Effects Of Morphine In Mice Research Articles

Morphine has an antinociceptive effect through activation of the okadaic-acid-sensitive Ser/Thr protein phosphatases PP2A and PP5 estimated by tail-pinch test in mice

Although the serine/threonine protein kinases involved in the pharmacological action of morphine are well recognized, the critical contribution of serine/threonine protein phosphatase (PP) has been appreciated on to a slight degree. We examined the involvement of subtypes of serine/threonine protein phosphatase (PP) in the antinociceptive effect of morphine in mice. The antinociceptive effect of subcutaneously administered morphine was attenuated by simultaneously intracerebroventricular (i.c.v.) or intrathecal (i.t.) injection of okadaic acid (OA), a PP inhibitor. To reveal which subtypes of PPs participated in the antinociceptive effect of morphine, mice received i.c.v. or i.t. injections of antisense oligodeoxynucleotide (AS-ODN) directed against either the PP2A or PP5 subtypes of PPs before assessment of morphine-induced antinociception. Pretreatment with AS-ODN against PP2A or PP5 via each route weakened the antinociceptive effect of morphine, accompanied by reduction of expression levels of PP in the periaqueductal gray (PAG) and the spinal cord. Subcutaneously administered morphine increased activity of OA-sensitive PPs in the PAG and the spinal cord in a dose-dependent manner; this was prevented by concurrent administration of naloxone. These results suggest that PP2A and PP5 are involved in the antinociceptive effect of morphine in mice.

Is the nociceptin (NOP) receptor involved in attenuation of the expression of sensitization to morphine-induced hyperlocomotion in mice?

In the present study we investigated whether synthetic agonists of the nociceptin (NOP) receptors, Ro 64-6198 [(1S,3aS)-8-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)-1-phenyl-1,3,8-triaza-spiro[4,5]decan-4-one] and Ro 65-6570 (8-acenaphthen-1-yl-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-one), influence the expression of sensitization to the locomotor stimulant effect of morphine in mice. Sensitization was produced by five repeated administrations of morphine (10 mg/kg, s.c.) at 3-day intervals. Seven days after the last morphine injection, Ro 64-6198 (1 and 3 mg/kg, i.p.) and Ro 65-6570 (3 and 6 mg/kg, i.p.) were given immediately before the challenge dose of morphine (10 mg/kg, s.c.). Both substances inhibited the expression of sensitization to the locomotor stimulant action of morphine. However, the selective NOP receptor antagonist, [Nphe1]NC(1-13)NH2 (30 nmol, i.c.v.) did not reverse the inhibitory effect of the Ro-compounds. Therefore, our results suggest that the NOP receptor may not be critical for the influence of Ro-compounds on the morphine-induced sensitization, or the observed effect may be attributed to one functional subset of this receptor, stimulation of which is not blocked by [Nphe1]NC(1-13)NH2.

HS014, a selective melanocortin-4 (MC4) receptor antagonist, modulates the behavioral effects of morphine in mice

Melanocortin and opioid systems regulate feeding as well as other behaviors; however, the relationship between the two systems is not yet defined. Since agonist-induced stimulation of melanocortin receptors blocks the behavioral effects of mu opioid receptor agonists, and melanocortin-4 (MC4) receptors and mu opioid receptors share a similar anatomical distribution in the central nervous system, MC4 receptor blockade may increase opioid responsiveness. The goal of this study was to test the hypothesis that blockade of MC4 receptors increases the behavioral effects of morphine. The effects of HS014 (0.0032, 0.032, and 1 nmol, i.c.v.), a selective MC4 antagonist, on morphine-induced (3.2, 10, and 32 mg/kg, i.p.) locomotor activity (measured in the open field for 15 min) and antinociception (measured in the hot plate at 55 degrees C) were assessed in C57Bl/6 mice. In addition, the effects of morphine were evaluated in A(y) mice, a genetic model for MC4 receptor blockade. The dose-effect curve of morphine for locomotor activity was shifted downwards in C57Bl/6 mice pretreated with HS014 and in A(y) mice. The dose-effect curve of morphine for antinociception was shifted two- and threefold to the left in C57Bl/6 mice pretreated with HS014 and in A(y) mice, respectively. These results indicate that blockade of MC4 receptors increases the antinociceptive effects of morphine without changing the potency of morphine for locomotor activity, suggesting that MC4 receptor antagonists may be candidate drugs that can be clinically used for the treatment of pain.

Fangchinoline inhibited the antinociceptive effect of morphine in mice

Fangchinoline (FAN), a non-specific calcium antagonist, is a major alkaloidal component of the creeper Stephania tetrandra S. Moore (or fenfangji). It has been shown to possess antagonistic activity on morphine-induced antinociception in mice. This study was undertaken to assess the antagonistic mechanism. The results demonstrated that FAN (IP) attenuated morphine (SC)-induced antinociception in a dose-dependent manner with significant effect at doses of 30 and 60mg/kg body wt. (IP) in the tail-flick test but not the tail-pinch tests, carried out in mice. This antagonism was abolished by pretreatment with a serotonin precursor, 5-hydroxytryptophan (5-HTP, IP), but not by pretreatment with a noradrenaline precursor, L-dihydroxyphenylalanine (L-DOPA, IP) in the tail-flick test. On the other hand, the development of morphine-induced analgesic tolerance was not prevented by FAN. These results suggest that the serotonergic pathway may be involved in the antagonism of morphine-induced antinociception by FAN and, in agreement with other reports, also indicates the possible dissociation of the morphine analgesic effect from its tolerance-development mechanism.

Effects of DA D1 and D2 antagonists on the sensitisation to the motor effects of morphine in mice

Acute morphine administration produces hyperactivity in mice and repeated treatment induces an enhancement of this effect. In this experiment, we study the sensitisation to the hyperactivity induced by intermittent morphine administration (40 mg/kg) and the effects of dopamine (DA) antagonists on this phenomenon. Animals received three injections, separated by 48 h, and after each injection, their activity was registered between 30 and 60 min. In Experiment 1, animals were divided into two groups, which received saline and morphine (S–S–M) or only morphine (M–M–M). In Experiment 2, animals were divided into 12 groups. Half, which was designed to study the effects of DA antagonists on the acquisition of morphine sensitisation, received morphine plus 0.125, 0.25, or 0.5 mg/kg SCH 23390 or raclopride in the two first administrations and only morphine in the third (M+SCH–M+SCH–M; M+R–M+R–M). The other groups, designed to study the effects of DA antagonists on the expression of morphine sensitisation, received morphine in the two first administrations and morphine plus DA antagonists in the last injection (M–M–M+SCH; M–M–M+R). Intermittent morphine administration produces greater hyperactivity than acute morphine. DA D1 antagonists reduce acquisition and block expression of sensitisation, while DA D2 antagonists only affect expression with the intermediate and high dose. These results support the implication of DA in the behavioural sensitisation of morphine in mice.

Memantine does not block antiaggressive effects of morphine in mice.

The action of the noncompetitive N-methyl-D-aspartate (NMDA) receptor blocker memantine (5, 10, 20 and 40 mg/kg) was evaluated during social encounters in mice. Although a dose-dependent increase in locomotion was observed, only with the highest dose did it reach statistical significance. Aggressive behavior was decreased with 20 and 40 mg/kg of memantine, social contacts being increased only with 20 mg/kg. Subsequently, the effect of these memantine doses on the antiaggressive actions of morphine (10 mg/kg) was evaluated. None of the doses affected the antiaggressive action of morphine. As memantine administration produced an antiaggressive effect only at doses that affected locomotion, it is unlikely that the glutamatergic system mediates the antiaggressive actions of morphine.

The role of nitric oxide in anticonvulsant and proconvulsant effects of morphine in mice

Acute subcutanous administration of lower doses of morphine (0.5, 1 and 3 mg/kg) increase the threshold of seizures induced by pentylenetetrazole (PTZ) in mice, whereas higher doses of morphine (15, 30 and 60 mg/kg) have proconvulsant effects. The effect of systemic administration of nitric oxide synthase (NOS) inhibitors N G-nitro- l-arginine methyl ester ( l-NAME) and N G-nitro- l-arginine ( l-NNA) and nitric oxide synthase (NOS) l-arginine on biphasic effect of morphine was investigated. Acute administration of both l-NAME (1, 3 and 10 mg/kg) and l-NNA (1 and 10 mg/kg) as well as chronic pretreatment with l-NAME (1 and 10 mg/kg, 4 days) dose-dependently inhibited both the anticonvulsant and proconvulsant effects of morphine (1 and 30 mg/kg, respectively). The inhibition was complete for anticonvulsant effect while partial for proconvulsant effect. l-arginine at doses that did not affect seizure threshold per se (acute, 30 and 60 mg/kg; chronic, 60 mg/kg) potentiated both anticonvulsant and proconvulsant properties of less potent doses of morphine (0.5 and 15 mg/kg, respectively). The l-arginine induced potentiation of both phases of morphine effect was blocked by l-NAME (0.5–30 mg/kg). Moreover, low and per se non-effective doses of naloxone (0.1 mg/kg) and l-NAME (0.3, 0.5 or 1 mg/kg) showed additive effects in inhibiting both phases of morphine effects. These results support the involvement of l-arginine/nitric oxide pathway in the modulation of seizure threshold by morphine.

Individual differences in the induction of sensitisation or tolerance to the motor effects of morphine in mice

AbstractAcute morphine administration produces hyperactivity in most strains of mice and some studies indicate that repeated treatment can induce a potentiation of this effect (sensitisation). With the object of determining whether the hyperactivity induced by morphine in OF1 mice shows sensitisation after repeated administration, we tested the effect of the pre‐exposure to six daily injections of morphine on the subsequent hyperactivity induced by the same dose of this drug. Animals were treated with 40 mg/kg of morphine for seven days. After the last injection they were tested in an actimeter at different points at time (15, 30, 45 and 60 min). This repeated schedule of treatment produced sensitisation in some animals but tolerance in others. These results suggest the existence of great individual differences in the motor effects of repeated morphine administration and that the development of sensitisation and tolerance in outbred mice may be subjected to genetic variation.

The novel κ-opioid receptor agonist TRK-820 suppresses the rewarding and locomotor-enhancing effects of morphine in mice

The effects of the novel κ-opioid receptor agonist TRK-820 on the rewarding and locomotor-enhancing effects of morphine were investigated in mice. Morphine (1–5 mg/kg, s.c.) caused a dose-related preference for the drug-associated place. In contrast, TRK-820 (0.003–0.03 mg/kg, s.c.) did not produce a significant preference for either compartment of the test box. In combination studies, co-injection of TRK-820 (0.01 and 0.03 mg/kg, s.c.) with morphine significantly suppressed the morphine (5 mg/kg, s.c.)-induced place preference, and this effect of TRK-820 was antagonized by pretreatment with nor-BNI (3 mg/kg, s.c.), a selective κ-opioid receptor antagonist. TRK-820 also suppressed morphine-induced hyperlocomotion, and this suppression was also blocked by nor-BNI. These results suggest that TRK-820 suppresses the rewarding and locomotor-enhancing effects of morphine through the activation of κ-opioid receptors. Thus, we propose that TRK-820 may be useful for controlling pain while reducing undesirable side-effects.

Role of nitric oxide in diabetes-induced attenuation of antinociceptive effect of morphine in mice

The study was designed to investigate the role of nitric oxide (NO) in the diabetes-induced decrease of the antinociceptive effect of morphine. The nociceptive threshold in diabetic and non-diabetic mice was measured in the tail-flick test. Streptozotocin (200 mg/kg i.p.) was administered to induce experimental diabetes in the mice. Four weeks after the administration of streptozotocin, the tail-flick test was performed and urinary nitrite concentration was estimated using Greiss reagent. Experimental diabetes markedly decreased the antinociceptive effect of morphine (10 μg in 5 μl/mice i.c.v.) and significantly increased the urinary nitrite concentration. Administration of aminoguanidine (12 mg/mice) markedly improved the antinociceptive effect of morphine and attenuated the increase in urinary nitrite concentration in diabetic mice. It may be tentatively concluded that an increase in NO formation may be responsible for the observed decrease in antinociceptive effect of morphine in diabetic mice.

Selective agonist of group II glutamate metabotropic receptors, LY354740, inhibits tolerance to analgesic effects of morphine in mice.

1. Antagonists of glutamate N-methyl-D-aspartate (NMDA) subtype receptor inhibit the development of tolerance to the antinociceptive effects of opioids. Another way to inhibit the function of glutamate receptors is the stimulation of presynaptic metabotropic group II (mGluRII) receptors. Because LY354740 ((+)-2-aminobicyclo [3,1,0] hexane-2,6-dicarboxylic acid) is the first systemically active agonist of group II mGlu receptors, we investigated if this compound might inhibit the development of tolerance to antinociceptive effects of morphine and fentanyl. 2. As assessed by cumulative dose-response approach in the tail-flick test, administration of 10 mg kg(-1) morphine bid s.c. to male Albino Swiss mice for 6 days, right-shifted morphine dose-response curve by approximately 4 fold. In a separate group of mice, 12 injections of 0.04 mg kg(-1) of fentanyl over 3 days, right-shifted fentanyl dose-response curve by approximately 3.3 fold. 3. In experiment 1, LY354740 (1 and 10, but not 0.1 mg kg(-1)) as well as the reference compound, an uncompetitive NMDA receptor antagonist memantine (7.5 mg kg(-1)) inhibited the development of morphine tolerance. Neither LY354740 (10 mg kg(-1)) nor memantine (7.5 mg kg(-1)) affected the development of tolerance to fentanyl. In experiment 2, neither LY354740 (1 and 10 mg kg(-1)) nor memantine (7.5 mg kg(-1)) affected the tail-flick antinociceptive response, or the acute antinociceptive effect of morphine. 4. The present results are the first to suggest that the development of antinociceptive morphine tolerance may be inhibited by metabotropic group II glutamate agonist.

Involvement of NMDA receptors and nitric oxide in the thermoregulatory effect of morphine in mice.

Morphine has long been known to have potent effects on body temperature. It has been suggested that both N-methyl-D-aspartate (NMDA) receptors and nitric oxide (NO) pathway are involved in thermoregulation and also known to play important roles in some of morphine effects. The aim of this study was therefore to investigate the contribution of NMDA receptors and NO to the thermoregulatory effect of morphine. Morphine produced a hypothermic effect, especially at the dose of 10mg/kg. Ketamine (5-40mg/kg, i.p.) and N(G)-nitro-L-arginine-methyl ester (L-NAME, 1-100mg/kg, i.p.) also produced hypothermic effects with their higher doses. At doses which themselves produced no effect on colonic temperature in mice, both ketamine (10mg/kg, i.p.) and L-NAME (10mg/kg, i.p.) enhanced the hypothermic effect of morphine (10mg/kg, i.p.). These results further support the relationship between NO and NMDA receptors and suggest a possible role of NMDA-NO pathway in the thermoregulatory effect of morphine.

Clinically available NMDA receptor antagonists memantine and dextromethorphan reverse existing tolerance to the antinociceptive effects of morphine in mice.

The tail-flick test was used to investigate the effects of chronic administration of the N-methyl-D-aspartate (NMDA) receptor antagonists, dextromethorphan, memantine and MRZ 2/579, on the development and reversal of morphine tolerance in mice in three separate experiments. Experiment 1 investigated the effects of NMDA receptor antagonists on the development of tolerance. Morphine (10 mg/kg for 6 days, twice daily) produced a 5.9-fold rightward shift of the cumulative dose-response curves. Co-administration of dextromethorphan, memantine or MRZ 2/579 between tests 1 and 2 dose-dependently (5-10 mg/kg) inhibited the development of morphine tolerance. In experiment 2, in which the effects on the reversal were investigated, morphine-tolerant mice were treated b.i.d. for an additional 6 days (between tests 2 and 3) with vehicle+vehicle, NMDA receptor antagonist+vehicle, vehicle+morphine or NMDA receptor antagonist+morphine. Morphine-tolerant mice treated with vehicle+vehicle remained morphine tolerant, whereas this residual morphine tolerance was inhibited by administration of all three NMDA antagonists (each 10 mg/kg). Morphine-tolerant mice receiving vehicle+morphine injections demonstrated an unchanged degree of antinociceptive tolerance. In these mice, the co-administration of memantine and MRZ 2/579, but not dextromethorphan, resulted in the reversal of morphine tolerance. In experiment 3, memantine and MRZ 2/579 (10 mg/kg) inhibited the acute antinociceptive effect of morphine, but dextromethorphan did not. These data indicate that low-affinity, clinically available and/or therapeutically promising NMDA receptor antagonists may be used to inhibit ongoing morphine tolerance.

Effects of brain natriuretic peptide on effects of morphine in mice.

Brain natriuretic peptide (BNP) is a member of the natriuretic peptide family. The effects of intracerebroventricularly administered BNP (in 0.002-200 ng doses) on the analgesic, tolerance-inducing and dependence-inducing actions of morphine were investigated in adult male CFLP mice. Graded doses of BNP centrally did not affect pain sensitivity itself in a tail-flick test. However, different doses of BNP depressed the acute nociceptive effect of a single subcutaneous dose of morphine (5 mg/kg), and BNP attenuated the development of acute and chronic tolerance to morphine. Withdrawal signs were studied by injecting naloxone (1 mg/kg s.c.). There was no significant difference in symptoms between the tolerant group and animals treated with BNP. The data obtained indicate that BNP can modify the analgesic action of morphine.

The role of histamine H 1 receptors in the thermoregulatory effect of morphine in mice

Morphine is known to release histamine from mast cells and increase the turnover of neuronal histamine. It is also known that histamine receptors mediate some of the morphine effects. The contribution of histamine H 1 and H 2 receptors to the thermoregulatory effect of morphine in mice was investigated in the present experiments. Morphine produced a hypothermic effect, especially at the dose of 10 mg/kg. Although the histamine H 1 receptor antagonist, dimethindene (0.1 mg/kg, i.p.), attenuated the hypothermic effect of morphine (10 mg/kg), a histamine H 2 receptor antagonist, ranitidine (100 mg/kg, i.p.), had no effect. These results suggest that the hypothermic effect of morphine in mice is mediated, at least partly, through histamine H 1 receptors.

Tolerance to the mydriatic effect of buprenorphine, butorphanol, nalbuphine, and cyclorphan, and cross-tolerance to morphine in mice

An increase in the use of opioid derivatives in the treatment of pain syndrome in clinical practice, and especially in the treatment of cancer, has added impetus to the search for an agent which does not induce tolerance and cross-tolerance to other opiodis. The mydriatic effect of opioids in mice, the correlation between analgesia and mydriasis, and tolerance to the analgesic effect of morphine in mice were evaluated previously. In the present work, tolerance to the mydriatic effect of four agonist-antagonists and cross-tolerance to morphine were examined. Measurement of the pupillary diameter was performed using a binocular operating microscope. Tolerance and cross-tolerance to morphine were developed following a chronic use of buprenorphine, nalbuphine, and cyclorphan. After chronic injection of butorphanol, no tolerance or cross-tolerance to morphine was observed.

Analgesic and reinforcing effects of morphine in mice. Influence of Bay K-8644 and nimodipine

The aim of the present work was to clarify the role of calcium influx through L-type calcium channels in the rewarding and analgesic effects of morphine. Therefore the effects of Bay K-8644 and nimodipine, dihydropyridine calcium agonist and antagonist, respectively, on the analgesic and rewarding effects of morphine in mice were studied. Morphine-induced analgesia was measured with the aid of writhing test, hot plate test and tail clip test. The rewarding properties of morphine were studied using i.v. self-administration in drug-naive mice. Bay K-8644 potentiated morphine-induced analgesia in all the tests. The influence of nimodipine on morphine analgesia was more complicated and depended on those of morphine and test used. In self-administration experiments morphine exhibited the bell-shaped concentration-response curve. Bay K-8644 produced a shift of the curve to the left, while nimodiine had the oposite action indicating, respectively, facilitating and inhibitory influence on morphine rewarding effect. It is concluded that nimodipine exhibites partial antagonistic properties towards the rewarding action of morphine and slightly potentiates morphine-induced analgesia while Bay K-8644 increases either the rewarding or the analgesic effects of morphine.

Role of central ATP-sensitive potassium channels in the hyperthermic effect of morphine in mice.

Morphine (10 mg/kg, SC) in combination with ICV vehicle induced a significant hyperthermic effect at 120 min (peak time) after injection compared to ICV vehicle plus SC saline (control group). Glibenclamide (50 micrograms, ICV), a selective adenosine triphosphate-sensitive potassium (KATP) channel blocker, in combination with SC saline hardly affected the rectal temperature compared to the control group. ICV glibenclamide antagonized the hyperthermia induced by SC morphine in a dose-dependent manner. From these results, we demonstrated that KATP channels play an important role as modulators of the hyperthermic effect of mu agonists.

The involvement of alpha-adrenoceptors in the intestinal effect of morphine in mice

The involvement of alpha-adrenoceptors in the intestinal effect of morphine in mice

Intracerebroventricular treatment of mice with pertussis toxin induces hyperalgesia and enhances 3H-nitrendipine binding to synaptic membranes: Similarity with morphine tolerance

The effect of intracerebroventricular treatment of mice with pertussis toxin (PTX) on pain perception and 3H-nitrendipine binding was examined to study a possible change in the GTP-binding proteins in morphine tolerant rodents. It was observed that both PTX treatment and chronic administration of morphine cause hyperalgesia in the acetic acid-induced writhing test. Analgesic effects brought by the acute administration of morphine or nifedipine, a calcium antagonist, were not affected by PTX treatment. In synaptic membrane fractions prepared from mice treated with PTX or morphine chronically, specific binding of 3H-nitrendipine was enhanced approximately 41.8% and 35.7%, respectively, without alteration in its affinity. Chronic administration of morphine followed by PTX treatment did not display further increases in 3H-nitrendipine binding. These results suggest that the PTX-sensitive GTP-binding proteins may not be involved in the manifestation of the analgesic effect of morphine in mice.