Endogenous opiates and behavior: 2004

Organization of enkephalinergic neuronal system in the central nervous system of the gecko Hemidactylus frenatus

Enkephalins are endogenous opioid pentapeptides that play a role in neurotransmission and pain modulation in vertebrates. However, the distribution pattern of enkephalinergic neurons in the brains of reptiles has been understudied. This study reports the organization of the methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK) neuronal systems in the central nervous system of the gecko Hemidactylus frenatus using an immunofluorescence labeling method. Although M-ENK and L-ENK-immunoreactive (ir) fibers extended throughout the pallial and subpallial subdivisions, including the olfactory bulbs, M-ENK and L-ENK-ir cells were found only in the dorsal septal nucleus. Enkephalinergic perikarya and fibers were highly concentrated in the periventricular and lateral preoptic areas, as well as in the anterior and lateral subdivisions of the hypothalamus, while enkephalinergic innervation was observed in the hypothalamic periventricular nucleus, infundibular recess nucleus and median eminence. The dense accumulation of enkephalinergic content was noticed in the pars distalis of the hypophysis. In the thalamus, the nucleus rotundus and the dorsolateral, medial, and medial posterior thalamic nuclei contained M-ENK and L-ENK-ir fibers, whereas clusters of M-ENK and L-ENK-ir neurons were observed in the pretectum, mesencephalon, and rhombencephalon. The enkephalinergic fibers were also seen in the area X around the central canal, as well as the dorsal and ventral horns. The widespread distribution of enkephalin-containing neurons within the central nervous system implies that enkephalins regulate a variety of functions in the gecko, including sensory, behavioral, hypophysiotropic, and neuroendocrine functions.

Effect of treadmill walking for anxiety, depression and social well-being in women with diabetes type 2: A randomized controlled trial

Anxiety and depression are higher in persons with diabetes leading to poor glycaemic control and diabetes-related emotional distress. Some diabetic women do not engage in exercises perceiving it to make their diabetes worse. The researchers' objective of this treadmill walking program was to determine its effect on anxiety, depression and social well-being in women with diabetes type 2 (DT2). We randomized 49 sedentary women with DT2 into treadmill walking at moderate intensity of 40-60% of their age-adjusted maximal heart rate, three times per week on alternate days for 12 weeks. The control attended electronic lectures on diet, diabetes and mental health. The treadmill group had no adverse effects and their anxiety, depression and social well-being scores improved with no significant changes for the control. We offer women with DT2 an easy, safe indoors exercise preventing them from abuse from men, erratic drivers and extreme weather conditions with positive physiological responses.

Second Wave of COVID-19 Pandemic in Argentinian Population: Vaccination Is Associated With a Decrease in Depressive Symptoms

BACKGROUND

Since the irruption of the coronavirus disease 2019 (COVID-19) the planet has submerged in a time of concern and uncertainty, with a direct impact on people's mental health. Moreover, the recurrent outbreaks that periodically harry different regions of the world constantly refocus people's concerns to the pandemic. Yet, each new wave heats the diverse countries in different situations, including the advances in their vaccination campaigns. In this research, we studied the levels of the general anxiety disorder (GAD) and depression in the Argentine population across the first and second waves of infections that occurred in our country.

METHODS

We conducted an on-line survey, within each peak of the pandemic. People were asked to self-report GAD and depression symptoms using the GAD-7 and PHQ-9 questioners, inform their vaccination status, the frequency they performed physical activity as well as working condition and modality. Here, we identified the more vulnerable groups and evaluated factors that could mitigate the rise of these mental disorders, focusing on vaccination.

RESULTS

Our data shows that reported GAD and depression levels were higher during the second wave than during the first one. More importantly, vaccinated people were less depressed than non-vaccinated people, while GAD levels remained equivalent in both groups. Other factors directly associated with lower GAD and depression levels were performing frequent physical activity and being employed, regardless of the employment modality. These observations were replicated in different age ranges and genders.

CONCLUSION

This work evidences GAD and depression in different pandemic waves in Argentina, as well the factors that may contribute to reducing the magnitude of these disorders, including vaccination.

An Effective and Safe Enkephalin Analog for Antinociception

Opioids account for 69,000 overdose deaths per annum worldwide and cause serious side effects. Safer analgesics are urgently needed. The endogenous opioid peptide Leu-Enkephalin (Leu-ENK) is ineffective when introduced peripherally due to poor stability and limited membrane permeability. We developed a focused library of Leu-ENK analogs containing small hydrophobic modifications. N-pivaloyl analog KK-103 showed the highest binding affinity to the delta opioid receptor (68% relative to Leu-ENK) and an extended plasma half-life of 37 h. In the murine hot-plate model, subcutaneous KK-103 showed 10-fold improved anticonception (142%MPE·h) compared to Leu-ENK (14%MPE·h). In the formalin model, KK-103 reduced the licking and biting time to ~50% relative to the vehicle group. KK-103 was shown to act through the opioid receptors in the central nervous system. In contrast to morphine, KK-103 was longer-lasting and did not induce breathing depression, physical dependence, and tolerance, showing potential as a safe and effective analgesic.

The impact of physical activity on psychological health during Covid-19 pandemic in Italy

The worldwide spread of COVID-19 has upset the normality of Italian daily life, forcing population to social distancing and self-isolation. Since the containment precautions also concern sport-related activities, home workout remained the only possibility to play sports and stay active during the pandemic. The present study aimed to examine changes in the physical activity levels during self-quarantine in Italy, and the impact of exercise on psychological health. A total of 2974 Italian subjects has completed an online survey, but only 2524 subjects resulted eligible for this study. The questionnaire measured the total weekly physical activity energy expenditure before and during quarantine (i.e. the sum of walking, moderate-intensity physical activities, and vigorous-intensity physical activities) in Metabolic Equivalent Task minutes per week (MET-min/wk) using an adapted version of International Physical Activity Questionnaire and their psychological well-being using the Psychological General Well Being Index. Of the 2524 Italian subjects included in the study, 1426 were females (56.4%) and 1098 males (43.6%). Total physical activity significantly decreased between before and during COVID-19 pandemic (Mean: 2429 vs. 1577 MET-min/wk, ∗∗∗∗p < 0.0001), in all age groups and especially in men (Female, mean: 1994 vs. 1443 MET-min/wk, ∗∗∗∗p < 0.0001; Male, mean: 2998 vs. 1754 MET-min/wk, ∗∗∗∗p < 0.0001). Furthermore, a significant positive correlation was found between the variation of physical activity and mental well-being (r = 0.07541, ∗∗∗p = 0.0002), suggesting that the reduction of total physical activity had a profoundly negative impact on psychological health and well-being of population. Based on this scientific evidence, maintaining a regular exercise routine is a key strategy for physical and mental health during a forced rest period like the current coronavirus emergency.

Aspects of Pain, Its Assessment and Evaluation from An Acupuncture Perspective

Pain is a major clinical problem that causes great suffering for the individual and incurs costs for society. Accurate assessment and evaluation of perceived pain is necessary for diagnosis, for choice of treatment, and for the evaluation of treatment efficacy. The assessment of an individual's pain is a challenge since pain is a subjective, multidimensional experience, and assessment is based on the person's own self-report. The results are often varied, possibly due to inter-individual variation, but also in relation to gender and aetiology.

A gold standard for pain assessment is still lacking, but rating scales, questionnaires, and methods derived from psychophysical concepts, such as threshold assessments and perceptual matching, are used. In the evaluation of pain and associated variables, both systematic and individual variation should be taken into account, as should pain-associated symptoms.

Recommendations for pain treatment should be based on the patient's specific needs. Therefore, it is important to assess the level of perceived pain taking individual variation into account. The methods used should preferably have proved to be useful in randomised controlled trials, and analysis of pain assessment should consider its non-metric properties. In the future, the use of studies with a naturalistic protocol together with individual assessment of individual pain responses could increase the internal and external validity.

Effect of swimming exercise on premenstrual syndrome

OBJECTIVE

To study the effectiveness of performing swimming on the severity of symptoms of premenstrual syndrome (PMS).

MATERIALS AND METHODS

A randomized controlled trial that was conducted on 70 women diagnosed with PMS divided randomly into two equal groups: Group I included women who engaged into exercise and group II controls. Daily Symptoms Report was filled at the start and at end of the study.

RESULTS

At the posttreatment evaluation, there was a highly significant difference between the study and control groups regarding anxiety (0 vs. 5), depression (3 vs. 12), tension (3 vs. 12), mood changes (0 vs. 7), feeling out of control (0 vs. 7), weak coordination (0 vs. 10), confusion (2 vs. 9), headache (3 vs. 15), tiredness (4 vs. 12), pains (5 vs. 11), tenderness of the breast (2 vs. 8), and cramps (6 vs. 17) (P < 0.001), but no such difference was found regarding irritability, insomnia, crying, swelling, or food craving. Regarding the percentage of symptoms changes, there was a highly significant difference between the study and control groups regarding anxiety (- 33.3 vs. 0), depression (- 79.29 vs. 15.56), tension (- 81.18 vs. - 6.79), mood changes (- 33.33 vs. 0), feeling out of control (- 91.67 vs. 0), weak coordination (- 100 vs. - 9.55), sleeplessness (- 71.43 vs. 0), confusion (- 84.17 vs. - 9.55), headache (- 77.78 vs. - 6.94), fatigue (- 65.69 vs. 0), pains (- 65.83 vs. - 8.93), breast tenderness (- 87.87 vs. 4.55), cramps (- 60.77 vs. 4.55), and swellings (- 55.05 vs. - 8.33), but no such difference was found regarding irritability, crying, or food craving.

CONCLUSIONS

There is beneficial effect of swimming on most of the physical and psychological symptoms of PMS.

CLINICAL TRIAL REGISTRY NO

NCT03264612.

Mechanisms involved in antinociception induced by a polysulfated fraction from seaweed Gracilaria cornea in the temporomandibular joint of rats

Temporomandibular disorder is a common clinical condition involving pain in the temporomandibular joint (TMJ) region. This study assessed the antinociceptive effects of a polysulfated fraction from the red seaweed Gracilaria cornea (Gc-FI) on the formalin-induced TMJ hypernociception in rats and investigated the involvement of different mechanisms. Male Wistar rats were pretreated with injection (sc) of saline or Gc-FI 1h before intra- TMJ injection of formalin to evaluate the nociception. The results showed that pretreatment with Gc-FI significantly reduced formalin-induced nociceptive behavior. Moreover, the antinociceptive effect of the Gc-FI was blocked by naloxone (a non-selective opioid antagonist), suggesting the involvement of opioids selective receptors. Thus, the pretreatment with selective opioids receptors antagonists, reversed the antinociceptive effect of the Gc-FI in the TMJ. The Gc-FI antinociceptive effect depends on the nitric oxide/cyclic GMP/protein kinase G/ATP-sensitive potassium channel (NO/cGMP/PKG/K⁺_ATP) pathway because it was prevented by pretreatment with inhibitors of nitric oxide synthase, guanylate cyclase enzyme, PKG and a K⁺_ATP blocker. In addition, after inhibition with a specific heme oxygenase-1 (HO-1) inhibitor, the antinociceptive effect of the Gc-FI was not observed. Collectively, these data suggest that the antinociceptive effect induced by Gc-FI is mediated by μ/δ/κ-opioid receptors and by activation NO/cGMP/PKG/K⁺_ATP channel pathway, besides of HO-1.

Kappa Opioids, Salvinorin A and Major Depressive Disorder

Opioids are traditionally associated with pain, analgesia and drug abuse. It is now clear, however, that the opioids are central players in mood. The implications for mood disorders, particularly clinical depression, suggest a paradigm shift from the monoamine neurotransmitters to the opioids either alone or in interaction with monoamine neurons. We have a special interest in dynorphin, the last of the major endogenous opioids to be isolated and identified. Dynorphin is derived from the Greek word for power, dynamis, which hints at the expectation that the neuropeptide held for its discoverers. Yet, dynorphin and its opioid receptor subtype, kappa, has always taken a backseat to the endogenous b-endorphin and the exogenous morphine that both bind the mu opioid receptor subtype. That may be changing as the dynorphin/ kappa system has been shown to have different, often opposite, neurophysiological and behavioral influences. This includes major depressive disorder (MDD). Here, we have undertaken a review of dynorphin/ kappa neurobiology as related to behaviors, especially MDD. Highlights include the unique features of dynorphin and kappa receptors and the special relation of a plant-based agonist of the kappa receptor salvinorin A. In addition to acting as a kappa opioid agonist, we conclude that salvinorin A has a complex pharmacologic profile, with potential additional mechanisms of action. Its unique neurophysiological effects make Salvinorina A an ideal candidate for MDD treatment research.

Long-term behavioral effects in a rat model of prolonged postnatal morphine exposure

Prolonged morphine treatment in neonatal pediatric populations is associated with a high incidence of opioid tolerance and dependence. Despite the clinical relevance of this problem, our knowledge of long-term consequences is sparse. The main objective of this study was to investigate whether prolonged morphine administration in a neonatal rat is associated with long-term behavioral changes in adulthood. Newborn animals received either morphine (10 mg/kg) or equal volume of saline subcutaneously twice daily for the first 2 weeks of life. Morphine-treated animals underwent 10 days of morphine weaning to reduce the potential for observable physical signs of withdrawal. Animals were subjected to nonstressful testing (locomotor activity recording and a novel-object recognition test) at a young age (Postnatal Days [PDs] 27-31) or later in adulthood (PDs 55-56), as well as stressful testing (calibrated forceps test, hot plate test, and forced swim test) only in adulthood. Analysis revealed that prolonged neonatal morphine exposure resulted in decreased thermal but not mechanical threshold. Importantly, no differences were found for total locomotor activity (proxy of drug reward/reinforcement behavior), individual forced swim test behaviors (proxy of affective processing), or novel-object recognition test. Performance on the novel-object recognition test was compromised in the morphine-treated group at the young age, but the effect disappeared in adulthood. These novel results provide insight into the long-term consequences of opioid treatment during an early developmental period and suggest long-term neuroplastic differences in sensory processing related to thermal stimuli.

New type of BACE1 siRNA delivery to cells

BACKGROUND

Small interfering RNA (siRNA) gene therapy is a new molecular approach in the search for an efficient therapy for Alzheimer disease (AD), based on the principle of RNA interference. Reducing BACE activity can have great therapeutic potential for the treatment of AD. In this study, receptor-mediated delivery was used to deliver opioid peptide-conjugated BACE 1 to INR-32 human neuroblastoma cells.

MATERIAL AND METHODS

An INR-32 human neuroblastoma cell line was stably transfected to express the APP cDNA coding fragment containing the predicted sites for cleavage by α, β, or γ-secretase. This was then treated with BACE 1 siRNA to silence BACE gene expression. BACE gene transcription and translation was determined using BACE-1 siRNA cross-linked with opioid peptide, together with RT-PCR, Western blot analysis, and ELISA.

RESULTS

Receptor-mediated delivery was used to introduce BACE1 siRNA to the APP - INR 32 human neuroblastoma cells. Decreased BACE mRNA and protein expression were observed after the cells were transfected with BACE1 siRNA.

CONCLUSIONS

Delivery of BACE1 siRNA appears to specifically reduce the cleavage of APP by inhibiting BACE1 activity.

Lentivirus-mediated α-melanocyte-stimulating hormone overexpression in the hypothalamus decreases diet induced obesity in mice

Melanocyte stimulating hormone (MSH) derived from the pro-hormone pro-opiomelanocortin (POMC) has potent effects on metabolism and feeding that lead to reduced body weight in the long-term. To determine the individual roles of POMC derived peptides and their sites of action, we created a method for the delivery of single MSH peptides using lentiviral vectors and studied the long-term anti-obesity effects of hypothalamic α-MSH overexpression in mice. An α-MSH lentivirus (LVi-α-MSH-EGFP) vector carrying the N'-terminal part of POMC and the α-MSH sequence was generated and shown to produce bioactive peptide in an in vitro melanin synthesis assay. Stereotaxis was used to deliver the LVi-α-MSH-EGFP or control LVi-EGFP vector to the arcuate nucleus (ARC) of the hypothalamus of male C57Bl/6N mice fed on a high-fat diet. The effects of 6-week-treatment on body weight, food intake, glucose tolerance and organ weights were determined. Additionally, a 14-day pairfeeding study was conducted to assess whether the weight decreasing effect of the LVi-α-MSH-EGFP treatment is dependent on decreased food intake. The 6-week LVi-α-MSH-EGFP treatment reduced weight gain (8.4 ± 0.4 g versus 12.3 ± 0.6 g; P < 0.05), which was statistically significant starting from 1 week after the injections. The weight of mesenteric fat was decreased and glucose tolerance was improved compared to LVi-EGFP treated mice. Food intake was decreased during the first week in the LVi-α-MSH-EGFP treated mice but subsequently increased to the level of LVi-EGFP treated mice. The LVi-EGFP injected control mice gained more weight even when pairfed to the level of food intake by LVi-α-MSH-EGFP treated mice. We demonstrate that gene transfer of α-MSH, a single peptide product of POMC, into the ARC of the hypothalamus, reduces obesity and improves glucose tolerance, and that factors other than decreased food intake also influence the weight decreasing effects of α-MSH overexpression in the ARC. Furthermore, viral MSH vectors delivered stereotaxically provide a novel tool for further exploration of chronic site-specific effects of POMC peptides.

Orexigenic effects of endomorphin-2 (EM-2) related to decreased CRH gene expression and increased dopamine and norepinephrine activity in the hypothalamus

Endomorphin-1 (EM-1) and endomorphin-2 (EM-2) are opioid peptides which are selective partial agonists of μ-opioid receptor. We studied the effects of EM-2 injected into the arcuate nucleus (ARC) of the hypothalamus on feeding behavior and gene expression of orexigenic [agouti-related peptide (AgRP), neuropeptide Y (NPY) and orexin-A] and anorexigenic [cocaine and amphetamine-regulated transcript (CART), corticotrophin releasing hormone (CRH) and proopiomelanocortin (POMC)] peptides in male Wistar rats fed a standard laboratory diet. Furthermore, we evaluated the effects of EM-2 on dopamine (DA), norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT) steady state concentrations, in the hypothalamus. 64 rats (16 for each group of treatment) were injected into the ARC, at 9.00 am, with either vehicle or EM-2 (0.50-0.75 μmol/kg) or EM-2 (0.50 μmol/kg) plus β-funaltrexamine (0.20 μmol/kg). Food intake was recorded through 24h following injection, and hypothalamic DA, NE, 5-HT levels and neuropeptide gene expression were evaluated 24h after EM-2 administration. Compared to vehicle, EM-2 significantly increased food intake, throughout 24h post-injection. Furthermore, EM-2 treatment led to a significant increase of DA and NE concentrations and a decrease of CRH mRNA levels. On the other hand, β-funaltrexamine administration reverted both feeding stimulatory and neuromodulatory effects induced by EM-2. We can conclude that the orexigenic effect of μ-opioid receptor activation by EM-2 could be related to both inhibition of CRH and stimulation of dopamine and norepinephrine levels, in the hypothalamus.

Leaf extract from Clusia nemorosa induces an antinociceptive effect in mice via a mechanism that is adrenergic systems dependent

Previous studies on the genus Clusia have shown anti-inflammatory and antiproliferative effects of the leaf extracts, but its antinociceptive activity has never been characterized. In the present study, the antinociceptive activity of the hexane extract of the leaves of Clusia nemorosa G. Mey, called HECn, was examined. Antinociceptive activity was evaluated using acetic acid-induced writhing, formalin, and hot-plate tests. All experiments were carried out on male Swiss mice. The extract (1-400 mg·kg(-1)), given by intraperitoneal route (i.p.) 1 h prior to testing, produced a dose-dependent inhibition on the number of abdominal writhings, with an ID50 of 62 mg·kg(-1). In addition, HECn was able to prevent the visceral pain induced by acetic acid in mice for at least 2 h. In the formalin test, HECn had no effect in the first phase, but produced an analgesic effect on the second phase with the inhibition of licking time. The HECn did not show a significant analgesic effect in the hot plate test. Pretreatment with yohimbine attenuated the antinociceptive effect induced by HECn in the writhing test. However, naloxone, atropine, or haloperidol did not affect antinociception induced by HECn in the writhing test. Together, these results indicate that the extract from the leaves of Clusia nemorosa produces antinociception in models of chemical pain through mechanisms that suggest participation of the adrenergic systems pathway.

The nociceptin/orphanin FQ-like opioid peptide in nervous periesophageal ganglia of land snail Helix aspersa

The neuropeptide nociceptin/orphanin FQ (N/OFQ) and its receptor are members of the endogenous opioid peptide family. In mammals N/OFQ modulates a variety of biological functions such as nociception, food intake, endocrine, control of neurotransmitter release, among others. In the molluscs Cepea nemoralis and Helix aspersa the administration of N/OFQ produces a thermopronociceptive effect. However, little is known about its existence and anatomic distribution in invertebrates. The aim of this study was to provide a detailed anatomical distribution of N/OFQ like peptide immunoreactivity (N/OFQ-IL), to quantify the tissue content of this peptide, as well as to demostrate molecular evidence of N/OFQ mRNA in the nervous tissue of periesophageal ganglia of the land snail H. aspersa. Immunohistochemical, immunocytochemical, radioimmunoanalysis (RIA) and reverse transcription-polymerase chain reaction (RT-PCR) techniques were used. With regard to RT-PCR, the primers to detect expression of mRNA transcripts from H. aspersa were derived from the rat N/OFQ opioid peptide. We show a wide distribution of N/OFQ-IL in neurons and fibers in all perioesophageal ganglia, fibers of the neuropile, nerves, periganglionar connective tissue, aortic wall and neurohemal sinuses. The total amount of N/OFQ-IL in the perioesophageal ganglia (7.75 ± 1.75 pmol/g of tissue) quantified by RIA was similar to that found in mouse hypothalamus (10.1 ± 1.6 pmol/g of tissue). In this study, we present molecular evidence of N/OFQ mRNA expression. Some N/OFQ-IL neurons have been identified as neuroendocrine or involved in olfaction, hydro-electrolyte regulation, feeding, and thermonociception. Therefore, we suggest that N/OFQ may participate in these snail functions.

The CB(1) receptor antagonist, AM281, improves recognition loss induced by naloxone in morphine withdrawal mice

Morphine withdrawal leads to the activation of endocannabinoid system and cognitive deficits. The aim of this study was to evaluate the effects of AM281, a cannabinoid antagonist/inverse agonist, on memory deficit following naloxone-precipitated morphine withdrawal in mice. Male mice were made dependent by increasing doses of morphine (30-90 mg/kg) twice daily for 3 days. The object recognition task was used to evaluate memory dysfunction. The test comprised three sections: habituation for 15 min., first trial for 12 min. and test trial for 5 min. In this learning paradigm, the difference in exploration between a previously seen object and a new object is taken as an index of memory performance (recognition index). The recognition index was assessed on the third day of morphine treatment by the injection of 0.1 mg/kg naloxone 3 hr after the last dose of morphine. Chronic administration of AM281 at 2.5 mg/kg significantly improved the memory impairment, producing a recognition index of 36.0 ± 3.9 as compared with vehicle-treated data (recognition index = -3.1 ± 8.2%). A single dose of AM281 at 5 mg/kg improved the recognition index from -1.5 ± 3.9% in morphine withdrawal animals to 18.5 ± 11.6%. Concurrent administration of AM281 with morphine proved to be more effective in protecting the animals from losing their memory compared to acute action of AM281. These results indicate that the contribution of the cannabinoid system to memory deficit is attributable to morphine withdrawal. By blocking cannabinoid receptors, AM281 may become useful in preventing memory deficit after morphine withdrawal.

Examination of the interaction between peripheral lumiracoxib and opioids on the 1% formalin test in rats

It has been shown that the association of non-steroidal anti-inflammatory drugs (NSAIDs) with opioid analgesic agents can increase their antinociceptive activity, allowing the use of lower doses and thus limiting side effects. Therefore, the aim of the present study was to examine the possible pharmacological interaction between lumiracoxib and codeine or nalbuphine at the local peripheral level in the rat using the 1% formalin test and isobolographic analysis. Lumiracoxib, codeine, nalbuphine or fixed-dose ratios lumiracoxib-codeine or lumiracoxib-nalbuphine combinations were administrated locally in the formalin-injured paw and the antinociceptive effect was evaluated using the 1% formalin test. All treatments produced a dose-dependent antinociceptive effect. ED(40) values were estimated for the individual drugs and an isobologram was constructed. The derived theoretical ED(40)'s for the lumiracoxib-codeine and lumiracoxib-nalbuphine combinations were 423.4+/-31.3 microg/paw and 310.9+/-24.2 microg/paw, respectively, being significantly higher than the actually observed experimental ED(40) values, 233.2+/-30.9 microg/paw and 132.7+/-11.6 microg/paw, respectively. These results correspond to a synergistic interaction between lumiracoxib and opioids at the local peripheral level, potency being about two times higher with regard to that expected from the addition of the effects of the individual drugs. Data suggest that low doses of the lumiracoxib-opioids combination can interact synergistically at the peripheral level and therefore this drug association may represent a therapeutic advantage for the clinical treatment of inflammatory pain.

Opioid-receptor gene expression and localization in cancer cells

This study examined the presence and cellular localization of three types of opioid receptors (MOR, DOR and KOR) in five human cancer cell lines: MCF-7, MDA-MB-231, HT-29, MGH-U1 and SH-SY5Y. Expression levels of opioid receptors were measured quantitatively using real-time PCR, and the localizations of the receptors in the cells were determined by immunocytochemistry. All three types of opioid receptors were present in each of the five cell lines examined. However, three of the cell lines (MCF-7, HT-29 and SH-SY5Y) showed significantly higher levels of MOR mRNA and protein than the other two types of receptors (DOR and KOR). Immunocytochemistry revealed that MOR, DOR and KOR receptors were predominantly present on the surface of cell membranes, although these receptors were also occasionally present in the cell cytoplasm.

Opioid system functional regulation in neurological disease management

There is increasing evidence to suggest a role for the opioid system in the control of pathophysiology of neurological disorders (Alzheimer's, Parkinson's, and Huntington's diseases, spinal cord injury, epilepsy, hypoxia, and autism). Resuscitation of the altered expression of the opioid system in various neurological disorders is of therapeutic importance. Such treatment may be beneficial in ameliorating the clinical symptoms of the disorder. This Mini-Review provides a brief update on opioid system regulation in neurological disorders and focuses on the opioids' pharmacological importance.

Exploring the Backbone of Enkephalins To Adjust Their Pharmacological Profile for the δ-Opioid Receptor

The role of each of the four amide bonds in Leu(5)-enkephalin was investigated by systematically and sequentially replacing each with its corresponding trans-alkene. Six Leu(5)-enkephalin analogs based on six dipeptide surrogates and two Met(5)-enkephalin analogs were synthesized and thoroughly tested using a δ-opioid receptor internalization assay, an ERK1/2 activation assay, and a competition binding assay to evaluate their biological properties. We observed that an E-alkene can efficiently replace the first amide bond of Leu(5)- and Met(5)-enkephalin without significantly affecting biological activity. By contrast, the second amide bond was found to be highly sensitive to the same modification, suggesting that it is involved in biologically essential intra- or intermolecular interactions. Finally, we observed that the affinity and activity of analogs containing an E-alkene at either the third or fourth position were partially reduced, indicating that these amide bonds are less important for these intra- or intermolecular interactions. Overall, our study demonstrates that the systematic and sequential replacement of amide bonds by E-alkene represents an efficient way to explore peptide backbones.

The effects of opioids and opioid analogs on animal and human endocrine systems

Opioid abuse has increased in the last decade, primarily as a result of increased access to prescription opioids. Physicians are also increasingly administering opioid analgesics for noncancer chronic pain. Thus, knowledge of the long-term consequences of opioid use/abuse has important implications for fully evaluating the clinical usefulness of opioid medications. Many studies have examined the effect of opioids on the endocrine system; however, a systematic review of the endocrine actions of opioids in both humans and animals has, to our knowledge, not been published since 1984. Thus, we reviewed the literature on the effect of opioids on the endocrine system. We included both acute and chronic effects of opioids, with the majority of the studies done on the acute effects although chronic effects are more physiologically relevant. In humans and laboratory animals, opioids generally increase GH and prolactin and decrease LH, testosterone, estradiol, and oxytocin. In humans, opioids increase TSH, whereas in rodents, TSH is decreased. In both rodents and humans, the reports of effects of opioids on arginine vasopressin and ACTH are conflicting. Opioids act preferentially at different receptor sites leading to stimulatory or inhibitory effects on hormone release. Increasing opioid abuse primarily leads to hypogonadism but may also affect the secretion of other pituitary hormones. The potential consequences of hypogonadism include decreased libido and erectile dysfunction in men, oligomenorrhea or amenorrhea in women, and bone loss or infertility in both sexes. Opioids may increase or decrease food intake, depending on the type of opioid and the duration of action. Additionally, opioids may act through the sympathetic nervous system to cause hyperglycemia and impaired insulin secretion. In this review, recent information regarding endocrine disorders among opioid abusers is presented.

Increase in brain corticosterone concentration and recognition memory impairment following morphine withdrawal in mice

Glucocorticoid hormones evidently affect memory. Morphine withdrawal causes a cognitive deficit and an increase in corticosterone secretion. In the present study brain corticosterone concentrations were determined after morphine withdrawal. Male mice were made dependent by increasing doses of morphine over 3 days. Blood and brain samples were collected following withdrawal induced by injection of naloxone (0.1 mg/kg) or spontaneously after 4 and 14 h. Brain corticosterone was extracted and measured by enzyme immunoassay. Short-term memory was determined in the novel object recognition task, using a 20 min interval between the learning trial and the test trial. In this memory trial, the difference in exploration between a previously seen object and a novel object is taken as an index of memory performance (recognition index, RI). RI in morphine dependent mice undergoing withdrawal was decreased compared to their control group. Brain corticosterone concentrations after naloxone withdrawal or 4 h after spontaneous withdrawal were respectively 22 and 34% greater than control values. Corticosterone concentration was normalized 14 h after the last dose of morphine. The results indicate that increase in brain corticosterone concentration may play an important role in short-term memory impairment following morphine withdrawal.

Mechanisms involved in the antinociception caused by ethanolic extract obtained from the leaves of Melissa officinalis (lemon balm) in mice

The present study examined the antinociceptive effect of the ethanolic extract from Melissa officinalis L. and of the rosmarinic acid in chemical behavioral models of nociception and investigates some of the mechanisms underlying this effect. The extract (3-1000 mg/kg), given orally (p.o.) 1 h prior to testing, produced dose-dependent inhibition of acetic acid-induced visceral pain, with ID50 value of 241.9 mg/kg. In the formalin test, the extract (30-1000 mg/kg, p.o.) also caused significant inhibition of both, the early (neurogenic pain) and the late (inflammatory pain), phases of formalin-induced licking. The extract (10-1000 mg/kg, p.o.) also caused significant and dose-dependent inhibition of glutamate-induced pain, with ID50 value of 198.5 mg/kg. Furthermore, the rosmarinic acid (0.3-3 mg/kg), given p.o. 1 h prior, produced dose-related inhibition of glutamate-induced pain, with ID50 value of 2.64 mg/kg. The antinociception caused by the extract (100 mg/kg, p.o.) in the glutamate test was significantly attenuated by intraperitoneal (i.p.) treatment of mice with atropine (1 mg/kg), mecamylamine (2 mg/kg) or l-arginine (40 mg/kg). In contrast, the extract (100 mg/kg, p.o.) antinociception was not affected by i.p. treatment with naloxone (1 mg/kg) or D-arginine (40 mg/kg). It was also not associated with non-specific effects, such as muscle relaxation or sedation. Collectively, the present results suggest that the extract produced dose-related antinociception in several models of chemical pain through mechanisms that involved cholinergic systems (i.e. through muscarinic and nicotinic acetylcholine receptors) and the L-arginine-nitric oxide pathway. In addition, the rosmarinic acid contained in this plant appears to contribute for the antinociceptive property of the extract. Moreover, the antinociceptive action demonstrated in the present study supports, at least partly, the ethnomedical uses of this plant.

Response of substances co-expressed in hypothalamic magnocellular neurons to osmotic challenges in normal and Brattleboro rats

The intention of this review is to emphasize the current knowledge about the extent and importance of the substances co-localized with magnocellular arginine vasopressin (AVP) and oxytocin (OXY) as potential candidates for the gradual clarification of their actual role in the regulation of hydromineral homeostasis. Maintenance of the body hydromineral balance depends on the coordinated action of principal biologically active compounds, AVP and OXY, synthesized in the hypothalamic supraoptic and paraventricular nuclei. However, on the regulation of water-salt balance, other substances, co-localized with the principal neuropetides, participate. These can be classified as (1) peptides co-localized with AVP or OXY with unambiguous osmotic function, including angiotensin II, apelin, corticotropin releasing hormone, and galanin and (2) peptides co-localized with AVP or OXY with an unknown role in osmotic regulation, including cholecystokinin, chromogranin/secretogranin, dynorphin, endothelin-1, enkephalin, ferritin protein, interleukin 6, kininogen, neurokinin B, neuropeptide Y, vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, TAFA5 protein, thyrotropin releasing hormone, tyrosine hydroxylase, and urocortin. In this brief review, also the responses of these substances to different hyperosmotic and hypoosmotic challenges are pointed out. Based on the literature data published recently, the functional implication of the majority of co-localized substances is still better understood in non-osmotic than osmotic functional circuits. Brattleboro strain of rats that does not express functional vasopressin was also included in this review. These animals suffer from chronic hypernatremia and hyperosmolality, accompanied by sustained increase in OXY mRNA in PVN and SON and OXY levels in plasma. They represent an important model of animals with constantly sustained osmolality, which in the future, will be utilizable for revealing the physiological importance of biologically active substances co-expressed with AVP and OXY, involved in the regulation of plasma osmolality.

Is it all about sex? Acupuncture for the treatment of pain from a biological and gender perspective

Pain is a unique personal experience showing variability where gender and sex related effects might contribute. The mechanisms underlying the differences between women and men are currently unknown but are likely to be complex and involving interactions between biological, sociocultural and psychological aspects. In women, painful experimental stimuli are generally reported to produce a greater intensity of pain than in men. Clinical pain is often reported with higher severity and frequency, longer duration, and present in a greater number of body regions in women than in men. Women are also more likely to experience a number of painful conditions such as fibromyalgia, temporomandibular dysfunction, migraine, rheumatoid arthritis and irritable bowel syndrome. With regard to biological factors, quantitative as well as qualitative differences in the endogenous pain inhibitory systems have been implicated, as well as an influence of gonadal hormones. Psychosocial factors like sex role beliefs, pain coping strategies, and pain related expectancies may also contribute to the differences. Being exposed to repeated painful visceral events (eg menses, labour) during life may contribute to an increased sensitivity to, and greater prevalence of, pain among women. When assessing the outcome of pharmacological and non-pharmacological therapies in pain treatment, the factors of gender and sex should be taken into account as the response to an intervention may differ. Preferably, treatment recommendations should be based on studies using both women and men as the norm. Due to variability in results, findings from animal studies and experiments in healthy subjects should be interpreted with care.

Enkephalin elevations contribute to neuronal and behavioral impairments in a transgenic mouse model of Alzheimer's disease

The enkephalin signaling pathway regulates various neural functions and can be altered by neurodegenerative disorders. In Alzheimer's disease (AD), elevated enkephalin levels may reflect compensatory processes or contribute to cognitive impairments. To differentiate between these possibilities, we studied transgenic mice that express human amyloid precursor protein (hAPP) and amyloid-beta (Abeta) peptides in neurons and exhibit key aspects of AD. Met-enkephalin levels in neuronal projections from the entorhinal cortex and dentate gyrus (brain regions important for memory that are affected in early stages of AD) were increased in hAPP mice, as were preproenkephalin mRNA levels. Genetic manipulations that exacerbate or prevent excitotoxicity also exacerbated or prevented the enkephalin alterations. In human AD brains, enkephalin levels in the dentate gyrus were also increased. In hAPP mice, enkephalin elevations correlated with the extent of Abeta-dependent neuronal and behavioral alterations, and memory deficits were reduced by irreversible blockade of mu-opioid receptors with the antagonist beta-funaltrexamine. We conclude that enkephalin elevations may contribute to cognitive impairments in hAPP mice and possibly in humans with AD. The therapeutic potential of reducing enkephalin production or signaling merits further exploration.

Electromagnetic millimeter wave induced hypoalgesia: frequency dependence and involvement of endogenous opioids

Millimeter wave treatment (MMWT) is based on the systemic biological effects that develop following local skin exposure to low power electromagnetic waves in the millimeter range. In the present set of experiments, the hypoalgesic effect of this treatment was analyzed in mice. The murine nose area was exposed to MMW of "therapeutic" frequencies: 42.25, 53.57, and 61.22 GHz. MMWT-induced hypoalgesia was shown to be frequency dependent in two experimental models: (1) the cold water tail-flick test (chronic non-neuropathic pain), and (2) the wire surface test (chronic neuropathic pain following unilateral constriction injury to the sciatic nerve). Maximum hypoalgesic effect was obtained when the frequency was 61.22 GHz. Other exposure parameters were: incident power density = 13.3 mW/cm(2), duration of each exposure = 15 min. Involvement of delta and kappa endogenous opioids in the MMWT-induced hypoalgesia was demonstrated using selective blockers of delta- and kappa-opioid receptors and the direct ELISA measurement of endogenous opioids in CNS tissue. Possible mechanisms of the effect and the perspectives of the clinical application of MMWT are discussed.

Behavioral actions of urotensin-II

Urotensin-II (U-II) and urotensin-II-related peptide (URP) have been identified as the endogenous ligands of the orphan G-protein-coupled receptor GPR14 now renamed UT. The occurrence of U-II and URP in the central nervous system, and the widespread distribution of UT in the brain suggest that U-II and URP may play various behavioral activities. Studies conducted in rodents have shown that central administration of U-II stimulates locomotion, provokes anxiety- and depressive-like states, enhances feeding activity and increases the duration of paradoxical sleep episodes. These observations indicate that, besides the endocrine/paracrine activities of U-II and URP on cardiovascular and kidney functions, these peptides may act as neurotransmitters and/or neuromodulators to regulate various neurobiological activities.

Opioid-induced regulation of µ-opioid receptor gene expression in the MCF-7 breast cancer cell line

The aim of the study was to investigate the presence of opioid receptor types in human breast adenocarcinoma MCF-7 cells and to characterize the changes in MOR expression induced by opioid agonist and antagonist treatment. We have shown that all three types of opioid receptors, but predominantly MOR, are expressed in MCF-7 cells. Selective MOR agonists, morphine, endomorphin-1, and endomorphin-2 downregulated MOR mRNA levels in a concentration- and time-dependent manner, but the effect produced by endomorphins was much stronger. Downregulation was blocked by the opioid antagonist naloxone. Naloxone alone produced a slight increase in MOR gene expression. Immunoblotting with antiserum against MOR-1 confirmed these results at the protein level. The results of our study indicate that, in MCF-7 cells, MOR gene expression is downregulated by opioid agonists and upregulated by opioid antagonists. We propose that the opioid-induced regulation of MOR mRNA expression is mediated by reduced binding of the transcription factors NFκB and AP-1 to the promoter region on the MOR gene.

Dynorphin and the pathophysiology of drug addiction

Drug addiction is a chronic relapsing disease in which drug administration becomes the primary stimulus that drives behavior regardless of the adverse consequence that may ensue. As drug use becomes more compulsive, motivation for natural rewards that normally drive behavior decreases. The discontinuation of drug use is associated with somatic signs of withdrawal, dysphoria, anxiety, and anhedonia. These consequences of drug use are thought to contribute to the maintenance of drug use and to the reinstatement of compulsive drug use that occurs during the early phase of abstinence. Even, however, after prolonged periods of abstinence, 80-90% of human addicts relapse to addiction, suggesting that repeated drug use produces enduring changes in brain circuits that subserve incentive motivation and stimulus-response (habit) learning. A major goal of addiction research is the identification of the neural mechanisms by which drugs of abuse produce these effects. This article will review data showing that the dynorphin/kappa-opioid receptor (KOPr) system serves an essential function in opposing alterations in behavior and brain neurochemistry that occur as a consequence of repeated drug use and that aberrant activity of this system may not only contribute to the dysregulation of behavior that characterizes addiction but to individual differences in vulnerability to the pharmacological actions of cocaine and alcohol. We will provide evidence that the repeated administration of cocaine and alcohol up-regulates the dynorphin/KOPr system and that pharmacological treatments that target this system may prove effective in the treatment of drug addiction.

Essential role of mu opioid receptor in the regulation of delta opioid receptor-mediated antihyperalgesia

Analgesic effects of delta opioid receptor (DOR) -selective agonists are enhanced during persistent inflammation and arthritis. Although the underlying mechanisms are still unknown, membrane density of DOR was shown to be increased 72 h after induction of inflammation, an effect abolished in mu opioid receptor (MOR) -knockout (KO) mice [Morinville A, Cahill CM, Kieffer B, Collier B, Beaudet A (2004b) Mu-opioid receptor knockout prevents changes in delta-opioid receptor trafficking induced by chronic inflammatory pain. Pain 109:266-273]. In this study, we demonstrated a crucial role of MOR in DOR-mediated antihyperalgesia. Intrathecal administration of the DOR selective agonist deltorphin II failed to induce antihyperalgesic effects in MOR-KO mice, whereas it dose-dependently reversed thermal hyperalgesia in wild-type mice. The antihyperalgesic effects of deltorphin II were blocked by naltrindole but not d-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP) suggesting that this agonist was mainly acting through DOR. SNC80-induced antihyperalgesic effects in MOR-KO mice were also attenuated as compared with littermate controls. In contrast, kappa opioid receptor knockout did not affect deltorphin II-induced antihyperalgesia. As evaluated using mice lacking endogenous opioid peptides, the regulation of DOR's effects was also independent of beta-endorphin, enkephalins, or dynorphin opioids known to be released during persistent inflammation. We therefore conclude that DOR-mediated antihyperalgesia is dependent on MOR expression but that activation of MOR by endogenous opioids is probably not required.

Orexigenic peptides and alcohol intake: differential effects of orexin, galanin, and ghrelin

BACKGROUND

The question is which hypothalamic systems for food intake might play a role in ethanol intake and contribute to alcohol abuse. The peptide orexin was found to exhibit similar properties to galanin in its relation to dietary fat and may therefore be similar to galanin in having a stimulatory effect on alcohol intake.

METHODS

Rats were trained to drink 10% ethanol, implanted with brain cannulas, and then injected in the paraventricular nucleus (PVN), lateral hypothalamus (LH), or nucleus accumbens (NAc) with galanin, orexin-A, and for comparison, ghrelin. Ethanol, food, and water intake were measured at 1, 2, and 4 hours postinjection.

RESULTS

In the PVN, both orexin and galanin significantly increased ethanol intake, whereas ghrelin increased food intake. In the LH, orexin again induced ethanol intake, while ghrelin increased eating. In the NAc, orexin failed to influence ethanol intake but did stimulate food intake.

CONCLUSIONS

In ethanol-drinking rats, injection of orexin or galanin into the appropriate locus in the hypothalamus induced significant ethanol intake instead of food intake. Ghrelin, as a positive control, failed to influence ethanol intake at the same hypothalamic sites. In the NAc, as an anatomical control, orexin augmented eating but not ethanol intake. Thus orexin and galanin in the hypothalamus selectively stimulated ethanol intake at sites where other studies have shown that both ethanol and fat increase expression of the endogenous peptides. Thus, a neural circuit that evolved with the capability to augment food intake is apparently co-opted by ethanol and may serve as a potential positive feedback circuit for alcohol abuse.

Distinct effects of individual opioids on the morphology of spines depend upon the internalization of mu opioid receptors

This study has examined the relationship between the effects of opioids on the internalization of mu opioid receptors (MORs) and the morphology of dendritic spines. Several opioids (morphine, etorphine, DAMGO or methadone) were applied to cultured hippocampal neurons. Live imaging and biochemical techniques were used to examine the dynamic changes in MOR internalization and spine morphology. This study reveals that MOR internalization can regulate opioid-induced morphological changes in dendritic spines: (1) Chronic treatment with morphine, which induced minimal receptor internalization, caused collapse of dendritic spines. In contrast, "internalizing" opioids such as DAMGO and etorphine induced the emergence of new spines. It reveals that opioid-induced changes in spines vary greatly depending on how the applied opioid agonist affects MOR internalization. (2) The blockade of receptor internalization by dominant negative mutant of dynamin, K44E, reversed the effects of DAMGO and etorphine. It indicates that receptor internalization is necessary for the distinct effects of DAMGO and etorphine on spines. (3) In neurons that were cultured from MOR knock-out mice and had been co-transfected with DsRed and MOR-GFP, morphine caused collapse of spines whereas DAMGO induced emergence of new spines, indicating that opioids can alter the structure of spines via postsynaptic MORs. (4) Methadone at a low concentration induced minimal internalization and had effects that were similar to morphine. At a high concentration, methadone induced robust internalization and had effects that are opposite to morphine. The concentration-dependent opioid-induced changes in dendritic spines might also contribute to the variation in the effects of individual opioids.

In vitro characterization of the effects of endomorphin 1 and 2, endogenous ligands for μ-opioid receptors, on mouse colonic motility

The effects of endomorphin 1 (EM1) and 2 (EM2) in colonic motility remain unknown. We investigated the effects and mechanisms of these endomorphins (EMs) on the colonic motility in vitro by applying various neural blocking agents and various opioid receptor antagonists. EMs (10(-9) to 10(-6)M) displayed significant stimulatory effects on the basal tonus or spontaneous activity of mouse colon but not of stomach and small intestine. It is noteworthy that the contractile actions of EMs varied slightly among different regions of colonic longitudinal muscle layers, whereas the contractile responses induced by EMs were significantly different among different regions of circular muscle layers. EMs-induced longitudinal or circular muscle contractions were not significantly affected by atropine, N(G)-nitro-l-arginine methyl ester, phentolamine, propranolol and methysergide. Tetrodotoxin, indomethacin and naloxone completely abolished the EMs-induced colonic contractions. Surprisingly, EMs (10(-7)M)-induced longitudinal muscle contractions were significantly attenuated by nor-binaltorphimine (3x10(-6)M). By contrast, pretreatment with naltrindole (10(-6)M) did not significantly affect EMs-induced longitudinal or circular muscle contractions. Interestingly, the circular muscle contractions in response to EM2 (10(-7)M) were not fully blocked by beta-funaltrexamine (6x10(-6)M). Naloxonazine (10(-6)M) almost fully antagonized the EMs-induced longitudinal or circular muscle contractions, and these effects could be only partially reversed by extensive washing. All the results indicated that the mechanisms and sites of actions of EMs were region-specific. Furthermore, these findings showed that the activation of multiple subtypes of opioid receptors, possibly including mu(1) (naloxonazine-sensitive), mu(2) and even other forms of muORs (beta-FNA-insensitive), was required for EMs-induced mouse colonic motility.

Opioid peptides as possible neuromodulators in the frog peripheral nerve system

Sciatic nerves of the frog Rana ridibunda were examined for the effects of applied opioid peptide, methionine-enkephalin, synthetic enkephalin analogue, leucine-enkephalin-NH(2) and opiate antagonist, naloxone. The effect of both peptides in concentrations of 1x10(-6) and 1x10(-5)M or naloxone in 1x10(-6)M was investigated on the action potential parameters using electrophysiological techniques. The isolated nerves were stimulated by single square pulses each of which lasted for 0.5ms at supramaximal strength. Effect of each single dose of peptides at 0min was compared with the remaining time segments. Both peptides produced changes in action potential of nerve when compared with untreated nerves. Methionine-enkephalin in both concentrations reduced the amplitude between 7% and 41% and conduction velocity at about 26-61%. This peptide in the same concentrations prolonged the duration around 12-53% and increased the stimulating voltage at about 9-50%. In contrast, leucine-enkephalin-NH(2) in both concentrations caused a decrease in amplitude between 13% and 48% and in conduction velocity around 20-50%. The same concentrations of this peptide prolonged the duration at about 3-33% and increased the stimulating voltage at about 10-56%, but naloxone in 1x10(-6)M antagonized the responses of both peptides over 75%. The results indicate that both opioid peptides produce changes in action potential parameters in frog peripheral nerve system and these changes are partially reversed by naloxone.

Reactivity and oxidative potential of fructose and glucose in enkephalin-sugar model systems

The reactions of Leu- and Met-enkephalin (Tyr-Gly-Gly-Phe-Leu/Met) with fructose resulted in the parallel formation of Heyns compounds (N-peptidyl-D-mannosamine and -D-glucosamine) and sugar-peptide generated imidazolidinone diastereomers. Glucose showed higher level of reactivity than fructose with respect to the extent of glycated product formation. The presence of fructose in the incubation mixtures makes Met residue more susceptible to oxidation than glucose.

Dexketoprofen-induced antinociception in animal models of acute pain: Synergy with morphine and paracetamol

The antinociceptive activity of dexketoprofen was studied in mice using the acetic acid writhing test (acute tonic pain), the tail flick test (acute phasic pain) and the formalin assay (inflammatory pain). Isobolographic analysis was used to study the antinociceptive interactions between morphine and paracetamol co-administered with dexketoprofen. In the writhing test, the intraperitoneal administration of dexketoprofen or ketoprofen resulted in parallel dose-response curves with equal efficacy, but higher relative potency for dexketoprofen. In the tail flick test, the curves were parallel with similar efficacy and potency. The administration of morphine or paracetamol in both tests resulted in dose-response curves not parallel with that of dexketoprofen, which showed a potency between morphine and paracetamol. In the formalin assay, the antinociceptive activity of morphine during phase I was 122, 295 and 1695 times higher than dexketoprofen, ketoprofen and paracetamol, respectively. Isobolographic analysis demonstrated that the combination of sub-analgesic doses of dexketoprofen with morphine or with paracetamol was strongly synergic in all three tests. Synergistic drug combinations should improve effective pharmacological treatment of pain, minimizing drug specific adverse effects. These findings are undoubtedly worthy of additional controlled clinical trials in severe pain syndromes.

Long-term feed intake regulation in sheep is mediated by opioid receptors

These experiments were conducted to determine if 1) syndyphalin-33 (SD33), a mu-opioid receptor ligand, affects feed intake; 2) SD33 effects on feed intake are mediated by actions on opioid receptors; and 3) its activity can counteract the reduction in feed intake associated with administration of bacterial endotoxin. In Exp. 1, 5 mixed-breed, castrate male sheep were housed indoors in individual pens. Animals had ad libitum access to water and concentrate feed. Saline (SAL; 0.9% NaCl) or SD33 (0.05 or 0.1 micromol/kg of BW) was injected i.v., and feed intake was determined at 2, 4, 6, 8, 24, and 48 h after the i.v. injections. Both doses of SD33 increased (at least P < 0.01) feed intake at 48 h relative to saline. In Exp. 2, SAL + SAL, SAL + SD33 (0.1 micromol/kg of BW), naloxone (NAL; 1 mg/kg of BW) + SAL, and NAL + SD33 were injected i.v. Food intake was determined as in Exp. 1. The SAL + SD33 treatment increased (P = 0.022) feed intake at 48 h relative to SAL + SAL. The NAL + SAL treatment reduced (at least P < 0.01) feed intake at 4, 6, 8, 24, and 48 h, whereas the combination of NAL and SD33 did not reduce feed intake at 24 (P = 0.969) or 48 h (P = 0.076) relative to the saline-treated sheep. In Exp. 3, sheep received 1 of 4 treatments: SAL + SAL, SAL + 0.1 micromol of SD33/kg of BW, 0.1 microg of lipopolysaccharide (LPS)/kg of BW + SAL, or LPS + SD33, and feed intake was monitored as in Exp. 1. Lipopolysaccharide suppressed cumulative feed intake for 48 h (P < 0.01) relative to saline control, but SD33 failed to reverse the reduction in feed intake during this period. These data indicate that SD33 increases feed intake in sheep after i.v. injection, and its effects are mediated via opioid receptors. However, the LPS-induced suppression in feed intake cannot be overcome by the opioid receptor ligand, SD33.

Unique neuronal functions of cathepsin L and cathepsin B in secretory vesicles: biosynthesis of peptides in neurotransmission and neurodegenerative disease

Proteases are required for the production of peptide neurotransmitters and toxic peptides in neurodegenerative diseases. Unique roles of the cysteine proteases cathepsin L and cathepsin B in secretory vesicles for the production of biologically active peptides have been demonstrated in recent studies. Secretory vesicle cathepsin L participates in the proteolytic conversion of proenkephalin into the active enkephalin, an opioid peptide neurotransmitter that mediates pain relief. Moreover, recent findings provide evidence that cathepsin B in regulated secretory vesicles participates in the production of toxic beta-amyloid peptides that are known to accumulate extracellularly in Alzheimer's disease brains. The neurobiological functions of cathepsins L and B demonstrate that these secretory vesicle cysteine proteases produce biologically active peptides. These results demonstrate newly identified roles for cathepsins L and B in neurosecretory vesicles in the production of biologically active peptides.