enkephalin--leucine-2-alanine and beta-funaltrexamine

The current study investigated the roles of various subtypes of opioid receptors expressed in the thalamic nucleus submedius (Sm) in inhibition of mirror-image allodynia induced by L5/L6 spinal nerve ligation in rats. Morphine was microinjected into the Sm, which produced a dose-dependent inhibition of mirror-image allodynia; this effect was antagonized by pretreatment with non-selective opioid receptor antagonist naloxone. Microinjections of endomorphin-1 (mu-receptor agonist), or [D-Ala(2), D-Leu(5)]-enkephalin (DADLE, delta-/mu-receptor agonist), also inhibited mirror-image allodynia, and these effects were blocked by the selective mu-receptor antagonist, beta-funaltrexamine hydrochloride. The DADLE-induced inhibition, however, was not influenced by the delta-receptor antagonist naltrindole. The kappa-receptor agonist, spiradoline mesylate salt, failed to alter the mirror-image allodynia. These results suggest that Sm opioid receptor signaling is involved in inhibition of mirror-image allodynia; this effect is mediated by mu- (but not delta- and kappa-) opioid receptors in the rat model of neuropathic pain.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Enkephalin, Leucine-2-Alanine; Hyperalgesia; Ligation; Male; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Neuralgia; Oligopeptides; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Spinal Nerves; Thalamic Nuclei

Opioid receptor subtypes may have site-specific effects and play different roles in modulating serotonergic neurotransmission in the mammalian central nervous system. To test this hypothesis, we used in vivo microdialysis to measure changes in extracellular serotonin (5-hydroxytryptamine; 5-HT) in response to local infusion of mu-, delta-, and kappa-opioid receptor ligands into the dorsal raphe nucleus (DRN), median raphe nucleus (MRN), and nucleus accumbens (NAcc) of freely behaving rats. The mu-opioids [D-Ala(2)-N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO), endomorphin-1, and endomorphin-2 were administered by reverse dialysis infusion into the DRN. In response, extracellular 5-HT was increased in the DRN, an effect that was blocked by the selective mu-receptor antagonist beta-funaltrexamine, but not by the delta-receptor antagonist N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH (ICI-174,864). Infusion of delta-receptor agonists, [D-Ala(2),D-Len(5)]enkephalin (DADLE), [D-Pen(2,5)]enkephalin (DPDPE), and deltophin-II into the DRN also increased extracellular 5-HT, an effect that was blocked by selective delta-receptor antagonists. In contrast to the DRN, local infusion of mu- and delta-opioids had no effect on 5-HT in the MRN or NAcc. These data indicate that mu- and delta-opioid ligands have a selective influence on serotonergic neurons in the DRN. Finally, the kappa-receptor agonist U-50,488 [trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide] produced similar decreases in 5-HT during local infusion into the DRN, MRN, and NAcc. These results provide evidence of differential regulation of 5-HT release by opioid receptor subtypes in the midbrain raphe and forebrain.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Opioid; Animals; Central Nervous System; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine-2-Alanine; Male; Microdialysis; Microinjections; Naltrexone; Nucleus Accumbens; Raphe Nuclei; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Serotonin

Opioid receptor subtype antagonists differentially alter food intake under deprivation (24 h), glucoprivic (2-deoxy-D-glucose, 500 mg/kg, i.p.) or palatable (10% sucrose) conditions with mu (beta-funaltrexamine) and kappa (nor-binaltorphamine), but not delta1 ([D-Ala2,Leu5,Cys6]enkephalin) opioid antagonists reducing each form of intake following ventricular microinjection. Both mu and kappa opioid antagonists microinjected into either the hypothalamic paraventricular nucleus or the nucleus accumbens reduce intake under deprivation and glucoprivic conditions. Palatable intake is reduced by both antagonists in the paraventricular nucleus, but only mu antagonists are active in the accumbens. Food intake is stimulated by mu and delta, but not kappa, opioid agonists microinjected into the ventral tegmental area. The present study examined whether food intake under either deprivation, glucoprivic or palatable conditions was altered by bilateral administration of general (naltrexone), mu, kappa, delta1 or delta2 (naltrindole isothiocyanate) opioid antagonists into the ventral tegmental area. Deprivation (24 h)-induced feeding was significantly reduced by high (50 microg), but not lower (10-20 microg) doses of naltrexone (21%), and by delta2 (4 microg, 19%) antagonism in the ventral tegmental area. 2-Deoxy-D-glucose (500 mg/kg, i.p.)-induced hyperphagia was significantly reduced by high (50 microg), but not lower (20 microg) doses of naltrexone (64%), and by delta2 (4 microg, 27%) antagonism in the ventral tegmental area. Sucrose (10%) intake was significantly reduced by naltrexone (20-50 microg, 25-39%) and delta2 (4 microg, 25%) antagonism in the ventral tegmental area. Neither mu, kappa nor delta1 antagonists were effective in reducing any form of intake following microinjection into the ventral tegmental area. These data indicate that the ventral tegmental area plays a relatively minor role in the elicitation of these forms of food intake, and that delta2, rather than mu, kappa or delta1 opioid receptors appear responsible for mediation of these forms of intake by this nucleus.

Topics: Deoxyglucose; Eating; Enkephalin, Leucine-2-Alanine; Evaluation Studies as Topic; Food Deprivation; Hyperphagia; Insulin; Naltrexone; Narcotic Antagonists; Sucrose; Ventral Tegmental Area

Different central opioid receptor subtypes participate in the mediation of intakes of simple (sucrose: mu, kappa 1) and complex (maltose dextrin: mu) carbohydrates as well as deprivation-induced water intake (mu) under real-feeding and real-drinking conditions. An identical pattern of mu and kappa 1 mediation of sucrose intake was observed in sham-feeding rats as well, suggesting their actions on orosensory mechanisms supporting sucose intake. The present study examined whether centrally administered general (naltrexone: 1-50 micrograms), mu (beta-funaltrexamine: 1-20 micrograms), mu 1 (naloxonazine: 50 micrograms), kappa 1 (nor-binaltorphamine: 1-20 micrograms), delta 1 ([D-Ala2, Leu5, Cys6]-enkephalin: 10-40 micrograms) or delta 2 (naltrindole isothiocyanate: 20 micrograms) opioid subtype antagonists altered either maltose dextrin (10%) intake during sham feeding or deprivation (24 h)-induced water intake during sham drinking in rats with gastric fistulas. Sham feeding significantly increased maltose dextrin intake (180%) and sham drinking significantly increased deprivation-induced water intake (256%) over a 60 min time course. Naltrexone significantly and dose-dependently reduced maltose dextrin intake (78%) in sham feeding rats, and deprivation-induced water intake (51%) in sham drinking rats. Maltose dextrin intake in sham feeding rats was significantly reduced by either kappa 1 (69%) or delta 1 (59%) opioid antagonism, was significantly increased by mu 1 antagonism (43%), and was not significantly affected by either mu or delta 2 opioid antagonism. Deprivation-induced water intake in sham drinking rats was significantly reduced by either mu (41%), mu 1 (28%), delta 1 (48%) or delta 2 (28%) opioid antagonism, but was not significantly affected by kappa 1 opioid antagonism. The difference in opioid receptor subtype mediation of maltose dextrin intake in real feeding and sham feeding conditions suggest that kappa 1 and delta 1 receptors are involved in the orosensory mechanisms supporting maltose dextrin intake, while mu receptors are involved in the ingestive and post-ingestive mechanisms supporting maltose dextrin intake. The different patterns of opioid involvement in sucrose and maltose dextrin intake in sham feeding and real feeding conditions provide further support for the hypothesis that at least two different carbohydrate taste systems exist. The difference in opioid receptor subtype mediation of deprivation-induced water intake in real drink

Topics: Animals; Dose-Response Relationship, Drug; Drinking; Eating; Enkephalin, Leucine-2-Alanine; Injections, Intraventricular; Male; Naloxone; Naltrexone; Narcotic Antagonists; Polysaccharides; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Water Deprivation

Intake of a palatable sucrose solution in real-fed rats is mediated in part by central mu and kappa opioid receptors. Since general opioid antagonists still inhibit sucrose intake in sham-fed rats, the present study examined whether centrally administered mu (beta-funaltrexamine: 5, 20 micrograms), mu1 (naloxonazine: 50 micrograms), kappa (nor-binaltorphamine: 1, 5, 20 micrograms), delta (naltrindole: 20 micrograms) or delta 1 (DALCE: 40 micrograms) opioid subtype antagonists altered sucrose intake in sham-fed rats in a similar manner to systemic naltrexone (0.01-1 mg/kg) and whether such effects were equivalent to altering the sucrose concentration. Sucrose (20%) intake in sham-fed rats was significantly and dose-dependently reduced by naltrexone (59%), beta-funaltrexamine (44%) and nor-binaltorphamine (62%), but not by naloxonazine, naltrindole or DALCE. The reductions in sham sucrose (20%) intake by general, mu and kappa antagonism were similar in pattern and magnitude to diluting sucrose concentration from 20% to 10% in untreated sham-fed rats. Since both real-fed and sham-fed rats share similar patterns of specificity of opioid effects, magnitudes and potencies of inhibition, it suggests that central mu and kappa antagonism acts on orosensory mechanisms supporting sucrose intake.

Topics: Animals; Cerebral Ventricles; Eating; Enkephalin, Leucine-2-Alanine; Infusions, Parenteral; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Receptors, Opioid, mu; Sucrose

Intake of either hypotonic or hypertonic saline solutions is modulated in part by the endogenous opioid system. Morphine and selective mu and delta opioid agonists increase saline intake, while general opioid antagonists reduce saline intake in rats. The present study evaluated whether intracerebroventricular administration of general (naltrexone) and selective mu (beta-funaltrexamine, 5-20 micrograms), mu, (naloxonazine, 50 micrograms), kappa (nor-binaltorphamine, 5-20 micrograms), delta (naltrindole, 20 micrograms), or delta 1 (DALCE, 40 micrograms) opioid receptor subtype antagonists altered water intake and either hypotonic (0.6%) or hypertonic (1.7%) saline intake in water-deprived (24 h) rats over a 3-h time course in a two-bottle choice test. Whereas peripheral naltrexone (0.5-2.5 mg/kg) significantly reduced water intake and hypertonic saline intake, central naltrexone (1-50 micrograms) significantly reduced water intake and hypotonic saline intake. Water intake was significantly reduced following mu and kappa receptor antagonism, but not following mu 1, delta, or delta 1 receptor antagonism. In contrast, neither hypotonic nor hypertonic saline intake was significantly altered by any selective antagonist. These data are discussed in terms of opioid receptor subtype control over saline intake relative to the animal's hydrational state and the roles of palatability and/or salt appetite.

Topics: Animals; Enkephalin, Leucine-2-Alanine; Hypotonic Solutions; Injections, Intraventricular; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Receptors, Opioid, mu; Saline Solution, Hypertonic; Water Deprivation

To determine whether the peripheral opioid system participates in hypertension development we studied responses to various opioid receptor agonists in field-stimulated isolated tail artery segments taken from spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats at different ages. The mu-selective agonist (DAGO) and the delta-selective D-Ala2-D-Leu5-enkephalin (DADLE) both suppressed the electrically stimulated vasoconstriction (EIC), but only in SHR arteries. The mu-selective antagonist beta-funaltrexamine reversed the effects of both DAGO and DADLE. Since the delta-selective antagonist ICI-174864 did not block DADLE inhibition, it is likely that both DAGO and DADLE effects were mu-receptor-mediated. Effects of DAGO and DADLE were qualitatively and quantitatively similar at all ages of SHR tested, and were not temporally related to hypertension development. Dynorphin (1-13) (DYN), a kappa-agonist, increased basal tone and EIC in all three rat strains. These responses were not blocked by nor-binaltorphimine, a selective kappa-opioid antagonist, suggesting that they may not involve kappa-receptor activation. There was a greater sensitivity to DYN at younger ages in all three rat strains and the sensitivity decreased with age. At 16 weeks when SHR hypertension was fully developed, SHR tail artery became almost totally insensitive to DYN in contrast to the continued responsiveness of 16-week-old WKY and SD arteries. The diminished effects to DYN in 16-week-old SHR tail arteries is suggestive of a compensatory mechanism to the hypertensive state. Collectively, the results establish that opioid receptor responses in SHR tail artery differ from those of normotensive rats. The significance of these differences to hypertension development in SHR remains to be determined.

Topics: Age Factors; Animals; Dose-Response Relationship, Drug; Dynorphins; Electric Stimulation; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine-2-Alanine; Enkephalins; Hypertension; In Vitro Techniques; Male; Naltrexone; Narcotic Antagonists; Phenylephrine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Sprague-Dawley; Receptors, Opioid; Tail; Vasoconstriction

Opioid receptor subtype antagonists differentially alter different types of water intake such that mu2 receptors modulate deprivation-induced water intake, kappa receptors modulate hypertonic saline-induced water intake, and mu2, delta1 and kappa receptors modulate water intake following Angiotensin II (ANG II). Water intake stimulated by peripheral administration of the beta-adrenergic agonist, isoproterenol is attenuated by naloxone and is thought to be mediated by release of renin and production of ANG II. The present study examined whether systemic and i.c.v. administration of general opioid antagonists and central administration of specific opioid receptor subtype antagonists would selectively alter water intake following isoproterenol in rats. Both systemic (1 mg/kg s.c.) and central (1-20 micrograms) naltrexone reduced water intake induced by isoproterenol (25 micrograms/kg s.c.) over a 2-h period. The mu receptor antagonist, beta-funaltrexamine (B-FNA: 1-20 micrograms), but not the mu1 antagonist, naloxonazine (50 micrograms), dose-dependently reduced isoproterenol drinking. Both the kappa antagonist, nor-binaltorphamine (Nor-BNI, 5-20 micrograms) and the delta1 antagonist, [D-Ala2, Leu5, Cys6]-enkephalin (DALCE, 1-40 micrograms) also dose-dependently reduced isoproterenol drinking. These data implicate mu2, kappa and delta1 sites in the opioid modulation of isoproterenol drinking.

Topics: Animals; Drinking; Enkephalin, Leucine-2-Alanine; Injections, Intraventricular; Injections, Subcutaneous; Isoproterenol; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Receptors, Opioid, mu

Opioid modulation of ingestion includes general opioid antagonism of different forms of water intake, mu 2 receptor modulation of deprivation-induced water intake and delta 2 receptor modulation of saccharin intake. Water intake is stimulated by both central administration of angiotensin II (ANG II) and peripheral administration of a hypertonic saline solution; both responses are reduced by general opioid antagonists. The present study examined whether specific opioid receptor subtype antagonists would selectively alter each form of water intake in rats. Whereas systemic naltrexone (0.1-2.5 mg/kg, s.c.) reduced water intake induced by either peripheral ANGII (500 micrograms/kg, s.c.) or hypertonic saline (3 ml/kg, 10%), intracerebroventricular (i.c.v.) naltrexone (1-50 micrograms) only inhibited central ANGII (20 ng)-induced hyperdipsia. Both forms of drinking were significantly and dose-dependently inhibited by the selective kappa antagonist, nor-binaltorphamine (Nor-BNI, 1-20 micrograms). Whereas both forms of drinking were transiently reduced by the mu-selective antagonist, beta-funaltrexamine (beta-FNA, 1-20 micrograms), the mu 1 antagonist, naloxonazine (40 micrograms) stimulated drinking following hypertonic saline. The delta 1 antagonist, [D-Ala2, Leu5, Cys6]-enkephalin (DALCE, 1-40 micrograms) significantly reduced drinking following ANGII, but not following hypertonic saline; the delta antagonist, naltrindole failed to exert significant effects. These data indicate that whereas kappa opioid binding sites modulate hyperdipsia following hypertonic saline, mu 2, delta 1, and kappa opioid binding sites modulate hyperdipsia following ANGII. The mu 1 opioid binding site may normally act to inhibit drinking following saline.

Topics: Angiotensin II; Animals; Drinking; Enkephalin, Leucine-2-Alanine; Male; Naltrexone; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Saline Solution, Hypertonic

The fumaramate derivative of naltrexone, beta-funaltrexamine (beta-FNA), is a highly selective long-lasting mu opioid receptor antagonist that is active both in vitro and in vivo, presumably as a result of covalent binding to a mu receptor-based sulfhydryl group. Glutathione, which occurs in significant levels in brain and liver, was found to undergo a Michael-type reaction with beta-FNA in the test tube to give a stable conjugate 3 which occurred as an isomeric mixture. When tested in the GPI and MVD smooth muscle preparations, 3 was found to possess one-tenth the agonist activity of beta-FNA is both tissues, but showed no irreversible antagonist activity. The same result was found for the cysteine conjugate 4, except for some irreversible antagonism in the MVD. Both conjugates antagonize the antinociceptive effect of morphine in the mouse radiant heat tail-flick assay on icv administration. This antagonism persisted and actually increased over 24 h and generally paralleled the duration profile of beta-FNA. On sc administration, beta-FNA and 3 showed similar duration of antagonistic effect, while 4 exhibited only marginal activity at the early time interval. When the compounds are compared by the dose to produce equivalent antagonism, beta-FNA and 3 appeared equally effective and accessible by either route, whereas 4 showed a large difference between the two routes. It is possible that the ultra-long antagonism of the conjugates may result from their enzymatic conversion to beta-FNA in the central nervous system in view of the fact that conjugate 5, which cannot be converted to beta-FNA, did not produce antagonism of long duration in vivo. Alternatively, the protracted antagonism could arise from sequestration of 3 and 4 in tissue compartments that interface with mu opioid receptors.

Topics: Analgesia; Animals; Enkephalin, Leucine-2-Alanine; Glutathione; Guinea Pigs; Kinetics; Male; Mice; Morphine; Muscles; Naltrexone; Receptors, Opioid, mu; Structure-Activity Relationship; Vas Deferens

Tail-pinch feeding (TPF) in rats is decreased following general (naltrexone, NTX) and mu (Cys2-Tyr3-Orn5-Pen7-amide, CTOP) opioid antagonists, but not following kappa (nor-binaltorphamine. Nor-BNI) or delta (naltrindole, NTI) opioid antagonists. Because multiple mu (mu1 and mu2) and delta (delta 1 and delta 2) opioid receptor subtypes have been characterized, the present study evaluated whether TPF was differentially altered following ICV administration of general (NTX), mu (beta-funaltrexamine, B-FNA), mu1 (naloxonazine, NAZ), kappa (Nor-BNI), delta 1 ([D-Ala2, Leu5, Cys6]-enkephalin, DALCE) and delta 2 (NTI) opioid antagonists. Like the reversible mu antagonist CTOP, the irreversible mu antagonist B-FNA significantly and dose-dependently (1-20 micrograms) reduced TPF by up to 28%. In contrast, whereas NAZ (50 micrograms) reduced TPF by 32%, this effect was highly variable and failed to achieve significance. Neither NTX (5-10 mg/kg, SC), Nor-BNI (20 micrograms), DALCE (40 micrograms) nor NTI (20 micrograms) significantly altered TPF, suggesting that kappa, delta 1 and delta 2 opioid receptor subtypes were not involved. Because no antagonist altered the duration of food contact during tail pinch, it appears that the opioid effect modulates ingestive rather than activational mechanisms. The reliable inhibition of TPF by B-FNA (mu1 and mu2), together with the variable effect of naloxonazine (mu1), appears to implicate both mu binding sites in this response.

Topics: Animals; Arousal; Enkephalin, Leucine-2-Alanine; Feeding Behavior; Indoles; Male; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; Nociceptors; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu

Opioid modulation of ingestion includes general opioid antagonism of deprivation-induced water intake and intake of sucrose and saccharin solutions. Previous studies using selective subtype antagonists indicated that opioid effects upon deprivation-induced water intake occurred through the mu2 receptor and that opioid effects upon sucrose intake occurred through kappa and mu2 receptors. The present study compared the effects of intracerebroventricular administration of opioid receptor subtype antagonists upon intakes of a saccharin solution and a maltose dextrin (MD) solution to determine which receptor subtypes were involved in modulation of ingestion of different preferred tastants. Significant reductions in saccharin intake (1 h) occurred following naltrexone (20-50 micrograms: 66%) and naltrindole (delta, 20 micrograms: 75%), whereas [D-Ala2, Leu5, Cys6]-enkephalin (DALCE, delta 1, 40 micrograms: 45%) had transient (5 min) effects. Neither beta-funaltrexamine (B-FNA, mu), naloxonazine (mu1), nor nor-binaltorphamine (Nor-BNI, kappa) significantly altered saccharin intake. Significant reductions in MD intake (1 h) occurred following naltrexone (5-50 micrograms: 69%) and B-FNA (1-20 micrograms: 38%). MD intake was not reduced by naltrindole, DALCE, naloxonazine and Nor-BNI. Peak antagonist effects were delayed (20-25 min) to reflect interference with the maintenance, rather than the initiation of saccharin or MD intake. Comparisons of opioid antagonist effects across intake situations revealed that naltrexone had consistently low ID40 values for saccharin (29 nmol), MD (25 nmol), sucrose (6 nmol) and deprivation (38 nmol) intake. Despite its significant effects relative to naloxonazine, B-FNA had significantly higher ID40 values for saccharin (800 nmol), MD (763 nmol) and sucrose (508 nmol) relative to deprivation (99 nmol) intake, suggesting that mu2 receptors may be mediating maintenance of intake rather than taste effects. Nor-BNI had low ID40 values for intake of sucrose (4 nmol), but not for saccharin (168 nmol), MD (153 nmol) and deprivation (176 nmol), suggesting that kappa receptors may mediate ingestion of sweet-tasting stimuli. That delta (naltrindole: ID40 = 60 nmol), but not delta 1 (DALCE: ID40 = 288 nmol) antagonists consistently reduce saccharin intake suggests a role for the delta 2 receptor subtype in the modulation of hedonic orosensory signals.

Topics: Animals; Drinking Behavior; Enkephalin, Leucine-2-Alanine; Injections, Intraventricular; Male; Naloxone; Naltrexone; Narcotic Antagonists; Polysaccharides; Rats; Rats, Sprague-Dawley; Saccharin

The effects of intracerebroventricular injections of opioid peptides such as DADL [( D-Ala2, D-Leu5]enkephalin) and DPLPE [( D-Pen2, L-Pen5]enkephalin) with different degrees of selectivity for delta- over mu-receptor on apomorphine (0.1, 0.3, 1.0 and/or 3.0 mg/kg)-induced motor activity were investigated in the mouse using multi-dimensional behavioral analyses. Lower doses (0.1 and 0.3 mg/kg) of apomorphine failed to affect significantly motor activity, whilst higher doses (1.0 and 3.0 mg/kg) of the drug produced a marked increase in linear locomotion, circling, rearing, and/or grooming behaviors. DADL (0.03, 0.1 or 0.3 microgram) by itself did not influence behaviors, while the peptide (0.1 and 0.3 microgram) produced a marked inhibition on apomorphine (1.0 but not 3.0 mg/kg)-induced increase in rearing behaviors. Furthermore, the inhibitory effect of DADL (0.3 micrograms) on the apomorphine (1.0 mg/kg)-induced increase in rearing was reversed by treatment with the alkylating agent beta-FNA (beta-funaltrexamine) (5.0 micrograms). In contrast to the effects of DADL, the much more delta-selective opioid agonist DPLPE (0.3, 1.0 or 1.75 micrograms) had no marked effects on apomorphine (1.0 mg/kg)-induced behaviors. These results suggest that delta opioid receptors do not play a principal role in the apomorphine-induced increase in circling, rearing or grooming behaviors.

Topics: Analgesics; Animals; Apomorphine; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine-2-Alanine; Enkephalins; Grooming; Injections, Intraventricular; Male; Mice; Mice, Inbred Strains; Motor Activity; Naltrexone; Narcotic Antagonists; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Stereotyped Behavior

beta-Funaltrexamine (beta-FNA) is an alkylating derivative of naltrexone. In addition to acting as an irreversible inhibitor of mu-receptor-mediated physiological effects, intracerebroventricular (i.c.v.) administration of beta-FNA to rat attenuates the ability of selective delta receptor antagonists and naloxone to reverse delta receptor-mediated effects. Moreover, recent work demonstrated that i.c.v. administration of beta-FNA alters the conformation of the opioid receptor complex, as inferred by a decrease in the Bmax of the lower affinity [3H][D-ala2,D-leu5]enkephalin binding site. Consistent with the decreased potency of naloxone as an inhibitor of delta receptor mediated effects, beta-FNA doubled the naloxone IC50 for displacing [3H][D-ala2,D-leu5]enkephalin from its lower affinity binding site. These data collectively support the hypothesis that the opioid receptor complex postulated to mediate mu-delta interactions in vivo is identical to the opioid receptor complex as defined by vitro ligand binding studies. A direct prediction of this hypothesis is that beta-FNA should increase the Kd of antagonists for the mu binding site (mu cx) of the receptor complex. The data reported in this paper demonstrate that beta-FNA doubled the IC50 of the potent narcotic antagonist, 6-desoxy-6 beta-fluoronaltrexone (cycloFOXY) for displacing [3H][D-ala2,D-leu5]enkephalin from its lower affinity binding site, and doubled the Kd of [3H]cycloFOXY for its mu binding site, providing additional data that the mu binding site labeled by [3H]cycloFOXY is the mu binding site of the opioid receptor complex. beta-FNA also altered the kappa binding site labeled by [3H]cycloFOXY, and when administered intrathecally to mice, beta-FNA produced a longlasting antinociception in the acetic acid writhing test.

Topics: Alkylating Agents; Alkylation; Analgesics; Animals; Brain; Enkephalin, Leucine-2-Alanine; Injections, Intraventricular; Kinetics; Ligands; Male; Mice; Mice, Inbred ICR; Naltrexone; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Surface Properties

DALCE (1-40 micrograms, ICV), a short-acting agonist and long-acting antagonist at the delta opioid receptor, was examined for its effects upon food intake in rats under spontaneous, deprivation, glucoprivic and palatable conditions. DALCE (10 micrograms) significantly stimulated free feeding for up to 10 h but only minimally decreased (40 micrograms) food intake and body weight after 24-72 h. DALCE, administered prior to food deprivation (24 h), failed to affect subsequent 24-h intake and sporadically decreased intake and body weight change after 48-72 h. 2-Deoxy-D-glucose (650 mg/kg, IP) hyperphagia was transiently (2 h) decreased by long-term DALCE (10 micrograms) pretreatment. Hyperphagia following exposure to a high-fat diet was significantly potentiated by long-term DALCE (1 microgram) pretreatment. DALCE (10 micrograms) hyperphagia (2-10 h) was eliminated by central pretreatment with either naltrexone (20 micrograms) or the kappa antagonist, nor-binaltorphamine (20 micrograms) but was minimally affected by central pretreatment with the mu antagonist, beta-funaltrexamine (20 micrograms) or long-term DALCE (40 micrograms). The general inability of the antagonist actions of DALCE to alter these forms of feeding argues against a role for the delta opioid receptor in these responses.

Topics: Animals; Deoxyglucose; Diet; Dietary Fats; Dose-Response Relationship, Drug; Enkephalin, Leucine-2-Alanine; Feeding Behavior; Food Deprivation; Glucose; Injections, Intraventricular; Male; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid, delta

This study examined the effect of beta-funaltrexamine (beta-FNA), an irreversible mu-receptor antagonist, on naltrexone-induced upregulation of mu-(mu cx + mu nex) and delta nex-opioid receptors. [The subscripts 'cx' and 'nex' denote binding sites 'in' (cx) and 'not in' (nex) the opioid receptor complex.] Rats were treated according to the following protocol. Two naltrexone or two placebo pellets were implanted subcutaneously in a nylon mesh on day 1. and were removed intact on day 8. Rats were given either saline or 20 nmol of beta-FNA in 10 microliters of saline (i.c.v.) on days 1, 3, 5 and 6, 60 min prior to implantation of the pellet. On day 9 frozen lysed-P2 membranes were prepared for assay of mu binding sites. In other experiments, membranes were depleted of mu-receptors by pretreatment with the site-directed acylating agent 2-(4-ethoxybenzyl)-l-diethylaminoethyl-5-isothiocyanatobenzimid azole.HCl (BIT) for assay of delta nex binding sites, using [3H] [D-ala2, D-leu5]enkephalin. The results demonstrated that beta-FNA did not upregulate the mu binding sites and also did not prevent naltrexone-induced upregulation of mu binding sites. Both beta-FNA and naltrexone increased the Bmax of delta nex binding sites and their effects were additive. These data suggest that the mechanism(s) responsible for antagonist-induced upregulation of opioid receptors are more complex than previously appreciated.

Topics: Animals; Brain; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine-2-Alanine; Enkephalins; In Vitro Techniques; Isothiocyanates; Kinetics; Naltrexone; Narcotic Antagonists; Oxymorphone; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, mu; Thiocyanates; Up-Regulation

From previous observations, we have suggested that an endogenous opioid input tonically inhibits the pressor neurons of the rostral ventrolateral medulla (RVLM) of rabbits. In the present studies, the specific opioid receptor subtype(s) which may be activated by such an endogenous innervation were examined using local administration of selective antagonists. The RVLM pressor region of chloralose-anesthetized and artificially ventilated rabbits was functionally identified by local administration of L-glutamate (5 nmol). Selective blockade of neither mu nor kappa receptors in the RVLM after bilateral injections of beta-funaltrexamine (300-900 pmol) or nor-binaltorphimine (1 nmol), respectively, had any effect on either mean arterial pressure or heart rate. Delta receptors were blocked with ICI 174,864 (30-300 pmol). After the highest dose, there was a significant pressor effect (+32 +/- 6 mm Hg, mean +/- S.E.), which was of immediate onset and rapid time course (approximately 15 min), and which was accompanied by a bradycardia. In contrast, vehicle injections or injection of an inactive analog (ICI 178,173) had no effects. These results, together with previous pharmacological and anatomical evidence, suggest that there exists an enkephalinergic input to the RVLM that tonically inhibits the presympathetic pressor neurons via activation of delta-opioid receptors.

Topics: Animals; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Glutamates; Glutamic Acid; Hemodynamics; Male; Medulla Oblongata; Microinjections; Naltrexone; Narcotic Antagonists; Pressoreceptors; Rabbits; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu

Naloxone enantiomorphs were given intracerebroventricularly (i.c.v.) to rats socially deprived for a brief period of time (7-14 days) in order to ascertain the mediation of central opiate receptors in the reversal effect of opiate antagonists on the high systolic blood pressure induced by this type of stress. While the active enantiomorph ((-)-naloxone, 20 nmol per rat) lowered the elevated blood pressure, the (+)-enantiomorph (which shows a 10,000-fold lower affinity for opiate receptors) had no effect. Additionally, the antihypertensive effect induced by i.c.v. administration of an antagonist of the mu-opiate receptor (beta-funaltrexamine, 20 nmol per rat), but not of the delta-opiate receptor (ICI 174,864, 15 nmol per rat) pointed to the involvement of mu-opiate receptors as the endogenous component of the hypertensive response of rats to stress.

Topics: Animals; Blood Pressure; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Hypertension; Injections, Intraventricular; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Social Isolation; Stereoisomerism; Stress, Psychological

The involvement of delta opioid receptors in supraspinal analgesia was investigated. With this aim, opioids that produced analgesia in the tail immersion test were administered i.c.v. to mice a few minutes before the irreversible antagonist, beta-funaltrexamine (beta-FNA). Protection of the respective analgesic effects from beta-FNA blockade was obtained when evaluated 24 h later. Moreover, mu ligands protected the analgesia evoked by ED50s of morphine, [D-Ala2,N-Me-Phe4,Met-(o)5-ol]enkephalin (FK 33-824), [D-Ala2,N-Me-Phe4,Gly-ol5]enkephalin (DAGO) and human beta-endorphin at doses (ED50s) lower than those required for delta ligands (approximately ED90s) to reach a similar protection. delta Preferential ligands effectively protected the analgesia induced by ED50s of [D-Ala2,D-Leu5]enkephalin (DADLE), [D-Thr2,Leu5]enkephalin-Thr6 (DTLET) and [D-Pen2,D-Pen5]enkephalin (DPDPE) from the beta-FNA-deteriorating effect. FK 33-824 and DAGO also provided good protection of the analgesia elicited by these delta ligands whereas morphine protected much less. Binding studies after i.c.v. injection of beta-FNA showed that its alkylating effect on opioid receptors was restricted to periventricular areas. In PAG, where the mu/delta receptor ratio is about 10, [3H]DADLE specific binding was still present after ED50s of DPDPE, DAGO, morphine and DADLE as protecting agents. [3H]Dihydromorphine [( 3H]DHM) binding was well protected by ED90s of morphine and DAGO, and to a lesser extent by DPDPE and DADLE. These results suggest that delta ligands, after binding to delta receptors, also need to act upon mu receptors to produce high levels of supraspinal analgesia in the tail immersion test.

Topics: Analgesics, Opioid; Animals; Brain Chemistry; Dihydromorphine; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; In Vitro Techniques; Injections, Intraventricular; Male; Mice; Morphine; Naltrexone; Narcotic Antagonists; Pain Measurement; Receptors, Opioid; Receptors, Opioid, delta

beta-Funaltrexamine (beta-FNA) is an alkylating derivative of naltrexone. Considerable data support its use as an irreversible mu receptor antagonist. However, pretreatment of rats with beta-FNA attenuates the ability of delta antagonists and naloxone to reverse delta receptor-mediated physiological effects, suggesting that physically adjacent mu and delta receptors interact in vivo. The purpose of this study was to determine which opiate receptor subtype is altered by i.c.v. injections of beta-FNA, as well as by in vitro incubations with beta-FNA, and then to examine the hypothesis that pretreatment of rats with beta-FNA increases the IC50 for naloxone at the altered binding site. The results demonstrate that beta-FNA alters the conformation of the opiate receptor complex, as evidenced by a decrease in the Bmax of the lower affinity [3H]D-Ala2-D-Leu5-enkephalin binding site and a doubling of the naloxone IC50 for displacing [3H]D-Ala3-D-Leu5-enkephalin from this site. [3H]D-Ala2-MePhe4,Gly-ol5-enkephalin binding sites were not detectably altered by i.c.v. injections of beta-FNA. These data collectively support the concept of coupling among opioid receptor subtypes.

Topics: Animals; Binding Sites; Binding, Competitive; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Injections, Intraventricular; Male; Naloxone; Naltrexone; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu

beta-Funaltrexamine (beta-FNA) potently competed with the binding of a series of radiolabeled opiates and opioid peptides in standard binding assays with IC50 values under 10 nM. In addition, higher concentrations of beta-FNA produced an irreversible inhibition of binding which was relatively selective for mu receptors; delta binding was not affected much. The production of irreversible inhibition of [3H]dihydromorphine binding required concentrations of beta-FNA over 10-fold higher than beta-FNA concentrations needed in standard competition studies. Both mu 1 and mu 2 sites were irreversibly inhibited by beta-FNA, but mu 1 sites were more sensitive. The reversible and irreversible inhibition in these in vitro binding assays by beta-FNA were quite similar to naloxonazine. However, the activity of beta-FNA in the guinea-pig ileum suggests that it may not distinguish between mu 1 and mu 2 receptors as effectively as naloxonazine in bioassays and in vivo.

Topics: Animals; Binding, Competitive; Dihydromorphine; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; In Vitro Techniques; Male; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, mu

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Benzodiazepines; Benzomorphans; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Male; Mice; Mice, Inbred ICR; Naltrexone; Narcotic Antagonists; Oligopeptides; Pyrrolidines; Receptors, Opioid; Vas Deferens

The opioid receptor types involved in the mediation of enkephalin-induced electroencephalographic (EEG) seizures were studied in unanesthetized, freely moving rats. Four receptor-selective peptide ligands were evaluated for effectiveness in producing nonconvulsive EEG seizures after i.c.v. administration; these included the mu agonist, [D-Ala2-N-methyl-Phe4-Gly5-ol]enkephalin (DAGO), the mixed mu-delta agonist, [D-Ala2-D-Leu5]enkephalin (DADLE), and the selective delta agonists, [D-Pen2-D-Pen5]enkephalin and [D-Pen2-L-Pen5]enkephalin. Only DAGO and DADLE were found to produce EEG seizures, with DAGO being 9 times more potent than DADLE. DAGO produced a greater number of seizure episodes with a greater overall incidence compared with DADLE, reflecting its potent effect to elicit EEG seizure activity in these rats. Injections of [D-Pen2-D-Pen5]enkephalin or [D-Pen2-L-Pen5]enkephalin, even at the highest doses tested, failed to produce seizure activity. Behaviorally, the DAGO and DADLE EEG seizures were nonconvulsive but were temporally associated with episodic bursts of wet-dog shakes. The enkephalin-induced responses were extremely sensitive to antagonism by naloxone and completely blocked by pretreatment with the irreversible mu antagonist beta-funaltrexamine. The selective delta opioid receptor antagonist ICI 174,864 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH) was ineffective. The use of the most selective agonists and antagonists for mu and delta opioid receptors suggests that, in rats, enkephalin-induced EEG seizures are mediated exclusively by mu opioid receptors and not by delta opioid systems.

Topics: Animals; Electroencephalography; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Male; Naloxone; Naltrexone; Rats; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

beta-Chlornaltrexamine and beta-funaltrexamine analogues 4-7 with different length "arms" to which an electrophilic moiety is attached were synthesized in an effort to obtain affinity labels that would selectively and irreversibly block specific opioid receptor types and subtypes. One of the compounds, 4, was a potent, irreversible blocker of opioid receptors in the guinea pig ileum and mouse vas deferens preparations. The results of this study suggest that nucleophiles that are remote from the recognition locus are capable of alkylation by reactive electrophiles.

Topics: Naltrexone; Narcotic Antagonists; Receptors, Opioid; Structure-Activity Relationship

The morphine-like discriminative stimulus effects of opioid peptides with selectivity for the mu- or delta-opioid receptors were examined in rats trained to discriminate 3.0 mg/kg of morphine (s.c.) from saline in a two-choice discrete-trial avoidance paradigm. The mu-selective peptides D-Ala2-NMePhe4-Gly5(ol)enkephalin, FK 33,824 and morphiceptin, the delta-selective peptides D-Ala2-D-Leu5enkephalin and metkephamid and beta-endorphin (mu- and delta-selective) produced morphine-like stimulus effects after administration into the lateral ventricle. Generalization with the morphine cue was dose-dependent and occurred over a wide range of doses (0.01-30 micrograms), depending upon peptide. On a molar basis, the order of relative potency of the peptides as morphine-like discriminative stimuli was: D-Ala2-NMePhe4-Gly5(ol)enkephalin = FK 33,824 greater than beta-endorphin greater than D-Ala2-D-Leu5enkephalin = metkephamid greater than morphiceptin. The discriminative effects of D-Ala2-NMePhe4-Gly5(ol)enkephalin, D-Ala2-D-Leu5enkephalin and beta-endorphin were antagonized by low doses of s.c. naltrexone (0.01-1.0 mg/kg). Furthermore, the stimulus effects of s.c. morphine were antagonized by 24-hr pretreatment of rats with the irreversible mu-antagonist beta-funaltrexamine (5.0 micrograms i.c.v.). Based upon the order of relative potency of the peptides and the relative potency for antagonism of their discriminative effects by naltrexone and beta-funaltrexamine, mu-opioid receptors in the brain appear to be an important element in the genesis of morphine-like discriminative effects by opioid peptides.

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

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 effect of beta-funaltrexamine (beta-FNA), an irreversible mu receptor blocker in isolated tissue bioassays, on mu, kappa and delta opioid receptor binding and the binding of beta-[3H]FNA were determined in guinea pig brain membranes. beta-FNA inhibited the binding of mu, kappa and delta opioid ligands to their receptors with Ki values of 2.2, 14 and 78 nM, respectively. Pretreatment of brain membranes with beta-FNA (less than 2 microM) followed by extensive washing inhibited mu binding and to a lesser degree delta binding, without changing kappa binding. The extent of the irreversible inhibition was dependent on the concentration of beta-FNA, and this inhibition on mu binding could be observed with as little as 1 nM beta-FNA. The irreversible inhibition of mu binding by beta-FNA pretreatment was due to a decrease in the number of binding sites with little change in Kd, and was more pronounced in the presence of increasing concentrations of NaCl. Specific binding of beta-[3H]FNA to opioid receptors was demonstrated. The rate of specific binding with 2 nM beta-[3H]FNA was rapid in the initial 10 min and did not reach maximum in 90 min. The dissociation of bound beta-[3H]FNA (5 nM added) by the addition of excess unlabeled naloxone reached maximum at 30 min with approximately 35% of specifically bound beta-[3H]FNA remaining. Mu opioids were most effective in preventing specific binding of beta-[3H]FNA when added before beta-[3H]FNA. Opioids added 1 hr after 2 nM beta-[3H]FNA could displace maximally only 70 to 75% of specific binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Brain; Cyclazocine; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Ethylketocyclazocine; Ethylmaleimide; Guinea Pigs; Kinetics; Male; Membranes; Naloxone; Naltrexone; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Sodium Chloride

Dose-response comparisons of the ability of the selective delta antagonist ICI 154,129 (12.5-50 nmol), the nonselective antagonist naloxone (29-290 nmol), and the irreversible selective mu antagonist beta-fNA (1.3-21 nmol) to alter the threshold response to DADLE or etorphine was studied in the rat flurothyl seizure test. DADLE (35 nmol, i.c.v.) and etorphine (122 nmol/kg, s.c.) both caused increases in seizure threshold which were differentially antagonized by pretreatment (i.c.v.) with the respective antagonists. For DADLE, only ICI 154,129 and naloxone produced a dose-related blockade of the increase in seizure threshold, with ICI 154,129 being more potent than naloxone. In contrast, the anticonvulsant action of etorphine was not antagonized by ICI 154,129 (50 nmol), but was blocked by a low dose of naloxone (29 nmol) or beta-fNA (21 nmol). In addition, prior occupancy of mu-sites with beta-fNA (21 nmol) significantly diminished the abilities of either ICI 154, 129 (50 nmol) or naloxone (290 nmol) to antagonize the anticonvulsant action of DADLE. The results of this study demonstrated that the effects of DADLE to increase seizure threshold in the rat were primarily mediated by activation of a delta-opioid receptor system. Furthermore, evidence has been provided for a functional interaction between delta and mu receptors in the opioid regulation of seizure threshold.

Topics: Animals; Anticonvulsants; Cerebral Ventricles; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Etorphine; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

Cryptic receptor sites in the guinea-pig ileum preparation have been uncovered by the treatment of the preparation with the highly selective, irreversible mu opioid receptor antagonist, beta-funaltrexamine. These beta-funaltrexamine-insensitive sites appear to interact only with opioid peptides ([D-Ala2, D-Leu5]enkephalin, [D-Ala2, Met5]enkephalinamide, Tyr-D-Ser-Gly-Phe-Leu-Thr and [D-Ala2, MePhe4, Gly-ol5]enkephalin) but not with nonpeptide agonists. These new sites could not be protected by either mu-selective (morphiceptin and [D-Ala2, MePhe4, Gly-ol5]enkephalin) or delta-selective ([D-Ala2, D-Leu5]enkephalin, Tyr-D-Ser-Gly-Phe-Leu-Thr, (Allyl)2-Tyr-Gly-Gly-psi-(CH2S)-Phe-Leu, and (Allyl)2-Tyr-Aib-Aib-Phe-Leu) peptides against beta-chlornaltrexamine alkylation. However, naloxone afforded full protection of these sites against beta-chlornaltrexamine alkylation. The delta-selective antagonist, (Allyl)2-Tyr-Aib-Aib-Phe-Leu, had no activity at these cryptic sites at concentrations that effectively blocked delta receptors in the mouse vas deferens. The cryptic sites do not appear to be typical mu or delta receptors. The new receptors were termed mu', a mu subtype, and a receptor model that is consonant with our data is presented.

Topics: Alkylation; Animals; Dose-Response Relationship, Drug; Electric Stimulation; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Enkephalins; Guinea Pigs; Ileum; Male; Mice; Naloxone; Naltrexone; Oligopeptides; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Vas Deferens

beta-FNA, the beta-fumaramate methyl ester of naltrexone, has been shown to antagonize irreversibly the actions of morphine on the guinea pig ileum and mouse vas deferens bioassays but does not affect the actions of delta-receptor ligands on the mouse vas deferens bioassay, suggesting that the compound does not irreversibly bind to the delta receptor. In this paper we examine the effect of beta-FNA on the binding of the prototypic delta agonists, Leu-enkephalin and D-Ala2-D-Leu5-enkephalin, its metabolically stable analogue, and show that treatment of membranes with beta-FNA does lead to alterations in the in vitro properties of delta receptors.

Topics: Animals; Brain; Cell Membrane; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Naloxone; Naltrexone; Oligopeptides; Protein Conformation; Rats; Receptors, Opioid

Topics: Animals; Disease Models, Animal; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

The opioid receptor preference of dynorphin A fragments, particularly of dynorphin A-(1-8) (DYN 8), has been evaluated in the mouse vas deferens by means of cross-tolerance studies, by their sensitivity to naloxone antagonism and by the use of the irreversible narcotic antagonist beta-funaltrexamine. The tolerance studies revealed kappa receptor activity for the longer fragments and delta activity for the shorter fragments. DYN 8 displayed kappa as well as delta activity, whereas no interaction with mu receptors was observed. The naloxone sensitivity of dynorphin A and its fragments was low with the exception of DYN 8, that displayed an intermediate sensitivity. There was no indication that this intermediate value for DYN 8 was due to an interaction with mu receptors. This conclusion was strengthened in experiments using beta-funaltrexamine. The kappa and delta activity of DYN 8 does not explain the intermediate sensitivity to naloxone. It is proposed that DYN 8 may interact in the mouse vas deferens with a different opioid receptor than the classical mu, kappa- and delta-type.

Topics: Animals; Drug Tolerance; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Fentanyl; Male; Mice; Naloxone; Naltrexone; Peptide Fragments; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Vas Deferens

Acute i.c.v. administration of ICI 154,129 (100-600 micrograms), a delta-opioid receptor antagonist, raised the seizure threshold in a dose-related manner in rats exposed to flurothyl, a volatile convulsant. Pretreatment with naloxone or beta-funaltrexamine (beta-FNA) antagonized this effect. Lower doses of ICI 154,129 (12.5-50 micrograms), which did not influence seizure threshold, selectively antagonized the anticonvulsant action of [D-Ala2,D-Leu5]enkephalin (DADLE) in the same procedure. Consequently, it may be inferred that ICI 154,129 at high doses has mu-agonist and at low doses delta-antagonist properties in the rat flurothyl test.

Topics: Animals; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Seizures

The antinociceptive properties of morphine (mu), ethylketazocine (kappa), nalorphine (kappa), [D-Ala2, D-Leu5]enkephalin (delta) and [D-Ala2, Met5]enkephalinamide (mu, delta) were assessed using the radiant heat tail-flick and acetic acid-induced writhing assays in mice. The apparent pA2 values for the interaction of naloxone with morphine were the same regardless of the nociceptive stimulus employed or the route of administration of morphine. The apparent pA2 values for the interactions of naloxone with ethylketazocine and nalorphine in the writhing test differed significantly from that for the interaction of morphine and naloxone. Nalorphine did not produce a consistent antinociceptive effect on the tail-flick test. The apparent pA2 values for the interaction of ethylketazocine (s.c. or i.c.v.) with naloxone were similar to those for morphine-naloxone interactions on the tail-flick assay. The apparent pA2 values for the interactions of naloxone with [D-Ala2, D-Leu5] enkephalin differed from those for morphine-naloxone interactions on the writhing test. The highly selective mu antagonist beta-funaltrexamine antagonized the agonist actions of morphine and [D-Ala2, D-Leu5]enkephalin, and, in a previous study, beta-funaltrexamine antagonized the antinociceptive actions of [D-Ala2, Met5]enkephalinamide, but not those of nalorphine. It was concluded that agonist interaction with mu or kappa receptors can result in antinociceptive effects in the acetic acid-induced writhing test, and that an agonist interaction with mu, but not kappa, receptors results in antinociceptive action on the radiant heat tail-flick test, and furthermore, that a possible combination of mu and delta receptor interaction can result in antinociceptive activity in both tests.

Topics: Acetates; Acetic Acid; Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Female; Hot Temperature; Male; Mice; Naloxone; Naltrexone; Pain; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu

Topics: Animals; Charcoal; Cyclazocine; Drug Interactions; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Ethylketocyclazocine; Female; Gastrointestinal Motility; Male; Mice; Morphine; Nalorphine; Naltrexone; Receptors, Opioid