enkephalin--leucine-2-alanine and Morphine-Dependence

The chronic use of several drugs, including opiates, results in the stereotypical behaviors characteristic of addiction. Alterations in gene expression have been associated with the use of these addictive drugs. Previous studies, however, have been limited to describing changes in amounts of individual mRNAs from single tissue samples. Cellular adaptation to opiates, reflected in the regulation of the expression of many different mRNAs, seems likely to contribute to the complicated behaviors of addiction. The present studies examined coordinate alterations in the amounts of multiple mRNAs in the rat striatum and in NG108-15 cells after opioid stimulation or the precipitated withdrawal of opioid use. The experimental approach combined amplification of the poly(A)+ RNA population with reverse Northern blot analysis to simultaneously characterize the relative changes in several mRNAs. Morphine treatment of rats for 5 days was associated with a reduction in the amount of striatal RNA for the voltage-sensitive K+ channel without significant changes in other ion channels. In NG108-15 cells stimulation with the delta-opiate receptor agonist [D-Ala2,D-Leu5]enkephalin (DADLE) alone and followed by naloxone (precipitated withdrawal) caused relative changes in the abundances of several mRNAs. The composite effects of alterations in the abundance of multiple mRNAs (and the proteins they encode) in response to opioid use likely contribute to the development and maintenance of opiate-mediated behaviors.

Topics: Animals; Corpus Striatum; Enkephalin, Leucine-2-Alanine; Gene Expression; Genes, fos; Genes, jun; GTP-Binding Proteins; Ion Channels; Male; Morphine; Morphine Dependence; Rats; Rats, Sprague-Dawley; Receptors, Retinoic Acid; RNA, Messenger

Previously, we demonstrated the enhanced affinity of opioid receptors for naloxone in striatal slices from morphine-dependent mice. In our present study, binding characteristics of the mu opioid receptor agonists, [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAMGO) and dihydromorphine, the delta opioid receptor agonist, [D-Ala2, D-Leu5]enkephalin (DADLE), and the opioid antagonist, naloxone, were examined in striatal slices from morphine-tolerant and -dependent mice. Striatal slices from mice that were implanted with a morphine pellet for 3,7 and 21 days displayed significant decreases in Kd values (5.1, 4.6 and 5.5 nM, respectively) of [3H]DAMGO when compared to those in slices from control animals that were not implanted or implanted with placebo pellets (9.6 and 9.3 nM, respectively). Also, a significant increase in the binding affinity of naloxone, but not that of dihydromorphine, was observed in striatal slices of mice that were implanted with a morphine pellet for 3 days. Significant increases in the Bmax of delta binding sites in striatal slices of mice that were implanted with a morphine pellet for 3, 7 and 21 days (20.7, 18.1 and 17.7 pmol/mg tissue, respectively) were observed when compared to that in slices from control mice that were implanted with placebo pellets (11.4 pmol/mg tissue). The enhancement in the binding affinity of DAMGO and naloxone and the increased density of DADLE binding sites paralleled the development of morphine tolerance and dependence and [D-Pen2,D-Pen5]enkephalin cross-tolerance in whole animals. An antinociceptive potentiation between morphine and DAMGO was observed in morphine-tolerant and -dependent mice whereas in naive animals the effects of the two drugs were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Analgesics; Animals; Binding Sites; Corpus Striatum; Drug Interactions; Drug Tolerance; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine-2-Alanine; Enkephalins; Male; Mice; Morphine; Morphine Dependence; Naloxone; Pain; Receptors, Opioid

The i.c.v. administration of opioid peptides having selectivity for the mu receptor (D-Ala2-NMePhe4-Gly5(ol)enkephalin and FK 33,824) produced effects on the locomotor activity of nondependent and morphine-dependent rats that differed both quantitatively and qualitatively from those effects produced by peptides having selectivity for the delta receptor (D-Ala2-D-Leu5enkephalin and metkephamid) and beta-endorphin, which has similar affinity for both receptors. Peptides selective for the mu receptor: had a biphasic effect on locomotor activity of nondependent rats, inducing an increase at low doses and an initial decrease followed by a later increase at higher doses and had an enhanced stimulant effect on locomotor activity with tolerance to the depressant effect in morphine-dependent rats. Peptides selective for the delta receptor and beta-endorphin: induced only a dose-related increase in the locomotor activity of nondependent rats and had effects on the locomotor activity of morphine-dependent rats that did not differ substantially from those in nondependent rats. Naltrexone (0.1 mg/kg s.c.) and beta-funaltrexamine (5.0 micrograms/rat i.c.v.), an irreversible antagonist, each blocked to a comparable extent the effects of D-Ala2-NMePhe4-Gly5(ol)enkephalin and DAla2-D-Leu5enkephalin on the locomotor activity of nondependent rats. Thus, effects of opioid peptides that act predominantly at mu or delta receptors on locomotor activity cannot be differentiated in nondependent rats by antagonists but can be differentiated in morphine-dependent rats. These results suggest that the depressant and stimulant effects of opioid peptides on locomotor activity are mediated by distinct neuronal sites.

Topics: Animals; beta-Endorphin; D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; Dose-Response Relationship, Drug; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Male; Morphine Dependence; Motor Activity; Naltrexone; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu

The effects of prolonged administration of morphine on the properties of opiate receptors of rat brain were studied. For this purpose the isotherms of binding of labeled mu-, delta-, and chi-ligands--morphine, D-Ala2, D-Leu5-enkephalin and ethylketocyclazocine--with brain membrane preparations of morphine-tolerant rats as well as those of control animals were analyzed. For quantitative determination of dissociation constants of the ligand-receptor complexes (K) and receptor concentrations ([Q]), the difference and simulation methods were used. It was shown that the values of K and [Q] vary within broad ranges in individual animals, whereas the individual variations of the [Q]/[K] ratios in controls or in morphine-tolerant rats are not so significant. This suggests [Q]/K to be one of the basic criteria for a comparison of properties of opiate receptors in different groups of animals. The use of this criterion and of the simulation method demonstrated that the development of tolerance causes changes in the properties of delta-receptors (the [Q]/K ratio decreases by greater than 50%). Unlike delta-receptors, the tolerance has no appreciable effect on the properties of mu- or chi-receptors or on the superhigh affinity binding sites of the ligands tested.

Topics: Animals; Brain; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Kinetics; Male; Morphine; Morphine Dependence; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Opioid

Topics: Animals; Drug Tolerance; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Humans; Hybrid Cells; Morphine; Morphine Dependence; Rats; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Substance Withdrawal Syndrome

Topics: Animals; Dose-Response Relationship, Drug; Endorphins; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Enkephalins; Humans; Male; Morphine; Morphine Dependence; Motor Activity; Naloxone; Rats; Time Factors

The effects of intraventricular morphine and the metabolically stable enkephalin analogs, D-ala2-leu- and D-ala2-met-enkephalinamide, were compared on food-reinforced operant responding in nondependent, morphine-dependent and postdependent rats. Dependence was induced and maintained by scheduled access to 0.05% morphine solution for 10 min every 6 hr for at least 8 weeks before testing. In nondependent animals, the lowest dose of the three drugs increased responding, whereas higher doses, i.e., 0.3 to 3.9 micrograms of morphine and 0.1 to 30 micrograms of the two enkephalins, produced graded decreases in responding. On a molar basis, morphine was 2 to 3 times more potent than the enkephalins in decreasing response rate. Naloxone (0.1 and 1.0 mg/kg) competitively antagonized the rate-decreasing effect of all three compounds. However, chronic morphine treatment produced varying changes in the effects of morphine and the enkephalins. Morphine-dependent rats were tolerant to the rate-decreasing action of morphine, whereas the rate-decreasing effect of D-ala2-met-enkephalinamide was unchanged and that of D-ala2-leu-enkephalinamide was enhanced. Protracted changes in the rate-decreasing effect of morphine, but not the enkephalins, were evident in postdependent animals that were tested 5 weeks after withdrawal from morphine. Thus, the effects of morphine and the enkephalins on operant responding are differentially altered as a result of chronic morphine treatment. These results could reflect an allosteric interaction between the neuronal binding sites for morphine and the enkephalins.

Topics: Animals; Conditioning, Operant; Dose-Response Relationship, Drug; Endorphins; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Enkephalins; Humans; Injections, Intraventricular; Male; Morphine; Morphine Dependence; Rats; Rats, Inbred Strains; Substance Withdrawal Syndrome