Endogenous opiates: 1986

Prevalence and correlates of epileptic seizure in substance-abusing subjects

Life-time prevalence of epileptic seizures was assessed in 626 consecutive patients treated for substance abuse. Seizures were reported in 8.63% (9.2% in alcohol abusers, 12.5% in opioid abusers). A total of 64.8% of the seizures were associated with substance use. These occurred during withdrawal in the alcohol cohort and during intoxication with dextropropoxyphene and withdrawal from heroin or poppy husk in the opioid cohort. Results indicate that seizures may be more common in older patients with longer duration of dependence among those abusing alcohol.

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

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

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

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

Effect of acute alcohol intoxication on the opioid system in humans

We investigated the possible relations between the endogenous opioid system and acute alcoholic intoxication in 21 subjects, of whom 13 were drinkers who came to the emergency service with evident symptoms of drunkenness, and 8 were nondrinkers who consumed 1 g alcohol per kg body weight over a short period. Different patterns of changes were found in the two groups for plasma concentrations of beta-endorphin and adrenocorticotropic hormone. In drinkers, plasma levels of both substances increased, whereas in nondrinkers both concentrations decreased, the declines being especially notable 15, 30, and 45 min after ingestion. We found no differences between the two groups in plasma cortisol concentrations. The different levels of these substances may reflect differences in drinking behavior between the two groups.

Classification of alcoholics on the basis of plasma beta-endorphin concentration

Recent findings suggest that a genetic deficit in opioid may be a biological marker of alcoholism. In other words, decreased plasma concentrations of opioids may be a predisposing factor, rather than a consequence, of alcohol consumption. We attempted to classify 88 randomly chosen individuals as alcoholics or nonalcoholics on the basis of plasma concentration of beta-endorphins. This criterion had a sensitivity of 73.30% and a specificity of 79.45%. Its positive predictive value was 42.30%, and its negative predictive value was 93.55%.

The Tyr-MIF-1 family of peptides

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

Drugs and endogenous ligands compete for receptor occupancy

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

Effects of space flight stress on proopiomelanocortin, proenkephalin A, and tachykinin neuropeptidergic systems in the rat posterior pituitary

beta-endorphin-like immunoreactivity (BE-li), methionine enkephalin-like immunoreactivity (ME-li), and substance P-like immunoreactivity (SP-li) were measured in the posterior pituitary of rats that experienced a 5-day space flight in a Space Shuttle. ME-li and SP-li were both significantly lower compared to the control rats. However, there was no difference in BE-li between flight and control rats. These data suggest that the space flight stress diminished the methionine enkephalin (ME) and substance P (SP) concentrations in the posterior pituitary without affecting the beta-endorphin (BE) concentration. Thus, the proenkephalin A and tachykinin, but not proopiomelanocortin, neuropeptidergic systems in the posterior pituitary may respond to this type of unique stress.

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

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

Age-related changes in the contents of neuropeptides in the rat brain and pituitary

beta-Endorphin, Leu-enkephalin, Met-enkephalin, substance P, somatostatin, and cholecystokinin were measured in the brain and the pituitary of male Sprague-Dawley rats aged 3 months, 12 months, and 22 months. beta-Endorphin, Met-enkephalin and Leu-enkephalin contents in the neurointermediate lobe, and the enkephalin levels in the anterior lobe of the pituitary increased with age. The increases in contents were both in the day and at night for beta-endorphin and Met-enkephalin. However, the increase for Leu-enkephalin content was in the day only. Hypothalamic beta-endorphin content decreased with age only in the day. beta-Endorphin and Leu-enkephalin contents in the brain stem, and Leu-enkephalin levels contents in the cortex decreased with age at night. Leu-enkephalin in the striatum decreased with age in the day. There was also an age-related decrease for somatostatin and substance P contents in the striatum and the hypothalamus in the day, and in cholecystokinin levels in the hippocampus, and the hypothalamus at night. It is concluded that there are age differences in neuropeptide levels, and that these changes may differ according to diurnal rhythms.

The presence and actions of opioid receptors in bovine pineal gland

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

Endorphins do not affect behavioral stress responses in mice

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

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

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

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

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

Plasma beta-endorphin levels in chronic alcoholics

In order to test the possible relationship between the chronic consumption of alcohol and the opioid system, we have measured the plasma levels of beta-endorphin in a group of 31 alcoholic patients and compared the results with those of a control group of 16 subjects. Our results show that chronic consumption of alcohol induces a significant decrease in beta-endorphin (beta-end) plasma levels regardless of either the disease suffered by the alcoholic patient or of the time of abstinence studied (one month maximum). Thus we believe that the beta-end decrease may well be due to the patients' alcoholism and that it might be mediated by the tetrahydroisoquinoline system, or be a cause of alcoholism rather than a consequence.

Effects of corticotropin-releasing factor (CRF) and opiates on amphibian locomotion

Male rough-skinned newts (Taricha granulosa) were used as a model for the study of the neuroendocrine regulation of locomotion. Intracerebroventricular (i.c.v.) injections of nanogram quantities of corticotropin-releasing factor (CRF) dose-dependently increased locomotion as measured in a circular open-field test arena. In other studies animals received intraperitoneal (i.p.) injections of saline or naloxone, a synthetic opioid antagonist, followed by i.c.v. injections of saline or CRF. With 1-min intervals between injections, neither i.p. saline nor naloxone injections modified the stimulatory effects of CRF injections on locomotor activity. In contrast, with 20-min intervals between injections, the naloxone-plus-CRF injected newts displayed more locomotor activity than the saline-plus-CRF injected newts, suggesting that the opioid system modulated the behavioral effects of CRF. An i.p. injection of bremazocine, an opiate kappa-receptor agonist, suppressed spontaneous locomotion but not CRF-induced locomotion. In contrast, an i.p. injection of morphine, an opiate mu-receptor agonist, did not affect spontaneous locomotion but reduced CRF-induced locomotion, indicating further that the opioid system may modulate the behavioral effects of CRF in this amphibian. The present study provides the first evidence that both CRF and opioids may be involved in the regulation of amphibian locomotor activity.

Effects of corticotropin-releasing factor (CRF), tuftsin and dermorphin on behavior of squirrel monkeys maintained by different events

The effects of intracerebroventricular (ICV) administration of ovine CRF (0.1-30.0 micrograms/kg), dermorphin (0.3-30.0 micrograms/kg) and tuftsin (10-3000 micrograms/kg) were examined in squirrel monkeys trained to respond under a multiple 3-min fixed-interval schedule of food presentation and either shock presentation or stimulus-shock termination. Initial administration of the 41-amino acid polypeptide CRF increased food-maintained responding by 150-200% in 2 of 3 subjects. However, no other doses tested affected response rates, a result that may have been due to the rapid development of tolerance. The tetrapeptide tuftsin selectively increased responding maintained by food presentation at doses that decreased shock-maintained responding. The heptapeptide dermorphin selectively increased food-maintained responding when responding in the other component of the multiple schedule was maintained by shock presentation. When responding was maintained by a multiple food, stimulus-shock termination schedule, dermorphin decreased response rates in both components. Dermorphin's rate increases were blocked by the opiate antagonist naloxone, indicating that dermorphin's actions were mediated through the opiate receptor. These results indicate that the behavioral effects of tuftsin, dermorphin, and perhaps CRF, depend on the manner in which responding is controlled by its consequences. While the actions of tuftsin and dermorphin are believed to be mediated through the opiate system, the behavioral effects observed in primates appear different from the effects of morphine under similar schedule conditions.

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

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

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

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

Analysis of the beta-endorphin structure-related activity on human monocyte chemotaxis: importance of the N- and C-terminal

We evaluated the chemotactic activity of beta-endorphin and beta-endorphin-related peptides on human monocytes. We tested beta-endorphin(1-31) and fragments (1-16), (1-17), (1-27) in which the N-terminal of the opioid is preserved, N-acetyl-beta-endorphin(1-31) and fragments (6-31) and (28-31) in which the C-terminal is preserved, and fragment (2-17) that lacks both the N- and C-terminal. The fragments in which the N- and C-terminal were preserved [with the exception of fragment (28-31)] showed a chemotactic effect, while the lack of both terminals deprived the peptides of any activity. Moreover, only the N-terminal-mediated effects were naloxone reversible, while the C-terminal effects were not. These results indicate that while the intact N-terminal is necessary for opioid like effects, both N- and C-terminal can mediate effects on the immune system, thus offering evidence for a nonopioid receptor-mediated effect of opioid peptides on the immune system.

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

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

Opioid peptides modulate immune functions. A review

In the past few years it has become evident that neuropeptides may be direct mediators in the modulation of the immune response and the unspecific defense by the brain. Lymphocytes have been thought to have opioid receptors and to respond to opioids with an increase in blastogenesis, cytotoxicity and factor release. Lymphocytes are said to release various neuropeptides. Furthermore, there are some unexplained effects of morphine on the immune system and of the immune system on morphine withdrawal. The purpose of this paper is to review what has been previously published in this field. The well established modulation of phagocyte functions by opioids will only be scanned.