Brain Β-endorphin Research Articles

Nicotine-induced changes of brain β-endorphin

A consensus has emerged that endogenous opioid peptides and their receptors play an important role in the psychoactive properties of nicotine. Although behavioral studies have shown that β-endorphin contributes to the rewarding and emotional effects of nicotine, whether the drug alters the function of brain endorphinergic neurons is not fully explored. These studies investigated the effect of acute, 1mg/kg, sc, and chronic, daily injection of 1mg/kg, sc, for 14 days, administration of free base nicotine on brain β-endorphin and its precursor proopiomelanocortin (POMC). Acute and chronic treatment with nicotine decreased β-endorphin content in hypothalamus, the principal site of β-endorphin producing neurons in the brain, and in the endorphinergic terminal fields in striatum and hippocampus. The acute effect of nicotine on β-endorphin was reversed by the nicotinic antagonist mecamylamine and the dopamine antagonist haloperidol, indicating pharmacological specificity and involvement of dopamine D2-like receptors. Similar observations were made in prefrontal cortex. POMC mRNA in hypothalamus and prefrontal cortex was unchanged following acute nicotine, but it decreased moderately with chronic treatment. The nicotine treatments had no effect on pituitary and plasma β-endorphin. Taken together, these results could be interpreted to indicate that nicotine alters the synthesis and release of β-endorphin in the limbic brain in vivo. Altered endorphinergic function may contribute to the behavioral effects of acute and chronic nicotine treatment and play a role in nicotine addiction.

Modulation of Brain β-Endorphin Concentration by the Specific Part of the Y Chromosome in Mice

BackgroundSeveral studies in animal models suggest a possible effect of the specific part of the Y-chromosome (YNPAR) on brain opioid, and more specifically on brain β-endorphin (BE). In humans, male prevalence is found in autistic disorder in which observation of abnormal peripheral or central BE levels are also reported. This suggests gender differences in BE associated with genetic factors and more precisely with YNPAR.Methodology/Principal FindingsBrain BE levels and plasma testosterone concentrations were measured in two highly inbred strains of mice, NZB/BlNJ (N) and CBA/HGnc (H), and their consomic strains for the YNPAR. An indirect effect of the YNPAR on brain BE level via plasma testosterone was also tested by studying the correlation between brain BE concentration and plasma testosterone concentration in eleven highly inbred strains. There was a significant and major effect (P<0.0001) of the YNPAR in interaction with the genetic background on brain BE levels. Effect size calculated using Cohen's procedure was large (56% of the total variance). The variations of BE levels were not correlated with plasma testosterone which was also dependent of the YNPAR.Conclusions/SignificanceThe contribution of YNPAR on brain BE concentration in interaction with the genetic background is the first demonstration of Y-chromosome mediated control of brain opioid. Given that none of the genes encompassed by the YNPAR encodes for BE or its precursor, our results suggest a contribution of the sex-determining region (Sry, carried by YNPAR) to brain BE concentration. Indeed, the transcription of the Melanocortin 2 receptor gene (Mc2R gene, identified as the proopiomelanocortin receptor gene) depends on the presence of Sry and BE is derived directly from proopiomelanocortin. The results shed light on the sex dependent differences in brain functioning and the role of Sry in the BE system might be related to the higher frequency of autistic disorder in males.

Effect of hyperglycemia on biogenic amines, beta-endorphin and insulin of the rat brain.

Three experiments were designed to study the changes in brain biogenic amines, beta-endorphin and insulin in response to hyperglycemia in adult male rats. In all three experiments, animals were decapitated 10 minutes post injection (IP) of either 2.5 ml of 40% glucose or 0.9% saline. In the first experiment brain DA, NE, 5-HT and 5-HIAA were measured using fluorometric method. Plasma glucose, insulin (RIA) and corticosterone (CPB) were also determined. In addition to these measurements, brain beta-endorphin was determined (RIA) in the second experiment and brain insulin (RIA) in the third experiment. In all three experiments the hyperglycemic groups showed a significant increase in plasma insulin, brain NE and 5-HT and a significant decrease in brain 5-HIAA and no significant change in plasma corticosterone, brain DA, beta-endorphin and insulin. The results obtained in these experiments suggest that high levels of glucose may have an inhibitory effect on the metabolism of NE and 5-HT resulting in increases in the level of both amines. They also suggest that brain insulin is independent of the pancreatic one since high blood glucose did not influence the central level.

Reduced sodium appetite and increased oxytocin gene expression in mutant mice lacking β-endorphin

Central opioid and oxytocinergic systems have been involved in the regulatory control of sodium appetite. In addition, previous studies support the existence of a functional interaction between opioid peptides and oxytocinergic pathways, and suggest that β-endorphin neurons would modulate the activity of central oxytocinergic pathways, its pituitary secretion and sodium appetite. To investigate the role of this opioid peptide in the control of oxytocin (OT) synthesis and sodium appetite regulation we used mice with gene dosage-dependent variations in brain β-endorphin content, expressing either 100%, 50%, or 0% of normal β-endorphin content. Our results show that β-endorphin knockout (KO) and heterozygous (HT) mutant mice consume approximately a 50% less 2% NaCl solution compared with wild type mice (WT), after furosemide and low sodium diet treatment. These data suggest that β-endorphin may facilitate induced sodium appetite, giving new evidence about the role of β-endorphin on sodium appetite behavior. Our data also indicate that OT mRNA levels evaluated by in situ hybridization significantly increased within the hypothalamic paraventricular nucleus of WT animals after induced sodium ingestion, giving support to former evidence indicating an inhibitory role for central OT in the control of sodium appetite. Moreover, β-endorphin mutated mice have similar higher levels of OT mRNA expression after the different conditions analyzed: basal, control or experimental, compared with WT mice. Both control HT and KO mice showed higher OT mRNA expression levels than control WT group and these levels did not change after induced sodium intake. Taken together, our data suggest that the reduced sodium ingestion observed in β-endorphin deficient mice could be due to a higher expression of the OT gene. This conclusion would support the hypothesis that OT inhibits sodium intake and provides new evidence about β-endorphin modulation of OT synthesis and sodium appetite.

Alterations in Endogenous Brain β-Endorphin Release by Adrenal Medullary Transplants in the Spinal Cord

While transplants of adrenal medullary cells into the spinal subarachnoid space may produce antinociception via inhibition of spinal pain transmission pathways, alterations at higher central nervous system (CNS) centers have not been addressed. Recent findings suggest that prolonged noxious stimulation results in release of endogenous β-endorphin in the brain, possibly as a compensatory mechanism to reduce nociception. The goal of this study was to determine whether adrenal medullary transplants in the spinal subarachnoid space alter endogenous β-endorphin secretion in the hypothalamic arcuate nucleus, its principal CNS source. Pain behaviors and arcuate β-endorphin secretion by microdialysis were monitored during the formalin pain test in animals with spinal adrenal medullary or control transplants. Basal levels of extracellular β-endorphin were 3-fold higher in adrenal medullary-implanted than in controls. In control animals, formalin induced robust pain behaviors and a marked transient increase in β-endorphin release 30–60 min following injection. In contrast, pain behaviors were attenuated and the formalin-induced increase in β-endorphin was completely blocked in adrenal medullary implanted animals. Findings from these studies indicate that adrenal medullary transplants in the spinal subarachnoid space can alter β-endorphin release in the arcuate nucleus both basally and in response to noxious stimuli. Thus, spinally placed adrenal medullary transplants not only alter local spinal cord pharmacology, but can alter endogenous neurochemistry at higher pain processing centers as well.

Pain threshold, learning and formation of brain edema in mice lacking the angiotensin II type 2 receptor

The main biological role of angiotensin II type 2 receptor (AT 2) has not been established. We made use of targeted disruption of the mouse AT 2 gene to examine the functional role of the AT 2 receptor in the central nervous system (CNS). We have previously shown that AT 2-deficient mice displayed anxiety-like behavior in comparisons with wild-type mice. In the present study, we analyzed the pain threshold, learning behavior and brain edema formation using the tail-flick test, the tail-pinch test, the passive avoidance task and cold injury, respectively. In the passive avoidance task and cold injury, no differences were found between wild-type mice and AT 2-deficient mice. In contrast, the pain threshold was significantly lower in AT 2-deficient mice, compared with findings in wild-type mice. The immunohistochemical distribution of β-endorphin in the brain was analyzed quantitatively in AT 2-deficient mice and wild-type mice, using microphotometry. The fluorescence intensity of β-endorphin in the arcuate nucleus of the medial basal hypothalamus (ARC) was significantly lower in AT 2-deficient mice, compared with findings in wild-type mice. We found that the AT 2 receptor does not influence learning behavior and brain edema formation. As AT 2-deficient mice have increased sensitivity to pain and decreased levels of brain β-endorphin, AT 2 receptors may perhaps mediate regulation of the pain threshold.

Alterations in brain and pituitary beta-endorphin content in genetically epilepsy-prone rats.

We measured beta-endorphin concentrations in the anterior and neurointermediate lobes of the pituitary gland and in microdissected brain regions of moderate-seizure genetically epilepsy-prone rats (GEPR-3), severe-seizure GEPR-9s and Sprague-Dawley non-epileptic control rats. Plasma concentrations of beta-endorphin and beta-melanocyte-stimulating hormone (alpha-MSH) were also measured as indicators of pituitary POMC-peptide secretion. Concentrations of beta-endorphin in the anterior lobe of GEPR-3s were 53% higher compared to controls and 57% higher compared to GEPR-9s. There were no differences in neurointermediate lobe beta-endorphin concentrations between control and either GEPR strain. Plasma beta-endorphin concentrations were significantly lower in GEPR-9s than controls. Plasma levels of alpha-MSH did not differ between control and GEPRs. In the hypothalamus of GEPR-9s beta-endorphin concentrations in the arcuate nucleus were significantly greater than in GEPR-3s. Concentrations of beta-endorphin in the central amygdala of GEPR-9s were two- to threefold greater than in control or GEPR-3s. Beta-Endorphin concentrations in the central gray of GEPR-3s were 58% lower than control or GEPR-9s. These data suggest that anterior lobe beta-endorphin secretion is reduced in GEPR-9s. Furthermore, brain endorphinergic pathways appear to be differentially altered in GEPR-3s and GEPR-9s. Alterations in pituitary beta-endorphin secretion and brain endorphinergic systems may contribute to seizure susceptibility in GEPRs and to differences in seizure severity between GEPR-3s and GEPR-9s.

Brain β-Endorphin Immunoreactivity as an Index of Cocaine and Combined Cocaine–Ethanol Toxicities

The present study examines alterations in the cytoplasmic immunoreactivity of brain β-endorphin, an endogenous opioid peptide regarded as the mediator of both euphoria and antinociceptive systems, in relation to toxicities due to cocaine and combined cocaine–ethanol. β-endorphin–immunoreactive cells were visualized and counted in adjacent sections from male rat brains at the level of the arcuate nucleus. In this region, cytoplasmic β-endorphin immunoreactivity is prevalent. An intraperitoneal injection of cocaine (75 or 15 mg/kg) was given 15 min after an intraperitoneal injection of 3 g/kg ethanol or vehicle. With a fatally toxic dose (75 mg/kg) of cocaine, the number of neurons exhibiting cytoplasmic β-endorphin immunoreactivity (immunoreactive nerve cells) was significantly increased immediately after the drug administration. Ethanol further enhanced the effects of both 15 and 75 mg/kg of cocaine. When the immunoreactivity was visually estimated by computer imaging analysis, lightly stained, weakly immunoreactive cells with photographic light absorption values greater than 50% were enhanced in the cocaine–ethanol groups compared to the cocaine only groups. Fatal toxicities were only observed in the groups treated with the high cocaine doses (75 mg/kg), with or without ethanol. In these groups, the number of strongly immunoreactive cells had increased significantly compared to the other groups. In the group treated with the high cocaine dose (75 mg/kg) plus ethanol, an increased frequency of late deaths that occurred over 1 h after the drug administration was observed, together with a decreased severity of cocaine-induced seizures and an early enhancement of weakly immunoreactive cells. Unlike the strongly immunoreactive cells, the weakly immunoreactive cells appeared to be continuously enhanced, based on an experiment examining β-endorphin immunoreactivity at 24 h after an injection of 50 mg/kg cocaine.

Nociceptive stimulus induces release of endogenous β-endorphin in the rat brain

The hypothesis that the naturally occurring analgesic peptide, β-endorphin, is released in the brain in response to pain had never been directly validated. In this study, we applied a brain microdialysis method for monitoring β-endorphin release in vivo, to test this hypothesis in the brains of conscious, freely moving rats. Herein we first show that endogenous β-endorphin can be measured in vivo in the brain under physiological conditions. Upon induction of a nociceptive stimulus by injection of formalin into the hind-paws of rats, the extracellular levels of β-endorphin in their arcuate nucleus increased by 88%, corresponding to their nociceptive response. This direct evidence for the release of endogenous β-endorphin in the brain in response to nociceptive stimulus indicates a possible mechanism for organisms to cope with pain.

Enhanced activity of the brain β-endorphin system by free-choice ethanol drinking in C57BL/6 but not DBA/2 mice

The objective of the present studies was to investigate the effect of voluntary ethanol consumption for 21 days on the brain β-endorphin system of C57BL/6 (alcohol-preferring) and DBA/2 )alcohol-avoiding) strains of mice. As expected, C57BL/6 mice consumed a significantly higher quantity of the 10% ethanol solution than the DBA/2 mice. Under basal conditions the content of β-endorphin like peptides differed only in the nucleus accumbens, higher levels being found in the DBA/2 mice. Voluntary ethanol consumption induced an increase in the hypothalamic content of mRNA coding for proopiomelanocortin, associated with a significant increase in the tissue content of β-endorphin-like peptides in the arcuate nucleus and septum of the C57BL/6 mice, but did not alter the activity of the brain β-endorphin system of the DBA/2 mice. Since voluntary ethanol consumption was not associated with nutritional deficits and stress, the ethanol-induced enhanced activity of the brain β-endorphin system of the C57BL/6 mice must be a direct effect of ethanol and may be important in controlling the voluntary ethanol consumption by this strain of mice.

Effect of opioid receptor antagonism on proopiomelanocortin peptide levels and gene expression in the hypothalamus

In order to determine how brain β-endorphin (β-EP) and its precursor proopiomelanocortin (POMC) adapt to chronic opioid blockade we have examined the effects of treatment with the opioid receptor antagonist naltrexone (NTX) on POMC gene expression and peptide levels in the hypothalamus. Male rats were treated with NTX by daily injection or constant minipump infusion. RNA was isolated from the medial basal hypothalamus (MBH) after an aliquot was removed for peptide RIA and the amount of POMC mRNA was measured by solution hybridization SI nuclease protection assay. β-EP and several other POMC-derived peptides including α-melanocyte-stimulating hormone (α-MSH) and corticotropin-like intermediate lobe peptide (CLIP) or γ 3-MSH were measured in the MBH and anterior hypothalamus (AH) by RIA. In an initial experiment POMC peptide levels were measured after 7 days of NTX (4.8 mg/day) infusion. There was a marked fall in the concentrations of β-EP, α-MSH, and CLIP; levels in the MBH declined by more than 60% ( P < 0.001). In the next experiment NTX (1 mg) was injected daily and POMC peptides and mRNA were measured after 2 and 5 days of treatment. (β-EP) and α-MSH levels fell progressively in the MBH and AH and were significantly less than those of the controls by 5 days of treatment ( P < 0.02). POMC mRNA levels, however, did not change after 2 or 5 days. When NTX was infused for 3 weeks there was a decrease in the concentrations of β-EP, α-MSH, and γ 3-MSH in the MBH ( P < 0.001). The concentration of POMC mRNA in the MBH, however, was significantly higher in the NTX-treated animals, 0.99 ± 0.06 pg/μg RNA vs 0.81 ± 0.05 pg/μg RNA ( P < 0.05). Since NTX can affect LH and testosterone release, the study was repeated in castrated rats. POMC peptide levels again fell after 3 weeks of NTX. POMC mRNA levels were higher in the castrated rats than in the intact rats, 1.14 ± 0.06 pg/μg RNA vs 0.85 ± 0.09 pg/μg RNA ( P < 0.05), consistent with our previous findings in longterm castrated rats. However POMC mRNA increased further to 1.40 ± 0.09 pg/μg RNA in the castrated animals treated with NTX ( P < 0.05). We conclude that opioid receptor blockade has significant effects on POMC peptide levels and gene expression in the MBH. The increase in POMC gene expression associated with a fall in peptide levels is consistent with a compensatory increase in brain β-EP synthesis and release in the setting of chronic opioid receptor blockade.

Oxytocin nerve fibers innervate beta-endorphin neurons in the arcuate nucleus of the rat hypothalamus.

Fine, varicose oxytocin-containing nerve fibers have been demonstrated in the hypothalamic arcuate nucleus in rats. Using Phaseolus vulgaris leukoagglutinin as an anterograde tracer, fine neuronal fibers of paraventricular nucleus origin could be seen throughout the arcuate nucleus. Using double immunostaining, oxytocin-immunoreactive varicose fibers were observed around or in the close vicinity of beta-endorphin-immunoreactive neurons. Silver-gold-labeled oxytocin-immunoreactive presynaptic boutons were shown to make synaptic contacts with diaminobenzidine-labeled beta-endorphin-immunoreactive neurons by electron microscopy. These findings provide morphological evidence for a possible influence of oxytocin on the activity of the brain beta-endorphin system at the hypothalamic level.

Pituitary and brain β-endorphin in male and female rats: Effects of shock and cues associated with shock

The present experiment was designed to study whether or not prior exposure to inescapable shock is accompanied by sex-dependent changes in pituitary and central levels of immunoreactive β-endorphin, which is proposed to play an important role in opioid analgesia induced by aversive stimulation. Further, the effects of brief reexposure (5 min) to the chamber where inescapable shock was experienced earlier, were established in both sexes. Elevated levels of β-endorphin were found 24 hours after inescapable shock, in the anterior pituitary of males and in the midbrain periaqueductal gray of both males and females. Reexposure to the experimental chamber only affected β-endorphin levels if shock had been experienced in this chamber. Reexposure after inescapable shock reduced β-endorphin content of the arcuate nucleus of males and β-endorphin content of the periaqueductal gray of males and females. The present results are related to previous findings of sensitization and conditioning of analgesic reactions. The sex differences found in the present experiment are discussed with respect to sex-dependent behavioral consequences of inescapable shock.

Effects of ceruletide and haloperidol on the hypothalamo-pituitary β-endorphin system and brain β-endorphin contents in the rat: With special reference to effects of ceruletide in chronically haloperidol-treated rats

Subcutaneous (sc) administration of 200 μg/kg ceruletide (CER), a decapeptide chemically related CCK-8, and 5 mg/kg haloperidol (HLP) to rats increased the plasma immunoreactive β-endorphin (ir-β-END) level. The combined injection of CER and haloperidol caused higher plasma ir-β-END levels than either drug alone. High plasma ir-β-END levels returned to control levels on the 2nd day. Prior intraperitoneal (ip) administration of a CCK receptor antagonist, L-364,718 (3 mg/kg), but not proglumide (400 mg/kg, ip), inhibited CER-induced, but not HLP-induced, elevation in plasma ir-β-END levels. The dopamine agonist, bromocriptine (1 mg/kg, ip) decreased plasma ir-β-END levels, but had not effect on CER-induced elevation in plasma ir-β-END levels, whereas bromocriptine-induced reduction in plasma ir-β-END levels was antagonised by HLP. CER injection to chronically HLP-treated rats caused a greater elevation of plasma ir-β-END levels compared to saline-injected rats. In contrast to the acute experiment, plasma ir-β-END levels remained elevated over a period of 24h. In the acute experiment, CER, HLP or the combined treatment with these two drugs had no effect on ir-β-END contents in the pituitary gland and brain. In the chronic experiment, HLP increased the adenohypophyseal and septal ir-β-END contents and decreased the hippocampal ir-β-END contents 24h after the final HLP injection. CER caused a small reduction only in the hippocampal ir-β-END contents of CER-injected rats 15 min after injection. When determined on the 2nd day, however, the increases in the adenohypophyseal and septal ir-β-END contents and the decrease in the hippocampal ir-β-END contents observed in CER-injected rats were of the same magnitude as those of rats not given the CER injection. These findings indicate that CER stimulates the release of ir-β-END from the adenohypophysis through CCK-A receptors and that elevated plasma ir-β-END levels is partly involved in some behavioural effects induced by CER. Furthermore, sustained elevation of plasma ir-β-END levels after a single injection of CER to chronically HLP-treated rats may explain its long-lasting therapeutic and behavioural effects.

Effect of posttraining and pretest β-endorphin and ACTH administration in normal and protein malnourished rats

Rats were submitted to a normal (25% casein) or a low protein diet (8% casein) from the day of birth until the age of 110 to 120 days. Hypothalamic β-endorphin-like immunoreactivity was lower in the animals raised and maintained with the low protein diet, and, in addition, it did not respond to training in a step-down inhibitory avoidance task with or without footshock with a depletion, as was the case with the normal diet animals. In the animals submitted to the normal protein diet posttraining ACTH (0.2 μg/kg) and β-endorphin (1.0 μg/kg) caused retrograde amnesia of a step-down inhibitory avoidance task, and pretest administration of these substances had no effect of its own, but was able to reverse the amnesia induced by their previous posttraining administration. In the animals submitted to the low protein diet, results were similar except that pretest β-endorphin caused amnesia on its own. On the basis of previous findings which suggest that pretest actions of ACTH and β-endorphin depend on their endogenous release at the time of training, the present results are compatible with a malfunction of the brain β-endorphin system in the undernourished animals.

Gonadal steroid and chronic morphine treatment do not change the posttranslational processing of β-endorphin in the rat brain

The present study examines whether two treatments known to induce refractoriness to exogenous morphine produce this desensitization through a change in the posttranslational processing of brain β-endorphin (β-End). The first experiment examined whether an ovarian steroid regimen which produces a transient desensitization of brain opiate receptor mechanisms alters β-End processing in the preoptic area (POA), medial basal hypothalamus (MBH), and brainstem (BS). The second experiment monitored the effects of morphine pellet treatment, known to produce morphine dependency, on immunoreactive β-End forms in the hypothalamus and periaquaductal gray area of the midbrain (PAG). The individual molecular forms of β-End were separated using ion exchange chromatography and collection fractions were quantitated for β-End immunoreactivity by RIA. The results show that regional differences occur in the posttranslational processing of β-End. In the hypothalamus, MBH and POA, β-End-(1–31) and its non-acetylated C- terminal cleavage products, β-End-(1–27) and β-End-(1–16) were the predominant forms of β-End. The PAG pools produced a β-End peptide elution profile similar to the hypothalamus, although small amounts of N-acetyl-β-End-(1–31) were also identified. The BS exhibited the least posttranslational processing of β-End; β-End-(1–31) was the primary product with smaller amounts of β-End-(1–27) and β-End-(1–26) observed. However, neither ovarian steroid treatment nor chronic morphine produced any changes in posttranslational processing of β-End or in total β-End concentration in any of the brain regions examined in these experiments. These data indicate that the refractoriness or tolerance to exogenous morphine associated with steroid or chronic morphine treatment cannot be explained by alterations in the biological activity of β-End resulting from the differential regulation of its posttranslational processing products.

Pre-test administration of β-endorphin, or of electroconvulsive shock reverses the memory disruptive effect of posttraining electroconvulsive shock

Memory disruption by posttraining electroconvulsive shock was studied in adult Wistar rats using three different tasks: step-down inhibitory avoidance, two-way active avoidance, and habituation of rearing to an open field. The animals were given training and test sessions 24 hours apart in each of these tasks. Immediate posttraining transcorneal, 15 mA, 60 Hz, 2 sec electroconvulsive shock disrupted memory of the three tasks. The effect was completely reversed by the IP administration of β-endorphin (2.0 μg/kg), 6 min prior to testing, or of another electroconvulsive shock, 30 min prior to testing. These findings indicate that the posttraining electroconvulsive shock did not affect memory storage. In view of the fact that electroconvulsive shock has been previously shown to cause a pronounced decrease of brain β-endorphin immunoreactivity, attributable to a release of the peptide, the present findings can be interpreted as showing that memory disruption by posttraining electroconvulsive shock results from the induction of state dependency on β-endorphin.

Influence of ethanol dependence on regional brain content of beta-endorphin in the mouse.

beta-Endorphin-like immunoreactivity (BE-LI) was measured in 7 brain regions of Swiss-Webster mice after 24, 48 and 72 h of exposure to ethanol vapor following a priming injection of ethanol and daily injections of pyrazole HCl to inhibit ethanol metabolism. Control mice in identical chambers received pyrazole injections but breathed air only. Ethanol dependence was confirmed by scoring additional groups of mice for handling-induced convulsions during withdrawal after each exposure duration. Measurement of anterior and neurointermediate (NIL) pituitary BE-LI, alpha-MSH and ACTH and plasma corticosterone confirmed earlier results showing NIL depletion of all 3 peptides at 24 h and increased plasma corticosterone concentrations at 72 h in ethanol-exposed mice. In brain extracts from ethanol-dependent mice, BE-LI was significantly reduced in the hypothalamus and midbrain with the greatest reduction occurring at 24 h. In forebrain, cerebral cortex, septum and hippocampus, pyrazole treatment significantly reduced BE-LI relative to an unhandled control group, and ethanol exposure tended to reverse this effect. HPLC of hypothalamic extracts revealed no differences in proportions of molecular forms of beta-endorphin-like peptides between 24 h control and ethanol-exposed groups. The predominant BE-LI peak in both groups co-eluted with opiate-active unmodified beta-endorphin. Ethanol dependence in mice is associated with regionally selective decreases in brain beta-endorphin concentration.

Discordant changes between immunoreactive ACTH and β-endorphin in rat brain and pituitary during early development

Discordant changes in brain concentrations of immunoreactive (IR-) adrenocorticotropic hormone (ACTH) or beta-endorphin, peptides derived from pro-opiomelanocortin (POMC), have been reported during the latter part of development and with subsequent aging. These changes were believed to be due to age-related alterations in the regulation of metabolism of POMC-related peptides. However, concentrations of IR-ACTH and IR-beta-endorphin have not been simultaneously studied during early development when many changes in brain development and behavior are occurring. To determine whether concentrations of IR-ACTH and IR-beta-endorphin change during early development and whether changes are discordant, concentrations of IR-ACTH and IR-beta-endorphin were measured in several brain regions and pituitary in rats at 10, 29 and 80 days after birth. Whereas IR-ACTH in extrahypothalamic brain increased at day 29, and decreased at day 80, it did not change in hypothalamus and pituitary. Between day 10 and 29, IR-beta-endorphin rose in all brain regions, but subsequent changes in different tissues were variable at day 80. Because concentration changes can be mediated by alterations in one or more regulatory mechanisms, chromatographic profiles of hypothalamus and amygdala and molar ratios of all tissues were subsequently studied to give further insight into the mechanisms of the discordant changes. Molecular profiles of hypothalamic IR-ACTH and amygdalar IR-beta-endorphin exhibited lesser proportions of large molecular forms and greater proportions of ACTH and beta-endorphin during development. Molar ratios of IR-ACTH/IR-beta-endorphin in all tissues and ratios of ACTH1-39/beta-endorphin in hypothalamus and amygdala changed during development. (1) changes in IR-ACTH and IR-beta-endorphin occur in rat pituitary and several brain regions at different ages during early development and are frequently discordant; (2) molecular profiles suggested that the activity of processing enzymes for POMC and its derivatives vary in hypothalamus and amygdala with respect to type of derivative, brain region, and developmental age; and (3) changes in some molecular profiles and changes in molar ratios of IR-ACTH/IR-beta-endorphin and ratios of ACTH1-39/beta-endorphin suggest that changes in processing and possibly changes in neurosecretion and degradation contribute to concentration changes independent of possible alterations in biosynthesis of POMC.

Differential effect of posttraining naloxone, β-endorphin, leu-enkephalin and electroconvulsive shock administration upon memory of an open-field habituation and of a water-finding task

Rats were trained and tested in an open field for habituation of rearing responses, for a waterfinding task, or for both tasks simultaneously. Training-test interval was 24 hr. The water-finding task consisted of locating a metal tube in one of the walls of the box, which was attached to a water bottle on the outside; animals were water deprived between training and testing. Retention was estimated by measuring the latency to lick from the tube on the test session. Rats learned this task either with or without water deprivation, also prior to training. Habituation learning (reduction of the number of rearings between the training and test session) occurred either simultaneously with the water-finding task or in animals trained without the water tube, so that they could not learn the water-finding task. As happens with many other tasks, training in the open field was followed by a large decrease of hypothalamic β-endorphin immunoreactivity, attributable to a release of this substance. Posttraining IP naloxone (1.6 mg/kg) administration facilitated, and posttraining β-endorphin (2.0 μg/kg), leu-enkephalin (5.0 μg/kg), or electroconvulsive shock (15 mA, 60 Hz, 2 sec) depressed the retention of habituation; this occurred regardless of whether the animals were trained and/or tested with or without water deprivation, and whether the task was acquired alone or simultaneously with the water-finding task. By contrast, none of these treatments had any effect on retention of the water finding task, acquired either with or without prior water deprivation. Thus, habituation was, and water-finding was not, sensitive to posttraining treatments known to affect endogenous opioids: the opioids themselves, their antagonist, naloxone, and electroconvulsive shock which releases brain opioids and causes naloxone-reversible retrograde amnesia. Learning of the water-finding task was merely incidental to exploration of the open field; it took place even when the animals were trained without the water tube. This suggests that the posttraining treatments that affect endogenous opioid function affect memory only of the task(s) that actually cause the release of brain β-endorphin (in this case, probably habituation), and not of others that may occur simultaneously but are merely incidental (water-finding). A feature apparently common to the former is that they must directly involve either the recognition of novelty, or the initiation of an interaction with a new environment, or perhaps the habituation of such interaction.