Endogenous opiates: 1985

Mild exercise suppresses exacerbation of dermatitis by increasing cleavage of the β-endorphin from proopiomelanocortin in NC/Nga mice

This study investigated the mechanism by which the strength and weakness of exercise stress affects the skin symptoms of atopic dermatitis (AD). Specific pathogen-free (SPF) and conventional NC/Nga mice were used. Conventional mice, but not the SPF, spontaneously develop dermal symptoms similar to that of patients with AD. There were two types of stress, mild (20 m/min for 60 min) or strong exercise (25 m/min for 90 min), using a treadmill four times per day. The symptom of the conventional group were strongly exacerbated by strong exercise but ameliorated by mild exercise. The plasma concentrations of α-melanocyte stimulating hormone (α-MSH) and the expression of melanocortin receptor-1 in skin elevated after strong exercise but decreased after mild exercise. The plasma levels of β-endorphin and the expression of µ-opioid receptor in skin were increased by mild exercise. In addition, the expression of prohormone convertase (PC) 1/3, PC2 and carboxypeptidase E (CPE) in pituitary gland were higher in the conventional group than in the SPF group. The level of PC2 was suppressed by mild exercise in the conventional groups, and elevated further by strong exercise. The level of PC1/3 becomes higher with the increase of the exercise load. On the other hand, the expression of the CPE was further increase by mild exercise but suppressed by strong exercise. These observations suggested that exercise-induced stress significantly affect the symptoms of AD in a pivotal manner depending on the levels of α-MSH and β-endorphin, and the expression of pituitary PC2 and CPE.

Mild exercise suppresses exacerbation of dermatitis by increasing cleavage of the β-endorphin from proopiomelanocortin in NC/Nga mice

This study investigated the mechanism by which the strength and weakness of exercise stress affects the skin symptoms of atopic dermatitis (AD). Specific pathogen-free (SPF) and conventional NC/Nga mice were used. Conventional mice, but not the SPF, spontaneously develop dermal symptoms similar to that of patients with AD. There were two types of stress, mild (20 m/min for 60 min) or strong exercise (25 m/min for 90 min), using a treadmill four times per day. The symptom of the conventional group were strongly exacerbated by strong exercise but ameliorated by mild exercise. The plasma concentrations of α-melanocyte stimulating hormone (α-MSH) and the expression of melanocortin receptor-1 in skin elevated after strong exercise but decreased after mild exercise. The plasma levels of β-endorphin and the expression of µ-opioid receptor in skin were increased by mild exercise. In addition, the expression of prohormone convertase (PC) 1/3, PC2 and carboxypeptidase E (CPE) in pituitary gland were higher in the conventional group than in the SPF group. The level of PC2 was suppressed by mild exercise in the conventional groups, and elevated further by strong exercise. The level of PC1/3 becomes higher with the increase of the exercise load. On the other hand, the expression of the CPE was further increase by mild exercise but suppressed by strong exercise. These observations suggested that exercise-induced stress significantly affect the symptoms of AD in a pivotal manner depending on the levels of α-MSH and β-endorphin, and the expression of pituitary PC2 and CPE.

Transepidermal water loss, serum IgE and beta-endorphin as important and independent biological markers for development of itch intensity in atopic dermatitis

BACKGROUND

Although itch is the predominant symptom of atopic dermatitis (AD), it is poorly characterized and subjective. The objective assessment of itch intensity is important for treatment and follow-up in patients with AD.

OBJECTIVES

To determine what objective clinical parameter(s) could be used as biomarker(s) for itch intensity in patients with AD.

METHODS

This is a retrospective and cross-sectional study. Seventy-five patients, aged 7 months-49 years with equal sex ratio, were enrolled in 2000 according to criteria proposed by Hanifin and Rajka. Thirty-five age- and sex-matched subjects who visited the dermatological clinic but were otherwise healthy served as controls. Subjective itch intensity was divided into four grades of severity. Disease severity was measured by SCORAD index, which also includes itch intensity as part of the measurement. Transepidermal water loss (TEWL) and skin surface pH were measured by noninvasive methods in clinically normal skin on the forearm. Serum beta-endorphin and vasoactive intestinal peptide (VIP) were determined by radioimmunoassay. Ordinal logistic regression was used to assess the trend of the subjective itch intensity and SCORAD index by serum IgE, beta-endorphin, VIP, TEWL and skin pH.

RESULTS

There were significant trends for itch intensity with IgE, beta-endorphin and TEWL. After adjustment for sex, age and other variables, the odds ratio (OR) for itch intensity by log IgE, beta-endorphin and TEWL was 2.103 [95% confidence interval (CI) 1.222-3.618], 1.100 (95% CI 1.005-1.203) and 1.081 (95% CI 1.009-1.158), respectively. The OR for disease severity by log IgE, beta-endorphin and TEWL was 2.250 (95% CI 1.149-4.407), 1.156 (95% CI 1.086-1.231) and 1.071 (95% CI 0.971-1.182), respectively. In contrast, there was no association between serum VIP concentration and itch intensity.

CONCLUSIONS

Beta-endorphin and IgE are both useful biomarkers for itch and disease severity in patients with AD, while TEWL is a good biomarker for itch intensity. These biomarkers provide a way to assess the itch intensity in patients with AD.

beta-Endorphin as a regulator of human hair follicle melanocyte biology

The pro-opiomelanocortin (POMC)-derived peptides, alpha-melanocyte-stimulating hormone, and adrenocorticotropic hormone, are important mediators of human skin pigmentation via action at the melanocortin-1 receptor. Recent data suggests that such a regulatory role also exists for the endogenous opiate, beta-endorphin (beta-END). A role for this beta-END in the regulation of follicular pigmentation, however, has not been determined. This study was designed to examine the involvement of the beta-END/mu-opiate receptor system in human follicular melanocyte biology. We employed RT-PCR, and immunohisto/cytochemistry and immunoelectron microscopy using beta-END and mu-opiate receptor specific antibodies and a functional role for beta-END was assessed by direct stimulation with the peptide. This study has demonstrated that human hair follicle melanocytes (HFM) express mRNA for the mu-opiate receptor and POMC. Furthermore, beta-END and its high affinity mu-opiate receptor are expressed at the protein level in glycoprotein100-positive follicular melanocytes and as a function of their anatomic location and differentiation status during the hair growth cycle. Functional studies revealed that beta-END is a modifier of HFM phenotype via its ability to upregulate melanogenesis, dendricity, and proliferation. These findings suggest a new regulatory role for beta-END in human HFM biology, providing a new research direction into the fundamental regulation of human hair pigmentation.

Characterization of bioactive peptides in bovine adrenal medulla by a combination of fast HPLC and ESI-MS

A method based upon a combination of fast high-performance liquid chromatography (HPLC) and electrospray ionization (ESI)-mass spectrometry (MS) is developed for the analysis of bioactive peptides in bovine adrenal medulla. The fast HPLC uses a short column (33 mm x 4.6 mm) packed with nonporous silica-based C-18 stationary phase. Prior to HPLC separation, the medulla was homogenized and the peptide-rich fraction was isolated from it by solid-phase extraction. In-source collision-induced dissociation and tandem MS were used to obtain the sequence of the suspected peptides. Several peptides, including Met-Enk, Leu-Enk, Leu-Enk-Lys, bovine adrenal medullary (BAM)-12 (Met-Enk-RRVGRPE), Leu-Enk-Arg, and YGGT, were unambiguously identified. The first four peptides are the products of proenkephalin A precursor protein and Leu-Enk-Arg belongs to the dynorphin family and is derived from proenkephalin B (prodynorphin) precursor. The database search revealed that YGGT is a part of the sequence of five different precursor proteins.

Functional continuum of regulatory peptides (RPs): vector model of RP-effects representation

During the past decades, bioactive (regulatory) peptides have been identified as the major players in the regulation of many important biological processes. Dozens of peptides have found their application as pharmaceutical agents, which further stimulated research in this field making it one of the most rapidly developing areas on the edge of biological science and medicine. However, the fast accumulation of enormous amounts of experimental data has revealed a great difficulty in their analysis and demanded the development of a systematic approach for generalization of the obtained information. We propose a new computer-based algorithm for studying biological activities of regulatory peptides and their groups based on their representation as vectors in n -dimensional functional space. Our method allows the rapid analysis of databases containing thousands of polyfunctional regulatory peptides with overlapping spectra of physiological activity. The described method permits to perform several types of correlations which, when applied to the large databases, could reveal new important information about the system of regulatory peptides. It can select the groups of peptides with similar physiological role (peptide constellations) and search for the optimal peptide combinations with predetermined spectrum of effects and minimal side effects for their further pharmacological application. It can also reveal the role of regulatory peptides in induction of chain physiological reactions.

beta-endorphin stimulates cytokeratin 16 expression and downregulates mu-opiate receptor expression in human epidermis

It has been reported that opioid peptides modulate the differentiation of normal human keratinocytes and that mu-opiate receptors are expressed in human epidermis. The regulation of keratinocyte differentiation is particularly important in psoriasis, and one of the markers for hyperproliferative and differentiating skin diseases is cytokeratin 16. The finding that the endogenous mu-opiate receptor ligand beta-endorphin is increased in serum of patients with psoriasis indicates that the mu-opiate system may play an important role in the pathophysiology of the skin. In this study, we addressed the question whether there is a link between mu-opiate receptor regulation and cytokeratin 16 expression in normal and psoriatic skin. Firstly, we demonstrate that beta-endorphin concentrations between 16 and 1000 nM significantly downregulate mu-opiate receptor expression in epidermis of cultured human skin after 48 h. Secondly, we show that beta-endorphin regulates cytokeratin 16 expression in the epidermis of skin organ cultures exposed to 41-125 nM beta-endorphin for 48 h, leading to elevated cytokeratin 16 production. As expected, the expression of cytokeratin 16 was detected primarily in the suprabasal layer. The same pattern was observed in psoriatic lesional skin, i.e., mu-opiate receptor expression was significantly downregulated and cytokeratin 16 expression upregulated. These results suggest that the mu-opiate receptor system and its ligand beta-endorphin are involved in the pathogenesis of psoriasis, especially in terms of differentiation.

Food cravings, endogenous opioid peptides, and food intake: a review

Extensive research indicates a strong relationship between endogenous opioid peptides (EOPs) and food intake. In the present paper, we propose that food cravings act as an intervening variable in this opioid-ingestion link. Specifically, we argue that altered EOP activity may elicit food cravings which in turn may influence food consumption. Correlational support for this opioidergic theory of food cravings is provided by examining various clinical conditions (e.g. pregnancy, menstruation, bulimia, stress, depression) which are associated with altered EOP levels, intensified food cravings, and increased food intake.

Binding of [3H][D-Ala2, MePhe4, Gly-ol5] enkephalin, [3H][D-Pen2, D-Pen5]enkephalin, and [3H]U-69,593 to airway and pulmonary tissues of normal and sensitized rats

The role of endogenous opioid peptides in the regulation of bronchomotor tone, as well as in the pathophysiology of asthma is uncertain. We have studied the binding of highly selective [3H]labeled ligands of mu-([D-Ala2, MePhe4, Gly-ol5]enkephalin; DAMGO), delta ([D-Pen2, D-Pen5]enkephalin; DPDPE), and kappa-(U-69,593) opioid receptors to membranes of trachea, main bronchus, lung parenchyma and pulmonary artery obtained from normal (unsensitized) and actively IgE-sensitized rats acutely challenged with the specific antigen. [3H]DAMGO, [3H]DPDPE and [3H]U-69,593 bound to membranes of normal and sensitized tissues at a saturable, single high-affinity site. The rank order of receptor densities in normal tissues was delta- > or = kappa- > or = mu-, with lung parenchyma exhibiting the greatest binding capacity for delta- and mu- receptors compared to the other regions examined. The Kd values showed small differences between ligands and regions tested. The mu- and delta-opioid receptor densities were decreased in sensitized main bronchus and lung parenchyma, respectively, compared to normal tissues. By contrast, kappa-opioid receptor density was augmented in sensitized lung parenchyma but an increase in Kd values was also observed. These differential changes in the density and affinity of opioid receptor types may be related to alterations in endogenous opioid peptides during the process of sensitization.

Alterations of beta-endorphin-like immunoreactivity in CSF following behavioral training using a passive avoidance procedure

The central opioid system may have an important influence on memory processes. In view of this, the concentration of beta-endorphin-like immunoreactivity (beta-ELIR) in cerebrospinal fluid (CSF) was measured by a radioimmunoassay in rats trained in a passive avoidance procedure. The beta-ELIR in CSF was examined immediately, 2, 5, 10, and 30 min after the learning trial in which rats were exposed to footshock (0, 0.25, or 1.0 mA for 3 s). Avoidance latency and beta-ELIR in CSF were examined 24 and 120 h after the learning trial. The beta-ELIR in CSF was increased at 5 min after the learning trial in rats exposed to footshock of 0.25 mA. The beta-ELIR in CSF was elevated at 5 and 10 min, followed by a significant decrease at 30 min after the learning trial in rats exposed to a footshock of 1.0 mA. Thus, although an increase in beta-ELIR in CSF was not, the duration of the increase was, related to the shock intensity. Interestingly, a decrease followed the increase in beta-ELIR in CSF which was significant only in rats exposed to the high shock intensity. Avoidance latencies were enhanced in a shock intensity-dependent manner at both 24 and 120 h retention tests. No change in beta-ELIR in CSF was found during retention trials. The results suggest that behavioral manipulations alter beta-ELIR in CSF. An increase in beta-ELIR in CSF may be highly associated with stressful and emotional responses during behavioral training.

Effect of dermorphin on thermoregulation in rats at selected ambient temperatures

Intraperitoneal administration of dermorphin caused dose-dependent changes in rats core temperature and tail skin temperature (indicative of compensatory thermoregulatory vasoreactions in rats). The character of these changes depended strongly on the environmental temperature at which the inversion of the dermorphin-induced thermoregulatory effect was observed. In the cold environment (4-7 degrees C) dermorphin caused a significant, stable, dose-dependent hypothermia. In the thermoneutral environment (27-28 degrees C) dermorphin also caused hypothermia, but this effect was less pronounced. In the hot environment (31-32 degrees C) dermorphin caused hyperthermia. Dermorphin-induced changes in tail skin temperature indicate that dermorphin suppresses the thermoregulatory peripheral compensatory vasomotor reactions. Pretreatment with naloxone attenuated dermorphin-induced effects on core temperature and partially enhanced vasomotor effects of dermorphin. The data obtained indicate that dermorphin affects the core temperature regulation via mu-opiate receptors, whereas vasomotor effects of the peptide are probably mediated via naloxone-insensitive receptors.

Differential effects of intrahypothalamic administration of opioids on food intake in naive and tolerant rats

We investigated the effects of intrahypothalamic administrations of the opioid agonists morphine (MOR) and ketocyclazocine (KCZ) and antagonists naltrexone (NALTX) and Mr2266 on food intake (FI) during light and dark phases of the diurnal cycle, after acute or chronic administration in rats. Acute intralateral hypothalamic (LH) administration of MOR or KCZ (1 microgram/rat) enhanced FI during dark and light phases, respectively, whereas intraventromedial hypothalamic (VMH) injections resulted in moderate hyperphagia during dark phases by both mu and kappa agonists. The receptor specificity was evident from blockade of the responses to MOR or KCZ by the respective antagonists NALTX and Mr2266. After repeated administrations of MOR and KCZ, FI responses to the test dose of these agonists injected in LH were modulated in opposite directions. However, the adaptative changes in FI after intra-VMH injection of KCZ were similar to those seen with MOR. These results are discussed in light of a differential opioid receptor involvement and their possible functional interactions within the hypothalamus during food intake.

The fetal expression of proenkephalin mRNAs and Met-enkephalin immunoreactivity in the hypothalamoseptal tract and adjacent hypothalamic areas of the guinea pig brain

The development of the enkephalinergic hypothalamoseptal tract in the guinea pig brain was studied from embryonic day 30 until birth. Proenkephalin (PE) mRNAs were detected in the hypothalamic magnocellular dorsal nucleus (MDN) by in situ hybridization with a synthetic 35S-labeled oligonucleotide. The Met-enkephalin-like immunoreactivity (Met-enk-LI) in the MDN and the lateral septum (LS) was detected with antibodies against Met-enkephalin, on adjacent cryostat sections. At the same time, an immunohistochemical study of the arrangement of enkephalinergic axon terminals in the LS at birth was performed at the electron microscopic level. PE mRNAs were first found to be expressed in the MDN at embryonic day 32 (E32) and increased to reach a maximal level at E48. Met-enk-LI was consistently detectable from E38 in numerous perikarya of the MDN as well as in nerve terminals of the LS. The number of Met-enk-LI cells of the MDN decreased after this stage until birth, whereas positive nerve endings in the LS increased. At the electron microscopic level, numerous cell bodies of the LS at birth were consistently surrounded by Met-enk immunoreactive nerve terminals. Cells expressing the PE gene and Met-enk-LI were also observed from E38 to E44 in the periventricular area. Some of these cells were found double-labeled with Met-enkephalin and Somatostatin antisera. The enkephalinergic system of the hypothalamoseptal tract appears at early embryonic stages and may be essential in regulating septal neuronal functions early in gestation. Differing ontogenic onsets of the enkephalinergic hypothalamoseptal and periventricular-median eminence tracts suggest possible developmental and functional differences.

Dynorphin A-(1-13) potently improves scopolamine-induced impairment of passive avoidance response in mice

The effects of intracerebroventricular administration of dynorphin A-(1-13) on scopolamine-induced amnesia were investigated in mice by using a step-down type passive avoidance task. The pre- or post-training, or pre-retention administration of dynorphin A-(1-13)(0.3-10 micrograms) alone failed to affect step-down latency of the passive avoidance response, while scopolamine (1 mg/kg) significantly shortened step-down latency. Dynorphin A-(1-13)(1 microgram) given 15 min before training and retention tests but not immediately after training significantly improved the scopolamine (1 mg/kg)-induced shortening of step-down latency of the passive avoidance response, indicating antiamnesic effects of dynorphin A-(1-13) (1 microgram). A lower dose (1 mg/kg) of the kappa-opioid receptor antagonist, (-)-(1R,5R,9R)-5,9-diethyl-2-(3-furyl-methyl)- 2'-hydroxy-6,7-benzomorphan, reversed the anti-amnesic effects of dynorphin A-(1-13) (1 microgram). These results suggest that the antiamnesic effects of dynorphin A-(1-13) depend on the timing of drug treatments.

The Tyr-MIF-1 family of peptides

A review of research on the Tyr-MIF-1 family of peptides is presented with emphasis on Tyr-MIF-1 and its structure, passage through the blood-brain barrier, and both opiate antagonist and agonist properties. Family members MIF-1, Tyr-W-MIF-1 and Tyr-K-MIF-1 are also included.

Drugs and endogenous ligands compete for receptor occupancy

Dietary and endogenous ligands compete with drugs for receptor occupancy and therefore should be considered during therapeutic interventions and during pharmacokinetic/pharmacodynamic modeling. When disease is the result of an overabundance of these natural ligands, antibodies and/or their Fab fragments may be useful as therapeutic agents to reverse the effects of the natural ligands.

Increased concentration of beta-endorphin in sera of patients with psoriasis and other inflammatory dermatoses

Serum beta-endorphin was quantified by radioimmunoassay in 71 patients with psoriasis vulgaris, other chronic inflammatory skin diseases with T-cell infiltrates [atopic dermatitis (n = 25), and systemic sclerosis (n = 34)], and 100 healthy subjects. The neuropeptide was found to be markedly (P < 0.001) increased in patients with psoriasis (14.4 pg/ml), atopic dermatitis (9.2 pg/ml) and systemic sclerosis (9.8 pg/ml) compared with normal controls (6.1 pg/ml). The highest values of beta-endorphin were found in patients with actively spreading plaque psoriasis (17.3 pg/ml), whereas lesion-free patients showed a reduction in neuropeptide concentration (10.2 pg/ml). The levels were much higher in patients with widespread psoriatic lesions (> 60% body surface; 16.2 pg/ml), which lasted longer than 3 months (15.8 pg/ml), whereas neither the presence of stress nor itching correlated with the serum peptide concentration. Our data suggest that beta-endorphin is produced in psoriatic lesions by inflammatory cells, rather than the increased levels being the result of activation of the pituitary-adrenal axis by chronic stress. The generation of neuropeptide in psoriatic lesions and its antinociceptive effect on the peripheral sensory nerves might explain why pruritus is a relatively rare phenomenon in psoriasis.

Neuropeptides in psoriasis: possible role of beta-endorphin in the pathomechanism of the disease

BACKGROUND

An increased concentration of neuropeptides in psoriatic lesional skin may be responsible for alterations in the neurogenic erythematous response and transmission of stimuli through sensory nerve fibers (sensation of pruritus).

METHODS

Increasing doses of capsaicin from 0.125 to 4 micrograms/cm2 were applied to nonlesional psoriatic skin to establish the minimal dose that induced the substance P-mediated neurogenic response in 30 patients with psoriasis. Plasma beta-endorphin was quantitated in 71 psoriatics by radioimmunoassay using NEN 1251-RIA kit.

RESULTS

The mean beta-endorphin concentration was increased about 2-fold compared to normals, whereas doses of capsaicin needed to induce erythema were higher (1-4 micrograms/cm2) in psoriatics (mainly in patients with type II psoriasis) than in healthy subjects (0.125-0.25 microgram/cm2).

CONCLUSIONS

The data indicate that increased beta-endorphin in psoriatic skin might affect both substance P-mediated neurogenic inflammation and transmission of sensory stimuli due to local antinociceptive effects of this opioid. The differences in the neurogenic response in type I and II psoriasis may be related to the degradation of substance P and beta-endorphin by neutral proteinases in the lesional skin.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

The Human-Animal Relationship in Agriculture and Its Consequences for the Animal

Although human factors are recognized as influential factors affecting the welfare and productivity of farm animals, only limited research has been conducted to identify these important human characteristics and to quantify their effects. During the last 13 years we have studied two apparently important human factors: the attitude and the behaviour of stockpersons towards farm animals.

We have proposed that in intensive animal production systems there are some important sequential relationships between the attitude and behaviour of the stockperson towards farm animals and the behaviour, performance and welfare of farm animals. Basically we have suggested that because a stockperson's behaviour towards animals is largely under volitional control it is strongly influenced by the attitudes and beliefs that the stockperson holds about the animals. Furthermore, the stockperson's behaviour towards animals affects the animals’ fear of humans which, in turn, affects the animals’ productivity and welfare. It is the occurrence of a stress response by animals which are highly fearful of humans which places their productivity and welfare at risk We have published data which strongly support these interrelationships between human attitude and behaviour and animal behaviour, productivity and welfare. This paper reviews this and other research on this subject. The results of research in the pig industry and to a lesser extent, the poultry industries indicate the excellent opportunity which exists to improve animal productivity and welfare by training and selecting stockpersons to have desirable attitudinal and behavioural profiles towards farm animals.

The presence and actions of opioid receptors in bovine pineal gland

The mammalian pineal gland and its main hormone, melatonin, working in conjunction with the hypothalamic suprachiasmatic nuclei, synchronize circadian rhythm and hence refine numerous physiological and biochemical parameters. An interaction among melatonin, opioids, and analgesia has been suspected for many years, since during nighttime, when the level of melatonin is high, the mammals are less sensitive to pain. In studying this phenomenon further, we have identified a single population of opioid receptors in the bovine pineal gland using [3H]-diprenorphine and other ligands. The receptors have a dissociation equilibrium constant (Kd) of 1.36 +/- 0.31 nM and a density (Bmax) of 17.93 +/- 5.22 fmol/mg protein. In competitive experiments, the concentration of drugs required to inhibit 50% of the [3H]-diprenorphine binding (IC50) in descending order of potency was found to be naltrexone > fentanyl > naloxone > nalbuphine > morphine > nalorphine > DAGO > dynorphin > metenkephalin. In order to delineate the function of the opioid system in the pineal gland, the effects of both opioid receptor agonists and antagonists on the basal activity of N-acetyltransferase were examined in the bovine pineal explants in culture. Morphine, an opioid receptor agonist, increased significantly the activity of N-acetyltransferase in a dose-dependent fashion. In addition, the stimulatory effect of morphine was inhibited by naloxone, an opioid receptor antagonist. The results of these studies indicate the existence of pineal opioid receptors, which play a pivotal role in the synthesis of melatonin and its action in synchronizing pineal events.

Endorphins do not affect behavioral stress responses in mice

Effects of endorphins on behavioral stress responses were investigated in mice. For this purpose, we used environment-induced conditioned suppression of motility and forced swimming-induced immobility. The cerebral ventricular administration of alpha-endorphin (2.5-10 nmol), beta-endorphin (0.38-1.5 nmol), or gamma-endorphin (2.5-10 nmol) failed to affect either the environment-induced conditioned suppression of motility or the forced swimming-induced immobility. We have indicated previously that enkephalins attenuate both stress responses and, in contrast, dynorphin potentiates them. These findings indicate that the endorphinergic systems are not responsible for behavioral stress responses and that the role played by endorphins in the present stressful situations may be different from that of enkephalin and dynorphin.

Plasma alpha-melanocyte-stimulating hormone, beta-endorphin, met-enkephalin, and natural killer cell activity in vitiligo

BACKGROUND

The immune system is important in the pathogenesis of vitiligo, and emotional stress has precipitated vitiligo in some patients. Opioid peptides, beta-endorphin, met-enkephalin, and alpha-melanocyte-stimulating hormone (MSH) act as immunomodulators, and their secretion increases during periods of stress.

OBJECTIVE

To see whether these three neuropeptides might be related to vitiligo itself or to some alterations of the immune system in patients with vitiligo, we compared circadian variations in their plasma concentrations and natural killer cell activity of peripheral blood lymphocytes in 14 patients with vitiligo with those of 12 healthy subjects.

METHODS

Plasma concentrations of neurohormones were evaluated by radioimmunoassay (immunoradiometric assay for beta-endorphin). Natural killer cell activity (NKCA) was assayed against K562 cells by 51Cr release technique. Data were compared by the Student t test and analyzed by cosinor analysis.

RESULTS

The NKCA in vitiligo patients was higher than in controls but had similar circadian rhythm. alpha-MSH had no circadian rhythm in controls or in patients; plasma alpha-MSH levels were the same. Daily met-enkephalin and beta-endorphin oscillations in patients were no longer circadian. beta-Endorphin plasma levels in stable vitiligo were higher than in controls. There were no differences between patients with active vitiligo and normal subjects. Met-enkephalin plasma levels were generally higher in vitiligo patients, especially in the one with active vitiligo, than in controls.

CONCLUSION

In vitiligo there are aberrations in neuropeptide, beta-endorphin, and met-enkephalin secretion. The plasma met-enkephalin level is positively correlated with the aggressiveness of the disease.

Stress-induced changes in brain Met-enkephalin, Leu-enkephalin and dynorphin concentrations

Methionine-enkephalin (Met-enkephalin), leucine-enkephalin (Leu-enkephalin) and dynorphin A (1-17) (dynorphin A) concentrations in discrete brain areas were determined in the mice showing behavioral changes induced by stress using radioimmunoassay (RIA). In the present experiment, we used environment-induced conditioned suppression of motility and forced swimming-induced immobility. In the environment-induced conditioned suppression of motility, Met-enkephalin concentration in the striatum and hypothalamus significantly decreased. Leu-enkephalin concentration in the hypothalamus also decreased. Dynorphin A concentration in the striatum decreased, but significantly increased in the hypothalamus and pituitary. In the forced swimming-induced immobility, Met-enkephalin concentration in the striatum significantly decreased. Leu-enkephalin concentration in the hypothalamus and pituitary significantly decreased. Dynorphin A concentration in the pituitary decreased, but significantly increased in the hypothalamus. Our results indicated that the concentrations of Met-enkephalin, Leu-enkephalin and dynorphin A in the discrete brain areas changed in two different stressful situations. These findings suggested that these peptides might modulate the behavioral changes induced by stressors.

"Paradoxical" effects of morphine on antipredator defense reactions in wild and laboratory rats

In a Fear/Defense Test Battery, measuring defensive reactions to a present, approaching and contacting predator, the highest dose of morphine tested (7.5 mg/kg) reliably reduced vocalization to dorsal contact, to vibrissae stimulation, and to an anesthetized conspecific in laboratory-bred wild R. norvegicus. Except for a dose-dependent reduction in flinch/jump reactions to dorsal contact (taps), other defensive behaviors (flight, freezing, etc.) were not reliably altered by morphine treatment (0, 1.0, 2.5, 7.5 mg/kg). Vocalization responses to vibrissae stimulation in wild-trapped R. rattus were reliably increased following naloxone (1.0 and 10.0 mg/kg) administration, lending support for opiate receptor involvement in the mediation of defensive vocalization. In the Anxiety/Defense Test Battery, measuring defensive reactions to situations associated with a predator (cat) or with cat odor, laboratory rats showed no decrease in defensive behavior with morphine (0, 1.0, 5.0 mg/kg). In direct contrast to the above findings, the effects of morphine treatment in this test battery suggested a generalized increase in defensiveness to noncontacting and nonpainful threat stimuli. These effects included a decrease in time spent near the cat compartment, with a complementary increase in time spent at maximum distance, a decrease in transits between these sections, an increase in crouching, and a decrease in grooming and rearing. This pattern of results suggests that morphine may have two opposing effects on defensive behavior, a generalized enhancement, together with a more specific reduction of responses to tactile or painful stimulation. A very widespread pattern of reliable sex or sex x drug effects in the Anxiety/Defense Test Battery was in good agreement with previous reports of sex differences in these tests, with females generally more defensive than males. Consonant with previous findings, no reliable sex differences were found with the Fear/Defense Test Battery, although several values approached an acceptable level of statistical significance.

Retrieval effects of beta-endorphin and naloxone, and the novelty-induced antinociception in the developing rat

Three experiments were conducted to assess the retrieval effects of a single dose of beta-endorphin and of naloxone, and of the novelty-induced antinociception response in the developing rat. Wistar rats 30, 45, 60, and 90 days old from our breeding stock were used. Animals were trained and tested, with a 24-h interval between sessions, in a two-way active avoidance task (using 20 presentations of a 5-s, 1-kHz tone and a 0.4-mA footshock) or in a step-down inhibitory avoidance task (using a 60-Hz, 0.2-mA footshock). Saline (1.0 ml/kg), beta-endorphin (2.0 microgram/Kg), or naloxone (0.8 mg/kg), was administered ip immediately after training, and saline or beta-endorphin was administered 6 min before testing. The retrieval enhancing effects of post-training naloxone and pretest beta-endorphin, and the retrieval impairing effect of post-training beta-endorphin, were consistently observed only in 60- and 90-day-old rats, on both tasks. In a third experiment, another group of naive rats was placed for 2 min in a novel environment (the shuttlebox) and nociception was assessed by the tail-flick method. Novelty-induced antinociception was observed only for 60- and 90-day-old rats, and this response was cancelled by naloxone given 6 min before exposure to novelty. These results suggest that both the retrieval effects of naloxone and beta-endorphin, in the doses used, and the novelty-induced antinociception response, which are possibly dependent on the activity of hypothalamic beta-endorphin system, become established between 45 and 60 days postnatal in the rat.

Retrieval effects of both post- and presession beta-endorphin administration in a three-session paradigm

Rats were submitted to three sessions, with a 24-hr interval between, of step-down inhibitory avoidance task using a 60-Hz, 0.3-mA footshock, or of two-way active avoidance task using 25 presentations of a 5-sec. 1-kHz tone and a 0.4-mA footshock. Animals received intraperitoneal injections of either saline or beta-endorphin (2.0 microgram/kg) after the first session, and before the second or the third sessions, in a 2 x 2 x 2 design. beta-Endorphin given before the second or the third sessions improved retention for both tasks, but when administered after the first session, it impaired retention for the second session. The administration of beta-endorphin after the first session prevented the retrieval enhancement by the opioid given before the third session. Rats receiving beta-endorphin both after the first and before the second sessions, whilst showing no retrieval impairment on the second session, also did not show the pre-third session beta-endorphin retrieval enhancing effect. These data suggest that the post-first session exaggeration of the endogenous opioid state by beta-endorphin administered after the first session causes a long-lasting change in retrievability for the active and inhibitory avoidance tasks, as shown by the lack of the retrieval enhancing effect of beta-endorphin given before the third session.

Dominant mice show much lower concentrations of methionine-enkephalin in brain tissue than subordinates: cause or effect?

Possible relationships between dominance rank and brain methionine-enkephalin content were studied by using a method of consecutive rank determination in groups of mice reassembled according to their initial ordinal dominance rank. Thus, 10 groups of 3 Balb/c AnN mice of identical ordinal rank were formed with the consecutive dominants of 3 groups of 10 mice. Dominant, subdominant, subordinate and non-aggressive mice were recognized in these groups. Rank order was strongly correlated with brain Met-enkephalin content. Dominant mice contain less than a fourth Met-enkephalin immunologic reactivity in the brainstem and about half the forebrain concentration than subordinates. Brainstem Met-enkephalin correlated with the final ordinal rank and, accordingly, it was found to decrease exponentially after mice acquired alpha-dominance status. Different concentrations in the forebrain correlated with the initial but not the final ordinal rank and, therefore, probably preceded dominance status.

Distinct mechanisms underlying memory modulation after the first and the second session of two avoidance tasks

Rats were subjected to three consecutive sessions, one session per day, of either a step-down inhibitory avoidance task using a 60-Hz. 0.3-mA footshock, or a two-way active avoidance task using 20 presentations of a 5-s, 1-kHz tone and a 0.3-mA footshock. After either the first or the second training session animals received an intraperitoneal injection of ACTH (0.2 microgram/kg), epinephrine-HCl (5.0 micrograms/kg), or naloxone-HCl (0.8 mg/kg). All these treatments caused memory facilitation on both tasks when administered after the first training session. When administered after the second training session only ACTH and adrenaline were effective, on both tasks. As previous physiological and pharmacological reports point to the activation of the brain beta-endorphin system after the first, but not the second, session of a task, we propose that (a) memory facilitation by naloxone depends on the previous activation of the brain beta-endorphin system; and (b) memory facilitation due to ACTH or epinephrine does not depend on the opioid activity, so their effects are expressed after both the first and the second training sessions. It was also observed that the enhancement of performance in the second training session due to post-training facilitatory treatments carried over to the test session. These results suggest that some form of consolidation occurs both after the first and after the second training session.

Beta-endorphin and central control of arterial blood pressure during challenge of circulatory homeostasis

A variety of neurotransmitters and neuropeptides appear to participate in the central control mechanisms of arterial blood pressure. Our knowledge of these mechanisms is limited as yet. In the present study the involvement of the opioid peptide beta-endorphin in circulatory homeostasis was studied. Under conditions in which beta-endorphin does not affect basal blood pressure and heart rate this peptide had a pronounced prohypotensive influence in normotensive rats. This was found for two conditions during which circulatory homeostasis was challenged. Firstly, during blood letting in a rat model employed to test blood pressure regulation during hemorrhage, and secondly, for the central hypotensive action of alpha-methyldopa. In the first model hypotension was produced by stepwise bleeding to respectively 80, 60 and 40 mmHg mean arterial pressure. Intracerebroventricular (i.c.v.) administration of an antiserum raised against beta-endorphin or of naloxone (s.c. or i.c.v.) caused a significant increase in the required bleeding volume, whereas an opposite action was observed after the injection of morphine (s.c.) or of beta-endorphin (i.c.v.). The role of beta-endorphin in the hypotensive action of alpha-methyldopa, given intracisternally (i.c.) was evaluated in conscious rats equipped with chronic cannulas. Pretreatment with the opiate antagonist naltrexone (i.c.) caused an inhibition of the hypotension and bradycardia induced by alpha-methyldopa. This effect of the receptor antagonist was mimicked by i.c. administration of a beta-endorphin antiserum. Taken together, these data point to a hypotensive influence exerted by endogenous beta-endorphin under conditions during which circulatory homeostasis are challenged.

Effect of centrally and peripherally administered beta-endorphin on food intake in rats

A role for beta-EP in the regulation of food intake has been suggested as a contributory factor in the obesity of some genetically obese animal models. Studies undertaken to determine whether continuous administration of beta-EP could alter food intake in normal rats are described. The present studies demonstrated that continuous subcutaneous infusion with beta-EP was ineffective in modulating food intake, but that acute intraperitoneal or intracerebroventricular administration stimulated food intake in previously food deprived or satiated animals, respectively. These results suggest that beta-EP is not involved in the long-term regulation of food intake, but under certain conditions it may play some role in the regulation of individual meals. It is speculated that the latter activity may result from the action of other appetitive regulatory hormones.

Effects of [D-Ala2] Met-enkephalinamide, a Met-enkephalin analog, on delayed response by squirrel monkeys

Squirrel monkeys were tested on an indirect spatial delayed response task after subcutaneous injections of either physiological saline, 100, or 500 microgram/kg [D-Ala2] methionine enkephalinamide (DAME). During Experiment 1 monkeys completed two-choice delayed response problems with 0-, 6-, 12- and 18- sec delays; DAME significantly enhanced performance at 18-sec delays but not for the shorter delay. During Experiment 2, monkeys performed a nine-choice spatial delayed response task with 0-, 4- and 8-sec delays. In Experiment 2, low but not high doses of DAME impaired performance. Memory functions represented by a bias-free performance measure paralleled percentage correct in both experiments. Therefore, DAME effect, in enhancing and in impairing performance, were not attributable to changes in the relative number of systematic spatial errors (positional win-shift; lose-stay, position perseveration, and position preference).

MIF-1 is active in a chronic stress animal model of depression

MIF-1 was tested in an animal model of depression that used unpredictable chronic stress. In this paradigm, rats received either no stressors or a daily protocol of a variety of stressors for 20 days, during which time daily, intraperitoneal injections of various compounds were given. The tricyclic antidepressant imipramine (5 mg/kg) and low doses (0.1 and 1.0 mg/kg) of MIF-1 significantly increased activity and decreased defecation in an open field on day 21. No dose of naloxone (0.01-10.0 mg/kg) acted as an antidepressant. A high dose (10.0 mg/kg) of MIF-1 significantly increased the effects of chronic stress and produced hyperalgesia. Chronically-stressed rats were significantly more analgesic than controls. The results indicate that MIF-1 can act as an antidepressant in this model.

Paradoxical and subtype-specific effects of opiate antagonists on the expression of opioid receptors in rat brain cultures

Cultures of aggregating fetal rat brain cells express mu, delta, and kappa opioid receptors. The potent and long-lasting opioid antagonist naltrexone was used to investigate whether different regulatory mechanisms are involved in the expression of the three receptor subtypes. In cultures treated for seven days, naltrexone increased dose-dependently the binding of 3H-diprenorphine to the three receptor subtypes, with the mu sites being affected at a lower concentration than the other two; A Scatchard analysis indicated that this receptor up-regulation was obtained by an increase in the BMax, with no significant change in the affinity of the ligand to the receptors. In contrast to these effects in cultures treated for 7 days, it was surprising to find that a 48 hr treatment with naltrexone had an apparent converse and subtype-specific influence; the antagonist decreased significantly the binding of 3H-diprenorphine to both mu and delta receptors but had no effect on kappa sites. Two other opioid antagonists, naloxone and levallorphan, had a similar effect. Further analysis of naltrexone's mode of action was obtained by studying its effect on the adenylate cyclase activity. Of several inducers of this enzyme, the beta-adrenergic inducer isoproterenol gave the highest increase in cyclic AMP. Naltrexone had no significant effect on the basal adenylate cyclase activity but it altered the pattern of cyclic AMP formation in isoproterenol-stimulated cultures. Overall, the results indicate that in addition to its classic antagonistic activity, naltrexone exhibits in fetal brain aggregates some properties associated with opiate agonists.

Regulation of endogenous acetylcholine release from mammalian brain slices by opiate receptors: hippocampus, striatum and cerebral cortex of guinea-pig and rat

The effects of opiate agonists on acetylcholine release from hippocampal, striatal and cerebral cortical slices were tested; tissue from rat was compared to that from guinea-pig. The results show that opiate receptors in each of these areas can alter the evoked release of acetylcholine from nerve terminals; however, there are species and tissue differences with respect to the apparent subtype of opiate receptor effective. In the hippocampus and striatum of the two species studied, opiates caused a dose-dependent decrease in evoked acetylcholine release from tissue slices but in the guinea-pig kappa-selective agonists were effective, and mu or delta agonists were not, whereas in the rat, mu-, but not delta- or kappa-selective drugs were effective. Opiates also altered acetylcholine release from the frontal, parietal and occipital cortex of both of these species. In all three regions of the guinea-pig cortex, kappa and delta agonists were active and in the parietal cortex mu agonists were also active; rat cortical slices showed similar results except that delta agonists were not effective. The inhibitory effects of the opiate agonists were effectively antagonized by the non-selective opiate antagonist naloxone and by the calcium channel agonists, BAY K 8644 or YC-170. In addition, the effects of the opiate drugs tested in this study on acetylcholine release were confined to evoked release, that is, spontaneous acetylcholine release was not affected. The results suggest that in guinea-pig and rat brain, opiate receptors regulate acetylcholine release, and that, although the subtypes of opiate receptors involved in this effect are different in the two species and in different tissues from the same species, the effect results from a common mechanism that involves alterations of calcium influx into the nerve terminals during depolarization.

Beta-endorphin administration interferes with the acquisition and initial maintenance of ethanol preference in the rat

Attention has been focused on the possibility of an interaction between the endorphinergic system and ethanol intake. In the present study, the effects of subcutaneous (SC) administration of beta-endorphin (beta-E) (0.25, 1 and 5 micrograms/kg) and/or naloxone (NX) (1 or 2.5 mg/kg) on ethanol preference (EP) have been investigated in rats. Under our procedural conditions, rats developed ethanol preference (EP) by a forced ethanol drinking session (conditioning session). Preconditioning administration of beta-E (1 microgram/kg) reduced later EP. When beta-E was administered postconditioning, the opioid affects ethanol preference depending on the dose: both 0.25 micrograms/kg and 5 microgram/kg reduced EP, but the dose of 1 microgram/kg did not alter it. Administration of beta-E (1 and 5 micrograms/kg) before the first testing session attenuated EP. NX antagonized the effects of beta-E on EP in the three experimental procedures used, indicating that mu-opioid receptors might be involved in the beta-E-induced reductions on EP. Our results provide further evidences for a beta-endorphinergic system involvement on the mechanism leading to consumption of ethanol.

Regulation of human natural cytotoxicity by enkephalins and selective opiate agonists

This study reports a bidirectional effect of the enkephalins and selective opiate receptor agonists on human natural killer (NK) cell activity. Peripheral blood mononuclear cells (PBMC) were obtained from healthy donors and enriched for T lymphocytes and large granular lymphocytes (LGL) by passage over nylon wool columns. Nylon wool nonadherent cell populations were preincubated for 18 h in the presence of fetal bovine serum with and without methionine-enkephalin, leucine-enkephalin, dynorphin (fragment 1-13), [D-Ser2]-leucine-enkephalin-Thr (DSLET), and [D-Ala2,N Me-Phe4, Gly-ol5]-enkephalin (DAGO). NK activity was measured by a standard 51Cr release assay with radiolabeled K562 cells. The cytolytic capacity of low NK responder populations was enhanced by the endogenous opioids while the NK activity of high responder populations was suppressed. These results suggest an immunoregulatory action of opioid peptides on NK activity. This possibility was confirmed using a serum-free system in conjunction with recombinant interferon-alpha. In addition, the classic opioid receptor antagonist naloxone displayed both antagonist and direct immunomodulatory properties, which may indicate the presence of lymphocyte derived opioid peptides in the culture system.

Immunohistochemical evidence for the presence of peptides derived from proenkephalin, prodynorphin and proopiomelanocortin in the guinea pig pineal gland

By using a plethora of region-specific antisera, this light microscopic immunohistochemical study revealed that derivatives from the three opioid precursors, i.e. proenkephalin, prodynorphin and proopiomelanocortin are differentially distributed in the pineal gland of guinea pig. Various molecular forms of immunoreactive opioid peptides derived from proenkephalin or prodynorphin were present in a minority of pinealocytes as well as in nerves. In contrast to this dual distribution pattern of opioid-active peptides, the opioid-inactive derivative from proopiomelanocortin, alpha-melanocyte stimulating hormone, was exclusively present in a large proportion of pinealocytes. A multiple and differential origin and function of opioidergic pineal innervation involving sympathetic, parasympathetic and sensory components is suggested. alpha-MSH is proposed as a pineal hormone which may act in concert with melatonin to regulate pineal rhythms or may function like MSH of pituitary origin.

Opiate antagonists and rewarding brain stimulation

This review examines the literature on the effects of opiate antagonists on brain stimulation (ICSS) reward. Antagonists should have predictable effects if endogenous opioids modulate ICSS. Naloxone is the antagonist most often used, and it has produced inconsistent results in some ICSS paradigms. When schedules of intermittent reinforcement are used, however, naloxone reliably reduces the rate of responding. It reverses the effects of opiate agonists on ICSS behavior, and it also attenuates the effects of psychomotor stimulants, such as amphetamine. The results produced by naloxone are consistent with a modulatory effect of endogenous opioid systems on reward, and suggest that the opiate and dopamine systems together exert significant control over ICSS. Further research is needed to characterize better the actions of the antagonists on ICSS behavior, and productive research directions are proposed. Data obtained in future studies might suggest how the endogenous opioid systems modulate both natural and brain stimulation reward.

Opiate mechanisms in the central amygdala and gastric stress pathology in rats

Bilateral microinjections of the opiate antagonist naloxone (0.1, 1.0 and 10.0 micrograms) into the central nucleus of the amygdala (CEA) produced a significant potentiation of cold restraint-induced gastric pathology in rats. The opiate agonist, beta-endorphin (0.1, 1.0 and 10.0 micrograms), on the other hand, inhibited stress ulcer formation in a dose-related manner. Stress ulcer-attenuating effects were also seen with intra-CEA injections of the enkephalin analogs [D-Ala2,D-Leu5]enkephalin (10.0 micrograms) and [D-Ala2]Met-enkephalinamide (10.0 micrograms). Pretreatment of rats with naloxone (1.0 microgram) completely antagonized and even reversed the gastric cytoprotective effects of beta-endorphin (1.0 and 10.0 micrograms). The results indicate that the CEA is important in the gastric cytomodulatory effects of endogenous opiates during stressful experiences.