Prolonged estrogen treatment induces changes in opiate, benzodiazepine and beta-adrenergic binding sites in female rat hypothalamus

Enhanced striatal β1-adrenergic receptor expression following hormone loss in adulthood is programmed by both early sexual differentiation and puberty: a study of humans and rats

After reproductive senescence or gonadectomy, changes occur in neural gene expression, ultimately altering brain function. The endocrine mechanisms underlying these changes in gene expression beyond immediate hormone loss are poorly understood. To investigate this, we measured changes in gene expression the dorsal striatum, where 17β-estradiol modulates catecholamine signaling. In human caudate, quantitative PCR determined a significant elevation in β1-adrenergic receptor (β1AR) expression in menopausal females when compared with similarly aged males. No differences were detected in β2-adrenergic and D1- and D2-dopamine receptor expression. Consistent with humans, adult ovariectomized female rats exhibited a similar increase in β1AR expression when compared with gonadectomized males. No sex difference in β1AR expression was detected between intact adults, prepubertal juveniles, or adults gonadectomized before puberty, indicating the necessity of pubertal development and adult ovariectomy. Additionally, increased β1AR expression in adult ovariectomized females was not observed if animals were masculinized/defeminized with testosterone injections as neonates. To generate a model system for assessing functional impact, increased β1AR expression was induced in female-derived cultured striatal neurons via exposure to and then removal of hormone-containing serum. Increased β1AR action on cAMP formation, cAMP response element-binding protein phosphorylation and gene expression was observed. This up-regulation of β1AR action was eliminated with 17β-estradiol addition to the media, directly implicating this hormone as a regulator of β1AR expression. Beyond having implications for the known sex differences in striatal function and pathologies, these data collectively demonstrate that critical periods early in life and at puberty program adult gene responsiveness to hormone loss after gonadectomy and potentially reproductive senescence.

Administration of 17alpha-ethinylestradiol during pregnancy elicits modifications of maternal behavior and emotional alteration of the offspring in the rat

Intraperitoneal administration of 17alpha-ethinylestradiol (15 microg.kg(-1)) in pregnant rats, every day from day 9 to day 14 of pregnancy, elicited a high percentage of abortions. Quantification of maternal behavior showed that treated dams took better care of their pups than control dams, injected with the vehicle only, did. Postnatal reflexes, which reflect maturational rate, were established more promptly in the offspring of treated dams than in the offspring of control dams. However, when adult, the rats born from treated dams developed anxiety- and depressive-like behaviors. All these results are explained by the effects of the exogenous estrogen on the developing brain of the fetuses.

Neuroendocrinology of female aging

BACKGROUND

Because the average human life span has increased, a greater part of more women's lives will be lived in a hypoestrogenic state.

OBJECTIVE

This article provides an overview of our current knowledge of the neuroendocrine processes in the aging female brain.

METHODS

Using the search terms cardiovascular disease, cognition, dementia, depression, estrogens, female aging, gonadotropins, immune function, mood, neuroendocrinology, neurotransmitters, osteoporosis, and ovarian steroids, a review of English-language literature on the MEDLINE database was conducted from 1970 through June 2004.

RESULTS

It is thought that the temporal patterns of neural signals are altered during middle age, leading to cessation of reproductive cycles, and that the complex interplay of ovarian and hypothalamic/pituitary pacemakers becomes increasingly dysfunctional with aging, ultimately resulting in menopause. Estrogen deficiency is associated with low mood, whereas estrogen therapy tends to be linked with improvements in measures of well-being and a decline in depression scores. It is likely that these effects of estrogens are mediated through changes in the metabolism of serotonin and nor epinephrine. Evidence exists to support the role of estrogens in specific effects on cognitive functioning in women, enhancing aspects of verbal memory, abstract reasoning, and information processing. Significant gender dimorphism is evident in both humoral and cell-mediated immune responses. The effects of estrogens on the cardiovascular system are complex; recent evidence suggests a negative role for oral estrogen in primary and secondary prevention of cardiovascular events. Additionally, estrogens increase the risk of stroke, and estrogen deficiency influences the pathogenesis of osteoporosis in both men and women.

CONCLUSIONS

Changes in the neuroendocrine system due to the loss of ovarian function at menopause have an important biological role in the control of reproductive and nonreproductive functions, and regulate mood, memory, cognition, behavior, immune function, the locomotor system, and cardiovascular functions. More detailed insights are needed into the complex mechanisms of neuroendocrine alterations with aging.

Noradrenergic regulation of prolactin secretion at the level of the paraventricular nucleus of the hypothalamus: functional significance of the alpha-1b and beta-adrenergic receptor subtypes

Previous research has demonstrated that in the Siberian hamster, both photoperiod and estrous cyclicity alter the profile of noradrenergic activity with the paraventricular nucleus of the hypothalamus (PVN), and that noradrenergic activity is correlated with changes in circulating levels of prolactin. Work from our laboratory has demonstrated an inhibitory role for norepinephrine (NE) acting at the alpha-2 receptor subtype within the PVN on serum prolactin levels; however, the functional significance of other adrenergic receptor subtypes on this system is unknown. The purpose of this study was to investigate the functional significance of the alpha-1b and beta-adrenergic receptor subtypes at the level of the PVN on circulating levels of prolactin. These experiments were performed in male Siberian hamsters using reverse microdialysis coupled with serial blood sampling. In Experiment 1, infusion of l-phenylephrine hydrochloride (alpha-1b agonist) initiated a dose-dependent increase in circulating prolactin, whereas infusion of chloroethylclonidine (alpha-1b antagonist) induced a significant dose-dependent decline in prolactin. In Experiment 2, intraparaventricular administration of propranolol (beta antagonist) initiated a significant increase in prolactin levels in a dose-dependent manner, whereas isoproterenol (beta agonist) induced a dose-dependent decline in prolactin. The results of this study indicate that both the alpha-1b and beta-adrenergic receptor subtypes have a significant role in regulating circulating levels of prolactin at the level of the PVN in the Siberian hamster.

Infusion of alpha-2-adrenergic agents into the paraventricular and arcuate nuclei of the hypothalamus in the Siberian hamster: opposing effects on basal prolactin

Although the alpha(2)-adrenergic receptor subtype has been shown to have a significant influence on circulating levels of prolactin (PRL), its exact role remains unclear. A multitude of studies have demonstrated that blockade of the alpha(2)-receptor can either elevate or decrease circulating levels of PRL. Alpha(2)-receptor-mediated control of both stimulatory and inhibitory arms of the PRL regulatory system may explain this discrepancy. Activation of the alpha(2)-receptor has been shown to inhibit the activity of its target cell, and therefore antagonism of the alpha(2)-receptor within a stimulatory component (e.g., paraventricular nucleus (PVN) of the hypothalamus) would theoretically have the opposite effect that it would have within an inhibitory component (arcuate nucleus of the hypothalamus). Thus, the purpose of this study was to investigate the functional role of the alpha(2)-adrenergic receptor in modulating circulating levels of PRL both at the level of the PVN and arcuate using reverse microdialysis of alpha(2)-adrenergic agents coupled with serial blood sampling in the male Siberian hamster. Male hamsters were fitted with a jugular cannula for serial blood sampling, and an indwelling microdialysis probe for intrahypothalamic drug administration between 08:00 and 10:00 h. Blood samples were collected every hour for 5 h (12:00-17:00 h). During the third sampling period, atipamezole (alpha(2)-antagonist) or medetomidine (alpha(2)-agonist) at one of three doses were infused into the PVN or the arcuate to assess effects on basal PRL. At the level of the PVN, infusion of atipamezole initiated an increase in basal PRL in a dose-dependent fashion, whereas infusion of medetomidine induced a significant decline in basal PRL in a dose-dependent fashion. In the arcuate, only the highest dose of atipamezole had an effect on PRL, and this was in the opposite direction from that seen in the PVN. Infusion of medetomidine did not have a significant effect on basal PRL levels; however, a trend toward a significant elevation was observed for the highest dose. These results suggest that the alpha(2)-receptor subtype may have opposite effects on circulating levels of PRL within the PVN and arcuate regions, and may explain why antagonism of the alpha(2)-receptor has been shown to initiate both surges and declines in basal levels of PRL.

Anxiolytic effects of steroid hormones during the estrous cycle. Interactions with ethanol

Behavioral differences in anxiety have been observed between both males and females and across the ovarian cycle in females. However, the data are not entirely consistent and the mechanisms of this potential interaction are largely unexplored. It appears that the GABA/BZ receptor complex is a site of action for steroids as well as for many anxiolytic drugs. Both natural steroids, such as progesterone and its metabolites, and synthetic steroids, such as alphaxalone, reduce anxiety-like behavior in rats. Alphaxolone also reverses the behavioral effects of potent anxiogenic agents in the conflict test of anxiety. Studies reported here found that ethanol administered to rats in different phases of the estrous cycle was more effective as an anxiolytic when hormone levels were high. The anticonflict response to chlordiazepoxide also was examined in ovariectomized and steroid-replaced female rats. Insight into the mechanisms and sites of action for these steroids can be gained from such an approach.

Prenatal exposure to ethinylestradiol elicits behavioral abnormalities in the rat

Pregnant rats were i.p. injected with a solution of 17alpha-ethinylestradiol (15 microg kg(-1)) every day between day 9 and day 14 of pregnancy and the behavior of the offspring was compared to that of rats born from dams injected with the vehicle only during the same gestational period. The percentage of neonatal death was dramatically high in the prenatally treated group. Growth of the surviving animals was even better than that of controls, but when adult, they exhibited a number of behavioral abnormalities: increased spontaneous motor activity, decreased exploratory behavior, impaired cognitive processing, qualitatively different exploratory drive, and/or persevering behavior, increased anxiety-like behavior and social neophobia. These behavioral alterations, which resemble a number of psychiatric syndromes, suggest that ethinylestradiol altered the ontogenesis of different parts of the central nervous system involved in cognitive and emotional processes. However, it cannot be excluded that the changes in behavior of ethinylestradiol exposed offspring were due to the abnormal maternal behavior of the estradiol treated dams.

Endocrinological basis of sex differences in cocaine-induced behavioral responses

Currently, 1.8 million Americans use cocaine, 30% of whom are females. Sex differences in the pattern of cocaine abuse may reside in neuroendocrinological modulations that affect the use of and/or dependence on cocaine. This review discusses sex differences in cocaine-induced behavioral and molecular alterations in the central nervous system, with emphasis on the role of endocrine responses in the neuronal modulations of this drug. Mechanisms and data supporting the role of the hypothalamic-gonadal axis in the modulation of cocaine-induced behavioral and molecular alterations are also provided.

The development of POMC gene expression in the medial basal hypothalamus of prepubertal rats

Alterations in brain opioid gene expression may underlie the dramatic change in the latency to display parental behavior in juvenile rats. Male and female juvenile rats (18-25 days of age) exhibit parental behavior either immediately or within 1-2 days after coming in contact with foster pups. By 30 days of age, however, their response latencies increase to adult levels of 5-10 days. Given the established involvement of the endogenous opioid system in adult maternal and juvenile parental behaviors, the objective of the present report was to determine possible changes in proopiomelanocortin (POMC) gene expression in the medial basal hypothalamus (MBH) during this early developmental window. We compared POMC gene expression in the MBH of male and female juvenile rats from 21 to 33 days of age by in situ hybridization histochemistry. A significant increase in the number of POMC cells in males and females was detected at 30 days of age in the central portion of the arcuate nucleus. This increase in POMC mRNA may contribute to the shift in parental behavior that occurs in male and female juvenile rats.

Estrogen regulation of mu-opioid receptor mRNA in the forebrain of female rats

Previous studies have suggested that opioids play a role in the regulation of reproductive behaviors in the female rat. The present study examined whether estrogen treatment alters mu-opioid receptor mRNA levels in different areas of the forebrain of ovariectomized (OVX) female rats using the in situ hybridization technique. We observed an increase in mu-opioid receptor mRNA levels in the ventromedial nucleus of the hypothalamus (VMH) and arcuate nucleus (ARN) after 48 h of 10 microg of 17-beta-estradiol-3-benzoate treatment when compared to OVX females. No effects of estrogen were observed on mu-opioid receptor mRNA levels in the posterior medial nucleus of the amygdala (MeAmyg), hippocampus, caudate-putamen (CPu) or the medial habenula. Our result suggests that the estrogenic regulation of mu-opioid receptor in the CNS may in part be mediated by de novo synthesis and/or stability of the mu-opioid receptor message.

Differential proopiomelanocortin gene expression in the medial basal hypothalamus of rats during pregnancy and lactation

Hypothalamic proopiomelanocortin (POMC) gene expression was determined using in situ hybridization histochemistry (ISHH) during pregnancy and lactation in rats with and without prior reproduction experience. POMC mRNA levels in the arcuate nucleus were compared between primigravid (first pregnancy) and multigravid (second pregnancy) and primiparous and multiparous lactating rats, and between these groups and age-matched, regularly cycling, nulliparous females in diestrus. Hybridizations were performed using a digoxigenin-labeled riboprobe complementary to 837 bp of the POMC gene. The number of cells expressing POMC mRNA in the arcuate nucleus decreased in primiparous rats on day 12 of lactation when compared with the number of POMC cells in the arcuate nucleus of nulliparous rats in diestrus. In addition, the number of cells expressing POMC mRNA in multigravid animals was significantly less than in the primigravid group on days 7 and 21 of pregnancy, and on day 12 of lactation in primiparous animals. Repeated reproductive experience affected the number of POMC mRNA positive cells; there were fewer cells expressing POMC mRNA in the multigravid females on day 7 of pregnancy and an increase in the number of POMC cells in the multiparous group on day 12 of lactation compared to the primiparous animals. Optical density measurements revealed a significant increase in reaction product in the labeled cells on all days of pregnancy compared with virgin females in diestrus and a significant decrease in reaction product on day 12 of lactation in the multiparous group. The results of the present study indicate that POMC gene expression changes across pregnancy and lactation and that repeated reproductive experience has long-term, possibly permanent, effects on the endogenous opioid system.

Benzodiazepine binding varies with stage of estrous cycle in unwashed membranes from mouse brain

The influence of the stage of the estrous cycle on binding of [3H]diazepam was examined in membranes from brains of female mice. In order to conserve endogenous factors such as progesterone, other steroids, or GABA, the assay was performed without the extensive washing procedures typically employed in measurements of benzodiazepine binding. Significant variations in the apparent maximal numbers of binding sites (Bmax) were noted during the estrous cycle in both hypothalamus and cortex. The Bmax measured in membranes from proestrus female mice was significantly higher than in membranes from mice at other stages in the estrous cycle. Variations in apparent equilibrium binding dissociation constants (Kd) were not statistically significant by stage of the estrous cycle. The demonstrated variations in binding suggest the existence of a factor which varies with the estrous cycle in female mice and modulates the activity of the GABAA receptor complex.

Estrogen-induced hypothalamic beta-endorphin neuron loss: a possible model of hypothalamic aging

Over the course of normal aging, all female mammals with regular cycles display an irreversible arrest of cyclicity at mid-life. Males, in contrast, exhibit gametogenesis until death. Although it is widely accepted that exposure to estradiol throughout life contributes to reproductive aging, a unified hypothesis of the role of estradiol in reproductive senescence has yet to emerge. Recent evidence derived from a rodent model of chronic estradiol-mediated accelerated reproductive senescence now suggests such a hypothesis. It has been shown that chronic estradiol exposure results in the destruction of greater than 60% of all beta-endorphin neurons in the arcuate nucleus while leaving other neuronal populations spared. This loss of opioid neurons is prevented by treatment with antioxidants indicating that it results from estradiol-induced formation of free radicals. Furthermore, we have shown that this beta-endorphin cell loss is followed by a compensatory upregulation of mu opioid receptors in the vicinity of LHRH cell bodies. The increment in mu opioid receptors presumably renders the opioid target cells supersensitive to either residual beta-endorphin or other endogenous mu ligands, such as met-enkephalin, thus resulting in chronic opioid suppression of the pattern of LHRH release, and subsequently that of LH. Indeed, prevention of the neuroendocrine effects of estradiol by antioxidant treatment also prevents the cascade of neuroendocrine aberrations resulting in anovulatory acyclicity. The loss of beta-endorphin neurons along with the paradoxical opioid supersensitivity which ensues, provides a unifying framework in which to interpret the diverse features that characterize the reproductively senescent female.

Effects of endogenous opioid peptides and their analogs on the activities of hypothalamic arcuate neurons in brain slices from diestrous and ovariectomized rats

Various endogenous opioid peptides and some of their analogs were used in this study to test their effects on the membrane activities of hypothalamic arcuate neurons in brain slices. Both ovariectomized and diestrous rats were used in the study, and freshly prepared brain slices from these animals were used for extracellular single-unit recording studies. All of the opioids exhibited potent inhibitory effects on the firing of arcuate neurons, viz., beta-endorphin inhibited 55% (n = 33), DAGO 62% (n = 21), dynorphin A 55% (n = 11), U50,488 36% (n = 39), Met-enkephalin 35% (n = 54), and DPDPE 50% (n = 8) of tested arcuate neurons from ovariectomized rats. Significantly higher percentage of inhibition was observed in slice preparations from diestrous rats for DAGO 86% (n = 22), and slightly higher for dynorphin A 59% (n = 22) and U50,488 53% (n = 15). Pretreatment with naloxone prevented most of the actions by beta-endorphin and DAGO, and nor-binaltorphimine prevented those by dynorphin A and U50,488. Most of the effects of Met-enkephalin could also be blocked by nor-binaltorphimine (67%, n = 6), but less by naltrindole (25%, n = 8). Naltrindole, however, seemed to be more effective in blocking the action of [D-Pen2,5]-enkephalin (100%, n = 2). In summary, all opioids tested exerted potent inhibitory effects upon the firing of arcuate neurons possibly through multiple opioid receptors, and the presence of ovarian hormones may have an effect on the neuron's responsiveness to opioid acting on mu type receptors.

Statistical quantification of 24-hour and monthly variabilities of spontaneous otoacoustic emission frequency in humans

Previous evidence has suggested a relationship between spontaneous otoacoustic emissions (SOAEs) and established, biological cycles, although detailed statistical quantifications of the suggested relationships do not exist in the literature. In an attempt to statistically quantify the purported circadian and monthly influences on this phenomenon, two experiments were undertaken. The first experiment was conducted over eight weeks, investigating 31 SOAEs recorded from eight women and two men. Time series statistical analysis examined whether daily, weekly, and/or monthly cycles characterized SOAE frequency variability. Results yielded a significant monthly cycle for the majority of SOAEs recorded from the women but for none of the SOAEs recorded from the men. These results suggest the possibility that SOAE frequency fluctuation in women may be entrained to the monthly menstrual cycle. In the second experiment, hourly SOAE frequency stability was examined over a 24-h period to ascertain the nature of the daily frequency variation as precisely as possible. Four SOAEs from two subjects were examined, and time series analysis of these data included (1) modelling the autocorrelation structure of the measurements, (2) resolving each 24-h series of measurements into cyclical components of various periodicities, and (3) testing the statistical significance of given cycles within the spectrum of each series. Findings included a significant 24-h variability of frequency for each SOAE, suggesting the possibility of a circadian influence on frequency fluctuation. Results from the two experiments provide quantitative evidence supporting a hypothetical relationship between SOAEs and established, biological cycles.

Modulation of hypothalamic mu-opioid receptor density by estrogen: a quantitative autoradiographic study of the female C57BL/6J mouse

The labelling of hypothalamic binding sites by [125I]-FK, a specific mu-opioid receptor ligand, was studied in female C57BL/6J mice to test whether removal of ovarian steroids affected the density of distribution of receptor binding. Labelling densities in the forebrain of normally cycling (intact) females (N = 12), were compared to those in mice that had been ovariectomized (OVX) for 6 weeks (n = 8) and in mice that had been OVX and implanted with an estradiol (E2) capsule (OVX+E2) for 6 weeks (n = 11). Frozen sections from the rostral forebrain were incubated with 1 nM [125I]-FK and processed for light microscopic autoradiography. The diagonal band of Broca (DBB), organum vasculosum lamina terminalis (OVLT), preoptic area (POA), septum, parietal cortex, and striatum were analyzed using computerized image analysis. The distribution of labelling was similar in all three experimental groups in all the regions; however, labelling was significantly reduced in the ventrolateral POA of OVX animals compared to intact females. Labelling densities in the OVX animals replaced with the gonadal steroid estradiol were not significantly different from those in normally cycling mice. This study demonstrates a region-specific loss of mu-opiate receptor labelling following long-term deprivation of gonadal steroids, and supports the hypothesis that estrogen directly or indirectly influences the density of mu-opioid receptors in the rostral forebrain of female mice.

Effect of adrenal and sex hormones on opioid analgesia and opioid receptor regulation

The role of endocrine factors on opioid analgesia (antinociception) and opioid receptors was studied in male and female Swiss-Webster mice. Morphine was more potent in male than in female mice, although this difference appears to be due to greater availability of morphine to the brain in males. Saturation binding studies indicated that the density and affinity of brain mu- and delta-opioid binding sites were equivalent in males and females. Males and females were implanted SC with naltrexone (NTX) or placebo pellets for 8 days, and then the pellets were removed. This treatment increased the density of mu and delta binding sites in brain and increased the potency of morphine for both sexes, although the increase in antinociceptive effects for males was greater than for females. Adrenalectomy (ADX) in male mice increased the potency of morphine and methadone but did not alter the brain levels of either drug. ADX did not alter brain opioid binding of either mu or delta ligands. When male ADX and control mice were treated with NTX, the potency of morphine and brain opioid binding sites were increased equivalently in both groups. Gonadectomy (GDX) in male mice tended to decrease morphine potency, although this was not found to be a very reliable effect. When male GDX and control mice were implanted with NTX, brain opioid binding was increased similarly in both groups, although morphine potency was increased less in GDX mice. Overall, these studies show that sex differences and hormones of the adrenals and gonads in male mice do not alter brain opioid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Influences of gender, gonadectomy 5 and estrous cycle on GABA/BZ receptors and benzodiazepine responses in rats

Benzodiazepines (BZ) and steroid hormone derivatives can potentiate the inhibitory actions of GABA through interactions with the GABAA/BZ/chloride ionophore complex. The present study examines whether the in vivo hormone milieu of rats modulates GABA/BZ receptors and/or benzodiazepine responses. The influences of gender, estrous cycle, and the diminution of steroid levels on GABA/BZ receptors and BZ anticonvulsant responses were tested by comparing these parameters in groups of intact male, intact female, orchidectomized, and ovariectomized rats. The hormonal milieu appears to modulate the GABA recognition site and possibly GABA-related responses in rats. This is evidenced by the decrease in cortical GABAA receptor affinity seen in females compared with other hormone groups and the gender-related difference observed in susceptibility to seizures induced by the GABA antagonist bicuculline. In cycling females, high circulating levels of progesterone were correlated with heightened seizure thresholds, suggesting that progestins serve a protective role in the control of seizure activity. Although a gender-related difference in cortical BZ binding affinity was observed, BZ receptor parameters in several other brain areas and BZ anticonvulsant responses were unaffected by physiological fluctuations in gonadal hormones.

Evidence that long-term estrogen treatment disrupts opioid involvement in the induction of pituitary LH surge

Recent evidence suggests that a decrease in the inhibitory opioid influence is a necessary hypothalamic neural event in the preovulatory and ovarian steroid-induced luteinizing hormone (LH) surge. Whether shifts in ovarian steroidal milieu disrupts this neural event is not known. Therefore, the effects of short-term (3 days) and long-term (13 or 17 days) estradiol 17 beta (E2) exposure on spontaneous, naloxone (NAL) and progesterone (P)-induced LH surges were assessed in ovariectomized (ovx) rats. Two weeks after ovariectomy, rats received subcutaneous Silastic capsules filled with crystalline E2. In rats exposed to E2 for 3 days and infused with saline intravenously between 11.00-14.00 h, plasma LH rose significantly at 17.00 h. NAL infusion between 11.00-14.00 h in these rats to decrease the inhibitory opioid influence, advanced both the onset of LH rise and amplified the secretion of LH in the afternoon. Continuation of E2 exposure for 13 days produced no deleterious effects on either the spontaneous or NAL-induced augmentation in LH responses. However, uninterrupted E2 exposure for 17 days abolished the spontaneous afternoon LH rise and drastically diminished the ability of NAL to advance and amplify the LH response. In the next experiment, we evaluated the effect of P injection (2 mg/rat) at 11.00 h on the afternoon LH release in rats similarly exposed to E2 for either 3 or 17 days. In rats exposed to E2 for 3 days, the P-induced LH release was significantly greater than that observed after saline or NAL infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of estradiol treatment on beta-endorphin content and release in the female rat hypothalamus

The purpose of the present study was to determine whether an injection of estradiol valerate or chronic estradiol treatment alters beta-endorphin-immunoreactive (IR) material in the hypothalamus. Hypothalamic beta-endorphin-IR material was significantly reduced (by 47%) 2 months following an estradiol valerate injection. In addition, both the basal and veratridine-evoked release of beta-endorphin-IR material from hypothalamic slices incubated in vitro were decreased 48% and 52%, respectively. The net release of beta-endorphin-IR material was decreased by 50% compared to control animals. Chronic estradiol treatment (2 months) did not alter the tissue content of beta-endorphin-IR material. Although, we noted a significant decrease (48%) of the basal release and a significant increase (45%) of the evoked release, the net release of beta-endorphin-IR material from slices was not altered (107% of control). The present results suggest that estradiol valerate treatment decreases the capacity of beta-endorphin neurons in the hypothalamus to synthesize and maintain the release of beta-endorphin.

Effects of estradiol and progesterone on the sensitivity to pain and on morphine-induced antinociception in female rats

Long-term ovariectomized (OVX) rats were exposed to 2- or 14-day replacement with pellets made of cholesterol (CHOL), estradiol (E2), progesterone (P4), or a combination of E2 and P4. Following the treatment with steroids the antinociceptive effect of morphine (5 mg/kg,sc) was measured by a hot-plate method. Pellets of E2 (0.5 and 5%) caused dose- and time-dependent reductions of morphine-induced antinociception as compared with OVX rats treated with CHOL pellets. Moreover, OVX rats pretreated with E2 pellets had decreased basic sensitivity to nociceptive stimulus (hyperalgesia). Treatment for 2 and 14 days with 75% P4 pellets produced significant reduction of MOR antinociception. The low dose of P4 (10% pellet) did not change the effect of MOR on Day 2 but significantly increased the antinociceptive effect of MOR on Day 14. Replacement of OVX rats with one 0.5% E2 pellet plus one 10% P4 pellet resulted in marked inhibition of the antinociceptive effect of MOR on Day 2 as well as on Day 14. Central injection 30 min before MOR of either LHRH antagonist or the antiserum against LHRH into OVX rats pretreated for 14 days with both steroids had no effect on the degree of the antinociception. The results suggest that the effects which ovarian steroids exert on opioid systems vary according to the dose, the duration of treatment, and the type of steroid administered.

Induction of Stein-Leventhal-like polycystic ovaries (PCO) in the rat: a new model for cystic ovarian disease

An injection of estradiol valerate (EV) in the rat produces an anovulatory polycystic ovarian (PCO) condition. Chronic estrogen exposure, produced by subcutaneously implanted, estradiol (E2)-containing chronic release capsules, results in acyclicity and in hypothalamic changes similar to those seen in the EV-injected rat. We, therefore, examined the ovarian histology and plasma gonadotropin patterns in the E2-implanted rat and found that this model exhibits a polycystic ovarian condition and a plasma gonadotropin pattern very different from those in the EV-treated model. The plasma patterns of LH and FSH are bimodal consisting of small frequent pulses as well as less frequent large episodes of long duration. The ovaries contain multiple small cysts, characterized by an extensively hypertrophied theca interna, and vast chords of hypertrophied secondary interstitial cells. In contrast, cystic follicles in EV-treated rats are fewer in number, but much larger than those in the E2-implanted animals. The cystic theca and the secondary interstitial cell clusters are also far less extensive in the EV-induced polycystic ovary. These and other differences between the two types of PCO indicate that they are produced by fundamentally different morphogenic mechanisms. The cystic ovary produced by the E2 implants is similar in appearance to that seen in the human Stein-Leventhal condition, and thus provides a new model for the study of cystic ovarian disease.

Neuronal membrane remodelling during the oestrus cycle: a freeze-fracture study in the arcuate nucleus of the rat hypothalamus

Freeze-fracture methodology was used to study the organization of the neuronal plasma membrane in the rat arcuate nucleus, an oestrogen sensitive area of the hypothalamus. The quantitative evaluation of freeze-fracture replicas of the perikarya, dendritic shafts and dendritic spines revealed that the numerical density of intramembranous particles varied during the ovarian cycle. The number of small (less than 10 nm) particles was decreased, and the number of large (greater than 10 nm) particles was increased, in the P-face of the perikaryal plasma membranes in prooestrus and oestrus when compared to dioestrus. This change was associated with a significant increase in the number of exo-endocytotic images in the perikaryal plasma membrane in prooestrus. Changes in intramembranous particles during the ovarian cycle were not detected in arcuate nucleus dendritic shafts and dendritic spines.

Preoptic area opioids and opiate receptors increase during pregnancy and decrease during lactation

Opiate receptor and endogenous opioid content were determined in pregnant, lactating, ovariectomized, and ovariectomized and subsequently estradiol- and progesterone-treated adult female rats. Levels of estradiol and progesterone produced by Silastic capsules implanted in animals of the ovariectomized, hormone-treated group were similar to natural levels of those hormones induced during pregnancy. Quantitative receptor autoradiography and radioimmunoassay were used to determine [3H]naloxone binding density and immunoreactive beta-endorphin content, respectively, in the preoptic area of the hypothalamus. Both opiate receptor binding density and beta-endorphin content in the preoptic area varied in the same direction in all experimental groups. The highest levels of both were observed during pregnancy and the lowest levels during lactation. Ovariectomy without subsequent hormone treatment produced intermediate levels of both opiate receptor and beta-endorphin. Ovariectomy with experimentally-induced estradiol and progesterone levels similar to those of pregnancy produced opiate receptor density and beta-endorphin content similar to those observed in pregnant animals. These data suggest that gonadal steroids are capable of altering function of the endogenous opiate system in the preoptic area. Moreover, preoptic area levels of opioids and opiate receptors are normally elevated during pregnancy and reduced during lactation. Since opiates are known to disrupt ongoing maternal behavior, a reduction of preoptic opiate function during lactation may be required to promote normal maternal behavior. The specific preoptic region involved in opiate regulation of maternal behavior may be illustrated by the zone of opiate receptor alteration observed herein.

Kinetics of drug action in disease states. XXII. Effects of contraceptive steroids on the pharmacodynamics of ethanol in rats

This investigation was designed to determine the effect of treatment with contraceptive steroids on the central nervous system depressant activity of ethanol. Adult female rats received oral doses of ethynyl estradiol (0.1 mg kg-1 day-1), ethynyl estradiol and norethindrone (0.1 and 10 mg kg-1 day-1), or vehicle only for 14 days. Ethanol was then infused slowly iv until the animals lost their righting reflex. The concentrations of ethanol at that time in serum and cerebrospinal fluid were statistically significantly higher in rats treated with the estrogen-progestin combination than in control animals. Ethanol concentrations in rats treated only with the estrogen were intermediate and did not differ significantly from control values. These results indicate that treatment with an estrogen-progestin combination is associated with a decreased sensitivity of the central nervous system to the hypnotic activity of ethanol. This evidence of a pharmacodynamic interaction between contraceptive steroids and ethanol in rats is consistent with a recent clinical report of significant contraceptive steroid-related improvement in tolerance to ethanol with no apparent effect on the pharmacokinetics of ethanol.

Gonadal steroid modulation of brain opioid systems

It is becoming increasingly clear that the effects of the opioids and their synthetic analogs on anterior pituitary function largely depend on the steroid milieu present in the animal at time of drug administration. However, it is still unclear whether gonadal steroids regulate the opioid-modulated mechanisms by affecting the number of opiate receptors in the brain. To further investigate these issues, the effects of opiate agonists and antagonists on LH, FSH and prolactin (Prl) secretion have been studied in: (a) normal and castrated male rats, and (b) normally cycling female rats. The binding characteristics of the brain subclass of mu opiate receptors have been analyzed in the same group of experimental animals; this type of receptors seems to be particularly involved in the control of gonadotropin and Prl release. When injected intraventricularly into normal male rats, morphine (200 micrograms/rat) induced in a significant elevation of serum LH levels at 10 and 20 min. In long-term castrated animals the administration of the drug significantly reduced LH secretion at 40 and 60 min after the injection, the inhibition lasted up to 180 min. Morphine, when given intraventricularly to normal males, induced a conspicuous and significant elevation of serum Prl levels at 10, 20, 40 and 60 min after treatment. However, when the drug was administered to castrated rats, it did not significantly affect Prl release at any time interval considered. Morphine intraventricular injections did not modify serum FSH levels either in normal or in castrated male rats. The concentration of mu opiate receptors was found to be similar when measured in the whole brain of normal and orchidectomized rats. In adult cycling female rats, s.c. injections of naloxone (2.5 mg/kg) stimulated LH release in every phase of the estrous cycle; the magnitude of the responses was highly variable, being particularly elevated at 16.00 h of the day of proestrous and at 10.00, 12.00 and 14.00 h of the day of estrous. Conversely, LH response to naloxone was totally obliterated at 18.00 and 20.00 h of the day of proestrous, when the preovulatory LH surge was found to occur. The concentration of brain opiate receptors of the mu type showed significant variations during the different phases of the estrous cycle, with higher levels at 12.00 h of the day of proestrous and at 18.00 h of the day of estrous.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptic remodelling in arcuate nucleus after injection of estradiol valerate in adult female rats

Adult female rats were injected with a single dose (20 mg/kg) of estradiol valerate (EV). The number of synapses was evaluated in thin sections of arcuate nucleus fixed 3, 8, 16 and 32 weeks after EV treatment and compared with the values obtained in the arcuate nucleus of uninjected proestrus control rats. By 8 weeks after EV treatment a significant (P less than 0.001) decrease was found in the number of axo-somatic and axo-dendritic synapses on dendritic shafts, but not in the number of axo-dendritic synapses on dendritic spines. However, by 32 weeks postinjection, the number of axo-somatic and axo-dendritic synapses had returned to control values. This transient decrease in the number of synapses was preceded by a massive appearance of neuronal degenerative images by 3 weeks after EV injection. These results are interpreted as reflecting a process of circuitry remodelling in the arcuate nucleus after a neuronal lesion induced by estrogen.

The effect of progesterone on kindling: a developmental study

Clinical epileptologists since Gowers have known that hormones may affect central nervous system excitability. Progesterone has been noted to have anticonvulsant properties in both clinical and animal studies. The effect of progesterone on central nervous excitability in the immature animal, however, has not been studied. This study evaluated the effects of progesterone on the rate of kindling in adult and immature animals. While progesterone has no effect on kindling in the adult animal, in the immature animal progesterone markedly inhibited kindling, preventing generalization of seizures. This study demonstrates that progesterone has a marked age-dependent effect on neuronal excitability.