The differential profiles of withdrawal symptoms induced by morphine and beta-endorphin administered intracerebroventricularly in mice.

In the present study, withdrawal symptoms induced by morphine or ß-endorphin administered intracerebroventricularly (i.c.v.) were compared in ICR mice. Naloxone (10mg/kg) was post-treated intraperitoneally (i.p.) 3h after either a single or repeated (1 time/day for 3 days) i.c.v. injections with opioids. Withdrawal symptoms such as jumping frequency, diarrhea, weight loss, rearing, penile licking and paw tremor were observed for 30 min immediately after naloxone treatment. Withdrawal symptoms (jumping, diarrhea, weight loss, rearing, penile licking and paw tremor) observed in the group treated with morphine was persistently increased during 3 days. On the other hand, withdrawal symptoms such as diarrhea, weight loss and rearing in ß-endorphin-treated group were increased after a single injection with ß-endorphin, but gradually decreased after the repeated injection. Furthermore, no jumping behavior, penile licking and paw tremor in ß-endorphin-treated group were observed throughout the whole period of time. In addition, the hypothalamic changes of several signal molecules such as pERK, pCaMK-IIα, c-FOS and pCREB expression were observed during the presence or absence of withdrawal responses induced by morphine or ß-endorphin administered once or repeatedly. Both hypothalamic pCaMK-IIα and c-FOS expressions were increased by naloxone treatment in acutely administered morphine group, whereas only pCaMK-IIα expression was elevated by naloxone treatment in repeatedly administered morphine group. In contrast with the findings in morphine-treated group, only pCaMK-IIα expression was decreased by naloxone treatment in repeatedly administered ß-endorphin group. Our results suggest that profiles of the withdrawal symptoms induced by morphine and ß-endorphin administered supraspinally appear to be differentially regulated. The pCaMK-IIα and the c-FOS protein expression may play important roles for the regulation of naloxone-precipitated withdrawal symptoms such as jumping, diarrhea, weight loss, rearing, penile licking and paw tremor induced by morphine-treated group, whereas the phosphorylation of hypothalamic pCaMK-IIα appears to be involved only in the regulation of naloxone-precipitated withdrawal symptoms such as diarrhea, weight loss and rearing in ß-endorphin-treated group.

The central effect of beta-endorphin and naloxone on the expression of GnRH Gene and GnRH receptor (GnRH-R) gene in the hypothalamus, and on GnRH-R gene in the anterior pituitary gland in follicular phase ewes.

The effect of prolonged intermittent infusion of beta-endorphin or naloxone into the third cerebral ventricle in ewes during the follicular phase of the estrous cycle on the expression of GnRH gene and GnRH-R gene in the hypothalamus and GnRH-R gene in the anterior pituitary gland was examined by Real time-PCR. Activation of micro opioid receptors decreased GnRH mRNA levels in the hypothalamus and led to complex changes in GnRH-R mRNA: an increase of GnRH-R mRNA in the preoptic area, no change in the anterior hypothalamus and decrease in the ventromedial hypothalamus and stalk/median eminence. In beta-endorphin treated ewes the levels of GnRH-R mRNA in the anterior pituitary gland also decreased significantly. These complex changes in the levels of GnRH mRNA and GnRH-R mRNA were reflected in the decrease of LH secretion. Blockade of micro opioid receptors affected neither GnRH mRNA and GnRH-R mRNA nor LH levels secretion. These results indicate that beta-endorphin displays a suppressive effect on the expression of the GnRH gene in the hypothalamus and GnRH-R gene in the anterior pituitary gland, but affects GnRH-R gene expression in a specific manner in the various parts of hypothalamus; altogether these events lead to the decrease in GnRH/LH secretion.

Formalin pretreatment attenuates tail-flick inhibition induced by beta-endorphin administered intracerebroventricularly or intrathecally in mice.

We examined the effect of the subcutaneous (s.c.) pretreatment of formalin into both hind paws of mice on the antinociception induced by the intracerebroventricularly (i.c.v.) or intrathecally (i.t.) administration of beta-endorphin using the tail-flick test. Pretreatment with formalin (5%) for 5 h had no affect on the i.c.v. administered beta-endorphin-induced tail-flick response. However, pretreatment with formalin for 40 h attenuated the tail-flick inhibition induced by i.c.v. administered beta-endorphin. This antinociceptive tolerance to i.c.v. beta-endorphin continued up to 1 week, but to a lesser extent. Pretreatment with formalin for 5 and 40 h significantly reduced the i.t. beta-endorphin-induced inhibition of the tail-flick response, which continued up to 1 week. The s.c. formalin treatment increased the hypothalamic pro-opiomelanocortin (POMC) mRNA level at 2 h, but this returned to the basal level after 40 h. Our results suggest that the increase in the POMC mRNA level in the hypothalamus appears to be involved in the supraspinal or spinal beta-endorphin-induced antinociceptive tolerance in formalin-induced inflammatory pain.

Endorphin excess at weaning durably influences sexual activity, uterine estrogen receptor's binding capacity and brain serotonin level of female rats.

Perinatally, the first encounter between the maturing receptor and its target hormone results in hormonal imprinting, which adjusts the binding capacity of the receptor for life. In the presence of an excess of the target hormone or foreign molecules than can be bound by the receptor, faulty imprinting carries life-long consequences. In cytogenic organs, imprinting could also be provoked in other periods of life (late imprinting). Imprinting also durably influences the production of the imprinter and related hormones. In the present study, single beta-endorphin doses was given to three-week old female rats at 3 microg/animal, and the serotonin in five brain regions (frontal cortex, striatum, hippocampus, hypothalamus and brain stem) and uterine estrogen receptor content were determined, thymic glucocorticoid receptor binding capacity was measured, and sexual behavior was tested at five months of age. Brain serotonin levels highly significantly decreased, while sexual activity (Meyerson index and lordosis quotient) increased. At the same time, uterine estrogen receptor affinity decreased. There was no change in receptor binding capacity in the thymus. We will go on to discuss interrelations between the results. The experiments demonstrate that a non-perinatal treatment with a molecule acting at receptor level (late imprinting) can also lastingly influence various indexes in non-cytogenic organs. The results call attention to the possible long-lasting influence of an endorphin surge (caused, for example, by pain) on brain serotonin content and sexual behavior.

Effects of ginsenosides injected intrathecally or intracerebroventricularly on antinociception induced by beta -endorphin administered intracerebroventricularly in the mouse.

The effect of total saponin fraction of ginseng injected intrathecally (i.t.) or intracerebroventricularly (i.c.v.) on the antinociception induced by beta-endorphin administered i.c.v. was studied in ICR mice in the present study. The antinociception was assessed by the tail-flick test. Total saponin fraction at doses 0.1 to 1.0 microgram, which administered i.t. alone did not affect the latencies of tail-flick threshold, attenuated dose-dependently the inhibition of the tail-flick response induced by i.c.v. administered beta-endorphin (1 microgram). However, total saponin fraction at doses 1 to 20 microgram, which administered i.c.v. alone did not affect the latencies of the tail-flick response, did not affect i.c.v. administered beta-endorphiun (1 microgram)-induced antinociception. The duration of antagonistic action of total saponin fraction against beta-endorphin-induced antinociception lasted at least for 6 h. Various doses (from 0.1 to 1 microgram) of ginsenoside R(c), but not R(b2), R(d), Rg(1), R(b1)and R(e)injected i.t. dose-dependently attenuated antinociception induced by beta-endorphin administered i.c.v. Our results indicate that total saponin fraction injected spinally appears to have antagonistic action against the antinociception induced by supraspinally applied beta-endorphin. Ginsenoside R(c)appears to be responsible for blocking i.c.v. administered beta-endorphin-induced antinociception. On the other hand, total ginseng fraction, at supraspinal sites, may not exert an antagonistic action against the antinociception induced by supraspinally administered beta-endorphin.

Intravenous beta-endorphin administration fails to alter hypothalamic blood flow in rats expressing normal or reduced nitric oxide synthase activity.

beta-Endorphin (beta-END) significantly contributes to the maintenance of hypothalamic blood flow (HBF) autoregulation during hemorrhagic hypotension in rats. Recently, several natural and synthetic opioid peptides were reported to induce nitric oxide (NO)-mediated dilation in the cerebrovascular bed. In the present study, the effect of beta-END was studied on HBF and hypothalamic vascular resistance (HVR) in vehicle-treated control rats and in rats after the pharmacological inhibition of the NO synthesis by chronic oral application of NG-nitro-L-arginine methyl ester. Intravenous beta-END administration failed to alter HBF or HVR either in control or in NO-blocked animals, and its transient hypotensive effect was not inhibited by NO blockade, indicating that beta-END may not have NO-mediated vasodilator effect in the hypothalamic or in the systemic circulation.

Beta-endorphin inhibits hypoglycemia-induced gene expression of corticotropin-releasing factor in the rat hypothalamus.

Endogenous opioid peptides have a role in the regulation of the hypothalamic-pituitary-adrenal axis. Recently, beta-endorphin (EP) has been thought to inhibit CRF release in vivo and in vitro. In the present study we examined the effects of central administration of EP on ACTH secretion and gene expression of both CRF in the hypothalamus and POMC in the anterior pituitary gland (AP) during basal and insulin-induced hypoglycemia in pentobarbital-anesthetized rats. Administration of EP in the lateral ventricle decreased basal CRF levels in the median eminence and inhibited basal and hypoglycemia-induced ACTH secretion in a dose-dependent manner. Hypoglycemia-induced POMC mRNA levels in the AP and CRF mRNA levels in the hypothalamus were also dose-dependently inhibited by the administration of EP. The inhibitory effect of EP was reversed by naloxone. These results suggest that 1) central administration of EP acts through the opioid receptor to inhibit hypoglycemia-induced CRF gene expression in the hypothalamus and CRF release, which results in a decrease in ACTH secretion and POMC mRNA levels in the AP; and 2) the active site of EP is the CRF neuron in the paraventricular nucleus.

Effect of posttraining and pretest beta-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 beta-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 micrograms/kg) and beta-endorphin (1.0 micrograms/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 beta-endorphin caused amnesia on its own. On the basis of previous findings which suggest that pretest actions of ACTH and beta-endorphin depend on their endogenous release at the time of training, the present results are compatible with a malfunction of the brain beta-endorphin system in the undernourished animals.

Cardiovascular effects of central administration of beta-endorphin in rats receiving neonatal injection of monosodium glutamate.

1. The effects of intracerebroventricular (i.c.v.) and intracisternal (i.c.) injection of beta-endorphin on arterial blood pressure (BP) in rats that received five intraperitoneal injections of monosodium glutamate (MSG) on alternate days in the first 10 days of life were studied. 2. beta-endorphin administered into the lateral ventricles caused a prolonged elevation in BP, whereas i.c. injection of the peptide resulted in an even longer lasting reduction in BP. In the MSG-treated rat, the prolonged hypertensive effect of i.c.v. injection of beta-endorphin was completely abolished, but the effect of i.c. injection of the peptide was the same as that in the control. Since MSG treatment destroyed selectively the structures around the third ventricle, it is suggested that these structures, including the arcuate nucleus, may be responsible for mediating the cardiovascular effects of beta-endorphin. 3. The effects of central administration of beta-endorphin were completely blocked by naloxone, which mainly antagonizes the actions of mu-receptor agonists and has no cardiovascular effects itself. The results suggest that mu-receptors may be involved in mediation of the effects of beta-endorphin on the cardiovascular system and that beta-endorphin in the brain may not exert a tonic influence on the cardiovascular functions.

Effects of undernutrition during suckling and of post-training beta-endorphin administration on avoidance performances of adult rats.

1. The effects of undernutrition during suckling and of post-training beta-endorphin administration on avoidance task were investigated in adult rats. 2. Young rats were undernourished from delivery until weaning (21 days) by feeding their mothers a diet containing 8% protein (w/w). Mothers of well-nourished rats were fed a 20% protein diet. After weaning, both groups of rats were fed a 20% protein diet until 90-120 days of age, when they were subjected to behavioral sessions. 3. Acquisition was measured in training sessions and retention in test sessions 24 h after training. Beta-endorphin or saline (control) was injected ip immediately after training. Rats were subjected to shuttle and step-down inhibitory avoidance sessions using footshock of 0.2 or 0.8 mA intensity. 4. Undernutrition during suckling caused hyperreactivity to 0.2 mA footshocks. Beta-endorphin caused amnesia to shuttle avoidance task only in normal rats trained with 0.8 mA footshocks. In the step-down inhibitory avoidance task, beta-endorphin was amnesic only for normal rats and only for 0.2 mA footshocks. Beta-endorphin was not amnesic in undernourished rats.

Effects of undernutrition during suckling and of post-training ß-endorphin administration on avoidance performances of adult rats

1. The effects of undernutrition during suckling and of post-training ß-endorphin administration on avoidance task were invstigated in adult rats. 2. young rats were undernourished from delivery until weaning (21 days) by feeding their mothers a diet conatining 8% protein (w/w). Mothers of well-nourished rats were fed a 20% protein diet. After weaning, both groups of rats were fed a 20% protein diet until 90-120 days if age, when they were subjected to behavioral sessions. 3. Acquistion was measured in training sessions and retention in test sessions 24 h after training. Beta-endorphin or salina (control) was injected ip immdiately after training. Rats were subjected to shuttle and step-down inhibitory avoidance sessions using footshock of 0.2 or 0.8 mA intensity. 4. Undernutrition during suckling caused hyperreactivity to 0.2 mA footshocks. Beta-endorphin caused amnesia to shuttle avoidance task only in normal rats trained with 0.8 mA. Foor-shocks. In the step-down inhibitory avoidance task, ß-endorphin was amnesic only for normal rats and only for 0.2-mA footshocks. Beta-endorphin was not amnesic in undernourished rats