Endogenous opiates: 1996

Evolution of gnathostome prodynorphin and proenkephalin: characterization of a shark proenkephalin and prodynorphin cDNAs

Analyses of prodynorphin and proenkephalin cDNAs cloned from the central nervous system of the shark, Heterodontus portusjacksoni, provided additional evidence that these two opioid precursor-coding genes were most likely directly derived from a common ancestral gene. The two cDNAs could be aligned by inserting only seven gaps. The prodynorphin cDNA encodes five opioid sequences which could be aligned to opioid positions B through F in the proenkephalin cDNA. The sequence identity within the opioid positions was 59% at the amino acid level. Shark α-neo-endorphin, dynorphin A, and dynorphin B have amino acid motifs in common with shark met-enkephalin-8, and shark proenkephalin opioid positions E and F, respectively, which have not been observed in other gnathostome prodynorphin and proenkephalin precursor sequences. Shark prodynorphin encodes both kappa (α-neo-endorphin, dynorphin A, and dynorphin B) and delta (met-enkephalin and leu-enkephalin) opioid sequences. Mixed function prodynorphin precursors (encoding both enkephalins and dynorphins) are also found in representatives of the teleost fishes, lungfishes, and amphibians. It appears that only mammals evolved a prodynorphin precursor that exclusively encodes kappa opioid agonists (dynorphins).

Opiate treatment for opiate withdrawal in newborn infants

BACKGROUND

Neonatal abstinence syndrome (NAS) due to opiate withdrawal may result in disruption of the mother-infant relationship, sleep-wake abnormalities, feeding difficulties, weight loss and seizures.

OBJECTIVES

To assess the effectiveness and safety of using an opiate compared to a sedative or non-pharmacological treatment for treatment of NAS due to withdrawal from opiates.

SEARCH STRATEGY

The review was updated in 2010 with additional searches CENTRAL, MEDLINE and EMBASE supplemented by searches of conference abstracts and citation lists of published articles.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of opiate treatment in infants with NAS born to mothers with opiate dependence.

DATA COLLECTION AND ANALYSIS

Each author assessed study quality and extracted data independently.

MAIN RESULTS

Nine studies enrolling 645 infants met inclusion criteria. There were substantial methodological concerns in all studies comparing an opiate with a sedative. Two small studies comparing different opiates were of good methodology.Opiate (morphine) versus supportive care (one study): A reduction in time to regain birth weight and duration of supportive care and a significant increase in hospital stay was noted.Opiate versus phenobarbitone (four studies): Meta-analysis found no significant difference in treatment failure. One study reported opiate treatment resulted in a significant reduction in treatment failure in infants of mothers using only opiates. One study reported a significant reduction in days treatment and admission to the nursery for infants receiving morphine. One study reported a reduction in seizures, of borderline statistical significance, with the use of opiate.Opiate versus diazepam (two studies): Meta-analysis found a significant reduction in treatment failure with the use of opiate.Different opiates (six studies): there is insufficient data to determine safety or efficacy of any specific opiate compared to another opiate.

AUTHORS' CONCLUSIONS

Opiates compared to supportive care may reduce time to regain birth weight and duration of supportive care but increase duration of hospital stay. When compared to phenobarbitone, opiates may reduce the incidence of seizures but there is no evidence of effect on treatment failure. One study reported a reduction in duration of treatment and nursery admission for infants on morphine. Compared to diazepam, opiates reduce the incidence of treatment failure. A post-hoc analysis generates the hypothesis that initial opiate treatment may be restricted to infants of mothers who used opiates only. In view of the methodologic limitations of the included studies the conclusions of this review should be treated with caution.

Sedatives for opiate withdrawal in newborn infants

BACKGROUND

Neonatal abstinence syndrome (NAS) due to opiate withdrawal may result in disruption of the mother-infant relationship, sleep-wake abnormalities, feeding difficulties, weight loss and seizures. Treatments used to ameliorate symptoms and reduce morbidity include opiates, sedatives and non-pharmacological treatments.

OBJECTIVES

To assess the effectiveness and safety of using a sedative compared to a non-opiate control for NAS due to withdrawal from opiates, and to determine which type of sedative is most effective and safe.

SEARCH STRATEGY

This update included searches of the Cochrane Central Register of Controlled Trials (Issue 1, 2010), MEDLINE 1966 to April 2010 and abstracts of conference proceedings.

SELECTION CRITERIA

Trials enrolling infants with NAS born to mothers with an opiate dependence with > 80% follow-up and using random or quasi-random allocation to sedative or control. Control could include another sedative or non-pharmacological treatment.

DATA COLLECTION AND ANALYSIS

Each author assessed study quality and extracted data independently.

MAIN RESULTS

Seven studies enrolling 385 patients were included. There were substantial methodological concerns for most studies including the use of quasi-random allocation methods and sizeable, largely unexplained differences in reported numbers allocated to each group.One study reported phenobarbitone compared to supportive care alone did not reduce treatment failure or time to regain birthweight, but resulted in a significant reduction in duration of supportive care (MD -162.1 min/day, 95% CI -249.2, -75.1). Comparing phenobarbitone to diazepam, meta-analysis of two studies found phenobarbitone resulted in a significant reduction in treatment failure (typical RR 0.39, 95% CI 0.24, 0.62). Comparing phenobarbitone with chlorpromazine, one study reported no significant difference in treatment failure.In infants treated with an opiate, one study reported addition of clonidine resulted in no significant difference in treatment failure, seizures or mortality. In infants treated with an opiate, one study reported addition of phenobarbitone significantly reduced the proportion of time infants had a high abstinence severity score, duration of hospitalisation and maximal daily dose of opiate.

AUTHORS' CONCLUSIONS

Infants with NAS due to opiate withdrawal should receive initial treatment with an opiate. Where a sedative is used, phenobarbitone should be used in preference to diazepam. In infants treated with an opiate, the addition of phenobarbitone or clonidine may reduce withdrawal severity. Further studies are needed to determine the role of sedatives in infants with NAS due to opiate withdrawal and the safety and efficacy of adding phenobarbitone or clonidine in infants treated with an opiate for NAS.

Differential regulation of morphine antinociceptive effects by endogenous enkephalinergic system in the forebrain of mice

BACKGROUND

Mice lacking the preproenkephalin (ppENK) gene are hyperalgesic and show more anxiety and aggression than wild-type (WT) mice. The marked behavioral changes in ppENK knock-out (KO) mice appeared to occur in supraspinal response to painful stimuli. However the functional role of enkephalins in the supraspinal nociceptive processing and their underlying mechanism is not clear. The aim of present study was to compare supraspinal nociceptive and morphine antinociceptive responses between WT and ppENK KO mice.

RESULTS

The genotypes of bred KO mice were confirmed by PCR. Met-enkephalin immunoreactive neurons were labeled in the caudate-putamen, intermediated part of lateral septum, lateral globus pallidus, intermediated part of lateral septum, hypothalamus, and amygdala of WT mice. Met-enkephalin immunoreactive neurons were not found in the same brain areas in KO mice. Tail withdrawal and von Frey test results did not differ between WT and KO mice. KO mice had shorter latency to start paw licking than WT mice in the hot plate test. The maximal percent effect of morphine treatments (5 mg/kg and 10 mg/kg, i.p.) differed between WT and KO mice in hot plate test. The current source density (CSD) profiles evoked by peripheral noxious stimuli in the primary somatosenstory cortex (S1) and anterior cingulate cortex (ACC) were similar in WT and KO mice. After morphine injection, the amplitude of the laser-evoked sink currents was decreased in S1 while the amplitude of electrical-evoked sink currents was increased in the ACC. These differential morphine effects in S1 and ACC were enhanced in KO mice. Facilitation of synaptic currents in the ACC is mediated by GABA inhibitory interneurons in the local circuitry. Percent increases in opioid receptor binding in S1 and ACC were 5.1% and 5.8%, respectively.

CONCLUSION

The present results indicate that the endogenous enkephalin system is not involved in acute nociceptive transmission in the spinal cord, S1, and ACC. However, morphine preferentially suppressed supraspinal related nociceptive behavior in KO mice. This effect was reflected in the potentiated differential effects of morphine in the S1 and ACC in KO mice. This potentiation may be due to an up-regulation of opioid receptors. Thus these findings strongly suggest an antagonistic interaction between the endogenous enkephalinergic system and exogenous opioid analgesic actions in the supraspinal brain structures.

Panic, suffocation false alarms, separation anxiety and endogenous opioids

This review paper presents an amplification of the suffocation false alarm theory (SFA) of spontaneous panic [Klein DF (1993). False suffocation alarms, spontaneous panics, and related conditions. An integrative hypothesis. Arch Gen Psychiatry; 50:306-17.]. SFA postulates the existence of an evolved physiologic suffocation alarm system that monitors information about potential suffocation. Panic attacks maladaptively occur when the alarm is erroneously triggered. That panic is distinct from Cannon's emergency fear response and Selye's General Alarm Syndrome is shown by the prominence of intense air hunger during these attacks. Further, panic sufferers have chronic sighing abnormalities outside of the acute attack. Another basic physiologic distinction between fear and panic is the counter-intuitive lack of hypothalamic-pituitary-adrenal (HPA) activation in panic. Understanding panic as provoked by indicators of potential suffocation, such as fluctuations in pCO(2) and brain lactate, as well as environmental circumstances fits the observed respiratory abnormalities. However, that sudden loss, bereavement and childhood separation anxiety are also antecedents of "spontaneous" panic requires an integrative explanation. Because of the opioid system's central regulatory role in both disordered breathing and separation distress, we detail the role of opioidergic dysfunction in decreasing the suffocation alarm threshold. We present results from our laboratory where the naloxone-lactate challenge in normals produces supportive evidence for the endorphinergic defect hypothesis in the form of a distress episode of specific tidal volume hyperventilation paralleling challenge-produced and clinical panic.

Association of liking and reinforcing value with children's physical activity

This study determined whether liking and relative reinforcing value (RRV) of physical activity were associated with time youth spend in moderate-to-vigorous physical activity (MVPA). Boys (n=21) and girls (n=15) age 8 to 12 years were measured for height, weight, aerobic fitness, liking and RRV of physical activity, and minutes in MVPA using accelerometers. Independence of liking and RRV of physical activity was established by a low correlation (r=0.08, p=0.64). Using MVPA as the dependent variable and hierarchical regression to control for individual differences in age, aerobic fitness, and time the accelerometer was worn in step 1 (R(2) of 0.60 for step 1), addition of liking and RRV of physical activity in step 2 produced an incremental increase in R(2) of 0.12 (p<0.01). When using median splits of the RRV and liking data to form subject groups, children with both a high liking and RRV of physical activity participated in greater (p< or = 0.02) MVPA (1340+/-70 min/week) than children with high RRV-low liking (1040+/-95 min/week), low RRV-high liking (978+/-88 min/week), or low RRV-low liking (1007+/-68 min/week) of physical activity. Thus, liking and RRV of physical activity are independently associated with MVPA. The combination of a high reinforcing value and liking of physical activity is associated with 33% greater participation in MVPA.

The endomorphin system and its evolving neurophysiological role

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2) are two endogenous opioid peptides with high affinity and remarkable selectivity for the mu-opioid receptor. The neuroanatomical distribution of endomorphins reflects their potential endogenous role in many major physiological processes, which include perception of pain, responses related to stress, and complex functions such as reward, arousal, and vigilance, as well as autonomic, cognitive, neuroendocrine, and limbic homeostasis. In this review we discuss the biological effects of endomorphin-1 and endomorphin-2 in relation to their distribution in the central and peripheral nervous systems. We describe the relationship between these two mu-opioid receptor-selective peptides and endogenous neurohormones and neurotransmitters. We also evaluate the role of endomorphins from the physiological point of view and report selectively on the most important findings in their pharmacology.

Translational repression of mouse mu opioid receptor expression via leaky scanning

Mu opioid receptor (MOR) expression is under temporal and spatial controls, but expression levels of the MOR gene are relatively low in vivo. In addition to transcriptional regulations, upstream AUGs (uAUGs) and open reading frames (uORFs) profoundly affect the translation of the primary ORF and thus the protein levels in several genes. The 5'-untranslated region (UTR) of mouse MOR mRNA contains three uORFs preceding the MOR main initiation codon. In MOR-fused EGFP or MOR promoter/luciferase reporter constructs, mutating each uAUG individually or in combinations increased MOR transient heterologous expression in neuroblastoma NMB and HEK293 cells significantly. Translation of such constructs increased up to 3-fold without altering the mRNA levels if either the third uAUG or both the second and third AUGs were mutated. Additionally, these uAUG-mediated translational inhibitions were independent of their peptide as confirmed by internal mutation analyses in each uORF. Translational studies indicated that protein syntheses were initiated at these uAUG initiation sites, with the third uAUG initiating the highest translation level. These results support the hypothesis that uORFs in mouse MOR mRNA act as negative regulators through a ribosome leaky scanning mechanism. Such leaky scanning resulted in the suppression of mouse MOR under normal conditions.

Trends in the Evolution of the Proenkephalin and Prodynorphin Genes in Gnathostomes

The opioid/orphanin gene family provides a model system for analyzing the outcomes of genome duplication events. Recent studies on the proenkephalin gene provide additional evidence that the organizational plan for this gene has been conserved throughout the extensive radiation of the gnathostome vertebrates. However, an analysis of the amino acid sequence of proenkephalin from the zebrafish, Danio rerio, suggests that novel forms of this opioid precursor may be evolving in teleosts. Analyses of sarcopterygian prodynorphin sequences revealed a proenkephalin signature in prodynorphin. Current studies on the opioid/orphanin gene family point to the duplication events that shaped this family occurring prior to the radiation of the gnathostomes.

Sedatives for opiate withdrawal in newborn infants

BACKGROUND

Neonatal abstinence syndrome (NAS) due to opiate withdrawal may result in disruption of the mother-infant relationship, sleep-wake abnormalities, feeding difficulties, weight loss and seizures. Treatments used to ameliorate symptoms and reduce morbidity include opiates, sedatives and non-pharmacological treatments.

OBJECTIVES

To assess the effectiveness and safety of using a sedative compared to a non-opiate control for NAS due to withdrawal from opiates, and to determine which type of sedative is most effective and safe.

SEARCH STRATEGY

The standard search strategy of the Neonatal Review Group was used. This update included searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2005), MEDLINE 1966-March 2005 and abstracts of conference proceedings.

SELECTION CRITERIA

Trials enrolling infants with NAS born to mothers with an opiate dependence, with > 80% follow up and using random or quasi-random allocation to sedative or control. Control could include another sedative or non-pharmacological treatment.

DATA COLLECTION AND ANALYSIS

Each author assessed study quality and extracted data independently. Primary outcomes included treatment failure (failure to achieve symptom control or use of additional drug treatment), seizure occurrence, mortality and neurodevelopment. Treatment effect was expressed using (RR), risk difference (RD), mean difference (MD) and weighted mean difference (WMD). Meta-analysis was performed using a fixed effect model.

MAIN RESULTS

Six studies enrolling a total of 305 patients met inclusion criteria (Coyle 2002; Finnegan 1984; Kahn 1969; Kaltenbach 1986; Khoo 1995; Madden 1977); however, two (Finnegan 1984; Kaltenbach 1986) may be sequential reports that include some identical patients. Methodological concerns included the use of quasi-random allocation methods in four studies, and sizeable, largely unexplained differences in reported numbers allocated to each group in three studies. Phenobarbitone compared to supportive care alone has not been shown to reduce treatment failure or time to regain birthweight (one study). However, the duration of supportive care given to infants was significantly reduced (MD -162.1 mins/day, 95% CI -249.2, -75.1). Comparing phenobarbitone to diazepam, meta-analysis of two studies found phenobarbitone produced a significant reduction in treatment failure (typical RR 0.39, 95% CI 0.24, 0.62). There was no significant difference in duration of treatment or hospital stay. Comparing phenobarbitone with chlorpromazine, one study found no significant difference in treatment failure rate. No data for neurodevelopment reported by treatment group of allocation were available. No trials were eligible that assessed clonidine for NAS. In infants treated with an opiate, a small quasi-random study reported a reduced severity of withdrawal. Infants were weaned from an opiate more quickly which allowed earlier hospital discharge and reduced hospital costs. These findings may reflect the low dose of opiate used for initial treatment and the policy of discharging infants home on phenobarbitone but not morphine.

AUTHORS' CONCLUSIONS

In newborn infants with NAS, there is no evidence that phenobarbitone compared with supportive care alone reduces treatment failure; however, phenobarbitone may reduce the daily duration of supportive care needed. Phenobarbitone, compared to diazepam, reduces treatment failure. In infants treated with an opiate, the addition of phenobarbitone may reduce withdrawal severity. Further trials are required to determine if this finding is applicable when a higher initial dose of opiate is used, and determine the effects of phenobabritone on infant development. There is insufficient evidence to support the use of chlorpromazine or clonidine in newborn infants with NAS. Clonidine and chlorpromazine should only be used in the context of a randomised clinical trial. This review should be taken in conjunction with the review "Opiate treatment for opiate withdrawal in newborn infants" (Osborn 2002a) which indicates that an opiate is the preferred initial therapy for NAS.

Opiate treatment for opiate withdrawal in newborn infants

BACKGROUND

Neonatal abstinence syndrome (NAS) due to opiate withdrawal may result in disruption of the mother-infant relationship, sleep-wake abnormalities, feeding difficulties, weight loss and seizures. Treatments used to ameliorate symptoms and reduce morbidity include opiates, sedatives and non-pharmacological treatments.

OBJECTIVES

To assess the effectiveness and safety of using an opiate, compared to a sedative or non-pharmacological treatment, for treatment of NAS due to withdrawal from opiates.

SEARCH STRATEGY

The previous review was updated with additional searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2005), MEDLINE (1966-December 2004) and EMBASE (1980-December 2004) supplemented by searches of conference abstracts and citation lists of published articles.

SELECTION CRITERIA

Trials enrolling infants with NAS born to mothers with an opiate dependence, with > 80% follow up and using random or quasi-random allocation to opiate or control. Control could include an opiate, sedative or non-pharmacological treatment.

DATA COLLECTION AND ANALYSIS

Each author assessed study quality and extracted data independently. Primary outcomes included control of symptoms, seizure occurrence, mortality and neurodevelopment. Treatment effect was expressed using relative risk (RR), risk difference (RD), mean difference (MD) and weighted mean difference (WMD). Meta-analysis was performed using a fixed effect model.

MAIN RESULTS

Seven studies enrolling a total of 585 infants met inclusion criteria (Carin 1983; Finnegan 1984; Jackson 2004; Kaltenbach 1986; Kandall 1983; Khoo 1995; Madden 1977); however, two (Finnegan 1984; Kaltenbach 1986) may be sequential reports that include some identical patients. The studies enrolled infants of mothers who had used opiates with or without other drugs during pregnancy. Methodological concerns included the use of quasi-random rather than random patient allocation methods in three studies; sizeable, largely unexplained differences in reported numbers allocated to each group in four studies; and imbalances in group characteristics after randomisation in one study. Opiate (morphine) vs supportive care only: One study (Khoo 1995) found no significant effect on treatment failure (RR 1.29, 95% CI 0.41, 4.07), a significant increase in hospital stay (MD 15.0 days, 95% CI 8.9, 21.1) and significant reductions in time to regain birthweight (MD -2.8 days, 95% -5.3, -0.3) and duration of supportive care (MD -197.2 minutes/day, 95% CI -274.2, -120.3). Opiate vs phenobarbitone: Meta-analysis of four studies found no significant difference in treatment failure (typical RR 0.76, 95% CI 0.51, 1.11). One of these studies (Finnegan 1984) reported that opiate treatment resulted in a significant reduction in treatment failure among infants of mothers who had used only opiates; however, as this was a post-hoc analysis, this result should be interpreted with caution. One study (Jackson 2004) reported a significant reduction in duration of treatment and admission to the nursery for infants receiving morphine compared to phenobarbitone. One study (Kandall 1983) reported a reduction in seizures, of borderline statistical significance, with the use of opiate. Opiate vs diazepam: Meta-analysis of two studies found a significant reduction in treatment failure (RR 0.43, 95% CI 0.23, 0.80) with the use of opiate. No study reported neurodevelopment by allocated treatment group.

AUTHORS' CONCLUSIONS

Opiates, as compared to supportive care only, appear to reduce the time to regain birth weight and reduce the duration of supportive care, but increase the duration of hospital stay; there is no evidence of effect on treatment failure. When compared to phenobarbitone, opiates may reduce the incidence of seizures but, overall, there is no evidence of effect on treatment failure. One study reported a reduction in duration of treatment and nursery admission for infants on morphine. When compared to diazepam, opiates reduce the incidence of treatment failure. A post-hoc analysis generates the hypothesis that treatment effects may vary according to whether the population includes infants born to all opiate users (i.e. with or without other drug exposure) or is restricted to infants of mothers who used opiates only. In view of the methodologic limitations of the included studies the conclusions of this review should be treated with caution.

Specific enkephalin-degrading aminopeptidase activity in the HPT and HPO axes of rats with breast cancer induced by N-methyl nitrosourea

State and function of breast depend on an endocrinological balance, the upsetting of which can be a factor favorable to the development of cancer. Enkephalins (ENK) have been considered as a particular form of adaptation to defense to the organism against neoplastic processes. However, ENK may modify the endocrine functions of glands such as the ovary or the thyroid through the hypothalamus-pituitary axis, acting direct or indirectly as endocrine, paracrine or autocrine stimulatory growth factors. The present work analyses enkephalin-degrading tyrosyl aminopeptidase (EDA) activity in the hypothalamus-pituitary-thyroid (HPT) and hypothalamus-pituitary-ovary (HPO) axes in a rat model of breast cancer induced by N-methyl-nitrosourea (NMU) to state the relationship between ENK levels modification through EDA activity at different neuroendocrine levels and breast cancer. Results obtained show a decrease in EDA activity in hypothalamus, anterior and posterior pituitary, thyroid and ovary, suggesting increased levels of ENK in all these locations. These ENK may induce breast cancer cell growth and progression not only at breast level, but also acting at several neuroendocrine levels such as the HPT and HPO axes, inducing an unbalance of several other hormones, which could also facilitate the progression of cancer as an undesirable concomitant effect.

Neuron-restrictive silencer factor (NRSF) functions as a repressor in neuronal cells to regulate the mu opioid receptor gene

The mu opioid receptor (MOR) is expressed in the central nervous system and specific cell lines with varying expression levels perhaps playing important roles. One of the neuronal-specific transcription regulators, neuron-restrictive silencer factor (NRSF), has been shown to repress the expression of neuron-specific genes in non-neuronal cells. However, we showed here that the neuron-restrictive silencer element (NRSE) of MOR functions as a critical regulator to repress the MOR gene expression in specific neuronal cells depending on NRSF expression level. Using co-transfection studies, we showed that the NRSE of the MOR promoter is functional in NRSF-positive cells (NS20Y and HeLa) but not in NRSF-negative cells (PC12). NRSF binds to the NRSE of the MOR gene in a sequence-specific manner confirmed by supershift and chromatin immunoprecipitation assays, respectively. The suppression of NRSF activity with either trichostatin A or a dominant-negative NRSF induced MOR promoter activity and transcription of the MOR gene. When the NRSF was disrupted in NS20Y and HeLa cells using small interfering RNA, the transcription of the endogenous target MOR gene increased significantly. This provides direct evidence the role of NRSF in the cells and also indicates that NRSF expression is regulated by post-translational modification in neuronal NMB cells. Our data suggested that NRSF can function as a repressor of MOR transcription in specific cells, via a mechanism dependent on the MOR NRSE.

Effects of naloxone on rewarding and aversive brain sites

The effects of naloxone on the rewarding and aversive properties of brain stimulation derived from the ventral tegmental area and the nucleus reticularis gigantocellularis, respectively, were assessed in rats, based on the following measures-the current threshold for latency to escape aversive nucleus reticularis gigantocellularis stimulation, the frequency threshold for rewarding ventral tegmental area stimulation, and the frequency threshold for self-stimulation obtained from delivery of concurrent ventral tegmental area and nucleus reticularis gigantocellularis stimulation, before and after three systemic doses of naloxone (0, 10, and 20mg/kg); in the latter case, the stimulation trains were interdigitated with an interpulse interval of 2 ms. Initially, thresholds for concurrent stimulation were elevated relative to the values obtained for ventral tegmental area stimulation alone, returning to baseline values only when the nucleus reticularis gigantocellularis stimulation no longer induced escape. After each pairing of the two sites, the current threshold for escape gradually increased until the maximum value administered, 700 microA, at which point aversive responses were no longer observed. This required very few pairings, between one and five trials across animals. Drug tests were then begun and produced a significant dose-response threshold increase across animals, without reinstating the latency to escape nucleus reticularis gigantocellularis stimulation. These findings are discussed in terms of a dissociation between the analgesic and rewarding properties of ventral tegmental area stimulation.

Mutations in the human proopiomelanocortin gene

The melanocortin peptides and their receptors represent one of the most complex systems in human endocrinology. Hormonal regulation includes pigmentation, weight maintenance, adrenal function, and exocrine gland secretion via endocrine, paracrine, autocrine, and neurocrine action of melanocortin peptides at five different but homologous melanocortin receptors. Genetic relevance of the melanocortin system for human physiology was initially shown by mutations in the different melanocortin receptor genes, first described in the melanocortin-2 receptor gene in 1993 as one reason for congenital hypocortisolism. Because all ligands within the melanocortin systems are derived from one single precursor hormone, proopiomelanocortin (POMC), a genetic defect in the POMC gene could have been expected to affect all functional components of the melanocortin system. Accordingly, patients with a complete defect of the POMC gene product due to homozygous or compound heterozygous loss of function mutations were shown to be affected mainly by red hair, early-onset obesity, and congenital hypocortisolism. No further obvious clinical problems were described in these patients, suggesting that no additional function of the melanocortin system has escaped recognition. However, whether partial loss of function mutations in the POMC gene might lead to more circumscribed phenotypes, especially common obesity, remains an open question.

Analyzing the evolution of the opioid/orphanin gene family

Advances in molecular biology have made it possible to rapidly obtain the amino acid sequence of neuropeptide precursors-either by cloning and sequencing the cDNA that encodes the precursor, or by reconstructing the arrangement of exons and introns in a neuropeptide-coding gene through genomic approaches. The databases generated from these molecular approaches have been used to design probes to identify the cells that express the gene, or to ascertain the rate of expression of the gene, and even to predict the post-translational modifications that can generate functional neuropeptides from a biologically inert precursor. Although the power of these approaches is substantial, it is appreciated that a gene sequence or an mRNA sequence reflects the potential products that may be assembled in a secretory cell. To understand the functional capabilities of the secretory cell, the molecular genetics approaches must be combined with procedures that actually characterize the end-products generated by the secretory cell. Recent advances in two-dimensional gel electrophoresis and mass spectrometry now make it possible to analyze neuropeptides from a relatively small amount of tissue. These procedures can reveal novel end-products, tissue-specific endoproteolytic cleavage events, and developmental shifts in post-translational processing schemes. A gene family that illustrates all of these processes and the advantages of combining genomics with proteomics is the opioid/orphanin gene family.

Potentiation of the excitatory action of NMDA in ventrolateral periaqueductal gray by the mu-opioid receptor agonist, DAMGO

Several lines of evidence have suggested that mu-opioids, generally regarded as inhibitory, also have effects that stimulate neural activity. To look for possible excitatory opioid action in the rat periaqueductal gray (PAG), we first re-examined data from a previous study and found that met-enkephalin could evoke a delayed, sluggish excitation, suggestive of modulation by the opioid on the action of certain excitants. This observation, coupled with other studies that show mu-opioids can modulate NMDA receptor activation, prompted us to perform extracellular recording of the responses of single ventrolateral PAG (vlPAG) neurons in brain slices to DAMGO, a mu-opioid, and to NMDA. When applied alone, DAMGO at nM concentrations, like met-enkephalin, often evoked the delayed excitation and occasionally an inhibition. When applied after a brief exposure to NMDA, DAMGO at doses as low as 0.1 nM potentiated the excitation produced by a subsequent pulse of NMDA. This occurred, depending on cell type, in 23-100% of vlPAG neurons. The potentiating action of DAMGO was blocked by naloxone, suggesting it was mediated by mu-opioid receptors. Characterization of these mu-opioid actions revealed that the potentiation and the delayed excitation, unlike the inhibition, was not blocked by another opioid antagonist, nalmefene, nor by an inhibitor of the G protein of the G(i) class, N-ethylmaleimide. Moreover, the potentiating action was distinct from the inhibition in that it was: (a) enhanced by repeated opioid applications, (b) exhibited low effective doses, (c) had a long time course (minutes to develop and last tens of minutes) and (d) was present in distinct though overlapping cell populations. These data reveal an unconventional action of opioids in PAG neurons, that is, a potentiation of excitation produced by NMDA. This effect appeared mechanistically distinct from opioid inhibition or disinhibition and may be related to established examples of direct opioid excitation. These observations may help understanding behaviorally important mechanisms linked to acute and chronic opioid functions in the vlPAG.

Effects of endomorphin-1 and -2 on mu-opioid receptors in myenteric neurons and in the peristaltic reflex in rat small intestine

1. The aim of the present investigations was to characterize the effect of endomorphins on the function of rat small intestine smooth muscle and on the electrically induced ascending and descending reflex pathway of rat small intestine in vitro. 2. Endomorphin-1 and -2 left the basal tonus and the pharmacologically stimulated smooth muscle unchanged. In contrast, electrically induced twitch contractions were significantly reduced by endomorphin-1 and -2 and this reduction was reversed by the mu-opioid receptor antagonist Cys-Tyr-Orn-Pen-amide (CTOP), suggesting a specific mu-opioid receptor-mediated effect on neural tissue. 3. In the reflex model, endomorphin-1 caused a significant inhibition (IC50 2.3 x 10(-8) mol/L) of the ascending contraction (10(-8) mol/L: -28.3 +/- 5.8%; 10(-7) mol/L: -94.7 +/- 0.2.8%; both P < 0.05; n = 7). Descending relaxation increased at a concentration of 10(-8) mol/L endomorphin-1 (+61.6 +/- 24.5%; 10(-7) mol/L: +237.0 +/- 65.4%; both P < 0.05; n = 6). 4. Endomorphin-1 caused a further significant increase in the latency of the ascending contraction (10(-8) mol/L: +44.7 +/- 20.5%; 10(-7) mol/L: +93.5 +/- 16.1%; both P < 0.05; n = 7), whereas the latency of the descending relaxation was unaltered (n = 7). Similar results were observed for endomorphin-2. 5. All effects could be reversed by a wash-out afterwards and were blocked by pre-incubation with CTOP (10-6 mol/L). 6. Reverse transcription-polymerase chain reaction demonstrated mRNA expression of mu-opioid receptors in the rat ileum longitudinal muscle/myenteric plexus preparation, as well as in the oesophagus and stomach. 7. Endomorphin-1 and -2 reduce the cholinergic-induced contractile response of the rat ileal smooth muscle preparation via a presynaptic mechanism. 8. By a specific and reversible interaction with mu-opioid receptors, the ascending excitatory and descending inhibitory reflex responses were attenuated or facilitated, respectively. 9. In conclusion, the endomorphins may be the physiological endogenous mu-opioid receptor agonists in the rat small intestine.

Sedatives for opiate withdrawal in newborn infants

BACKGROUND

Neonatal abstinence syndrome (NAS) due to opiate withdrawal may result in disruption of the mother-infant relationship, sleep-wake abnormalities, feeding difficulties, weight loss and seizures. Treatments used to ameliorate symptoms and reduce morbidity include opiates, sedatives and non-pharmacological treatments.

OBJECTIVES

To assess the effectiveness and safety of using a sedative compared to a non-opiate control for NAS due to withdrawal from opiates, and to determine which type of sedative is most effective and safe.

SEARCH STRATEGY

The standard search strategy of the Neonatal Review Group was used. This included searches of the Cochrane Controlled Trials Register (The Cochrane Library, Issue 1, 2002) and MEDLINE 1966-2002.

SELECTION CRITERIA

Trials enrolling infants with NAS born to mothers with an opiate dependence, with > 80% follow up and using random or quasi-random allocation to sedative or control. Control could include another sedative or non-pharmacological treatment.

DATA COLLECTION AND ANALYSIS

Each author assessed study quality and extracted data independently. Primary outcomes included treatment failure (failure to achieve symptom control or use of additional drug treatment), seizure occurrence, mortality and neurodevelopment. Treatment effect was expressed using (RR), risk difference (RD), mean difference (MD) and weighted mean difference (WMD). Meta-analysis was performed using a fixed effect model.

MAIN RESULTS

Five studies enrolling a total of 285 patients met inclusion criteria (Finnegan 1984, Kahn 1969, Kaltenbach 1986, Khoo 1995, Madden 1977); however, two (Finnegan 1984, Kaltenbach 1986) may be sequential reports that include some identical patients. Methodological concerns included the use of quasi-random rather than random patient allocation methods in three studies, and sizeable, largely unexplained differences in reported numbers allocated to each group in three studies. Phenobarbital compared to supportive care alone has not been shown to reduce treatment failure or time to regain birthweight (one study). However, the duration of supportive care required to be given to infants each day was significantly reduced (MD -162.1 minutes/day, 95% CI -249.2, -75.1). Comparing phenobarbital to diazepam, meta-analysis of two studies found that phenobarbital produced a significant reduction in treatment failure (typical RR 0.39, 95% CI 0.24, 0.62). There was no significant difference in duration of treatment or duration of hospital stay. Comparing phenobarbital with chlorpromazine, one study found no significant difference in treatment failure rate. No data for neurodevelopment were available, reported by treatment group as allocated. No trials were eligible that assessed clonidine for NAS.

REVIEWER'S CONCLUSIONS

In newborn infants with NAS, there is no evidence that phenobarbital, compared with supportive care alone, reduces treatment failure; however, phenobarbital may reduce the daily duration of supportive care needed. Phenobarbital, compared to diazepam, reduces treatment failure. There is insufficient evidence to support the use of chlorpromazine or clonidine in newborn infants with NAS. Clonidine and chlorpromazine should only be used in the context of a randomised clinical trial. The results of this review, taken in conjunction with the related review, Opiate treatment for opiate withdrawal in newborn infants (Osborn 2002), indicate that treatment with opiates is the preferred initial therapy for NAS. It is hypothesised that this is particularly true for infants whose mothers have used only opiates during pregnancy. If a sedative is used, phenobarbital is preferred to diazepam. The results of an ongoing trial of the addition of phenobarbital to an opiate are awaited.

Opiate treatment for opiate withdrawal in newborn infants

BACKGROUND

Neonatal abstinence syndrome (NAS) due to opiate withdrawal may result in disruption of the mother-infant relationship, sleep-wake abnormalities, feeding difficulties, weight loss and seizures. Treatments used to ameliorate symptoms and reduce morbidity include opiates, sedatives and non-pharmacological treatments.

OBJECTIVES

To assess the effectiveness and safety of using an opiate, compared to a sedative or non-pharmacological treatment, for treatment of NAS due to withdrawal from opiates. The evidence for use of different opiates was assessed in subgroup analyses.

SEARCH STRATEGY

The standard search strategy of the Cochrane Neonatal Review Group including searches (up to March 2002) of the Oxford Database of Perinatal Trials, Cochrane Controlled Trials Register (The Cochrane Library, Issue 1, 2002), MEDLINE (1966-March 2002), previous reviews including cross references, abstracts, conferences and symposia proceedings, expert informants, journal handsearching mainly in the English language.

SELECTION CRITERIA

Trials enrolling infants with NAS born to mothers with an opiate dependence, with > 80% follow up and using random or quasi-random allocation to opiate or control. Control could include an opiate, sedative or non-pharmacological treatment.

DATA COLLECTION AND ANALYSIS

Each author assessed study quality and extracted data independently. Primary outcomes included control of symptoms, seizure occurrence, mortality and neurodevelopment. Treatment effect was expressed using relative risk (RR), risk difference (RD), mean difference (MD) and weighted mean difference (WMD). Meta-analysis was performed using a fixed effect model.

MAIN RESULTS

Six studies enrolling a total of 511 infants met inclusion criteria (Carin 1983, Finnegan 1984, Kaltenbach 1986, Kandall 1983, Khoo 1995, Madden 1977); however, two (Finnegan 1984, Kaltenbach 1986) may be sequential reports that include some identical patients. The studies enrolled infants of mothers who had used opiates with or without other drugs during pregnancy. Methodological concerns included the use of quasi-random rather than random patient allocation methods in three studies, and sizeable, largely unexplained differences in reported numbers allocated to each group in four studies. Opiate (morphine) vs supportive care only: One study (Khoo 1995) found no significant effect on treatment failure (RR 1.29, 95% CI 0.41, 4.07), a significant increase in hospital stay (MD 15.0 days, 95% CI 8.9, 21.1) and significant reductions in time to regain birthweight (MD -2.8 days, 95% -5.3, -0.3) and duration of supportive care (MD -197.2 minutes/day, 95% CI -274.2, -120.3). Opiate vs phenobarbital: Meta-analysis of three studies found no significant difference in treatment failure (typical RR 0.78, 95% CI 0.46, 1.32). One of these studies (Finnegan 1984) reported that opiate treatment resulted in a significant reduction in treatment failure among infants of mothers who had used only opiates; however, as this was a post-hoc analysis, this result should be interpreted with caution. One study (Kandall 1983) reported a reduction in seizures, of borderline statistical significance, with the use of opiate. Opiate vs diazepam: Meta-analysis of two studies found a significant reduction in treatment failure (RR 0.43, 95% CI 0.23, 0.80) with the use of opiate. No study reported neurodevelopment by allocated treatment group.

REVIEWER'S CONCLUSIONS

Opiates, as compared to supportive care only, appear to reduce the time to regain birth weight and reduce the duration of supportive care, but increase the duration of hospital stay; there is no evidence of effect on treatment failure. When compared to phenobarbital, opiates may reduce the incidence of seizures but, overall, there is no evidence of effect on treatment failure. When compared to diazepam, opiates reduce the incidence of treatment failure. A post-hoc analysis generates the hypothesis that treatment effects may vary according to whether the population includes infants born to all opiate users (i.e. with or without other drug exposure) or is restricted to infants of mothers who used opiates only. In view of the methodologic limitations of the included studies the conclusions of this review should be treated with caution. Further research is needed.

Effects of stress and relaxation on capsaicin-induced pain

A sizable body of research has been devoted to understanding the relationship between pain sensitivity and the psychological state of the individual. Considerable disagreement as to the direction of the association still exists. This study examines the effects of 2 experimental manipulations, cognitive/emotional stress and relaxation, on capsaicin-induced pain. Subjects were pretrained in relaxation and then randomized to experimental stress produced by a 20-minute Stroop test, relaxation (tape), or a control condition (neutral video), followed by a capsaicin injection in the forearm. Cardiovascular measures were taken at regular intervals, and cortisol, norepinephrine (NE), and self-reports of arousal (relaxation index) were taken immediately before and after the experimental task. The manipulation significantly interacted with sex to predict capsaicin-induced maximum pain. Women in the stress condition reported greater pain than both men in the stress condition and women in the relaxation condition. Pain was correlated negatively with task-induced changes in NE and cortisol and positively with self-reported arousal (decreased relaxation). However, separate analyses showed that some physiologic indexes of heightened arousal (increased blood pressure and NE) predicted lower pain only in men, whereas subjective increases in arousal predicted higher pain only in women. Multiple hierarchical regression analyses confirmed that physiologic and self-reported arousal predicted pain independently and in opposite directions, and a model including both accounted for 56% of the overall variance. These findings suggest that a unidimensional model of arousal may be insufficient to explain the effects of stress on pain and that these effects operate differently in men and women.

Spectroscopic evidence of beta-turn in N-glycated peptidomimetics related to leucine-enkephalin

The conformational differences caused by N-glycation of the amide bond in endogenous opioid pentapeptide leucine-enkephalin (Tyr-Gly-Gly-Phe-Leu) have been explored in solution using FTIR spectroscopy, NMR and molecular modelling. The compounds studied include protected and unprotected enkephalin analogues N-alkylated at the second (Gly2) amino acid residue with a 6-deoxy-D-galactose moiety (1-3). Comparison of the amide I component bands in the FTIR spectra, measured in trifluoroethanol (TFE), CHCl3 and DMSO, revealed significant differences in the intensity as well as shifts in component band frequencies for glycopeptides 1-3. We found that only the FTIR spectrum of the fully protected compound 1 indicated the presence of a higher population of beta-turns, while the spectra of the partially protected and unprotected glycopeptides 2 and 3 reflected the dominance of unordered or open structures, with some low population of turns. The observed NOE connectivities in CDCl3 for both isomers of the fully protected compound 1, the all-trans one and another with Tyr1-Gly2 peptide bond in cis conformation, indicate the presence of a beta-like turn conformation. Molecular dynamics simulations of the glycopeptide 1 obtained by unconstrained energy minimization of trans- and cis-1 shows that one of trans form conformations is consistent with beta-turn whereas cis isomer has revealed less-compact turn.

Endogenous opioids modulate ventilation and peak oxygen consumption in obese Zucker rats

Levels of endogenous opioids are increased in morbidly obese humans and obese rats. Endogenous opioids are important neuromodulators, and are involved in a wide range of functions including ventilatory control. We studied eight lean and eight obese Zucker (Z) rats at 6 and 16 wk of age. We assessed minute ventilation (V E) at rest and during hypercapnic challenges, as well as peak oxygen consumption (V O(2peak)) after the administration of saline (control), naloxone hydrochloride (N(HCl)), and naloxone methiodide (N(M)). Administration of N(HCl) and N(M) to lean animals had no effect on V E and V O(2peak). Similarly, N(M) failed to alter V E and V O(2peak) in obese rats studied at 6 or 16 wk of age. In young obese rats, N(HCl) significantly (p < 0.05) increased resting V E (721 +/- 154 [mean +/- SD] ml/kg/min versus 937 +/- 207 ml/kg/min, saline versus N(HCl), respectively); VE in response to 4% CO(2) (924 +/- 110 ml/kg/min versus 1,212 +/- 172 ml/ kg/min); V E in response to 8% CO(2) (1,233 +/- 172 ml/kg/min versus 1,565 +/- 327 ml/kg/min); and V O(2peak) (90.8 +/- 9.6 ml/kg(0.75)/min versus 98.3 +/- 5.9 ml/kg(0.75)/min). However, N(HCl) administration had no effect on V E or V O(2peak) in obese rats retested at 16 wk of age. Thus, endogenous opioids modulate resting ventilation, ventilatory responsiveness to CO(2), and V O(2peak) in young obese rats by acting specifically on receptors located within the central nervous system. This modulation disappears once the animals reach 16 wk of age.

Detection of neuropeptides using on-capillary copper complexation and capillary electrophoresis with electrochemical detection

Capillary electrophoresis with electrochemical detection using a carbon fiber electrode in conjunction with on-capillary copper complexation was evaluated for the determination of peptides in standard and biological matrices. Peptides composed of 2-10 amino acids were investigated. A comparison was made between the responses obtained for peptides containing the oxidizable residue tyrosine and those obtained for their respective copper complexes. Electrochemical detection of non-tyrosine-containing peptides and a cyclic peptide was also demonstrated. A separation of leucine (Leu)-enkephalin and five metabolites was developed and then used for the investigation of Leu-enkephalin metabolism in plasma. The appearance of the des-tyrosine (des-Tyr) Leu-enkephalin, which cannot be detected directly at a carbon electrode, was monitored using the on-capillary complexation technique. Direct injection of the plasma sample was possible using this methodology.

Chronic blockade of hippocampal kappa receptors increases arterial pressure in conscious spontaneously hypertensive rats but not in normotensive Wistar Kyoto rats

Previous studies in this laboratory have shown that dynorphins acting on hippocampal kappa opioid receptors in rat brain exert a restraining influence on arterial blood pressure and that a relative deficiency of their production in the spontaneously hypertensive rat (SHR) may be involved in SHR hypertension. Kappa receptor blockade should therefore exacerbate hypertension in SHR. We explored the latter possibility by chronic unilateral infusion of nor-binaltorphimine dihydrochloride (nor-BNI), a selective kappa receptor antagonist, into the right dorsal hippocampus of conscious SHR and normotensive Wistar-Kyoto (WKY) controls over a 14 day period. Additional controls consisted of similar hippocampal infusions of equivalent volumes of drug vehicle in both rat strains. Mean arterial pressure (MAP) and heart rates (HR) were determined in each animal once daily by the tail cuff method during this period. Nor-BNI induced a sustained increase in the basal high level of MAP in SHR from 132 +/- 8 to 150 +/- 10 mmHg throughout the 14 days and an increased HR from 427 +/- 17 to 477 +/- 30 on day 3 to 5 following the drug. By contrast, nor-BNI had no significant effects on either MAP or HR in WKY rats and control infusions of drug vehicle were similarly without effect in both strains. The results support our previous suggestion that the kappa opioid system of the hippocampus ordinarily restrains arterial blood pressure in SHR since prolonged hippocampal kappa receptor blockade results in augmented hypertension in this strain.

Delta opioid receptor immunoreactive boutons appose bulbospinal CI neurons in the rat

Bulbospinal sympathoexcitatory neurons in the rostral ventrolateral medulla are inhibited by activation of delta opioid receptors. However, it is not known whether this opioidergic effect is pre- or post- synaptic. Here, using retrograde tracing and immunocytochemistry in adult rats, we provide evidence that the delta opioid receptor is located on boutons that are presynaptic to both catecholaminergic and non-catecholaminergic neurons that project to the spinal cord. We suggest that the sympathoinhibitory action of delta opioid receptor activation in the rostral ventrolateral medulla is mediated presynaptically, resulting in a reduction of excitatory neurotransmitter release from boutons that oppose sympathoexcitatory bulbospinal neurons.

Implications of proopiomelanocortin (POMC) mutations in humans: the POMC deficiency syndrome

The recent discovery of the contribution of proopiomelanocortin (POMC)-derived peptides to the regulation of energy homeostasis and exocrine gland secretion in mice aroused new interest in the complex function of the endocrine POMC network. In addition, the first mutations in the gene encoding POMC have been identified in two patients affected by adrenal insufficiency, early onset severe obesity and red hair pigmentation. Therefore, the focus of this brief review will be the detailed discussion of the implications of these new findings in the physiology of the human POMC ligand-receptor system.

The development of POMC gene expression in the medial basal hypothalamus of prepubertal rats

Alterations in brain opioid gene expression may underlie the dramatic change in the latency to display parental behavior in juvenile rats. Male and female juvenile rats (18-25 days of age) exhibit parental behavior either immediately or within 1-2 days after coming in contact with foster pups. By 30 days of age, however, their response latencies increase to adult levels of 5-10 days. Given the established involvement of the endogenous opioid system in adult maternal and juvenile parental behaviors, the objective of the present report was to determine possible changes in proopiomelanocortin (POMC) gene expression in the medial basal hypothalamus (MBH) during this early developmental window. We compared POMC gene expression in the MBH of male and female juvenile rats from 21 to 33 days of age by in situ hybridization histochemistry. A significant increase in the number of POMC cells in males and females was detected at 30 days of age in the central portion of the arcuate nucleus. This increase in POMC mRNA may contribute to the shift in parental behavior that occurs in male and female juvenile rats.

Proopiomelanocortin gene expression is decreased in the infundibular nucleus of postmenopausal women

Previous studies have shown that estrogen withdrawal decreases the secretion of beta-endorphin from the monkey hypothalamus. In addition, there are consistent age-associated changes in beta-endorphin neurons in the rodent. Based on these findings, we hypothesized that the activity of hypothalamic beta-endorphin neurons would be decreased in the hypothalamus of postmenopausal women. In the present study, we examined the expression of proopiomelanocortin (POMC) mRNA, the precursor mRNA for beta-endorphin, in the medial basal hypothalamus of premenopausal and postmenopausal women. Every 20th sagittal section through the hypothalamus was hybridized with a synthetic [35S]labeled, 48-base oligonucleotide probe complementary to POMC mRNA. Labeled neurons were counted and their somatic profile areas were measured with an image-combining computer microscope system. The number of POMC mRNA-containing neurons/section in the infundibular nucleus was reduced by 65% in postmenopausal women. In contrast, there was no significant difference in the number of neurons expressing POMC gene transcripts in the retrochiasmatic region. The POMC neurons in the retrochiasmatic area were also distinct morphologically from those in the infundibular nucleus. The differences between the infundibular and retrochiasmatic regions suggest that functional subgroups of POMC neurons exist in the human hypothalamus. Our findings provide evidence that the activity of hypothalamic POMC neurons is decreased in the infundibular nucleus of postmenopausal women. Both aging and gonadal steroid withdrawal may contribute to the decline in POMC gene expression in postmenopausal women.

Molecular evolution of the opioid/orphanin gene family

Gene duplication is a recurring theme in the evolution of vertebrate polypeptide hormones and neuropeptides. These duplication events can lead to the formation of gene families in which divergence of function is the usual outcome. In the case of the opioid/orphanin family of genes, duplication events have proceeded along two paths: (a) an apparent duplication of function as seen in the analgesic activity of Proenkephalin and Prodynorphin end-products; and (b) divergence of function as seen in the nociceptic activity of Proorphanin end-products or the melanocortin (color change and chronic stress regulation) activity of Proopiomelanocortin end-products. Although genes coding for Proopiomelanocortin, Proenkephalin, Prodynorphin, and Proorphanin have been extensively studied in mammals, the distribution and radiation of these genes in nonmammalian vertebrates is less well understood. This review will present the hypothesis that the radiation of the opioid/orphanin gene family is the result of the duplication and divergence of the Proenkephalin gene during the radiation of the chordates. To evaluate the Proenkephalin gene duplication hypothesis, a 3'RACE procedure was used to screen for the presence of Prodynorphin-related, Proenkephalin-related, and Proorphanin-related cDNAs expressed in the brains of nonmammalian vertebrates.

What peptides these deltorphins be

The deltorphins are a class of highly selective delta-opioid heptapeptides from the skin of the Amazonian frogs Phyllomedusa sauvagei and P. bicolor. The first of these fascinating peptides came to light in 1987 by cloning of the cDNA of from frog skins, while the other members of this family were identified either by cDNA or isolation of the peptides. The distinctive feature of deltorphins is the presence of a naturally occurring D-enantiomer at the second position in their common N-terminal sequence, Tyr-D-Xaa-Phe, comparable to dermorphin, which is the prototype of a group of mu-selective opioids from the same source. The D-amino acid and the anionic residues, either Glu or Asp, as well as their unique amino acid compositions are responsible for the remarkable biostability, high delta-receptor affinity, bioactivity and peptide conformation. This review summarizes a decade of research from many laboratories that defined which residues and substituents in the deltorphins interact with the delta-receptor and characterized pharmacological and physiological activities in vitro and in vivo. It begins with a historical description of the topic and presents general schema for the synthesis of peptide analogues of deltorphins A, B and C as a means to document the methods employed in producing a myriad of analogues. Structure activity studies of the peptides and their pharmacological activities in vitro are detailed in abundantly tabulated data. A brief compendium of the current level of knowledge of the delta-receptor assists the reader to appreciate the rationale for the design of these analogues. Discussion of the conformation of these peptides addresses how structure leads to further hypotheses regarding ligand receptor interaction. The review ends with a broad discussion of the potential applications of these peptides in clinical and therapeutic settings.

Mouse mu opioid receptor gene expression. A 34-base pair cis-acting element inhibits transcription of the mu opioid receptor gene from the distal promoter

The 5'-flanking region of the mouse mu opioid receptor (MOR) gene has two promoters, referred to as distal and proximal, and the activities of each in the brain are quite different from each other. The 5'-distal promoter regulatory sequences (5'-DPRS), positioned between these two promoters, have strong inhibitory effects on the reporter gene expression driven by the MOR distal promoter. In our studies, detailed 3' deletion mapping of the 5'-DPRS narrowed down the negative cis-acting element to a 34-base pair (bp) segment (position -721 to -687). This 34-bp cis-acting element functions in both neuronal (NMB) and non-neuronal (CHO and RAW264.7) cultured cells. S1 nuclease protection assays indicated that this 34-bp cis-acting element suppresses distal promoter activity at the transcriptional level. Linker scanning mutagenesis demonstrated that nucleotides around position -721 and -689 in the 34-bp cis-acting element are essential for the regulation of distal promoter activity. Operational characterization of the 34-bp cis-acting element in the homologous MOR distal promoter and the heterologous SV40 promoter showed that its effects are position- and promoter-dependent while being orientation-independent in both promoters. Collectively, these data suggested that this 34-bp segment is a conditional transcriptional cis-acting element that blocks mouse MOR gene expression from the distal promoter.

Authentic cell-specific and developmentally regulated expression of pro-opiomelanocortin genomic fragments in hypothalamic and hindbrain neurons of transgenic mice

The pro-opiomelanocortin (POMC) gene is expressed in a subset of hypothalamic and hindbrain neurons and in pituitary melanotrophs and corticotrophs. POMC neurons release the potent opioid beta-endorphin and several active melanocortins that control homeostasis and feeding behavior. POMC gene expression in the CNS is believed to be controlled by distinct cis-acting regulatory sequences. To analyze the transcriptional regulation of POMC in neuronal and endocrine cells, we produced transgenic mice carrying POMC27*, a transgene containing the entire 6 kb of the POMC transcriptional unit together with 13 kb of 5' flanking regions and 8 kb of 3' flanking regions. POMC27* was tagged with a heterologous 30 bp oligonucleotide in the third exon. In situ hybridization studies showed an accurate cell-specific pattern of expression of POMC27* in the arcuate nucleus and the pituitary. Hypothalamic mRNA-positive neurons colocalized entirely with beta-endorphin immunoreactivity. No ectopic transgenic expression was detected in the brain. Deletional analyses demonstrated that neuron-specific expression of POMC transgenes required distal 5' sequences localized upstream of the pituitary-responsive proximal cis-acting elements that were identified previously. POMC27* exhibited a spatial and temporal pattern of expression throughout development that exactly paralleled endogenous POMC. RNase protection assays revealed that POMC27* expression mimicked that of POMC in different areas of the CNS and most peripheral organs with no detectable ectopic expression. Hormonal regulation of POMC27* and POMC was identical in the hypothalamus and pituitary. These results show that distal 5' sequences of the POMC gene located between -13 and -2 kb target expression into the CNS of transgenic mice in a precise neuron-specific, developmentally and hormonally regulated manner.