Vasopressin release by D-aspartic acid,morphine and Prolyl-leucyl-glycinamide (PLG) in DI Brattleboro rats

The L-asparaginase activities of the brains of the Wistar, heterozygous and homozygous Brattleboro rats divided into three parts namely the anterior, middle and posterior which respectively contained cerebral cortex, hippocampus + midbrain + thalamus + hypothalamus and cerebellum + pons + medulla oblongata were estimated. The L-asparaginase activities of all the three parts in the homozygous Brattleboro rats were significantly higher than in the Wistar rats as well as in the heterozygous Brattleboro rats. Twenty min following the injections of 200 mg/kg D-aspartic acid, 20 mg/kg morphine, 200 mg/kg D-aspartic acid + 20 mg/kg morphine, 6 mg/kg prolyl-leucyl-glycinamide (PLG) and 6 mg/kg PLG + 20 mg/kg morphine the L-asparaginase activities of all three parts of the homozygous Brattleboro rat brains were found to be significantly inhibited. After having seen the suppressive effect of the drugs and their combinations used before the homozygous Brattleboro rats were given D-aspartic acid, morphine, D-aspartic acid + morphine, PLG and PLG + morphine for seven days. Then their plasma vasopressin levels were determined by RIA. The treatments applied to the homozygous Brattleboro rats caused the appearance of a significant amount vasopressin in the plasma. The results were interpreted as evidence for the fact that the inhibition of the brain L-asparaginase provides and/or accelerates the biosynthesis and/or release of vasopressin. As morphine has a vasopressin releasing and a brain L-asparaginase inhibiting effect the antidiuretic action of morphine was considered to be linked to its inhibitory effect on the brain L-asparaginase.     

Dual action of methadone on 5-HT synthesis and metabolism

Summary The main purpose of these experiments was to compare the effects of methadone and morphine on cerebral 5-hydroxytryptamine (5-HT) synthesis and 5-hydroxyindoleacetic acid (5-HIAA) formation. In addition the rate of catecholamine synthesis and the concentrations of tyrosine and tryptophan in the brain were measured, as well as the effects of naloxone were investigated.Morphine (34 mg/kg, 2h) increased the synthesis of 5-HT and catecholamines, determined by measuring the accumulation of 5-hydroxytryptophan (5-HTP) and dopa in the whole brain of rats treated with an inhibitor of the aromatic l-amino acid decarboxylase (3-hydroxybenzylhydrazine hydrochloride, NSD 1015). Morphine also increased the cerebral 5-HIAA concentration both in rats treated with NSD 1015 or probenecid. Naloxone antagonized all these effects of morphine. A lower dose of naloxone was needed to antagonize the effect of morphine on 5-HT than on catecholamine synthesis, Similarly to morphine methadone (9 mg/kg, 2 h) increased the cerebral 5-HIAA concentration, but methadone alone did not alter the rate of formation of 5-HTP. However, in combination with naloxone methadone decreased the concentration of 5-HIAA and the accumulation of 5-HTP depending both on the dose of methadone and that of naloxone. Similarly to morphine, methadone stimulated and never reduced the catecholamine synthesis; naloxone antagonized this effect. Both morphine and methadone increased the cerebral concentrations of tryptophan and tyrosine and naloxone antagonized these effects. In addition naloxone alone (2+2 mg/kg, 1+2h) decreased the cerebral tyrosine concentration significantly suggesting that the opiate receptors are involved in the control of cerebral tyrosine concentration.Our results suggest that methadone similarly to morphine stimulates the cerebral 5-HT and catecholamine synthesis, and that these effects are most probably mediated via opiate receptors. However, when opiate receptors are blocked, methadone is able to decrease the cerebral 5-HT synthesis and cerebral 5-HIAA concentration probably via a feedback mechanism produced by blockade of 5-HT reuptake.     

Role of brain catecholamines and 5-hydroxytryptamine in morphine induced temperature changes in normal and tolerant rats and mice

Summary Morphine (5–20 mg/kg) produced hyperthermia in normal, unrestrained rats. Rats which were chronically treated with morphine became tolerant and physically dependent but did not develop tolerance to the acute hyperthermia. Pretreatment of rats with 6-hydroxydopamine to deplete brain catecholamines potentiated the acute morphine hyperthermia in normal rats but not in tolerant rats. The effect is probably related to brain dopamine. Depletion of brain 5-hydroxytryptamine (5-HT) produced by 5,6-dihydroxytryptamine pretreatment, antagonized the acute morphine hyperthermia in both normal and tolerant rats. Morphine (5–20 mg/kg) produced hypothermia in both normal and morphine tolerant mice. Pretreatment of normal mice with 6-hydroxydopamine depleted brain noradrenaline and dopamine and antagonized the hypothermia. Pretreatment with pargyline and 6-hydroxydopamine caused a greater loss of cerebral dopamine than 6-hydroxydopamine alone and resulted in an acute morphine hyperthermia. Morphine also caused hyperthermia when given to tolerant mice pretreated with 6-hydroxydopamine. Pretreatment of normal mice with 5,6-dihydroxytryptamine totally abolished the acute morphine hypothermia. In tolerant mice treated with 5,6-dihydroxytryptamine morphine caused a rise in temperature. It is concluded that (1) a single dose of morphine given to normal rats shifts a hypothalamic 5-HT: dopamine balance in favour of 5-HT; (2) activation of a 5-HT mechanism causes hyperthermia whereas dopamine mediates hypothermia; (3) rats chronically treated with morphine do not become tolerant to the acute hyperthermia because morphine tolerance has little effect on 5-HT; (4) brain dopamine mechanisms readily develop tolerance to morphine; (5) the hypothermia produced by a single dose of morphine in normal mice is mediated by dopamine and, to a lesser extent, 5-HT mechanisms; (6) the hypothermic mechanisms rapidly develop tolerance to morphine; (7) loss of cerebral dopamine and 5-HT in morphine tolerant mice leads to an acute morphine hyperthermia due to another neurotransmitter.     

Effects of mu- and kappa-opioid receptor agonists on urinary output in mice

The effects of ethylketazocine, morphine, bremazocine and naloxone were determined on urinary output and weight loss in Cox mice. Morphine and fentanyl were also studied in Harlan mice. Bremazocine, ethylketazocine and morphine markedly increased urinary output and weight loss within 5 hr after injection. Naloxone antagonized the diuretic actions of morphine (5 mg/kg) and bremazocine (0.06 mg/kg) over a similar dose range (0.3--10 mg/kg). By comparison with the other agonists, fentanyl had little effect on urinary output or weight loss. These results suggest that kappa agonist activity increases urinary output in mice just as reported for rats. The data also suggest that in mice morphine has some kappa agonist activity, whereas fentanyl does not.     

Interaction of morphine and 5-hydroxytryptamine in the raphe-hippocampus system

In order to describe the interaction of morphine and 5-hydroxytryptamine (5-HT) in the raphe-hippocampus system we tested the influence on the antinocifensive effect of topic administrations of morphine and serotonergic substances into the dorsal hippocampus and the median raphe nucleus in rats. 5-HT administered into the dorsal hippocampus increased the morphine analgesia. Lysergic acid diethylamide injected into the raphe nucleus antagonized the morphine effect. Morphine given into the raphe nucleus was highly effective, while its injection into the striatum was ineffective. The effect of the intrahippocampal morphine was antagonized by methysergide. The results indicate the important role of the serotonergic raphe-hippocampus system in the mechanism of the morphine analgesia.     

Effect of selective monoamine oxidase inhibitors on the morphine-induced hypothermia in restrained rats

Morphine (30 mg/kg i.p.) produced a hypothermic effect in restrained rats which was antagonized by naloxone pretreatment (10 mg/kg s.c.). This hypothermia was inhibited by deprenyl pretreatment (5 mg/kg i.p.) and by beta-phenylethylamine treatment (25 mg/kg i.p.). However, the effect of morphine was partially potentiated when a higher dose of deprenyl (10 mg/kg i.p.) was administered. Pretreatment with clorgyline (1 mg/kg i.p.) potentiated the morphine-induced hypothermia. In contrast, the effect of morphine was antagonized when a higher dose of clorgyline was used (5 mg/kg i.p.). Based on these results, a possible role of brain serotonin and dopamine in the thermoregulatory effects of morphine is proposed in this paper.     

Shaking behaviour induced by putrescine in naive rats: a pharmacological and histological study

In untreated rats, the intraperitoneal injection of putrescine evoked a typical wet-dog shake response, that was maximal at a dose of 300 mg/kg and at room temperature (22 degrees) (number of shakes: 84.00 +/- 17.90/hr). In a hot environment (30 degrees) the number of shakes was markedly reduced (26.90 +/- 5.19/hr). The putrescine-induced shaking behaviour was unaffected by atropine, bicuculline, chlorpheniramine, cimetidine, methysergide, naloxone and noradrenaline, but was markedly antagonized by morphine. Naloxone pretreatment nullified the antagonistic activity of morphine. Histological studies showed marked alterations in brain vascular permeability, which was increased by putrescine. Morphine completely prevented this putrescine-induced vascular effect. These results suggest a correlation between WDS produced by putrescine and increase in brain vascular permeability. Furthermore they show that morphine can affect brain vascular permeability.     

The effect of morphine, naloxone, D- and L-aspartic acid on the brain and lung ACE in mice

The brain and lung angiotensin converting enzyme (ACE) activities of the mice injected with 10 mg/kg morphine and/or naloxone, 200 mg/kg D- and/or L-aspartic acid were spectrophotometrically determined. Morphine, naloxone, D- and L-aspartic acid alone inhibited both brain and lung ACE activities whereas the combinations of morphine with naloxone, D-aspartic acid with L-aspartic acid and morphine with naloxone + L-aspartic acid showed no inhibitory effect on the brain ACE. While naloxone or L-aspartic acid partly antagonized the suppression of morphine on the lung ACE their combination completely prevented morphine from inhibiting the lung ACE. In the in vivo experiments performed on the brain and lung homogenates of the untreated mice the determination of the ACE activity in the incubating media containing 3.10(-3) M morphine or naloxone, 10(-2) M D- or L-aspartic acid showed a significant decrease in the activity. But no in vitro antagonistic effect was found by using the combinations of the drugs used in the study. The antagonism seen in the in vivo experiments was considered as an indirect one. And the relationship between the inhibitory effect of morphine, naloxone and D-aspartic acid, their suppressive effect on drinking and their beneficial effects in various forms of shock was discussed.     

Involvement of Opioid Receptors in Shaking Behaviour Induced by Paraquat in Rats

Paraquat (30-70 mg/kg intraperitoneally) caused typical shaking behaviour in rats in a dose-dependent manner. Myoclonus also appeared after the shaking behaviour in several rats treated with the highest dose of paraquat. Morphine (5 mg/kg intraperitoneally, 30 min. before paraquat) significantly reduced the frequency of shaking behaviour. The alleviation by morphine disappeared when naloxone (1.5 mg/kg intraperitoneally 15 min. after morphine) was coadministered. Although there was no histological change in brain slices of paraquat-treated rats (70 mg/kg intraperitoneally), the fluorescein uptake into brain was increased by the treatment. Morphine prevented the increase of fluorescein uptake, but naloxone failed to antagonize this effect. On the other hand, intracerebroventricularly administered paraquat (25.7 μg/rat) caused tremor in all rats, but not shaking behaviour nor myoclonus. These findings suggest that paraquat administered systemically as well as centrally may be toxic to the brain. Although the actions of paraquat on the brain seem to be complicated, opioid receptors may play a role in the actions.     

Morphine-induced inhibition of different pain responses in relation to the regional turnover of rat brain noradrenaline and dopamine

The influence of morphine on different pain reactions integrated at different levels of the central nervous system was studied in rats together with the determination of the turnover rate of noradrenaline and dopamine in discrete areas of the brain.Morphine was found to increase the thresholds for vocalisation and vocalisation afterdischarge leaving the threshold for motor response unaffected. The effect of morphine on the threshold for vocalisation was found to be antagonized by naloxone and yohimbine and increased by -methyl-p-tyrosine, FLA 63, phenoxybenzamine, chlorpromazine and pimozide. The effects on the threshold for vocalisation afterdischarge were antagonized by naloxone, and reduced by -methyl-p-tyrosine, pimozide and chlorpromazine and were enhanced by phenoxybenzamine and yohimbine. Atropine did not change the morphine effect on either threshold. Morphine (5 mg/kg s.c.) was found to increase the turnover rate of dopamine in the telencephalic cortex and the diencephalons-mesencephalon-striatum and that of noradrenaline in the medulla oblongata-pons region. Both increases were antagonized by naloxone.The ability of morphine to increase the threshold for vocalisation afterdischarge (proposed to reflect the emotional component of pain reactions) is suggested to be closely related to the increased turnover of dopamine in limbic structures of the brain, most probably by an increased release of this transmitter. The effect of morphine on the threshold for vocalisation remains to be evaluated but a decreased activity of noradrenaline and dopamine neurotransmission was found to increase the morphine effect on this threshold.     

The effects of acutely administered analgesics on the turnover of noradrenaline and dopamine in various regions of the rat brain

1 Noradrenaline and dopamine turnover rates were determined following blockade of synthesis by alpha-methyl-p-tyrosine. Morphine, pentazocine and methadone had no effect on steady state levels or on turnover of noradrenaline in whole brain and in the hypothalamus. Although morphine was without action on medulla-pons noradrenaline steady state levels, a drug-induced increase in turnover rate was observed which was antagonized by pretreatment with naloxone (5 mg/kg). Pentazocine and methadone failed to alter either the steady state level of noradrenaline in the medulla-pons or its turnover rate.2 Morphine accelerated the decline in striatal alpha-methyl-m-tyramine levels following subcutaneous injection of alpha-methyl-m-tyrosine 18 h previously.3 All three drugs increased the turnover of dopamine in whole brain and corpus striatum although the striatal effect was prevented by naloxone pretreatment. The minimum doses of morphine, pentazocine and methadone required to elicit a significant effect on striatal dopamine turnover were 10 mg/kg, 30 mg/kg and 10 mg/kg respectively.4 The possibility of a dopaminergic involvement in the antinociceptive effect of analgesics is discussed.     

Acute effects of morphine on rat intestinal motility

Systemic injection of morphine (0.5–16 mg/kg) caused dose-related increases in intestinal intraluminal pressure in anesthetized rats. Injection of morphine into cerebral ventricles was no more effective than the intravenous (i.v) route. Decapitation of the animals did not prevent the intestinal stimulatory effect of i.v. morphine. The intestinal stimulation induced by i.v. morphine and 5-hydroxytryptamine (5-HT), but not that induced by cholecystokinin octapeptide, was antagonized by methysergide. Morphine appears to stimulate contractions of intestinal circular muscle in the rat by release of local, endogenous 5-HT.     

The effects of narcotic analgesics on the turning behaviour of rats with 6-hydroxydopamine-induced unilateral nigro-striatal lesions

Morphine at 5, 10 and 20 mg/kg intraperitoneally caused a dose-dependent, naloxone-reversible, antagonism of d-amphetamine-induced ipsilateral circling in rats lesioned with 6-hydroxydopamine in one substantia nigra. Morphine (10 mg/kg) weakly antagonized apomorphine-induced contralateral circling. Morphine, levorphanol and phenazocine were potent antagonists of d-amphetamine-induced circling in rats with a 6-hydroxydopamine lesion of one neostriatum. Pentazocine, pethidine and ethyl-ketocyclazocine were weak antagonists. It is proposed that a major action of morphine and some closely related opiate analgesics is to reduce the release of dopamine from nigro-striatal nerve terminals in the rat by acting upon specific opiate receptors.     

EFFECTS OF MORPHINE ON BRAIN HISTAMINE, ANTINOCICEPTION AND ACTIVITY IN MICE

1. The effect of morphine on the histamine content of the mouse brain has been investigated. The changes in the brain histamine level have been related to morphine-induced analgesia and morphine-induced changes in locomotor activity. 2. With doses of morphine between 1 and 5 mg/kg there was a significant increase in histamine levels. The time required to produce a maximal rise in the brain histamine level with 5 mg/kg of morphine was 15 min. 3. There was a significant decrease in brain histamine levels with doses of morphine between 7.5 and 100 mg/kg. The time at which the greatest decrease was produced with 50 mg/kg was 30 min. 4. The time course of the alteration of brain histamine by morphine did not correlate with its antinociceptive activity. Both the 5 and 50 mg/kg doses of morphine produced analgesia in mice whereas brain histamine levels were increased and decreased, respectively. 5. Pretreating mice with compounds which modify histaminergic function did not modify the antinociceptive action of morphine. 6. Morphine produced a biphasic effect on locomotor activity when the dose was increased from 0.5 through to 100 mg/kg. Doses up to 2.5 mg/kg caused a reduction of activity and doses above this produced significant increases. 7. There appears to be an inverse relationship between the morphine-induced changes of brain histamine and the morphine-induced changes in locomotor activity.     

Central monoaminergic changes induced by morphine in hypoalgesic and hyperalgesic strains of domestic fowl.

The present research examined morphine dose-response effects on both the formalin test and on CNS monoamine (MA) levels and the metabolites dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in hypoalgesic (76) and hyperalgesic (SN) strains of domestic fowl. Morphine produced a significant hypoalgesic response in the 76 strain at 15-45 mg/kg and a significant hyperalgesic response in the SN strain at 5-10 mg/kg. In subsequent experiments, analyses of whole brain (minus tectum), brainstem, and spinal cord MA, DOPAC, and 5-HIAA via high-performance liquid chromatography with electrochemical detection (HPLC-EC) were performed following morphine administration in both the 76 and SN strains. Morphine produced a significant elevation of brain dopamine (DA) and a significant elevation of brain, brainstem, and spinal cord serotonin (5-HT) in both the 76 and SN strains. Morphine elevated brain norepinephrine (NE) in the 76 strain. However, morphine failed to affect brain NE in the SN strain. This distinct morphine effect on brain NE differentiates strain-dependent hypoalgesia and hyperalgesia in domestic fowl.     

Effects of Selective Opioid Receptor Antagonists on Morphine-Induced Changes in Striatal and Limbic Dopamine Metabolism

Abstract: The effects of selective opioid receptor antagonists, β-funaltrexamine (selective for μ receptor), naloxonazine (μl) and naltrindole (δ) on morphine-induced changes in striatal and limbic dopamine (DA) metabolism were studied in rats. β-Funaltrexamine (20 μg intracerebroventricularly) and naloxonazine (15 mg/kg intraperitoneally) were given 24 hr before morphine (15 mg/kg subcutaneously), and the rats were decapitated 60 min. after morphine. Naltrindole (1 mg/kg intraperitoneally) was given twice, 15 min. before and after morphine. Morphine significantly increased the concentrations of DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). This effect was significantly antagonized by pretreatment with β-funaltrexamine but not by naloxonazine or naltrindole. However, naloxonazine attenuated the antinociceptive effect of morphine in the hot-plate test. The concentration of DA was not significantly altered by any of the drugs studied. These results show that selective blockade of μ-opioid receptors totally blocks the increase of striatal and limbic DA metabolism induced by morphine. It seems that μ2-subtype of μ-opioid receptor predominantly mediates this effect. Blockade of δ-opioid receptor did not alter these effects of morphine.     

Involvement of opioid mu1-receptors in opioid-induced acceleration of striatal and limbic dopaminergic transmission.

The role of mu1-opioid receptors in the acceleration of cerebral dopaminergic transmission induced by morphine and the putative mu1-opioid agonist, etonitazene, was studied in rats by measuring the tissue levels of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the dorsal striatum and nucleus accumbens. The striatal extracellular concentrations of DA and its metabolites in freely moving rats were estimated as well. Morphine (3 mg/kg) and etonitazene (2.5 microg/kg) increased the striatal and accumbal dopamine metabolism as measured by the tissue ratios of DOPAC/DA and HVA/DA. The mu1-opioid receptor antagonist, naloxonazine (15 mg/kg), significantly antagonized these elevations except the morphine-induced elevation of striatal HVA/DA ratio. Both morphine (3 mg/kg) and etonitazene (1, 2.5, and 5 microg/kg) elevated the striatal extracellular DA, DOPAC, and HVA. Naloxonazine antagonized the effects of morphine and etonitazene on striatal extracellular DA concentration as well as etonitazene's effects on DOPAC and HVA, but not morphine's effects on DOPAC and HVA. As we previously showed concerning morphine, the conditioned place preference induced by etonitazene was inhibited by naloxonazine. These findings emphasize the role of mu1-opioid receptors in opioid reward, in which the mesolimbic dopaminergic system is considered to be importantly involved. Our results clearly show that in addition to the mesolimbic dopaminergic system the mu1-opioid receptors are also involved in the control of nigrostriatal DA release and metabolism. However, the effects of etonitazene on the striatal DA differ from those of morphine, suggesting that the opioid mechanisms regulating these two DA systems differ.     

Modification of serotonin metabolism in rat brain after acute or chronic administration of morphine

The steady state concentration of 5-hydroxyindoleacetic acid (5-HIAA) was elevated in rat brain for at least 4 hr after administration of a single dose of morphine sulfate (30 mg/kg, s.c.), and for more than 40 hr after subcutaneous implantation of pellets of morphine alkaloid. The concentration of 5-HIAA returned to normal 3 days after pellet implantation at a rate that paralleled the development of tolerance to the analgesic and other overt actions of morphine. Morphine did not modify the steady state concentration of serotonin under any of the treatment conditions. The turnover of brain serotonin was increased significantly during the 90-min period following a single injection of morphine sulfate (30 mg/kg, s.c.), as indicated by an increased rate of accumulation of 5-HIAA after blockade of efflux of 5-HIAA by probenecid in morphinetreated animals. As judged either by the rate of accumulation of 5-HIAA after administration of probenecid, or by the rate of accumulation of serotonin after treatment with pargyline, an increase in turnover of serotonin was evident in brains of tolerant rats 72 hr after pellet implantation. The rate of efflux of 5-HIAA from the brain was the same in control and morphine-tolerant rats. These results indicate that changes in brain serotonin metabolism are associated with both the acute effects of morphine and with morphine tolerance.     

Effect of dopaminergic stimulation or blockade on morphine-withdrawal aggression

The effects of morphine (10 mg/kg), nalorphine (1 and 10 mg/kg), and naloxone (1 mg/kg) were studied on the neocortical release of acetylcholine (ACh) in midpontine pretrigeminal transected rats. Morphine and, to a lesser extent, nalorphine decreased ACh release. Naloxone was ineffective alone but antagonized the action of morphine.Predoctoral fellow with scholarships from Laval University and Province of Quebec, Canada.This research was supported in part by USPHS grant MH-11846.     

Comparison of the antinociceptive activities of physostigmine, oxotremorine and morphine in the mouse

1. Morphine, oxotremorine and physostigmine showed antinociceptive activity in mice using the hot plate reaction time test.2. The action of morphine, but not that of oxotremorine, was antagonized by naloxone and by nalorphine, whereas the effect of physostigmine was unaffected by naloxone and increased by nalorphine.3. The antinociceptive effects of morphine and of physostigmine were increased by procedures reported to increase the ratio of 5-hydroxytryptamine to dopamine in the brain. It was decreased by procedures reported to cause a fall in brain 5-hydroxytryptamine or a rise in dopamine relative to 5-hydroxytryptamine.4. The antinociceptive effect of oxotremorine was potentiated by procedures reported to decrease brain noradrenaline and was unaffected by procedures altering brain 5-hydroxytryptamine.5. The results suggest differences in the mode of action of morphine and physostigmine on the one hand and of oxotremorine on the other.