF experiments and once a day in tail-flick studies. Obestatin (1.5μg/2μl) was administrated once a day in all experiments. Furthermore, 0.2mg/kg naloxone or saline was administered after the final injection of morphine at a dose of 20mg/kg in EPM and OF. These behavioral parameters were monitored in the OF: the percentage of center ambulation time and distance; whereas in the EPM: the time spent in open arms and the entries into open arms compared to the total time (%OAT) and entries (%OAE). In the OF, obestatin significantly decreased the percentage of time spent in the center in mice undergoing naloxone-precipitated mild morphine withdrawal. EPM results were similar to open field, but obestatin had no significant effect on parameters mentioned above. Besides, obestatin maintained the analgesic effect of morphine 90 and 120min after morphine injection in mice treated with morphine receiving obestatin compared to mice treated with morphine. In tolerance studies, obestatin diminished the analgesic tolerance to morphine on the 5th day. In this study we confirmed that obestatin reversed the effect of mild morphine withdrawal and enhances the analgesic effect of morphine. These data suggest that obestatin may have a role in opioid-induced analgesia and in behavioral responses induced by opioid withdrawal.

Thermal sensitivity as a measure of spontaneous morphine withdrawal in mice

IntroductionOpioid withdrawal syndrome is a critical component of opioid abuse and consists of a wide array of symptoms including increases in pain sensitivity (hyperalgesia). A reliable preclinical model of hyperalgesia during opioid withdrawal is needed to evaluate possible interventions to alleviate withdrawal. The following study describes a method for assessing increases in thermal sensitivity on the hotplate in a mouse model of spontaneous morphine withdrawal. MethodsC57BL/6J mice received 5.5days of 30, 56, or 100mg/kg morphine or saline (s.c., twice daily). In Experiment I, thermal sensitivity data were collected at baseline and at 8, 24, 32, 48h and 1week following the final injection. Thermal sensitivity was assessed by examining latency to respond on a hotplate across a range of temperatures (50, 52, 54, and 56°C). In Experiment II, 0.01mg/kg buprenorphine was administered 30min prior to each testing session during the withdrawal period. In Experiment III, jumping during a 30min period was assessed at baseline and at 0, 8, 24, 32, and 48h following the final morphine injection. ResultsDuring the withdrawal period, thermal sensitivity increased significantly in all morphine-treated mice as compared to saline-treated mice. Thermal sensitivity was greater in mice treated with 56mg/kg morphine compared to 30mg/kg and peaked earlier than in mice treated with 100mg/kg (32h v 1wk). The increase in thermal sensitivity following 56mg/kg morphine was attenuated by a dose of buprenorphine that did not produce antinociception alone (i.e., 0.01mg/kg). In general, the results of the jumping experiment paralleled those obtained in Experiment I. DiscussionResponse latency on the hotplate is a reliable and sensitive measure of spontaneous morphine withdrawal in mice, making it an ideal behavior for assessing the potential of medications and environmental interventions to alleviate opioid withdrawal.

Thermal sensitivity as a measure of spontaneous morphine withdrawal in mice

Thermal sensitivity as a measure of spontaneous morphine withdrawal in mice

The effect of nimodipine on memory impairment during spontaneous morphine withdrawal in mice: Corticosterone interaction

Effects of the nimodipine, L-type calcium channel antagonist, has been studied on memory loss caused by spontaneous morphine withdrawal in mice. Mice were made dependent by increasing doses of morphine over three days. Memory was evaluated using object recognition task, which is based on tendency of rodents to exploration of new objects. The test was comprised of three sections: 15min habitation, 12min first trial and 5min test trial. Recognition index was evaluated 4h after the last dose of morphine. Nimodipine was administrated either in chronic form (1, 5 and 10mg/kg) with daily doses of morphine or it was given as a single injection (5 and 10mg/kg) on the last day. Nimodipine in both treatment forms prevented the memory impairment following spontaneous morphine withdrawal. Corticosterone concentration was increased in brain and blood of mice during abstinence phase and pretreatment with nimodipine prevented the increase in brain and blood corticosterone concentration. The results show that blockade of L-type calcium channels improves memory deficits caused by morphine withdrawal. This indicates that some kind of treatments, such as nimodipine, administrated over the acute withdrawal phase, can prevent memory deficit during withdrawal.