Identification of an opioid peptide secreted by rat embryonic mixed brain cells as a promoter of macrophage migration

Conditioned media from embryonic mixed cells from the rat brain were used in a chemotaxis assay to look for potential chemotactic activity which could account for the infiltration of the developing central nervous system (CNS) by macrophage precursors. The most potent chemotactic activity was found in the conditioned medium from E17 mixed brain cells (E17-CM). Based upon checkerboard analysis, this activity was shown to be chemotactic rather than chemokinetic. This chemoattraction was not restricted to brain macrophages (BM) because it was as pronounced on bone marrow-derived macrophages. The implication of a peptide compound in this activity was suggested by its resistance to heat as well as acid treatments, and by its sensitivity to aminopeptidase M digestion. In agreement with the opioid nature of the peptide, not only naloxone, but also the delta opioid receptor antagonist ICI-174 reduced the migration of BM in response to E17-CM by 60%. This migratory activity was no longer effective when pertussis toxin-treated BM were used. When the chemotactic effects of selective opioid agonists were compared to that of E17-CM, DPDPE, the delta agonist, was the most efficient in attracting BM. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicated that delta as well as other known opioid receptors were expressed in both BM and E17 mixed brain cells. Finally, a Met-enkephalin-like reactivity was found by RIA in the E17-CM. Altogether, these observations suggest that a delta-like opioid peptide released from embryonic mixed brain cells could be responsible for the infiltration of the developing CNS by macrophages precursors.

New opioid peptides, peptidomimetics, and heterocyclic compounds from combinatorial libraries

Here we review the use of combinatorial libraries in opioid receptor assays. Following a brief description of the history of the combinatorial field, methods for the generation of synthetic libraries and the deconvolution of mixture-based libraries are presented. Case studies involving opioid assays used to demonstrate the viability of combinatorial libraries are described. The identification of new opioid peptides from combinatorial libraries is reviewed. The peptides found are composed of L-amino acids, D-amino acids, or L-, D-, and unnatural amino acids, and range from tetrapeptides to decapeptides. Likewise, new opioid compounds identified from peptidomimetic libraries, such as peptoids and alkylated dipeptides, and those identified from acyclic (e.g., polyamine, urea) and heterocyclic (e.g., bicyclic guanidine) libraries, are reviewed.

Identification of a high-affinity orphanin FQ/nociceptin(1-11) binding site in mouse brain

The presence of pairs of basic amino acids within the orphanin FQ/Nociceptin (OFQ/N) sequence has raised the possibility that truncated versions of the peptide might be physiologically important. OFQ/N(1-11) is pharmacologically active in mice, despite its poor affinity in binding assays (K(i) > 250 nM) for the OFQ/N receptor. Using an analog of OFQ/N(1-11), [(125)I][Tyr(10)]OFQ/N(1-11), we identified a high-affinity binding site (K(D) 234 pM; B(max) 43 fmol/mg protein) with a selectivity profile distinct from the OFQ/N receptor and all the traditional opioid receptors. This site had very high affinity for OFQ/N and its related peptides. The most striking differences between the new site and the OFQ/N receptor previously observed in brain were seen with traditional opioids. Dynorphin A analogs and alpha-neoendorphin competed with [(125)I][Tyr(10)]OFQ/N(1-11) binding in mouse brain with K(i) values below 10 nM, while naloxone benzoylhydrazone (K(i) 3.9 nM) labeled the [(125)I][Tyr(10)]OFQ/N(1-11) binding site as potently as many traditional opioid receptors. Several other opioids, including fentanyl, (-)cyclazocine, levallorphan, naltrindole, and diprenorphine, also displayed moderate affinities for this site. Finally, the [(125)I][Tyr(10)]OFQ/N(1-11) site had a unique regional distribution consistent with a distinct receptor. Thus, [(125)I][Tyr(10)]OFQ/N(1-11) labels a novel site in brain with a selectivity profile intermediate between that of either opioid or OFQ/N receptors.

Identification of the G-protein-coupled ORL1 receptor in the mouse spinal cord by [35S]-GTPgammaS binding and immunohistochemistry

1 Although the ORL1 receptor is clearly located within the spinal cord, the functional signalling mechanism of the ORL1 receptor in the spinal cord has not been clearly documented. The present study was then to investigate the guanine nucleotide binding protein (G-protein) activation mediated through by the ORL1 receptor in the mouse spinal cord, measuring the modulation of guanosine-5'-o-(3-[35S]-thio) triphosphate ([35S]-GTPgammaS) binding by the putative endogenous ligand nociceptin, also referred as orphanin FQ. We also studied the anatomical distribution of nociceptin-like immunoreactivity and nociceptin-stimulated [35S]-GTPgammaS autoradiography in the spinal cord. 2 Immunohistochemical staining of mouse spinal cord sections revealed a dense plexus of nociceptin-like immunoreactive fibres in the superficial layers of the dorsal horn throughout the entire length of the spinal cord. In addition, networks of fibres were seen projecting from the lateral border of the dorsal horn to the lateral grey matter and around the central canal. 3 In vitro [35S]-GTPgammaS autoradiography showed high levels of nociceptin-stimulated [35S]-GTPgammaS binding in the superficial layers of the mouse dorsal horn and around the central canal, corresponding to the areas where nociceptin-like immunoreactive fibres were concentrated. 4 In [35S]-GTPgammaS membrane assay, nociceptin increased [35S]-GTPgammaS binding of mouse spinal cord membranes in a concentration-dependent and saturable manner, affording maximal stimulation of 64.1+/-2.4%. This effect was markedly inhibited by the specific ORL1 receptor antagonist [Phe1Psi (CH2-NH) Gly2] nociceptin (1 - 13) NH2. None of the mu-, delta-, and kappa-opioid and other G-protein-coupled receptor antagonists had a significant effect on basal or nociceptin-stimulated [35S]-GTPgammaS binding. 5 These findings suggest that nociceptin-containing fibres terminate in the superficial layers of the dorsal horn and the central canal and that nociceptin released in these areas may selectively stimulate the ORL1 receptor to activate G-protein. Furthermore, the unique pattern of G-protein activation in the present study provide additional evidence that nociceptin is distinct from the mu-, delta- or kappa-opioid system.

Neither nociceptin nor its receptor are present in human synovial fluid or tissue

Our aim was to identify the nociceptin receptor and its endogenous ligand, nociceptin, in human peripheral tissue. Synovial tissue was obtained from 11 patients (ASA I-III, 66-84 yr) undergoing elective total knee replacement. Synovial fluid was obtained from another 10 patients (ASA I-III, 57-81 yr). Fluid was mixed with trifluoroacetic acid and the tissue with isopentone before freezing at -70 degrees C. Nociceptin receptor identification was performed using a [3H]nociceptin binding assay and nociceptin detection by radioimmunoassay. There was no specific [3H]nociceptin binding to knee synovial tissue and radioimmunoassay did not detect nociceptin. Neither the nociceptin receptor nor nociceptin was found in human synovial tissue or fluid.

Identification of human, rat and mouse nocistatin in brain and human nocistatin in brain and human cerebrospinal fluid

Nocistatin was recently isolated from bovine brain and shown to block hyperalgesia and allodynia induced by nociceptin and prostaglandin (PG) E2. The counterparts of human, rat and mouse are deduced from their precursor prepronociceptin to be 30, 35, and 41 residue peptide respectively. To identify these mature forms of nocistatin, three peptides were synthesized and a detection program for nocistatin was developed, using high pressure liquid chromatography (HPLC) along with specific radioimmunoassay (RIA). Nocistatin extracted from human, rat and mouse brain were subjected to HPLC and nocistatin-like immunoreactivity (NST-IR) was determined. All three species showed two NST-IR peaks, one of which coincided with that of the corresponding putative nocistatin. The same NST-IR was also detected in human cerebrospinal fluid (CSF).

Accelerated release and production of orphanin FQ in brain of chronic morphine tolerant rats

Orphanin FQ has been shown to possess anti-opioid activity at supraspinal level. Our previous work revealed that chronic morphine tolerance could be reversed by intracerebroventricular (i.c.v.) injection of OFQ IgG to rats. In this study, we used radioimmunoassay (RIA) to assess the changes of Orphanin FQ immunoreactivity (OFQ-ir) in cerebroventricular perfusate, periaqueductal gray (PAG) and amygdala of rats made tolerance to morphine (10-60 mg/kg, s.c., t.i.d., for 5 days). The results indicated that: (1) In rats administrated with morphine for 3 and 5 days, the content of OFQ-ir in cerebroventricular perfusate increased by 25% and 52% over the NS control group. (2) The content of OFQ-ir in PAG of rats receiving 1d, 3d and 5d injections of morphine showed an increase of 17%, 48% and 81% respectively over NS group. (3) The content of OFQ-ir in amygdala of rats given 3d and 5d of morphine showed a 36% and 55% increase compared with corresponding control group. It is suggested that continuous use of high doses of morphine accelerated the release and biosynthesis of OFQ in rat brain to antagonize the effect of opioids, which may play a role in the development of morphine tolerance, and that brain OFQ may serve as a delayed negative feedback control on opioid analgesia.

Localization of orphanin FQ (nociceptin) peptide and messenger RNA in the central nervous system of the rat

Orphanin FQ (OFQ) is the endogenous agonist of the opioid receptor-like receptor (ORL-1). It and its precursor, prepro-OFQ, exhibit structural features suggestive of the opioid peptides. A cDNA encoding the OFQ precursor sequence in the rat recently has been cloned, and the authors recently generated a polyclonal antibody directed against the OFQ peptide. In the present study, the authors used in situ hybridization and immunohistochemistry to examine the distribution of OFQ peptide and mRNA in the central nervous system of the adult rat. OFQ immunoreactivity and prepro-OFQ mRNA expression correlated virtually in all brain areas studied. In the forebrain, OFQ peptide and mRNA were prominent in the neocortex endopiriform nucleus, claustrum, lateral septum, ventral forebrain, hypothalamus, mammillary bodies, central and medial nuclei of the amygdala, hippocampal formation, paratenial and reticular nuclei of the thalamus, medial habenula, and zona incerta. No OFQ was observed in the pineal or pituitary glands. In the brainstem, OFQ was prominent in the ventral tegmental area, substantia nigra, nucleus of the posterior commissure, central gray, nucleus of Darkschewitsch, peripeduncular nucleus, interpeduncular nucleus, tegmental nuclei, locus coeruleus, raphe complex, lateral parabrachial nucleus, inferior olivary complex, vestibular nuclear complex, prepositus hypoglossus, solitary nucleus, nucleus ambiguous, caudal spinal trigeminal nucleus, and reticular formation. In the spinal cord, OFQ was observed throughout the dorsal and ventral horns. The wide distribution of this peptide provides support for its role in a multitude of functions, including not only nociception but also motor and balance control, special sensory processing, and various autonomic and physiologic processes.

Family history of alcoholism and hypothalamic opioidergic activity

BACKGROUND

This study was designed to assess whether nonalcoholic offspring from families with a high density of alcohol-dependent individuals have altered endogenous central nervous system opioid activity. Naloxone hydrochloride stimulates plasma cortisol by blocking opioidergic input on the corticotropin-releasing factor neuron, thereby providing a noninvasive method for measuring hypothalamic opioid tone.

METHODS

Forty-eight nonalcoholic subjects aged 18 to 25 years were enrolled in a protocol to measure endogenous opioid activity by inducing opioid receptor blockade with the receptor antagonist, naloxone. Twenty-six subjects were offspring from families with a high density of alcohol dependence and were designated as family history-positive subjects. Twenty-two subjects were biological offspring of nonalcohol-dependent parents and designated as family history-negative subjects. Subjects received naloxone hydrochloride (0, 125, and 375 microg/kg) in double-blind, randomized order. Serum cortisol levels were monitored.

RESULTS

Family history-negative subjects had a graded cortisol response to each dose of naloxone. In contrast, family history-positive subjects achieved a maximal cortisol response to the 125-microg/kg dose of naloxone hydrochloride with no further increase in cortisol levels observed following the 375-microg/kg dose. Family history-negative subjects had a diminished cortisol response to the 125-microg/kg dose compared with the family history-positive subjects. Plasma naloxone concentrations did not differ between family history groups.

CONCLUSIONS

Individuals from families with a high density of alcohol dependence are more sensitive to naloxone compared with offspring of nonalcohol-dependent parents. This implies that individuals with a family history of alcohol dependence have diminished endogenous hypothalamic opioid activity.

[The role and place of central mediators and peptide bioregulators in the pathogenesis of emotional disorders in neurotic patients]

The accumulated evidence on central mediators indicates that they may play an important part in the maintenance of emotional activity. Their significance is also great in the pathogenesis of affective disorders, including endogenous psychoses and borderline states. But further work in this area is needed relative to interrelation of the above mediators to a new class of bioregulators, viz peptide regulators. The results obtained suggest the existence of differentiated brain mechanisms of formation of emotional disturbances in different forms of neurosis that provide criteria for the diagnosis thereof and differential diagnosis and should be considered in conducting an adequate pathogenetically validated therapy.

Orphanin FQ is the major OFQ1-17-containing peptide produced in the rodent and monkey hypothalamus

In order to investigate the processing of OFQ containing peptides in the hypothalamus we have developed a sensitive and quantitative radioimmunoassay for OFQ. We fractionated rodent and monkey hypothalamic extracts by reversed-phase high performance liquid chromatography and found that the extracts contained multiple peaks of OFQ immunoreactivity with the major peak co-eluting with synthetic OFQ1-17. Mouse hypothalamic extracts were also fractionated by SDS-PAGE to determine the apparent molecular weights of molecules containing the OFQ peptide. Multiple peaks of OFQ immunoreactivity, ranging in size from approximately 1 to 30 kilodaltons, were detected by this method. These results suggest that OFQ1-17 is processed to smaller peptides in mouse and monkey hypothalamic neurons.

Distribution of nociceptin/orphanin FQ receptor transcript in human central nervous system and immune cells

We have examined the distribution of the opioid receptor-like-1 (ORL-1) transcript in the human CNS as well as human immune cells by RT-PCR and RNAse protection. The hORL-1 mRNA was distributed throughout the brain and particularly abundant in cortical areas, striatum, thalamus and hypothalamus. In the immune system, gene transcription was observed in normal circulating lymphocytes and monocytes as well as in T, B and monocytic cell lines. A splice variant, lacking 15 nucleotides at the junction between exon 1 and exon 2, showed a distribution similar to the already known ORL-1 transcript. Altogether these results show comparable expression levels of the hORL-1 gene in both nervous and immune systems, suggesting that the ORL-1-encoded receptor may participate to neuronal and non-neuronal physiological functions in humans.

Orphanin FQ/nociceptin in the ventromedial nucleus facilitates lordosis in female rats

The localization of opioid receptor-like (ORL-1) orphan receptor in the ventromedial nucleus of the hypothalamus (VMH) suggested a role for this opioid system in the regulation of lordosis behavior. Recently, the ligand for ORL-1, orphanin FQ/nociceptin (OFQ/N), has been characterized and also demonstrated to be present in the VMH. The present experiments examined whether OFQ/N in the VMH facilitates lordosis behavior in estrogen-primed, sexually unreceptive female rats, and whether estrogen regulates ORL-1 levels in the VMH. Estrogen was shown to increase ORL-1 immunoreactivity in the VMH, and microinfusions of OFQ/N into the VMH facilitated lordosis behavior in a dose-dependent manner.

Nociceptin-like immunoreactivity in autonomic nuclei of the rat spinal cord

Immunohistochemical techniques were used to localize nociceptin-like immunoreactivity (NOCI-LI) in the rat spinal cords. NOCI-LI nerve fibers were distributed in three fairly well-define regions: superficial layers of the dorsal horn, central canal area, and intermediolateral cell column (ILp) of lower cervical, thoracic, upper lumbar, and sacral segments of the spinal cord. A few NOCI-LI somata of small diameter were noted in the dorsal horn; NOCI-LI cell bodies were infrequently observed in the ILp or ventral horn. Concentration of NOCI-LI in nerve fibers of the superficial layers and in fibers projecting into the spinal sympathetic and parasympathetic nuclei suggests that the peptide may participate in sensory as well as autonomic functions.

Nociceptin and its receptor in guinea-pig sympathetic ganglia

The occurrence and distribution of nociceptin, a 17-amino acid peptide with structural similarity to dynorphin A, and its receptor, opioid receptor-like-1 (ORL1) receptor, were investigated in the guinea-pig sympathetic nervous system by means of immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR), respectively. Immunofluorescence revealed varicose nociceptin-immunoreactive axons and some paraganglionic cells in prevertebral (coeliaco-superior mesenteric, inferior mesenteric), but not in paravertebral (superior cervical, stellate, lumbar chain) sympathetic ganglia. Messenger RNA for the ORL1 receptor, however, was detected by RT-PCR in both para- and prevertebral ganglia. The findings suggest participation of the nociceptin/ORL1 receptor signalling pathway in processing of information within prevertebral ganglia, and a general responsiveness of sympathetic neurons to nociceptin.

Overexpression of a neuropeptide nociceptin/orphanin FQ precursor gene, N23K/N27K, induces neurite outgrowth in mouse NS20Y cells

We recently discovered N23K and its splicing variant N27K as transcripts upregulated in mouse NS20Y cells after differentiation induced by dibutylyl cyclic AMP (dbcAMP) treatment. N23K and N27K encode precursor proteins for an opioid neuropeptide, nociceptin/orphanin FQ, but the transient expression of N23K and N27K suggests that it may be involved in neuronal differentiation. In the present study, we report that NS20Y cells transfected with N23K and/or N27K but not with vector alone formed neurites, with the expressed protein distributed in the perinuclear region and distal parts of the neurites. The granular staining of the N23K and N27K proteins was also colocalized with secretogranin I, indicating incorporation into large dense core vesicles. This cellular targeting of the N23K and/or N27K protein is similar to that of dbcAMP-induced processes in nontransfected NS20Y cells. In addition, the neurites of transfectants that expressed both N23K and N27K were longer than those of the transfectants that expressed N23K or N27K alone. Our results demonstrate that N23K and N27K participate in the regulation of neurite outgrowth.

Mass spectrometric identification and quantification of hemorphins extracted from human adrenal and pheochromocytoma tissue

The hemorphins are a family of recently identified opioid receptor binding peptides derived from the proteolytic processing of the beta, gamma, delta, and epsilon chains of hemoglobin. They have previously been identified at high concentration in human pituitary glands and in the CSF of patients with cerebral bleeding. Hemorphins are potent inhibitors of angiotensin converting enzyme and therefore possibly have a role to play in blood pressure regulation. We report the presence of four hemorphin peptides in extracts of normal adrenal tissue and in pheochromocytoma tumors. The hemorphins were quantified and structurally characterized using mass spectrometry. High concentrations of hemorphins were found in all samples, comparable with the levels reported in the literature for pituitary and brain tissue.

Determination of nociceptin-like immunoreactivity in the rat dorsal spinal cord

An endogenous ligand for the opioid receptor-like (ORL1) receptor has been characterized recently. This 17 amino acid peptide, nociceptin, has potent effects on pain processing in experimental animals. In the present study, we describe the development of a radio-immunoassay for nociceptin, suitable for quantification of immunoreactivity in the rat spinal cord. in the dorsal spinal cord we found 641 fmol nociceptin-like immunoreactivity (IR)/mg protein, while in the ventral spinal cord the amount was below the detection limit of the assay (11 fmol/mg protein). High pressure liquid chromatography (HPLC) showed that the immunoreactive material was heterogeneous with the major part eluting at the position of synthetic nociceptin. The presence of nociceptin in the dorsal spinal cord is compatible with its proposed involvement in modulating afferent transmission.

Identification and localization of a [Met5]-enkephalin-like peptide in the mollusc, Lymnaea stagnalis

The goal of this study was to determine whether [Met5]-enkephalin, or an analog, is present in identified neurons in the central nervous system (CNS) of the freshwater snail, Lymnaea stagnalis. High performance liquid chromatography and radioimmunoassay of CNS tissue homogenates revealed both [Met5]-enkephalin and oxidized [Met5]-enkephalin. NO [Leu5]-enkephalin, [Met5]-enkephalin-Arg6-Phe7 or [Met5]-enkephalin-Arg6-Gly7-Leu8 were detected. Quantification of [Met5]-enkephalin, by radioimmunoassay, revealed that the Lymnaea CNS contains approximately 2.2 fmol/CNS (undigested tissue) and 4.5 fmol/CNS (tissue enzymatically digested with trypsin and carboxypeptidase B). The increased amount of [Met5]-enkephalin following tissue digestion indicates the presence of as yet unidentified extended forms of [Met5]-enkephalin in Lymnaea. Using indirect immunocytochemistry, a [Met5]-enkephalin-like peptide was localized to individual cells and cell clusters within the CNS, as well as to fibers in the atrium of the heart. A neuronal map depicting [Met5]-enkephalin-like immunoreactive cells was produced. Among the immunoreactive neurons were four identified, well-characterized, giant cells: VD1, RPD2, LB1 and RB1. Identifiable [Met5]-enkephalin-like immunoreactive neurons were characterized electrophysiologically and morphologically. Additionally, neurons VD1 and RPD2 were confirmed to be immunoreactive to Lymnaea alpha-peptide. The lack of both cross reactivity and sequence homology between alpha-peptide and [Met5]-enkephalin suggests that a [Met5]-enkephalin-like peptide and alpha-peptide are co-localized within these neurons.

Ultrastructural relationships between leu-enkephalin- and GABA-containing neurons differ within the hippocampal formation

Electrophysiological studies have suggested that the excitatory actions of opioids in the hippocampal formation are mediated by inhibition of interneurons containing GABA; however, an anatomical basis for this interaction has never been established. Thus, we sought to determine the relationship between leu-enkephalin (LE)-containing axon terminals and GABAergic neurons using dual labeling immunohistochemistry and electron microscopy. In the CA1 region of the hippocampus, LE-labeled terminals (n = 99) were in direct contact with GABA-labeled perikarya and dendrites (18%), and directly apposed to GABA-labeled axon terminals (14%). In the molecular layer of the dentate gyrus, LE-containing terminals (n = 125) occasionally apposed GABA-containing terminals (8%). In the hilus of the dentate gyrus, LE-containing terminals (n = 165) often contacted GABA-containing perikarya and dendrites (39%), but rarely apposed GABA-containing terminals (3%). In the CA3 region of the hippocampus, only a few LE-labeled mossy fiber boutons (n = 102) contacted the shafts of GABA-labeled dendrites (4%). The results demonstrate that leu-enkephalin-containing terminals have a different anatomical relationship with GABA-containing profiles in each subregion of the hippocampal formation. In the CA1 region of the hippocampus, the data support the numerous electrophysiological studies indicating that LE functions in modulating inhibitory GABAergic neurons by both pre- and postsynaptic mechanisms. In the outer molecular layer of the dentate gyrus the localization suggests some presynaptic regulation of GABAergic terminals. In the hilus of the dentate gyrus, the study also supports the contention that LE may have an important role in regulating inhibition of GABA-containing neurons. In comparison, in the CA3 region of the hippocampus, LE may have a more limited role in regulating GABAergic inhibition by direct association.

An immunocytochemical mapping of beta-endorphin (1-27) in the cat diencephalon

The distribution of beta-endorphin (1-27) immunoreactive cell bodies and fibres was studied in the diencephalon of the cat using an indirect immunoperoxidase technique. In the thalamus, almost all the immunoreactive fibres were found in the midline region and in nuclei located near the midline, whereas in the hypothalamus fibres containing beta-endorphin (1-27) were visualized extending by the whole structure. The hypothalamus showed a higher density of beta-endorphin (1-27) immunoreactive fibres than the thalamus, as well as immunoreactive cell bodies, since in the thalamus no beta-endorphin (1-27) immunoreactive neuron was located. The densest network of immunoreactive fibres was observed in the epithalamus (nucleus periventricularis anterior) and in the hypothalamic nuclei arcuatus, hypothalami ventromedialis, suprachiasmaticus, periventricularis hypothalami, hypothalamus dorsomedialis, area hypothalamica dorsalis, hypothalamus anterior, filiformis, hypothalamus posterior and regio praeoptica. In the hypothalamus, a high density of perikarya containing beta-endorphin (1-27) was observed in the nucleus arcuatus and a low density in the nucleus hypothalami ventromedialis. The distribution of beta-endorphin (1-27) immunoreactive fibres and perikarya is compared with the location of other neuropeptides in the cat diencephalon. Our findings reveal that b-endorphin (1-27) immunoreactive structures are widely distributed in the cat diencephalon, suggesting that the peptide might be involved in several physiological functions.

Orphanin FQ/nociceptin-immunoreactive nerve fibers parallel those containing endogenous opioids in rat spinal cord

Antisera were developed that specifically recognize orphanin FQ/nociceptin, the 17 amino acid peptide reported to be the endogenous ligand for the orphan opioid receptor. Immunocytochemical localizations in rat spinal cord demonstrated that orphanin FQ /nociceptin-immunoreactivity (-ir) was abundant in superficial dorsal horn, lateral spinal nucleus and the region dorsal to the central canal, areas that also exhibit prominent enkephalin-and dynorphin-ir. Orphanin FQ/nociceptin-ir was not affected by dorsal rhizotomy, indicating that in spinal cord the peptide is produced by central rather than primary afferent neurons. thus, the distribution of orphanin FQ/nociceptin-ir appeared in neuronal circuits that parallel those containing enkephalin- and dynorphin-ir, with only modest co-existence of these peptides.

Endogenous opioid peptides in parasympathetic, sympathetic and sensory nerves in the guinea-pig heart

Research has suggested that exogenous opioid substances can have direct effects on cardiac muscle or influence neurotransmitter release via presynaptic modulation of neuronal inputs to the heart. In the present study, multiple-labelling immunohistochemistry was employed to determine the distribution of endogenous opioid peptides within the guinea-pig heart. Approximately 40% of cardiac ganglion cells contained immunoreactivity for dynorphin A (1-8), dynorphin A (1-17) and dynorphin B whilst 20% displayed leu-enkephalin immunoreactivity. Different populations of opioid-containing ganglion cells were identified according to the co-existence of opioid immunoreactivity with immunoreactivity for somatostatin and neuropeptide Y. Immunoreactivity for prodynorphin-derived peptides was observed in many sympathetic axons in the heart and was also observed, though to a lesser extent, in sensory axons. Leu-enkephalin immunoreactivity was observed in occasional sympathetic and sensory axons. No immunoreactivity was observed for met-enkephalin-arg-gly-leu or for beta-endorphin. These results demonstrate that prodynorphin-derived peptides are present in parasympathetic, sympathetic and sensory nerves within the heart, but suggest that only the prodynorphin gene is expressed in guinea-pig cardiac nerves. This study has shown that endogenous opioid peptides are well placed to regulate cardiac function via both autonomic and sensory pathways.

Mass spectrometry, high performance liquid chromatography, and brain peptides

This paper is a personal recollection of some of the events and research that surrounded the amino acid sequence determination of the hypothalamic releasing factor, TRF (now known as TRH), by mass spectrometry (MS), and the development of reverse phase high performance liquid chromatography (RP-HPLC) MS and tandem MS (MS/MS) methods for the qualitative and quantitative analysis of native opioid neuropeptides in human pituitary tissue extracts.