Porcine pituitary dynorphin: complete amino acid sequence of the biologically active heptadecapeptide

Dynorphin-phospholipid membrane interactions: role of phospholipid head-group and cholesterol

The interaction of the kappa-opioid receptor-selective heptadecapeptide dynorphin A(1-17) (Tyr1-Gly-Gly-Phe-Leu5-Arg-Arg-Ile-Arg-Pro10-Lys-Leu-Lys-Trp-As p15-Asn-Glu) with phospholipid membranes has been investigated by monitoring the leakage of the internal aqueous contents of liposomes, the changes in the tryptophan emission spectrum, and the collisional quenching of tryptophan fluorescence by brominated lipids. The peptide induces more extensive leakage of contents from phosphatidylserine than from phosphatidylcholine vesicles, and experiences a blue shift of the Trp fluorescence emission maximum in the presence of phosphatidylserine vesicles. In the presence of phosphatidylcholine vesicles, however, the Trp fluorescence intensity is reduced without a blue shift. In phosphatidylserine membranes containing 10 mol% phosphatidylcholine, the intensity of the blue-shifted fluorescence is enhanced. This avid interaction of dynorphin A(1-17) with phosphatidylserine membranes is likely to be mediated by the positively charged Arg and Lys groups. It is proposed that, while the N-terminus of the peptide may be embedded in the bilayer in analogy with dynorphin (1-13), the C-terminal region of dynorphin A (1-17) bends back onto the bilayer/water interphase, and that the Trp14 residue is stabilized in a hydrophobic pocked near the interphase by the interaction of the neighboring charged amino acids with the phosphate, carboxyl and amino groups on phosphatidylserine.

Isolation and structure of the endogenous agonist of opioid receptor-like ORL1 receptor

The ORL1 receptor, an orphan receptor whose human and murine complementary DNAs have recently been characterized, structurally resembles opioid receptors and is negatively coupled with adenylate cyclase. ORL1 transcripts are particularly abundant in the central nervous system. Here we report the isolation, on the basis of its ability to inhibit the cyclase in a stable recombinant CHO(ORL1+) cell line, of a neuropeptide that resembles dynorphin A9 and whose amino acid sequence is Phe-Gly-Gly-Phe-Thr-Gly-Ala-Arg-Lys-Ser-Ala-Arg-Lys-Leu-Ala-Asn-Gln. The rat-brain cDNA encodes the peptide flanked by Lys-Arg proteolytic cleavage motifs. The synthetic heptadecapeptide potently inhibits adenylate cyclase in CHO(ORL1+) cells in culture and induces hyperalgesia when administered intracerebroventricularly to mice. Taken together, these data indicate that the newly discovered heptadecapeptide is an endogenous agonist of the ORL1 receptor and that it may be endowed with pro-nociceptive properties.

Identification of dynorphins as endogenous ligands for an opioid receptor-like orphan receptor

To identify the endogenous ligands for a cloned orphan receptor that shares high degrees of sequence homology with opioid receptors, this orphan receptor was expressed in Xenopus oocytes and in mammalian cell lines CHO-K1 and HEK-293. The coupling of the receptor to a G protein-activated K+ channel was used as a functional assay in oocytes. Endogenous opioid peptide dynorphins were found to activate the K+ channel by stimulating the orphan receptor. This activation was dose-dependent, with EC50 values at 45 and 37 nM for dynorphin A and dynorphin A-(1-13), respectively. The dynorphin effect was antagonized by the non-selective opioid antagonist naloxone but at rather high concentrations in the micromolar range. Naloxone also caused a rightward shift of the dose-response curve for dynorphin A, suggesting a competitive antagonism mechanism. In transiently transfected cells, 5 microM dynorphin A-(1-13) inhibited the forskolin-stimulated cyclic AMP increase by 51 and 35% in CHO-K1 and HEK-293 cells, respectively. Other classes of endogenous opioids, i.e. enkephalins and endorphins, caused very little activation of this receptor. These results suggest that this orphan receptor is a member of the opioid receptor family and that dynorphins are endogenous ligands for this receptor.

Synthesis and opioid activity of 2-substituted dynorphin A-(1-13) amide analogues

A series of 2-substituted dynorphin A-(1-13) amide (Dyn A-(1-13)NH2) analogues was prepared by solid phase peptide synthesis and evaluated for opioid receptor affinities in radioligand binding assays and for opioid activity in the guinea pig ileum (GPI) assay. Amino acid substitution at the 2 position produced marked differences in both opioid receptor affinities and potency in the GPI assay; Ki values for the analogues in the radioligand binding assays and IC50 values in the GPI assay varied over three to four orders of magnitude. The parent peptide, Dyn A-(1-13)NH2, exhibited the greatest affinity and selectivity for kappa receptors and was the most potent peptide examined in the GPI assay. The most important determinant of opioid receptor selectivity and opioid potency for the synthetic analogues was the stereochemistry of the amino acid at the 2 position. Except for [D-Lys2]Dyn A-(1-13)NH2 in the kappa receptor binding assay, the analogues containing a D-amino acid at position 2 were much more potent in all of the assays than their corresponding isomers containing an L-amino acid at this position. The L-amino acid-substituted analogues generally retained some selectivity for kappa opioid receptors. The more potent derivatives with a D-amino acid in position 2, however, preferentially interacted with mu opioid receptors. Introduction of a positively charged amino acid into the 2 position generally decreased opioid receptor affinities and potency in the GPI assay.

Dynorphin-degrading cysteine protease is highly specific for paired arginine residues

The cleavage of dynorphin and three analogs containing paired basic residues by several proteases was investigated. The cysteine protease of neuroblastoma cells cleaved only the bond between Arg-Arg residues. Submandibular arginyl-endopeptidase, however, cleaved bonds between both Arg-Arg and Arg-Lys residues, and pancreatic trypsin at the carboxyl sides of both arginine and lysine residues. This shows that the cysteine protease is highly specific for paired arginine residues.

Pain and tooth pulp evoked potentials

The purpose of this study was to verify whether the late components (N 140) of TPEPs were a reliable index of pain intensity. In the group with acute pain, except for higher amplitudes of the second negative wave, the plateau phenomenon has been noted. Analgesic and placebo effects indicated that the method used offers more objective than subjective components, because the real value of amplitudes is about 10% of control values for analgesic and between 60 and 70% for placebo. Shorter latency periods were observed in all parts of evoked potentials in the patients suffering from trigeminal neuralgia, as occurrence of a greater number of waves; while amplitudes on the affected side were significantly higher than on the healthy side.

Opioid receptors and their pharmacological profiles

Opioid receptors can be divided into three major classes, which are called mu, delta and kappa-receptors. The molecular basis of the receptors is discussed and a hypothesis of the binding of bivalent ligands to the receptor is presented. Furthermore the mechanism of action, the distribution and the probable function of these classes is overviewed. Increasing evidence is accumulating that the classical binding model cannot explain completely the interaction of opioids with their receptors. In addition to the mu-receptors, high affinity mu 1 binding sites have been demonstrated. Similarly, the delta receptors may be divided in delta 1 and delta 2. The significance of these subclasses is not yet fully understood. The high affinity mu 1-binding sites, however, represent probably an activated receptor complex, e.g. the complex between the receptor and the guanine-nucleotide-binding protein.

Subcellular localization, partial purification, and characterization of a dynorphin processing endopeptidase from bovine pituitary

An enzyme capable of cleaving dynorphin B-29 to dynorphin B-13 is present in bovine pituitary, with 40- to 50-fold higher specific activity in the posterior and intermediate lobes than in the anterior lobe. Subcellular fractionation of bovine neurointermediate pituitary shows that this enzyme is present in the peptide-containing secretory vesicles. The enzyme has been purified 2,800-fold from whole bovine pituitaries using ion-exchange and gel filtration chromatography. Purified dynorphin-converting enzyme has a neutral pH optimum, and is subsantially inhibited by the thiol-protease inhibitor p-chloromercuriphenylsulfonic acid, but not by serine or metalloprotease inhibitors. The purified enzyme processes dynorphin B-29 at Arg14, producing both dynorphin B-14 and dynorphin B-13 in a 5:1 ratio. No other cleavages are observed, suggesting that the activity is free from other proteases and is specific for single Arg sequences. Purified enzyme also processes dynorphin A-17 at the single Arg cleavage site, generating both dynorphin A-8 and A-9 in a 7:1 ratio. The tissue distribution, subcellular localization, and substrate specificity of this enzyme are consistent with a physiological role in the processing of dynorphin B-29 and dynorphin A-17, and possibly other peptides, at single Arg residues.

An inhibitor of endopeptidase-24.15 blocks the degradation of intraventricularly administered dynorphins

Conversion of the octapeptide dynorphin (Dyn) A-(1-8) to Leu5-enkephalin (LE) by endopeptidase EC 3.4.24.15 (EP-24.15) in vivo was examined using the technique of ventriculocisternal perfusion. Peptides were administered intracerebroventricularly in the presence or absence of the EP-24.15 inhibitor N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate (cFPAAF-pAB) via cannulae placed into the lateral ventricle of urethane-anesthetized rats. The concentration of Dyn-like peptides and LE within the CSF was monitored by radioimmunoassay in samples of CSF taken from a second cannula placed in the cisterna magna. In the absence of inhibitor, less than 5% of the Dyn A-(1-8) administered was recovered in CSF. Immunoreactive LE, which is normally not found in CSF, increased rapidly in content following Dyn A-(1-8) infusion, an observation suggesting that the larger peptide is converted to LE. When the inhibitor cFPAAF-pAB was coadministered with Dyn A-(1-8), the concentration of immunoreactive Dyn A-(1-8) after 5 min was 40 times higher than that found in the absence of inhibitor. The angiotensin converting enzyme inhibitor captopril reduced the degradation of Dyn A-(1-8) to a much lesser degree. The inhibitor of EP-24.15 also afforded some protection of other Dyn-like peptides. No EP-24.15 activity was found in rat CSF, whereas high activity was found in the choroid plexus. Taken together, these data clearly indicate that an ectoenzyme form of EP-24.15 rapidly converts intracerebroventricularly administered Dyn-like peptides to LE.

Peptides and transmitter enzymes in hypothalamic magnocellular neurons after administration of hyperosmotic stimuli: comparison between messenger RNA and peptide/protein levels

In situ hybridization histochemistry and indirect immunofluorescence histochemistry were used to study changes in the expression of vasopressin (VP), oxytocin (OXY), tyrosine hydroxylase (TH), galanin (GAL), dynorphin (DYN) and cholecystokinin (CCK) in hypothalamic magnocellular neurons of the paraventricular (PVN) and supraoptic (SON) nuclei of rats. After prolonged administration of 2% sodium chloride as drinking water (salt-loading), the treatment increased the levels of VP, OXY, TH, GAL, DYN and CCK mRNA in the PVN and SON. The increase in CCK mRNA was, however, proportionally higher in the PVN than in the SON. Within cell bodies of the PVN and SON of salt-loaded rats, a depletion of VP- and OXY-like immunoreactivity (LI) and an increase in TH-LI were seen. In salt-loaded/colchicine-treated rats, a marked decrease in GAL- and DYN-LI, but no specific changes in CCK-LI were observed. Within nerve fibers of the posterior pituitary of salt-loaded rats, a marked depletion of VP-, GAL- and DYN-LI was found. Less pronounced depletion was observed in OXY- and CCK-LI, and no specific changes in TH-LI were seen. The results show that high plasma osmolality induces increased mRNA levels for VP, OXY, TH, GAL, DYN and CCK, presumably indicating increased synthesis, an increased export from cell somata of VP, OXY, GAL and DYN, and a decrease in levels of these peptides in the posterior pituitary, suggesting increased release. The catecholamine-synthesizing enzyme TH, however, which has a cytoplasmic localization and is not released from nerve endings, remains high in the cell bodies and nerve endings during this state of increased activity.

Chimeric opioid peptides: tools for identifying opioid receptor types

We synthesized several chimeric peptides in which the N-terminal nine residues of dynorphin-32, a peptide selective for the kappa opioid receptor, were replaced by opioid peptides selective for other opioid receptor types. Each chimeric peptide retained the high affinity and type selectivity characteristic of its N-terminal sequence. The common C-terminal two-thirds of the chimeric peptides served as an epitope recognized by the same monoclonal antibody. When bound to receptors on a cell surface or membrane preparation, these peptides could still bind specifically to the monoclonal antibody. These chimeric peptides should be useful for isolating mu, delta, and kappa opioid receptors and for identifying opioid receptors on transfected cells in expression cloning procedures. The general approach using chimeric peptides should be applicable to other peptide receptors.

Expression and Post-Translational Processing of Preprodynorphin in the Rat Anterior Pituitary Cell Line, GH4C1

Abstract A recombinant plasmid containing the rat preprodynorphin cDNA was introduced into the rat anterior pituitary cell line, GH4C1. These cells normally express growth hormone and prolactin but not prodynorphin. Stable transformants were isolated and analyzed for the expression and processing of prodynorphin. Chromatographic analyses demonstrated that the prodynorphin was incompletely processed in GH4C1 cells. Analyses of the peptides by specific radioimmunoassays to chemically synthesized peptides showed that the cells have the ability to process both at dibasic and monobasic cleavage sites. The release of prodynorphin-derived peptides paralleled that of prolactin upon stimulation with thyrotropin-releasing hormone, forskolin or carbachol suggesting that the prodynorphin-derived peptides and prolactin are sequestered in similar physiologically responsive compartments. These data suggest that the GH4C1 cells incompletely process prodynorphin. The processing in GH4C1 cells occurs both at monobasic and dibasic cleavage sites.

Bioactive conformation of linear peptides in solution: an elusive goal?

Bioactive peptides of natural origin have, in general, short linear sequences, and are characterized by a large conformational flexibility. It is very difficult to study their conformation in solution since they exist, almost invariably, as a complex mixture of numerous conformers, most of which are extended. The so-called bioactive conformation may be one of them, although the solvents used in solution studies often have properties drastically different from those of the biological system in which the peptide acts. There is, however, no simple way of identifying the bioactive conformation amid the many existing conformers. It is possible to approach a solution to this problem using two distinct strategies: (a) Limiting the conformational freedom of the peptide, e.g., by increasing the viscosity of the solution and decreasing the temperature, in the assumption that the bioactive conformation is, even slightly, more stable than the others. (b) Trying to mimic in solution the physicochemical features of the more reliable receptor models. These two approaches will be illustrated with examples taken mainly from opioid peptides.

Characterization of cysteine proteases functioning in degradation of dynorphin in neuroblastoma cells: evidence for the presence of a novel enzyme with strict specificity toward paired basic residues

Two dynorphin-degrading cysteine proteases, I and II, were extracted with Triton X-100 from neuroblastoma cell membrane, isolated from accompanying dynorphin-degrading trypsin-like enzyme by affinity chromatography on columns of soybean trypsin inhibitor-immobilized Sepharose and p-mercuribenzoate-Sepharose, and separated by ion-exchange chromatography on diethylaminoethyl (DEAE)-cellulose and TSK gel DEAE-5PW columns. Cysteine protease II was purified further by hydroxyapatite chromatography and gel filtration. The molecular weights of cysteine proteases I and II were estimated to be 100,000 and 70,000, respectively, by gel filtration. Both of the enzymes, were inhibited by p-chloromercuribenzoate, N-ethylmaleimide, and high-molecular-weight kininogen, but not or only slightly inhibited by diisopropylphosphorofluoridate, antipain, leupeptin, E-64, calpain inhibitor, and phosphoramidon. Cysteine protease I cleaved dynorphin(1-17) at the Arg6-Arg7 bond with the optimum pH of 8.0, whereas II cleaved dynorphin(1-17) at the Lys11-Leu12 bond and the Leu12-Lys13 bond with the optimum pH values of 8.0 and 6.0, respectively. These bonds corresponded to those that had been proposed as the initial sites of degradation by neuroblastoma cell membrane. Cysteine protease I was further found to show strict specificity toward the Arg-Arg doublet, when susceptibilities of various peptides containing paired basic residues were examined as substrates for the enzyme.

"DAKLI": a multipurpose ligand with high affinity and selectivity for dynorphin (kappa opioid) binding sites

We describe a synthetic ligand, "DAKLI" (Dynorphin A-analogue Kappa LIgand), related to the opioid peptide dynorphin A. A single reactive amino group at the extended carboxyl terminus permits various reporter groups to be attached, such as 125I-labeled Bolton-Hunter reagent, fluorescein isothiocyanate, or biotin. These derivatives have high affinity and selectivity for the dynorphin (kappa opioid) receptor. An incidental finding is that untreated guinea pig brain membranes have saturable avidin binding sites.

Membrane receptors in the gastrointestinal tract

This review focusses on the roles that membrane receptors and their transducers play in the physiology and pathology of the gastrointestinal tract. The multifactorial regulation of [correction] mucosal growth and function is discussed in relation to the heterogeneity of exocrine and endocrine populations that originate from progenitor cells in stomach and intestine.

kappa-Opioid agonists produce antinociception after i.v. and i.c.v. but not intrathecal administration in the rat

1. Nociceptive thresholds to noxious mechanical (paw pressure) and thermal (tail flick) stimuli were recorded in conscious rats. The effects of three selective kappa-opioid receptor agonists on the responses to these stimuli were determined following intravenous, intracerebroventricular or intrathecal administration. Results were compared with those obtained with morphine. 2. Following intravenous administration PD117302, U50488, U69593 and morphine produced steep parallel dose-response curves indicating antinociceptive activity when evaluated in the paw pressure test. When U50488 and U69593 were tested at a single dose of 3.3 mg kg-1 no effect was seen in the tail flick test. 3. When given by the intrathecal route only morphine was effective at increasing the nociceptive threshold. PD117302, U50488 and U69593 were without effect in either the paw pressure or tail flick tests when tested at doses up to 100 micrograms per rat. PD117302 caused flaccid paralysis of the hindlimbs following intrathecal administration at the top dose tested. This effect was not reversible by naloxone. 4. All three kappa-opioid receptor agonists produced naloxone-reversible antinociception in the paw pressure test, and to a lesser extent in the tail flick test, when injected directly into the third cerebral ventricle with the maximum effect occurring between 5 and 10 min after administration and declining back to control levels by 60 min. Morphine had a much slower onset of action with the peak effect being observed 30 min after dosing. 5. It is concluded that, under our experimental conditions in the rat, the antinociceptive effects of kappa-agonists are likely to be operated via an action at a supraspinal rather than a spinal site.

Dynorphin A selectively reduces a large transient (N-type) calcium current of mouse dorsal root ganglion neurons in cell culture

Opioid receptors are differentially coupled to ion channels. Mu- and delta-opioid receptors are coupled to calcium- and/or voltage-dependent potassium channels and kappa-opioid receptors are coupled to voltage-dependent calcium channels. Using the single-electrode voltage-clamp technique, we investigated the effect of the kappa-opioid receptor agonist dynorphin A on somatic calcium currents of mouse dorsal root ganglion (DRG) neurons in culture. Three different calcium currents were recorded: a small transient current activated positive to -60 mV; a large, inactivating current activated positive to -50 mV; and a moderate, slowly inactivating current activated positive to -40 mV. The first was less sensitive to cadmium block than the others. These calcium currents were similar to those described in other cells, which have been designated T, N, and L calcium currents, respectively. The opioid peptide dynorphin A reduced calcium current by selectively reducing the large inactivating (N) calcium current. Naloxone, an opioid receptor antagonist, reversed this action of dynorphin A. N calcium current is the predominant calcium current in DRG neurons. If N calcium channels are present in primary afferent terminals, and if they are coupled to kappa-opioid receptors as in the soma, these results suggest a mechanism by which dynorphin A inhibits calcium influx and neurotransmitter release.

Opioids and opioid receptors in peripheral tissues

Opioid peptides belonging to the enkephalin, beta-endorphin or dynorphin family, acting on specific opiate receptors may be found in peripheral tissues. Enkephalins have a widespread peripheral distribution, while beta-endorphin and dynorphin may be found locally in the enteric nervous system. The peptides of the various families are formed from specific precursor molecules. Apart from the enteric nervous system, opioids are also found in the adrenal medulla as well as in several autonomic ganglia. There is some evidence of three different classes of opioid receptors in peripheral tissues, i.e. mu-, delta- and kappa-receptors. These receptors are not only found on enteric nervous and mucosa cells but also on various cells in the immune system where opioid peptides seem to have important actions and appear to link the neuroendocrine and immune systems to control immunological functions. The physiological as well as the pathophysiological role of opioid peptides in the periphery is gradually being elucidated and, based on such knowledge, new therapeutic implications in gastrointestinal or immune diseases may be developed.

Dynorphin(1-8) immunoreactivity in brainstem and hypothalamic nuclei of normotensive and age-matched hypertensive rat strains

The concentration of dynorphin (1-8) immunoreactivity [ir-dyn(1-8)] was measured in 10 hypothalamic and 11 brainstem nuclei of Sprague-Dawley (SD) and 6- and 14-week old Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats. The highest concentrations of ir-dyn(1-8) were found in the lateral preoptic and lateral hypothalamic areas of the hypothalamus and the solitary tract nucleus of the brainstem. Levels of the peptide were low in other brainstem nuclei compared to hypothalamic areas. There was a significant reduction in ir-dyn(1-8) concentrations at 14 weeks of age compared to 6 weeks of age in all 9 nuclei examined in SH and WKY rats. However, there were no differences between the strains at either age. These changes may be related to the increase in blood pressure that occurs in both SH and WKY rats over this age range although other factors must also be involved to produce the higher blood pressure levels of the SH rat.

Subunit structure and purification of opioid receptors

Considerable evidence indicates the existence of multiple types of opioid receptors. The three major types have been named mu, delta and kappa. The earlier evidence was based on pharmacological as well as membrane binding experiments. This paper will emphasize more recent studies using solubilized opioid binding sites. Several laboratories, including our own, have succeeded in separating kappa receptors from other types. A similar separation of mu from delta receptors has not yet been achieved. By crosslinking experiments with 125I- human beta-endorphin we have been able to provide strong evidence for differences in molecular size between the major binding components of mu (65K) and delta (53K) receptors. It is not yet established whether the difference resides in the protein or carbohydrate portion of these glycoproteins. These results suggest that the three major types of opioid receptors represent distinct molecular entities. An active opioid binding protein solubilized from bovine striatal membranes has been purified to apparent homogeneity. The major purification steps involve affinity chromatography and lectin chromatography on immobilized wheat germ agglutinin. The purified material gave a single band of molecular weight 65K Da on SDS-PAGE. Its specific activity for opioid binding was ca. 13,000 pmol/mg protein and its properties are those of a component of the mu receptor.

Are opioid peptides co-localized with vasopressin or oxytocin in the neural lobe of the rat?

The content of vasopressin, oxytocin, neurophysin, leucine-enkephalin, methionine-enkephalin, dynorphin-(1-13), and alpha-neoendorphin in the rat neurohypophysis was measured after different periods of dehydration and after depolarisation of isolated neural lobes and of neurosecretory nerve endings. The rates at which the amount of neurohypophysial hormone and opioid peptides decreased, and the changes in the ratios between the amount of vasopressin or oxytocin and opioid peptide in the neurohypophysis after dehydration and in the incubation medium after depolarization in vitro cast some doubt on, and can be explained by mechanisms other than co-localisation of the different peptides.

Striato-nigral dynorphin and substance P pathways in the rat. I. Biochemical and immunohistochemical studies

The effect of striatal ibotenic acid lesions on dynorphin-, substance P- and enkephalin-like immunoreactivities in the substantia nigra has been studied with immunohistochemistry as well as biochemistry. A comparison was made with the effects produced by intranigral ibotenic acid lesion and by 6-hydroxy-dopamine injection into the medial forebrain bundle. In addition, the effect of the striatal lesions on nigral glutamic acid decarboxylase (GAD)-positive structures was analysed with immunohistochemistry. The effect of the lesions was analysed functionally in the Ungerstedt rotational model, in order to obtain a preliminary evaluation of the extent of the lesions. The striatal lesions produced a parallel depletion of dynorphin and substance P levels in the substantia nigra, pars reticulata, ipsilateral to the treated side, which was dependent upon the extent and location of the lesion. Ibotenic acid lesions into the tail and the corpus of the striatum produced stronger nigral-peptide depletion than lesions in the head and the corpus of the striatum. Comparison of placement of lesions and localization of depleted area in the substantia nigra revealed a topographical relationship. Furthermore, the nigral depletion patterns of dynorphin and substance P were similar. The immunohistochemical analysis revealed that also GAD-positive fibers in the pars reticulata to a large extent disappeared after striatal lesions, in parallel to the dynorphin- and substance P-positive fibers. However, the depletion was less pronounced for GAD than for the peptides, probably related to presence of local GABA neurons in the zona reticulata of the substantia nigra. These results indicate that with the types of lesion used in this study it is not possible to provide evidence for a differential localization within the striatum of dynorphin-, substance P- and GABA-positive cell bodies projecting to the substantia nigra. The radioimmunoassay showed that (Leu)- but not (Met)-enkephalin was affected to the same extent as the dynorphin peptides, supporting the view that (Leu)-enkephalin in the pars reticulata of the substantia nigra is derived from proenkephalin B and not from proenkephalin A. In the immunohistochemical analysis (Met)-enkephalin-like immunoreactivity could only be detected in the pars compacta of the substantia nigra and did not seem to be affected by any of the lesions. The striatal lesions produced a behavioural asymmetry, which could be disclosed by stimulating the rats with apomorphine, which produced ipsilateral rotation.(ABSTRACT TRUNCATED AT 400 WORDS)

Striato-nigral dynorphin and substance P pathways in the rat. II. Functional analysis

In the present study the functional role of the striato-nigral dynorphin and substance P pathways in rat brain has been studied using the rotational behavioural model and an intracerebral dialysis technique complemented with brain lesions and immunohistochemical analysis. Attempts were made to evaluate whether these striato-nigral neurons have a feed-back modulatory action on the dopaminergic nigro-striatal system, or whether they represent an outflow pathway conveying motor information from the striatum. Unilateral injection of dynorphin A into the substantia nigra reticulata of naive rats induced contralateral rotational behaviour. This effect was dose-dependent and mimicked by the kappa-opioid receptor agonist, U50,488H. Intranigral injection of substance P, as well as substance K, also produced dose-dependent contralateral rotational behaviour. Unilateral injections of ibotenic acid into various sites of the striatum were used to destroy the striato-nigral pathways. The lesions produced a depletion of dynorphin- and substance P-like immunoreactivity in the pars reticulata of the substantia nigra ipsilateral to the lesion and markedly affected the behavioural responses to intranigral peptide injections. Dynorphin A more potently induced contralateral rotation in the lesioned compared to naive non-lesioned rats, suggesting development of supersensitivity for this peptide. Substance P on the other hand, was markedly less potent in inducing rotation in lesioned animals. The rotational responses to both dynorphin A and substance P were potentiated by injection of amphetamine 1 h later, suggesting that both peptides act via nigro-striatal dopamine neurons. However, in rats with unilateral nigro-striatal dopamine denervation, produced with 6-hydroxy-dopamine, dynorphin A retained its potency to induce rotational behaviour; substance P was again much less potent. Thus, both the ibotenic acid and 6-hydroxy-dopamine lesions differently affect the action of dynorphin A and substance P in the zona reticulata of the substantia nigra. The data suggests that substance P requires an intact dopamine pathway to produce the rotational response, while dynorphin A does not. Direct evidence that behavioural activation produced by dynorphin A is not dependent upon dopamine stimulation was obtained by intrastriatal dialysis experiments in which changes in striatal dopamine release were measured following intranigral injection of dynorphin A or substance P. Intranigral dynorphin A in fact reduced, while substance P increased the release of dopamine.(ABSTRACT TRUNCATED AT 400 WORDS)

Current contributions of peptide synthesis to studies on brain-gut-skin triangle peptides

The usefulness of a strong acid, such as MSA or TFMSA/TFA, as a deprotecting reagent in peptide synthesis was examined. By synthesizing several structurally related brain-gut-skin triangle peptides, a number of advantageous features of the thioanisole-mediated deprotecting procedure were demonstrated. New amino acid derivatives, Arg(Mts), Trp(Mts) and Asp(OChp), were introduced to improve the synthetic methodology of complex peptides and the superior properties of Cys(Ad) were evaluated.

Sequence and expression of the rat prodynorphin gene

We report here the isolation of a lambda genomic clone that contains the nucleotide sequence coding for the main exon of the rat prodynorphin (proenkephalin B) gene. This exon codes for the majority of the translated region of prodynorphin mRNA including the opioid peptides alpha-neo-endorphin, dynorphin A, and dynorphin B. The entire 3' untranslated region is also contained on the lambda clone. Nucleotide sequence comparison with the main exon of the human prodynorphin gene reveals both structural and sequence homology. RNA blot analysis reveals that prodynorphin transcripts can be seen in numerous regions of the rat brain and in the adrenal gland, spinal cord, testis, and anterior pituitary.

The stimulation of glycogenolysis in isolated hepatocytes by opioid peptides

Addition of the opioid peptides, [Leu]enkephalin and [Met]enkephalin, to isolated hepatocytes was shown to produce a stimulation of glycogenolysis comparable with that observed in the presence of maximal concentrations of glucagon, adrenaline or angiotensin. This stimulation was demonstrated to be the result of an activation of phosphorylase by a rapid Ca2+-dependent mechanism and was not decreased by the presence or either alpha- or beta-adrenergic antagonists, although it was dependent on the presence of the N-terminal tyrosine residue in the enkephalin molecule. It is suggested that this may be further evidence for specific opioid receptors in the liver. Addition of [Leu]enkephalin also inhibited lactate formation, indicating that the opioid peptides exert a concerted effect on hepatic carbohydrate metabolism to enhance glucose output. The transient nature of the effect of the enkephalins was shown to be the result of a rapid breakdown of the peptides in the incubation as a result of aminopeptidase activity, the initial product being the inactive des-tyrosine derivative.

Peptide neuroregulators: the opioid system as a model

Aaron Lerner's work provides a stunning set of examples of substances that help to transmit information in the brain and body. His characterization of alpha-MSH and melatonin and his sparking of interest in the further discovery of previously unknown substances have been of inestimable value for the field of neurobiology. Efforts such as those that Lerner undertook so successfully in the field of investigative dermatology now constitute a major research thrust in the field of behavioral neurochemistry and are directly related to advances in psychiatry and neurology. This review considers aspects of research on the neuropeptides, with particular attention to the endogenous opioid (morphine-like) peptides that are active on neural tissue. Neuropeptide research can be categorized broadly as efforts to discover and characterize new families and classes of active agents, investigations of their genetic and molecular processing, and studies of their relationships to behavior in animals and human beings. This review selectively considers some key research questions and strategies that arise from such research.

Immunoreactive pro-enkephalin and prodynorphin products are differentially distributed within the nucleus of the solitary tract of the rat

In this study we examined the distribution of two different endogenous opioid peptides in the nucleus of the solitary tract of the rat medulla. As a marker for immunoreactive enkephalin, we used an antiserum directed against one of the proenkephalin products, methionine enkephalin-arg-gly-leu (m-Enk). To identify immunoreactive dynorphin we used an antiserum directed against the prodynorphin product, dynorphin B (Dyn B). The PAP method was used on both colchicine and normal animals. Caudal to the obex, within the commissural nucleus, there is extensive overlap of both immunoreactive m-Enk and Dyn B terminals and cells. While the cells are morphologically similar, the immunoreactive dynorphin cells are somewhat larger. Rostral to the obex, there is a marked difference in the distribution of the two compounds. Immunoreactive m-Enk terminals are concentrated medial to the solitary tract; there is minimal staining laterally. In contrast, immunoreactive Dyn B terminals are concentrated lateral to the solitary tract. The rostral cellular distribution of the two opioid peptides follows a similar pattern. The morphology of the medially located m-Enk and laterally located Dyn B cells is also readily distinguished. The former are small, round cells with minimal dendritic labelling; the latter are larger, pyramidal neurons with prominent apical and basal dendrites. Since the medial and lateral nuclei of the solitary tract have been associated with cardiovascular and respiratory control, respectively, these data suggest that different endorphin families have different functional actions within the nucleus of the solitary tract.

Dynorphin(1-13) improves survival in cats with focal cerebral ischaemia

Since the discovery of opiate receptors in the central nervous system (CNS), it has become apparent that endogenous opiate ligands are involved in CNS function. Most attention has focused on their role in modulating pain, but they have also been implicated in various physiological functions and in disease states. We are concerned with evidence that endogenous opioid peptides may also contribute to the neurological deficits arising from cerebral ischaemia. Dynorphin, which is widely distributed in the brain and pituitary, has been reported to produce unusual motor and behavioural effects and may act as a regulatory neuropeptide, not as a classical opiate agonist or antagonist. We have therefore administered to cats in which the right middle cerebral artery had been occluded both dynorphin (1-13) and analogue and control materials. We find that dynorphin (1-13) prolongs survival.

Subcellular distribution of opioid peptides in rat hypothalamus and pituitary

Homogenates of rat anterior lobe (AL) and neurointermediate lobe (NIL) pituitary and rat hypothalamus were subjected to subcellular fractionation and density gradient centrifugation. The subcellular distribution of immunoreactive dynorophin A (ir-Dyn A) in NIL was found to be similar to that of ir-arginine vasopressin (ir-AVP). ir-Dyn A migrated as a discrete band on sucrose density gradients, which corresponded in sedimentation rate to that of ir-AVP, suggesting that these two peptides are stored within organelles of similar size and density. Two other products of prodynorphin, ir-alpha-neoendorphin (ir-alpha-nEND) and ir-Dyn A-(1-8) also comigrated with ir-AVP. ir-[Leu5]-enkephalin (ir-LE), which may be a product of prodynorphin or proenkephalin, was also found to migrate in this region of the gradient. When a homogenate of rat hypothalamus was prepared using a method that has been developed for synaptosome isolation, ir-Dyn A was found to comigrate with Na+/K+-activated adenosine triphosphatase (Na/K-ATPase), a synaptosomal marker enzyme. Using a more concentrated homogenate ir-Dyn A was found to migrate to a less dense region where peptide-containing synaptic vesicles have previously been localized. When a synaptosomal preparation was lysed in hypotonic solution a shift was seen in the migration rate of ir-Dyn A to this region of the gradient (containing putative synaptic vesicles). Thus the bulk of hypothalamic dynorphin appears to be present within synaptosome-like structures which, upon lysis, release a less dense, smaller subcellular organelle corresponding in sedimentation characteristics to other types of peptide-containing synaptic vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential processing of prodynorphin and proenkephalin in specific regions of the rat brain

Prodynorphin-derived peptides [dynorphin A (Dyn A)-(1-17), Dyn A-(1-8), Dyn B, alpha-neo-endorphin, and beta-neo-endorphin] and proenkephalin-derived peptides [[Leu]enkephalin [( Leu]Enk) and [Met]enkephalin-Arg6-Gly7-Leu8 [( Met]Enk-Arg-Gly-Leu]) in selected brain areas of the rat were measured by specific radioimmunoassays. We report here that different regions of rat brain contain strikingly different proportions of the prodynorphin and proenkephalin-derived peptides. There is a molar excess of alpha-neo-endorphin-derived peptides over Dyn B and Dyn A-derived peptides in many brain areas. [Leu]Enk concentrations exceed those of [Met]Enk-Arg-Gly-Leu in certain brain areas such as the substantia nigra, dentate gyrus, globus pallidus, and median eminence (areas rich in dynorphin-related peptides). These results indicated that (i) there is differential processing of prodynorphin in different brain regions and (ii) [Leu]Enk may be derived from Dyn A or Dyn B (or both). In certain brain regions [Leu]Enk may derive from two separate precursors (prodynorphin and proenkephalin) in two distinct neuronal systems.

Tissue distribution of messenger RNAs coding for opioid peptide precursors and related RNA

All of the endogenous opioid peptides thus far identified are derived from three types of precursors, i.e. the corticotropin/beta-lipotropin precursor, preproenkephalin A and preproenkephalin B. Poly(A)-containing RNA from various bovine and porcine tissues has been subjected to blot hybridization analysis with the use of cDNA probes specific for the three opioid peptide precursors. Analysis with a corticotropin/beta-lipotropin precursor cDNA probe has revealed, in addition to the pituitary mRNA, a smaller hybridizable RNA species present in bovine extrapituitary tissues, such as the adrenal medulla, thyroid, thymus, duodenum and lung. The hypothalamus contains both these RNA species. DNA complementary to the smaller RNA species from the bovine adrenal medulla has been cloned. Analysis of the cloned cDNA, in conjunction with endonuclease S1 mapping of poly(A)-rich RNA from the adrenal medulla, has indicated that the smaller RNA species represents the 3'-terminal 712-729 nucleotides, excluding the poly(A) tail, of the pituitary corticotropin/beta-lipotropin precursor mRNA, having heterogeneous start sites. Analysis with a preproenkephalin A cDNA probe has shown the presence of hybridizable RNA in the bovine hypothalamus, duodenum and pituitary neurointermediate lobe in addition to the adrenal medulla. The hybridizable RNA species from all these tissues are indistinguishable in size. RNA hybridizable with a preproenkephalin B cDNA probe has been found in the porcine spinal cord and ileum besides the hypothalamus, and these RNA species exhibit an indistinguishable size. The results presented indicate that each opioid peptide precursor is synthesized in different tissues.

Histamine release induced by dynorphin-(1-13) from rat mast cells

Dynorphin is a potent opioid peptide. A synthetic dynorphin-(1-13) (Dyn) induced histamine release accompanied by degranulation from isolated rat mast cells in a dose-dependent manner over the concentration range 10(-7)-10(-5) M. Dynorphin-(1-13)-induced histamine release completed within 10 sec at 37 degrees C, and the release was not accompanied by the leakage of lactate dehydrogenase. Calcium (10(-5)-10(-3) M) enhanced the release, although higher concentration than 10(-3) M suppressed the release. The pH for the maximum release by Dyn was about 7.3. Disodium cromoglycate (5 X 10(-6)-10(-4) M) inhibited the histamine release by Dyn, but naloxone and leucine-enkephalin did not. These results indicate that Dyn-induced histamine release was not mediated by opioid receptors of the mast cells. Its mode of action appeared to that of anaphylactic histamine release.

Which opioid receptor mechanism modulates feeding?

There is substantial evidence for the role of endogenous opioid peptides in the regulation of appetite. This communication examines the possible opioid peptide mechanism(s) which are involved in appetite regulation. In the rat, activation of both the dynorphin-kappa opioid receptor and the beta-endorphin-epsilon opioid receptor appear to enhance feeding, most probably acting in different areas of the central nervous system. It also appears that rats may have a mu anorectic system. Too few studies have been undertaken to define whether the delta or sigma receptor systems are also involved in feeding responses. It is becoming apparent that a great deal of species diversity exists in the feeding responses to opiates, making it difficult to extrapolate the results obtained in rats to other species. In humans, studies with naloxone suggest an opioid sensitive feeding system which possibly is specifically involved in the regulation of carbohydrate uptake. In addition, we report here preliminary data suggesting the presence of a mu anorectic system in humans. Thus, analogous to the findings for the role of opioid receptors in analgesia, it appears that multiple opioid receptors may be involved in appetite regulation, each receptor relating to a different aspect of feeding.

Dynorphin converting enzyme with unusual specificity from rat brain

A rat brain membrane extract was shown to convert synthetic dynorphin B-29 ("leumorphin") to dynorphin B [dynorphin B-29-(1-13), "rimorphin"]. This represents a "single arginine cleavage" at Thr-Arg at positions 13 and 14 of the substrate. The product was identified by immunoprecipitation with a highly specific dynorphin B antiserum and by coelution with radiolabeled dynorphin B on reversed-phase high-performance liquid chromatography. The converting activity exhibits a pH optimum of 8. It is inhibited by a thiol protease inhibitor but not by inhibitors of cathepsin B or of serine proteases. It is inhibited by dynorphin A but not by various dynorphin A fragments. These results suggest that the converting activity is due to a novel thiol protease distinct from any known protease believed to function in the processing of biologically active peptides.

Evidence for a selective processing of proenkephalin B into different opioid peptide forms in particular regions of rat brain and pituitary

The distribution of five major products of proenkephalin B [dynorphin1-17, dynorphin B, dynorphin1-8, alpha-neo-endorphin and beta-neo-endorphin] was studied in regions of rat brain and pituitary. The distribution pattern of immunoreactive (ir) dynorphin B (= rimorphin) was found to be similar to that of ir-dynorphin1-17, with the highest concentrations being present in the posterior pituitary and the hypothalamus. HPLC and gel filtration showed the tridecapeptide dynorphin B to be the predominant immunoreactive species recognized by dynorphin B antibodies in all brain areas and in the posterior pituitary. In addition, two putative common precursor forms of dynorphin B and dynorphin1-17 with apparent molecular weights of 3,200 and 6,000 were detected in brain and the posterior pituitary. The 3,200 dalton species coeluted with dynorphin1-32 on HPLC. In contrast with all other tissues, anterior pituitary ir-dynorphin B and ir-dynorphin1-17 consisted exclusively of the 6,000 dalton species. Concentrations of dynorphin1-8 were several times higher than those of dynorphin1-17 in striatum, thalamus, and midbrain while posterior pituitary, hypothalamus, pons/medulla, and cortex contained roughly equal concentrations of these two opioid peptides. No dynorphin1-8 was detected in the anterior pituitary. Concentrations of beta-neo-endorphin were similar to those of alpha-neo-endorphin in the posterior pituitary. In contrast, in all brain tissues alpha-neo-endorphin was found to be the predominant peptide, with tissue levels in striatum and thalamus almost 20 times higher than those of beta-neo-endorphin. These findings indicate that differential proteolytic processing of proenkephalin B occurs within different regions of brain and pituitary. Moreover, evidence is provided that, in addition to the paired basic amino acids -Lys-Arg- as the "typical" cleavage site for peptide hormone precursors, other cleavage signals also seem to exist for the processing of proenkephalin B.

A dynorphinergic pathway of Leu-enkephalin production in rat substantia nigra

The amino acid sequence of the opioid peptide Leu-enkephalin is found within several larger peptides, which are generated from the precursors proenkephalin and prodynorphin. Proenkephalin contains four copies of the sequence of Met-enkephalin, a single copy of the sequence of Leu-enkephalin and one copy each of two extended Met-enkephalin sequences. Proenkephalin contains three peptides--alpha-neo-endorphin, dynorphin A and dynorphin B--the N-terminal sequences of which are identical to that of Leu-enkephalin. There is good evidence that the large amounts of Leu-enkephalin found in the adrenal medulla are generated from the precursor proenkephalin, but as yet prodynorphin has not been shown to be processed to yield Leu-enkephalin. We show here that the relatively high levels of Leu-enkephalin found in the rat substantia nigra are supplied by striatonigral axons and generated from the precursor prodynorphin.