Direct correlation between level of morphine and its biochemical effect on monoamine systems in mouse brain. Evidence for involvement of dopaminergic neurons in the pharmacological action of acute morphine

Morphine-induced conditioned place preference and effects of morphine pre-exposure in adolescent and adult male C57BL/6J mice

RATIONALE

Given the increasing abuse of prescription opioids, particularly in adolescents, surprisingly few preclinical studies have explored effects of opioids in adolescents (versus adults).

OBJECTIVES

This study compared the conditioned rewarding effects of morphine, without (experiment 1) and with morphine pre-exposure (experiment 2), in adolescent and adult male mice.

METHODS

Experiment 1: On each of three consecutive days, one of the two conditioning sessions was preceded by an injection of a particular dose of morphine (0.1, 0.32, 1, 3.2, 10, 32, or 100 mg/kg, intraperitoneal) and the other by saline; place preference was tested on day 4. Experiment 2: Mice received once daily injections of saline or a particular dose of morphine (17.8 or 56 mg/kg) for 4 days, and 3 days later, place conditioning with morphine (0.32, 1, 3.2, or 10 mg/kg) began.

RESULTS

In both experiments, morphine induced conditioned place preference along similar inverted U-shaped dose-response curves in adolescent and adult mice, with maximal effects between 0.32 and 10 mg/kg. Morphine pre-exposure did not sensitize morphine-induced conditioned place preference; instead, tolerance occurred, but only in adults. Adolescents were more sensitive than adults to morphine-induced locomotor stimulation. Response to novelty predicted the locomotor stimulating effects of morphine in adolescents, but not its rewarding effects.

CONCLUSIONS

The rewarding effects of morphine were similar in adolescent and adult mice but showed differential tolerance after morphine pre-exposure. Adolescents were more sensitive than adults to the acute locomotor stimulating effects of morphine, consistent with dopamine systems involved in locomotor activity being overactive during adolescence.

Temporal and anatomic patterns of immediate-early gene expression in the forebrain of C57BL/6 and DBA/2 mice after morphine administration

Although morphine was previously reported to produce an instant induction of c-fos in the striatum, our recent studies have demonstrated that the expression of numerous immediate early genes (IEGs) is significantly elevated at delayed time-points (several hours) after morphine administration. To better dissect the time-course of opioid-produced IEG induction, we used in situ hybridization to examine the expression of the IEGs c-fos, zif268 and arc in the mouse forebrain at several time-points after acute morphine injection. To link drug-produced behavioral changes with the activity of specific neuronal complexes, this study was performed comparatively in the C57BL/6 and DBA/2 mouse strains, which differ markedly in their locomotor responses to opioids and opioid reward. Our study demonstrates that morphine produces two episodes of IEG induction, which are separate in time (30 min vs. 4-6 h) and which have different neuroanatomic distribution. At 30 min, one or more IEGs were induced in circumscribed subregions of the dorsal striatum (dStr) and of the nucleus accumbens (NAc) shell, as well as in the lateral septum. The observed inter-strain differences in IEG expression at 30 min support earlier proposals that activation of the dorsomedial striatum may mediate morphine-elicited locomotor stimulation (both effects were present only in the C57BL/6 strain). In contrast, NAc shell activation does not appear to be linked to morphine-elicited changes in locomotor behavior. The second IEG induction (of arc and of zif268) was more widespread, involving most of the dStr and the cortex. The second IEG induction peaked earlier in the DBA/2 mice than in the C57BL/6 mice (4 h compared with 6 h) and displayed no apparent relation to locomotor behavior. This delayed episode of IEG activation, which has largely been overlooked thus far, may contribute to the development of long-term effects of opioids such as tolerance, dependence and/or addiction.

Comparison of the effect of levodopa and bromocriptine on naloxone-precipitated morphine withdrawal symptoms in mice

In this study, the effect of l-dopa and bromocriptine on morphine withdrawal syndrome was compared. Both l-dopa (125, 250 mg/kg, i.p.) and low doses of bromocriptine (0.04, 0.08 mg/kg, i.p.) potentiated naloxone-induced morphine withdrawal symptoms such as jumping, climbing and rearing in mice. Higher doses of bromocriptine (0.16, 0.32 mg/kg, i.p.) attenuated these naloxone-induced symptoms. SKF 83566, D(1) dopamine antagonist (0.4, 0.8 mg/kg, i.p.) and sulpiride, D(2) dopamine antagonist (5, 10 mg/kg, i.p.) when used alone, also produced inhibitory effects on naloxone-induced morphine withdrawal symptoms. Pretreatment with sulpiride (5, 10 mg/kg, i.p.) and SKF 83566 (0.4, 0.8 mg/kg, i.p.) attenuated the potentiating effects of l-dopa on withdrawal symptoms significantly. Pretreatment with sulpiride also decreased the potentiating effect of bromocriptine and reinforced the inhibitory action of it, but SKF 83566 pretreatment just reinforced the effect of higher doses of bromocriptine. Concurrent pretreatment of animals with sulpiride (10 mg/kg, i.p.) and SKF 83566 (0.8 mg/kg, i.p.) markedly decreased the potentiating effects of l-dopa and bromocriptine and reinforced the inhibitory action of bromocriptine on the naloxone-induced morphine withdrawal syndrome. Prazosin, alpha(1) antagonist (1, 2 mg/kg, i.p.) decreased the naloxone-induced morphine withdrawal syndrome significantly. Pretreatment with yohimbine, alpha(2)-antagonist (5 mg/kg, i.p.) reversed the inhibitory effects of bromocriptine (0.16, 0.32 mg/kg, i.p.) on naloxone-induced morphine withdrawal syndrome significantly. In conclusion, our results show that bromocriptine at lower doses (0.04, 0.08 mg/kg, i.p.) acts similar to l-dopa, but at higher doses (0.16, 0.32 mg/kg, i.p.) shows different effects on naloxone-induced morphine withdrawal syndrome which may be due to the interaction of bromocriptine with alpha-adrenoceptors. Copyright 2000 John Wiley & Sons, Ltd.

Dexamethasone pretreatment reduces the psychomotor stimulant effects induced by cocaine and amphetamine in mice

1. The present study examined a comparison of the effect of DEX on psychomotor stimulant effects of cocaine and amphetamine in mice by using the locomotor activity test. 2. Cocaine (10 mg/kg/i.p.) and amphetamine (5 mg/kg/i.p.) increased markedly locomotor activity of mice whereas DEX per se (0.1-1.0-10 mg/kg/i.p.) did not modify the activity of control mice. 3. DEX pretreatment decreased the stimulating effects induced both by cocaine and amphetamine but no consistent dose-related effects were observed. 4. The results suggest that DEX may play an important role on the stimulating effects of cocaine and amphetamine and that it may be of some utility in the clinical management of psychostimulants abuse.

Behavioral significance of phasic changes in mesolimbic dopamine-dependent electrochemical signal associated with heroin self-injections

High-speed chronoamperometry with monoamine-selective carbon fiber electrodes was used in rats to monitor, during 5-6 consecutive daily sessions, changes in DA-dependent electrochemical signal in the nucleus accumbens (NAcc) during intravenous heroin (0.1 mg/kg) self-administration (SA) behavior and passive repeated drug injections performed with a temporal scheme similar to that in the SA experiment. In trained animals, biphasic signal fluctuations time-locked to the individual lever-presses were found to accompany all but the first daily SAs. The signal gradually increased by 30-40 nM for the 10 minutes preceding the SA, reached a peak at the moment of lever-press and decreased abruptly by approximately 40 nM for 3-4 min after heroin SA. The cycle then repeated, reaching a new peak at the moment of the next lever-press. Rapid bi-directional fluctuations in signal associated with individual heroin SAs were superimposed on substantial tonic increase in signal baseline (400-500 nM). This increase quickly developed after presentation of heroin-related light cue and the first SA, was relatively stable during all subsequent SAs and decreased towards the baseline after the last SA of a session. Changes in signal baseline induced by repeated heroin SAs depended strongly upon the signal's basal level (r = -0.787); that signal preferentially increased when its basal values were low (0-300 nM), and decreased when signal was tonically elevated (> 600 nM). Repeated passive heroin injections also induced biphasic signal fluctuations and a similar tonic increase in signal baseline. Although a transient signal decrease (25 nM for 2-4 minutes) followed by a prolonged signal increase occurred after each but not the first passive injection, the gradual pre-injection signal acceleration was absent. Although DOPAC, a principal DA metabolite, may significantly contribute to the tonic increase in electrochemical signal seen during SA session, the changes in extracellular DA may be the main contributor to both the rapid signal increases preceding drug-taking and the transient signal decreases following heroin SA. If so, the present findings suggest that activation of mesolimbic DA cells and increase in DA transmission may be involved in the mediation of motivational and/or activational components of drug-seeking and drug-taking behavior. An acute termination of previous drug- and behavior-associated DA activation with a transient inhibition of DA release, immediately following heroin SA may correlate with the drug's rewarding action, representing a part of a mechanism regulating drug-taking behavior.

Naloxone affects both pharmacokinetics and pharmacodynamics of morphine. Application of direct correlation analysis

Direct correlation analyses between the distribution of morphine (pharmacokinetics) and the biochemical effects of the drug on monoamine metabolism (pharmacodynamics) are reported for dissected regions of the brain. Determinations of morphine and monoamine-related substances were carried out in the same sample by high performance liquid chromatography with electrochemical detection. Naloxone, an antagonist of morphine, significantly shortened the biological half lives of morphine in both the blood and brain tissue. Such pharmacokinetic behavior appeared to be related to the contractive effect of morphine on the bile duct, and naloxone facilitated the excretion of morphine via this route. In the striatum, significant correlations were observed between the concentrations of the metabolites of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and morphine with a shift to the right in the concentration-response curve on naloxone treatment indicating competitive antagonism. While significant correlations were also observed in this brain region for the metabolites of noradrenaline, 3-methoxy-4-hydroxyphenylethylene glycol (MOPEG), and 5-hydroxytryptamine, 5-hydroxyindoleacetic acid (5-HIAA), a shift to the right did not occur. Significant correlations and shifts were noted for DOPAC, HVA and MOPEG in the hypothalamus. However, no correlation was found between the concentrations of 5-HIAA and morphine in this region. In other regions such as the hippocampus and medulla oblongata, similar correlations and shifts were not observed for MOPEG and 5-HIAA or for DOPAC and HVA.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of morphine-induced analgesia, tolerance and dependence by bromocriptine

The effect of two doses of bromocriptine, a dopamine agonist, on morphine-induced analgesia, tolerance and dependence was investigated in mice. Bromocriptine at doses of 0.04 and 0.08 mg/kg did not affect the baseline tail flick latency of mice but potentiated the morphine analgesia. Pretreatment of mice with 5 mg/kg of sulpiride, a D-2 antagonist, not only blocked the effect of 0.08 mg/kg of bromocriptine but also antagonized the morphine analgesia. Control animals given daily injections of 10 mg/kg of morphine rapidly developed tolerance to the analgesic effect. A combined treatment of bromocriptine with morphine given daily suppressed the development of tolerance to morphine analgesia. However, development of tolerance to morphine analgesia was not significantly modified in the animals treated daily with bromocriptine (0.08 mg/kg) plus sulpiride (5 mg/kg). Acute dependence was induced by the administration of 100 mg/kg of morphine. The administration of bromocriptine 30 min before naloxone significantly decreased the ED50 value for naloxone for inducing jumping in mice. Coadministration of sulpiride and bromocriptine attenuated the ability of bromocriptine to potentiate the withdrawal syndrome of morphine dependence. The results indicate that bromocriptine potentiates morphine analgesia, suppresses the development of tolerance to morphine analgesia but exacerbates opiate withdrawal signs in morphine-dependent mice. These effects of bromocriptine appear to be mediated via D-2 receptors.

Neurophysiology and neurochemistry of drug dependence: a review

To understand the neurophysiological and neurochemical mechanisms of drug dependence, the functional significance of dopamine, noradrenaline and endogenous opioid peptides in the mediation of natural, self-stimulation and pharmacological reinforcement are discussed. Data on search of system(s), mediator(s) and neurons of reinforcement as well as my own notions on reinforcement as a critical element in organization and regulation of the organism's adaptive activity in variable environments are presented. The role of chronic drug-induced stable modification of central neurochemical systems' functioning as a basis for the alteration of endogenous reinforcement processes and raising drug dependence are examined in detail for main addictive drugs, opiates and psychomotor stimulants.

Effect of barbitone sodium and thiopental sodium on brain dopamine, noradrenaline, serotonin and 5-hydroxyindoleacetic acid content in Arvicanthis niloticus

The quantitative estimation of total dopamine (DA), noradrenaline (NE), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content in the whole brain tissue of normal Nile grass rat, Arvicanthis niloticus, gives and average of 631 +/- 12 ng DA/g, 366 +/- 12 ng NE/g, 617 +/- 15 ng 5-HT/g and 431 +/- 10 ng 5-HIAA/g fresh brain tissue. The effect of barbitone sodium and thiopental sodium on the total DA, NE, 5-HT and 5-HIAA content in the brain tissue of the Nile grass rat, Arvicanthis niloticus, was studied. The total DA, NE, 5-HT and 5-HIAA contents were determined 5 hr after i.p. injection of different doses of barbitone sodium (20, 40 and 80 mg/ml/100 g body wt) and thiopental sodium (5, 10 and 20 mg/ml/100 g body wt). The effect of different time intervals (1, 10, 30 min, 1, 2.5, 5, 8, 16, 24 and 48 hr) on the total brain DA, NE, 5-HT and 5-HIAA content was investigated after i.p. injection of 40 mg of barbitone sodium and 10 mg of thiopental sodium/ml/100 g body wt. Both barbitone sodium and thiopental sodium caused an increase in DA, NE and 5-HT content and a decrease in 5-HIAA content in the brain tissue of Arvicanthis niloticus. The increase in the whole brain contents of DA, NE and 5-HT after the administration of barbitone sodium and thiopental sodium may be due either to inhibition of transmitter release by an action at the monoamine nerve terminal or to effects causing a decrease in nerve impulse flow. On the other hand, the decrease in 5-HIAA may be due to the decrease in the turnover of 5-HT.

Simultaneous determination of the pharmacokinetics and pharmacodynamics of chlorpromazine in the brain of mice

The direct correlation analyses between the distribution of chlorpromazine (pharmacokinetics) and the biochemical effects of the drug on monoamine metabolisms (pharmacodynamics) are reported. Both samples for quantitative determination of CPZ and of monoamine transmitters and metabolites were obtained by organic extraction procedures from the same sample. The determinations were carried out by high performance liquid chromatography with electrochemical detection. CPZ affected the concentrations of metabolites of noradrenaline, dopamine and 5-hydroxytryptamine, but not those of the monoamine transmitters themselves. However, simultaneous assay demonstrated differences in effects of the drug on the transmitter systems. The concentrations of HVA and DOPAC were increased over a wide range of intracerebral concentrations of the drug, but those of MOPEG, in the range of higher concentrations. On the other hand, CPZ did not reveal any correlations between the intracerebral concentrations of the drug and 5-HIAA. These results suggest that CPZ affected primarily the dopaminergic system rather than the serotonergic one in the early stage of its biochemical actions. The proposed procedure is demonstrated to be simple and useful as a new approach in biochemical pharmacology. The same procedure can be applicable for other centrally acting drugs.

Increased sensitivity to dopamine agonists following a single dose of morphine or levorphanol in mice

Acute administration of an opiate has been suggested to result in the development of supersensitive dopamine receptors. This hypothesis was tested in mice by determining the effect of a single administration of morphine or levorphanol on dopamine agonist-induced stereotypic behaviors and [3H]spiroperidol binding. Administration of morphine (1.0 mg/kg s.c.), which itself had no significant effect on spontaneous locomotor activity 3 h following administration, significantly potentiated locomotor activity induced by 1.5 or 4.5 mg/kg of apomorphine (i.p.) administered 3 h later. Morphine (10 mg/kg, s.c.) or levorphanol (0.2 and 2.0 mg/kg, s.c.), but not dextrorphan (up to 20 mg/kg, s.c.), enhanced climbing behavior induced by apomorphine (i.p.) or (-)-N-n-propylnorapomorphine (i.p.; NPA) administered 3 h later. An increase in whole brain and striatal [3H]spiroperidol binding sites was found 3 h after administration of 10 mg/kg of morphine. Concurrent administration of 5 mEq/kg of LiCl (i.p.) or 5 mg/kg of naloxone (i.p.; administered twice) attenuated both the potentiation of the climbing behavior induced by the two dopamine agonists and the increase in [3H]spiroperidol binding sites. These results suggest that a single administration of an opiate can induce the development of supersensitive dopamine receptors that is mediated by an interaction at opioid receptors.

Changes in 5-HIAA and 5-HT levels in lumbar CSF following morphine administration to conscious dogs

Monoamine metabolites in the lumbar cerebrospinal fluid were measured by high-performance liquid chromatography with electrochemical detection (HPLC-ECD) in 6 conscious dogs after administration of morphine. The concentrations of dopamine and its metabolites exhibited only small variations whereas a significant increase in serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) occurred after a latency of 5 min and culminated after 1 h. The increased release of 5-HT and 5-HIAA and behavioral changes (restlessness, sialorrhea) induced by morphine were prevented by administration of naloxone or nalorphine.