Endogenous opiates: 1995

Effect of Severity of Opiate Use on Cardiometabolic Profile of Chronic Opiate Dependents of Western Rajasthan

Lack of cardiometabolic profile data based on severity of opiate dependence for opiate abusers. The study aimed to evaluate the effect severity of opiate abuse on the cardiometabolic profile of male opiate abusers without co-morbidities. The study included 30 healthy controls (HCs), 90 prospective chronic opiate (opium and heroin) abusers, with and without co-dependence of smoking and tobacco-chewing. The subjects were categorized based on severity of opiate dependence questionnaire (SODQ) and metabolic syndrome (MS) based on NCEP ATP-III criteria and fasting blood samples analyzed for sugar, insulin, insulin resistance (IR), lipid profile, Hs-CRP and total antioxidant capacity (TAC). There was higher prevalence of MS in opiate abusers as compared to HCs. Majority of the patients fell in grade 2 and 3 of severity. There was significant difference across groups for WHR (p < 0.001), SBP (p < 0.03), FBS (p < 0.001), insulin (p < 0.02), IR (p < 0.03) and TAC (p < 0.01). Multiple regression analysis of SODQ grades 2 and 3 independently predicted TAC by Hs-CRP (p = 0.032 and 0.042). There was a significant correlation of TAC with serum insulin, IR and Hs-CRP in SODQ grade 2 and serum insulin and Hs-CRP in SODQ grade 3. Chronic opiate abuse is not benign and predisposes abusers to cardiometabolic risk with increasing severity of dependence, owing to oxidative stress and chronic low-grade inflammation.

Effects of opiate dependence through different administration routes on pulmonary inflammation and its severity

Background

Serious health problems and socioeconomic consequences of the illicit use of opiates have been proved in both developed and developing societies

Objectives

We aimed to evaluate" The effects of opiate addiction through different administration routes on pulmonary inflammation and its severity."

Materials and Methods

Our experiments were performed on eighteen adult male Syrian golden hamsters which were allocated to one of the three groups (n = 6): control group which did not receive opiate; the first study group were administered oral opiate via stomach tube; and another study group were administered inhaled opiate. After four weeks, all hamsters were anesthetized with diethyl ether and their lung tissues were isolated for pathological assessment.

Results

Severe perivascular inflammation was detected in 33.3% of the samples with oral opiate dependence and 20% of the cases addicted to opiate through inhalation. Also, severe peribronchial inflammation was observed in only 20% of the samples addicted to inhaled opiate and was not found in the other groups. No significant differences were found in the severity of perivascular and peribronchial inflammation across the three groups. Although the mean of total inflammation scale in the subjects with oral opiate dependence (3.00 ± 1.79) was numerically higher than that in the inhaled dependence group (1.40 ± 2.60) and the controls (2.25 ± 1.26), this difference was not statistically significant.

Conclusions

Administration did not influence the appearance or severity of pulmonary inflammation in animal models addicted to opiate.

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.

Prenatal exposure to valproic acid disturbs the enkephalinergic system functioning, basal hedonic tone, and emotional responses in an animal model of autism

RATIONALE

It has been suggested that behavioral aberrations observed in autism could be the result of dysfunction of the neuroregulatory role performed by the endogenous opioid peptides. Many of those aberrations have been recently modeled in rats exposed to valproic acid (VPA) on the 12th day of gestation (VPA rats).

OBJECTIVES

The aim of the present study was to elucidate functioning of the enkephalinergic system, one of the endogenous opioid peptide systems strongly involved in emotional responses, in VPA rats using both biochemical and behavioral methods.

MATERIALS AND METHODS

In situ hybridization was used to measure proenkephalin mRNA expression in adult VPA rats' central nucleus of the amygdala, the dorsal striatum, and the nucleus accumbens. Additional groups of animals were examined in a conditioned place aversion to naloxone, the elevated plus maze, and object recognition tests to assess their basal hedonic tone, anxiety, learning and memory, respectively.

RESULTS

Prenatal exposure to VPA decreased proenkephalin mRNA expression in the dorsal striatum and the nucleus accumbens but not in the central nucleus of the amygdala. It also increased anxiety and attenuated conditioned place aversion to naloxone but had no impact on learning and memory.

CONCLUSIONS

The present results suggest that prenatal exposure to VPA may lead to the decreased activity of the striatal enkephalinergic system and in consequence to increased anxiety and disregulated basal hedonic tone observed in VPA rats. Presented results are discussed in light of interactions between enkephalinergic, GABAergic, and dopaminergic systems in the striatum and mesolimbic areas of the brain.

Role of endogenous opioid system in the regulation of the stress response

Numerous studies and reviews support an important contribution of endogenous opioid peptide systems in the mediation, modulation, and regulation of stress responses including endocrine (hypothalamopituitary-adrenal, HPA axis), autonomic nervous system (ANS axis), and behavioral responses. Although several discrepancies exist, the most consistent finding among such studies using different species and stressors is that opioids not only diminish stress-induced neuroendocrine and autonomic responses, but also stimulate these effector systems in the non-stressed state. A distinctive feature of the analgesic action of opioids is the blunting of the distressing, affective component of pain without dulling the sensation itself. Therefore, opioid peptides may diminish the impact of stress by attenuating an array of physiologic responses including emotional and affective states. The widespread distribution of enkephalin (ENK) throughout the limbic system (including the extended amygdala, cingulate cortex, entorhinal cortex, septum, hippocampus, and the hypothalamus) is consistent with a direct role in the modulation the stress responses. The predictability of stressful events reduces the impact of a wide range of stressors and ENK appears to play an important role in this process. Therefore, ENK and its receptors could represent a major modulatory system in the adaptation of an organism to stress, balancing the response that the stressor places on the central stress system with the potentially detrimental effects that a sustained stress may produce. Chronic neurogenic stressors will induce changes in specific components of the stress-induced ENKergic system, including ENK, delta- and mu-opioid receptors. This review presents evidences for adaptive cellular mechanisms underlying the response of the central stress system when assaulted by repeated psychogenic stress, and the involvement of ENK in these processes.

Selective distribution of mu-opioid receptors in C1 adrenergic neurons and their afferents

Agonists of the mu-opioid receptor (MOR) have profound effects on blood pressure, heart rate, and respiration that may be mediated by C1 adrenergic neurons in the rostral ventrolateral medulla (RVL). C1 neurons are sympathoexcitatory and are involved in both tonic and reflex regulation of sympathetic outflow. This study was designed to determine whether C1 neurons, or their afferents, contain MOR. C1 neurons were identified by using an antibody against the epinephrine synthesizing enzyme phenylethanolamine-N-methyl transferase (PNMT), whereas MOR was localized by using an antipeptide antibody that recognizes the cloned MOR, MOR1. Combined immunoperoxidase and immunogold methods were used to examine the cellular distribution of MOR1 relative to PNMT-containing neurons in the RVL. MOR1 was found in 22% of PNMT-containing dendrites (n = 392), whereas MOR1-containing axons or axon terminals contacted 14% of PNMT-containing dendrites. This distribution was heterogenous with regard to dendritic size: PNMT-labeled dendrites containing MOR1 were usually large (60% were >1.2 microm), whereas PNMT-containing dendrites that received MOR1-labeled afferents were usually small (79% were <1.2 microm). Individual dendrites rarely contained MOR1 at both pre- and postsynaptic sites. Together these results suggest that MOR agonists may directly influence the activity of C1 neurons, as well as the activity of select afferents to these cells. Plasmalemmal membrane labeling for MOR1 was more frequent in smaller PNMT-containing dendrites, suggesting that postsynaptic receptors are more readily available for ligand binding in small dendrites, although the receptor was more frequently detected in larger PNMT dendrites. The selective distribution of MORs to specific pre- and postsynaptic sites suggests the receptor may be selectively trafficked to positions where it may regulate afferent activity that is heterogeneously distributed along the dendritic tree of C1 neurons.

Mu-opioid receptors are present in functionally identified sympathoexcitatory neurons in the rat rostral ventrolateral medulla

Agonists of the mu-opioid receptor (MOR) produce profound hypotension and sympathoinhibition when microinjected into the rostral ventrolateral medulla (RVL). These effects are likely to be mediated by the inhibition of adrenergic and other presympathetic vasomotor neurons located in the RVL. The present ultrastructural studies were designed to determine whether these vasomotor neurons, or their afferents, contain MORs. RVL bulbospinal barosensitive neurons were recorded in anesthetized rats and filled individually with biotinamide by using a juxtacellular labeling method. Biotinamide was visualized by using a peroxidase method and MOR was identified by using immunogold localization of an antipeptide antibody that recognizes the cloned MOR, MOR1. The subcellular relationship of MOR1 to RVL neurons with fast- or slow-conducting spinal axons was examined by electron microscopy. Fast- and slow-conducting cells were not morphologically distinguishable. Immunogold-labeling for MOR1 was found in all RVL bulbospinal barosensitive neurons examined (9 of 9). MOR1 was present in 52% of the dendrites from both types of cells and in approximately half of these dendrites the MOR1 was at nonsynaptic plasmalemmal sites. A smaller portion of biotinamide-labeled dendrites (16%) from both types of cells were contacted by MOR1-containing axons or axon terminals. Together, these results suggest that MOR agonists can directly influence the activity of all types of RVL sympathoexcitatory neurons and that MOR agonists may also influence the activity of afferent inputs to these cells. The heterogenous distribution of MORs within individual RVL neurons indicates that the receptor is selectively targeted to specific pre- and postsynaptic sites.

Further evidence for a significant participation of the melanocortin 4 receptor in the preovulatory prolactin surge in the rat

We previously reported that the melanocortin 4 receptor may play a significant role in mediating the preovulatory surges of luteinizing hormone and prolactin in the rat. In order to confirm this previous finding, in the present study we examined and compared the effects of intracerebroventricular administrations of 1.0 nmol of MT II (a non-selective melanocortin 3 and 4 receptor agonist) and 10 nmol of gamma(1)-melanocyte-stimulating hormone (a selective melanocortin 3 receptor agonist) on luteinizing hormone and prolactin surges in starved, gonadal steroid-primed ovariectomized female rats, which is a model deprived of inherent surges of the two hormones. MT II significantly recovered the surge of prolactin, but not of luteinizing hormone (although a tendency to increase was seen), and gamma(1)-melanocyte-stimulating hormone was without effect on both hormones. This study corroborated our previous report through a different and direct approach that the melanocortin 4 receptor, but not the melanocortin 3 receptor, plays a significant role in mediating the preovulatory prolactin surge in the rat.

Plasma concentrations of beta-endorphin in smokers who consume different numbers of cigarettes per day

The harmful effects of smoking on health have been widely documented, although it is as yet unclear whether tobacco dependence is only psychological in nature, or both psychological and physical. We studied plasma concentrations of beta-endorphin, cortisol, and adrenocorticotropic hormone (ACTH) in healthy persons who consumed different numbers of cigarettes per day, and compared the findings with those in a control group of nonsmokers. Beta-endorphin levels were significantly higher than in controls only in persons who smoked fewer than 10 cigarettes per day. Cortisol levels were significantly higher in smokers who consumed more than 20 cigarettes per day. There were no significant differences between any of the groups in plasma ACTH concentrations.

Plasma adrenocorticotropin responses to opioid blockade with naloxone: generating a dose-response curve in a single session

We examined two methods of generating a dose-response curve to the opioid receptor antagonist naloxone. In 15 healthy male subjects (18-25 years) plasma adrenocorticotropin (ACTH) responses to five doses of naloxone studied over 5 separate days were compared to plasma ACTH responses to five incremental doses of naloxone studied within a single session. There was a statistically significant positive correlation in ACTH responses (area under the curve and peak) between dosing methods. Furthermore, the doses of naloxone that produced half-maximal and maximal ACTH response were similar. The comparability of ACTH responses between the two naloxone dosing techniques, combined with the safety and ease associated with the single-session methodology, underscores the usefulness of the single-session technique for future investigations.

Melanocortin-3 receptor mRNA expression in pro-opiomelanocortin neurones of the rat arcuate nucleus

The melanocortins alpha- and gamma-melanocyte-stimulating hormones (alpha- and gamma-MSH) derive from the pro-opiomelanocortin (POMC) precursor. Melanocortins exert a wide range of biological activities in the brain through activation of at least three distinct melanocortin receptor (MC-R) subtypes. In order to determine whether POMC neurones can modulate their own activity, we looked for the possible expression of the MC3-R gene in POMC-positive cell bodies in the rat hypothalamus. In situ hybridization experiments revealed that the density of MC3-R mRNA is particularly high in the arcuate nucleus which contains the main population of POMC neurones in the brain. The occurrence of MC3-R mRNA in POMC-positive cell bodies was demonstrated using a double-labelling in situ hybridization technique. The proportion of POMC neurones expressing MC3-R mRNA was significantly higher in the most rostral (43.5%) than in the most posterior part of the arcuate nucleus (8.2%). These results indicate that melanocortins likely exert a direct regulatory feedback on POMC neurones through activation of MC3-R receptors. Our data also suggest that MC3-R may be involved in the neuroendocrine responses induced by centrally administered melanocortins.

Effect of stress exposure on the activation pattern of enkephalin-containing perikarya in the rat ventral medulla

We examined the effects of acute and chronic psychogenic stress on the activation pattern of enkephalin-containing perikarya in the rat ventrolateral medulla. Rats allocated to the chronic stress groups were subjected to 90 min of immobilization for 10 days. On the 11th day, the chronically stressed rats were exposed to homotypic (90-min immobilization) or to heterotypic but still psychogenic (90-min immobilization coupled to air jet stress) stress. The acute stress group was subjected once to an acute 90-min immobilization. For each group, the rats were anesthetized either before stress (time 0) or 90, 180, and 270 min after the onset of stress. Brain sections were then processed using immunocytochemistry (Fos protein) followed by radioactive in situ hybridization histochemistry (enkephalin mRNA). Following immobilization, the acute group displayed a marked increase in the number of activated enkephalin-containing perikarya within the paragigantocellularis and lateral reticular nuclei. This level of activation was sustained up to 180 min following the onset of the immobilization stress and had returned to baseline levels by 270 min from the initiation of the stress. However, this stress-induced activation of enkephalin-containing perikarya of the ventrolateral medulla was not seen following either homotypic or heterotypic stress in the chronically stressed group. These results provide evidence that enkephalin-containing perikarya of the ventrolateral medulla may constitute a potential circuit through which they regulate some aspect of the stress responses. Conversely, this enkephalinergic influence from the ventrolateral medulla was shown to be absent following chronic stress exposure. This would suggest a decrease in enkephalin inhibitory input originating from the ventrolateral medulla, thereby allowing a neuroendocrine and/or autonomic response to chronic stress.

3D modeling, ligand binding and activation studies of the cloned mouse delta, mu; and kappa opioid receptors

Refined 3D models of the transmembrane domains of the cloned delta, mu and kappa opioid receptors belonging to the superfamily of G-protein coupled receptors (GPCRs) were constructed from a multiple sequence alignment using the alpha carbon template of rhodopsin recently reported. Other key steps in the procedure were relaxation of the 3D helix bundle by unconstrained energy optimization and assessment of the stability of the structure by performing unconstrained molecular dynamics simulations of the energy optimized structure. The results were stable ligand-free models of the TM domains of the three opioid receptors. The ligand-free delta receptor was then used to develop a systematic and reliable procedure to identify and assess putative binding sites that would be suitable for similar investigation of the other two receptors and GPCRs in general. To this end, a non-selective, 'universal' antagonist, naltrexone, and agonist, etorphine, were used as probes. These ligands were first docked in all sites of the model delta opioid receptor which were sterically accessible and to which the protonated amine of the ligands could be anchored to a complementary proton-accepting residue. Using these criteria, nine ligand-receptor complexes with different binding pockets were identified and refined by energy minimization. The properties of all these possible ligand-substrate complexes were then examined for consistency with known experimental results of mutations in both opioid and other GPCRs. Using this procedure, the lowest energy agonist-receptor and antagonist-receptor complexes consistent with these experimental results were identified. These complexes were then used to probe the mechanism of receptor activation by identifying differences in receptor conformation between the agonist and the antagonist complex during unconstrained dynamics simulation. The results lent support to a possible activation mechanism of the mouse delta opioid receptor similar to that recently proposed for several other GPCRs. They also allowed the selection of candidate sites for future mutagenesis experiments.

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.

Increased anxiety and impaired pain response in puromycin-sensitive aminopeptidase gene-deficient mice obtained by a mouse gene-trap method

A mouse mutation, termed goku, was generated by a gene-trap strategy. goku homozygous mice showed dwarfism, a marked increase in anxiety, and an analgesic effect. Molecular analysis indicated that the mutated gene encodes a puromycin-sensitive aminopeptidase (Psa; EC 3. 4.11.14), whose functions in vivo are unknown. Transcriptional arrest of the Psa gene and a drastic decrease of aminopeptidase activity indicated that the function of Psa is disrupted in homozygous mice. Together with the finding that the Psa gene is strongly expressed in the brain, especially in the striatum and hippocampus, these results suggest that the Psa gene is required for normal growth and the behavior associated with anxiety and pain.

Association of the enkephalinase gene with low amplitude P300 waves

Low amplitude of the P300 evoked potential waves has been linked to substance abuse. Defects in opioidergic genes regulating reward pathways have been implicated as risk factors in substance abuse. Since the rate of degradation of enkephalins regulates their CNS level, we focused on the MME gene for metallo-membrane endopeptidase (neutral endopeptidase, enkephalinase). We identified a GT repeat polymorphism 5' to the gene and examined its potential association with P300 wave amplitude in 25 male subjects with substance abuse. There was significant association of low mol. wt alleles with low amplitude of the P300 wave at the parietal (p = 0.0087) and coronal (p = 0.009) leads. These results support a role of endogenous opioids in the regulation of P300 wave amplitude.

Beta-endorphin-like immunoreactivity in the forebrain and pituitary of the teleost Clarias batrachus (Linn.)

The organization of beta-endorphin-like immunoreactivity in the olfactory system, forebrain, and pituitary of the teleost Clarias batrachus was investigated. Immunoreactivity was prominently seen in the sensory neurons and basal cells in the olfactory epithelium and in some cells in the periphery and center (granule cells) of the olfactory bulb. Immunoreactive fibers in the olfactory nerve enter the olfactory nerve layer of the olfactory bulb and branch profusely to form tufts organized as spherical neuropils in the glomerular layer. While fascicles of immunoreactive fibers were seen in the medial olfactory tracts, the lateral olfactory tracts showed individual immunoreactive fibers. Immunoreactive fibers in the medial olfactory tract extend into the telencephalon and form terminal fields in discrete telencephalic and preoptic areas; some immunoreactive fibers decussate in the anterior commissure, while others pass into the thalamus. While neurons of the nucleus lateralis tuberis revealed weak immunoreactivity, densely staining somata were seen at discrete sites along the wall of the third ventricle. Although a large population of immunoreactive cells was seen in the pars intermedia of the pituitary gland, few were seen in the rostral pars distalis and proximal pars distalis; immunoreactive fibers were seen throughout the pituitary gland.

Opioids: first lessons from knockout mice

Opioid receptors of the mu-, delta- and kappa-subtypes mediate the potent analgesic and addictive actions of opioid drugs. They also regulate responses to pain, stress and emotions when activated by endogenous opioid peptides. Recently, mice lacking opioid receptors or opioid peptides have been produced by gene targeting, providing molecular tools to study opioid function in vivo. Observations on mutant mice have shed new light on the mode of action of opioids, opioid receptor heterogeneity and interactions, and the involvement of each component of the opioid system in mouse physiology. In this article, Brigitte L. Kieffer reviews the first reported studies and discusses their therapeutic implications.

Adrenocorticotropin responses to naloxone in sons of alcohol-dependent men

The endogenous opioid system is part of a neural circuitry functionally related to alcohol-seeking behaviors. A family history of alcoholism is the strongest predictor of future development of alcohol dependence. This study was designed to evaluate ACTH responses to opioid receptor blockade as a function of family history for alcohol dependence. The nonselective opioid antagonist naloxone stimulates ACTH secretion by blocking opioidergic input on paraventricular corticotropin-releasing factor neurons, thereby providing a methodology for comparing hypothalamic opioid tone between study groups. Sixty nonalcoholic subjects, aged 18-25 yr, were enrolled in a protocol to measure the ACTH response to naloxone. Thirty-two subjects were offspring from families with a high density of alcohol dependence and were designated as family history-positive subjects. Twenty-eight subjects were offspring of nonalcohol-dependent parents and were designated family history-negative subjects. Subjects received naloxone (125 microg/kg) or placebo (0.9% saline) in double blind, randomized order. Plasma ACTH was monitored. Family history-positive men had increased ACTH response to naloxone compared to 1) family history-positive women, 2) family history-negative men, and 3) family history-negative women. Despite differences in plasma ACTH levels after naloxone administration, plasma naloxone concentrations did not differ between study groups. This finding suggests that nonalcoholic male offspring of alcohol-dependent men have altered endogenous opioid activity directed at hypothalamic corticotropin-releasing factor neurons.

Nociceptin, a novel endogenous ligand for the ORL1 receptor, dilates isolated resistance arteries from the rat

The heptadecapeptide nociceptin, also known as Orphanin FQ, is a recently discovered endogenous ligand for the opioid-like G-protein coupled receptor, ORL1. In the present study, responses to nociceptin were investigated in isolated pressurized resistance arteries from the rat mesenteric vascular bed. Nociceptin in bath concentrations of 10(-9)-10(-6) M induced concentration-dependent increases in arterial diameter when the artery was precontracted with U46619; and administration of the structurally related opioid agonists, dynorphin A and met-enkephalin, had no effect on arterial diameter. Vasodilator responses to nociceptin were not altered by the opioid receptor antagonist naloxone or by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine. Responses to nociceptin were not altered by the muscarinic receptor blocking agent atropine or phentolamine, or the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP-(8-37). These data suggest that nociceptin has direct vasodilator activity that is not dependent upon the activation of a traditional opioid receptor, muscarinic or CGRP receptors, an inhibitory effect on the adrenergic nervous system, or the release of nitric oxide in isolated resistance arteries from the rat mesentery.

Endogenous opioids modulate allograft rejection time in mice: possible relation with Th1/Th2 cytokines

The continuous infusion of the opioid peptide beta-endorphin prolongs skin allograft survival in mice, while the opiate receptor antagonist naloxone, administered together with the opioid at the time of transplantation, abolishes the effect of the opioid. Consistently, naloxone, when given alone at the time of transplantation, but not later, accelerates graft rejection and increases splenocyte IL-2 and interferon-gamma (IFN-gamma) production. Splenocyte beta-endorphin concentrations are lower in transplanted animals. The effects of exogenous beta-endorphin and naloxone suggest that the endogenous opioid peptide beta-endorphin exerts a tonic inhibitory effect over early events of T cell-mediated immune responses in vivo. The effects of beta-endorphin and naloxone are consistent with the previously shown role of the opioid system in the modulation of the Th1/Th2 cytokine pattern.

Synthesis and biological activity of a novel methylamine-bridged enkephalin analogue (MABE): a new route to cyclic peptides and peptidomimetics

The synthesis and biological activity of a methylamine-bridged enkephalin analogue (MABE) is presented. The key step in the synthesis of the target compound involves the ring opening of Cbz-d-serine beta-lactone with Boc-Phe-NHCH2CH2NHCH3. Further synthetic elaboration of the resulting building block yielded compound 1 (MABE, Tyr-c[(NbetaCH3)-D-A2pr-Gly-Phe-NHCH2CH2-], where A2pr is a 2,3-diaminopropionic acid residue). Utilizing a combination of NMR and molecular modeling, the structure-biological activity relationships for compound 1 were studied. Using an in vitro isolated receptor assay, MABE was found to have affinities for isolated mu delta, and kappa opioid receptors of 1.6, 2.1, and 340 nM, respectively. By an in vivo thermal escape assay, MABE was found to have an ED50 of 0.027 microg in the rat when administered intrathecally. This effect was reversed by naloxone. By comparison, DAMGO, morphine, and DPDPE were found to yield ED50 values of 0.14, 2.4, and 54 microg, respectively, in the same assay.

Abolition of morphine-immunosuppression in mice lacking the mu-opioid receptor gene

Opiates are potent analgesic and addictive compounds. They also act on immune responses, and morphine, the prototypic opiate, has been repeatedly described as an immunosuppressive drug. Pharmacological studies have suggested that the inhibitory action of opiates on immunity is mediated by multiple opioid receptor sites but molecular evidence has remained elusive. Recently, three genes encoding mu- (MOR), delta-, and kappa-opioid receptors have been cloned. To investigate whether the mu-opioid receptor is functionally implicated in morphine immunosuppression in vivo, we have examined immune responses of mice with a genetic disruption of the MOR gene. In the absence of drug, there was no difference between wild-type and mutant mice with regard to a large number of immunological endpoints, suggesting that the lack of MOR-encoded protein has little consequence on immune status. Chronic morphine administration induced lymphoid organ atrophy, diminished the ratio of CD4(+)CD8(+) cells in the thymus and strongly reduced natural killer activity in wild-type mice. None of these effects was observed in MOR-deficient mice after morphine treatment. This demonstrates that the MOR gene product represents a major molecular target for morphine action on the immune system. Because our previous studies of MOR-deficient mice have shown that this receptor protein is also responsible for morphine analgesia, reward, and physical dependence, the present results imply that MOR-targeted therapeutic drugs that are developed for the treatment of pain or opiate addiction may concomitantly influence immune responses.

Disruption of the kappa-opioid receptor gene in mice enhances sensitivity to chemical visceral pain, impairs pharmacological actions of the selective kappa-agonist U-50,488H and attenuates morphine withdrawal

***micro***-, delta- and kappa-opioid receptors are widely expressed in the central nervous system where they mediate the strong analgesic and mood-altering actions of opioids, and modulate numerous endogenous functions. To investigate the contribution of the kappa-opioid receptor (KOR) to opioid function in vivo, we have generated KOR-deficient mice by gene targeting. We show that absence of KOR does not modify expression of the other components of the opioid system, and behavioural tests indicate that spontaneous activity is not altered in mutant mice. The analysis of responses to various nociceptive stimuli suggests that the KOR gene product is implicated in the perception of visceral chemical pain. We further demonstrate that KOR is critical to mediate the hypolocomotor, analgesic and aversive actions of the prototypic kappa-agonist U-50, 488H. Finally, our results indicate that this receptor does not contribute to morphine analgesia and reward, but participates in the expression of morphine abstinence. Together, our data demonstrate that the KOR-encoded receptor plays a modulatory role in specific aspects of opioid function.