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Alcoholism, Clinical and Experimental... Feb 2010Specialized hypothalamic systems that increase food intake might also increase ethanol intake. To test this possibility, morphine and receptor-specific opioid agonists...
BACKGROUND
Specialized hypothalamic systems that increase food intake might also increase ethanol intake. To test this possibility, morphine and receptor-specific opioid agonists were microinjected in the paraventricular nucleus (PVN) of rats that had learned to drink ethanol. To cross-validate the results, naloxone methiodide (m-naloxone), an opioid antagonist, was microinjected with the expectation that it would have the opposite effect of morphine and the specific opioid agonists.
METHODS
Sprague-Dawley rats were trained, without sugar, to drink 4 or 7% ethanol and were then implanted with chronic brain cannulas aimed at the PVN. After recovery, those drinking 7% ethanol, with food and water available, were injected with 2 doses each of morphine or m-naloxone. To test for receptor specificity, 2 doses each of the mu-receptor agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-Enkephalin (DAMGO), delta-receptor agonist D-Ala-Gly-Phe-Met-NH2 (DALA), or kappa-receptor agonist U-50,488H were injected. DAMGO was also tested in rats drinking 4% ethanol without food or water available. As an anatomical control for drug reflux, injections were made 2 mm dorsal to the PVN.
RESULTS
A main result was a significant increase in ethanol intake induced by PVN injection of morphine. The opposite effect was produced by m-naloxone. The effects of morphine and m-naloxone were exclusively on intake of ethanol, even though food and water were freely available. In the analysis with specific receptor agonists, PVN injection of the delta-agonist DALA significantly increased 7% ethanol intake without affecting food or water intake. This is in contrast to the kappa-agonist U-50,488H, which decreased ethanol intake, and the mu-agonist DAMGO, which had no effect on ethanol intake in the presence or absence of food and water. In the anatomical control location 2 mm dorsal to the PVN, no drug caused any significant changes in ethanol, food, or water intake, providing evidence that the active site was close to the cannula tip.
CONCLUSIONS
The delta-opioid receptor agonist in the PVN increased ethanol intake in strong preference over food and water, while the kappa-opioid agonist suppressed ethanol intake. Prior studies show that learning to drink ethanol stimulates PVN expression and production of the peptides enkephalin and dynorphin, which are endogenous agonists for the delta- and kappa-receptors, respectively. These results suggest that enkephalin via the delta-opioid system can function locally within a positive feedback circuit to cause ethanol intake to escalate and ultimately contribute to the abuse of ethanol. This is in contrast to dynorphin via the kappa-opioid system, which may act to counter this escalation. Naltrexone therapy for alcoholism may act, in part, by blocking the enkephalin-triggered positive feedback cycle.
Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Alcohol Drinking; Analgesics, Opioid; Animals; Central Nervous System Depressants; Drinking; Eating; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Methionine; Ethanol; Male; Microinjections; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Paraventricular Hypothalamic Nucleus; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Stimulation, Chemical
PubMed: 19951300
DOI: 10.1111/j.1530-0277.2009.01084.x -
Gut Sep 1984VIP-, substance P- and met-enkephalin-containing innervation of the human gastroduodenal mucosa and Brunner's glands was studied by immunocytochemistry on whole mount...
VIP-, substance P- and met-enkephalin-containing innervation of the human gastroduodenal mucosa and Brunner's glands was studied by immunocytochemistry on whole mount tissue preparations. A dense VIP-containing nerve supply was found around fundic and pyloric glands, while the few and scattered substance P-immunoreactive fibres tended to run across the full thickness of the gastric mucosa. In the duodenum, both VIP and substance P were present in a striking nerve network in the villi as well as in the muscularis mucosae and around blood vessels. Both peptides were also immunostained in nerve bundles and neuronal perikarya between the lobules of Brunner's glands, while only very few fibres reached the proximity of acinar cells. Met-enkephalin-immunoreactivity was detected in a small number of nerve fibres, virtually confined to the basal parts of the mucosa and to the duodenal submucous plexus.
Topics: Duodenum; Enkephalin, Methionine; Fluorescent Antibody Technique; Humans; Intestinal Mucosa; Stomach; Substance P; Vasoactive Intestinal Peptide
PubMed: 6205942
DOI: 10.1136/gut.25.9.948 -
The EMBO Journal Jan 1992This study shows that cultured human articular chondrocytes express high levels of 1.4 kb prepro-enkephalin mRNA. Chondrocytes store met-enkephalin intracellularly and...
This study shows that cultured human articular chondrocytes express high levels of 1.4 kb prepro-enkephalin mRNA. Chondrocytes store met-enkephalin intracellularly and secrete this neuropeptide in mature as well as in precursor form. Gene expression is inducible by serum factors. High levels of prepro-enkephalin mRNA are detected in proliferating chondrocytes but not in confluent, contact-inhibited cells. Phorbol myristate acetate and dibutyryl cyclic AMP, but not dexamethasone, increase levels of prepro-enkephalin mRNA. Furthermore, transforming growth factor beta (TGF beta) and platelet derived growth factor (PDGF) upregulate gene expression, whereas retinoic acid, which inhibits chondrocyte proliferation, suppresses both basal and induced gene expression. Using in situ hybridization it is shown that only 1-3% of primary chondrocytes express prepro-enkephalin mRNA, whereas 52 +/- 12% of subcultured cells are strongly positive. Analysis of DNA synthesis, by autoradiography of incorporated [3H]thymidine, shows that these numbers correspond to the percentage of cells in S-phase of the cell cycle. In cultures of primary chondrocytes TGF beta promotes the formation of cartilage nodules and stimulates proliferation of adherent cells. This is associated with high levels of prepro-enkephalin mRNA in proliferating cells but not in contact-inhibited cells in cartilage nodules. In contrast, formation of cartilage nodules, proliferation and the expression of enkephalin are suppressed by interleukin-1 beta. In summary, expression of prepro-enkephalin in human articular chondrocytes is differentially controlled by cartilage regulatory factors and closely associated with cell proliferation.
Topics: Base Sequence; Bucladesine; Cartilage, Articular; Cell Division; Cells, Cultured; Dexamethasone; Enkephalin, Methionine; Enkephalins; Gene Expression Regulation; Growth Substances; Humans; Interleukin-1; Molecular Sequence Data; Protein Precursors; RNA, Messenger; Second Messenger Systems; Tetradecanoylphorbol Acetate; Tretinoin; Up-Regulation
PubMed: 1310929
DOI: 10.1002/j.1460-2075.1992.tb05036.x -
Acta Dermato-venereologica Jan 1999Methionine-enkephalin (met-enk) detected in monocytes in psoriatic skin can modulate inflammatory processes and keratinocyte differentiation/proliferation in vitro. The... (Clinical Trial)
Clinical Trial
Methionine-enkephalin (met-enk) detected in monocytes in psoriatic skin can modulate inflammatory processes and keratinocyte differentiation/proliferation in vitro. The purpose of the present study was to determine the effect of intradermal injection of met-enk on normal human skin and on the development of a delayed type skin hypersensitivity reaction. In 6 healthy volunteers, 50 microl of met-enk (16, 30, and 45 nmol) was injected once in the forearm and the reaction was evaluated clinically and by video-optical recording for 120 min. Compared to vehicle (0.9% saline), met-enk induced a time- and dose-dependent flare reaction, but no significant stimulation of a weal reaction. The flare reaction was maximal after 1 min and disappeared within 45 min. Pre-treatment with the antihistamine cetirizine reduced the flare reaction. Furthermore, the effect of met-enk on lymphocyte/monocyte infiltration and epidermal proliferation in normal skin and on a delayed type skin hypersensitivity reaction was assessed. Met-enk (45 nmol/ 50 microl) was injected at 0, 24 and 48 h. In normal skin, met-enk increased the number of dermal lymphocytes/monocytes (CD3/CD68 positive cells) and the degree of epidermal proliferation (MIBI-Ki67). In a delayed type hypersensitivity reaction induced by tuberculin (PPD), the degree of epidermal proliferation and the number of infiltrating lymphocytes/monocytes were reduced compared to PPD alone. Our study suggests that intradermal injection of met-enk in normal human skin induces an inflammatory reaction that may involve the release of histamine. In contrast, met-enk seems to down-regulate the development of a delayed type skin hypersensitivity reaction. These results may indicate that the direction of the effect of the opioid peptide met-enk on human skin depends on the rate of epidermal proliferation and the activity of immunocompetent cells.
Topics: Adult; Anti-Allergic Agents; Antigens, CD; Antigens, Differentiation, Myelomonocytic; CD3 Complex; Cell Division; Cetirizine; Enkephalin, Methionine; Erythema; Female; Humans; Immunohistochemistry; Injections, Intradermal; Ki-67 Antigen; Lymphocytes; Male; Middle Aged; Monocytes; Skin; Time Factors; Tuberculin
PubMed: 10086853
DOI: 10.1080/000155599750011642 -
European Cytokine Network 2001The protective effect of co-administration of recombinant mouse granulocyte-macrophage colony-stimulating factor (rmGM-CSF) and synthetic peptide met-enkephalin (M-ENK)...
The protective effect of co-administration of recombinant mouse granulocyte-macrophage colony-stimulating factor (rmGM-CSF) and synthetic peptide met-enkephalin (M-ENK) against blood-induced Plasmodium berghei infection in Swiss mice was investigated. Mice co-administered with rmGM-CSF (10.0 mug/kg) and M-ENK (2.0 mg/kg) x 3/day, i.p., beginning on day -1 and continuing through day +4 after the initiation of infection, showed significant suppression (p < 0.05) (sometimes even complete elimination) of parasitaemia compared to vehicle-treated controls. However, when administered separately, neither of these agents induced any detectable protective effect. Surprisingly, mice similarly co-administered with rmGM-CSF (10.0 mug/kg) and higher doses of M-ENK (10.0 mg/kg), showed no protection. Polyclonal neutralizing (100%) antibody to rmGM-CSF abrogated the combined protective effect of these agents. Additionally, naloxone (10.0 mg/kg/day x 6, i.p.), a non-selective, opioid receptor antagonist, also blocked the combined protection. Mice that survived the challenge showed a significant increase (p < 0.05) in total circulating leukocytes counts, and the pool-size and the phagocytic activity of both the peritoneal and splenic macrophages, ex vivo. Silica (3.0 mg/mouse, i.v.) abrogated the combined protective effect of rmGM-CSF and M-ENK. These results indicate that co-administration of rmGM-CSF and dose dependent quantities of M-ENK in P. berghei-infected mice can protect against malaria, apparently through macrophage-mediated mechanisms.
Topics: Animals; Antibodies; Drug Combinations; Enkephalin, Methionine; Female; Granulocyte-Macrophage Colony-Stimulating Factor; Leukocyte Count; Leukocytes; Macrophages; Malaria; Male; Mice; Naloxone; Phagocytosis; Plasmodium berghei; Recombinant Proteins; Silicon Dioxide
PubMed: 11566634
DOI: No ID Found -
British Journal of Pharmacology Sep 19811 Slices of cerebral cortex from Wistar rats, TO mice or C57 mice were preincubated with [3H]-adenosine, and labelled purines were subsequently releases by electrical...
1 Slices of cerebral cortex from Wistar rats, TO mice or C57 mice were preincubated with [3H]-adenosine, and labelled purines were subsequently releases by electrical stimulation or by perfusing with ouabain, 100 micro M. 2 Electrically-evoked purine release was substantially reduced when the Ca2+ concentration in the medium was lowered from 2.4 to 0.1 mM. In both rats and mice, the electrically-evoked release was increased by morphine and methionine-enkephalin (Met-enkephalin), 10 micro M, and in rats and TO mice by morphine 1 micro M, both drug effects being prevented by naloxone. 3 Purine release evoked by ouabain was also increased by morphine 1 and 10 micro M, though not by Met-enkephalin, from slices of rat cortex. Ouabain-induced release from TO mice was reduced by morphine, and from C57 mice was unchanged. 4 The enhancement by morphine of electrically-evoked purine release may indicate that purines mediate some effects of morphine in the CNS.
Topics: Animals; Calcium; Cerebral Cortex; Electric Stimulation; Endorphins; Enkephalin, Methionine; Enkephalins; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Morphine; Ouabain; Purine Nucleosides; Rats; Rats, Inbred Strains
PubMed: 7272599
DOI: 10.1111/j.1476-5381.1981.tb09970.x -
British Journal of Pharmacology Jul 19801 The effect of intravenous administration of thyrotrophin-releasing hormone (TRH) and methionine-enkephalin on gastric acid and pepsin secretions was investigated in...
1 The effect of intravenous administration of thyrotrophin-releasing hormone (TRH) and methionine-enkephalin on gastric acid and pepsin secretions was investigated in conscious cats prepared with chronic gastric fistulae.2 TRH, 20 mug kg(-1) h(-1), did not influence unstimulated gastric acid secretion, nor gastric acid secretion stimulated by submaximal doses of pentagastrin or histamine. Pepsin secretion stimulated by pentagastrin was not influenced by TRH.3 TRH, 20 mug kg(-1) h(-1), significantly reduced the gastric acid and pepsin responses to intravenous infusion of insulin. TRH also significantly reduced the degree of hypoglycaemia seen in response to insulin. TRH, 20 mug kg(-1) h(-1), but not 5 mug kg(-1) h(-1), infused alone resulted in a significant hyperglycaemia.4 It is concluded that the reduction of insulin-stimulated gastric secretion by TRH is not dependent on the hyperglycaemic action of the peptide. The mechanism of action of TRH on insulin-stimulated secretion is discussed with respect to its site of action.5 Methionine-enkephalin or the potent analogue, D-Ala(2), Met-enkephalinamide were without effect on unstimulated gastric secretion, or secretion stimulated by pentagastrin, histamine, and insulin. The opiate receptor antagonist, naloxone, did not significantly alter the gastric acid or pepsin response to insulin.6 It is concluded that there is no evidence that opiates stimulate oxyntic glands directly, nor that the oxyntic cells may possess high affinity binding sites for opiates, nor that endogenous opiates are involved in the control of gastric secretion.
Topics: Animals; Blood Glucose; Cats; Endorphins; Enkephalin, Methionine; Enkephalins; Gastric Juice; Insulin; Naloxone; Pentagastrin; Pepsin A; Thyrotropin-Releasing Hormone; Time Factors
PubMed: 6772265
DOI: 10.1111/j.1476-5381.1980.tb07044.x -
Annals of Surgery Jul 1982In four dogs with chronic gastric fistulae, bombesin infusion was used to stimulate the release of gastrin and pancreatic polypeptide (PP) as well as rates of gastric...
In four dogs with chronic gastric fistulae, bombesin infusion was used to stimulate the release of gastrin and pancreatic polypeptide (PP) as well as rates of gastric acid secretion. Neither methionine-enkephalin (met-enkephalin) nor naloxone alone or the combination of these agents altered bombesin-stimulated gastrin release. met-enkephalin alone (but not naloxone) significantly inhibited the gastric secretory response to bombesin, but this inhibitory effect was not influenced by the simultaneous infusion of naloxone; the data suggested that the effect of met-enkephalin was indirect, and perhaps modulated by another inhibitory mechanism. Whereas PP release induced by bombesin was not affected by naloxone, it was significantly suppressed by met-enkaphalin; since this inhibition was virtually totally reversed by naloxone, the data suggested that the effect of opiate peptides on the release of pancreatic polypeptide was direct and mediated by a specific opiate receptor.
Topics: Animals; Bombesin; Dogs; Endorphins; Enkephalin, Methionine; Enkephalins; Gastric Acid; Gastrins; Infusions, Parenteral; Naloxone; Pancreatic Polypeptide; Peptides; Stimulation, Chemical; Time Factors
PubMed: 7092351
DOI: 10.1097/00000658-198207000-00011 -
Inflammation Research : Official... Mar 2014Previous studies found that neuron specific enolase promoter (Nse-BMP4) transgenic mice have increased expression of the nociceptive mediator, substance P and...
INTRODUCTION
Previous studies found that neuron specific enolase promoter (Nse-BMP4) transgenic mice have increased expression of the nociceptive mediator, substance P and exaggerated local injury responses associated with heterotopic ossification (HO). It is of interest great to know the pain responses in these mice and how the opioid signaling is involved in the downstream events such as mast cell (MC) activation.
MATERIALS AND METHODS
This study utilized a transgenic mouse model of HO in which BMP4 is expressed under the control of the Nse-BMP4. The tactile sensitivity and the cold sensitivity of the mice were measured in a classic inflammatory pain model (carrageenan solution injected into the plantar surface of the left hind paw). The MC activation and the expression profiles of different components in the opioid signaling were demonstrated through routine histology and immunohistochemistry and Western blotting, in the superficial and deep muscle injury models.
RESULTS
We found that the pain responses in these mice were paradoxically attenuated or unchanged, and we also found increased expression of both Methionine Enkephalin (Met-Enk), and the μ-opioid receptor (MOR). Met-Enk and MOR both co-localized within activated MCs in limb tissues. Further, Nse-BMP4;MOR(-/-) double mutant mice showed attenuated MC activation and had a significant reduction in HO formation in response to injuries.
CONCLUSIONS
These observations suggest that opioid signaling may play a key role in MC activation and the downstream inflammatory responses associated with HO. In addition to providing insight into the role of MC activation and associated injury responses in HO, these findings suggest opioid signaling as a potential therapeutic target in HO and possibly others disorders involving MC activation.
Topics: Animals; Bone Morphogenetic Protein 4; Cold Temperature; Enkephalin, Methionine; Immunohistochemistry; Inflammation; Mast Cells; Mice; Mice, Knockout; Mice, Transgenic; Muscle, Skeletal; Mutation; Nociception; Ossification, Heterotopic; Pain Measurement; Phosphopyruvate Hydratase; Physical Stimulation; Receptors, Opioid, mu; Signal Transduction
PubMed: 24327087
DOI: 10.1007/s00011-013-0690-4 -
The Journal of Neuroscience : the... May 2008The enkephalin signaling pathway regulates various neural functions and can be altered by neurodegenerative disorders. In Alzheimer's disease (AD), elevated enkephalin...
The enkephalin signaling pathway regulates various neural functions and can be altered by neurodegenerative disorders. In Alzheimer's disease (AD), elevated enkephalin levels may reflect compensatory processes or contribute to cognitive impairments. To differentiate between these possibilities, we studied transgenic mice that express human amyloid precursor protein (hAPP) and amyloid-beta (Abeta) peptides in neurons and exhibit key aspects of AD. Met-enkephalin levels in neuronal projections from the entorhinal cortex and dentate gyrus (brain regions important for memory that are affected in early stages of AD) were increased in hAPP mice, as were preproenkephalin mRNA levels. Genetic manipulations that exacerbate or prevent excitotoxicity also exacerbated or prevented the enkephalin alterations. In human AD brains, enkephalin levels in the dentate gyrus were also increased. In hAPP mice, enkephalin elevations correlated with the extent of Abeta-dependent neuronal and behavioral alterations, and memory deficits were reduced by irreversible blockade of mu-opioid receptors with the antagonist beta-funaltrexamine. We conclude that enkephalin elevations may contribute to cognitive impairments in hAPP mice and possibly in humans with AD. The therapeutic potential of reducing enkephalin production or signaling merits further exploration.
Topics: Aged; Aged, 80 and over; Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Behavior, Animal; Dentate Gyrus; Disease Models, Animal; Enkephalin, Methionine; Enkephalins; Entorhinal Cortex; Female; Humans; Male; Mice; Mice, Transgenic; Neural Pathways; Neurons; Protein Precursors; RNA, Messenger; Up-Regulation
PubMed: 18463254
DOI: 10.1523/JNEUROSCI.0590-08.2008