Production and characterization of antibodies for the specific determination of the opioid peptide Met5-Enkephalin-Arg6-Phe7

Endogenous opioids serve as modulators of neuroendocrine and immune system processes, the investigation of which calls for high-specificity radioimmunoassays (RIAs). This study focuses on the development and use of a specific radioimmunoassay for the opioid peptide Met5-Enkephalin-Arg6-Phe7 (MEAP), the C-terminus part of proenkephalin A. Antibodies were raised in four rabbits and investigated in terms of titre, avidity and specificity, followed by finding ideal conditions for these antibodies in RIA. MEAP concentrations were determined in crude extracts of rat hypothalamus, dorsal root ganglia, adrenals and ankle using this standardized assay after an oxidizing process. At reverse-phase high-pressure liquid chromatography (HPLC), the position of immunoreactive material from rat hypothalamus eluted as two peaks out of which one was compatible with that of synthetic MEAP. All rabbits exhibited individual differences in relative immune response and time of its onset. The avidity constant was 10 times higher on a molar basis for ab 4108 compared with ab 4182. There was no cross-reactivity for ab 4182 to related peptides, such as enkephalins and dynorphin B, and negligible background values for ab 4108. The relative levels ofimmunoreactive MEAP from the CNS versus peripheral tissues contrasted in accordance with current knowledge. It is suggested that reports with RIA results should include characterization of antibodies, extraction procedures, standard curves and compositions of buffers. Furthermore, the results should preferably be expressed in relation to total protein content.

The effects of different exercise training modalities on plasma proenkephalin Peptide F in women

Due to the important interactions of proenkephalin fragments (e.g., proenkephalin [107-140] Peptide F) to enhance activation of immune cells and potentially combat pain associated with exercise-induced muscle tissue damage, we examined the differential plasma responses of Peptide F to different exercise training programs. Participants were tested pre-training (T1), and after 8 weeks (T2) of training. Fifty-nine healthy women were matched and then randomly assigned to one of four groups: heavy resistance strength training (STR, n=18), high intensity endurance training (END, n=14), combined strength and endurance training (CMB, n=17), or control (CON, n=10). Blood was collected using a cannula inserted into a superficial vein in the antecubital fossa with samples collected at rest and immediately after an acute bout of 6 X 10 RM in a squat resistance exercise before training and after training. Prior to any training, no significant differences were observed for any of the groups before or after acute exercise. With training, significant (P≤0.95) elevations were observed with acute exercise in each of the exercise training groups and this effect was significantly greater in the CMB group. These data indicate that in untrained women exercise training will not change resting of plasma Peptide F concentrations unless both forms of exercise are performed but will result in significant increases in the immediate post-exercise responses. Such findings appear to indicate adrenal medullary adaptations opioid production significantly altered with exercise training.

The effects of exercise training programs on plasma concentrations of proenkephalin Peptide F and catecholamines

To determine if exercise training alters the pattern and magnitude of plasma concentrations of proenkephalin Peptide F and epinephrine, plasma proenkephalin [107-140] Peptide F(ir) and catecholamines were examined pre-training (T-1), and after 4- (T-2), 8- (T-3), and 12-weeks (T-4) of training. 26 healthy men were matched and randomly assigned to one of three groups: heavy resistance strength training (Strength, n=9), high intensity endurance training (Endurance, n=8), or both training modalities combined (Combined, n=9). Blood was collected using a syringe with a cannula inserted into a superficial arm vein with samples collected at rest, after each 7 min stage and 5 and 15 min into recovery. With training, all groups observed shifted plasma Peptide F responses to graded exercise, where significant increases were observed at lower exercise intensities. Increases in plasma epinephrine with exercise were observed in all groups. The Combined group saw increases at 25% at T-3 and for 50% at T-2, T-3, and T-4 which was higher than T-1. The Endurance group demonstrated increases for 50% at T-1, T-2, T-3 but not at T-4. The plasma epinephrine response to graded exercise was reduced in the Strength group. Increases in plasma norepinephrine above rest were observed starting at 50% . The Strength group demonstrated a significant reduction in norepinephrine observed at 100% at T-3 and T-4. Peptide F and catecholamines responses to graded exercise can be altered by different types of physical exercise training. Simultaneous high intensity training may produce adrenal medulla exhaustion when compared to single mode training.

Single housing during early adolescence causes time-, area- and peptide-specific alterations in endogenous opioids of rat brain

BACKGROUND AND PURPOSE

A number of experimental procedures require single housing to assess individual behaviour and physiological responses to pharmacological treatments. The endogenous opioids are closely linked to social interaction, especially early in life, and disturbance in the social environment may affect opioid peptides and thereby confound experimental outcome. The aim of the present study was to examine time-dependent effects of single housing on opioid peptides in rats.

EXPERIMENTAL APPROACH

Early adolescent Sprague Dawley rats (post-natal day 22) were subjected to either prolonged (7 days) or short (30 min) single housing. Several brain regions were dissected and immunoreactive levels of Met-enkephalin-Arg(6) Phe(7) (MEAP), dynorphin B and nociception/orphanin FQ, as well as serum corticosterone were measured using RIA.

KEY RESULTS

Prolonged single housing reduced immunoreactive MEAP in hypothalamus, cortical regions, amygdala, substantia nigra and periaqueductal grey. Short single housing resulted in an acute stress response as indicated by high levels of corticosterone, accompanied by elevated immunoreactive nociceptin/orphanin FQ in medial prefrontal cortex, nucleus accumbens and amygdala. Neither short nor prolonged single housing affected dynorphin B.

CONCLUSIONS AND IMPLICATIONS

Disruption in social environmental conditions of rats, through single housing during early adolescence, resulted in time-, area- and peptide-specific alterations in endogenous opioids in the brain. These results provide further evidence for an association between early life social environment and opioids. Furthermore, the results have implications for experimental design; in any pharmacological study involving opioid peptides, it is important to distinguish between effects induced by housing and treatment.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Effects of synthetic analogues of human opiorphin on rat brain opioid receptors

Human opiorphin (Gln-Arg-Phe-Ser-Arg; QRFSR-peptide) is a physiological inhibitor of enkephalin-inactivating peptidases. We previously demonstrated that opiorphin can substitute for the classic mixture of peptidase inhibitors and greatly improves the specific binding and affinity of the enkephalin-related peptide [(3)H]MERF (Tyr-Gly-Gly-Phe-Met-Arg-Phe; YGGFMRF) for rat brain opioid receptors. To extend the metabolic stability of opiorphin in human plasma two functional derivatives were designed, i.e., Cys-[(CH(2))(6)]-QRF-[Ser-O-octanoyl]-R peptide (monomeric CC6-opiorphin) and its cystine-dipeptide (dimeric CC6-opiorphin) derivative. We found that, in homologous competition experiments, the affinity of [(3)H]MERF for rat brain opioid receptors was significantly increased in the presence of monomeric and dimeric CC6-opiorphin, compared to control-Tris buffer. In addition ten times lower concentrations (5 μM) than those required for native opiorphin (50 μM) were sufficient. In heterologous competition experiments, using unlabeled dynorphin(1-10), affinity increases were also observed: increases in binding were similar with either monomeric or dimeric CC6-opiorphin. Surprisingly, these opiorphin analogues displayed weak competitive effects on [(3)H]MERF binding to rat brain opioid receptors in the absence of unlabeled MERF, effects never observed for the native opiorphin. In conclusion, CC6-opiorphin compounds are certainly more potent than the native opiorphin in increasing the binding and the affinity of homologous and heterologous competition, but the binding enhancement occurs only at temperatures much higher than 0°C, specifically at 24°C.

Effects of rearing conditions on behaviour and endogenous opioids in rats with alcohol access during adolescence

Causal links between early-life stress, genes and later psychiatric diagnoses are not possible to fully address in human studies. Animal models therefore provide an important complement in which conditions can be well controlled and are here used to study and distinguish effects of early-life stress and alcohol exposure. The objective of this study was to investigate the impact of rearing conditions on behaviour in young rats and if these changes could be followed over time and to examine interaction effects between early-life environment and adolescent alcohol drinking on behaviour and immunoreactive levels of the opioid peptides dynorphin B, met-enkephalin-Arg(6)Phe(7) and beta-endorphin. We employed a rodent model, maternal separation, to study the impact of rearing conditions on behaviour, voluntary alcohol consumption and alcohol-induced effects. The consequences of short, 15 min (MS 15), and long, 360 min (MS 360), maternal separation in combination with adolescent voluntary alcohol consumption on behaviour and peptides were examined. A difference in the development of risk taking behaviour was found between the MS15 and MS360 while the development of general activity was found to differ between intake groups. Beta-endorphin levels in the pituitary and the periaqueductal gray area was found to be higher in the MS15 than the MS360. Adolescent drinking resulted in higher dynorphin B levels in the hippocampus and higher met-enkephalin-Arg(6)Phe(7) levels in the amygdala. Amygdala and hippocampus are involved in addiction processes and changes in these brain areas after adolescent alcohol drinking may have consequences for cognitive function and drug consumption behaviour in adulthood. The study shows that individual behavioural profiling over time in combination with neurobiological investigations provides means for studies of causality between early-life stress, behaviour and vulnerability to psychiatric disorders.

Responses of proenkephalin Peptide F to aerobic exercise stress in the plasma and white blood cell biocompartments

Proenkephalin Peptide F [107-140] is an enkephalin-containing peptide found predominantly within the adrenal medulla, co-packaged with epinephrine within the chromaffin granules. In vivo studies indicate that Peptide F has classic opioid analgesia effects; in vitro studies suggest potential immune cell interactions. In this investigation we examined patterns of Peptide F concentrations in different bio-compartments of the blood at rest and following sub-maximal cycle exercise to determine if Peptide F interacts with the white blood cell (WBC) bio-compartment during aerobic exercise. Eight physically active men (n=8) performed sub-maximal (80-85% V˙O2peak) cycle ergometer exercise for 30 min. Plasma Peptide F and WBC Peptide F immunoreactivity were examined pre-exercise, mid-exercise and immediately post-, 5-min post-, 15-min post-, 30-min post- and 60-min post-exercise and at similar time-points during a control condition (30 min rest). Peptide F concentrations significantly (p<0.05) increased at 5 and 60 min post-exercise, compared to pre-exercise concentrations. No significant increases in Peptide F concentrations in the WBC fraction were observed during or after exercise. However, a significant decrease was observed at 30 min post-exercise. An ultradian pattern of Peptide F distribution was apparent during rest. Furthermore, concentrations of T cells, B cells, NK cells, and total WBCs demonstrated significant changes in response to aerobic exercise. Data indicated that Peptide F was bound in significant molar concentrations in the WBC fraction and that this biocompartment may be one of the tissue targets for binding interactions. These data indicate that Peptide F is involved with immune cell modulation in the white blood circulatory biocompartment of blood.

Disturbances in behavior and cortical enkephalin gene expression during the anticipation of ethanol in rats characterized as high drinkers

The process of ethanol anticipation is a particularly important phenomenon that can determine subsequent drug-taking behavior. Recent studies suggest that systems within the medial prefrontal cortex (mPFC), during anticipation, may contribute to the goal-directed seeking of ethanol. The current investigation examined the possibility that the opioid peptide enkephalin (ENK), known to mediate some of the reinforcing properties of ethanol, may function in the mPFC during the anticipation of ethanol access. Using a limited access (3 h/d) paradigm for 10 days with 20% ethanol, Sprague-Dawley rats were first identified either as low drinkers (LD, <1.0 g/kg/3 h) or as high drinkers (HD, >2.0 g/kg/3 h) that exhibited a long-term phenotype of high ethanol consumption and a significant ethanol deprivation effect. During the anticipation period immediately preceding daily ethanol access, the HD rats compared to LD or Control animals with ad libitum ethanol access exhibited increased anticipatory behaviors, including greater exploratory behavior in a novel open field as revealed by significantly more time spent in the rearing position (+53-65%, p < 0.05) and increased number of rears made (+33-44%, p < 0.05) and greater novelty-seeking behavior in a hole-board apparatus revealed by an increase in total (+50-52%, p < 0.05) and novel nose pokes (+45-48%, p < 0.05). In the HD rats, analysis of the mPFC using real-time quantitative PCR showed significantly greater mRNA levels of ENK (p < 0.05) and the mu-opioid receptor (MOR) (p < 0.05), but not delta-opioid receptor (DOR), and this increase in ENK expression was found, using in situ hybridization, to occur specifically in the prelimbic (PrL) subregion of the mPFC. When injected into the PrL during the anticipation period, a MOR agonist but not DOR agonist significantly increased consumption of 20% ethanol (p < 0.05). These findings support the role of ENK, acting through MOR within the PrL to promote the anticipation and excessive consumption of ethanol.

Differences in basal and ethanol-induced levels of opioid peptides in Wistar rats from five different suppliers

One major cause for discrepancies in results from animal experimental studies is the use of different animal strains and suppliers. We have previously reported that Wistar rats from five different suppliers display profound differences in ethanol intake and behavior. One of the neurobiological processes that could be underlying these differences is the endogenous opioid system, which has been implicated in the rewarding and reinforcing effects of alcohol. We therefore hypothesized that the differences between the supplier groups would also be evident in the endogenous opioid system. Radioimmunoassay was used to determine the levels of the opioid peptides Met-enkephalin-Arg(6)Phe(7) and dynorphin B in several brain areas of ethanol-drinking and ethanol naïve Wistar rats from five different suppliers. In the ethanol naïve animals, differences between the supplier groups were found in the pituitary gland, hypothalamus, frontal cortex, dorsal striatum and hippocampus. In the ethanol-drinking rats, differences were found in the same structures, with the addition of medial prefrontal cortex and substantia nigra. Correlations between ethanol intake and peptide levels were also found in several of the areas examined. The structures in which differences were found have all been implicated in the transition from drug use to addiction and these differences may lead to different propensities and vulnerability to this transition. Because the endogenous opioids have been suggested to be involved in a number of neurobiological disorders the results do not only have implications for research on alcohol or drug addiction, but many other fields as well.

The action of a synthetic derivative of Met5-enkephalin-Arg6-Phe7 on behavioral and endocrine responses

The neuroendocrine and behavioral effects of Tyr-D-Ala-Gly-Phe-D-Nle-Arg-Phe (DADN), a more stable derivative of the endogenous opiate Met-enkephalin related peptide Met(5)-enkephalin-Arg(6)-Phe(7) were investigated in mice. The behavioral experiments consisted of monitoring the horizontal (square crossing) and vertical (rearing) locomotion in the open field system. To evaluate the effect of the heptapeptide on the hypothalamo-pituitary-adrenal (HPA) axis, the plasma corticosterone level was measured. DADN induced dose-dependent increases in locomotion and rearing 30 min after intracerebroventricular injection and also elicited marked activation of the hormonal stress response. To elucidate the receptors involved in the mediation of these actions, animals were pretreated with the nonselective opioid antagonist naloxone, the selective κ-receptor antagonist nor-binaltorphimine or the μ(1)-receptor blocker naloxonazine. Both the HPA activation and the behavioral responses were diminished by the preadministration of naloxone. Nor-binaltorphimine did not display a significant effect, while naloxonazine completely abolished the hyperactivity and the corticosterone elevation elicited by the analog. These findings suggest that μ-receptors predominate in the mediation of the neuroendocrine actions of DADN, while κ-receptors do not play a significant role.

[Bovine adrenal medulla 22 attenuates hyperalgesia in the early phase of complete Freund's adjuvant-induced inflammation in rats]

The present study investigated the effects of intrathecal (i.t.) application of bovine adrenal medulla 22 (BAM22), an endogenous opioid peptide potently activating opioid receptors and sensory neuron-specific receptor (SNSR), on a model of complete Freund's adjuvant (CFA)-induced inflammatory pain. Unilateral, but not bilateral, inflammatory pain was induced by intraplantar (i.pl.) injection of CFA in one side, as indicated by the shortened paw withdrawal latency and the increased edema of paw. Paw withdrawal latency test, paw edema determination and immunohistochemistry were used in CFA-induced inflammatory pain model after i.t. administration of BAM22 or saline. It was found that administration of BAM22 dose-dependently attenuated CFA-induced hyperalgesia and edema, and resumed antinociceptive effects against thermal stimulation in behavioral test. In 10 nmol BAM22 group, paw withdrawal latency was resumed to 83.2% of normal, and edema increased only by 60% of normal at 48 h. The potency of BAM22 was 33.5% of maximal possible effect (MPE) at 24 h, and the antinociception persisted for at least 1 h. Furthermore, i.t. treatment of 10 nmol BAM22 evidently decreased the expressions of CFA-evoked neuronal nitric oxide synthase (nNOS)-positive cells and calcitonin gene-related peptide (CGRP)-immunoreactivity positive nerve fibers by 25.6% (P<0.01) and 25.2% (P<0.001) compared with saline group, respectively, at L3-L5 segments of the spinal cord. Small and medium CGRP-positive cells were 57.4% and 35.2% in dorsal root ganglion (DRG) in 10 nmol BAM22 group, respectively, which were remarkably lower than those in saline group (P<0.001). The present study suggests that BAM22 relieves CFA-induced thermal hyperalgesia in the early phase and resumes antinociceptive effects through down-regulation of nNOS and CGRP expressions in DRG and spinal cord, which is possibly mediated via SNSR.

Investigation of the pyrolysis products of methionine-enkephalin-Arg-Gly-Leu using liquid chromatography-tandem mass spectrometry

Low-temperature pyrolysis of methionine-enkephalin-Arg-Gly-Leu has been carried out and the non-volatile residues have been analyzed. The fragments were separated and characterized by LC-UV/Vis-MS/MS. Two major types of pyrolysis products were identified by matching the experimental results with a theoretical list that contains the expected fragments. These products were mainly composed of cyclic oligopeptides and linear fragments produced from the peptide backbone. These fragments have preserved the sequence of amino acids in the peptide. In some cases, a complete or partial loss of an amino-acid side group was observed. Tandem mass spectrometry and cyanogen bromide cleavage experiments were used to confirm the nature of the cyclic and linear pyrolysates, in addition to chromatographic and mass spectrometric data of actual standard synthetic cyclic peptides.

The pharmacological modification of secretory responses

Electrolyte transport across the intestinal mucosa can be modulated by several neurotransmitters, hormones and drugs. Opiate agonists and endogenous opioid peptides inhibit electrolyte secretion both in vitro and in vivo. These drugs appear to act at several levels. Thus, opioid effects can be elicited at the local mucosal level. Secondly, antisecretory effects can be demonstrated when opioids are administered into the brain. These central effects appear to involve activation of the sympathetic innervation of the intestine. Thirdly, some antidiarrhoeal drugs such as loperamide may have ancillary non-opiate-like actions that contribute to their effectiveness. In cases of inflammatory bowel disease where local concentrations of inflammatory mediators such as kinins and eicosanoids may be high, non-steroidal anti-inflammatory drugs may be effective in treating diarrhoeal symptoms. The existence of many types of receptors on mucosal cells indicates that several pharmacological approaches exist for the potential modulation of electrolyte transport.

The impact of postnatal environment on opioid peptides in young and adult male Wistar rats

Early environmental influences can change the neuronal development and thereby affect behavior in adult life. The aim in the present study was to thoroughly examine the impact of early environmental factors on endogenous opioids by using a rodent maternal separation (MS) model. The endogenous opioid peptide system is not fully developed at birth, and short- and/or long-term alterations may occur in these neural networks in animals exposed to manipulation of the postnatal environment. Rat pups were subjected to one of five rearing conditions; 15 min (MS15) litter (l) or individual (i), 360 min (MS360) l or i daily MS, or housed under normal animal facility rearing (AFR) conditions during postnatal days 1-21. Measurements of immunoreactive (ir) Met-enkephalin-Arg6Phe7 (MEAP) and dynorphin B (DYNB) peptide levels in the pituitary gland and in a number of brain areas, were performed at three and 10 weeks of age, respectively. MS-induced changes were more pronounced in ir MEAP levels, especially in individually separated rats at three weeks of age and in litter-separated rats at 10 weeks of age. The enkephalin and dynorphin systems have different developmental patterns, dynorphin appearing earlier, which may point at a more sensitive enkephalin system during the early postnatal weeks. The results provide evidence that opioid peptides are sensitive for early environmental factors and show that the separation conditions are critical and also result in changes manifesting at different time points. MS-induced effects were observed in areas related to stress, drug reward and dependence mechanisms. By describing effects on opioid peptides, the study addresses the possible role of a deranged endogenous opioid system in the previously described behavioral consequences of MS.

Endogenous heptapeptide Met-enkephalin-Gly-Tyr binds differentially to duplicate delta opioid receptors from zebrafish

Met-enkephalin-Gly-Tyr (MEGY) is an endogenous peptide that binds to opioid sites in zebrafish and in rat brain homogenates. The aim of this work is to characterize the binding profile of this opioid ligand on two duplicate delta receptors from zebrafish, ZFOR1 and ZFOR4. Our results show that, while ZFOR1 presents one single binding site for [(3)H]-MEGY (K(D)=4.0+/-0.4 nM), the experimental data from ZFOR4 fit better to the two-site binding model (K(D1)=0.8+/-0.2 nM and K(D2)=30.2+/-10.2 nM). Two other MEGY synthetic analogues, (D-Ala(2))-MEGY and (D-Ala(2), Val(5))-MEGY were also prepared and tested, together with the original peptide MEGY and other opioid ligands, in competition binding assays. While these peptides presented K(i) values on the nanomolar range when using [(3)H]-MEGY as radioligand, these parameters were two orders higher in competition binding assays with the antagonist [(3)H]-diprenorphine. Functional [(35)S]GTPgammaS stimulation analysis has revealed that these two receptors can be activated by several opioid agonists. Our results prove that although the MEGY peptide acts as an agonist on ZFOR1 and ZFOR4, there are subtle pharmacological differences between these two delta opioid receptors from zebrafish.

The enhancing effects of peptidase inhibitors on the antinociceptive action of [Met5]enkephalin-Arg6-Phe7 in rats

Previous in vitro studies have shown that the degradation of [Met(5)]enkephalin-Arg(6)-Phe(7) during incubation with cerebral membrane preparations is largely prevented by a mixture of three peptidase inhibitors: amastatin, captopril, and phosphoramidon. The present in vivo study shows that the inhibitory effect of [Met(5)]enkephalin-Arg(6)-Phe(7) administered intra-third-ventricularly on the tail-flick response was increased more than 1000-fold by the intra-third-ventricular pretreatment with three peptidase inhibitors. The antinociceptive effect produced by the [Met(5)]enkephalin-Arg(6)-Phe(7) in rats pretreated with any combination of two peptidase inhibitors was significantly smaller than that in rats pretreated with three peptidase inhibitors, indicating that any residual single peptidase could inactivate significant amounts of the [Met(5)]enkephalin-Arg(6)-Phe(7). The present data, together with those obtained from previous studies, clearly show that amastatin-, captopril-, and phosphoramidon-sensitive enzymes play important roles in the inactivation of endogenous opioid peptides, such as [Met(5)]enkephalin, [Met(5)]enkephalin-Arg(6)-Phe(7), [Met(5)]enkephalin-Arg(6)-Gly(7)-Leu(8), and dynorphin A (1-8), administered intra-third-ventricularly to rats.

The involvement of spinal bovine adrenal medulla 22-like peptide, the proenkephalin derivative, in modulation of nociceptive processing

Bovine adrenal medulla 22 (BAM22), one of the cleavage products of proenkephalin A, possesses high affinity for opioid receptors and sensory neuron-specific receptor (SNSR). The present study was designed to examine the expression of BAM22 in the spinal cord and dorsal root ganglion (DRG) of naive rats as well as in a model of inflammation. BAM22-like immunoreactivity (BAM22-IR) was expressed in fibers in the spinal cord, with high density seen in lamina I in naïve rats. The expression of BAM22-IR in the superficial laminae was greatly reduced following dorsal rhizotomy. BAM22-IR was also located in 19% of DRG cells, mainly in the small- and medium-sized subpopulations. Following injection of complete Freund's adjuvant (CFA) in the hindpaw, the expression of BAM22-IR in the superficial laminae of the spinal cord and small-sized DRG neurons on the ipsilateral side was markedly increased. Double labeling showed that the Fos-positive nucleus was surrounded by BAM22-IR cytoplasm in the spinal dorsal horn neurons or closely associated with BAM22-IR fibers in the superficial laminae. Furthermore, CFA-induced mechanical allodynia in the inflamed paw was potentiated by intrathecal administration of anti-BAM22 antibody. Together, these results demonstrate for the first time that BAM22-like peptide is mainly located in the superficial laminae of the spinal cord and mostly originates from nociceptive DRG neurons. BAM22 could thus act as a ligand for presynaptic opioid receptors and SNSR. Our study also provides evidence suggesting that BAM22 plays a role in the modulation of nociceptive processing at the spinal level under normal and inflammatory conditions.

Sensitisation of TRPV1 in rat sensory neurones by activation of SNSRs

The novel sensory neurone specific receptor (SNSR) family of G-protein coupled receptors are activated by non-opiate fragments of opioid precursor peptides. SNSRs are expressed in nociceptors, and SNSR agonists have been found to cause sensitisation to painful stimuli in vivo. We explored the basis of sensitisation caused by SNSR agonists in sensory neurones by investigating the effect of the SNSR-selective agonist bovine adrenal medulla peptide 8-22 (BAM (8-22)) on gating of the heat and capsaicin-sensitive ion channel TRPV1. Using calcium imaging we found that BAM (8-22) caused sensitisation of the TRPV1 response in approximately 13% of DRG neurones. Sensitisation of TRPV1 in a similar proportion of neurones was observed using whole-cell patch clamping. The PKC-specific inhibitor Ro-31-8220 reduced but did not completely abolish sensitisation, while the protein kinase A inhibitor H-89 was without significant effect. No translocation of the PKC delta, epsilon and zeta isoforms to the cell membrane was observed in response to BAM (8-22). These observations implicate PKC in the sensitisation of TRPV1, but suggest that other pathways are also involved.

Sensory neuron-specific receptor agonist BAM8-22 inhibits the development and expression of tolerance to morphine in rats

We observed that intrathecal (i.t.) bovine adrenal medulla 22, an endogenous opioid peptide, partially reverses morphine tolerance. However, its mechanism remains unclear. The present study determined the effects of BAM8-22, a derivative of BAM22 and selective sensory neuron-specific receptor (SNSR) agonist, on the development and maintenance of tolerance to spinal morphine. Intrathecal administration of BAM8-22 at various doses (0.1, 1 and 10nmol) did not alter withdraw latencies assessed in both paw withdraw and tail flick tests. Co-administration of BAM8-22 (0.1nmol) every other day, but not daily, with morphine remarkably attenuated the development of morphine tolerance. Pretreatment and co-treatment with BAM8-22 (0.1nmol) significantly reversed established morphine tolerance. Furthermore, intermittent administration of BAM8-22 with morphine consistently resumed morphine-induced antinociception. However, i.t. BAM8-22 did not alter morphine-induced hyperalgesia. These results suggested that SNSR may be able to modulate the sensitivity of opioid receptor serving as a most probable underlying mechanism for the effects of BAM8-22 on morphine tolerance. This study also demonstrated that intermittent combination of SNSR agonist BAM8-22 with morphine might be better regimen for long-term use of opioids to treat chronic pain.

Repeated δ1-opioid receptor stimulation reduces δ2-opioid receptor responses in the SA node

Ultra-low-dose methionine-enkephalin-arginine-phenylalanine improves vagal transmission (vagotonic) and decreases heart rate via δ1-opioid receptors within the sinoatrial (SA) node. Higher doses activate δ2-opioid receptors, interrupt vagal transmission (vagolytic), and reduce the bradycardia. Preconditioning-like occlusion of the nodal artery produced a vagotonic response that was reversed by the δ1-antagonist 7-benzylidenaltrexone (BNTX). The following study tested the hypothesis that extended δ1-opioid receptor stimulation reduces subsequent δ2-receptor responses. The δ2-agonist deltorphin II was introduced in the SA node by microdialysis to evaluate δ2 responses before and after infusion of the δ1-agonist TAN-67. TAN-67 reduced the vagolytic effect of deltorphin by two-thirds. When the δ1-antagonist BNTX was combined with TAN-67, the deltorphin response was preserved, suggesting that attrition of the prior response was mediated by δ1 activity. When TAN-67 was omitted in time control studies, some loss of δ2 responses was apparent in the absence of the δ1 treatment. This loss was also eliminated by BNTX, suggesting that the attenuation of the response after deltorphin alone was also the result of δ1 activity. Additional studies tested TAN-67 alone in the absence of prior deltorphin. When time controls were conducted without the initial deltorphin treatment, a robust vagolytic response was observed. When TAN-67 preceded the delayed deltorphin, the vagolytic response was eroded, indicating an independent effect of TAN-67. BNTX infused afterward was unable to restore the δ2 response. These data support the conclusion that the loss of the δ2 response resulted from reduced δ2 activity mediated by continued δ1-receptor stimulation and not the arithmetic consequence of increased competition from that same δ1 receptor.

Met5-enkephalin-Arg6-Phe7 (MEAP): a cardioprotective hormonal opioid

BACKGROUND

Acute myocardial ischemia is an important cause of morbidity and mortality worldwide. The heart and other organs can be rendered more resistant to the deleterious effects of ischemia through a variety of preconditioning strategies, including treadmill exercise and brief ischemia of skeletal muscle. Some of the beneficial effects of these preconditioning strategies appear to be mediated by as-of-yet unidentified hormonal opioids.

OBJECTIVES

To test the hypothesis that endogenous opioids of the enkephalin class are capable of improving ischemic tolerance and acting in a hormonal manner.

METHODS

In phase one of the investigation, the authors assessed the cardioprotective potential of all four known enkephalins. This was achieved by subjecting isolated buffer-perfused rabbit hearts to a 25-minute period of test ischemia and two hours of reperfusion (protocol 1) after receiving treatment with either saline vehicle (controls) or increasing concentrations of purified enkephalins. On the basis of results from these initial studies, the authors performed additional experiments (protocol 2) to determine whether Met5-enkephalin-Arg6-Phe7 (MEAP) could be absorbed from skeletal muscle and exert a cardioprotective effect. Specifically, MEAP or vehicle (controls) was given intramuscularly 24 hours before the hearts were harvested. A similar assessment of ischemic tolerance as described in protocol 1 was then performed. Postischemic myocardial viability (infarct size) was assessed in all cases by triphenyltetrazolium chloride (TTC) staining. Hemodynamic parameters and infarct sizes for concentration-dependence studies were compared by two-way analysis of variance, and infarct sizes from protocol 2 studies were compared by using Student's t-test (significance set at p < or = 0.05).

RESULTS

Mean infarct size in control hearts (+/- SEM) was 33% (+/- 4%) and 36% (+/- 6%) for protocol 1 and 2, respectively. Of the four enkephalins tested in protocol 1, only MEAP treatment showed a tendency toward cardioprotection. Interestingly, an alternative enkephalin, methionine5-enkephalin-Arg6-Gly7-Leu8, tended to exert an injurious effect. In protocol 2, MEAP treatment 24 hours before ischemia significantly reduced infarct size (14% +/- 4%) compared with controls, suggesting that it can be released from muscle and exert a distant cardioprotective effect.

CONCLUSIONS

When given either directly to the heart or absorbed from a distant tissue, MEAP induces cardioprotection, supporting the hypothesis that it can act as a hormonal modulator of ischemic tolerance.

Effect of starvation on Fos and neuropeptide immunoreactivities in the brain and pituitary gland of Xenopus laevis

In mammals complex interactions between various brain structures and neuropeptides such as corticotropin-releasing factor (CRF) and urocortin 1 (Ucn1) underlay the control of feeding by the brain. Recently, in the amphibian Xenopus laevis, CRF- and Ucn1-immunoreactivities were shown in the hypothalamic magnocellular nucleus (Mg) and evidence was obtained for their involvement in food intake. To gain a better understanding of the brain structures controlling feeding in X. laevis, the effects of 16 weeks starvation on neurones immunoreactive (ir) to Fos and neuropeptides in various brain structures were quantified. In the Mg, compared to controls, starved animals showed fewer neurones immunopositive for Fos (-55.9%), Ucn1 (-44.0%), cocaine and amphetamine-regulated transcript (CART) (-94.3%) and metenkephalin (ENK) (-65.0%), whereas CRF-ir neurones were 2.1 times more numerous. These differences were mainly apparent in the ventral part of the Mg, followed by the medial and dorsal part of the nucleus. In the neural lobe of the pituitary gland a 22.5% lower optical density of CART-ir was observed. In the four other brain structures investigated, starvation had different effects. The dorsomedial part of the suprachiasmatic nucleus showed 5.9 times more NPY-ir cells and in the ventromedial thalamic area a lower number of NPY-ir cells (-33.6%) was found, whereas the Edinger-Westphal nucleus contained fewer CART-ir cells (-42.2%); no effect of starvation was seen in the ventral hypothalamic nucleus. Our results support the hypothesis that in X. laevis, the Mg plays a pivotal role in feeding-related processes and, moreover, that starvation also has neuropeptide- and brain structure-specific effects in other parts of the brain and in the pituitary gland, suggesting particular roles of these structures and their neuropeptides in physiological adaptation to starvation.

The monosialosyl ganglioside GM-1 reduces the vagolytic efficacy of delta2-opioid receptor stimulation

The cardiac enkephalin, methionine-enkephalin-arginine-phenylalanine (MEAP), alters vagally induced bradycardia when introduced by microdialysis into the sinoatrial (SA) node. The responses to MEAP are bimodal; lower doses enhance bradycardia and higher doses suppress bradycardia. The opposing vagotonic and vagolytic effects are mediated, respectively, by delta(1) and delta(2) phenotypes of the same receptor. Stimulation of the delta(1) receptor reduced the subsequent delta(2) responses. Experiments were conducted to test the hypothesis that the delta-receptor interactions were mediated by the monosialosyl ganglioside GM-1. When the mixed agonist MEAP was evaluated after nodal GM-1 treatment, delta(1)-mediated vagotonic responses were enhanced, and delta(2)-mediated vagolytic responses were reduced. Prior treatment with the delta(1)-selective antagonist 7-benzylidenaltrexone (BNTX) failed to prevent attrition of the delta(2)-vagolytic response or restore it when added afterward. Thus the GM-1-mediated attrition was not mediated by delta(1) receptors or increased competition from delta(1)-mediated vagotonic responses. When GM-1 was omitted, deltorphin produced a similar but less robust loss in the vagolytic response. In contrast, however, to GM-1, the deltorphin-mediated attrition was prevented by pretreatment with BNTX, indicating that the decline in response after deltorphin alone was mediated by delta(1) receptors and that GM-1 effectively bypassed the receptor. Whether deltorphin has intrinsic delta(1) activity or causes the release of an endogenous delta(1)-agonist is unclear. When both GM-1 and deltorphin were omitted, the subsequent vagolytic response was more intense. Thus GM-1, deltorphin, and time all interact to modify subsequent delta(2)-mediated vagolytic responses. The data support the hypothesis that delta(1)-receptor stimulation may reduce delta(2)-vagolytic responses by stimulating the GM-1 synthesis.

Proenkephalin peptide F immunoreactivity in different circulatory biocompartments after exercise

This study was the first study to examine the three circulatory biocompartments (plasma, white blood cell layer (WBC) and red blood cell layer (RBC)) and determine PF concentrations before and after exercise. Proenkephalin peptide F (PF) is an enkephalin-containing peptide found predominantly within the adrenal medulla. PF is co-packaged with epinephrine, and both can be co-secreted in response to similar stimuli. PF and epinephrine have shown immunomodulating properties. Ten healthy resistance trained men performed six sets of 10 RM squats with 2 min rest periods between sets and 10 healthy active men were matched and served as resting controls. Blood samples were obtained pre-exercise, immediately post-exercise and 15 min post-exercise and were analyzed for lactate, cortisol, epinephrine and biocompartmentalized PF. There was no change in resting control values measured across time within respective PF biocompartments and endocrine profile, indicating stability and technique validity of peptide F across the time period measured. As expected, the acute resistance exercise protocol caused an increase in lactate at 15 min post-exercise. Circulating epinephrine increased immediately post-exercise and returned to baseline during 15 min into recovery. Plasma PF increased immediate post-exercise and 15 min post-exercise, while WBC-PF and RBC-PF only increased at 15 min into recovery. For all time points tested, resting and exercise WBC-PF and RBC-PF concentrations were lower than plasma PF thus indicating a concentration difference across the three different biocompartments within the same blood sample. The presence of PF within all three biocompartments of whole blood may indicate the potential for biological transport and interactions with other cells in other biocompartments of the blood.

Tumor-Cell-Targeted Methionine-enkephalin Analogues Containing Unnatural Amino Acids: Design, Synthesis, and in Vitro Antitumor Activity

A series of new peptides (8-25) containing different unnatural amino acids of the adamantane type (1-6), was synthesized. Possible cytotoxic activity on human cervical adenocarcinoma (HeLa), larynx carcinoma (HEp-2), colon carcinomas (HT-29, Caco-2), poorly differentiated cells from lymph node metastasis of colon carcinoma (SW-620), mammary gland adenocarcinoma (MCF-7), and melanoma (HBL) cells were tested by the MTT assay. The results were compared with the effect of methionine-enkephalin (Tyr-Gly-Gly-Phe-Met, or opioid growth factor, OGF), and its shorter N-terminal fragments. Peptide analogues containing C(alpha alpha)-dialkylated glycine (Aaa1, 1) or C(alpha)-alkylated glycine (Aaa2, 2) amino acid residues showed antitumor activity against melanoma, larynx carcinoma, colon carcinomas, and colon metastasis cell lines in vitro. The pentapeptide Tyr-(R,S)-Aaa2-Gly-Phe-Met (18) was the most effective analogue especially against the most antitumor drug-resistant cell lines HEp-2 and SW-620. Apoptosis as a mode of cell death was confirmed in these tumor cells after exposure to pentapeptide 18.

Variations in opioid peptide levels during the estrous cycle in Sprague-Dawley rats

The estrous cycle, with its various hormonal conditions, may provide us with the means of understanding how endocrine states relate to opioid mechanisms. There has been increasing experimental support for interaction between sex steroids and opioid peptides in the central nervous system. Here, we describe fluctuations in endogenous brain immunoreactive (ir) peptide levels during various phases of the estrous cycle in the female Sprague-Dawley rat. Ir levels of dynorphin A, dynorphin B, Leu-enkephalin-Arg(6), Met-enkephalin-Arg(6)Phe(7) and nociceptin/orphanin FQ were measured in the pituitary gland and in 10 areas of the brain during the diestrus, proestrus and estrus phase. In several areas of the brain, basal levels of endogenous opioid peptides showed variation during the course of the estrous cycle. Significant differences were found between the diestrus state and the proestrus and/or estrus conditions, particularly in the nucleus accumbens, caudate putamen and the substantia nigra. The ir levels of the endogenous peptide nociceptin/orphanin FQ became altered in only one of the areas measured, indicating less variance during the estrous cycle. Correlation analyses revealed that significant associations between dynorphin A or dynorphin B and Leu-enkephalin-Arg(6) were found more often during estrus than during the diestrus and proestrus conditions. The ratio between the ir levels of Leu-enkephalin-Arg(6), a cleavage product of the enzymatic conversion of dynorphin peptides into shorter peptides in vivo, and dynorphin peptides was calculated. The significantly lower ratio between Leu-enkephalin-Arg(6) and dynorphin B in diestrus than in proestrus and estrus also indicates cyclic fluctuations in the enzymatic cleavage of dynorphin. These findings are discussed in relation to the possible role of interactions between sex steroids and opioid peptide mechanisms during the normal estrous cycle.

Simultaneous activation of the delta opioid receptor (deltaOR)/sensory neuron-specific receptor-4 (SNSR-4) hetero-oligomer by the mixed bivalent agonist bovine adrenal medulla peptide 22 activates SNSR-4 but inhibits deltaOR signaling

Hetero-oligomerization among G protein-coupled receptors has been proposed to contribute to signal integration. Because sensory neuron-specific receptors (SNSRs) and the opioid receptors (OR) share a common ligand, the bovine adrenal medulla peptide (BAM) 22, and have opposite effects on pain modulation, we investigated the possible consequences of deltaOR/SNSR-4 hetero-oligomerization on the signaling properties of both receptor subtypes. Bioluminescence resonance energy transfer revealed that the human deltaOR has similar propensity to homo-oligomerize and to form hetero-oligomers with human SNSR-4 when coexpressed in human embryonic kidney 293 cells. The hetero-oligomerization leads to a receptor form displaying unique functional properties. Individual activation of either deltaOR or SNSR-4 in cells coexpressing the two receptors led to the modulation of their respective signaling pathways; inhibition of adenylyl cyclase and activation of phospholipase C, respectively. In contrast, the deltaOR/SNSR-4 bivalent agonist BAM22, which could activate each receptor expressed individually, fully activated the SNSR-4-dependent phospholipase C but did not promote deltaOR-mediated inhibition of adenylyl cyclase in deltaOR/SNSR-4-coexpressing cells. Likewise, concomitant activation of the deltaOR/SNSR-4 hetero-oligomer by selective deltaOR and SNSR-4 agonists promoted SNSR-4 but not deltaOR signaling, revealing an agonist-dependent dominant-negative effect of SNSR-4 on deltaOR signaling. Furthermore, the deltaOR selective antagonist naltrexone trans-inhibited the SNSR-4-promoted phospholipase C activation mediated by BAM22 but not by the SNSR-4-selective agonists, suggesting a bivalent binding mode of BAM22 to the deltaOR/SNSR-4 hetero-oligomer. The observation that BAM22 inhibited the Leu-enkephalin-promoted cAMP inhibition in rat dorsal root ganglia neurons supports the potential physiological implication of such regulatory mechanism.

Vagotonic effects of enkephalin are not mediated by sympatholytic mechanisms

This study examined the hypothesis that vagotonic and sympatholytic effects of cardiac enkephalins are independently mediated by different receptors. A dose-response was constructed by administering the delta-receptor opioid methionine-enkephalin-arginine-phenylalanine (MEAP) by microdialysis into the interstitium of the canine sinoatrial node during vagal and sympathetic stimulation. The right cardiac sympathetic nerves were stimulated as they exited the stellate ganglion at frequencies selected to increase heart rate approximately 35 bpm. The right cervical vagus was stimulated at frequencies selected to produce a two-step decline in heart rate of 25 and 50 bpm. A six-step dose-response was constructed by recording heart rates during nerve stimulation as the dose of MEAP was increased between 0.05 pmol/min and 1.5 nmol/min. Vagal transmission improved during MEAP at 0.5 pmol/min. However, sympathetically mediated tachycardia was unaltered with any dose of MEAP. In Study 2, a similar dose-response was constructed with the kappa-opioid receptor agonist trans(+/-)-3-4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide-HCl (U-50488H) to illustrate an independent sympatholytic effect and to verify its kappa-receptor character. U-50488H gradually suppressed the sympathetic tachycardia, with a significant effect obtained only at the highest dose (1.5 nmol/min). U-50488H had no effect on vagally mediated bradycardia. Surprisingly, the sympatholytic effect was not reversed by withdrawing U-50488H or by the subsequent addition of the kappa-antagonist 17,17'-(dichloropropylmethyl)-6,6',7,7'-6,6'-imino-7,7'-binorphinan-3,4',14,14'-tetroldi-hydrochloride (norBNI). Study 3 was conducted to determine whether the sympatholytic effect of U-50488H could be prevented by norBNI. NorBNI blocked the sympatholytic effect of the U50488H for 90 mins. When norBNI was discontinued afterward and U-50488H was continued alone, a sympatholytic effect emerged within 30 mins. Collectively these observations support the hypothesis that the vagotonic influence of MEAP is not dependent on a sympatholytic influence. Furthermore, the sympatholytic effect is mediated independently by kappa-receptors. The sympatholytic effect of sustained kappa-receptor stimulation appears to evolve gradually into a functional state not easily reversed.

Bovine adrenal medulla 22 reverses antinociceptive morphine tolerance in the rat

Acute intrathecal (i.t.) bovine adrenal medulla 22 (BAM22, 10 nmol), an endogenous opioid peptide, induced equipotent thermal antinociception in naïve and morphine-tolerant rats while chronic BAM22 resulted in hyperalgesia and decrease in the effectiveness of antinociception. In rats made tolerant to morphine, prior administration of BAM22 (10 nmol, i.t.) significantly resumed antinociceptive response of morphine. The present study demonstrated that BAM22 was able to modulate maintenance of morphine tolerance.

Influence of the menstrual cycle on proenkephalin peptide F responses to maximal cycle exercise

Proenkephalin peptide F [107-140] is an enkephalin-containing peptide found predominantly within the adrenal medulla and is co-packaged with epinephrine within adrenal medullary chromaffin granules. Peptide F has been shown to have the classic opioid analgesia effects along with immune cell interactions. This is only the second peptide F study in women, and in it we compare the responses of peptide F to a maximal cycle exercise test and recovery values over the follicular and luteal phases of the menstrual cycle. Eight untrained (directly documented in this study) women who were eumenorrheic performed a progressive maximal exercise test to volitional exhaustion on a cycle ergometer, once during the follicular phase, and once during the luteal phases of the menstrual cycle. Blood was obtained pre-exercise, immediately post-exercise and at 0, 15, and 30 min into recovery. Typical exercise changes in response to the cycle tests were observed with blood lactate increases that remained elevated 30 min into recovery. No significant exercise-induced elevations were observed for peptide F concentrations with exercise nor were any differences observed between the two menstrual phases. Thus, the effects of the menstrual cycle on peptide F concentrations appear to be minimal under the conditions of this investigation. With high concentrations of peptide F observed at rest (approx. 0.2-0.3 pmol ml(-1)) pre-exercise arousal mechanisms may have obviated any exercise-induced response. In addition, inhibition via elevated epinephrine may have inhibited any post-exercise increases and finally adrenal medullary capacity for circulatory concentrations of peptide F may have been reached in such untrained women. Pre-exercise arousal mechanisms potentially related to analgesia may also be involved to prepare untrained women for the stress of maximal exercise.

Synthesis, conformational and pharmacological studies of glycosylated chimeric peptides of Met-enkephalin and FMRFa

Our previous study showed that a chimeric peptide of Met-enkephalin and FMRFamide, YFa (YGGFMKKKFMRFa) not only caused antinociception and potentiated morphine analgesia but also blocked the development of tolerance and physical dependence. In the continuation of that study three chimeric analogues of YFa, [Ser5]YFa, [O-Glu-Ser5]YFa and [O-Gal-Ser5]YFa, were synthesized. To increase the bioavailability and penetration of blood brain barrier (BBB), glycosylated analogues, [O-Glu-Ser5]YFa and [O-Gal-Ser5]YFa, have been synthesized by solid phase peptide synthesis by building block method using anomeric acetate activation method. Circular dichroism studies showed that all the three chimeric peptides are stable and have a propensity for adopting helical conformation in the presence of membrane mimicking solvent. In comparison of parent chimeric peptide YFa, helicity of [Ser5]YFa, [O-Glu-Ser5]YFa and [O-Gal-Ser5]YFa has decreased. Pharmacological studies using tail-flick latency in mice showed that [O-Glu-Ser5]YFa have increased analgesia and bioavailability in comparison of [O-Gal-Ser5]YFa and non-glycosylated analogue [Ser5]YFa. Exhibition of enhanced analgesia by [O-Glu-Ser5]YFa as compared to [O-Gal-Ser5]YFa seems to be due to preference of GLUT-1 transporter system for glucose.

Ischemic preconditioning increases the bioavailability of cardiac enkephalins

Growing evidence suggests that cardiac enkephalins and their receptors are involved in ischemic preconditioning (IPC). Because there is no evidence for vesicular storage of small bioactive enkephalins in the heart, studies were designed to test the hypothesis that ischemia depletes cardiac enkephalins and that IPC preserves the same enkephalins by accelerating their processing from the larger proenkephalin precursor (PEP) pool. The precursors and two bioactive representatives, Met-enkephalin (ME) and Met-enkephalin-Arg-Phe (MEAP), were separated by size-exclusion chromatography and quantified by radioimmunoassay. Isolated perfused rat hearts were prepared and exposed to global ischemia. After 30 min of global ischemia and 40 min of reflow, the PEP pool was reduced (from 17.99 ± 1.52 to 14.20 ± 2.38 pmol/g wet wt), MEAP increased by 53%, and ME declined by 68%. The sum of the two smaller peptides was unchanged (9.78 ± 0.83 vs. 9.33 ± 2.81). Thus the total enkephalin peptide content was not altered (27.77 ± 1.69 vs. 24.10 ± 4.75). Peptide distribution after ischemia and reflow was also unaltered by pretreatment with peptidase inhibitors. However, when the hearts were preconditioned, the PEP pool remained significantly lower and both of the bioactive peptides, MEAP and ME, were elevated (+49% and +86%, respectively). The decline in the PEP pool was prevented by peptidase inhibition and the rise in MEAP was exaggerated. In separate protocols, synthetic enkephalins (ME, MEAP, and Leu-enkephalin) were added to the coronary inflow before 30 min of global ischemia and throughout the subsequent reflow. The added enkephalins (10−8M) had no inotropic effect on baseline function but completely prevented the mechanical dysfunction observed in untreated controls during reflow. Thus IPC appears to increase available bioactive enkephalins (MEAP + ME) within the heart by enhancing synthesis of precursors and their subsequent processing from the PEP pool.

Effects of maternal separation on voluntary ethanol intake and brain peptide systems in female Wistar rats

In previous studies, changes in adult ethanol intake after early environmental experiences, such as short and prolonged maternal separation, have been described in male rats. The aim of this study was to further investigate long-term effects of maternal separation on voluntary ethanol intake as well as brain opioid and nociceptin/orphanin FQ (N/OFQ) peptides in female Wistar rats. During postnatal days (PNDs) 1-21, rat pups were subjected to 15 min (MS15) or 360 min (MS360) of daily maternal separation, or were kept under normal animal facility rearing (AFR) conditions. At 10 weeks of age, ethanol intake was measured using a two-bottle free choice paradigm and dynorphin B (DYNB), Met-enkephalin-Arg6-Phe7 (MEAP) and N/OFQ levels were analyzed. MS15 resulted in changes in hypothalamus (DYNB), medial prefrontal cortex and nucleus accumbens (MEAP), and amygdala (N/OFQ). MS360 induced alterations in medial prefrontal cortex (MEAP) and amygdala (N/OFQ). MS15 and MS360 had no effect on ethanol intake. However, 4 weeks of ethanol intake affected peptide levels differently in MS15, MS360 and AFR rats and resulted in attenuation of the separation-induced differences. These results show that even though maternal separation has no effect on voluntary ethanol intake in female rats, the ethanol-induced effects on peptide levels depend on the early environmental setting.

Binding Profile of the Endogenous Novel Heptapeptide Met-Enkephalin-Gly-Tyr in Zebrafish and Rat Brain

Zebrafish is considered a model organism, not only for the study of the biological functions of vertebrates but also as a tool to analyze the effects of some drugs or toxic agents. Five opioid precursor genes homologous to the mammalian opioid propeptide genes have recently been identified; one of these, the zebrafish proenkephalin, codes a novel heptapeptide, the Met-enkephalin-Gly-Tyr (MEGY). To analyze the pharmacological properties of this novel ligand, we have labeled it with tritium ([(3)H]MEGY). In addition, we have also synthesized two analogs: (d-Ala(2))-MEGY (Y-d-Ala-GFMGY) and (d-Ala(2), Val(5))-MEGY (Y-d-Ala-GFVGY). The binding profile of these three agents has been studied in zebrafish and rat brain membranes. [(3)H]MEGY presents one binding site in zebrafish, as well as in rat brain membranes, although it shows a slight higher affinity in zebrafish brain. The observed saturable binding is displaced by naloxone, thus confirming the opioid nature of the binding sites. Competition binding assays indicate that the methionine residue is essential for high-affinity binding of MEGY and probably of other peptidic agonists in zebrafish, whereas the change of a Gly for a d-Ala does not dramatically affect the ligand affinity. Our results show that the percentage of [(3)H]MEGY displaced by all the ligands studied is higher than 100%, thus inferring that naloxone (used to determine nonspecific binding) does not bind to all the sites labeled by [(3)H]MEGY. Therefore, we can deduct that some of the MEGY binding sites should not be considered classical opioid sites.

Spatial Structure of BAM-12P Dodecapeptide and Its Analogues

Theoretical conformational analysis was used to study the spatial structure and conformational properties of the bovine adrenal medulla dodecapeptide BAM-12P (Tyr1-Gly2-Gly3-Phe4-Met5-Arg6-Arg7-Val8-Gly9-Arg10-Pro11-Glu12). Twenty-three low-energy conformations of the BAM-12P backbone were shown to represent the spatial structure of the peptide. The inverse structural problem was solved, and synthetic analogues of BAM-12P were proposed, the spatial structures of which correspond to a set of low-energy potentially physiologically active conformations of the natural dodecapeptide. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 3; see also http://www.maik.ru.

Cerebrospinal fluid levels of opioid peptides in fibromyalgia and chronic low back pain

BACKGROUND

The mechanism(s) of nociceptive dysfunction and potential roles of opioid neurotransmitters are unresolved in the chronic pain syndromes of fibromyalgia and chronic low back pain.

METHODS

History and physical examinations, tender point examinations, and questionnaires were used to identify 14 fibromyalgia, 10 chronic low back pain and 6 normal control subjects. Lumbar punctures were performed. Met-enkephalin-Arg6-Phe7 (MEAP) and nociceptin immunoreactive materials were measured in the cerebrospinal fluid by radioimmunoassays.

RESULTS

Fibromyalgia (117.6 pg/ml; 85.9 to 149.4; mean, 95% C.I.; p = 0.009) and low back pain (92.3 pg/ml; 56.9 to 127.7; p = 0.049) groups had significantly higher MEAP than the normal control group (35.7 pg/ml; 15.0 to 56.5). MEAP was inversely correlated to systemic pain thresholds. Nociceptin was not different between groups. Systemic Complaints questionnaire responses were significantly ranked as fibromyalgia > back pain > normal. SF-36 domains demonstrated severe disability for the low back pain group, intermediate results in fibromyalgia, and high function in the normal group.

CONCLUSIONS

Fibromyalgia was distinguished by higher cerebrospinal fluid MEAP, systemic complaints, and manual tender points; intermediate SF-36 scores; and lower pain thresholds compared to the low back pain and normal groups. MEAP and systemic pain thresholds were inversely correlated in low back pain subjects. Central nervous system opioid dysfunction may contribute to pain in fibromyalgia.

Effects of intrathecal BAM22 on noxious stimulus-evoked c-fos expression in the rat spinal dorsal horn

The effects of bovine adrenal medulla 22 (BAM22), a cleaved product of proenkephalin A, were investigated on the noxious stimulus-evoked expressions of spinal c-fos-like immunoreactivity (FLI). Heat (51 degrees C) applied to the tail evoked FLI predominantly in laminae I-II of the sacral spinal cord. Intrathecal (i.t.) BAM22 at a dose of 7 nmol decreased the expressions of the heat-evoked FLI by 68%, 64% and 56% in laminae I-II, III-IV and V-VI, respectively, and the decrease pattern was comparable to that induced by i.t. morphine (10 mug). Naloxone (1 mg/kg, i.p.) significantly enhanced the heat-evoked FLI in laminae III-VI, prevented the morphine-induced inhibition, and decreased the potencies of BAM22 in laminae I-II and V-VI by 23-40%. Higher dose of naloxone (10 mg/kg, i.p.) also partially reduced the BAM22-induced suppression. Following intraplantar injection of formalin (2.5%), FLI neurons were preferentially distributed not only in laminae I-II but also in laminae III-IV and V-VI of segments L4-L5. Pretreatment with BAM22 (7 nmol, i.t.) reduced the formalin-evoked FLI neurons by 72%, 61% and 58%, in laminae I-II, III-IV and V-VI, respectively. Naloxone (1 mg/kg. i.p.) enhanced the formalin-evoked expressions of FLI in laminae III-VI and decreased the potencies of BAM22 by 22-38% in laminae I-II and V-VI. The present study provided evidence at a cellular level showing that opioid and non-opioid effects of BAM22 on nociceptive processing in acute and persistent pain models were associated with modulation of noxious stimulus-evoked activity of the spinal dorsal horn neurons.

Evidence for the involvement of an opioid system in sciatic nerve of Rana ridibunda

The effect of opioid peptide, D-alanine2-leucine-enkephalin and opioid homolog peptide, des-tyrosine-methionine-enkephalin in concentrations of 1 x 10(-6) and 1 x 10(-5) M was investigated on the action potential parameters of frog sciatic nerve. Des-tyrosine-methionine-enkephalin was used as the control to prove the opioid action of the peptide. The effects of both peptides were examined by means of the extracellular electrophysiological technique. The isolated sciatic nerves were stimulated by single square pulses each of which lasted for 0.5 ms at supramaximal strength. Effect of each single dose of peptides at 0 min was compared with the remaining time segments. Both peptides produced changes on action potential of Rana ridibunda sciatic nerve when compared with untreated nerves. D-alanine2-leucine-enkephalin decreased significantly the amplitude at about 34-83%, the area at about 34-92%. The same concentrations of this peptide decreased significantly the conduction velocity around 35-78%. In contrast, des-tyrosine-methionine-enkephalin reduced the action potential amplitude between 8% and 80%. The same concentrations of this peptide decreased significantly the area at about 12-76% and the conduction velocity around 42-70%. The depression of both peptides in action potential parameters was partially blocked by 1 x 10(-6) M naloxone.

Differential regulation of hippocampal progenitor proliferation by opioid receptor antagonists in running and non-running spontaneously hypertensive rats

Voluntary running in mice and forced treadmill running in rats have been shown to increase the amount of proliferating cells in the hippocampus. Little is known as yet about the mechanisms involved in these processes. It is well known that the endogenous opioid system is affected during running and other forms of physical exercise. In this study, we evaluated the involvement of the endogenous opioids in the regulation of hippocampal proliferation in non-running and voluntary running rats. Nine days of wheel running was compared with non-running in spontaneously hypertensive rats (SHR), a rat strain known to run voluntarily. On the last 2 days of the experimental period all rats received two daily injections of the opioid receptor antagonists naltrexone or naltrindole together with injections of bromodeoxyuridine to label dividing cells. Brain sections from the running rats showed approximately a five-fold increase in newly generated cells in the hippocampus, and this increase was partly reduced by naltrexone but not by naltrindole. By contrast, both naltrexone and naltrindole increased hippocampal proliferation in non-running rats. In non-running rats the administration of naltrexone decreased corticosterone levels and adrenal gland weights, whereas no significant effects on these parameters could be detected for naltrindole. However, adrenal gland weights were increased in naltrexone- but not in naltrindole-administered running rats. In addition, in voluntary running rats there was a three-fold increase in the hippocampal levels of Met-enkephalin-Arg-Phe compared with non-runners, indicating an increase in opioid activity in the hippocampus during running. These data suggest an involvement of endogenous opioids in the regulation of hippocampal proliferation in non-running rats, probably through hypothalamic-pituitary-adrenal axis modulation. During voluntary running in SHR naltrexone altered hippocampal proliferation via as yet unknown mechanisms.

Effect of estradiol on expression and activation of Akt protein in rat hypothalamus exposed to chronic [D-Met2, Pro5]-enkephalinamide treatment

Adult ovariectomized rats were implanted with [D-Met2, Pro5]-enkephalinamide (ENK)-containing osmotic minipumps. Two hours prior to sacrifice, some animals were treated with estradiol-17beta (E2) at a dose 10 microg/100 g bodyweight (BW). Expression and activation of Akt proteins, nuclear [3H]estradiol binding, and the expression of estrogen receptor alpha (ERalpha) and beta (ERbeta) and of progesterone receptor (PR) were investigated. Estradiol increased the level of activated Akt protein (pAkt473) in the hypothalamus by 52 +/- 11% in comparison to the vehicle-treated controls. No such effect of E2 was observed 24 and 48 h after ENK implantation. This effect of ENK was abolished by concomitant treatment with naloxone. Time-dependent changes in nuclear [3H]estradiol binding and the expression of estrogen and progesterone receptors were also detected in the hypothalamus of ENK-implanted and E2-treated rats. At 24-48 h following ENK implantation, expression of ERalpha and high affinity [3H]estradiol binding decreased. At this time point, the PR level was also reduced, while the ERbeta level was augmented. In conclusion, these results suggest that the stimulatory effects of E2 on the expression and activation of Akt protein and the expression of ERalpha and PR are negatively regulated in rat hypothalamus exposed to chronic ENK treatment.

Responses of plasma proenkephalin peptide F in rats following 14 days of spaceflight

INTRODUCTION

. Proenkephalin peptide F [107-140] is related to the enhancement of immune function, while microgravity has been shown to cause immuno-suppression. We investigated the physiological response of proenkephalin peptide F to microgravity.

METHODS

There were 12 Fischer 344 female rats, ovariectomized at 10.5 wk of age, used to determine plasma concentrations of peptide F in response to a 14-d flight aboard the Columbia Space Shuttle mission STS-62. There were 36 other such rats that served as ground-based controls to separate the effects of microgravity from those of thermal stress, flight stress, and crowded habitats. Control groups of 12 rats each were kept under the following conditions: 1) 22 degrees C vivarium, 2) 28 degrees C vivarium, and 3) variable (Var) to mimic flight. The flight and control groups were housed in animal enclosure modules 21 d prior to flight and for the duration of the study. The rats were sacrificed within 4-5 h after landing, at which time blood samples were obtained.

RESULTS

Body weights were obtained prior to sacrifice; mean values were flight, 199 g; 22 degrees C, 193 g; 28 degrees C, 192 g; and Var, 194 g. The flight group produced a significantly greater (p < or = 0.05) level of plasma peptide F (0.056 pmol x ml(-1)) compared with the controls (0.016, 0.022, and 0.016 pmol x ml(-1) for 22 degrees C, 28 degrees C, and Var, respectively). Flight animals demonstrated higher corticosterone concentrations and reduced T and B cell splenocyte counts than controls.

CONCLUSIONS

These data indicate that the increases in proenkephalin peptide F observed with exposure to microgravity may present an adrenal-medullary response to cope with the decreased immune function and increased stress experienced during spaceflight and landing.

Dual effects of intrathecal BAM22 on nociceptive responses in acute and persistent pain--potential function of a novel receptor

Bovine adrenal medulla 22 (BAM22) peptide is one of the cleavage products of proenkephalin A. It binds with high affinity to both opioid receptors and a newly discovered receptor in vitro. This latter receptor was first named sensory neuron-specific receptor and is here named BAM peptide-activated receptor with non-opioid activity (BPAR). BPAR is uniquely distributed in small-diameter DRG neurons, most of which are associated with the IB4 class of nociceptor afferent. The present study examined the effects of intrathecal administration of BAM22 on formalin-induced nocifensive behaviors and tail-withdrawal latency in the rat. Intrathecal (i.t.) administration of BAM22 decreased nocifensive behavior scores, measured as the sum of flinching and lifting/licking, in the first and second phases of the formalin test. This decrease was partially attenuated by systemic injection of naloxone. In the presence of naloxone, i.t. BAM22 produced a dose-dependent suppression of the nocifensive behaviors observed during the formalin test. The ratio of the efficacy of BAM22 (5 nmol) in the presence of naloxone over that in the absence of naloxone was 0.65 for flinching and 0.74 for lifting/licking in the second phase. BAM22 at a dose of 5 nmol increased the tail-withdrawal latency by 193 and 119% of baseline in the absence and presence of naloxone, respectively. Systemic administration of naloxone alone enhanced the nocifensive behaviors in the second, but not in the first phase of the formalin test. Naloxone treatment did not alter the tail-withdrawal latency. These data confirm earlier in vitro data showing that BAM22 has both opioid and non-opioid biological actions. The non-opioid action of BAM22 involves inhibition of acute and persistent nociceptive behaviors at the spinal level, presumably mediated via BPAR. The name suggested for this novel receptor, its potential physiological function and its ligand are discussed. British Journal of Pharmacology (2004) 141, 423-430. doi:10.1038/sj.bjp.0705637

Maternal separation alters maternal care, but has minor effects on behavior and brain opioid peptides in adult offspring

The aim of the study was to investigate the effect of repeated maternal separation (MS; 4 hr per day) during postnatal Days 1 to 15 on emotionality and voluntary ethanol intake in adult male and female Wistar rat offspring relative to controls exposed to a brief (5-min) daily handling procedure. Brain immunoreactive opioid peptide levels and plasma levels of corticosterone also were measured. There were mainly no alterations in any of the tested behaviors (i.e., fleeing and freezing responses, exploratory behavior, spontaneous and amphetamine-induced locomotor activity and competitive behavior), ethanol intake, or immunoreactive opioid peptide levels in MS offspring, either in males or females, compared to their respective controls nor were there any differences in plasma corticosterone between groups. In addition, the dams' retrieval behavior of the pups also was studied, showing that MS dams spent more time in the nest with the pups after the 4-hr separation period compared to control dams. With respect to the used protocol of the MS procedure in the present study, our results do not provide support for the suggestion that this procedure is a relevant model for studying development of psychopathology and vulnerability to drug abuse.

Immunocytochemical distribution of Met-enkephalin-Arg6-Gly7-Leu8 (Met-8) in the auditory system of the rat

Methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) (Met(8)) is known to act as a neurotransmitter or neuromodulator and it has been implicated in pain, cardiovascular and motor mechanisms, but its role in audition is currently unknown. In the present study we have applied an immunocytochemical technique and describe the distribution of cell bodies and fibers containing Met(8) in the auditory pathway of the rat. The main finding is that we found either Met(8)-immunoreactive fibers or cell bodies or both in virtually all nuclei of the rat auditory system except for the medial superior olive and the ventral division of the medial geniculate body in which we did not find any immunoreactivity for Met(8). This suggests that the neuropeptide Met(8) is widely distributed throughout the auditory system of the rat. Our results suggest that Met(8) could play at least two roles in hearing. It seems to be involved in the processing of the descending auditory pathway, and it may be implicated in the multisensory integration of auditory information that takes place in the non-lemniscal auditory pathway.

An immunocytochemical mapping of methionine-enkephalin-arg6-gly7-leu8 in the human brainstem

Using an indirect immunoperoxidase technique, we studied the distribution of immunoreactive fibers and cell bodies containing methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) in the adult human brainstem. Immunoreactive cell bodies were found in the reticular formation of the medulla oblongata (in which we observed the highest density of immunoreactive cell bodies) and the pons, the solitary nucleus, the hypoglossal nucleus, the medial and spinal vestibular nuclei, the lateral cuneate nucleus, the nucleus prepositus, the central gray of the pons and mesencephalon, the central and pericentral nuclei of the inferior colliculus, the superior colliculus, ventral to the superior olive and in the midline region of the pons and mesencephalon. The highest density of immunoreactive fibers containing methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) was found in the spinal trigeminal nucleus, the central gray and the reticular formation of the medulla oblongata, pons and mesencephalon, the solitary nucleus, the spinal vestibular nucleus, the dorsal accessory olivary nucleus, the raphe obscurus, the substantia nigra and in the interpeduncular nucleus. The widespread distribution of immunoreactive structures containing methionine-enkephalin-Arg(6)-Gly(7)-Leu(8) in the human brainstem indicates that this neuropeptide might be involved in several physiological mechanisms, acting as a neurotransmitter and/or neuromodulator.

Cardiac enkephalins attenuate vagal bradycardia: interactions with NOS-1-cGMP systems in canine sinoatrial node

Endogenous opioids and nitric oxide (NO) are recognized modulators of cardiac function. Enkephalins and inhibitors of NO synthase (NOS) both produce similar interruptions in the vagal control of heart rate. This study was conducted to test the hypothesis that NO systems within the canine sinoatrial (SA) node facilitate local vagal transmission and that the endogenous enkephalin methionine-enkephalin-arginine-phenylalanine (MEAP) attenuates vagal bradycardia by interrupting the NOS-cGMP pathway. Microdialysis probes were inserted into the SA node, and they were perfused with nonselective (Nomega-nitro-l-arginine methyl ester) and neuronal (7-nitroindazole) NOS inhibitors. The right vagus nerve was stimulated and both inhibitors gradually attenuated the resulting vagal bradycardia. The specificity of these inhibitions was verified by an equally gradual reversal of the inhibition with an excess of the NOS substrate l-arginine. Introduction of MEAP into the nodal interstitium produced a quickly developing but quantitatively similar interruption of vagal bradycardia that was also slowly reversed by the addition of l-arginine and not by d-arginine. Additional support for convergence of opioid and NO pathways was provided when the vagolytic effects of MEAP were also reversed by the addition of the NO donor S-nitroso-N-acetyl-penicillamine, the protein kinase G activator 8-bromo-cGMP, or the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. MEAP and 7-nitroindazole were individually combined with the direct acting muscarinic agonist methacholine to evaluate potential interactions with muscarinic receptors within the SA node. MEAP and 7-nitroindazole were unable to overcome the bradycardia produced by methacholine. These data suggest that NO and enkephalins moderate the vagal control of heart rate via interaction with converging systems that involve the regulation of cAMP within nodal parasympathetic nerve terminals.

Bimodal delta-opioid receptors regulate vagal bradycardia in canine sinoatrial node

Methionine-enkephalin-arginine-phenylalanine (MEAP) introduced into the interstitium of the canine sinoatrial (SA) node by microdialysis interrupts vagal bradycardia. In contrast, raising endogenous MEAP by occluding the SA node artery improves vagal bradycardia. Both are blocked by the same delta-selective antagonist, naltrindole. We tested the hypothesis that vagal responses to intranodal enkephalin are bimodal and that the polarity of the response is both dose- and opioid receptor subtype dependent. Ultralow doses of MEAP were introduced into the canine SA node by microdialysis. Heart rate frequency responses were constructed by stimulating the right vagus nerve at 1, 2, and 3 Hz. Ultralow MEAP infusions produced a 50-100% increase in bradycardia during vagal stimulation. Maximal improvement was observed at a dose rate of 500 fmol/min with an ED50 near 50 fmol/min. Vagal improvement was returned to control when MEAP was combined with the delta-antagonist naltrindole. The dose of naltrindole (500 fmol/min) was previously determined as ineffective vs. the vagolytic effect of higher dose MEAP. When MEAP was later reintroduced in the same animals at nanomoles per minute, a clear vagolytic response was observed. The delta1-selective antagonist 7-benzylidenenaltrexone (BNTX) reversed the vagal improvement with an ED50 near 1 x 10-21 mol/min, whereas the delta2-antagonist naltriben had no effect through 10-9 mol/min. Finally, the improved vagal bradycardia previously associated with nodal artery occlusion and endogenous MEAP was blocked by the selective delta1-antagonist BNTX. These data support the hypothesis that opioid effects within the SA node are bimodal in character, that low doses are vagotonic, acting on delta1-receptors, and that higher doses are vagolytic, acting on delta2-receptors.

Developmental changes in the inhibition of cultured rat uterine cell proliferation by opioid peptides

Opioid peptides are negative regulators of cell proliferation in several organs including the uterus. In the present study, the ontogeny of the direct inhibitory action of opioid peptides on the proliferation of cultured rat uterine cells was investigated. Uteri of 7, 14, 21, 28, 35 and 60-day-old rats were removed in a sterile way. Tissue blocks were dispersed by limited digestions with trypsin and collagenase. Cells were cultured in enriched Dulbecco's modified Eagle's medium (DMEM). Treatments were present during the entire culture period. Cell densities of the monolayers were determined by counting the cells following trypsinization and trypan blue exclusion. Rat uterine mixed cell cultures grew to confluence within 10 days. The average population doubling time gradually increased with the age of animals. Epidermal growth factor (EGF) increased cell densities of cultures from all age groups. The oestradiol (E2)-responsiveness appeared at 21 days of age. The effect of [D-Met2-Pro5]-enkephalinamide (ENK) was biphasic. ENK and [Met5]-enkephalin (OGF) decreased cell densities of both unstimulated and EGF-stimulated cultures from 7-day-old rats to the same extent. ENK failed to act in 14-day-old animals. From 21 days of age on, the E2- or EGF-stimulated proliferation was inhibited only by ENK and DAMGO, while 30 nm DPDPE, Dynorhin-A, OGF, [Leu5]-enkephalin, beta-endorphin, and morphiceptin were ineffective. The half-inhibitory concentration of ENK was 0.3 nm. The effects of ENK were prevented by concomitant treatment with naloxone. Our novel data demonstrate two different phases of the inhibitory action of opioid peptides on rat uterine cell proliferation during ontogeny with an insensitive interval in between.

Long-term effects of short and long periods of maternal separation on brain opioid peptide levels in male Wistar rats

Environmental manipulations early in life may induce persistent alterations in adult behaviour and physiology. The underlying neural mechanisms of these responses are not yet clear. We have previously reported long-term changes in brain opioid peptide levels in male and female Sprague-Dawley rats after short periods (15 min, known as neonatal handling) of maternal separation (MS) until weaning. To study this further, we investigated behavioural and neurochemical effects of repeated MS in male Wistar rats. The rat pups were separated from their dams in litters for either 360 min (MS360) or 15 min (MS15) daily from postnatal day 1 to 21 or exposed to normal animal facility rearing. Behavioural analysis showed that MS360 rats had increased ultrasonic calls on postnatal day 5 compared to MS15 rats, but not on postnatal day 6. Moreover, the MS360 rats had more animals with higher frequency of calls at day 5 than 6 than the MS15 rats. Analysis of the opioid peptides dynorphin B and Met-enkephalin-Arg(6)Phe(7) with radioimmunoassay 7 weeks after the MS procedure, revealed long-term neurochemical changes in several brain areas and in the pituitary gland. Immunoreactive dynorphin B and Met-enkephalin-Arg(6)Phe(7) levels were affected in the hypothalamus and dynorphin B levels in the neurointermediate pituitary lobe, amygdala, substantia nigra and the periaqueductal gray. Together, these findings show that repeated periods of MS early in life in male Wistar rats affect the development of the ultrasonic call response and induce long-lasting and possibly permanent alterations in the opioid peptide systems.

Uterus-innervating neurones in porcine inferior mesenteric ganglion: an immunohistochemical characteristic

The presence of tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, galanin, Met-enkephalin-Arg-Gly-Leu, substance P and calcitonin gene-related peptide was studied with immunohistochemistry in uterus-innervating neurones found in the inferior mesenteric ganglia after fluorescent tracer (Fast Blue) injection into different regions of the porcine uterus (uterine cervix, paracervical, middle and paraoviductal part of the uterine horn). Virtually all Fast Blue-positive neurones found in the inferior mesenteric ganglia after tracer injection into all studied parts of the uterus contained tyrosine hydroxylase and ca. 45% of them contained neuropeptide Y. Single galanin-positive/Fast Blue-positive cells were found in the ganglia only after tracer injections into uterine cervix. No other studied substances were found in the Fast-Blue positive neurones of the inferior mesenteric ganglia.