Cell nuclear accumulation of estrogen receptors in rat brain and pituitary gland after treatment with a dopamine-beta-hydroxylase inhibitor

The dopamine β-hydroxylase gene in Chinese goose (Anas cygnoides): cloning, characterization, and expression during the reproductive cycle

BACKGROUND

Dopamine β-hydroxylase (DBH) is a critical enzyme in the biosynthesis of catecholamines. This enzyme's role in neuroendocrine regulation is well known, but there are some indications that it may also modulate reproduction and endocrine in mammals and birds. We selected goose (Anas cygnoides) as an ideal model species for investigating the role of DBH in avian reproduction.

RESULTS

Full-length cDNA encoding DBH was cloned from Zhedong goose using reverse transcription PCR and rapid amplification of cDNA ends. The cDNA consisted of a 126-base pair (bp) 5'-untranslated region (UTR), a 379-bp 3'-UTR, and an 1896-bp open reading frame encoding a polypeptide of 631 amino acids. The deduced amino acid sequence of gDBH shared high homology with an analogue from other birds and contained three conserved domains from a mono-oxygenase family including a DOMON domain and two Cu2_mono-oxygen domains. Real-time quantitative PCR analysis showed that gDBH mRNA was expressed in both reproductive and endocrine tissues of Zhedong goose, specifically in the hypothalamus, pituitary, ovary, and oviduct. More DBH mRNA of reproductive and endocrine tissues was detected at ovulation than at oviposition in Zhedong goose. Evidence of opposite trend of gDBH expression was found between the hypothalamus-pituitary and oviduct during the ovulation phase and the broody phase. In addition, we assessed DBH mRNA expression during ovulation in two breeds of geese that differ in egg production. The reproductive and endocrine tissues of Yangzhou geese with higher egg production had more gDBH expression than Zhedong geese. Finally, the five non-synonymous SNP(c.1739 C > T, c.1760G > T, c.1765A > G, c.1792 T > C and c.1861G > C) were identified in the coding region of DBH gene between Zhedong goose and Yangzhou goose.

CONCLUSIONS

We conclude that goose DBH mRNA show obvious periodically variation in reproductive and endocrine tissues during the reproductive cycle in geese.

Dopamine modulates male sexual behavior in Japanese quail in part via actions on noradrenergic receptors

In rats, dopamine (DA) facilitates male sexual behavior through its combined action on D1- and D2-like receptors, in the medial preoptic area (MPOA) as well as other brain areas. In Japanese quail, systemic injections of dopaminergic drugs suggested a similar pharmacology but central injections have never been performed. Recent electrophysiological experiments demonstrated that DA effects in the MPOA of quail are mediated mainly through the activation of alpha2-noradrenergic receptors. Previous studies of DA action on behavior used specific dopaminergic agonists/antagonists and therefore unintentionally avoided the potential cross-reaction with alpha2-receptors. The present study was thus designed to investigate directly the effects of DA on male sexual behavior and to test whether the interaction of DA with heterologous receptors affects this behavior. Intracerebroventricular (i.c.v.) injection of DA or NE inhibited copulation in a dose-dependent manner. Systemic injections of yohimbine, an alpha2-noradrenergic antagonist, modulated copulation in a bimodal manner depending on the dose injected. Interestingly, a behaviorally ineffective dose of yohimbine markedly reduced the inhibitory effects of DA when injected 15min before. Together, these results show for the first time that i.c.v. injections of DA itself inhibit male sexual behavior in quail and suggest that the interaction of DA with alpha2-receptors has behavioral significance.

Co-regulation of female sexual behavior and pregnancy induction: an exploratory synthesis

This paper will review both new and old data that address the question of whether brain mechanisms involved in reproductive function act in a coordinated way to control female sexual behavior and the induction of pregnancy/pseudopregnancy (P/PSP) by vaginocervical stimulation. Although it is clear that female sexual behavior, including pacing behavior, is important for induction of P/PSP, there has been no concerted effort to examine whether or how common mechanisms may control both functions. Because initiation of P/PSP requires that the female receive vaginocervical stimulation, central mechanisms controlling P/PSP may be modulated by or interactive with those that control female sexual behavior. This paper presents a synthesis of the literature and recent data from our lab for the purpose of examining whether there are interactions between behavioral and neuroendocrine mechanisms which reciprocally influence both reproductive functions.

Minireview: Neuronal steroid hormone receptors: they're not just for hormones anymore

The ovarian steroid hormones have numerous effects on the brain, many of which are mediated, at least in part, by interaction with intracellular steroid hormone receptors acting as regulators of transcription. These intracellular steroid hormone receptors have often been considered to be activated solely by cognate hormone. However, during the past decade, numerous studies have shown that the receptors can be activated by neurotransmitters and intracellular signaling systems, through a process that does not require hormone. Although most of these have been in vitro experiments, others have been in vivo. Evidence from a wide variety of tissues and cells suggests that steroid hormone receptors are transcription factors that can be activated by a wide variety of factors, only one of which is cognate hormone. Furthermore, ligand-independent activation of neural steroid hormone receptors, rather than being a pharmacological or in vitro curiosity, seems to be a process that occurs in the normal physiology of animals. Thinking of steroid hormone receptors only as ligand-activated proteins may constrain our thinking about the many factors that may activate the receptors and cause receptor-dependent changes in neural gene expression and neuroendocrine function.

Effect of 6-hydroxydopamine and 5,7-dihydroxytryptamine on tissue uptake and cell nuclear retention of corticosterone in the rat hypothalamus

Previous studies have shown that norepinephrine and serotonin can modulate the glucocorticoid (GC) binding capacity in the hippocampus. The aim of the present study was to evaluate the role of these neurotransmitters in regulating GC receptors in the hypothalamus. Injection of the neurotoxin 6-hydroxydopamine (6-OHDA) into the ventral noradrenergic bundle (VNAB) and 5,7-dihydroxytryptamine (5,7-DHT) into the raphe nuclei caused a marked depletion in norepinephrine and serotonin, respectively, in the paraventricular nucleus (PVN) and mediobasal hypothalamus (MBH). The injection of these neurotoxins did not change the basal levels of ACTH and corticosterone. Injection of 6-OHDA into the VNAB caused a significant reduction in the cell nuclear binding of corticosterone in the PVN but not in the MBH. Conversely, injection of 5,7-DHT into the raphe nuclei caused a significant reduction in cell nuclear binding of corticosterone in the MBH but did not affect binding in the PVN. These results demonstrate that at least part of the nuclear corticosteroid receptors in the PVN and MBH are differentially regulated by the noradrenergic and serotonergic systems.

Alpha-adrenergic regulation of androgen receptor concentration in the preoptic area of the rat

We examined the effect of the pharmacological disruption of the catecholaminergic system on the concentration of nuclear androgen receptor, as measured by the in vitro binding of methyltrienolone ([3H]R1881) to salt extracts of anterior pituitary (AP), preoptic area (POA) and medial basal hypothalamus (MBH). Treatment of gonadectomized male and female rats with the dopamine-beta-hydroxylase inhibitor, diethyldithiocarbamate (400 mg/kg b. wt.), 30 min before treatment with dihydrotestosterone (1 mg/animal) produced a decrease in the number of nuclear androgen receptor compared with saline-treated controls (P less than 0.05). This effect was specific for the POA and was not present 15 h after DHT treatment. There was no effect on cytosolic androgen receptor nor was there a drug effect on the apparent dissociation constant (Kd) of [3H]R1881 binding to hypothalamus-preoptic area cytosols. Treatment of intact males and castrated, testosterone-treated males with the alpha 1- and alpha 2-adrenergic antagonists, prazosin (5 mg/kg b. wt.) and yohimbine (2 mg/kg b. wt.), respectively, resulted in a significant decrease in the number of nuclear AR 2 h following drug treatment (P less than 0.05). There was no effect of the beta-adrenergic receptor antagonist propranolol (10 mg/kg b. wt.) when given to intact animals, nor was there an effect of idazoxan (5 mg/kg) when given to testosterone-treated animals. The effects of yohimbine and prazosin were restricted to the POA. None of the drugs competed with the binding of [3H]R1881 for the androgen receptor nor did they alter the Kd of cytosol or nuclear androgen receptor. These data provide evidence for an adrenergic interaction with the POA androgen receptor and suggest a role for catecholamines in modulating androgen sensitivity in the rat brain.

Bethanechol-induced increase in hypothalamic estrogen receptor binding in female rats is related to capacity for estrogen-dependent reproductive behavior

Neuroactive agents associated with different neurotransmitter systems can modulate the number of hypothalamic estrogen binding sites. It has been demonstrated previously that the muscarinic cholinergic agonist, bethanechol, administered 30 min prior to in vitro estrogen receptor assays increases the concentration of hypothalamic estrogen binding sites by 30-35% in female rats. Bethanechol was without effect on male hypothalamic preparations. In order to investigate further this sex difference and in an attempt to determine a relationship between the modulation of estrogen binding sites and a sexually differentiated function, bethanechol was given to female rats rendered either anovulatory and capable of displaying lordosis or anovulatory and behaviorally insensitive to estrogen. The results showed that bethanechol significantly increased the number of estrogen binding sites in females capable of displaying lordosis but not in females which did not show this estrogen-dependent behavior. It is possible that the capacity for drug-induced modulation of estrogen binding sites could be related functionally to the ability to display lordosis behavior.

Inhibitory action of alpha-melanocyte stimulating hormone on lordosis in rats: possible involvement of serotonin

Alpha-melanocyte stimulating hormone (MSH) has been found to exert a short- and a long-term inhibitory action on lordosis. The present series of experiments examined the possibility that these effects are mediated by MSH-induced alterations in activity at serotonin type II receptors. In Experiment 1, quipazine (serotonin type II agonist) was found to significantly attenuate the short-term effect of MSH while only partially attenuating the long-term action of MSH. In the second experiment, doses of MSH and of pirenperone (serotonin type II antagonist) that did not inhibit lordotic responding when administered alone were found to inhibit responding when administered together. It was also found that 20 ng MSH produced a long-term, but not a short-term inhibition of receptivity. The results of Experiment 3 indicated that the inhibition observed in Experiment 2 could be reversed by quipazine. These results suggest that alterations in serotonin activity are one mechanism by which the effects of MSH are produced. The relevance of this to the regulation of reproductive states is discussed.

Atropine sulfate modulates estrogen binding by female, but not male, rat hypothalamus

Studies have shown that pharmacological manipulation of the dopamine, norepinephrine and muscarinic cholinergic neurotransmitter systems modulates the number of neural estrogen binding sites. Previously, we reported that the muscarinic agonist, bethanechol, increased estrogen receptor binding by hypothalamic cytosols from female, but not male, rats. Moreover, pretreatment with atropine prevented the bethanechol-induced effect. The experiments reported here were executed with the expectation that atropine alone would either decrease or fail to alter estrogen binding. However, the present data show that atropine increases estrogen binding by female, but not male, hypothalamic cytosols. Thus, it appears that a muscarinic antagonist and agonist can similarly affect the concentration of estrogen binding sites in female rat hypothalamus.

Further evidence of noradrenergic regulation of rat hypothalamic estrogen receptor concentration: possible non-functional increase and functional decrease

The regulation of estrogen receptors by the alpha 2-noradrenergic system was studied. A single injection of the alpha 2-noradrenergic antagonist, yohimbine, caused a biphasic effect on the concentration of cytosol estrogen receptors in the mediobasal hypothalamus and anterior pituitary gland. A short-latency increase was seen at 1.5-3 h, followed by a longer-lasting decrease at 8-16 h. Scatchard analysis revealed that the apparent, short-latency increase is in the concentration of binding sites, not in the affinity of the receptor for [3H]estradiol. The increase in the concentration of cytosol estrogen receptors is not blocked by pretreatment with the alpha 2-noradrenergic agonist, clonidine. In addition, no increase is detected in the concentration of cell nuclear estrogen receptors accumulating in response to a saturating dose of estradiol. Therefore, the apparent increase in the concentration of cytosol estrogen receptors may not represent a functional increase in receptors. The decrease in the concentration of estrogen receptors, which occurs 8-16 h after yohimbine treatment, is also seen after injection of the alpha 2-adrenergic antagonist, idazoxan, and is not due to a change in the in vitro rate of association of the receptors with [3H]estradiol. Furthermore, the decrease seems to be a functional decrease in the concentration of receptors capable of cell nuclear accumulation in response to estradiol injection, as indicated by the results of experiments in which the concentration of cell nuclear estrogen receptors was assayed after estradiol injection. These experiments provide further support for the hypothesis that the alpha-noradrenergic system, and perhaps specifically the alpha 2-subtype, is involved in decreasing the concentration of estrogen receptors in parts of the brain and pituitary gland. This interaction provides a mechanism by which the environment could regulate the sensitivity of certain neurons to estradiol. However, the finding that the initial increase in the concentration of cytosol estrogen receptors after yohimbine treatment is not followed by the predicted increase in cell nuclear estrogen receptors after estradiol injection raises questions about the physiological relevance of the apparent increase under some conditions.

The alpha 1-noradrenergic antagonist prazosin decreases the concentration of estrogen receptors in female rat hypothalamus

A series of experiments was performed to determine the effects of the alpha 1-noradrenergic antagonist, prazosin, on the concentration of estrogen receptors in female rat brain and pituitary gland. Prazosin caused a dose-dependent decrease in the concentration of cytosol estrogen receptors in mediobasal hypothalamus when injected 10 and 16 h prior to assay. The drug was without effect on the concentration of nuclear estrogen receptors in the absence of estradiol, indicating that the decreased concentration of cytosol estrogen receptors is not due to nuclear estrogen receptor accumulation. Scatchard analysis confirmed that prazosin treatment decreases the concentration of cytosol estrogen receptors without influencing the apparent affinity of the receptors for [3H]estradiol. The prazosin-induced decrease in the concentration of cytosol estrogen receptors in the mediobasal hypothalamus was transient with maximal effects occurring between 8 and 12 h after a single injection. Competition analysis confirmed that prazosin is not an effective competitor for binding to the estrogen receptor in vitro. The effects of prazosin on the estrogen receptor system could not be attributed to modulation of the levels of norepinephrine or dopamine. Assay of the levels of norepinephrine and dopamine in hypothalamus and preoptic area after prazosin injection revealed no effects of prazosin on the level of either of these catecholamines. An estradiol injection resulted in the predicted decrease in the concentration of estrogen receptors accumulating in hypothalamic cell nuclei, suggesting that the cytosol estrogen receptors that decrease in concentration are functional receptors. Prazosin treatment did not result in a decrease in the effectiveness of estradiol in the induction of cytosol progestin receptors in the mediobasal hypothalamus, suggesting that the cells are regulated by the alpha 1-noradrenergic system may not be those cells in which progestin receptors are also induced. These experiments provide further evidence that the noradrenergic system modulates the concentration of estrogen receptors, and perhaps sensitivity to estradiol, in some cells within the rat hypothalamus.

Noradrenergic regulation of cytosol estrogen receptors in female rat hypothalamus: possible role of alpha 2-noradrenergic receptors

Because of the previous work demonstrating that the alpha 1-noradrenergic receptor antagonist, prazosin, decreases the concentration of cytosol estrogen receptors in rat mediobasal hypothalamus, a series of experiments was performed to determine the specificity of this effect to the alpha 1-noradrenergic system. Injection of the alpha 2-noradrenergic antagonist, yohimbine, caused a decrease in the concentration of estrogen receptors in mediobasal hypothalamus. In addition, the down-regulation of cytosol estrogen receptors by either the alpha 1-noradrenergic antagonist, prazosin, or the alpha 2-noradrenergic antagonist, yohimbine, could be blocked by pretreatment with the alpha 2-noradrenergic agonist, clonidine. The alpha 1-noradrenergic agonist, phenylephrine, was ineffective in blocking the effects of the alpha 1-noradrenergic antagonist, prazosin. These results add further support to the hypothesis that the alpha-noradrenergic system modulates the concentration of cytosol estrogen receptors in the rat hypothalamus. They suggest that the modulation may occur by way of alpha 2-noradrenergic receptors in addition to, or instead of, alpha 1-noradrenergic receptors.