Reciprocal antagonism between ACTH1-24 and beta-endorphin in rats

The Melanocortin and Endorphin Neuropeptides in Patients with Restless Legs Syndrome

OBJECTIVE

Based upon similarities between the urge to move and sensory discomfort of restless legs syndrome (RLS) and properties of melanocortin hormones, including their incitement of movement and hyperalgesia, we assessed plasma and cerebrospinal fluid (CSF) α-melanocyte-stimulating hormone (α-MSH) and β-endorphin in RLS patients and controls.

METHODS

Forty-two untreated moderate-to-severe RLS patients and 44 matched controls underwent venipuncture at 19:00, 20:30, and 22:00; 37 RLS and 36 controls had lumbar puncture at 21:30. CSF and plasma were analyzed for pro-opiomelanocortin (POMC), adrenocorticotropin hormone (ACTH), α-MSH, β-MSH, and β-endorphin by immunoassay. RLS severity was assessed by International RLS Study Group Severity Scale.

RESULTS

RLS participants were 52.7 ± 12.0 years old, 61.9% were women, 21.4% had painful RLS, and RLS severity was 24.8 ± 9.0. Controls had similar age and sex. Plasma ACTH, α-MSH, and β-endorphin were similar between groups. Plasma POMC was significantly greater in RLS than controls (17.0 ± 11.5 vs 12.7 ± 6.1fmol/ml, p = 0.048). CSF ACTH was similar between groups. CSF β-MSH was significantly higher in painful than nonpainful RLS or controls (48.2 ± 24.8 vs 32.1 ± 14.8 vs 32.6 ± 15.2pg/ml, analysis of variance [ANOVA] p = 0.03). CSF α-MSH was higher in RLS than controls (34.2 ± 40.9 vs 20.3 ± 11.0pg/ml, p = 0.062). CSF β-EDP was lowest in painful RLS, intermediate in nonpainful RLS, and highest in controls (8.0 ± 3.4 vs 10.8 ± 3.1 vs 12.3 ± 5.0pg/ml, ANOVA p = 0.049). The ratio of the sum of CSF α- and β-MSH to CSF β-endorphin was highest, intermediate, and lowest in painful RLS, nonpainful RLS, and controls (p = 0.007).

INTERPRETATION

CSF β-MSH is increased and CSF β-endorphin decreased in RLS patients with painful symptoms. ANN NEUROL 2024;95:688-699.

Fetal alcohol spectrum disorders and their transmission through genetic and epigenetic mechanisms

Fetal alcohol spectrum disorders (FASD) are a group of related conditions that arise from prenatal exposure to maternal consumption of the teratogen, ethanol. It has been estimated that roughly 1% of children in the US suffer from FASD (Sampson etal., 1997), though in some world populations, such as inhabitants of some poorer regions of South Africa, the rate can climb to as high as 20% (May etal., 2013). FASD are the largest cause of mental retardation in U.S. neonates, and ironically, are entirely preventable. FASD have been linked to major changes in the hypothalamic-pituitary-adrenal (HPA) axis, resulting in lifelong impairments through mental disorders, retardation, and sensitivity to stress. FASD are linked to an impaired immune system which consequently leads to an elevated risk of cancer and other diseases. FASD arise from a complex interplay of genetic and epigenetic factors. Here, we review current literature on the topic to tease apart what is known in these areas particularly emphasizing HPA axis dysfunction and how this ties into new studies of transgenerational inheritance in FASD.

Influence of beta-Endorphin on anxious behavior in mice: interaction with EtOH

RATIONALE

The opioid peptide beta-endorphin (beta-E) is synthesized by the pro-opiomelanocortin gene in response to environmental stressors and alcohol administration and is implicated in the behavioral sequelae associated with these stimuli.

OBJECTIVES

We sought to determine the influence of beta-E on the stress response by evaluating basal measures of anxiety as well as on EtOH-induced anxiolytic behavior using transgenic mice that differ with respect to beta-E.

METHODS

Anxious behavior was evaluated for male and female heterozygous, wild-type, and beta-E knockout mice using the Light-Dark Box and Plus Maze assays. Subsequent tests evaluated behavior 20 min after administration of intraperitoneal saline or EtOH (0.5, 1.0, and 1.5 g/kg).

RESULTS

We observed a direct relationship between beta-E levels and the percentage of entries into open arms of the Plus Maze as well as the time spent in either the open arms or the light compartment of the Light-Dark box during basal conditions, suggesting that this peptide normally inhibits anxious behavior. However, mice lacking beta-E demonstrated an exaggerated anxiolytic response to EtOH in these assays.

CONCLUSIONS

These data suggest that beta-E moderates the response to stressful stimuli and supports the hypothesis that this peptide influences the behavioral effects of EtOH.

Role of melanocortins in the central control of feeding

The injection of a melanocortin peptide or of melanocortin peptide analogues into the cerebrospinal fluid or into the ventromedial hypothalamus in nanomolar or subnanomolar doses induces a long-lasting inhibition of food intake. The effect keeps significant for up to 9 h and has been observed in all animal species so far tested, the most susceptible being the rabbit. The anorectic effect of these peptides is a primary one, not secondary to the shift towards other components of the complex melanocortin-induced behavioral syndrome, in particular grooming. The site of action is in the brain, and the effect is not adrenal-mediated because it is fully exhibited also by adrenalectomized animals. It is a very strong effect, because the degree of feeding inhibition is not reduced in conditions of hunger, either induced by 24 h starvation, or by insulin-induced hypoglycemia, or by stimulation of gamma-aminobutyric acid (GABA), noradrenergic or opioid systems. The microstructural analysis of feeding behavior suggests that melanocortins act as satiety-inducing agents, because they do not significantly modify the latencies to start eating, but shorten the latencies to stop eating. The mechanism of action involves the activation of melanocortin MC(4) receptors, because selective melanocortin MC(4) receptor antagonists inhibit the anorectic effect of melanocortins, while inducing per se a strong stimulation of food intake and a significant increase in body weight. Melanocortins seem to play an important role in stress-induced anorexia, because such condition, in rats, is significantly attenuated by the blockage of melanocortin MC(4) receptors; such a role is not secondary to an increased release of corticotropin-releasing factor (CRF), because, on the other hand, the CRF-induced anorexia is not affected at all by the blockage of melanocortin MC(4) receptors. The physiological meaning of the feeding inhibitory effect of melanocortins, and, by consequence, the physiological role of melanocortins in the complex machinery responsible for body weight homeostasis, is testified by the hyperphagia/obesity syndromes caused by mutations in the pro-opiomelanocortin (POMC) gene, or in the melanocortin MC(4) receptor gene, or in the agouti locus. Finally, recent evidences suggest that melanocortins could be involved in mediating the effects of leptin, and in controlling the expression of neuropeptide Y (NPY).

Comparative study of the roles of ACTH and beta-endorphin in regulating conditioned reflex activity in the hedgehog

Data on the relative effects of the neurohormone ACTH1-39 and the opioid peptide beta-endorphin on conditioned reflex activity in the hedgehog are presented. It was demonstrated that administration of ACTH (30-50 micrograms/kg s.c.) led to facilitation of learning and strengthening of memory processes (conditioned reflex traces). ACTH promoted strengthening of movement, orientational-investigative, and intersignal activities, produced hyperalgesia, and blocked the effects of naloxone. Administration of beta-endorphin (30-40 micrograms/kg s.c.) lengthened the latent periods of conditioned reflexes, produced a pronounced analgesic effect, and reduced movement and intersignal activities. The effects of beta-endorphin were eliminated by dosage with naloxone. Administration of beta-endorphin blocked the inhibitor effects of stimulation of the limbic cortex; doses of ACTH produced partial release of inhibitory effects. The differences between the effects of ACTH and beta-endorphin on higher nervous activity are discussed, as are the possible mechanisms of these effects.

Blockade of the polyamine site of NMDA receptors produces antinociception and enhances the effect of morphine, in mice

The possible effect of ifenprodil--a potent antagonist at the polyamine site of the NMDA receptor complex--on nociceptive threshold and morphine analgesia was investigated in mice. In the hot plate test, the intraperitoneal (i.p.) injection of ifenprodil significantly prolonged the reaction time of mice at the dose of 30 mg/kg, and increased the analgesic effect of morphine. In the phenylquinone writhing test, ifenprodil reduced the number of abdominal constrictions of mice starting from the dose of 2.5 mg/kg i.p., and increased the effect of morphine. The effect of ifenprodil on pain threshold was prevented by naloxone. Moreover, ifenprodil antagonized the pain threshold-reducing effect of alpha-melanocyte-stimulating hormone (0.05 microgram/mouse, intracerebroventricularly). These data show that blockade of the polyamine site of the NMDA receptor complex produces analgesia and increases the analgesic effect of morphine.

The opioid/anti-opioid balance in shock: a new target for therapy in resuscitation

Teleologically, pain is of paramount importance for survival and induces the organism to cope in an active way with aggressions from a basically hostile environment. While the activation of endogenous analgesic (opioid) systems typically occurs in conditions of surrender (pre-terminal conditions, sustained tortures, etc.), the activation of endogenous anti-analgesic systems triggers mechanisms of active or passive defence (such as camouflage) aimed at survival. The distinctive features of the main anti-analgesic systems (melanocortinergic, cholecystokininergic, thyroliberinergic) and the dramatic results obtained in experimental pre-terminal conditions (hemorrhagic shock, prolonged respiratory arrest) with the administration of their neuropeptide transmitters (ACTH and several ACTH-fragments, including alpha-MSH, CCK peptides and thyrotropin-releasing hormone) are here reviewed. The study of the mechanisms underlying the resuscitating effects of these neuropeptides has led to the discovery of the (often extremely potent) resuscitating effect of other drugs (protoveratrines, nicotine, centrally-acting cholinergic agents, ganglion-stimulating drugs). It is particularly remarkable that in pre-terminal conditions these neuropeptides and drugs have highly impressive effects on cardiocirculatory parameters at doses that are almost or actually inactive under normal conditions, and that their resuscitating effect is obtained without the need for any other supportive treatment and at dose-levels well below toxic ranges. Finally, in hemorrhage-shocked animals, the treatment with anti-analgesic neuropeptides shortly after bleeding considerably extends the time-limit for an effective and definitively curing blood reinfusion. This would be of self-evident importance in clinical practice, because an extremely simple, non-toxic first-aid treatment in the field, shortly after a massive hemorrhage, could resuscitate the patient for a period sufficient to effectively set up the most appropriate in-hospital treatment.

Opening of brain potassium-channels inhibits the ACTH-induced behavioral syndrome in the male rat

In adult male rats, the intracerebroventricular (i.c.v.) injection of pinacidil, a potassium channel opener, at the doses of 100, 200 or 300 micrograms/rat, dose-dependently reduced the display of the most typical behavioral symptoms (excessive grooming, stretching, yawning, penile erections) induced by the i.c.v. administration of ACTH-(1-24) (4 micrograms/rat). These data indicate that the complex mechanism of the melanocortin-induced behavioral syndrome involves closure of potassium channels in target neurons, and provide further experimental support to the idea that melanocortins are functional antagonists of opioids.

Tetracosactrin vs. methylprednisolone in the prevention of emesis in patients receiving FEC regimen for breast cancer

0.5 mg tetracosactrin is considered to be equivalent to 40 mg methylprednisolone with regard to the induced cortisol secretion. 97 female breast cancer patients who received their first two FEC courses (epirubicin 50-75 mg/m2, 5-fluorouracil 500 mg/m2, cyclophosphamide 500 mg/m2) entered this randomised crossover study (76 had previously received an adjuvant treatment); tetracosactrin was administered intramuscularly and methylprednisolone intravenously immediately before chemotherapy administration. The tolerability was evaluated using a diary card during 5 days and patients were asked for their preference at the end of the two cycles. There was no difference either for vomiting (dry heaves were included) or nausea between the two treatments (the analysis was performed on day 1, the worse day of days 2 and 3 and the worse day of days 4 and 5). At day 1, 49% of the patients experienced no or mild nausea after tetracosactrin and 62% after methylprednisolone (not significant) (first period analysis); a complete control of vomiting (including dry heaves) was observed in 49% of the patients after tetracosactrin and 53% after methylprednisolone (not significant). No difference was observed between patients with or without previous chemotherapy. However, slightly more patients preferred tetracosactrin (P = 0.048).

Electroacupuncture analgesia in naive rats: effects of brainstem and spinal cord lesions, and role of pituitary-adrenal axis

Recent studies have shown that analgesia is potentiated by naltrexone (NTX) and naloxone (NAL) pretreatment in rats exposed for the first time to electroacupuncture (EA). In the present study, we have investigated the role of the pituitary-adrenal axis and of brainstem and spinal cord structures in EA analgesia and its potentiation by NTX. The pituitary and adrenal glands do not participate in the production of EA analgesia, but may produce a non-opioid substance which interferes with the development of EA analgesia. Spinalization or dorsolateral funiculi lesions blocked EA analgesia, and intrathecal NTX had no effect. These results indicate that supraspinal structures are necessary to produce and potentiate EA analgesia. Contrary to their critical role in morphine and other models of environmentally produced analgesia nucleus raphe alatus and raphe structures dorsal to it are not necessary for the development of EA analgesia. These structures, however, may contain opiate synapses on which NTX may act as an agonist to potentiate analgesia. The various components which appear to participate in the production of EA analgesia imply a complex circuit of pain modulation systems and indicate that an organism can adapt to distinct environmental conditions with versatile means to avoid pain.

Effects of ACTH(1-24) on single unit activity in the brainstem of the rat

Central administration of corticotropin-like peptides generally blocks the analgesic action of opiate ligands, yet it is unclear whether this is due to an independent hyperalgesic action of corticotropin or to some other mechanism. Single cells in the ventromedial medulla of the anaesthetized rat were characterized as either excited by noxious stimuli or inhibited. Injections of ACTH(1-24) excited cells that were excited by noxious stimuli and inhibited cells that were inhibited by noxious stimuli. The results support an independent role for corticotropin-like peptides in pain-modulating mechanisms.

Action of pro-opiomelanocortin products on the rat vas deferens

Behavioral study of pro-opiomelanocortin products indicates that beta-endorphin and corticotrophin-like peptides have antagonistic effects. However, these peptides have similar actions on the rat vas deferens. beta-endorphin, alpha-MSH and ACTH each inhibit electrically evoked contraction of the duct, but the corticotrophin derived peptides are tenfold more potent on a molar basis (ED50 = 9 nM). Pharmacological analysis shows that the action of corticotrophin-derived peptides does not involve an opiate receptor mechanism. The results are discussed in terms of the central action of the peptides.

Influence of centrally administered peptides on ear withdrawal from heat in the rabbit

Certain neuropeptides previously linked to stress and implicated in CNS control of analgesia/algesia were tested using a recently developed analgesiometric model, the rabbit ear-withdrawal test. The latency to ear withdrawal increased in a dose-related manner after beta-endorphin was injected intracerebroventricularly (IVC). Intermediate doses (0.5 and 1.0 micrograms) of adrenocorticotropic hormone (ACTH) caused hyperalgesia as indicated by decreases in latency. Corticotropin-releasing factor (CRF, 0.5 and 1.0 micrograms) also caused significant hyperalgesia late in the testing period. alpha-Melanocyte stimulating hormone (alpha-MSH, 0.25-2.0 micrograms), a molecule that shares the first 13 amino acid sequence with ACTH, and somatostatin (0.25-2.0 micrograms), caused no significant change in latency. However, 1.0 microgram doses of each peptide antagonized the analgesic effect of beta-endorphin (1.0 microgram) in the following order of potency: ACTH = alpha-MSH greater than CRF greater than somatostatin. The results support the idea that CNS peptides that are released during stress can exert opposing actions on acute pain, even though they may cause little effect alone.

Opiate dependence and withdrawal--a new synthesis?

There is a growing body of evidence to suggest that adrenocorticotropin (ACTH) may have a physiological role as an endogenous contra-opioid agonist. In addition to having appreciable affinity for opiate receptors and inducing many behavioural and intracellular effects opposite to those observed following opioid administration, ACTH may interact with endorphins in a mutually antagonistic manner. On the basis of these data a model of opiate dependence is proposed whereby several aspects of the opiate abstinence syndrome may be attributed to the excitatory actions of ACTH acting at opiate receptors. Thus, it may be predicted that opiate antagonist administration during primary abstinence should significantly attenuate many aspects of this behavioural syndrome. The present study was conducted in order to investigate this hypothesis. Results indicated that whilst naloxone (1.5 mg/kg) exerted little influence in non-dependent animals, it significantly attenuated abstinence-exacerbated grooming, body shaking, teeth chattering and sneezing, in addition to completely antagonizing withdrawal hyperalgesia in post-dependent animals. These data are consistent with the proposed existence of an endogenous contra-opioid ligand, the antagonism of which markedly reduces the severity of the morphine withdrawal syndrome.

Opioid modulation of appetite

The discovery of opiate receptors and endogenous opioid peptides within the central nervous system has resulted in a number of speculations concerning the physiological significance of these peptides. In the present article, we review the evidence suggesting a primary role for some of the opioid peptides as regulators of ingestive behavior. In particular, we elaborate a hypothesis in which we suggest that in some species opioid peptides may play a role as a tonic inducer of ingestive behaviors, held in check by a variety of neuropeptides and monoamines. This review explores in detail the role of the opioid peptides as major mediators of the reward system and as a link between reward and feeding behaviors. Finally, a teleological role for opioid peptides in species preservation, which may explain the discrepancies in the role of the opioid peptides in feeding behavior in different species is proposed. It is suggested that the feeding profile of the animal provides important clues as to whether or not the animal has an opiate-sensitive feeding system. We stress that interactions with ingested nutrients and the milieu interieur provide an important means by which animals modulate the opiate-entrained feeding drives.

Endogenous opiates: 1981

This paper is the fourth of an annual series reviewing the research concerning the endogenous opiate peptides. This installment covers only work published during 1981 and attempts to provide a comprehensive, but not exhaustive, survey of the area. Previous papers in the series have dealt with research done before 1981. Topics concerning endogenous opiates reviewed here include a delineation of their receptors, their distribution, their precursors and degradation, behavioral effects resulting from their administration, their possible involvement in physiological responses, and their interactions with other peptides and hormones. Due to the burgeoning literature in this field, the comprehensive nature of this review in the future will be limited to considerations of behavioral phenomena related to the endogenous opiates.

Potentiation of the aphrodisiac effect of N-n-propyl-norapomorphine by naloxone

N-n-Propyl-norapomorphine (NPA), a potent dopamine (DA) receptor stimulant, in doses from 0.4 to 80 micrograms/kg i.p. produced a dose-related sexual stimulant effect characterized by recurrent episodes of penile erection (PE). The number of episodes and percentage of responding subjects were proportional to the dose. However, above the maximal effective dose, the effect decreased in a dose-related fashion until beyond 2.5 mg/kg even the natural occurrence of PE was suppressed. Morphine (5 mg/kg), as well as haloperidol (0.3 mg/kg), prevented NPA stimulation. Naloxone, which per se caused a modest increase in PE, markedly potentiated the stimulant effect of low doses of NPA, reversing the inhibitory component of higher doses. We suggest that NPA stimulation of DNA receptors causes release of opiate peptides, dampening the sexual stimulant response. The combination of DA receptor stimulants with naloxone might offer a new possibility for erection defect therapy.