Opiocortin peptides: localization, source and avenues of transport

Beta-Endorphin and Oxytocin in Patients with Alcohol Use Disorder and Comorbid Depression

Background: The neuropeptides β-endorphin and oxytocin are released into the bloodstream as hormones from the pituitary gland but also have an important function as neuroregulators in the forebrain. The blood levels of both polypeptides have been shown to reflect depressive symptoms. β-Endorphin, in particular, is also involved in abstinence from alcohol. Methods: The serum levels of β-endorphin and oxytocin were measured during the early withdrawal phase in patients with alcohol use disorder (AUD) with (N = 35) or without (N = 45) depressive comorbidity and compared with those in healthy volunteers (N = 23). In addition to comparing the groups, the study examined whether serum levels correlated with various psychometric measures of dependence, depression and aggression, as well as with clinical characteristics of dependence. Results: Both serum levels of beta-endorphin and oxytocin were significantly lower in patients than those in healthy controls (p = 0.011 for β-endorphin and p = 0.005 for oxytocin, Kruskal–Wallis test). In patients with depressive comorbidity, the significance was greatest (p = 0.005 for β-endorphin and p = 0.004 for oxytocin, U-test). There was no correlation with clinical or psychometric parameters (p > 0.05, Spearman test), but beta-endorphin levels did correlate significantly with physical aggression (p = 0.026, Spearman test). Conclusions: Serum levels of β-endorphin and oxytocin are lower in patients with AUD, particularly in those with depressive comorbidity. β-Endorphin levels correlated with physical aggression according to the Buss–Durkee (BDHI) estimates.

Posttraumatic and depressive symptoms in β-endorphin dynamics

A disturbed beta-endorphin system can be a part of the post-traumatic stress disorder (PTSD) and depression allostasis. Study subjects (N=392) included those with PTSD and/or (stress-induced) depression, and healthy controls with and without traumas. The aim of the study was to examine the network of relations centered around plasma beta-endorphin. The network included anxiety (as a personality trait), traumatic events, pain, aggressiveness, depressive symptoms, and three clusters of PTSD symptoms: intrusions, avoidance, and hyperarousal. Beta-endorphin was represented by individual mean from 13 time points (BEmean), reflecting the total amount of the peripherally secreted hormone, and the coefficient of variation (BEvar), calculated as the ratio of standard deviation to the mean, reflecting the hormone׳s dynamics. BEvar correlated with all other variables, BEmean had no correlations. Structural equation modeling (SEM) was used to examine all interrelations (including their directions) of BEvar and the state/trait variables in the context of their entirety. The model revealed that hyperarousal and anxiety were the only direct agents of peripheral beta-endorphin fluctuations, mediating the effects of other variables. Traumatic events and intrusions act on BEvar via hyperarousal, while depressive symptoms, avoidance, and pain act via anxiety. Hyperarousal should be emphasized as the main agent not only because its effect on BEvar is larger than that of anxiety, but also because it increases anxiety itself (via avoidance and pain). All influences on BEvar are positive and they indicate long-term (sensitizing) effects (as opposed to direct stimulation, for example, by acute pain, anger, etc.). Relations apart from beta-endorphin are also discussed.

Volume transmission of beta-endorphin via the cerebrospinal fluid; a review

There is increasing evidence that non-synaptic communication by volume transmission in the flowing CSF plays an important role in neural mechanisms, especially for extending the duration of behavioral effects. In the present review, we explore the mechanisms involved in the behavioral and physiological effects of β-endorphin (β-END), especially those involving the cerebrospinal fluid (CSF), as a message transport system to reach distant brain areas. The major source of β-END are the pro-opio-melano-cortin (POMC) neurons, located in the arcuate hypothalamic nucleus (ARH), bordering the 3^rd ventricle. In addition, numerous varicose β-END-immunoreactive fibers are situated close to the ventricular surfaces. In the present paper we surveyed the evidence that volume transmission via the CSF can be considered as an option for messages to reach remote brain areas. Some of the points discussed in the present review are: release mechanisms of β-END, independence of peripheral versus central levels, central β-END migration over considerable distances, behavioral effects of β-END depend on location of ventricular administration, and abundance of mu and delta opioid receptors in the periventricular regions of the brain.

Physiological neuroendocrinology of peptides, steroids and other hormones in cerebrospinal fluid

Cerebrospinal fluid acts as a conduit in neuroendocrine regulation. Valid assessment of normal cerebrospinal fluid levels of peptides, steroids and other hormones requires clarification of reference concentrations in control patients and normal volunteers. Awareness of factors which may alter neuronal activity and, in turn, the relative composition of cerebrospinal fluid constituents is essential to the accurate sampling and hormonal analysis of cerebrospinal fluid.

Alterations in Na(+)-K(+)-ATPase activity and beta-endorphin content in acute ischemic brain with and without naloxone treatment

The Na(+)-K(+)-adenosine triphosphatase (Na(+)-K(+)-ATPase) activity and beta-endorphin immunoreactivity were determined in rat brain at the acute stage of ischemia produced by unilateral occlusion of the middle cerebral artery (MCA). The effect of pretreatment with naloxone on these activities was also evaluated in the same model. After MCA occlusion, Na(+)-K(+)-ATPase activity was promptly reduced in the ischemic hemisphere and remained at a lower level than in the contralateral hemisphere during 90 minutes of ischemia. A single intraperitoneal 0.5-mg injection of naloxone prior to MCA occlusion attenuated the inactivation. On the other hand, beta-endorphin immunoreactivity was significantly increased following ischemia. The increase was marked in the ischemic hemisphere and was also observed in the contralateral hemisphere; this increase was not affected by the administration of naloxone. These results indicate the possibility that naloxone contributes to protecting the brain from ischemia through stabilizing the cellular membrane. The possible mechanism by which naloxone attenuates the inactivation of Na(+)-K(+)-ATPase in the ischemic brain is discussed in view of alterations of the central beta-endorphin system during ischemia.

Increased cerebrospinal fluid beta-endorphin immunoreactivity in infants with apnea and in siblings of victims of sudden infant death syndrome

To gain further insight into the possible role of endogenous opioid peptides in the respiratory difficulties associated with the apnea of infancy and other disorders possibly related to apnea, the levels of beta-endorphin immunoreactivity were measured in the cerebrospinal fluid (CSF) of five groups of infants: (1) infants with proved apnea, (2) infants with histories of an apparent life-threatening event (ALTE), (3) siblings of victims of the sudden infant death syndrome (SIDS), (4) infants with suspected but unproved apnea, and (5) infants undergoing investigation for other acute illnesses. Twenty-two infants considered at risk for an ALTE (groups 1 to 3) had significantly higher CSF beta-endorphin equivalents (88 +/- 7 pg/mL) than did the 22 control patients in groups 4 and 5 (31 +/- 3 pg/mL). Plasma beta-endorphin immunoreactivity, which was also measured in some of the infants, did not correlate with levels in CSF and, in fact, was significantly lower in the groups at risk for an ALTE (50 +/- 9 pg/mL; n = 14) than in the control subjects (80 +/- 6 pg/mL; n = 11). These studies indicate that elevated beta-endorphin immunoreactivity in CSF may be a marker in infants who have apnea and who may be considered at risk for an ALTE.

The effects of nitrous oxide on the secretory activity of pro-opiomelanocortin peptides from basal hypothalamic cells attached to cytodex beads in a superfusion in vitro system

Dispersed cells from adult rat basal hypothalami, attached to Cytodex-3 microcarrier beads, were placed in a column and superfused with aerated high glucose media or media enriched with variable concentrations of nitrous oxide with oxygen. beta-Endorphin and alpha-MSH content was measured in the effluent collected during superfusion and demonstrated a near constant baseline release. Nitrous oxide, 60% (P less than 0.025) and 80% (P less than 0.02), caused significant increases in release of beta-endorphin. Potassium chloride (50 mM) caused a significant increase in release (P less than 0.007) of beta-endorphin whereas saline and 30% nitrous oxide did not. Neither nitrous oxide-enriched media nor potassium chloride had any statistically significant effect on alpha-MSH release. The increase in beta-endorphin secretory activity during exposure to nitrous oxide demonstrates that nitrous oxide may have a stimulatory effect on central pro-opiomelanocortin neurons.

The hypothalamus in Parkinson disease

It is currently believed that Parkinson disease (PD) is due to a degenerative process that independently damages multiple areas of the central and peripheral nervous system. Loss of nigrostriatal dopamine is now widely recognized as being directly related to the motor symptoms in Parkinson's disease. Parkinsonian patients also exhibit symptoms and signs suggestive of hypothalamic dysfunction (e.g. dysautonomia, impaired heat tolerance). The latter clinical features are supported by pathological, biochemical and endocrinological findings. Lewy body formation has been demonstrated in every nucleus of the hypothalamus, specifically the tuberomamillary and posterior hypothalamic. Preferential involvement of the hypothalamus was also noted in patients after post-encephalitic parkinsonism. Loss of dopamine (30-40%) in the hypothalamus of affected patients has been shown in recent studies, and is compatible with the reported abnormalities of growth hormone release in response to L-dopa administration, elevated plasma levels of MSH, and reduced CSF levels of somatostatin and beta-endorphins in these patients. Deranged immunological mechanisms have been found in PD patients including the presence of autoantibodies against sympathetic ganglia neurons, adrenal medulla and caudate nucleus. On the evidence of on pathological studies demonstrating the early vulnerability of the hypothalamus in aging and PD, and the known role of the hypothalamus in immune modulation, we expect that it will be shown that primary damage of the hypothalamus leads to subsequent secondary degeneration of structures receiving direct projections from the hypothalamus. Within this framework, the dopaminergic systems may be damaged, since striatal dopamine synthesis and receptor sensitivity have been shown to be regulated by ACTH and alpha-MSH through direct arcuate nucleus-striatal projections.(ABSTRACT TRUNCATED AT 250 WORDS)

beta-Endorphin levels in the cerebrospinal fluid of male talapoin monkeys in social groups related to dominance status and the luteinizing hormone response to naloxone

beta-Endorphin-like immunoreactivity was measured in the cerebrospinal fluid of 20 male talapoin monkeys living in mixed-sex social groups. It was shown that beta-endorphin was the major immunoreactive peptide; there was no evidence for high molecular weight precursors, or for either N-acetyl or C-shortened metabolites. Dominant males (those at the top of the social hierarchy) had lower levels of beta-endorphin than those of intermediate rank; subordinate males had higher levels than either of the other two ranks--about three times those measured in dominants. There were significant negative correlations between beta-endorphin in cerebrospinal fluid and both the amount of aggression given and sexual behaviour shown towards females. The response of the hypothalamo-pituitary system to opiate blockade was tested by giving the males naloxone in doses of 0.125, 0.25, 0.5, 1.0 and 5.0 mg/kg and assaying serum levels of luteinizing hormone 20 min later. Dominant males released significant amounts of luteinizing hormone at doses of 0.25 and higher; there was no release in either intermediate or subordinate monkeys at any dose. These findings show that an animal's rank in the social group in which it lives is strongly correlated with beta-endorphin levels in the cerebrospinal fluid, and with changes in the neuroendocrine response to opiate blockade. Altered opiate neural activity may be responsible for the depressed levels of sexual behaviour and gonadal function observed in monkeys at the bottom of the hierarchy.

Altered stress responsiveness in adult rats exposed to ethanol in utero: neuroendocrine mechanisms

In our first studies the activity of the hypothalamo-pituitary-adrenal (HPA) axis was found to be significantly greater in response to certain stressors, including ethanol, in adult rats exposed to ethanol as fetuses (fetal ethanol-exposed [FEE] rats) than in pair-fed-derived or normal controls. Stress responsiveness in FEE rats was examined further by measuring stress-induced analgesia after inescapable footshock. Analgesia was enhanced in adult FEE rats by a prolonged/intermittent naloxone-reversible form of footshock, but not by a brief/continuous naloxone-insensitive form, suggesting that the effect was opioid-mediated. Adult FEE rats showed greater analgesic and plasma corticosterone responses to morphine challenges than control rats. Preliminary results also indicated that when adult FEE rats were exposed daily to the intermittent footshock stress (10 min/day) they consumed significantly more ethanol than controls. Whether the altered stress responsiveness reflects fetal ethanol-induced effects on the development of the HPA axis was determined by measuring brain and plasma content of corticosterone in FEE and control neonates. At birth, in FEE pups, whole brain and plasma corticosterone levels are significantly raised. On postnatal day 7, when basal plasma corticosterone concentrations have attained normal values, FEE rats display blunted corticosterone responses to ethanol administration, indicating persistent effects of the fetal ethanol exposure despite its termination one week previously. The precise contribution of these neonatal hormonal alterations to the long-term effects of fetal ethanol exposure on stress responsiveness remains to be determined.

Levels of arginine-vasopressin in cerebrospinal fluid during passive avoidance behavior in rats

The concentration of immunoreactive arginine-vasopressin (IR-AVP) was measured in the cerebrospinal fluid (CSF) during acquisition and retention of passive avoidance behavior. IR-AVP level in CSF of male Wistar rats immediately after the learning trial was increased; the rate of which was related to the intensity of the electric footshock during the learning trial and the avoidance latency as measured 1 day after the learning trial. Immediately after the 24 h retention test IR-AVP levels were significantly increased in rats subjected to the low (0.25 mA) shock intensity during the learning trial, but IR-AVP levels of rats exposed to the high shock (1.0 mA) were under the limit of detection. If the retention test was postponed till 5 days after the learning trial, the increase of IR-AVP level in the CSF was related to avoidance latencies which reflect the intensity of aversive stimulation (electric footshock). The results suggest an association between central AVP release and passive avoidance behavior and may be indicative of the role of this peptide in neuronal mechanisms underlying learning and memory processes.

"Joining peptide" of pro-opiomelanocortin. I. Radioimmunoassay and extraction of related peptides from pituitary glands

In order to immunoassay the specific region of bovine pituitary pro-opiomelanocortin (POMC) between ACTH and gamma-MSH, referred to as "joining peptide," antisera were prepared against the synthetic amidated decapeptide Val-Ala-Val-Gly-Glu-Gly-Pro-Gly-Pro-Arg-NH2. The non-amidated peptide represents residues -23 to -14 of bovine POMC. An NH2-terminal tyrosine analog of the decapeptide was used as the radioligand. Under optimal conditions, immunoassay with selected antisera exhibited a sensitivity (50% displacement of the radioligand) toward the decapeptide in the range of 31-55 pg. Immunoreactivity found in extracts of fresh or lyophilized bovine pituitary glands displaced the iodinated Tyr-decapeptide in the RIA in a parallel manner. The amount of immunoreactive (ir)-material was dependent upon the state of preservation of the tissue, the method of extraction, and the particular antiserum used. Extractable immunoreactivity was separated into low (Mr 1,500) and high (Mr 17,000) molecular weight peptides using gel chromatography (G-75). Additional ir-material appeared in the void volume (Mr greater than 22,500). Thus, these antisera have the capacity to interact not only with a region of the joining peptide but also with its larger, and apparent precursor forms. The immunoassay developed should be valuable in understanding the disposition and processing in this specific region of POMC.

"Joining peptide" of pro-opiomelanocortin. II. Interspecies heterogeneity of the joining peptide fragment

The use of an antiserum raised against the joining peptide sequence -23 to -14 of bovine pro-opiomelanocortin (POMC) enabled the detection of related immunoreactive sequences of peptides in bovine, porcine, mouse and guinea-pig pituitaries, as well as in mouse brain and cerebral cortex, guinea-pig cerebral cortex, and bovine hypothalamus. Gel chromatography of pituitary extracts (Sephadex G-75 and Bio-Gel P-4) indicated the presence of several immunoreactive joining peptide fragments ranging in the molecular weight range (Mr) of 1,500 to 2,300. Furthermore, high molecular weight (Mr greater than 22,500) immunoreactive-precursor from bovine anterior pituitary was readily digested with trypsin into an immunoreactive fragment of approximately Mr 1,500. Analyses of these immunoreactive peptides by reverse-phase high-performance liquid chromatography (HPLC) led to their resolution into six distinct peptides. The only apparent correspondence in the elution profiles of immunoreactive peptide profiles between different mammalian species was the identification of a similar fragment (Mr 2,000) from bovine and guinea-pig pituitaries. Thus, we conclude that immunoreactivity to the joining peptide region of POMC from various mammalian species exhibits a degree of heterogeneity in its composition. The relatively low levels of immunoreactivity in comparison to that of ACTH also suggest that the joining peptide domain may be further processed. The hormonal status of the joining peptide region remains to be determined.

Minireview. Peptides and the blood-brain barrier

Most neuropeptides are known to occur both in the central nervous system and in blood. This, as well as the occurrence of central nervous peptide effects after peripheral administration, show the importance of studying the relationships between the peptides in the two compartments. For many peptides, such as the enkephalins, TRH, somatostatin and MIF-1, poor penetration of the blood-brain barrier was shown. In other cases, including beta-endorphin and angiotensin, peptides are rapidly degraded during or just after their entry into brain or cerebrospinal fluid. Some peptides, such as insulin, delta-sleep-inducing peptide, and the lipotropin-derived peptides, enter the cerebrospinal fluid to a slight or moderate extent in the intact form. Many peptide hormones, such as insulin, calcitonin and angiotensin, act directly on receptors in the circumventricular organs, where the blood-brain barrier is absent. Oxytocin, vasopressin, MSH, and an MSH-analog alter the properties of the blood-brain barrier, which may result in altered nutritient supply to the brain. In conclusion, the diffusion of most peptides across the brain vascular endothelium seems to be severely restricted. There are, however, several alternative routes for peripheral peptides to act on the central nervous system. The blood-brain barrier is a major obstacle for the development of pharmaceutically useful peptides, as in the case of synthetic enkephalin-analogs.

Pituitary stalk section transiently impairs the acquisition of shuttle box avoidance behavior

Three days after stalk section, rats displayed a marked deficit in acquiring a shuttle box avoidance response. The performance of stalk sectioned rats was similar to that of 3-day hypophysectomized rats. At eighteen days after stalk section acquisition of the avoidance response was, however, not different from that of sham-operated controls. Stalk sectioned rats that showed poor performance at three days and that were tested again at eighteen days displayed similar avoidance behavior at eighteen days as their sham-operated controls. The results suggest that pituitary stalk section impairs performance of an active avoidance response. The transient nature of this effect may be due to disruption and subsequent regeneration of vascular contact between pituitary and brain.

Circadian variations in beta-endorphin concentrations in pituitary and in some brain nuclei of the adult male rat

Using both the 'punch' microdissection and a radioimmunological technique, circadian variations in beta-endorphin concentrations can be observed in the pituitary and in some discrete brain regions of the male rat (Wistar CFY). Animals were synchronized with light from 06.00 to 18.00 h, then darkness. Water and food were available ad libitum. Very well marked circadian rhythms were in evidence in the anterior lobe of the pituitary, the septum, the pons, the medulla oblongata and the cerebellum. There crest time locations were situated between 20.00 and 24.00 h. No significant circadian rhythms but biphasic variations were observed in the intermediate lobe of the pituitary, the POA, the thalamus, the central gray and the caudatus. There crest time locations were synchronized around 08.00 and 20.00 h. The most striking finding was that, regardless of the brain area investigated so far, maximal values were observed a short time after the beginning of the activity period of rats. This fact is identical with the one which has been observed for substance P and LH-RH contents in brain areas where these peptides are mostly present in nerve terminals in high concentrations.

Cardiovascular effects of beta-endorphin after microinjection into the nucleus tractus solitarii of the anaesthetised rat

The cardiovascular effects of beta-endorphin after administration directly into the nucleus tractus solitari (NTS) of urethane-anaesthetised rats were investigated. Unilateral injection resulted in a U-shaped dose-response relationship with a fall in mean arterial pressure and heart rate occurring at low doses (less than 10 ng). No change in respiratory frequency was observed at any of the doses examined. The hypotensive effects of beta-endorphin were anatomically specific and restricted to the NTS. The depressor response was prevented and bradycardia reduced by naloxone (1 mg/kg s.c. or 10 ng injected into the NTS) and also by beta-endorphin antiserum (1:50 dilution) but not by antiserum to [Met5]enkephalin (1:50 dilution) applied locally into the NTS. The beta-endorphin antiserum caused a rise in blood pressure when administered alone. Conversely microinjection of antiserum to [Met 5]enkephalin resulted in a brief depressor response. Doses of beta-endorphin larger than 10 ng induced a rise in blood pressure accompanied by variable effects on heart rate. Similarly unilateral administration of Des-tyr-endorphin (100 pg) resulted in a blood pressure increase and [D-Ala2,Met5]enkephalin produced a dose-related pressor response and tachycardia. The results indicate that at least two separate endorphin systems are involved in cardiovascular control at the level of NTS, one being depressor in nature (beta-endorphin-like) and the other pressor ([met5]enkephalin-like).