The effects of beta-endorphin: state change modification

Beta-endorphin (β-END) is an opioid neuropeptide which has an important role in the development of hypotheses concerning the non-synaptic or paracrine communication of brain messages. This kind of communication between neurons has been designated volume transmission (VT) to differentiate it clearly from synaptic communication. VT occurs over short as well as long distances via the extracellular space in the brain, as well as via the cerebrospinal fluid (CSF) flowing through the ventricular spaces inside the brain and the arachnoid space surrounding the central nervous system (CNS). To understand how β-END can have specific behavioral effects, we use the notion behavioral state, inspired by the concept of machine state, coming from Turing (Proc London Math Soc, Series 2,42:230-265, 1937). In section 1.4 the sequential organization of male rat behavior is explained showing that an animal is not free to switch into another state at any given moment. Funneling-constraints restrict the number of possible behavioral transitions in specific phases while at other moments in the sequence the transition to other behavioral states is almost completely open. The effects of β-END on behaviors like food intake and sexual behavior, and the mechanisms involved in reward, meditation and pain control are discussed in detail. The effects on the sequential organization of behavior and on state transitions dominate the description of these effects.

Possible involvement of prolonging spinal µ-opioid receptor desensitization in the development of antihyperalgesic tolerance to µ-opioids under a neuropathic pain-like state

In the present study, we investigated the possible development of tolerance to the antihyperalgesic effect of µ-opioid receptor (MOR) agonists under a neuropathic pain-like state. Repeated treatment with fentanyl, but not morphine or oxycodone, produced a rapid development of tolerance to its antihyperalgesic effect in mice with sciatic nerve ligation. Like the behavioral study, G-protein activation induced by fentanyl was significantly reduced in membranes obtained from the spinal cord of nerve-ligated mice with in vivo repeated injection of fentanyl. In β-endorphin-knockout mice with nerve ligation, developed tolerance to the antihyperalgesic effect of fentanyl was abolished, and reduced G-protein activation by fentanyl after nerve ligation with fentanyl was reversed to the normal level. The present findings indicate that released β-endorphin within the spinal cord may be implicated in the rapid development of tolerance to fentanyl under a neuropathic pain-like state.

[Factor analysis model for studying the influence of psychological stress on the endocrine network of reproduction axis]

In order to explore the influence of psychological stress on the reproductive axis, we started with the original data of biology from animal experiments, then we conducted the factor analysis of 6 important bio-regulatory factors and established the Factor Analysis Model for the endocrine network of reproduction axis under psychological stress. Based on the biological data obtained from animal experiments, it is found that, compared with the relationship seen in the factor analysis model in normal condition, the relationship among the biological factors is more complicated. The key factor, GnRH, has lost its strong regulating action on the subordinate factors, especially on E2; on the other hand, beta-EP has very strong regulating action on E2, and E2 is controlled mainly by beta-EP.

[Difference in tolerance to anti-hyperalgesic effect and its molecular mechanisms between chronic treatment with morphine, fentanyl and oxycodone in a chronic pain-like state]

In the present study, we demonstrated that repeated treatment with fentanyl, but not morphine or oxycodone, causes a rapid desensitization to its ability to block the hyperalgesia associated with the attenuation of mu-opioid receptor resensitization in mice in a chronic pain-like state. In contrast, no such effect was noted in beta-endorphin knockout mice under the chronic pain-like conditions. On the assumption that beta-endorphin might be released within the spinal cord under pain-like conditions, we further examined whether beta-endorphin could be responsible for a desensitization and resensitization of fentanyl under the chronic pain. In cultured cells, unlike morphine, fentanyl and oxycodone induced a robust mu-opioid receptor internalization and, in turn, its resensitization. In the presence of beta-endorphin, the internalized mu-opioid receptor induced by fentanyl, but not oxycodone, remained within the cytosolic component even after washing out. The findings suggest that beta-endorphin could attenuate the resensitization of mu-opioid receptors. This phenomenon may explain the high degree of tolerance to fentanyl that develops with hyperalgesia caused by a chronic pain-like state.

[Pharmacological effects of a mu-opioid receptor antagonist naltrexone on alcohol dependence]

Alcohol is one of the most commonly abused substances, and its chronic intake leads to the development of ethanol dependence in both humans and laboratory animals. In many countries, a mu-opioid receptor antagonist naltrexone has been used in the treatment of alcohol dependence. The introduction of naltrexone for the treatment of alcohol dependence has been mainly based on behavioral animal models that provide evidence of the involvement of the endogenous opioid system in alcohol drinking and dependence. It has been well known that alcohol leads to the activation of the endogenous opioid system. The endogenous opioid agonists, such as beta-endorphin, increase the activity of the mesolimbic dopaminergic system through the inhibition of the gamma-aminobutyric acid (GABA)-containing inhibitory interneurons in the ventral tegmental area, resulting in the expression of alcohol reinforcement and/or rewarding effect. Therefore, naltrexone, which is useful for alcohol dependence therapy, may attenuate the rewarding effect of ethanol by interfering with the ethanol-induced stimulation of the mesolimbic dopaminergic system. The following review provides a summary of the interactions between endogenous opioid system and mesolimbic dopaminergic system in alcohol dependence.

Beta-endorphin and drug-induced reward and reinforcement

Although drugs of abuse have different acute mechanisms of action, their brain pathways of reward exhibit common functional effects upon both acute and chronic administration. Long known for its analgesic effect, the opioid beta-endorphin is now shown to induce euphoria, and to have rewarding and reinforcing properties. In this review, we will summarize the present neurobiological and behavioral evidences that support involvement of beta-endorphin in drug-induced reward and reinforcement. Currently, evidence supports a prominent role for beta-endorphin in the reward pathways of cocaine and alcohol. The existing information indicating the importance of beta-endorphin neurotransmission in mediating the reward pathways of nicotine and THC, is thus far circumstantial. The studies described herein employed diverse techniques, such as biochemical measurements of beta-endorphin in various brain sites and plasma, and behavioral measurements, conducted following elimination (via administration of anti-beta-endorphin antibodies or using mutant mice) or augmentation (by intracerebral administration) of beta-endorphin. We suggest that the reward pathways for different addictive drugs converge to a common pathway in which beta-endorphin is a modulating element. Beta-endorphin is involved also with distress. However, reviewing the data collected so far implies a discrete role, beyond that of a stress response, for beta-endorphin in mediating the substance of abuse reward pathway. This may occur via interacting with the mesolimbic dopaminergic system and also by its interesting effects on learning and memory. The functional meaning of beta-endorphin in the process of drug-seeking behavior is discussed.

Glycyl-glutamine reduces ethanol intake at three reward sites in P rats

beta-endorphin, implicated in modulation of ethyl alcohol reward, has neuron terminals in several reward sites. Alcohol consumption was reduced after ventricular or site-specific injections into the nucleus accumbens of an opioid-derived dipeptide, glycyl-glutamine. The current study examined the effects of this dipeptide after site-specific injections into additional reward sites. Alcohol-preferring (P) rats, stereotaxically implanted with bilateral guide cannulae into the nucleus accumbens, ventral tegmental area, and the central nucleus of the amygdala were given 30% alcohol and water in a 24h voluntary two-bottle choice paradigm. Upon achieving stable baseline intakes, glycyl-glutamine (GQ) doses were injected bilaterally, and the alcohol and water intakes and body weight recorded for the response and recovery. The data show reduced alcohol intake by 32-49.5% after 100-pmol glycyl-glutamine into reward sites (nucleus accumbens, ventral tegmental area, and central nucleus of the amygdala), but not after injections into control sites dorsal to reward sites. The order of sensitivity to the 1-fmol dose was amygdala > or = ventral tegmental area > accumbens. GQ was effective in reducing ethanol intake at reported beta-endorphin terminal regions in each of the three reward sites tested. The effective doses were similar to reported endogenous GQ levels, consistent with the notion that it may function as part of an endogenous counter regulatory mechanism and represent a "stop drinking" signal in the high drinking, P rats at these three reward sites.

Response to delivery stress is not mediated by beta-endorphin (1–31)

OBJECTIVE

The aim of the study was to determine the reaction of the melanotroph and corticotroph-type pituitary proopiomelanocortin (POMC) response to vaginal delivery and caesarean section stress. Furthermore, the relationship between the release of pituitary POMC fragments, gonadotropins and sexual steroids were examined.

STUDY DESIGN

Blood samples were obtained from 10 women in labour on arrival in the birth room (t(A)), at cervix dilatation of 5 cm (t(B)) and immediately after spontaneous delivery (t(C)) and in 16 patients undergoing elective caesarean section before induction of anaesthesia (t(B)) and immediately after delivery (t(C)). Samples were analysed for cortisol, ACTH, authentic beta-endorphin, beta-endorphin immunoreactive material (IRM), acetyl-N-beta-endorphin IRM (NAC), beta-lipotropin (beta-LPH) IRM, oestradiol (E(2)), progesterone (P), prolactin (PRL), FSH and LH.

RESULTS

NAC representing the melanotroph-type pituitary POMC system did not increase during the course of caesarean section or spontaneous labour. In contrast, a significant increase of beta-endorphin IRM, beta-LPH IRM and ACTH were observed, representing an activation of the corticotroph-type POMC system. Highly significant correlations between POMC fragment concentrations during caesarean section and spontaneous labour were also observed. Sexual steroids (E(2) and P) decreased significantly. Except for beta-endorphin IRM and E(2) in course of spontaneous delivery no significant correlation was observed between POMC fragment and gonadotropins or sexual steroids.

CONCLUSION

Caesarean section and spontaneous delivery activated the corticotroph but not the melanotroph POMC system.

Alcohol exposure during the developmental period induces beta-endorphin neuronal death and causes alteration in the opioid control of stress axis function

Proopiomelanocortin-producing neurons in the arcuate nucleus of the hypothalamus secrete beta-endorphin (beta-EP), which controls varieties of body functions including the feedback regulation of the CRH neuronal activity in the paraventricular nucleus of the hypothalamus. Whether ethanol exposure in developing rats induces beta-EP neuronal death and alters their influence on CRH neurons in vivo has not been determined. We report here that binge-like ethanol exposures in newborn rats increased the number of apoptotic beta-EP neurons in the arcuate nucleus of the hypothalamus. We also found that immediately after ethanol treatments there was a significant reduction in the expression of proopiomelanocortin and adenylyl cyclases mRNA and an increased expression of several TGF-beta1-linked apoptotic genes in beta-EP neurons isolated by laser-captured microdissection from arcuate nuclei of young rats. Several weeks after the ethanol treatment, we detected a reduction in the number of beta-EP neuronal perikarya in arcuate nuclei and in the number of beta-EP neuronal terminals in paraventricular nuclei of the hypothalamus in the treated rats. Additionally, these rats showed increased response of the hypothalamic CRH mRNA to the lipopolysaccharide challenge. The ethanol-treated animals also showed incompetent ability to respond to exogenous beta-EP to alter the lipopolysaccharide-induced CRH mRNA levels. These data suggest that ethanol exposure during the developmental period causes beta-EP neuronal death by cellular mechanisms involving the suppression of cyclic AMP production and activation of TGF-beta1-linked apoptotic signaling and produces long-term structural and functional deficiency of beta-EP neurons in the hypothalamus.

Beta-endorphin alters electrical activity of gonadotropin releasing hormone neurons located in the terminal nerve of the teleost medaka (Oryzias latipes)

Endogenous opioid peptides (EOPs) are an important class of modulators of the hypothalamo-pituitary axis; treatment with opiates leads to inhibition of GnRH and LH secretion and suppression of reproductive functions. However, little work has been done to investigate the effect of opiates on the electrical activity of GnRH neurons, which ultimately controls GnRH secretion. The purpose of the present study was to investigate the effects of the EOP beta-endorphin on electrical activity of GnRH neurons located in the terminal nerve (TN) associated with the olfactory bulb. We used an excised intact brain preparation from transgenic medaka in which green fluorescent protein (GFP) is genetically expressed in TN-GnRH neurons. These GFP-expressing neurons were then targeted for whole-cell current clamp recordings. Treatment with beta-endorphin led to changes in several characteristics of electrical activity, including depolarization of membrane potential and a decrease in spike amplitude--similar to that observed in response to depolarizing high K(+) treatment. This finding suggests a model in which beta-endorphin depolarizes membrane potential leading to Na(+)-channel inactivation, and subsequent suppression of action-potential amplitude. On the other hand, beta-endorphin had no effect on membrane potential in synaptically isolated GnRH neurons. These results suggest that beta-endorphin is acting indirectly on TN-GnRH neurons to inhibit action potential firing.

The contribution of endogenous opioids to food reward is dependent on sex and background strain

Complex behaviors such as those associated with reward to unconditioned positive reinforcers are polygenic processes. In studies using genetically modified mice specific for the endogenous opioid systems an observed phenotype in a complex behavior is likely to be dependent on interacting genes which, in inbred mouse lines, influence that phenotype. To address this issue we examined operant responding for palatable food reinforcers in mice lacking the expression of beta-endorphin, enkephalin or both peptides congenic to two different genetic backgrounds; C57BL/6J and DBA/2J. These two inbred strains were chosen because their endogenous opioid states differ and they respond differently to exogenous opioids in many behavioral assays. We found that wildtype and mutant C57BL/6J mice acquired operant responding for food reinforcers faster than DBA/2J mice, regardless of their opioid genotype. Although wildtype DBA/2J mice had a significant deficit in acquisition of bar-pressing behavior to reach a pre-established performance criterion, no subsequent deficit was observed under two different schedules of reinforcement. Additionally, we found that mice lacking enkephalin had decreased motivation to bar press for palatable food reinforcers under a progressive ratio regardless of sex or background strain. In contrast, the only subset of beta-endorphin-deficient mice that had decreased motivation to bar press under a progressive ratio was males on the C57BL/6J background. Of the two classical endogenous opioid peptides with preferential activation of the mu opioid receptor, the knockout models would suggest that enkephalins play a more consistent role than beta-endorphin in mediating the motivation for food reward when tested under a progressive ratio.

Role of beta-endorphin, corticotropin-releasing hormone, and autonomic nervous system in mediation of the effect of chronic ethanol on natural killer cell cytolytic activity

BACKGROUND

We have recently shown that alcohol feeding suppresses natural killer (NK) cell cytolytic activity partly by decreasing the function of hypothalamic beta-endorphin (beta-EP) neurons. The neuronal mechanism by which hypothalamic beta-EP communicates with the spleen to regulate the action of ethanol on NK cells is not known. In the present study, we evaluated the roles of beta-EP neurons, corticotropin releasing hormone (CRH) neurons, and the autonomic nervous system (ANS) in regulation of the ethanol effect on splenic NK cell cytolytic function.

METHODS

Male rats were fed an ethanol-containing liquid diet or control diets. These rats were used to determine the hormone release from the paraventricular nuclei (PVN) of the hypothalamus or used to determine the splenic NK cell cytolytic function after PVN administration of CRH or intraperitoneal (i.p.) administration of a ganglionic blocker chlorisondamine. The release of hormones from the PVN was measured using the push-pull perfusion method. Splenic cytolytic activity was determined using the 4-hour (51)Cr release assay against YAC-1 lymphoma target cells.

RESULTS

Alcohol feeding decreased the amount of beta-EP but increased the amount of CRH in the push-pull perfusate (PPP) samples collected from the PVN. When exogenous beta-EP was perfused into the PVN, it suppressed the release of endogenous CRH found in PPP samples of the PVN. Conversely, perfusion of an opiate antagonist naltrexone into the PVN increased the levels of endogenous CRH in PPP samples of the PVN. In addition, administration of exogenous beta-EP in the PVN stimulated the cytolytic function of NK cells, an action that was antagonized by CRH as well as by ethanol. Corticotropin-releasing hormone and ethanol alone also had an inhibitory action on NK cells. Finally, the ganglionic blocker used prevented the effect that ethanol, beta-EP, and CRH had on NK cells. These data suggest that ethanol inhibits the function of NK cells partly by suppressing the influence of the beta-EP-CRH-ANS signal to the spleen.

β-Endorphin involvement in the regulatory response to body sodium overload

The present study was performed to examine the role of the endogenous beta-endorphinergic system on blood pressure regulation, sympathetic and brain activity during body sodium overload. Beta-endorphin knockout (beta end-/-), heterozygous (beta end+/-) and wild-type (beta end+/+) mice were submitted for two weeks to either a normal- or a high-sodium diet (NSD and HSD, respectively), and systolic blood pressure (SBP), urinary catecholamines (as an index of sympathetic nervous system activity), and the brain pattern of Fos-like immunoreactivity (as a marker of neuronal activation) were evaluated in each group. HSD caused a significant increase in SBP in beta end-/- mutant mice compared with beta end+/+ mice kept in the same experimental conditions (P < 0.01), but no statistical differences were observed between beta end+/- and beta end+/+ on a HSD. Moreover, when animals from the three genetic lines were fed with a NSD no changes in SBP were evidenced. With regard to brain activity, beta end-/- mice maintained on a HSD showed a significant increase in Fos-like immunoreactive neurons in the median preoptic nucleus (P < 0.01) compared with beta end+/- and beta end+/+ animals. Additionally, beta end-/- mice had higher levels of urinary epinephrine excretion (P < 0.05) on a HSD in comparison to beta end+/+ and beta end+/- animals in the same experimental conditions. No differences, however, were registered in norepinephrine and dopamine urinary excretion in animals from the three genetic lines after two weeks on either a HSD or a NSD. In summary, our results indicate that the beta-endorphinergic system may play a part in the compensatory response to sodium overload, since the absence of beta-endorphin causes an increase in systolic blood pressure, and increases median preoptic nucleus neural activity and urinary epinephrine excretion.

Role of limbic peptidergic circuits in regulation of arterial pressure, relevant to development of essential hypertension

It is generally accepted that the essential hypertension (EH) is caused by interactions among congenital gene, multiple pathogenetic pressor factors, and disorder of physiologic depressor factors. The central nervous system may play a key role in the development of EH. The underlying mechanisms, however, are not well understood. Studies show that peptidergic transmitters in the limbic forebrain are involved in long-term regulation of arterial pressure and in the pathogenesis of EH. In the limbic forebrain there are peptidergic pressor and depressor circuits. The former includes corticotropin releasing factor-, substance P-, and angiotensin II-circuits; and the latter includes beta-endorphin- and atrial natriuretic peptide-circuits. These circuits extensively interconnect and interact with each other. The altered functions of them may be the pathogenesis of EH. In this review, we focus on the roles of limbic peptidergic circuits in regulation of arterial pressure, relevant to the neurogenetic mechanisms in developing EH.

A possible involvement of β-endorphin, substance P, and serotonin in rat analgesia induced by extremely low frequency magnetic field

Most of the research concerning magnetic antinociception was focused on brief exposure less than 1 h. The main purpose of the present study was to determine the effect of extremely low frequency (ELF) magnetic field (MF) repeated exposures on rats in inducing antinociception and to find the effective analgesic "time window." Meanwhile this investigation was to examine the role of central beta-endorphin, substance P, and 5-HT in magnetic analgesia. We found tail flick latencies (TFLs) increased significantly after the rats were exposed to 55.6 Hz, 8.1 mT magnetic field for 4 days, 6 h each day. The analgesic effects seemed to decrease gradually when the rats were exposed daily for another 10 days. Their levels of TFLs decreased within 1 day when the rats were removed after a 4-day exposure. The concentrations of hypothalamus beta-endorphin, substance P, and brainstem serotonin (5-HT) were increased significantly on Day 4. However, no differences were found when rats were exposed for another 10 days, and there were no significant increases when rats were removed after the fourth day of exposure and tested for nociception on Days 5 and 7 with no changes in the biochemical markers at 7 days. These results suggest that the ELF magnetic field has analgesic effect, but only on Days 3 and 4. The effect may be associated with increases in endogenous beta-endorphin, substance P, and 5-HT stimulated by the 55.6 Hz, 8.1 mT magnetic field.

Naltrexone inhibits alcohol-mediated enhancement of HIV infection of T lymphocytes

Acute and chronic alcohol abuse impairs various functions of the immune system and thus, has been implicated as a cofactor in the immunopathogenesis of human immunodeficiency virus (HIV) disease progression. We determined whether naltrexone, an opioid receptor antagonist widely used in the treatment of alcoholism, inhibits alcohol-mediated enhancement of HIV infection of T cells. Alcohol enhanced HIV infection of peripheral blood lymphocytes (PBL) and a human lymphoid cell line (CEMX174). Alcohol increased HIV X4 envelope (Env), not murine leukemia virus Env-pseudotyped infection of CEMX174 cells. Naltrexone antagonized the enhancing effect of alcohol on HIV infection of PBL and CEMX174 cells. The specific mu-opioid receptor antagonist, Cys2, Tyr3, Arg5, Pen7 (CTAP) amide, also blocked the enhancing effect of alcohol on HIV infection. Investigation of the underlying mechanism for the alcohol action showed that alcohol significantly increased endogenous beta-endorphin production and induced mu-opioid receptor mRNA expression in PBL and CEMX174 cells. The role of beta-endorphin in alcohol-mediated enhancement of HIV infection was indicated by the observations that naltrexone and CTAP antagonized ether alcohol- or exogenous beta-endorphin-mediated enhancement of HIV infection. These findings suggest a biological mechanism for the potential therapeutic benefit of naltrexone in treating HIV-infected alcoholics.

Hyper-anxiety in early sobriety: psychopharmacological treatment strategies

The importance of recognizing and treating anxiety disorders that co-occur with alcohol use disorders should not be underestimated, whether the anxiety is state (a transient condition) or trait (a chronic disorder). This article will discuss hyper-anxiety, a term the authors use to describe the uncomfortable, excessively anxious state that contributes to relapse. In addition, psychopharmacological strategies for relief of hyper-anxiety are suggested, and implications for recovery are discussed.

Habituation to test procedure modulates the involvement of dopamine D2- but not D1-receptors in ethanol-induced locomotor stimulation in mice

RATIONALE

Novelty associated with behavioral testing has been shown to enhance psychostimulant- and morphine-induced locomotor stimulation. Evidence has demonstrated that novelty increases dopamine (DA) activity, and habituation to a novel environment reduces such activation. However, it is not clear whether novelty modulates ethanol-induced behavioral stimulation and whether DA plays a role in this effect.

OBJECTIVES

The present work sought to demonstrate a role of habituation to test procedure as a factor that could modulate the involvement of DA in ethanol-induced locomotor stimulation.

METHODS

Non-habituated (NH) and habituated (H) Swiss mice pretreated with DA D1- (SCH23390; 0-0.045 mg/kg) or D2-receptor (sulpiride; 0-50 mg/kg) antagonists were tested for ethanol (0-2.5 g/kg)-induced locomotor stimulation. Experiments with amphetamine (0-4 mg/kg), morphine (0-5 mg/kg) and caffeine (0-15 mg/kg)were designed to compare their results to those obtained with ethanol. The effect of the non-selective opioid receptor antagonist naltrexone (0-1.5 mg/kg) was also tested on ethanol-induced locomotor stimulation.

RESULTS

NH and H animals did not differ in their locomotor response to ethanol or caffeine; however, amphetamine- and morphine-induced stimulation was greater in NH than in H mice. SCH23390 only reduced ethanol-induced stimulation at doses that also reduced spontaneous activity in both NH and H mice. Sulpiride decreased ethanol-stimulated behavior only in the NH condition. Habituation did not modify the effect of sulpiride on amphetamine-, morphine- or caffeine-induced activation. Naltrexone (0-1.5 mg/kg) reduced ethanol-induced stimulation regardless of habituation.

CONCLUSIONS

The present data suggest that the participation of DA D2-receptors in ethanol-induced behavioral stimulation requires the presence of novelty. Results also support the involvement of neurotransmitter systems other than DA (i.e., endogenous opioid system) as important substrates mediating ethanol-induced locomotor activation.

The endocrinology of sexual arousal

The relevance of testosterone, oestradiol and certain peptides (oxytocin (OT), beta-endorphin and prolactin (PRL)) to sexual arousal in humans is reviewed. In addition to behavioural studies, evidence of distribution of gonadal steroid receptors in the brain and the limited evidence from brain imaging are also considered. Testosterone plays a key role in the adult male, with clear, consistent evidence from studies of hypogonadal and eugonadal men. The roles of testosterone in the development of sexual arousability, and in the aging male, are less clear. The relevance of aromatization and of non-sexual effects of testosterone which might indirectly influence sexual arousal are not well understood. Testosterone in the female presents a more complex, less consistent picture. One possible explanation is a much greater variability across women in responsiveness to testosterone. A 'desensitization hypothesis' to account for the striking gender differences is offered. There is limited evidence of a direct effect of oestradiol on sexual arousability in women. The extent to which testosterone in women acts by conversion to oestradiol or by increase of free oestradiol is not yet clear. The role of peptides in sexual arousal remains uncertain, partly because of the multiple roles and sites of action of most peptides. OT and beta-endorphin appear to have both excitatory and inhibitory effects. PRL has been proposed as an inhibitory factor via direct inhibition of dopaminergic activity, but the evidence for this is inconclusive. Whereas the traditional concept of 'hormone' continues to apply to the role of testosterone and oestradiol in sexual arousal, peptides present a more complex role.

Mediation of beta-endorphin in exercise-induced improvement in insulin resistance in obese Zucker rats

BACKGROUND

Aerobic exercise including treadmill running has long been used to successfully treat and/or prevent insulin resistance and type-2 diabetes. Increase of plasma beta-endorphin is observed with exercise. The present study was designed to clarify the role of endogenous beta-endorphin in exercise-induced improvement in insulin resistance.

METHODS

We used a moderate exercise program consisting of treadmill running at 20 m/min and 0% grade for 1 h/day, 7 days/week, for 8 weeks. Plasma glucose concentration was assessed by the glucose oxidase method. The enzyme-linked immunosorbent assay was performed to quantify the plasma level of beta-endorphin-like immunoreactivity (BER). The glucose disposal rate (GDR) was measured by the hyperinsulinemic euglycemic clamp technique. Changes of the insulin signaling in isolated soleus muscle were then detected by immunoprecipitation and immunoblotting.

RESULTS

An increase of plasma BER in parallel with the reduction of plasma glucose was obtained in exercise-trained obese Zucker rats. Different from a marked reduction in sedentary obese rats, the value of insulin-stimulated GDR obtained from the exercised obese rats was reversed to near that of the sedentary lean group, eight weeks after the last period of exercise. This effect of exercise was inhibited by naloxone or naloxonazine at doses sufficient to block opioid micro-receptors. Signaling-related defects in the soleus muscle of sedentary obese Zucker rats, which impaired glucose transporter subtype 4 (GLUT 4), included decreased phosphorylation of insulin receptor substrate (IRS)-1, as well as an attenuated p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3 kinase) and Akt serine phosphorylation. In contrast, exercise training failed to modify the levels of insulin receptor (IR), IRS-1, and IR tyrosine autophosphorylation in obese Zucker rats.

CONCLUSION

Enhanced insulin sensitivity via exercise training might be mediated by endogenous beta-endorphin through an increase of postreceptor insulin signaling related to the IRS-1-associated PI3-kinase step that leads to the enhancement of GLUT 4 translocation and improved glucose disposal in obese Zucker rats.

Operant self-administration of ethanol in C57BL/6 mice lacking beta-endorphin and enkephalin

To test whether endogenous opioid peptides are necessary for the rewarding effects of ethanol, we examined operant oral self-administration of ethanol in mice congenic to the C57BL/6J strain but lacking expression of beta-endorphin, enkephalin or both peptides. The influences of prandial state, schedule interval and type, and ethanol concentration were all examined. Food-restricted subjects were tested in postprandial and preprandial states and subsequently at normal body weight when feeding ad libitum (ad lib). Operant studies were conducted using fixed ratio (FR) intervals of 2 and 8 as well as a progressive ratio (PR) interval of 2. The main significant effect relevant to our hypothesis was increased responding by female mice lacking beta-endorphin under ad lib feeding conditions and only for lower ethanol concentrations (3% and 6%). Importantly, all subjects including those lacking both beta-endorphin and enkephalins learned to self-administer ethanol similarly to wild-type mice and maintained responding for ethanol under a variety of procedural variables. Consequently, the two opioid peptides believed to be the endogenous ligands for the micro-opioid receptor (MOR) were not necessary to shape or perpetuate ethanol-reinforced operant responding. These results suggest that the rewarding effects of ethanol do not require beta-endorphin or enkephalin signaling.

[Individuality of emotional stress]

The author postulates a need of individual evaluation of experimental data characterizing emotional stress. In typical conflict situations inducing emotional stress, there are animals resistant or predisposed to disturbance of different physiological functions. Prognostic criteria of individual resistance of animals to stressors are presented. Stress resistance depends in large on neuromediators and neuropeptides content, in particular Substance P, a peptide responsible for delta-sleep, and beta-endorphin, in brain structures and peripheral tissues. It is emphasized that individual estimation of clinical indices of emotional stress is needed.

Neuroendocrine pathways of addictive behaviour

Alcohol intake is known to modulate plasma concentrations of neuroendocrine peptides. However, recent results suggest that the endocrine system may not only respond passively to alcohol intake but that, vice versa, it also actively modulates alcohol intake behaviour. The most coherent body of data concerns the hypothalamo-pituitary-adrenocortical (HPA) axis, with low corticotrophin-releasing hormone (CRH) being associated with more intense craving and increased probability of relapse after acute detoxification. Leptin, beta-endorphin and atrial natriuretic peptide (ANP), which indirectly regulate the HPA system, also may modulate the intensity of craving or the intensity of the alcohol withdrawal syndrome. Although most of the currently available data demonstrate association rather than causality between neuroendocrine changes and alcohol-related behaviours, they do provide testable hypotheses and open up perspectives of treating alcohol dependence via manipulation of the neuroendocrine axis.

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.

Non-opioid actions of opioid peptides

Beside the well known actions of opioid peptides on mu-, delta- and kappa-opioid receptors, increasing amount of pharmacological and biochemical evidence has recently been published about non-opioid actions of various opioid peptides. These effects are not abolished by naloxone treatments. Such non-opioid effects are observed both in nervous tissues and in the cellular elements of the immune system. Peptides exhibiting non-opioid effects include beta-endorphin, dynorphin A, nociceptin/OFQ, endomorphins, hemorphins and a number of Proenkephalin A derived peptides, such as Met-enkephalin, Met-enkephalin-Arg-Phe (MERF) and bovine adrenal medullary peptide (BAM22). Non-opioid actions are exerted through different neuronal receptors, e.g., dynorphin hyperalgesia through NMDA receptor, Met-enkephalin induced regulation of cell growth through zeta receptors, pain modulation by nociceptin through ORL-1 or NOP receptors, while BAM22 acts through sensory neuron specific G protein-coupled receptors (SNSR). We have investigated Met-enkephalin-Arg-Phe (MERF) and its analogues by the means of direct and indirect radioligand binding assays. It has been found that in addition to kappa(2) and delta-opioid receptors, MERF can act also through sigma(2)- or probably via FMRF-NH(2) receptors in rat cerebellum. A role of functionally assembling heterodimer receptors in mediating the non-conventional actions of these peptide ligands can not be excluded as well.

A critical role for β-endorphin in cocaine-seeking behavior

Endogenous beta-endorphin levels in the brain are elevated in response to cocaine and are downstream of the mesolimbic dopaminergic system. However, beta-endorphin's direct involvement in cocaine reinforcement has not been demonstrated. In the present study, a single bilateral microinjection of anti-beta-endorphin antibodies (4 microg) to the nucleus accumbens during the maintenance phase of cocaine self-administration (1 mg/kg/infusion) significantly increased the number of active and inactive lever responses. The increase in lever responses is reminiscent of rat behavior during extinction of cocaine self-administration. Further, a cocaine dose-response demonstrates that the increased lever presses in anti-beta-endorphin antibody-injected rats was still present after substitution with a lower dose of cocaine. These findings support a critical role for beta-endorphin in the cocaine brain reward system.

Adrenalectomy affects pain behavior of rats after formalin injection

Stressful stimuli can activate the hypothalamo-pituitary-adrenal-axis and the endogenous opioid system. In addition, corticosterone and opioid release might cause analgesia. This rat study used adrenalectomy for corticosterone withdrawal and naloxone administration for opioid antagonism in order to study pain behavior and hypophyseal hormone release in the plasma after a formalin test. Twelve days before the formalin testing, male Sprague Dawley rats underwent adrenalectomy or sham-adrenalectomy, and non-operated rats were used as reference. The number of flinches and the duration of licking or biting behavior were measured during the early and late phase. In reference and sham-operated rats, injection of formalin 5% resulted in a marked pain behavior in the early and late phase with significant increases in ACTH and corticosterone plasma levels. In adrenalectomized rats, pain behavior was decreased during both phases. Naloxone, administered before the late phase, did not alter pain behavior in sham or reference rats, whereas in adrenalectomized rats pain reactivity returned to those levels observed in reference rats. Beta-endorphin plasma levels above the detection limit were more frequently found in adrenalectomized rats. Thyrotropin and prolactin levels were not different between studied groups. We speculate that the observed reduced pain behavior in adrenalectomized rats after formalin, is the result of an increased production of pro-opiomelanocortin, the pro-drug of both adrenocorticotrophic hormone and beta-endorphin.

Beta-endorphin modulates the acute response to a social conflict in male mice but does not play a role in stress-induced changes in sleep

Beta-endorphin is an endogenous opioid peptide that is released during stress and has been associated with many physiological functions. In this experiment beta-endorphin deficient mice were used to study the role of endorphins in the acute physiological and behavioral responses to a social conflict, as well as their role in social stress-induced changes in sleep. Adult male beta-endorphin deficient and wild type mice were subjected to the stress of a 1 h social conflict with an aggressive dominant conspecific. After the conflict, the beta-endorphin deficient mice had higher corticosterone levels but the peak increase in body temperature was not different from that in wild type animals. In fact, body temperature returned to baseline levels faster in the beta-endorphin deficient mice. During their interaction with the aggressive conspecific several of the beta-endorphin deficient mice showed clear signs of counter aggression whereas this was not seen in any of the wild type mice. Overall, the beta-endorphin deficient mice and wild type mice had fairly similar sleep patterns under baseline conditions and also showed similar amounts of NREM sleep, REM sleep and EEG slow-wave energy after the social conflict. In addition, no differences were found in the sleep patterns of mice that showed counter aggression and mice that did not. In conclusion, the results suggest that beta-endorphin modulates the acute endocrine, thermoregulatory and behavioral response to a social conflict but the data do not support a major role for beta-endorphin in the regulation of sleep or social stress-induced alterations in sleep.

Involvement of endogenous beta-endorphin in antinociception in the arcuate nucleus of hypothalamus in rats with inflammation

Although exogenous administration of beta-endorphin to the arcuate nucleus of hypothalamus (ARC) had been shown to produce antinociception, the role of endogenous beta-endorphin of the ARC in nociceptive processing has not been studied directly. The aim of the present study was to investigate the effect of endogenous beta-endorphin in the ARC on nociception in rats with carrageenan-induced inflammation. The hindpaw withdrawal latency (HWL) to noxious thermal and mechanical stimulation was assessed by the hot-plate test and the Randall Selitto Test. Intra-ARC injection of naloxone had no significant influence on the HWL to thermal and mechanical stimulation in intact rats. The HWL decreased significantly after intra-ARC injection of 1 or 10 microg of naloxone in rats with inflammation, but not with 0.1 microg of naloxone. Furthermore, intra-ARC administration of the selective mu-opioid receptor antagonist beta-funaltrexamine (beta-FNA) decreased the nociceptive response latencies to both stimulation in a dose-dependent manner in rats with inflammation, while intra-ARC administration of the selective delta-opioid receptor antagonist naltrindole or the selective kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI) showed no influences on the nociceptive response latency. The antiserum against beta-endorphin, administered to the ARC, also dose-dependently reduced the HWL in rats with inflammation. The results indicate that endogenous beta-endorphin in the ARC plays an important role in the endogenous antinociceptive system in rats with inflammation, and that its effect is predominantly mediated by the mu-opioid receptor.

Regulation of human epidermal melanocyte biology by beta-endorphin

beta-Endorphin is an opioid peptide cleaved from the precursor pro-hormone pro-opiomelanocortin, from which other peptides such as adrenocorticotropic hormone, beta-lipotropic hormone, and alpha-melanocyte-stimulating hormone are also derived. alpha-Melanocyte-stimulating hormone and adrenocorticotropic hormone are well documented to regulate human skin pigmentation via action at the melanocortin-1 receptor. Whereas plasma beta-endorphin is reported to increase after exposure to ultraviolet radiation, to date a functional role for beta-endorphin in the regulation of human epidermal melanocyte biology has not been demonstrated. This study was designed to examine the involvement of the beta-endorphin/mu-opiate receptor system in human epidermal melanocytes. To address this question we employed reverse transcription-polymerase chain reaction, and immunohistochemistry/cytochemistry and immunoelectron microscopy using beta-endorphin and mu-opiate receptor specific antibodies. A functional role for beta-endorphin was assessed in epidermal melanocyte cultures by direct stimulation with the peptide. This study demonstrated the expression of mu-opiate receptor mRNA in cultured epidermal melanocytes, as well as mRNA for pro-opiomelanocortin. In addition, we have shown that beta-endorphin and mu-opiate receptor are expressed at the protein level in situ in glycoprotein100-positive melanocytes. The expression of both beta-endorphin and mu-opiate receptor correlated positively with their differentiation status in vitro. Furthermore, immunoelectron microscopy studies revealed an association of beta-endorphin with melanosomes. Functional studies showed that beta-endorphin has potent melanogenic, mitogenic, and dendritogenic effects in cultured epidermal melanocytes deprived of any exogenous supply of pro-opiomelanocortin peptides. Thus, we report that human epidermal melanocytes express a fully functioning beta-endorphin/mu-opiate receptor system. In the absence of any data showing cross-talk between the mu-opiate receptor and the melanocortin-1 receptor, we conclude that the beta-endorphin/mu-opiate receptor system participates in the regulation of skin pigmentation.

A role for the endogenous opioid beta-endorphin in energy homeostasis

Proopiomelanocortin (POMC) neurons in the hypothalamus are direct targets of the adipostatic hormone leptin and contribute to energy homeostasis by integrating peripheral and central information. The melanocortin and beta-endorphin neuropeptides are processed from POMC and putatively coreleased at axon terminals. Melanocortins have been shown by a combination of pharmacological and genetic methods to have inhibitory effects on appetite and body weight. In contrast, pharmacological studies have generally indicated that opioids stimulate food intake. Here we report that male mice engineered to selectively lack beta-endorphin, but that retained normal melanocortin signaling, were hyperphagic and obese. Furthermore, beta-endorphin mutant and wild-type mice had identical orexigenic responses to exogenous opioids and identical anorectic responses to the nonselective opioid antagonist naloxone, implicating an alternative endogenous opioid tone to beta-endorphin that physiologically stimulates feeding. These genetic data indicate that beta-endorphin is required for normal regulation of feeding, but, in contrast to earlier reports suggesting opposing actions of beta-endorphin and melanocortins on appetite, our results suggest a more complementary interaction between the endogenously released POMC-derived peptides in the regulation of energy homeostasis.

Increased splenocyte proliferative response and cytokine production in beta-endorphin-deficient mice

We used beta-endorphin-deficient mice as a novel approach to confirm the physiological role that opioid peptides play in the development or regulation of the immune system. We found that mice lacking beta-endorphin possessed an enhanced immune response, measured in terms of splenocyte proliferation and interleukin (IL)-2 mRNA levels, in vitro production of the splenic macrophage inflammatory cytokines IL-6 and Tumor Necrosis Factor (TNF)-alpha and plasma IL-6 following lipopolysaccharide (LPS) administration. beta-Endorphin-deficient mice had attenuated increases of plasma ACTH and corticosterone levels in response to LPS. These results are consistent with a postulated inhibitory role of endogenous beta-endorphin on the immune system at multiple levels.

Obesity and the polycystic ovary syndrome

The polycystic ovary syndrome (PCOS) is a condition characterized by hyperandrogenism and chronic oligo-anovulation. However, many features of the metabolic syndrome are inconsistently present in the majority of women with PCOS. Approximately 50% of PCOS women are overweight or obese and most of them have the abdominal phenotype. Obesity may play a pathogenetic role in the development of the syndrome in susceptible individuals. In fact, insulin possesses true gonadotrophic function and an increased insulin availability at the level of ovarian tissue may favour excess androgen synthesis. Obesity, particularly the abdominal phenotype, may be partly responsible for insulin resistance and associated hyperinsulinemia in women with PCOS. Therefore, obesity-related hyperinsulinemia may play a key role in favouring hyperandrogenism in these women. Other factors such as increased estrogen production rate, increased activity of the opioid system and of the hypothalamic-pituitary-adrenal axis, decreased sex hormone binding globulin synthesis and, possibly, high dietary lipid intake, may be additional mechanisms by which obesity favours the development of hyperandrogenism in PCOS. Irrespective of the pathogenetic mechanism involved, obese PCOS women have more severe hyperandrogenism and related clinical features (such as hirsutism, menstrual abnormalities and anovulation) than normal-weight PCOS women. This picture tends to be more pronounced in obese PCOS women with the abdominal phenotype. Body weight loss is associated with beneficial effects on hormones, metabolism and clinical features. A further clinical and endocrinological improvement can also be achieved by adding insulin-sensitizing agents and/or antiandrogens to weight reduction programmes. These obviously emphasize the role of obesity in the pathophysiology of PCOS.

Injection of alpha-MSH, but not beta-endorphin, into the PVN decreases POMC gene expression in the ARC

beta-Endorphin (beta-END) and alpha-melanocyte stimulating hormone (alpha-MSH), neuropeptides derived from proopiomelanocortin (POMC), have opposite effects on eating behavior. We injected rats with alpha-MSH (0.6 nmol) or beta-END (1 nmol) into the PVN (three times in a 26 h period). These doses of alpha-MSH and beta-END decreased and increased feeding respectively. Following alpha-MSH administration into the PVN, mRNA levels of POMC decreased by 17%, whereas there was no significant change in gene expression of either proDynorphin or proEnkephalin. PVN injection of beta-END failed to alter gene expression of POMC, proDynorphin or proEnkephalin. These data suggest that a feedback pathway exists between the PVN and ARC for alpha-MSH and POMC, but not for beta-END and POMC.

Metabolic control through L calcium channel, PKC and opioid receptors modulation by an association of naloxone and calcium salts

beta-endorphins (beta-ends) are released from the anterior pituitary and from lymphocytes directly into inflamed tissue in response to stress and pain. At the site of inflammation and trauma, the link of beta- ends to opioid receptors hyperpolarizes nerve terminal, by blocking L-calcium gated channels, induces modifications of receptor stereoisomerism and alters the bond-energy. Opioids increase potassium and decrease calcium and sodium currents through interactions with G-protein. In some pathologies, it has been found a loss of desensitization and down regulation of opioid receptors by means of Ca++ blocking that, in turn, inhibits PKC-activation. The physiopathological mechanism dependent on the high concentration of linked opioids affects cellular level of Ca++, ATP and NADH. This biochemical reaction exerts deep influence on energetic cell status and metabolism. In gram negative bacteria, expression of mu-receptors on cell surface has been observed, with a possibility to interfere with host cell metabolism. There are many human and veterinary pathologies in which the reported mechanisms are well known: polycystic ovary syndrome, gross cystic breast disease, milk fever, ruminal tympanites, pyometra, equine colic syndrome, ovarian follicular cyst in dairy cows, calcium deficit in post-partum cows, uterine involution in cows. Also incoming pathologies such as Electro-Magnetic-Field exposure may induce alteration of calcium channel activity through the same mechanism. On clinical bases, it has been pointed out that the therapeutic administration of an association of calcium salts and naloxone controls calcium turnover, pain and functional activity of endocrine glands, via down regulation/desensitization of opioid receptors, PKC stimulation and energy restoration.

Effect of the mu-opioid agonist DAMGO on medial basal hypothalamic neurons in beta-endorphin knockout mice

The endogenous opioid neurotransmitter beta-endorphin (beta-END), a product of the proopiomelanocortin (POMC) gene, is strongly implicated in the control of the female reproductive cycle, stress responses, and antinociception. Using selective gene targeting, we have generated a strain of mice that do not express any beta-END. These mice exhibit both normal reproduction and normal basal and stress-induced hypothalamic-pituitary-axis activity, but exhibit a significantly attenuated opioid-mediated stress-induced analgesia. To further understand the cellular bases of these responses, we have studied mediobasal hypothalamic (MBH) neurons, including POMC neurons, using whole-cell patch recording in an in vitro slice preparation. Twenty-seven MBH cells were recorded in wild-type and 25 MBH cells were recorded in beta-END knockout mice. Neurons from both genotypes showed a significant positive correlation between DAMGO concentration (from 30 nM to 10 microM) and the induced outward K(+) current. The genotypes did not differ, however, in either the DAMGO-induced maximum outward current response or EC(50), or for the maximal response to the GABA(B) agonist baclofen. Furthermore, quantitative receptor autoradiography utilizing (3)H-DAMGO did not reveal any differences in total mu-opioid receptor binding between genotypes. Therefore, we conclude that the complete absence of beta-END throughout development did not alter either the expression of mu-opioid receptors or their coupling to K(+) channels in MBH neurons.

[The mechanisms of the GABA-ergic regulation of beta-endorphin levels in the hypothalamic structures of prenatally stressed male rats]

The effect of GABA receptors agonists on the stress-induced beta-endorphin levels in the preoptic area and mediobasal hypothalamus of the intact and prenatally stressed male albino rats was studied. It has been found out that stimulation of GABAa-receptor complex by means of the muscimol leads to increasing of beta-endorphin levels in the preoptic area and mediobasal hypothalamus of the control animals. GABAb receptor activation by means of the baclofen decreases opioids level in the mediobasal hypothalamus. Prenatal stress eliminates stimulant effect of the muscimol on beta-endorphin levels in the investigated brain structures and leads to the opioid level decreasing after baclofen influence in preoptic area.

Involvement of dynorphin in immobilization stress-induced antinociception in the mouse

The effect of antiserum against [Met(5)]-enkephalin, [Leu(5)]-enkephalin, beta-endorphin, or dynorphin A-(1-13) administered intracerebroventricularly (i.c.v.) or intrathecally (i. t.) on immobilization-induced antinociception was studied in ICR mice. Antinociception was assessed by the tail-flick assay. Immobilization of the mouse increased inhibition of the tail-flick response at least 1 h. The i.c.v. or i.t. injection with antiserum against dynorphin A-(1-13) at the dose of 200 microg significantly attenuated immobilization-induced inhibition of the tail-flick response. However, antiserum against [Met(5)]-enkephalin, [Leu(5)]-enkephalin, or beta-endorphin did not affect the immobilization stress-induced antinociception. Furthermore, i.c.v. or i.t. injection with nor-binaltorphimine (Nor-BNI; from 1 to 20 microg) effectively inhibited immobilization stress-induced inhibition of the tail-flick response in a dose-dependent manner. However, beta-FNA (from 0.5 to 2 microg) or naltrindole (from 1 to 20 microg) administered i.c.v. or i.t. did not affect immobilization stress-induced antinociception. Our results suggest that supraspinally and spinally located dynorphin appears to be involved in the production of immobilization stress-induced antinociception via stimulating kappa-opioid receptors.

Methadone-related opioid agonist pharmacotherapy for heroin addiction. History, recent molecular and neurochemical research and future in mainstream medicine

In 1963, Professor Vincent P. Dole at the Rockefeller University formed a small team to develop a pharmacotherapy for the management of heroin addiction. They hypothesized that heroin addiction is a disease of the brain with behavioral manifestations, and not merely a personality disorder or criminal behavior and began to address the specific question of whether a long-acting opioid agonist could be used in the long-term maintenance treatment of heroin addiction. Over the next 35 years, many studies documented the safety, efficacy and effectiveness of methadone pharmacotherapy for heroin addiction, but Federal regulations and stigmatization of heroin addiction prevented implementation of treatment. Finally, in 1999, NIH published a report unequivocally supporting methadone maintenance pharmacotherapy for heroin addiction. Two other effective opioid agonist treatments have been developed: the even longer acting opioid agonist l-alpha-acetylmethadol (LAAM) has been approved for pharmacotherapy for heroin addiction, and still under study is the opioid partial agonist-antagonist buprenorphine-naloxone combination. A variety of studies, both laboratory based and clinical, have revealed the mechanisms of action of long-acting opioid agonists in treatment, including prevention of disruption of molecular, cellular and physiologic events and, in fact, allowing normalization of those functions disrupted by chronic heroin use. Recent molecular biological studies have revealed single nucleotide polymorphisms of the human mu opioid receptor gene; the mu opioid receptor is the site of action of heroin, the major opiate drug of abuse, analgesic agents such as morphine, and the major treatment agents for heroin addiction. These findings support the early hypotheses of our laboratory that addiction may be due to a combination of genetic, drug-induced and environmental (including behavioral) factors and also, that atypical stress responsivity may contribute to the acquisition and persistence of, as well as relapse to, use of addictive drugs.

The role of corticotropin-releasing factor in pain and analgesia

Corticotropin-releasing factor (CRF) is a peptide that is released from the hypothalamus and in widespread areas of the brain following exposure to stressors. It is considered to be a mediator of many of the effects of stress, and its analgesic properties have been demonstrated in many studies. However, for primarily methodological reasons, the effects of CRF in the central nervous system have been neglected whereas the peripheral effects of CRF have been overemphasized. We present evidence that: (1) CRF can act at all levels of the neuraxis to produce analgesia; (2) the release of beta-endorphin does not explain the analgesia following intravenous or intracranial CRF administration; (3) inflammation must be present for local CRF to evoke analgesia and (4) the analgesic effects of CRF show specificity for prolonged pain. These findings suggest that CRF may have a significant role in chronic pain syndromes associated with hypothalamic-pituitary-adrenal axis abnormalities. Furthermore, CRF may represent a new class of analgesics that merits further study. Implications for the relationship between stress and pain are discussed.

The physiological role of beta-endorphin in porcine ovarian follicles

Beta-endorphin-like immunoreactivity (beta-END-LI) was measured by radioimmunoassay in porcine ovarian follicular fluid (FF) from small, medium and large follicles throughout the oestrous cycle. The concentration of beta-END-LI in FF from small follicles collected on days 1-5 of the cycle was at least tenfold higher than in the fluid from any other follicles independently from their size and the period of the cycle. The level of beta-END-LI in small follicles on days 6-10 was drastically decreased. Subsequently, on days 11-16 its concentration was enhanced and reduced again in pre-ovulatory period of the cycle. Concentrations of beta-END-LI in FF from medium follicles were relatively equal throughout the cycle (days 6-21). No significant differences in beta-END-LI levels were found between small, medium and large follicles from days 17-21. However, beta-END-LI concentrations in medium follicles on days 11-13 and 14-16 were statistically lower than those in small follicles. Moreover, the effects of FSH, prolactin (PRL), progesterone (P4), testosterone (T) and 17 beta-oestradiol (E2) on beta-END-LI release by granulosa cells (GCs) from large follicles and, on the other hand, the effects of the opioid agonist FK 33-824 alone or in combination with FSH, PRL or naloxone (NAL) on follicular steroidogenesis were studied. FSH drastically increased beta-END-LI output in a dose-dependent fashion. This stimulatory effect of the gonadotrophin was inhibited by the highest dose of P4 (10(-5) M). The effect of PRL and the steroids added to the cultures on beta-END-LI release was negligible. FSH- or PRL-induced P4 secretion by GCs was essentially abolished by both FK 33-824 and NAL. However, androstenedione (A4) and testosterone output by the cells was greatly potentiated by FK 33-824. In the presence of NAL, FSH or PRL, A4 release stimulated by FK 33-824 was suppressed to the basal level. Secretion of E2 was completely free from the influence of FK 33-824 or NAL; only oestrone (E1) output was modulated by them in cultures where FSH or PRL was present. In conclusion, FSH appears to be the key regulator of beta-END-LI secretion by porcine granulosa cells. Moreover, steroidogenesis in pig granulosa cells is modulated by opioid peptides acting both alone and by way of interaction with FSH or PRL.

POMC-derived peptides and their biological action

It has long been known that a large number of POMC-related peptides are found in skin. In this introduction I describe the formation of POMC-derived peptides in various tissues to indicate that processing is largely tissue-dependent. I focus on the peptides from the N-terminal fragment, such as gamma-MSH, ACTH and alpha-MSH, and beta-lipopropin as well as beta-endorphin. I touch on the factors that control the synthesis of the various peptides, which are now numerous and varied, and again are tissue specific. The biologic activity of the peptides generated from POMC are described in relation to their possible action in skin. In addition, I describe a new class of peptides induced in skin following injury and which are of great interest.

The skin POMC system (SPS). Leads and lessons from the hair follicle

Human and murine skin are prominent extrapituitary sources and targets for POMC products. The expression of, for example, ACTH, alpha-MSH, beta-endorphin, and MC-1-receptors fluctuates during synchronized hair follicle cycling in C57BL/6 mice. Since hair growth can be induced by ACTH injections in mice and mink, and since high doses of MSH peptides modulate epidermal and/or follicle keratinocyte proliferation in murine skin organ culture, some POMC products may operate as locally generated growth modulators, in addition to their roles in cutaneous pigment and immunobiology. Intrafollicularly generated ACTH and alpha-MSH as well as their cognate receptors may assist in the maintenance of the peculiar immune privilege of the anagen hair bulb. Possibly, they are also involved in the development of the follicle pigmentary unit, with whose generation their expression coincides. Given that murine skin also expresses (in a hair-cycle-dependent way) CRH and CRH-R, which control pituitary POMC expression and in view of the fact that CRH arrests follicles in telogen, this suggests the existence of a local skin POMC system (SPS). This may be an integral component of cutaneous stress response-systems, and may most instructively be studied using the murine hair cycle as a model.