Hypothalamic Β-endorphin Research Articles

Protective effects of hypothalamic beta-endorphin neurons against alcohol-induced liver injuries and liver cancers in rat animal models.

Recently, retrograde tracing has provided evidence for an influence of hypothalamic β-endorphin (BEP) neurons on the liver, but functions of these neurons are not known. We evaluated the effect of BEP neuronal activation on alcohol-induced liver injury and hepatocellular cancer. Male rats received either BEP neuron transplants or control transplants in the hypothalamus and were randomly assigned to feeding alcohol-containing liquid diet or control liquid diet for 8weeks or to treatment of a carcinogen diethylnitrosamine (DEN). Liver tissues of these animals were analyzed histochemically and biochemically for tissue injuries or cancer. Alcohol feeding increased liver weight and induced several histopathological changes such as prominent microvesicular steatosis and hepatic fibrosis. Alcohol feeding also increased the levels of triglyceride, hepatic stellate cell (HSC) activation factors, and catecholamines in the liver and endotoxin levels in the plasma. However, these effects of alcohol on the liver were reduced in animals with BEP neuron transplants. BEP neuron transplants also suppressed carcinogen-induced liver histopathologies such as extensive fibrosis, large focus of inflammatory infiltration, hepatocellular carcinoma (HCC), collagen deposition, numbers of preneoplastic foci, levels of HSC activation factors and catecholamines, as well as inflammatory milieu and increased the levels of natural killer cell cytotoxic factors in the liver. These findings are the first evidence for a role of hypothalamic BEP neurons in influencing liver functions. Additionally, the data identify that BEP neuron transplantation prevents hepatocellular injury and HCC formation possibly via influencing the immune function.

Heshouwu decoction, a Chinese herb for tonifying kidney, ameliorates hypothalamic-pituitary- testicular axis secretion in aging rats.

An increasing amount of evidence demonstrates the anti-aging effect of Heshouwu in pill form. In this study, a subacute aging rat model was established by continuous intraperitoneal injection of D-galactose and treated with Heshouwu decoction (a Chinese herb for tonifying the kidney, comprising Heshouwu pill, Herba Epimedii, Radix Salviae Miltiorrhiae, and Poria). Heshouwu pill treated rats were the positive control group. Radioimmunoassay, immunohistochemical staining, and western blot assay showed hypothalamic gonadotropin-releasing hormone, hypothalamic substance P, and serum gonadotropin levels to be significantly increased in the model rats; the concentrations of hypothalamic β-endorphin, and serum levels of insulin-like growth factor 1 and testosterone were significantly decreased. 17β- and 3β-hydroxysteroid dehydrogenase expression in testicular tissue was also decreased. Intragastric administration of Heshouwu decoction at high (9.6 g/mL/100 g), medium (4.8 g/mL/100 g), and low (2.4 g/mL/100 g) doses, Heshouwu decoction pretreatment at a medium dose (4.8 g/mL/100 g), and Heshouwu pill (2.06 g/mL/100 g) significantly reversed these changes. Heshouwu decoction pretreatment and high-dose Heshouwu decoction had the greatest anti-aging effects. These experimental findings indicate that Heshouwu decoction can improve hypothalamic-pituitary-testicular axis secretion in a subacute aging rat model, and prevent and delay gonadal axis aging, with an effect superior to that of Heshouwu pill.

Ethanol injected into the hypothalamic arcuate nucleus induces behavioral stimulation in rats: an effect prevented by catalase inhibition and naltrexone

It is suggested that some of the behavioral effects of ethanol, including its psychomotor properties, are mediated by beta-endorphin and opioid receptors. Ethanol-induced increases in the release of hypothalamic beta-endorphin depend on the catalasemic conversion of ethanol to acetaldehyde. Here, we evaluated the locomotor activity in rats microinjected with ethanol directly into the hypothalamic arcuate nucleus (ArcN), the main site of beta-endorphin synthesis in the brain and a region with high levels of catalase expression. Intra-ArcN ethanol-induced changes in motor activity were also investigated in rats pretreated with the opioid receptor antagonist, naltrexone (0-2 mg/kg) or the catalase inhibitor 3-amino-1,2,4-triazole (AT; 0-1 g/kg). We found that ethanol microinjections of 64 or 128, but not 256 microg, produced locomotor stimulation. Intra-ArcN ethanol (128 microg)-induced activation was prevented by naltrexone and AT, whereas these compounds did not affect spontaneous activity. The present results support earlier evidence indicating that the ArcN and the beta-endorphinic neurons of this nucleus are necessary for ethanol to induce stimulation. In addition, our data suggest that brain structures that, as the ArcN, are rich in catalase may support the formation of ethanol-derived pharmacologically relevant concentrations of acetaldehyde and, thus be of particular importance for the behavioral effects of ethanol.

Hypothalamic–pituitary–adrenal axis, neuroendocrine factors and stress

The stress system coordinates the adaptive responses of the organism to stressors of any kind. 1 1 “Stress” is defined as a state of disharmony or threatened homeostasis. The concepts of stress and homeostasis can be traced back to ancient Greek history, however, the integration of these notions with related physiologic and pathophysiologic mechanisms and their association with specific illnesses are much more recent. In the present overview, we focus on the cellular and molecular infrastructure of the physiologic and behavioral adaptive responses to stress and we define the pathophysiologic effects of the dysregulation of the stress response, which may result in vulnerability to several disease entities, such as anxiety or depression and chronic inflammatory processes. The main components of the stress system are the corticotropin-releasing hormone (CRH) and locus ceruleus–norepinephrine (LC/NE)-autonomic systems and their peripheral effectors, the pituitary–adrenal axis, and the limbs of the autonomic system. Activation of the stress system leads to behavioral and peripheral changes that improve the ability of the organism to adjust homeostasis and increase its chances for survival. The CRH and LC/NE systems stimulate arousal and attention, as well as the mesocorticolimbic dopaminergic system, which is involved in anticipatory and reward phenomena, and the hypothalamic β-endorphin system, which suppresses pain sensation and, hence, increases analgesia. CRH inhibits appetite and activates thermogenesis via the catecholaminergic system. Also, reciprocal interactions exist between the amygdala and the hippocampus and the stress system, which stimulates these elements and is regulated by them. CRH plays an important role in inhibiting GnRH secretion during stress, while, via somatostatin, it also inhibits GH, TRH and TSH secretion, suppressing, thus, the reproductive, growth and thyroid functions. Interestingly, all three of these functions receive and depend on positive catecholaminergic input. The end-hormones of the hypothalamic–pituitary–adrenal (HPA) axis, glucocorticoids, on the other hand, have multiple roles. They simultaneously inhibit the CRH, LC/NE and β-endorphin systems and stimulate the mesocorticolimbic dopaminergic system and the CRH peptidergic central nucleus of the amygdala. In addition, they directly inhibit pituitary gonadotropin, GH and TSH secretion, render the target tissues of sex steroids and growth factors resistant to these substances and suppress the 5′ deiodinase, which converts the relatively inactive tetraiodothyronine (T 4) to triiodothyronine (T 3), contributing further to the suppression of reproductive, growth and thyroid functions. They also have direct as well as insulin-mediated effects on adipose tissue, ultimately promoting visceral adiposity, insulin resistance, dyslipidemia and hypertension (metabolic syndrome X) and direct effects on the bone, causing “low turnover” osteoporosis. Central CRH, via glucocorticoids and catecholamines, inhibits the inflammatory reaction, while directly secreted by peripheral nerves CRH stimulates local inflammation ( immune CRH). CRH antagonists may be useful in human pathologic states, such as melancholic depression and chronic anxiety, associated with chronic hyperactivity of the stress system, along with predictable behavioral, neuroendocrine, metabolic and immune changes, based on the interrelations outlined above. Conversely, potentiators of CRH secretion/action may be useful to treat atypical depression, postpartum depression and the fibromyalgia/chronic fatigue syndromes, all characterized by low HPA axis and LC/NE activity, fatigue, depressive symptomatology, hyperalgesia and increased immune/inflammatory responses to stimuli.

Proopiomelanocortin (POMC) mRNA expression: distribution and region-specific down-regulation by chronic morphine in female guinea pig hypothalamus

There is compelling evidence that endogenous opioid peptides are regulated by exogenous opiates. Our previous studies have shown that the μ-opioid receptor protein and mRNA are down-regulated in the mediobasal hypothalamus of the female guinea pig following chronic morphine treatment. In addition, electrophysiological studies have shown that hypothalamic β-endorphin ( β-EP) neurons express μ-opioid receptors that are uncoupled and down-regulated following chronic morphine treatment. Currently, we tested the hypothesis that chronic morphine, which produces down-regulation of μ-opioid receptors, causes a down-regulation of pro-opiomelanocortin (POMC, the precursor of β-EP) mRNA expression in female guinea pig hypothalamus. Female guinea pigs were ovariectomized and implanted subcutaneously (s.c.) with 4×75 mg pellets for 2 days plus six more pellets of either morphine ( n=6) or placebo ( n=6) for another 5 days. Animals were sacrificed between 1000 and 1100 h on day 7. The expression of POMC mRNA were investigated using in situ hybridization histochemistry with a guinea pig specific 35S-labeled cRNA probe in hypothalamic tissue sections. POMC mRNA was localized to the arcuate nucleus (Arc) and median eminence (ME) of the medial basal hypothalamus. The distribution pattern was the same in both morphine and placebo control animals. However, the density of silver grains was less in morphine treated animals versus placebo control animals. Overall, the level of POMC mRNA was decreased by 22% in the Arc of morphine-treated guinea pigs as compared with the placebo controls ( p<0.05). This decrease in POMC mRNA expression was even greater in the caudal Arc (28%, p<0.01) in morphine-treated animals. These results suggested that the biosynthetic activity of POMC neurons is down-regulated with chronic exposure to morphine.

The secretory response of hypothalamic β-endorphin neurons to acute and chronic nicotine treatments and following nicotine withdrawal

In the present study, we determined the effect of acute and chronic nicotine treatments on the secretion of immunoreactive β-endorphin (IR-β-EP) and cell viability of cultured hypothalamic neurons. Also, we determined the secretory response of IR-β-EP following withdrawal from a long-term nicotine treatment. Fetal hypothalamic cells were dissociated and maintained in cultures for 9 days and were treated with various doses of nicotine (1, 6,12 and 18 μM) for 6 h (acute treatment) or treated with nicotine at 12 h intervals for 96 h (chronic treatment). Determination of IR-β-EP concentrations in the media revealed that 6–18 μM doses of nicotine increased IR-β-EP secretion from these cultures for a period of 24 h; after this period, the cultured cells did not respond to these doses of nicotine. The desensitization of β-EP neurons 24 h after treatment with nicotine did not appear to be related to the loss of viable cells. Determination of withdrawal response after 72 h of constant nicotine (6 μM) treatments revealed that the hypothalamic neurons secrete elevated amounts of IR-β-EP for a period of 72 h after nicotine withdrawal. These results suggest that: 1) acute treatment with nicotine stimulates hypothalamic IR-β-EP release; 2) chronic nicotine treatment desensitizes β-EP-secreting neurons and, 3) β-EP neurons in primary culture show withdrawal response to nicotine.

Immunohistochemical detection of progestin receptors in hypothalamic beta-endorphin and substance P neurons of steroid-treated monkeys.

Progesterone (P) acts in the central nervous system to increase prolactin secretion in estrogen (E)-primed female monkeys. beta-Endorphin (BE) and Substance P (SP) are two hypothalamic peptides which increase prolactin secretion when administered to rats and monkeys. Studies were performed to determine if P acts on these two potential prolactin-releasing systems. The presence of a nuclear steroid receptor defines the cell as a target for the cognate hormone. Therefore, the hypothalamic populations of BE and SP neurons were examined for the presence and regulation of nuclear progestin receptors (PR) in spayed, E-treated (28 days) and E + P-treated monkeys (14 days E + 14 days E + P). Hypothalamic blocks were prepared after perfusion fixation with 4% paraformaldehyde. Cryosectioning (10 mu m) was followed by double immunocytochemistry (ICC) for PR (black nuclear stain) and either BE or SP (brown cytoplasmic stain). Sections were processed for ICC at 100- or 200-mu m intervals through the hypothalamic block. Peptidergic neurons with and without PR were counted in each section. The E + P-treated monkeys exhibited a significant increase in serum prolactin. BE neurons were found only in the arcuate nucleus (ARC) and median eminence (ME). The colocalization of BE and PR equaled 2% in spayed controls, 21% in the E-treated group and 25% in the E + P-treated group. SP neurons were located in a dorsomedial hypothalamic (DMH) subpopulation which extended caudally under the mamillary nuclei and in a subpopulation located in the ARC and ME. Neither the DMH or submamillary SP neurons contained PR. The percent colocalization of SP and PR in the ARC/ME equaled 5, 26 and 10% in the spayed, E- and E + P-treated groups, respectively. The decrease in PR + SP colocalization with P treatment is probably due to a decrease in SP and not to a decrease in PR immunoreactivity. In summary, E treatment induced PR in BE and SP neurons. Addition of P to the E treatment did not alter the expression of PR in BE neurons, but PR colocalization decreased in SP neurons. Therefore, it is unlikely that SP neurons could transduce the action of P on prolactin secretion in primates, but BE neurons may play an intermediary role.

Progesterone, but not estrogen, modulates the cAMP system mediated ir-β-endorphin secretion and POMC mRNA expression from rat hypothalamic cells in culture

It is now evident that hypothalamic β-endorphin (βEP) modulates reproductive physiology at the central level by inhibiting the function of neurons producing gonadotropin-releasing hormone (GnRH). Increasing evidence suggests that gonadal steroids, which play an important role in the long-loop negative feedback on the hypothalamus-pituitary-gonadal axis, may exert its indirect inhibitory action through modulating the production and release of hypothalamic βEP. However, it remains unclear whether progesterone or estrogen alone or their combination is important to exert this effect. Employing long-term monolayer neonatal hypothalamic cell cultures, we reported here that whereas progesterone significantly enhanced forskolin-, N 6,2′- O-dibutyryladenosine-3′5′-cyclic monophosphate [(Bu) 2cAMP]-, 3-isobutyl-1-methylxanthine (IBMX)- or cholera toxin-stimulated immunoreactive (ir)-βEP release from cultures treated daily for 4 consecutive days, the steroid alone produced little effect. This potentiation of progesterone was time-related and dose-dependent with an EC 50 value of the steroid being approximately 25 nM; at this concentration the steroid increased ir-βEP secretion about 1.6 times ( P < 0.05) that induced by 5 μM forskolin alone. Similar effects were also observed for POMC mRNA levels in cultures subjected to 6 h of the above treatment regime. This potentiating effect appears specific as it can be mimicked by progestin, a progesterone receptor agonist and blocked by the progesterone receptor antagonist RU38486, but not RU28318, a mineralocorticoid receptor antagonist. Furthermore, β-estradiol alone failed to exert a significant effect on basal, forskolin-induced or on forskolin and progesterone co-stimulated βEP release or POMC mRNA levels in hypothalamic cell cultures. Hence, our present results substantiate findings from in vivo studies suggesting that progesterone may play an important role in augmenting hypothalamic βEP production and release to inhibit GnRH secretion. Our present findings are thus consistent with the notion that in the central nervous system, progesterone, but not estrogen, appears to be the major ovarian steroid that exerts an indirect long-loop negative feedback on the hypothalamus-pituitary-gonadal axis of the female rat.

Effects of progesterone on prolactin, hypothalamic beta-endorphin, hypothalamic substance P, and midbrain serotonin in guinea pigs.

Unlike rats, but similar to primates, guinea pigs exhibit prolonged function of the corpus luteum and elevated progesterone secretion after ovulation. The gonadotropins, estrogen (E) and progesterone (P) have been examined throughout the guinea pig estrous cycle. However, neither prolactin secretion nor its regulation by steroid hormones has been characterized, perhaps due to the lack of a specific radioimmunoassay. beta-Endorphin (BE), substance P (SP), and serotonin (5-HT) increase prolactin secretion in rats and monkeys. BE and SP neurons in guinea pigs and 5-HT neurons in monkeys contain progestin receptors which could mediate neuroendocrine effects of steroid hormones. Therefore, the effects of E and P on prolactin, BE, SP, and 5-HT and its metabolite 5-HIAA were examined in guinea pigs which were ovariectomized, E treated (28 days), and E+P treated (14 days E+14 days E+P). The rat NB2 lymphoma cell line was used as a bioassay for serum prolactin. BE and SP levels were measured by radioimmunoassay in four hypothalamic areas: the preoptic region (POA), the mediobasal hypothalamus (MBH), the dorsomedial hypothalamus (DMH), and the mamillary bodies (MB). 5-HT and 5-HIAA were measured in the midbrain raphe area by high-pressure liquid chromatography. E alone had little effect on serum prolactin levels, but E+P significantly increased prolactin as compared with ovariectomized controls. The BE levels increased with E treatment and remained elevated with E+P treatment in MBH and POA. The BE content was stimulated in DMH and MB by E+P treatment and not with E alone. The SP content in MBH, DMH, and MB increased in E-treated guinea pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoperiodic effects on hypothalamic β-endorphin and POMC mRNA

Photoperiodic effects on hypothalamic β-endorphin and POMC mRNA

Cardiovascular and analgesic effects of a highly palatable diet in spontaneously hypertensive and Wistar-Kyoto rats

Ingestion of highly palatable diets (HPDs), rich in sucrose and fat, has been shown to lead to obesity and alterations in cardiovascular function in animal models. A hypothesis has been advanced which suggests that ingestion of an HPD increases hypothalamic β-endorphin release, an effect which results in an increase in sympathetic nerve outflow during the development of obesity. The hypothesis was tested by chronic (10 weeks) feeding of male spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs) with the HPD or normal rat chow (ND). Cardiovascular function (systolic blood pressure, heart rate) and body weight gain were monitored during the feeding period. Pain sensitivity was tested weekly by measuring tail-flick latency. Body weight gain was greater in WKY rats than in SHRs, but ingestion of the HPD had no effect in either strain. Terminal organ analysis indicated differences between strains of SHRs and WKYs in the heart, the adrenal and pituitary glands, peritesticular fat pad, and testis weights expressed by organ weight/body weight. The heart weight was greater in SHRs on the HPD than in SHRs on the ND. The ingestion of the HPD significantly increased blood pressure only in SHRs, following 10 weeks of dietary intervention. However, tail-flick latency was prolonged in both SHRs and WKYs during ingestion of the HPD. Increases in tail-flick latency suggest that the HPD increases brain opiate levels in both SHRs and WKYs. Exaggerated increases in heart weight and blood pressure were noted in SHRs following feeding with the HPD, indicating enhanced sensitivity of SHRs to HPD-induced hypertension.

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

β-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. β-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 β-endorphin and Met-enkephalin. However, the increase for Leu-enkephalin content was in the day only. Hypothalamic β-endorphin content decreased with age only in the day. β-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.

β-endorphin and dynorphin abnormalities in rats subjected to exercise and restricted feeding: relationship to anorexia nervosa?

Exercise and the endogenous opioids have been linked to anorexia nervosa. This investigation determined the effects of the weight-loss syndrome induced by voluntary exercise (22.5 h/day) in food-restricted rats (1.5 h/day food access) on the endogenous opioids. The animals were tested under resting-fed and 2-deoxy- d-glucose (2DG) stimulated conditions. Weight-matched, freely fed exercised and ad libitum fed unexercised groups served as controls. Specific opioid abnormalities were found in the syndrome. These included a basal elevation in plasma β-endorphin, which was abnormally suppressed by 2DG, and 2DG-induced elevations in arcuate hypothalamic β-endorphin content and supraoptic hypothalamic dynorphin-A content. None of these changes occurred in controls. Finally, it was found that short-term moderate exercise itself chronically reduced adenohypophysial β-endorphin content and elevated supraoptic dynorphin-A content. The relationship of the syndrome's hyperendorphinism to the hypothalamo-pituitary-adrenal axis and the auto-addiction hypothesis of anorexia nervosa was considered, as was the significance of the supraoptic dynorphin-A abnormality to the hypothalamo-neuropophysical system. The differential sensitivity of the supraoptic dynorphin-A system compared to the arcuate hypothalamic β-endorphin system to moderate exercise was also discussed.

Effects of oestrogen on hypothalamic β-endorphin in ovariectomized and old rats

Immunocytochemical β-endorphin (β-EP) staining and ultrastructual observations in the hypothalamus were compared in normal mature female rats, ovariectomized rats, and aged female rats. The effects of oestradiol benzoate (EB) on the hypothalamus were studied. The female Wistar rats were divided into seven groups, as follows: 40-day-old rats (Mature), 54-day-old rats ovariectomized at 40 days (Ovx), rats ovariectomized at 40 days and injected with 0.1 mg EB daily for 7 days (Ovx + e), rats ovariectomized and injected with one dose of 1 mg EB (Ovx + E), 500-day-old (Old), old rats injected with 0.1 mg EB daily for 7 days (Old + e), and old rats injected with 1 mg EB (Old + E). In the Ovx and Old groups, β-EP-positive cells in the arucuate nucleus were rarely seen, as compared with the Mature group. The staining of β-EP-positive cells in Ovx + e was slightly recovered and that in Ovx + E was almost completely recovered. However, no recovery of β-EP-positive cells was seen in the Old + e or Old + E groups. The number of nerve fibers in the median eminence were reduced in both the Ovx and Old groups, as compared with the Mature group. There was no relationship between changes in these numbers and oestrogen replacement in the Old group, but in the Ovx group oestrogen replacement brought about recovery of these numbers. The number of glial cells increased after oestrogen replacement in both the Ovx and Old groups. The frequency of giant mitochondria in the neurons in the arcuate nucleus decreased after oestrogen replacement in the Old group.

The β-endorphin response to prenatal stress during postnatal development in the rat

We examined the hypothalamic β-endorphin (B-END) levels in offspring (postnatal day 10) from stressed female rats in different period of gestation: group 1, restraint stress from day 2 to 6; group 2, from day 7 to 11 and group 3, from day 2 to 16. The hypothalamic levels of B-END in the offspring from group 1 were significantly ( P < 0.001) higher to that obtained in the control. Similar results were obtained in the group 2. However, in rat pups from female stressed during 15 days of gestation hypothalamic levels of B-END were similar to control group.

Effects of single and repeated exposures to ethanol on hypothalamic beta-endorphin and CRH release by the C57BL/6 and DBA/2 strains of mice.

Ethanol has been shown to enhance the in vitro release of hypothalamic beta-endorphin (beta-EP). In the present study, the pattern of beta-EP release by the hypothalamus of two strains of mice, bred selectively for their preference (C57BL/6) or aversion (DBA/2) to ethanol, was investigated using a tissue perifusion system. The tissues were perifused with 20 mM ethanol for 30 min and the immunoreactive beta-EP content was estimated in perifusates collected every 2 min. Ethanol induced an enhanced release of hypothalamic beta-EP characterized by an initial spike followed by a gradual decrease toward baseline levels in both strains of mice. The ethanol-induced increase in beta-EP release by the hypothalamus of the C57BL/6 mice was more pronounced and longer lasting than that by the hypothalamus of the DBA/2 mice. Similar to beta-EP, an immediate sharp increase of corticotropin-releasing hormone (CRH) release was induced by ethanol which, however, did not present a spike but was maintained significantly higher than spontaneous release for the duration of ethanol exposure. Both ethanol-induced beta-EP and CRH release returned to basal levels within 10 min following removal of ethanol. That beta-EP levels did not remain elevated for the duration of ethanol exposure was not due to tissue depletion of releasable beta-EP pool, since exposure of the hypothalami to 10(-8) M CRH for 10 min, immediately after the perifusion with 20 mM ethanol, resulted in a large increase of beta-EP release. A second ethanol exposure 30 min after the first one did not induce an increase in beta-EP release. However, when the recovery period from the first ethanol exposure was extended to 60 min, a significant increase in the release of hypothalamic beta-EP was observed from the hypothalamus of the C57BL/6 but not of the DBA/2 mice. It is concluded that hypothalamic endorphinergic neurons present a fast, transient increase of beta-EP release in the presence of 20 mM ethanol, and become insensitive to subsequent ethanol exposures for a period of about 60 min. In addition, genetically determined differences exist with regards to the magnitude and duration of the ethanol-stimulated release of beta-EP, as well as on the length of the ethanol nonresponsive period. These differences may explain in part the differences in the voluntary ethanol consumption exhibited by these strains of mice.

Sucrose drinking reduces dorsal hypothalamic β-endorphin levels in spontaneously hypertensive rats but not in Wistar-Kyoto rats

The present study was performed to test whether drinking of a 10% sucrose solution would preferentially alter tissue content of β-endorphin in dorsal and ventral hypothalamic fragments from the spontaneously hypertensive rat (SHR), as opposed to the Wistar-Kyoto rat (WKY). Changes were correlated with cardiovascular function and circulating catecholamine levels to asses the role of hypothalamic β-endorphin, a putative mediator of sucrose-induced changes in cardiovascular sympathetic nervous tone. Male rats were trained to consume their total 24-h water intake in a single period between 0900–1100 h. Catheters were chronically implanted to sample blood and to record arterial blood pressure and heart rate. The experimental protocol consisted of a recording session, which included a 10-min drinking period wherein rats consumed 8 ml of either sucrose solution or deionized water. Rats were sacrificed and hypothalami removed for analysis of β-endorphin content. Comparable increases in blood pressure were noted in SHR and WKY during drinking of either sucrose or water. Drinking-induced tachycardia was blunted in SHR drinking sucrose. Plasma norepinephrine was increased only in sucrose-drinking SHR. Plasma glucose levels were elevated in both SHR and WKY following drinking of sucrose, but not water. β-Endorphin levels were reduced ( p < 0.05) in dorsal, but not ventral, hypothalamic fragments only in SHR drinking sucrose. The sucrose-induced changes in β-endorphin did not correlate with blood pressure responses. The results indicate an exaggerated stimulation of β-endorphin release in the dorsal hypothalamus following sucrose ingestion in SHR.

Pituitary-adrenal function and hypothalamic beta-endorphin release in vitro following food deprivation

Basal and dexamethasone-suppressed adrenal gluco- corticoid secretion and hypothalamic β-endorphin (BE) release in vitro were investigated in rats deprived of food for 24, 48, 72, and 96 h. Fasting for up to 48 h neither caused significant changes in serum corticosterone levels nor in the suppressive effect of dexamethasone. Food deprivation for 72–96 h resulted in increased basal serum corticosterone, diminished suppression by dexa- methasone, and a significant involution of the thymus. Basal in vitro BE release from hypothalamic expiants was significantly increased after the first day of food deprivation, and in vitro perifusion with corticotropin-releasing hormone (CRH) failed to enhance BE release further. With continuing food deprivation, basal BE release remained significantly greater than that from hypothalami originating from normally fed control rats. The stimulatory effect of CRH on BE release was only partially restored after 2 days of fasting. The results suggest that food deprivation for more than 2 days increases basal glucocorticoid secretion, and signs of impairment in hypothalamic-pituitary-adrenal regulation become apparent. These findings might be implicated in the pathogenetic mechanisms of endocrine dysregulation in diseases related to caloric reduction.

GABAergic and catecholaminergic innervation of mediobasal hypothalamic β-endorphin cells projecting to the medial preoptic area

In the absence of cellular estrogen receptors or proven direct estrogen action in the rat, it is assumed that estrogen indirectly regulates the secretory activity of the preoptic area luteinizing hormone-releasing hormone-producing cells. We have previously shown that pro-opiomelanocortin neurons in the arcuate nucleus of the rat send axons rostrally to connect with luteinizing hormonereleasing hormone neurons of the preoptic area. An experiment combining retrograde tracing and double-immunostaining was used to test the hypothesis that rat GABAergic and/or catecholaminergic neurons can influence luteinizing hormone-releasing hormone-producing cells via mediobasal hypothalamic β-endorphin neurons. The retrograde tracer horseradish peroxidase was injected into the medial preoptic area; two days later, arcuate nucleus Vibratome sections were double-immunostained for β-endorphin and glutamate decar☐ylase or tyrosine hydroxylase. Light and electron microscopic analysis of these triple-labeled sections demonstrated that a population of β-endorphin-immunoreactive neurons concentrated in the ventromedial arcuate nucleus contain retrogradely transported horseradish peroxidase granules and form synaptic contacts with glutamate decar☐ylase- and tyrosine hydroxylase-immuno-reactive axon terminals. The present data suggest that arcuate nucleus GABA and catecholamine fibers may influence luteinizing hormone-releasing hormone-containing neurons via projective pro-opiomelanocortin cells.

Progesterone and corticosteroid regulation of hypothalamic and pituitary opioid content during LH surge induction

The purpose of this study was to determine whether steroid hormones affect brain opioid content during the time of gonadotropin surge induction. Ovariectomized rats (26 days old) were primed with estradiol (E 2) (2 μg) for 2 days. E 2 treatment markedly suppressed hypothalamic β-endorphin content at 1500 h, 1800 h (Day 29), and 0800 h (Day 30) but had no effect on pituitary β-endorphin levels. The administration of progesterone (P 4) at 0900 h on Day 29 caused a luteinizing hormone (LH) and a follicle-stimulating hormone (FSH) surge at 1500 h that same day. Interestingly, hypothalamic β-endorphin content was unchanged during the LH surge induced by P 4, although a nonsignificant elevation of hypothalamic β-endorphin levels was noticed in P 4-treated rats the morning after the surge. Triamcinolone acetonide (TA) treatment induced a large LH and FSH surge at 1500 h. Similar to P 4, TA did not alter hypothalamic β-endorphin levels during the time of the LH surge; however, after the surge, TA-treated rats had a significant increase in hypothalamic β-endorphin levels at 1800 h (Day 29) and 0800 h the next morning. Cortisol had no effect on LH levels but increased FSH levels at 0800 h on Day 30. Similar to TA, cortisol caused an elevation in hypothalamic β-endorphin levels at 1800 h and 0800 h the next day. Finally, pituitary dynorphin A 1–13 content was not affected by any of the steroids. This study suggests that E 2 is principally responsible for reducing hypothalamic opioid content. The stimulatory effect of progesterone and TA on gonadotropin secretion appears to be due to the turning on of an excitatory signal rather than the turning off of an inhibitory opioid signal.