The opioid peptide ß-endorphin interferes with the pituitary-testis axis in the Mozambique tilapia Oreochromis mossambicus.

Although the involvement of ß-endorphin (ß-ERP) in vertebrate reproduction has been suggested, its role in testicular activity is not clear in fish. We describe the influence of ß-ERP on spermatogenesis in a cichlid fish in the present paper. In comparison to the control group, the administration of ß-ERP (3 µg) caused a significant increase in the number of spermatogonia-A and spermatids. Following treatment with ß-ERP (6 µg), a significant increase in the number of spermatogonia-A was observed, whereas the numbers of all the other germ cells, excluding spermatogonia-B, significantly decreased in comparison to those in the control group. In addition, treatment of fish with 6 µg ß-ERP resulted in a significant reduction in the dimensions of the lumen and seminiferous lobules, the level of immunopositive androgen receptor (AR) expression in Sertoli cells, and the percentage of luteinizing hormone (LH) immunolabeled in the pituitary compared to those in the control group or the group treated with 3 µg ß-ERP. In contrast, the intensity of AR immunoreactivity and the percentage of LH immunolabeling were substantially increased in fish treated with 3 µg ß-ERP compared to those in the control group. These findings reveal for the first time that a low dose of ß-ERP stimulates the recruitment of spermatogonia as well as spermateleosis, whereas a high concentration affects the recruitment of germ cells prior to meiotic division in tilapia. These results suggest that ß-ERP exerts modulatory effects at the testicular and hypophysial levels through alterations in AR expression and LH secretory activity, respectively, in teleosts.

Inhibition of POMC neurons in mice undergoing activity-based anorexia selectively blunts food anticipatory activity without affecting body weight or food intake.

Anorexia nervosa (AN) is a debilitating eating disorder characterized by severely restricted eating and significant body weight loss. In addition, many individuals also report engaging in excessive exercise. Previous research using the activity-based anorexia (ABA) model has implicated the hypothalamic proopiomelanocortin (POMC) system. Using the ABA model, Pomc mRNA has been shown to be transiently elevated in both male and female rodents undergoing ABA. In addition, the POMC peptide ß-endorphin appears to contribute to food anticipatory activity (FAA), a characteristic of ABA, as both deletion and antagonism of the µ opioid receptor (MOR) that ß-endorphin targets, results in decreased FAA. The role of ß-endorphin in reduced food intake in ABA is unknown and POMC neurons release multiple transmitters in addition to ß-endorphin. In the current study, we set out to determine whether targeted inhibition of POMC neurons themselves rather than their peptide products would lessen the severity of ABA. Inhibition of POMC neurons during ABA via chemogenetic Designer Receptors Exclusively Activated by Designer Drugs (DREADD) technology resulted in reduced FAA in both male and female mice with no significant changes in body weight or food intake. The selective reduction in FAA persisted even in the face of concurrent chemogenetic inhibition of additional cell types in the hypothalamic arcuate nucleus. The results suggest that POMC neurons could be contributing preferentially to excessive exercise habits in patients with AN. Furthermore, the results also suggest that metabolic control during ABA appears to take place via a POMC neuron-independent mechanism.

The Clash of Two Epidemics: the Relationship Between Opioids and Glucose Metabolism.

PURPOSE OF REVIEW: We are currently in the midst of a global opioid epidemic. Opioids affect many physiological processes, but one side effect that is not often taken into consideration is the opioid-induced alteration in blood glucose levels. RECENT FINDINGS: This review shows that the vast majority of studies report that opioid stimulation increases blood glucose levels. In addition, plasma levels of the endogenous opioid ß-endorphin rise in response to low blood glucose. In contrast, in hyperglycaemic baseline conditions such as in patients with type 2 diabetes mellitus (T2DM), opioid stimulation lowers blood glucose levels. Furthermore, obesity itself alters sensitivity to opioids, changes opioid receptor expression and increases plasma ß-endorphin levels. Thus, opioid stimulation can have various side effects on glycaemia that should be taken into consideration upon prescribing opioid-based medication, and more research is needed to unravel the interaction between obesity, glycaemia and opioid use.

ß-Neoendorphin Enhances Wound Healing by Promoting Cell Migration in Keratinocyte.

The skin is the largest and a remarkably plastic organ that serves as a protective barrier against environmental stimuli and injuries throughout life. Skin injuries are serious health problems, and wound healing is a critical process to replace devitalized cellular and tissue structures. Although some endogenous opioids are known to be involved in the modulation of wound healing, it remains to be determined whether the ß-neoendorphin (ß-NEP), an endogenous opioid, has beneficial effects on wound repair in human keratinocyte. In this study, we found that ß-NEP accelerated wound repair through activation of mitogen-activated protein kinase (MAPK)/Erk1/2 signaling pathways in human keratinocytes. Moreover, the wound healing effect of ß-NEP is mainly through the acceleration of keratinocyte migration without affecting cell proliferation. Therefore, our studies reveal that ß-NEP plays an important role in the regulation of wound repair and suggest a therapeutic strategy to promote wound healing using ß-NEP.

DNA Methylation of the Leptin Gene Promoter is Altered by Chronic Alcohol Exposure in an Animal Model for Alcohol Dependence.

Appetite-regulating peptides, such as leptin, are linked to craving and have been in the focus of alcohol dependence research for years. The objective of our study was to investigate the dynamics of leptin gene promoter methylation during alcohol withdrawal and specific treatment in a rodent (rat) model for alcohol dependence. DNA methylation was measured using direct bisulfite sequencing at 0 h, 24 h, and 6 days of alcohol withdrawal as well as after treatment with alpha-melanocyte-stimulating hormone (alpha-MSH), Beta-Endorphin, or saline. We found significantly lower methylation levels in alcohol-consuming animals compared to alcohol-naïve animals. During 6 days of alcohol deprivation, this difference in methylation vanished. Leptin methylation of the alpha-MSH-treated group and 6 days alcohol-deprived animals was significantly higher than that in saline-treated animals, possibly indicating compensatory effects of the treatment. Our results further expand on previous findings from human studies that explain leptin's role in bridging the gap between alcohol consumption and appetite regulation.

Sensitivity of T-Lymphocytes to Hormones of the Anterior Pituitary Gland.

The review provides information about the features of the sensitivity of thymocytes, lymphoid organs' cells and T-lymphocytes of peripheral blood to the hormones secreted by anterior pituitary gland's cells: growth hormone, thyrotropin, adrenocorticotropic hormone, prolactin and ß-endorphin. Some aspects of the T-lymphocytes's response to humoral signals from the hypophysis are shown in the article. Also the pituitary hormones' role in the regulation of proliferation, differentiation, and cytokine production of T-lymphocytes in normal and pathological conditions of the organism being discussed.

Effect of Naltrexone on photoperiodic regulation of testicular steroidogenesis in adult golden hamster, Mesocricetus auratus.

Photoperiodic regulation of testicular steroidogenesis through modulation of MT1R expression and local melatonin content is well established. However, additional mediators besides local melatonergic system in photoperiodic control of testicular steroidogenesis in golden hamster have not been studied in detail. Endogenous opioid peptides (EOP) are known to regulate reproduction via acting at multiple levels of the hypothalamus-pituitary-gonadal (HPG) axis. The presence of ß-endorphin, a naturally occurring opioid peptide, and its receptor (µ-opioid receptor, µOR) has been reported in rat testes; however the functional significance of photoperiodic regulation µOR in testicular steroidogenesis is not clear. In the present study, we assessed the effect of Naltrexone (Nal), a µOR antagonist, in photoperiodic regulation of testicular steroidogenesis. Immunohistochemical (IHC) localization and expression of µOR along with the expression of steroidogenic markers in testes was analyzed through western blot analyses. IHC suggest immunoreactivity for µOR in Leydig cells with strong immunoreactivity under SD (short-day) condition, whereas weak immunoreactivity was observed under LD (long-day). The expression of µOR was significantly decreased following Nal administration in both the photoperiodic conditions. The localization and differential photoperiodic regulation of µOR in Leydig cells suggests its involvement in testicular steroidogenesis. Further, Nal administration significantly increased the expression of steroidogenic markers (AR, StAR, P450SCC, LH-R, 3ß-HSD and 17-HSD) and plasma testosterone concentration under SD condition as compared to SD-control. We may therefore suggest that photoperiod differentially regulates the expression of µOR which thereby mediates the inhibitory effect of melatonin on testicular steroidogenesis.

The Central Effect of ß-Endorphin and Naloxone on The Biosynthesis of GnRH and GnRH Receptor (GnRHR) in The Hypothalamic-Pituitary Unit of Follicular-Phase Ewes.

The effects of prolonged, intermittent infusion of ß-endorphin or naloxone into the third cerebral ventricle of follicular-phase ewes on the expression of genes encoding GnRH and GnRHR in the hypothalamus and GnRHR in the anterior pituitary gland (AP) were examined by an enzyme-linked immunoabsorbent assay. Activation or blockade of µ-opioid receptors significantly decreased or increased the GnRH concentration and GnRHR abundance in the hypothalamus, respectively, and affected in the same way GnRHR quantity in the AP gland. The changes in the levels of GnRH and GnRHR after treatment with ß-endorphin as well as following action of naloxone were reflected in fluctuations of plasma LH concentrations. On the basis of these results, it is suggested that ß-endorphinergic system in the hypothalamus of follicular-phase ewes affects directly or via ß-endorphin-sensitive interneurons GnRH and GnRHR biosynthesis leading to suppression in secretory activity of the hypothalamic-pituitary axis.

Endomorphins and ß-Endorphin Do Not Affect Heart Tolerance to the Pathogenic Effect of Reperfusion.

Selective agonists of µ1- and µ2-opioid receptors endomorphin-2 and endomorphin-1 injected intravenously in a dose of 4500 nmol/kg in 5 min before coronary blood flow resumption had no effect on cardiac reperfusion damage. Consequently, µ1- and µ2-opioid receptors are not involved in the regulation of heart tolerance to reperfusion injury. Nonselective opioid receptor agonist ß-endorphin (100 nmol/kg) also did not affect heart tolerance to the pathogenic effect of reperfusion.

Effects of ß-endorphin on the production of reactive oxygen species, IL-1ß, Tnf-Α, and IL-10 by murine peritoneal macrophages in vivo.

It has been demonstrated that ß-endorphin stimulates the zymosan-induced secretion of reactive oxygen species and suppresses the spontaneous production of IL-1ß and IL-10 by murine peritoneal macrophages in vivo.

Effects of ß-endorphin on functional activity of mouse splenocytes under conditions of in vivo blockade of µ,δ-opioid receptors.

Blockade of δ-receptors with naltrindole under conditions of systemic immunization abolished the stimulatory effect of ß-endorphin (0.0005 µg/kg) on the counts of antibody-producing cells and the titer of antierythrocyte antibodies. Injection of ß-endorphin to mice led to stimulation of concanavalin A-induced proliferative activity of splenocytes and IL-4 secretion by the naloxone-dependent mechanism. The peptide did not modify the production of IL-2 and IFN-γ.

[Agonists of µ- and δ-Opioid Receptors in the Regulation of IL-2, IL-4 and IFN-γ Production by Peripheral Blood Cells in vitro].

It was found that ß-endorphin stimulates the PHA (phytohemagglutinin)-induced production of interleukin-4 and has no affect on the production of interferon-gamma in unfractionated leukocytic suspension. In the culture of purified CD4+ T cells, ß-endorphin does not affect the concentration of IL-2, IL-4, and IFN-γ, but stimulates the production of IL-4 and inhibits the production of IFN-γ when adding monocytes to the culture. Selective δ-agonist DADLE enhances the PHA-induced production of IL-4 in unfractionated leukocytic suspension and in CD4+ lymphocytes+monocytes system. The synthesis of IFN-γ by purified CD4+ lymphocytes is not afected by the presence of DADLE, DAGO ad Deltorphin II; but when adding monocytes to the culture, the synthesis rate decreases. ß-endorphin and selective µ-agonist DAGO enhance the production of IFN-γ by stimulated neutrophils. The production of IFN-γ in CD8+ lymphocytes is not affected by ß-endorphin. Thus, opioid peptides have a predominantly Th2 polarizing effect, which is monocyte-mediated, hindering the development of cell response by inhibiting IFN-γ, and stimulating the production of I L-4 by activating δ-receptor. On the other hand, neutrophils can enhance the production of IFN-γ by stimulating µ-receptor.

Inhibitory effects of ß-endorphin on cortisol release from goldfish (Carassius auratus) head kidney: an in vitro study.

ß-Endorphin (ß-END) is an endogenous opioid peptide derived from the common precursor proopiomelanocortin, together with adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH). Although the roles of ACTH and MSH in fish are well known, the roles of circulating ß-END have not been elucidated. In the present study, we evaluated the biological roles of ß-END in the goldfish. First, we cloned the cDNAs of the delta opioid receptor (DOR), kappa opioid receptor (KOR), and mu opioid receptor (MOR) from the brain of the goldfish. Second, we analyzed the tissues that expressed these genes by using reverse transcription polymerase chain reaction. Among the several tissues that contained the opioid gene transcripts, the mRNAs of DOR, KOR, and MOR were detected in interrenal cells of the head kidney, which produce cortisol. On the basis of these results, the effects of ß-END on cortisol release were examined in vitro. ß-END alone suppressed the basal release of cortisol in a dose-dependent manner. Moreover, ß-END inhibited the cortisol-releasing activity of ACTH1-24. Therefore, it is probable that the role of ß-END in the interrenal cells is the suppression of cortisol release. Interestingly, the suppression of cortisol release was not observed with N-acetyl-ß-END, indicating that acetylation decreases the activity of ß-END in interrenal cells.

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions.

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) are blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupts the behavioral effects of ketamine. Ketamine treatment rapidly increases levels of ß-endorphin and the expression of the µ-opioid receptor gene (Oprm1) in the mPFC, and the expression of gene that encodes proopiomelanocortin, the precursor of ß-endorphin, in the hypothalamus, in vivo. Finally, neutralization of ß-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolishes both behavioral and molecular effects. Together, these findings indicate that presence of ß-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

Interaction of synthetic peptide octarphin (TPLVTLFK) with human blood lymphocytes.

The synthetic peptide octarphin (TPLVTLFK) corresponding to the sequence 12-19 of ß-endorphin, a selective agonist of non-opioid ß-endorphin receptor, was labeled with tritium to specific activity of 29 Ci/mmol. The analysis of [(3) H]octarphin binding to human T and B lymphocytes separated from normal human blood revealed the existence of one type of high-affinity binding sites (receptors): Kd 3.0 and 3.2 nM, respectively. Besides unlabeled octarphin, unlabeled ß-endorphin possessed the ability to inhibit the specific binding of [(3) H]octarphin to Т and B lymphocytes (Ki 1.9 and 2.2 nМ, respectively). Tests of the specificity of the receptors revealed that they are not sensitive to naloxone, α-endorphin, γ-endorphin, [Met(5) ]enkephalin, and [Leu(5) ]enkephalin. Thus, both T and B lymphocytes from normal human blood express non-opioid receptor for ß-endorphin. Binding of the hormone to the receptor provides a fragment 12-19.

Naltrexone attenuates stress-induced suppression of LH secretion in the pituitary gland in the Cichlid fish Oreochromis mossambicus: evidence for the opioidergic mediation of reproductive stress response.

Opioid peptide ß-endorphin (ß-EP) plays a modulatory role in vertebrate reproduction. However, the role of opioid peptides in reproductive stress response is least understood in fishes. The aim of the present study was to determine the effect of different doses of ß-EP on luteinizing hormone (LH) secretion in normal and the opioid receptor antagonist naltrexone (NALT) in stressed female tilapia Oreochromis mossambicus. Administration of 4 µg ß-EP, but not 0.5 or 1.5 µg ß-EP, daily for 22 days caused suppression of LH-secreting cells at the proximal pars distalis of the pituitary gland, concomitant with a significant reduction in the mean GSI and HSI in 4 µg ß-EP-treated fish compared to controls. On the other hand, exposure of the fish to mild acute stressors for 22 days caused changes in the LH-secreting cells similar to that of high dose of ß-EP, whereas administration of NALT attenuated these effects. Taken together, the results indicate that increased concentration of ß-EP as may occur during stressful conditions can cause suppression of LH secretion, leading to the inhibition of spawning, and that treatment of NALT attenuates the stress-induced inhibition of LH secretion in fish.

[Influence of beta-endorphin on the proliferative and phagocytic activity of peripheral blood cells from males and females in different age groups].

It was revealed that beta-endorphin modulation of lymphocyte proliferative activity in male donors was predominantly observed under younger age groups of 20-29 and 30-39 years, while with age it gradually decreased and disappeared as such in group of donors under 50-60 years. Meanwhile, females demonstrated prolonged modulating effect of peptide on the proliferation. In female group under 50-59 years the peptide was found to render marked promoting effect on the spontaneous proliferation in concentrations of 10(-7), 10(-8), and 10(-10) M that was induced by suboptimal PHA concentration of 10(-10) M, whereas women in the range of 30-39 years showed that beta-endorphin suppressed the PHA-induced proliferative response. Male donors in age group of 20-29 years demonstrated beta-endorphin-stimulated and in age group of 50-59 years beta-endorphin-suppressed uptake capacity of neutrophils. In female donors from all age groups the effect of beta-endorphin on neutrophil phagocyte activity was not observed.

Interactions between ß-endorphin and kisspeptin neurons of the ewe arcuate nucleus are modulated by photoperiod.

Opioid peptides are well-known modulators of the central control of reproduction. Among them, dynorphin coexpressed in kisspeptin (KP) neurons of the arcuate nucleus (ARC) has been thoroughly studied for its autocrine effect on KP release through κ opioid receptors. Other studies have suggested a role for ß-endorphin (BEND), a peptide cleaved from the pro-opiomelanocortin precursor, on food intake and central control of reproduction. Similar to KP, BEND content in the ARC of sheep is modulated by day length and BEND modulates food intake in a dose-dependent manner. Because KP levels in the ARC vary with photoperiodic and metabolic status, a photoperiod-driven influence of BEND neurons on neighboring KP neurons is plausible. The present study aimed to investigate a possible modulatory action of BEND on KP neurons located in the ovine ARC. Using confocal microscopy, numerous KP appositions on BEND neurons were found but there was no photoperiodic variation of the number of these interactions in ovariectomized, estradiol-replaced ewes. By contrast, BEND terminals on KP neurons were twice as numerous under short days, in ewes having an activated gonadotropic axis, compared to anestrus ewes under long days. Injection of 5 µg BEND into the third ventricle of short-day ewes induced a significant and specific increase of activated KP neurons (16% vs. 9% in controls), whereas the percentage of overall activated (c-Fos positive) neurons, was similar between both groups. These data suggest a photoperiod-dependent influence of BEND on KP neurons of the ARC, which may influence gonadotropin-releasing hormone pulsatile secretion and inform KP neurons about metabolic status.

Nucleus accumbens µ-opioid receptors mediate social reward.

Positive social interactions are essential for emotional well-being and proper behavioral development of young individuals. Here, we studied the neural underpinnings of social reward by investigating the involvement of opioid neurotransmission in the nucleus accumbens (NAc) in social play behavior, a highly rewarding social interaction in adolescent rats. Intra-NAc infusion of morphine (0.05-0.1 µg) increased pinning and pouncing, characteristic elements of social play behavior in rats, and blockade of NAc opioid receptors with naloxone (0.5 µg) prevented the play-enhancing effects of systemic morphine (1 mg/kg, s.c.) administration. Thus, stimulation of opioid receptors in the NAc was necessary and sufficient for morphine to increase social play. Intra-NAc treatment with the selective µ-opioid receptor agonist [D-Ala(2),N-MePhe(4),Gly(5)-ol]enkephalin (DAMGO) (0.1-10 ng) and the µ-opioid receptor antagonist Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP) (0.3-3 µg) increased and decreased social play, respectively. The δ-opioid receptor agonist DPDPE ([D-Pen(2),D-Pen(5)]-enkephalin) (0.3-3 µg) had no effects, whereas the κ-opioid receptor agonist U69593 (N-methyl-2-phenyl-N-[(5R,7S,8S)-7-(pyrrolidin-1-yl)-1-oxaspiro[4.5]dec-8-yl]acetamide) (0.01-1 µg) decreased social play. Intra-NAc treatment with ß-endorphin (0.01-1 µg) increased social play, but met-enkephalin (0.1-5 µg) and the enkephalinase inhibitor thiorphan (0.1-1 µg) were ineffective. DAMGO (0.1-10 ng) increased social play after infusion into both the shell and core subregions of the NAc. Last, intra-NAc infusion of CTAP (3 µg) prevented the development of social play-induced conditioned place preference. These findings identify NAc µ-opioid receptor stimulation as an important neural mechanism for the attribution of positive value to social interactions in adolescent rats. Altered NAc µ-opioid receptor function may underlie social impairments in psychiatric disorders such as autism, schizophrenia, or personality disorders.

[Investigation of beta-endorphin nonopioid reception in preimplantation development of mouse embryo in vitro].

The effect of beta-endorphin on 2-, 4- and 8-cell embryo development in vitro was studied. It is shown, that hormone has no effect on 2-cell embryos development, but it has enhanced viability of 4- and 8-cell mouse embryos. The number ofblastocyst formation increases in presence of 0.1 microM beta-endorphin in embryo cultured medium but the number of blastocyst with abnormal structure decreases. The effect of hormone on the change of intracellular concentration of Ca2+ ion in 2-, 4- and 8-cell mouse embryo has been studied with the help of fluorescent microscopy. The effect of adenylate cyclase, and phospholipase activity blockers and opioid blocker naloxone on the change of intracellular concentration of Ca2+ ion in early mouse embryo in the presence of beta-endorphin have been also studied. It is shown that 2-cell embryo has opioid and nonopioid beta-endorphin receptors, whereas 4- and 8-cell mouse embryos have only nonopoioid beta-endorphin receptors. It is also shown that the effect of beta-endorphin in the early mouse embryo through a nonopioid receptors occurs with the participation of intracellular Ca2+ and adenylate cyclase signaling system.