Induction Of Morphine Dependence Research Articles

Curcumin attenuates morphine dependence by modulating μ-opioid receptors and glial cell-activated neuroinflammation in rat

In recent years, the association between neuroinflammation and opioid dependence has attracted considerable attention. Curcumin, a component of the Curcuma longa, has been shown to act as a suppressor of glial cells and inflammatory cytokines. The main goal of this study was to explore the attenuating effects of curcumin on morphine dependence with a focus on neuroinflammation and μ-opioid receptors in the rat prefrontal cortex. To induce morphine dependence in male Wistar rats, morphine was administered i.p. once daily for 18 days in an escalating dose of 10, 20, and 40 mg/kg. Curcumin (2.5, 5, and 10 mg/kg, i.p.) was given from the days 10th to 18th. Immunofluorescence staining and ELISA methods were used to evaluate glial cells activity and inflammatory cytokines levels, respectively. Western blotting was used to evaluate the expression of μ-opioid receptors. The administration of curcumin (2.5, 5, and 10 mg/kg) for 9 days significantly attenuated the symptoms of morphine withdrawal syndrome. The prefrontal cortex concentration of TNF-α and IL-6 was also reduced by curcumin (2.5, 5, and 10 mg/kg) significantly. Furthermore, curcumin decreased the number of Iba1 and GFAP positive cells in morphine-dependent rats. Moreover, the expression of μ-opioid receptors was significantly reduced by curcumin (10 mg/kg). The results of this study demonstrate that curcumin attenuates morphine dependence in rats through an inhibitory effect on neuroinflammation and a decrease in the expression of μ-opioid receptors in the prefrontal cortex.

Repeated Use of Morphine Induces Anxiety by Affecting a Proinflammatory Cytokine Signaling Pathway in the Prefrontal Cortex in Rats.

We examined the role of toll-like receptors (TLRs) and proinflammatory cytokine signaling pathways in the prefrontal cortex (PFC) in anxiety-like behaviors after repeated use of morphine. Morphine (10mg/kg) was used twice daily for 8days to induce morphine dependence in male Wistar rats. On day 8, opioid dependence was confirmed by measuring naloxone-precipitated withdrawal signs. On days 1 and 8, anxiety-like behaviors were evaluated using a light/dark box test. Expression of TLR1 and 4, proinflammatory cytokines, and some of the downstream signaling molecules was also evaluated in the bilateral PFC at mRNA and protein levels following morphine dependence. The results revealed that morphine caused anxiolytic-like effects on day 1 while induced anxiety following 8days of repeated injection. On day 8, a significant decrease in TLR1 expression was detected in the PFC in morphine-dependent rats, but TLR4 remained unaffected. Repeated morphine injection significantly increased IL1-β, TNFα, and IL6 expression, but decreased IL1R and TNFR at mRNA and protein levels except for IL6R at the protein level in the PFC. The p38α mitogen-activated protein (MAP) kinase expression significantly increased but the JNK3 expression decreased in the PFC in morphine-dependent rats. Repeated injection of morphine also significantly increased the NF-κB expression in the PFC. Further, significant increases in Let-7c, mir-133b, and mir-365 were detected in the PFC in morphine-dependent rats. We conclude that TLR1 and proinflammatory cytokines signaling pathways in the PFC are associated with the anxiogenic-like effects of morphine following its chronic use in rats via a MAP kinase/NF-κB pathway.

Attenuation of Morphine Dependence by Ganoderma lucidum Extract in Mice

Background: Opioids are the principal drugs of choice for managing acute severe pain; however, physical dependence is still reported as one of the main limiting factors in the clinical application of these drugs. In the present study, the effect of Ganoderma lucidum was assessed on morphine dependence in mice. Methods: A 19-day administration schedule was applied to induce morphine dependence in male adult NMRI mice. The mice were given intraperitoneal (i.p.) morphine sulfate once daily in an increasing dose of 10, 20, and 40 mg/kg. Then, G. lucidum hydroalcoholic extract (12.5, 25, and 50 mg/kg, i.p.) was given to the mice from days 10 to 18. Another group of mice received single doses of the extract (50, 100, and 200 mg/kg, i.p.) only on the 19th day. Naloxone (3 mg/kg, i.p.) was used to precipitate withdrawal syndrome. Normal saline and diazepam (0.25 mg/kg) were used as the negative and positive controls, respectively. Results: The administration of single doses of G. lucidum extract (100 and 200 mg/kg, i.p.) significantly decreased the number of jumps, leanings, and diarrhea in mice subjected to morphine dependence. The repeated administration of G. lucidum extract (25 and 50 mg/kg for nine days) significantly attenuated the number of jumps, leanings, and diarrhea in morphine-dependent mice. Conclusions: Overall, G. lucidum extract attenuates induced morphine dependence and inhibits withdrawal syndrome symptoms in mice.

The effect of different exercise training modes on dentate gyrus neurodegeneration and synaptic plasticity in morphine-dependent rats

Various impacts of exercise on brain performance following the induction of morphine dependence have been documented; however, the underlying neuronal mechanisms are still unclear. The present research was done to investigate the impact of different exercise training modes on apoptosis, neuronal maturation, and synaptic plasticity in the perforant pathway (PP)-dentate gyrus (DG) synapses in the morphine-dependent rats. Five groups, including a control group (Con, ten healthy rats) and forty morphine-dependent rats were considered as follows (n = 10/group): 1) sedentary-dependent (Sed-D); 2) endurance exercise-dependent (En-D); 3) strength exercise-dependent (St-D); and 4) concurrent exercise-dependent (Co-D). The exercise training groups were subjected to endurance, strength, and concurrent training five days a week for ten weeks. After training sessions, the field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude in the DG were determined in response to high-frequency stimulation (HFS) of the PP. For assessing neurogenesis and apoptosis, NeuroD and Caspase-3 expression levels were evaluated after all experiments. Concurrent training increased PS amplitude and EPSP compared to the control group. NeuroD in the morphine-dependent rats significantly decreased, but concurrent training returned the NeuroD to its levels in healthy rats. Furthermore, Caspase-3 expression levels in morphine-dependent rats remarkably increased and concurrent training significantly reduced Caspase-3 expression levels compared to the Sed-D group. Concurrent training can ameliorate synaptic plasticity impairment in morphine-dependent rats through neurogenesis promotion and apoptosis reduction. According to the results, concurrent training can be an appropriate novel candidate for treating opioid addiction.

Saffron (Crocus sativus L.) stigma reduces symptoms of morphine-induced dependence and spontaneous withdrawal in rats

ABSTRACT Background: Chronic morphine induces physical and psychological dependence signs. Saffron (Crocus sativus L.) stigma has been shown to have anxiolytic, antidepressant, and antinociceptive properties and to alleviate naloxone-precipitated withdrawal signs. Objectives: Therefore, this study was designed to examine the effects of saffron aqueous extract on the severity of physical-psychological dependence, voluntary morphine consumption, and the cerebrospinal fluid (CSF) serotonin levels following locomotor sensitization in morphine-dependent rats and in rats undergoing morphine withdrawal. Materials: Adult male rats were treated with morphine (10 mg/kg, sc twice daily) for 10 days. Rats received saffron extract (60 mg/kg, ip) daily, during the induction of morphine dependence and/or withdrawal. Then, rats were tested for spontaneous withdrawal signs, anxiety using the elevated plus-maze, depression using sucrose preference test, and voluntary morphine consumption using a two-bottle choice paradigm, and then challenged with morphine (1 mg/kg, ip) to evaluate of locomotor sensitization and CSF serotonin levels. Results: The results showed saffron extract during induction of morphine dependence decreased the severity of withdrawal signs (P = .05), while it had no effect on anxiety and depression-like behaviors. Saffron extract during morphine withdrawal exhibited an increase in the percentage (or ratio) of open/total arm entries (P = .017), higher levels of sucrose preference (P = .0001), a lower morphine preference ratio (P = .02) and also, a decrease in locomotor activity (P = .004) and an increase in the CSF serotonin levels (P = .041) in rats challenged to morphine. Conclusions: Saffron extract may exert a protective effect against morphine-induced behavioral sensitization in rats, probably through increasing serotonin levels.

Slow-sustained delivery of naloxone reduces typical naloxone-induced precipitated opioid withdrawal effects in male morphine-dependent mice.

Thousands of individuals die each year from opioid-related overdoses. While naloxone (Narcan®) is currently the most widely employed treatment to reverse opioid toxicity, high or repeated doses of this antidote often lead to precipitated opioid withdrawal (POW). We hypothesized that a slow linear release of naloxone from a nanoparticle would induce fewer POW symptoms compared to high-dose free naloxone. First, we measured the acute impact of covalent naloxone nanoparticles (Nal-cNPs) on morphine-induced antinociception in the hotplate test. We found that Nal-cNP treatment blocked the antinociceptive effect of morphine within 15min of administration. Next, we tested the impact of Nal-cNPs on POW symptoms in male morphine-dependent mice. To induce morphine dependence, mice were treated with 5mg/kg morphine (or saline) twice-daily for six consecutive days. On day 7 mice received 5mg/kg morphine (or saline) injections 2hr prior to receiving treatment of either unmodified free naloxone, a high or low dose of Nal-cNP, empty nanoparticle (cNP-empty), or saline. Behavior was analyzed for 0-6hr followed by 24 and 48hr time points after treatment. As expected, free naloxone induced a significant increase in POW behavior in morphine-dependent mice compared to saline-treated mice upon free naloxone administration. In comparison, reduced POW behavior was observed with both doses of Nal-cNP. Side effects of Nal-cNP on locomotion and fecal boli production were measured and no significant side-effects were observed. Overall, our data show that sustained release of naloxone from a covalent nanoparticle does not induce severe POW symptoms in morphine-dependent mice.

The Attenuating Effect of Curcumin on Morphine Dependence in Rats: The Involvement of Spinal Microglial Cells and Inflammatory Cytokines.

New evidence suggests an important role for spinal glial cells in the development of opioid dependence. Curcumin, a component of the Curcuma Longa, has shown to act as a suppressor of microglial cells. The main goal of this study was to explore the attenuating effects of curcumin on morphine dependence with a focus on spinal microglial cells and inflammatory cytokines. In order to induce morphine dependence in male Wistar rats, morphine was administered intraperitoneally (i.p.) once daily for 9 days in an increasing dose of 10, 20, and 40 mg/kg. Curcumin (2.5, 5, and 10 mg/kg, i.p.) was given from the days 10th to 18th. Naloxone-precipitated abstinence syndrome was used to assess the behavioral symptoms of morphine dependence. Immunofluorescence staining of Iba1 and ELISA test were used to measure spinal microglial activity and inflammatory cytokines levels, respectively.The results showed that curcumin (2.5, 5, and 10 mg/kg) significantly decreased jumping, leaning, and diarrhea in morphine-dependent rats. In addition, the spinal concentration of TNF-α and IL-6 was reduced by curcumin (2.5, 5, and 10 mg/kg) significantly. Moreover, curcumin showed a potent attenuating effect on the number of Iba1 positive cells in rats which were subjected to morphine dependence. The results of this study demonstrated that curcumin exerts a remarkable reducing effect on morphine dependence in rats. The findings showed that the therapeutic effect of curcumin on morphine dependence is mediated through the suppression of activated microglial cells and reduction of inflammatory cytokines levels in the spinal cord.

Central antagonism of orexin type-1 receptors attenuates the development of morphine dependence in rat locus coeruleus neurons

Prolonged use/abuse of opioid agonists leads to development of severe dependence to these drugs. Orexin-A has a crucial role in development of morphine dependence. The locus coeruleus (LC) is implicated in the expression of morphine withdrawal signs. Hyperactivity of LC neurons as well as increased intracellular cyclic adenosine monophosphate (cAMP) level temporally corresponds to the expression of opioid withdrawal behaviors. In this study the effect of central OX1R blockade on neuronal activity and cAMP content of LC neurons was investigated following naloxone administration in morphine-dependent rats. Male Wistar rats weighing 250–300g were used in this study. To induce morphine dependence, morphine was injected intraperitoneally (10mg/kg, i.p.) once a day for seven consecutive days. A selective OX1R antagonist (SB-334867) was microinjected into the cerebral ventricle (10µg/10µl) immediately before each morphine injection. The activity of LC neurons was investigated using in vivo extracellular single-unit recording on day 8 and naloxone (2mg/kg, i.p.) was administered after 10-min baseline recording. In addition, immunohistofluorescence method was used to measure the effect of naloxone on coerulear cAMP level. Chronic morphine injection induced morphine dependence in LC neurons which was revealed as a significant increase in LC neuronal firing rate in response to naloxone. The results of this study indicated that SB-334867 administration prior to each morphine injection prevents naloxone-elicited neuronal activation within the LC. In addition, naloxone injection enhanced the cAMP concentration in LC neurons of morphine-dependent animals and this effect was significantly reduced by OX1R blockade.

Cholecystokinin octapeptide induces endogenous opioid-dependent anxiolytic effects in morphine-withdrawal rats

Cholecystokinin octapeptide (CCK-8), a brain–gut peptide, plays an important role in several opioid addictive behaviors. We previously reported that CCK-8 attenuated the expression and reinstatement of morphine-induced conditioned place preference. The possible effects of CCK-8 on the negative affective components of drug abstinence are not clear. There are no studies evaluating the effect of CCK-8 on emotional symptoms, such as anxiety, in morphine-withdrawal animals. We investigated the effects of CCK-8 on the anxiety-like behavior in morphine-withdrawal rats using an elevated plus-maze. Morphine withdrawal elicited time-dependent anxiety-like behaviors with peak effects on day 10 (5days after induction of morphine dependence). Treatment with CCK-8 (0.1 and 1μg, i.c.v.) blocked this anxiety in a dose-dependent fashion. A CCK1 receptor antagonist (L-364,718, 10μg, i.c.v.) blocked the effect of CCK-8. Mu-opioid receptor antagonism with CTAP (10μg, i.c.v.) decreased the ‘anxiolytic’ effect. CCK-8 inhibited anxiety-like behaviors in morphine-withdrawal rats by up-regulating endogenous opioids via the CCK1 receptor in rats. This study clearly identifies a distinct function of CCK-8 and a potential medication target of central CCK1 receptors for drugs aimed at ameliorating drug addiction.

Desmopressin accelerates the rate of urinary morphine excretion and attenuates withdrawal symptoms in rats

The aim of this study was to examine the effects of desmopressin on morphine withdrawal symptoms and vasopressin level in morphine-dependent subjects. Wistar male rats were injected s.c. with morphine once per day for 5 consecutive days to induce morphine dependence. After morphine use ceased on day 5, an equal number of rats were assigned to one of four groups for either saline or desmopressin by either intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) injection. From days 5 to 10, urine was collected daily and tested for the presence of morphine, and withdrawal symptoms were monitored to assess the effects of desmopressin. Significant weight loss occurred among all morphine-addicted rats during the withdrawal period. With both methods (i.p. and i.c.v.), the period of urinary morphine excretion was shorter for the two groups that were given desmopressin (experimental groups) than the two groups that were not given desmopressin (control groups), and no significant difference in urinary morphine excretion was found between the two experimental groups. During the early stage of withdrawal, the severity of the withdrawal symptoms in the experimental groups was significantly lower than that in the control groups. Desmopressin decreases the extent of morphine withdrawal symptoms, indicating that this agent might be appropriate for treating morphine addiction. Desmopressin appears to reduce withdrawal symptoms not by exerting an anti-diuretic effect but rather by exerting an effect on the central nervous system.

Mineralocorticoid Receptors Mediate Cardiac Remodelling in Morphine‐Dependent Rats

Acute morphine administration decreases cardiac responses to ischaemic injury. This project has determined whether induction of morphine dependence in rats by gradually increasing morphine doses for 21days induces structural and functional changes in the cardiovascular system because of mineralocorticoid receptor activation, as morphine increases plasma corticosterone concentrations. Morphine-dependent rats showed ventricular hypertrophy, increased collagen deposition in the left ventricle together with an increased ventricular stiffness and increased plasma malondialdehyde concentrations without changes in systolic blood pressure or thoracic aortic responsiveness. These parameters were attenuated or normalised in morphine-dependent rats treated with spironolactone (50mg/kg/day) from days 14-21. These results suggest that morphine dependence induces ventricular remodelling and increased oxidative stress that can be prevented by the mineralocorticoid receptor antagonist, spironolactone.

Effect of Linalool on Morphine Tolerance and Dependence in Mice

Linalool, a terpene alcohol, has been shown to interact with the opioid system and N-methyl-D-aspartate (NMDA) receptor. Therefore, the effect of linalool on morphine dependence and tolerance was studied. Dependence and tolerance were induced in mice using subcutaneous morphine injections, three times a day (50, 50 and 75 mg/kg /day) for 3 days. To evaluate the effect of agents on the induction of morphine dependence and tolerance, linalool (50, 75 and 100 mg/kg), clonidine (positive control), alpha-2 receptor agonist, (0.1 mg/kg), memantine, NMDA receptor antagonist (positive control), (30 mg/kg) and saline were injected intraperitoneally three times a day for 3 days. To determine the expression of morphine dependence and tolerance, all compounds were injected once intraperitoneally on the day of experiment. The effect of linalool and other agents on dependence were evaluated by counting the number of jumps (induced by naloxone 5 mg/kg). The tolerance was evaluated by the tail-flick test. The results showed that linalool in the induction and expression phase increased the nociception threshold. Linalool (48% and 95.6% at doses 75 and 100 mg/kg, respectively), clonidine and memantine reduced the severity of withdrawal signs in the induction and expression phases. This study indicated that linalool has a significant effect on morphine tolerance and dependence. This effect may be mediated partially through the inhibition of NMDA receptors.

The Effects of Angiotensin II and Captopril on Expression of Morphine Withdrawal Signs in Rat

The mechanisms of drug dependence and rewarding properties of opiates are not exactly known and several neurotransmitters seem to be involved. It is possible that the rennin-angiotensin system could interact with the opioid system, since it has been shown that angiotensin II(Ang) and ACE inhibitors have analgesic, anticonvulsant and antidepression effects and in some cases they could antagonize the effect of morphine. In the present study, the effect of Ang II and captopril on withdrawal signs was evaluated. Male wistar rats were anesthetized and i.c.v cannula implanted and allowed to recover from surgery. Morphine was injected (i.p, 3 times a day) for 4 days to induce morphine dependence. The animals were divided into 3 groups and received saline, captopril, Ang II, and i.c.v, before naloxone injection. Naloxone precipitated morphine withdrawal signs, compared to the morphine dependent rats in saline, captopril and Ang II groups. Results showed that in the captopril group, some of the withdrawal signs were significantly lower than the saline group (p<0.05 and p<0.01). In the Ang II group, some of the withdrawal signs were greater than the saline group (p<0.01 and p<0.001). Considering the fact that captopril can reduce endogenous opioid degradation, it could probably reduce the morphine withdrawal signs in this way. On the other hand, captopril and Ang II can interact with dopamine, serotonin, substance p, acetylcholine or nitric oxide in different brain regions and alter morphine withdrawal signs.

Effects of polyinosinic–polycytidylic acid (Poly I:C) on naloxone-precipitated withdrawal in morphine-dependent mice

Viral infections are frequently found in opioid addicts, subjecting them to immune challenge. However, the effects of immune challenge on opioid withdrawal are not fully understood. In the present study, mice were intraperitoneally injected with 2mg/kg polyinosinic–polycytidylic acid (Poly I:C, a viral mimetic) for 3 days to induce an immune challenge, followed by subcutaneous injection of morphine 3 times per day for 3 days to induce morphine dependence. Withdrawal was induced by an intraperitoneal injection of 5mg/kg naloxone, an opioid receptor antagonist. The results showed that Poly I:C pretreatment did not alter body weight loss, jumping behavior, or locomotion during naloxone-precipitated withdrawal. In contrast, Poly I:C pretreatment significantly increased immobility time in the tail suspension test. Our findings suggest that Poly I:C-induced immune challenge has no effects on acute physical opioid withdrawal symptoms but facilitates depression-like behavior.

Reducing the time and dose of morphine application used in Marshall and Grahame-Smith method for induction of morphine tolerance and dependence in mice

To induce morphine dependence, different programs have been used and a wide range of behaviors evaluated. A quantitative method based on mice withdrawal jumping behavior has been suggested and later described by Marshall and Grahame-Smith. The purpose of this work was to evaluate different aspects of this method using variations in doses and duration of the protocol. All experiments were done in three parallel methods according to the Marshall protocol: (i) except the dose of morphine ( n = 20) where we divided all morphine doses by two in first 3 days, (ii) 2-day (M100%-2D, n = 14) and (iii) 1-day morphine application (M100%-1D; n = 13). The results showed that only 50% doses of morphine that are used according to Marshall method is sufficient to induce morphine dependence whereas they are not able to induce tolerance. On the other hand, M100%-2D protocol could induce morphine tolerance but not dependence whereas M100%-1D group could induce neither morphine tolerance nor dependence in mice. Therefore, these simple modifications in dose and period of morphine application in Marshall method resulted in distinct protocols for induction of morphine tolerance and dependence along with saving of drug and time.

P.6.043 Pirlindol in the treatment of heroin addicted patients

Viral infections are frequently found in opioid addicts, subjecting them to immune challenge. However, the effects of immune challenge on opioid withdrawal are not fully understood. In the present study, mice were intraperitoneally injected with 2 mg/kg polyinosinic–polycytidylic acid (Poly I:C, a viral mimetic) for 3 days to induce an immune challenge, followed by subcutaneous injection of morphine 3 times per day for 3 days to induce morphine dependence. Withdrawal was induced by an intraperitoneal injection of 5 mg/kg naloxone, an opioid receptor antagonist. The results showed that Poly I:C pretreatment did not alter body weight loss, jumping behavior, or locomotion during naloxone-precipitated withdrawal. In contrast, Poly I:C pretreatment significantly increased immobility time in the tail suspension test. Our findings suggest that Poly I:C-induced immune challenge has no effects on acute physical opioid withdrawal symptoms but facilitates depression-like behavior.

Memantine presents different effects from MK-801 in motivational and physical signs of morphine withdrawal

Adaptive changes in neural systems due to chronic opiate exposure are related to the neural plasticity phenomenon, NMDA receptors being implicated in these processes, e.g. tolerance, dependence or withdrawal. In this work, we investigated the effect of two non-competitive NMDA antagonists, memantine and MK-801, in motivational (Conditioned Place Aversion paradigm, CPA) and physical aspects of morphine withdrawal. After the induction of morphine dependence, animals in which the CPA was studied, received memantine (5 and 10 mg/kg) or MK-801 (0.3–0.006 mg/kg) either during the acquisition (conditioning) or expression (test) phase of this procedure. Both drugs were capable of inhibiting conditioned aversion when administered in any phase. In a second experiment, the effects of these drugs were evaluated in the intensity of the physical signs of withdrawal, only memantine administration being efficient. In addition to these studies, the intensity of morphine dependence was investigated under the blockade of NMDA receptors, i.e. morphine was co-administered with memantine or MK-801. These animals did not develop CPA and present less intensity in the physical signs of morphine withdrawal. Our results support the idea that NMDA receptors are involved in the behavioural changes and therefore in the neural adaptations produced by repeated morphine administration.

The effect of cyclosporin A on morphine tolerance and dependence: involvement of l-arginine/nitric oxide pathway

Cyclosporin A is known to decrease nitric oxide (NO) production in nervous tissues. The effects of systemic cyclosporine A on the induction and expression of morphine tolerance and dependence, acute morphine-induced antinociception, and the probable involvement of the l-arginine/nitric oxide pathway in these effects were assessed in mice. Cyclosporin A (20 mg/kg), N G-nitro- l-arginine methyl ester ( l-NAME) (10 mg/kg) and a combination of the two at lower and per se non-effective doses (5 and 3 mg/kg, respectively) showed a similar pattern of action, inhibiting the induction of tolerance to morphine-induced antinociception and increasing the antinociception threshold in the expression phase of morphine tolerance. These agents also inhibited the expression of morphine dependence as assessed by naloxone-precipitated withdrawal signs, while having no effect on the induction of morphine dependence. l-Arginine, at a per se non-effective dose (60 mg/kg), inhibited the effects of Cyclosporin A. Moreover, acute administration of Cyclosporin A (20 mg/kg) or l-NAME (10 mg/kg) enhanced the antinociception induced by acute administration of morphine (5 mg/kg), while chronic pretreatment with Cyclosporin A (20 mg/kg) or l-NAME (10 mg/kg) for 2 days (twice daily) did not affect morphine-induced antinociception. The inducible nitric oxide synthase inhibitor, aminoguanidine (100 mg/kg), did not alter morphine antinociception, tolerance or dependence. In conclusion, decreasing NO production through constitutive nitric oxide synthase may be a mechanism through which cyclosporin A differentially modulates mophine tolerance, dependence and antinociception.

Role of nitric oxide in catalepsy and hyperthermia in morphine-dependent rats

The possible involvement of nitric oxide (NO) in morphine-induced catalepsy and hyperthermia was studied in morphine-dependent rats. Four days repeated injection regimen was used to induce morphine dependence, which was assessed by naloxone challenge (0.5 mg kg −1, s.c.). Pretreatment of rats with the NO synthase inhibitor, NG-nitro-l-arginine (l-NA, 8 mg kg −1twice daily, i.p.) potentiated the cataleptic response of morphine as shown by a rightward shift in the morphine-log dose–response curve. Prior treatment of rats with the NO precursor, l-arginine (200 mg kg −1, twice daily, i.p.) abolished the potent effect of l-NA and restored the cataleptic scores to levels similar to those of morphine-dependent rats. The same dose of l-NA significantly blocked morphine-induced hyperthermia at the dose levels of morphine (15–105 mg kg −1) and this effect was reversed by l-arginine. These data provide the first experimental evidence that NO is involved in morphine induced catalepsy and hyperthermia and demonstrated that blockade of NO synthesis may suggest a dangerous interaction with opioids in the control of motor function.

Absorption of morphine from a slow-release emulsion used to induce morphine dependence in rats

This study was performed to measure absorption of morphine from the injection site following treatment of rats with slow-release emulsions formulated with morphine hydrochloride and morphine base. Samples of emulsion were collected from the injection site of halothane anesthetized animals at 24 and 48 h following emulsion treatment and concentrations of morphine remaining in the emulsion were analyzed using high-performance liquid chromatography (HPLC). In another group of morphine-treated rats, at times equivalent to collecting samples of emulsion, the intensity of naloxone-precipitated withdrawal behaviors was monitored. Both morphine base- and hydrochloride-containing emulsions induced a high degree of physical dependence in animals treated over 48 h. Release of morphine from emulsions containing morphine base was slower than that from the hydrochloride formulations. In the 24-h morphine base-treated animals, approximately 45% was absorbed from the injection site as opposed to 99% in the 24-h morphine hydrochloride-treated animals. These results suggest that morphine base containing emulsions provide a more sustained exposure to the opioid.