Discrete cues paired with naloxone-precipitated withdrawal from acute morphine dependence elicit conditioned withdrawal responses

Acute bolus doses of morphine induce a state of acute opioid dependence as measured by naloxone-precipitated withdrawal. Repeated morphine and precipitated withdrawal experience further enhances naloxone-induced withdrawal severity, partly because of direct neuroadaptation to repeated morphine, and partly because of conditioned associations of context and withdrawal experience. To determine whether a discrete tone/light conditioned stimulus could elicit conditioned withdrawal responses in acute dependence, rats trained on a fixed-ratio-15 operant schedule for food reward received morphine (5.6 mg/kg) 4x at daily or weekly intervals, with each morphine injection followed at 4 h by naloxone (1.0 mg/kg) and an operant session. The conditioned stimulus was presented to a Paired group after each naloxone injection. Separate control groups experienced the conditioned stimulus either at a different time of the day or on a different day of the week than naloxone (Unpaired), received naloxone without any conditioned stimulus exposure [Paired-no conditioned stimulus (Paired-NO CS)] or received vehicle instead of naloxone before conditioned stimulus presentation (NaI-Naive). On the test day, all rats received vehicle before conditioned stimulus exposure. The conditioned stimulus alone reliably suppressed responding in Paired groups relative to control conditions with either daily or weekly intervals between conditioning sessions. The administration of morphine 4 h before conditioned stimulus exposure on the test day was not necessary to observe conditioned withdrawal. Thus, conditioned withdrawal is reliably established to discrete cues associated with naloxone-precipitated withdrawal from acute, infrequent (weekly) opioid exposure.     

Voluntary morphine ingestion, morphine dependence, and recovery from withdrawal signs.

We are reporting on conditions (without forced drinking or premedications) where rats voluntarily drink high quantities of sucrose-morphine solutions in preference to water. The volume ingested is inversely related to the morphine concentration in the liquid. The morphine antagonist, nalorphine, produced a clear set of opiate withdrawal signs in these (voluntarily) morphine-drinking rats. The severity of withdrawal signs was a function of the amount of ingested morphine. The present finding is the first report to show that rats ingest high quantities of sucrose-morphine without premedication or forced hydration procedures.     

Opiate dependence following acute injections of morphine and naloxone: The assessment of various withdrawal signs

The injection of high dose of naloxone 15 minutes after a single injection of morphine in mice was found to produce a jumping response which was behaviorly similar to the jumping response observed during the withdrawal from chronic morphine administration. In addition the jumping response following the acute administration of morphine-naloxone was increased by the injection of atropine and attenuated by oxotremorine. These data are consistent with the reports of effect of these cholinergic drugs on the jumping response which occurred during withdrawal after chronic morphine administration. However, other symptoms associated with opiate withdrawal (hypothermia, weight loss and diarrhea) were not produced by the acute injection of morphine-naloxone. It is therefore suggested that this single injection paradigm is particular to the jumping response than a demonstration of the rapid development of opiate dependence.     

Selective potentiation by ouabain of naloxone-induced withdrawal contractions of isolated guinea-pig ileum following acute exposure to morphine

1. Ouabain, an inhibitor of Na⁺/K⁺ ATPase induces the release of acetylcholine from central and myenteric cholinergic neurones principally due to partial depolarization of the cell membrane. The effect of ouabain has been examined on neurogenic contractions in the guinea-pig ileum arising from either electrical field stimulation or from naloxone in morphine-exposed preparations.
2. Guinea-pig isolated ileum preparations were stimulated transmurally (0.1 Hz, 0.3 ms, 200 mA) to elicit contractions of the myenteric plexus-longitudinal smooth muscle.
3. Incubation with morphine (0.3 μM, 60 min) was followed by naloxone (1 μM) which produced withdrawal contractions in 16/26 preparations (median of 10.7 [2.2–40.0]% of a maximal contracture to KCl (60 mM)).
4. In parallel experiments, ouabain (1 μM) was added to the tissue before exposure to morphine (0.3 μM, 60 min). Naloxone (1 μM) subsequently displayed a withdrawal contraction in all 26/26 tissues (57.9 [30.5–151.7]% of a maximal contracture to KCl (60 mM).
5. Ouabain neither affected the concentration-dependent contractions of guinea-pig ileum produced by carbachol nor the inhibition of electrically-evoked contraction produced by morphine (0.3 μM).
6. The muscarinic antagonist atropine (0.1 μM) antagonized control naloxone withdrawal responses. The atropine resistant component, evident in ouabain-treated tissues, was blocked by SR140333((S)1-{2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)piperidin-3-yl]ethyl}-4-phenyl-1-azoniabicyclo[2.2.2]octane, chloride), a substance P antagonist.
7. Clonidine (α₂-adrenoceptor agonist) inhibited electrically-evoked contractions. Exposure to the α₂-adrenoceptor antagonist RX811059 (2-(2-ethoxy-1,4-benzodioxan-2-yl)-2-imidazoline), resulted in a contracture which was not significantly enhanced by ouabain (1 μM).
8. Ouabain selectively potentiates the naloxone-induced withdrawal contraction following acute exposure to morphine the major components of which are mediated by both acetylcholine and substance P.

     

Involvement of glial glutamate transporters in morphine dependence and naloxone-precipitated withdrawal

A body of evidence supports that excitatory amino acid systems, particularly glutamatergic one, participate in morphine dependence and naloxone-precipitated withdrawal. In this study, we examined the involvement of glial glutamate transporters, GLT-1 and GLAST, in them. Rats were rendered morphine-dependent by subcutaneous implantation of two 75 mg morphine pellets for 5 days. Intracerebroventricular administration of DL-threo-beta-benzyloxyaspartate, a glutamate transporter inhibitor significantly facilitated various naloxone-precipitated withdrawal signs. By northern blot analysis, the expression of GLT-1 mRNA was found to decrease significantly in the striatum and thalamus of morphine-dependent rats, and to increase significantly in the striatum 2 hr after the naloxone-precipitated withdrawal. On the other hand, there were no significant changes in GLAST mRNA levels in any brain regions. In vivo microdialysis experiments revealed that the extracellular glutamate levels was elevated in the striatum and nucleus accumbens, in which the changes of GLT-1 mRNA level were observed, during naloxone-precipitated morphine withdrawal. In cultured astrocytes, the expression of GLT-1 mRNA was regulated by agents activating the cAMP pathway, as well as beta-adrenergic agonist and dopamine, but not morphine. These results suggest that the changes of GLT-1 expression, which alter the glutamate uptake and affect the glutamatergic transmission efficiency, play a role in the development of morphine dependence and the expression of morphine withdrawal.     

Repeated experience with naloxone facilitates acute morphine withdrawal: potential role for conditioning processes in acute opioid dependence

Single injections with morphine can induce a state of acute opioid dependence in humans and animals, typically measured as precipitated withdrawal when an antagonist such as naloxone is administered 4-24 h after morphine. Repeated treatment with morphine at 24-h intervals can result in a progressive shift in potency of naloxone to produce such acute withdrawal signs, including suppression of operant responding for food reward. The current study characterized fully both morphine and naloxone dose-effect functions in an effort to establish the relative contributions of repeated morphine vs. repeated naloxone (Nal) experience to these potency shifts. Rats trained on an FR15 schedule for food received four vehicle or morphine injections (0.56-5.6 mg/kg sc), spaced 24 h apart. Four hours after each morphine pretreatment (Repeat Nal), or 4 h after the fourth and final morphine pretreatment only (Single Nal), a cumulative dose-effect function for naloxone-induced suppression of responding was determined. Vehicle-pretreated (Morphine Naive) rats showed little change in the naloxone dose effect function even after four cumulative dose-effect determinations. By contrast, a progressive increase in naloxone potency was observed following successive pretreatments with morphine under Repeat Nal conditions, and the magnitude of naloxone potency shift was morphine dose dependent. At a morphine dose of 5.6 mg/kg, repeated naloxone experience in the presence of morphine was not an absolute requirement to produce an increase in naloxone potency across days, but repeated naloxone could potentiate the magnitude of the observed shift, indicating both experience-independent and experience-dependent processes at work. At lower doses of morphine (1.0 and 3.3 mg/kg) no shift in naloxone potency was observed across days of morphine treatment in the absence of repeated naloxone experience (Single Nal conditions), indicating an increasing contribution of naloxone experience-dependent processes as dose of morphine was decreased. It is argued that these experience-dependent processes in the progressive shift of naloxone potency observed in the current study may reflect an important role of conditioning in the early development of opioid dependence.     

Ketanserin and pirenperone attenuate acute morphine withdrawal in rats

The involvement of serotonin2 (5-HT2) receptors in the expression of opiate withdrawal was examined using a behavioral test for acute morphine dependence. The 5-HT2 antagonists, ketanserin and pirenperone, injected shortly before naloxone, attenuated the naloxone-induced suppression of an autoshaped lever-touch response in rats treated 4 h earlier with a moderate dose of morphine. A low dose of pirenperone was also effective in blocking withdrawal-induced hypothermia. These data support the hypothesis that 5-HT is involved in the expression of opiate withdrawal.     

Reduction of morphine dependence and potentiation of analgesia by chronic co-administration of nifedipine

Nifedipine, 5 mg/kg IP, potentiated the morphine-induced analgesia measured in the hot-plate, but not in the tail-flick test. Further experiments were carried out using the hot-plate test only. Pretreatment with nifedipine partially restores the analgesic action of morphine in morphine-tolerant rats. Co-administration of nifedipine with morphine in a chronic experiment did not prevent the loss of morphine efficiency (an increase in latency of 44% was not significant) and did not prevent the debilitating effect of chronic morphine administration reflected by an inhibition of the body weight gain, but prevented naloxone-induced withdrawal syndrome (quantified by counting head shakes) in the test carried out 24 h after the injection of nifedipine, when the drug did not affect morphine analgesia. Chronic treatment with either morphine or nifedipine did not produce a significant increase in the density of [³H] naloxone or [³H]prazosin binding sites in the cortex and in the rest of the brain (measured 24 h after the last dose), but the combined treatment resulted in a significant increase in the cortical [³H]prazosin binding site density. The present results suggest that opiate tolerance and physical dependence may be separated by coadministration of nifedipine and suggest that the combined chronic treatment with morphine and nifedipine may increase the efficacy of morphine during chronic treatment and prevent development of abstinence.     

Effects of morphine dependence and withdrawal on levels of neurosteroids in rat brain

AIM: To investigate the effects of morphine dependence and withdrawal on the concentrations of neurosteroids in rat brain. METHODS: A method of simultaneous quantification of neurosteroids by gas chromatography-mass spectrometry (GC-MS) had been established. RESULTS: The chronic morphine administration (ip) resulted in a marked decrease in the brain concentrations of pregnenolone (PREG), progesterone (PROG), and pregenenolone sulfate (PREGS) in rats killed 6 h after the last treatment. In contrast, there were no significant effects of morphine dependence on the brain concentrations of allopregnanolone (AP), dihydroepiandrosterone (DHEA), and dihydroepiandrosterone sulfate (DHEAS). Naloxone-induced withdrawal produced a significant increase in the concentrations of PREG, PROG, AP, DHEA, PREGS, and DHEAS as compared with the control group. CONCLUSION: Morphine dependence and withdrawal affected the concentrations of neurosteroids in rat brain, which suggests that endogenous neurosteroids in brain might be     

Attenuation of morphine dependence and withdrawal by glycine B site antagonists in rats

Numerous data indicate that noncompetitive and competitive N-methyl-D-aspartate (NMDA) receptor antagonists inhibit the development of physical dependence on opioids when these substances are administered together, and NMDA receptor antagonists are used at lower range of doses. Higher doses of these antagonists can enhance some opioid-induced effects. The present study extends these findings to the effects of NMDA/glycine (glycine(B)) site antagonists. Wistar rats were rendered dependent on morphine by implantation of morphine pellets. Both of the glycine(B) site antagonists used, 7-chloro-4-hydroxy-3-(3-phenoxy)-phenyl-2(H)-quinolone (L-701,324; 2.5 and 5.0 mg/kg) and 5,7-dichlorokynurenic acid (5,7-DCKA; 25, 50, and 100 mg/kg), suppressed the expression of morphine withdrawal syndrome estimated as wet dog shakes. Furthermore, L-701,324 (2.5 and 5 mg/kg), given twice a day during the development of morphine dependence, attenuated the development of morphine dependence, and the results were comparable to those obtained after administration of noncompetitive NMDA receptor antagonist - MK801 (0.1 mg/kg). Our data suggest that glycine(B) site antagonists may attenuate wet dog shakes (withdrawal) and the development of dependence, both being induced by chronic morphine administration in rats.     

Elevated startle during withdrawal from acute morphine: a model of opiate withdrawal and anxiety

Rationale An elevated startle response has been observed in humans and animals during withdrawal from multiple substances of abuse, a phenomenon thought to reflect the anxiogenic effects of withdrawal. Although anxiety is a common symptom of opiate withdrawal, few studies have examined the effects of morphine withdrawal on acoustic startle.Objective To develop a procedure for assessing opiate dependence through measurement of the startle reflex in rats.Methods The effects of opiate withdrawal on startle were evaluated using both spontaneous and naloxone-precipitated withdrawal from an acute dose of morphine. The ability of the treatment drugs clonidine and chlordiazepoxide to block withdrawal-induced increases in startle was also tested.Results Spontaneous withdrawal from an injection of morphine sulfate produced a significant increase in acoustic startle 2 h (3.2 mg/kg) or 4 h (10 mg/kg) after drug administration. Morphine withdrawal (10 mg/kg morphine sulfate) precipitated by the opiate antagonist naloxone (2.5 mg/kg) also produced a significant increase in startle magnitude. This elevation of startle was blocked by both clonidine (35 g/kg) and chlordiazepoxide (10 mg/kg).Conclusions These data demonstrate that both spontaneous and precipitated withdrawal from an acutely administered opiate produce anxiety-like effects on acoustic startle. This paradigm may be useful in the study of anxiety and the early mechanisms of drug dependence.     

Co-release of noradrenaline and dopamine in the prefrontal cortex after acute morphine and during morphine withdrawal

RATIONALE: Acute morphine and abstinence from chronic morphine have been shown to increase and to decrease extracellular dopamine (DA) in the nucleus accumbens, respectively. In contrast, extracellular DA in the prefrontal cortex (PFC) is not modified by acute morphine and is markedly increased during abstinence syndrome. OBJECTIVES: We investigated whether the peculiar behaviour of PFC DA might depend on the fact that extracellular DA originates not only from DA but, mainly, noradrenaline (NA) terminals. Accordingly, we studied if the effect of acute morphine and morphine-abstinence was modified by the inhibition of DA or NA neurons. METHODS: Extracellular DA and noradrenaline (NA) concentrations were determined by microdialysis in the PFC (densely innervated by DA) and in the parietal cortex (lacking DA afferents) both after acute morphine and in morphine-dependent rats during naloxone-precipitated abstinence syndrome. Dialysate catecholamine levels were evaluated by high performance liquid chromatography (HPLC) with electrochemical detection. RESULTS: Acute morphine (5 mg/kg IP) reduced extracellular NA (by 30%) and failed to modify extracellular DA level in the PFC, but reduced both amines by 40% in the parietal cortex. The co-administration of morphine and the D(2) agonist quinpirole (0.5 mg/kg IP) decreased both extracellular DA and NA by 40% in the PFC. In morphine dependent rats the administration of naloxone (1.0 mg/kg, SC) precipitated a typical abstinence syndrome associated with a concomitant dramatic increase in extracellular DA and NA by about 200 and 100%, respectively, in the PFC. The alpha(2)-adrenoceptor agonist clonidine (0.15 mg/kg IP) suppressed naloxone precipitated abstinence symptoms and brought both NA and DA output in the PFC to <50% baseline values. In contrast, quinpirole was totally ineffective. CONCLUSIONS: The results suggest that: a) morphine-stimulated DA release from DA terminals is compensated by reduced DA release from NA terminals; b) morphine abstinence-induced inhibition of DA release from DA terminals is overshadowed by a marked increase in DA released from NA terminals. Thus, the paradoxical response of PFC DA to morphine and morphine abstinence may be explained by the fact that extracellular DA in the PFC mainly represents the amine co-released from NA terminals.     

Opiate withdrawal signs precipitated by naloxone following a single exposure to morphine: potentiation with a second morphine exposure

Recent studies in humans with no prior history of opiate abuse indicated that naloxone-precipitated signs of opiate withdrawal could be observed after a single exposure to morphine, and that the severity of withdrawal was enhanced following a second morphine exposure 24 h later. The current study was conducted to establish a paradigm in rodents that resembled these conditions described in humans. To that end, naloxone-precipitated (0.03–3.0 mg/kg) suppression of operant response rates and somatic signs of withdrawal following single or repeated treatments with morphine (5.0 mg/kg) were assessed in previously opiate-naive rats. In one group of rats, naloxone was administered 4 h after both the first and second morphine pretreatment, while in a separate group of rats naloxone was administered 4h after the second morphine pretreatment only. A single morphine pretreatment significantly increased naloxone’s potency to suppress operant response rates, and resulted in the precipitation by naloxone of certain somatic signs of withdrawal. The effects of naloxone on both dependent measures (operant response rates and somatic signs) were potentiated following a second morphine pretreatment, regardless of whether naloxone was administered following both morphine exposures or only following the second morphine exposure. Thus, repeated morphine administration appears to be the critical factor underlying the progressive increase in antagonist potency, whereas prior experience with naloxone is not a necessary factor. The results provide additional support for the hypothesis that the development of dependence on opiates is a progressive phenomenon that may begin with a single dosing. Received: 30 May 1996/Final version: 5 August 1996     

The mechanisms of morphine dependence and it's withdrawal syndrome: study in mutant mice

To investigate the involvement of catecholamines and/or the cyclic AMP (cAMP) systems in the development of drug dependence, we examined whether morphine dependence was developed in tyrosine hydroxylase (TH) heterozygous (TH+/-) and cAMP response element binding protein (CREB) binding protein (CBP) heterozygous (CBP+/-) mice. Morphine (10 mg/kg) induced place preference in the wild-type mice. In the TH+/- and CBP+/- mice, however, we could not find any morphine-induced place preference. When the wild-type mice pretreated with morphine (10 mg/kg) twice a day for 5 days were challenged with naloxone (5 mg/kg), they showed increased numbers of jumping, rearing and forepaw tremor as a sign of withdrawal symptom and increased level of cAMP in the thalamus/hypothalamus, but not in the striatum. However, increased numbers of jumping and forepaw tremor in the TH+/- and CBP+/- mice and increased level of cAMP in the thalamus/hypothalamus of TH+/- mice were not observed. These results suggest that catecholamines and CBP are involved in the development of morphine dependence, and that some changes in the catecholaminergic and/or cAMP system induced by repeated morphine treatment play an important role in the addiction of morphine.     

Relative potency of the opioid antagonists naloxone and 6-alpha-naloxol to precipitate withdrawal from acute morphine dependence varies with time post-antagonist

The current study compared the potency of naloxone versus 6-alpha-naloxol to precipitate opioid withdrawal under varying conditions of morphine pretreatment history using suppression of operant responding for food reward as the index of withdrawal. Male Wistar rats trained to respond on a lever for food reward received pretreatment with either Vehicle (Morphine-Naïve), a single subcutaneous (SC) injection of 5.6 mg/kg morphine (Single Morphine), or two morphine injections at 24 h intervals (Repeat Morphine), with varying doses of naloxone or 6-alpha-naloxol injected SC 4 h post-morphine and 5 min prior to the 30 min test session. When responding over the entire 30 min operant session was examined, naloxone was only 5-fold more potent than 6-alpha-naloxol in suppressing operant responding under Morphine Naïve conditions, but this increased to a 65-fold potency difference after Single or Repeat Morphine pretreatment. Examination of the relative potency of these antagonists in the Early Phase of operant testing (5-15 min post-antagonist) revealed an even greater 100-fold potency difference between naloxone and 6-alpha-naloxol, but in the Late Phase of testing (25-35 min post-antagonist), this had declined to a 9-fold potency difference, comparable to the relative potency of naloxone to 6-alpha-naloxol under Morphine-Naïve conditions. The results confirm a differential potency of naloxone to its reduced conjugate 6-alpha-naloxol in vivo, and extend the observation of this phenomenon to an acute (single) pretreatment with a low dose of morphine and an additional sign of opioid withdrawal to those previously used. However, the results also indicate that delay in onset of action of 6-alpha-naloxol at opioid receptors in the central nervous system may contribute significantly to its reduced potency relative to naloxone under certain morphine pretreatment conditions.     

Precipitated opioid withdrawal across acute physical dependence induction methods

The phenomenon of acute opioid physical dependence (APD) is an established and well-characterized experimental model for studying the clinical phenomenon of physical dependence to opioids in humans. In this paradigm, an opioid withdrawal syndrome is elicited in non-opioid-dependent humans by the parenteral administration of naloxone (NX) following a single large dose of opioid agonist. Although induced by various opioids and NX administration schedules, lacking is a direct comparison of different induction protocols with respect to withdrawal severity. Using a crossover design, we compared withdrawal severity in four healthy male subjects pretreated with morphine (MS; 18 mg/70 kg im), MS (10 mg/70 kg iv) and hydromorphone (HM; 2 mg/70 kg) followed 2 or 6 h later with NX (10 mg/70 kg iv). Dependent measures included both physiological and subjective indicators of withdrawal. All opioid pretreatments reliably induced APD and repeated-measures analysis of variance (ANOVA) showed that both pattern and severity of precipitated withdrawal were similar across conditions. Thus, despite altering the pretreatment opioid and route of administration, all three APD protocols produced similar and reliable withdrawal symptoms in humans.     

Acceleration of cerebral noradrenaline turnover after morphine withdrawal and its retardation by acute morphine administration in rats

Summary To clarify the effects of withdrawal from chronic morphine treatment on cerebral noradrenaline (NA) turnover, we have measured the -methyl-p-tyrosine (MT)-induced depletion of NA in five brain areas of male Wistar rats given morphine twice daily for 40 or 60 days. After the last morphine dose (50 or 70 mg/kg) the rats were withdrawn for 1, 2 or 4 days. In order to study the development of tolerance a challenge dose of 10 mg/kg of morphine was given to some of the rats.Withdrawal of morphine accelerated the MT-induced NA depletion clearly in the hemispheres and the lower brain stem and slightly in the diencephalon. The acceleration was more pronounced in the brains of rats treated for 60 days than of those treated for 40 days. In the hemispheres the acceleration of NA depletion occurred at 1 and 2 days, in the diencephalon at 2 days, and in the lower brain stem at 2 and 4 days after morphine withdrawal. The most pronounced acceleration of NA depletion coincided with the maximum withdrawal-induced weight loss. The challenge dose of morphine clearly retarded the MT-induced NA depletion in the hemispheres of control rats treated chronically with saline. This retardation was even more pronounced in rats withdrawn from chronic morphine treatment for 1 or 2 days. The challenge dose slightly accelerated the MT-induced NA depletion in the lower brain stem of control rats. However, in rats withdrawn from chronic morphine treatment for 1 or 2 days the challenge dose instead of accelerating, clearly retarded, the NA depletion in the lower brain stem.Our results show that cerebral NA turnover is accelerated in rats withdrawn from morphine. The degree of this acceleration is proportional to the duration of chronic treatment. Tolerance does not seem to develop towards the NA release-inhibiting effect of morphine in the hemispheres, but develops towards the NA release-accelerating effect of morphine in the lower brain stem.     

Intra-administration associations and withdrawal symptoms: morphine-elicited morphine withdrawal

On the basis of a conditioning analysis, some drug "withdrawal symptoms" are conditional responses elicited by stimuli paired with the drug effect. Prior demonstrations of conditional elicitation of withdrawal symptoms evaluated the role of environmental cues; however, pharmacological cues also typically signal a drug effect. Within each administration, early drug onset cues (DOCs) may become associated with the later, larger drug effect (intra-administration associations). This experiment evaluated the contribution of intra-administration associations to withdrawal symptoms. The results indicated that (a). 5 mg/kg morphine elicited behavioral and thermic withdrawal symptoms in rats previously injected on a number of occasions with 50 mg/kg morphine and that (b). DOC-elicited withdrawal symptoms are not a sensitized response to the opiate but rather an associative phenomenon.     

Catecholamine utilization in distinct mouse brain nuclei during acute morphine treatment, morphine tolerance and withdrawal syndrome

The steady-state levels and utilization (alpha-MPT-induced disappearance) of noradrenaline (NA) and dopamine (DA) were measured in distinct mouse brain nuclei after acute morphine challenge, in mice rendered tolerant to morphine, and during the naloxone-precipitated morphine withdrawal syndrome. Mouse brain nuclei containing mainly the cell body areas and some terminal projections of major NA- and DA-containing pathways were selected (nucleus tractus solitarii, locus coeruleus, substantia nigra, area tegmentalis ventralis and nucleus caudatus, nucleus accumbens, gyrus dentatus hippocampi, nucleus raphe dorsalis respectively). Acute morphine treatment reduced the utilization of NA in all brain nuclei but the substantia nigra. In morphine-tolerant mice, all changes characteristic for acute morphine treatment disappeared. Instead, an increased NA utilization was observed in the nucleus tractus solitarii and the area tegmentalis ventralis in the tolerant animals. During morphine withdrawal, an abrupt decrease was observed in the utilization of NA in the nucleus tractus solitarii, whereas the NA utilization in the gyrus dentatus abruptly increased, as compared to the tolerant state. Acute morphine challenge decreased the utilization of DA in the nucleus caudatus, locus coeruleus and nucleus raphe dorsalis. In the tolerant mouse, an increased utilization of DA was observed in the nucleus tractus solitarii. During morphine withdrawal, DA utilization was decreased in the substantia nigra and the area tegmentalis ventralis, while in the nucleus accumbens withdrawal resulted in an increase of DA utilization. The data suggest that acute effects of morphine as well as morphine tolerance/dependence are accompanied by, and likely to be associated with, distinct changes in the catecholamine metabolism of specific mouse brain nuclei.