Mating-activated brainstem catecholaminergic neurons in the female rat

Sex differences in the expression of estrogen receptor alpha within noradrenergic neurons in the sheep brain stem

In female sheep, high levels of estrogen exert a positive feedback action on gonadotropin releasing hormone (GnRH) secretion to stimulate a surge in luteinizing hormone (LH) secretion. Part of this action appears to be via brain stem noradrenergic neurons. By contrast, estrogen action in male sheep has a negative feedback action to inhibit GnRH and LH secretion. To investigate whether part of this sex difference is due to differences in estrogen action in the brain stem, we tested the hypothesis that the distribution of estrogen receptor α (ERα) within noradrenergic neurons in the brain stem differs between rams and ewes. To determine the distribution of ERα, we used double-label fluorescence immunohistochemistry for dopamine β-Hydroxylase, as a marker for noradrenergic and adrenergic cells, and ERα. In the ventrolateral medulla (A1 region), most ERα-immunoreactive (-ir) cells were located in the caudal part of the nucleus. Overall, there were more ERα-ir cells in rams than ewes, but the proportion of double-labeled cells was did not differ between sexes. Much greater numbers of ERα-ir cells were found in the nucleus of the solitary tract (A2 region), but <10% were double labeled and there were no sex differences. The majority of ERα-labeled cells in this nucleus was located in the more rostral areas. ERα-labeled cells were found in several rostral brain stem regions but none of these were double labeled and so were not quantified. Because there was no sex difference in the number of ERα-ir cells in the brain stem that were noradrenergic, the sex difference in the action of estrogen on gonadotropin secretion in sheep is unlikely to involve actions on brain stem noradrenergic cells.

Cervical stimulation activates A1 and locus coeruleus neurons that project to the paraventricular nucleus of the hypothalamus

In female rats, stimulation of the uterine cervix during mating induces two daily surges of prolactin. Inhibition of hypothalamic dopamine release and stimulation of oxytocin neurons in the paraventricular nucleus (PVN) are required for prolactin secretion. We aim to better understand how stimulation of the uterine cervix is translated into two daily prolactin surges. We hypothesize that noradrenergic neurons in the A1, A2, and locus coeruleus (LC) are responsible for conveying the peripheral stimulus to the PVN. In order to determine whether projections from these neurons to the PVN are activated by cervical stimulation (CS), we injected a retrograde tracer, Fluoro-Gold (FG), into the PVN of ovariectomized rats. Fourteen days after injection, animals were submitted to artificial CS or handling and perfused with a fixative solution. Brains were removed and sectioned from the A1, A2, and LC for c-Fos, tyrosine hydroxylase (TH), and FG triple-labeling using immunohistochemistry. CS increased the percentage of TH/FG+ double-labeled neurons expressing c-Fos in the A1 and LC. CS also increased the percentage of TH+ neurons expressing c-Fos within the A1 and A2, independent of their projections to the PVN. Our data reinforce the significant contributions of the A1 and A2 to carry sensory information during mating, and provide evidence of a functional pathway in which CS activates A1 and LC neurons projecting to the PVN, which is potentially involved in the translation of CS into two daily prolactin surges.

Noradrenergic nuclei that receive sensory input during mating and project to the ventromedial hypothalamus play a role in mating-induced pseudopregnancy in the female rat

In female rats, vaginal-cervical stimulation (VCS) received during mating induces bicircadian prolactin surges that are required for the maintenance of pregnancy or pseudopregnancy (PSP). The neural circuits that transmit VCS inputs to the brain have not been fully described, although mating stimulation is known to activate medullary noradrenergic cell groups that project to the forebrain. In response to VCS, these neurones release noradrenaline within the ventrolateral division of the ventromedial hypothalamus (VMHvl) and the posterodorsal medial amygdala (MePD), two forebrain sites that are implicated in the initiation of PSP. Noradrenaline receptor activation within the VMHvl is both necessary and sufficient for PSP induction, suggesting that noradrenaline acting within the VMHvl is particularly important in mediating the effects of VCS towards the establishment of PSP. We therefore investigated whether or not endogenous, VCS-induced noradrenaline release within the VMHvl is involved in PSP induction in the rat. Before the receipt of sufficient mating stimulation to induce PSP, a retrograde neurotoxin, dopamine-β-hydroxylase-saporin (DBH-SAP), was infused bilaterally into the either the VMHvl or the MePD to selectively destroy afferent noradrenergic nuclei in the brainstem. DBH-SAP infusions into the VMHvl lesioned mating-responsive noradrenergic neurones in A1 and A2 medullary nuclei and reduced the incidence of PSP by 50%. Infusions of DBH-SAP into the MePD had no effect on the subsequent induction of PSP. These results suggest that VCS is conveyed to mating-responsive forebrain areas by brainstem noradrenergic neurones, and that the activity of noradrenergic cells projecting to the VMHvl is involved in the induction of PSP.

Changes in oestrogen receptor alpha expression in the nucleus of the solitary tract of the rat over the oestrous cycle and following ovariectomy

Oestrogen is capable of modulating autonomic outflow and baroreflex function via actions on groups of neurones in the brainstem. We investigated the presence of oestrogen receptor (ER) alpha in a part of the nucleus of the solitary tract (NTS) associated with central cardiovascular control, aiming to determine whether ERalpha mRNA and protein expression is correlated with levels of circulating oestrogen during the oestrous cycle. Polymerase chain reaction (PCR) detected ERalpha mRNA in the NTS at each stage of the oestrous cycle, from ovariectomised, sham-operated and male rats. Real-time PCR showed variations in ERalpha mRNA expression during the oestrous cycle, with the highest levels seen in oestrus, and lowest levels in metoestrus (P < 0.05 versus oestrus) and proestrus (P < 0.05 versus oestrus). Expression in males was lower than in dioestrus and oestrus females (P < 0.05). After ovariectomy, ERalpha mRNA levels were decreased compared to sham-operated animals (P < 0.01). Confocal fluorescence immunohistochemistry with stereological analysis showed that numbers of ERalpha immunoreactive cell nuclei per mm(3) of tissue in the caudal NTS were significantly greater in proestrus than in other groups of rats (P < 0.05). There were also differences among the groups in the extent of colocalisation of ERalpha in neurones immunoreactive for tyrosine hydroxylase and nitric oxide synthase. These results imply a complex pattern of region-specific oestrogen signalling in the NTS and suggest that ERalpha expression in this important autonomic nucleus may be related to circulating oestrogen levels. This may have consequences for the regulation of autonomic tone and baroreflex sensitivity when oestrogen levels decline, for example following menopause.

Oestrogen receptors in the central nervous system and evidence for their role in the control of cardiovascular function

Oestrogen is considered beneficial to cardiovascular health through protective effects not only on the heart and vasculature, but also on the autonomic nervous system via actions on oestrogen receptors. A plethora of evidence supports a role for the hormone within the central nervous system in modulating the pathways regulating cardiovascular function. A complex interaction of several brainstem, spinal and forebrain nuclei is required to receive, integrate and co-ordinate inputs that contribute appropriate autonomic reflex responses to changes in blood pressure and other cardiovascular parameters. Central effects of oestrogen and oestrogen receptors have already been demonstrated in many of these areas. In addition to the classical nuclear oestrogen receptors (ERalpha and ERbeta) a recently discovered G-protein coupled receptor, GPR30, has been shown to be a novel mediator of oestrogenic action. Many anatomical and molecular studies have described a considerable overlap in the regional expression of these receptors; however, the receptors do exhibit specific characteristics and subtype specific expression is found in many autonomic brain areas, for example ERbeta appears to predominate in the hypothalamic paraventricular nucleus, whilst ERalpha is important in the nucleus of the solitary tract. This review provides an overview of the available information on the localisation of oestrogen receptor subtypes and their multitude of possible modulatory actions in different groups of neurochemically and functionally defined neurones in autonomic-related areas of the brain.

Neurotoxic effects of DSP-4 on the central noradrenergic system in male zebra finches

When administered systemically, the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) appears to target the noradrenergic innervation originating in the locus coeruleus causing long-term decrements in noradrenergic function. In songbirds, DSP-4-treatment decreased female-directed singing by males and copulation solicitation responses of females to male songs. However, DSP-4 treatment in songbirds did not lower measures of NE function in the brain to the same extent as it does in mammals. The current study had two goals: determining if two DSP-4 treatments 10 days apart would cause significant decrements in noradrenergic function in male zebra finches and determining if, as in other species, the noradrenergic innervation of midbrain and cortical areas would be profoundly affected while hypothalamic areas were spared. Dopamine-beta-hydroxylase immunoreactivity (DBH-ir) was quantified in thirteen brain regions (five vocal control nuclei, one auditory nucleus, two hypothalamic nuclei, and five additional areas that demonstrated high DBH labeling in controls). Within 20 days, DSP-4 treatment profoundly reduced the number of DBH-ir cells in both the locus coeruleus and ventral subcoeruleus. Unlike a previous study, DBH labeling delineated four out of five vocal control nuclei and an auditory nucleus. As expected, DSP-4 treatment significantly decreased DBH labeling in all areas examined in the mesencephalon and telencephalon without significantly affecting DBH-ir in hypothalamic areas. This double treatment regime appears to be much more effective in decreasing noradrenergic function in songbirds than the single treatment typically used.

Adrenal adrenaline- and noradrenaline-containing cells and celiac sympathetic ganglia are differentially controlled by centrally administered corticotropin-releasing factor and arginine-vasopressin in rats

The adrenal glands and sympathetic celiac ganglia are innervated mainly by the greater splanchnic nerves, which contain preganglionic sympathetic nerves that originated from the thoracic spinal cord. The adrenal medulla has two separate populations of chromaffin cells, adrenaline-containing cells (A-cells) and noradrenaline-containing cells (NA-cells), which have been shown to be differentially innervated by separate groups of the preganglionic sympathetic neurons. The present study was designed to characterize the centrally activating mechanisms of the adrenal A-cells, NA-cells and celiac sympathetic ganglia with expression of cFos (a marker for neural excitation), in regard to the brain prostanoids, in anesthetized rats. Intracerebroventricularly (i.c.v.) administered corticotropin-releasing factor (CRF) induced cFos expression in the adrenal A-cells, but not NA-cells, and celiac ganglia. On the other hand, i.c.v. administered arginine-vasopressin (AVP) resulted in cFos induction in both A-cells and NA-cells in the adrenal medulla, but not in the celiac ganglia. Intracerebroventricular pretreatment with indomethacin (an inhibitor of cyclooxygenase) abolished the CRF- and AVP-induced cFos expression in all regions described above. On the other hand, intracerebroventricular pretreatment with furegrelate (an inhibitor of thromboxane A2 synthase) abolished the CRF-induced cFos expression in the adrenal A-cells, but not in the celiac ganglia, and also abolished the AVP-induced cFos expression in both A-cells and NA-cells in the adrenal medulla. These results suggest that centrally administered CRF activates adrenal A-cells and celiac sympathetic ganglia by brain thromboxane A2-mediated and other prostanoid than thromboxane A2 (probably prostaglandin E2)-mediated mechanisms, respectively. On the other hand, centrally administered AVP activates adrenal A-cells and NA-cells by brain thromboxane A2-mediated mechanisms in rats.

Medullary noradrenergic neurons release norepinephrine in the medial amygdala in females in response to mating stimulation sufficient for pseudopregnancy

In the female rat, stimuli from the uterine cervix and vagina are carried to the brain areas involved in the mating-induced pseudopregnancy (PSP) response via the ventral noradrenergic bundle. Noradrenergic neurons projecting through this tract synapse in many forebrain areas including the amygdala, and neurons in the posterodorsal medial amygdala (MePD) are activated following mating. The goal of this experiment was to investigate whether norepinephrine (NE) is released into the MePD after mating using microdialysis and to determine the origin of this release. Ovariectomized estrogen- and progesterone-treated rats were implanted unilaterally with guide cannulae aimed at the MePD. Females were placed with males until they received 15 intromissions (15I), 5 intromissions (5I) or 15 mounts-without-intromission (MO). Dialysate samples collected every 20 min for 2 h before to 3 h after mating were analyzed for NE using HPLC with electrochemical detection. A significant increase in mean NE release in the MePD was seen at 80 min after mating onset in females receiving 15I, and no increase was seen in animals receiving 5I or MO. The time of peak NE release varied in 15I animals from 60 to 160 min after mating. Mean baseline levels of NE did not differ between groups. The retrograde tracer FluoroGold (FG), administered through the probe after cessation of dialysis sampling, was observed within identified noradrenergic cells primarily within the A1 and A2 cell groups. Infusion of anti-dopamine-beta-hydroxylase-saporin (DBH-SAP) into the MePD lesioned noradrenergic neurons located in the A1 and A2 cell groups. Because high levels of NE release occurred in the MePD only after the females received a number of intromissions sufficient to induce PSP, these results suggest that NE release within the MePD may be important for the establishment of PSP.

Prazosin blocks the glutamatergic effects of N-methyl-D-aspartic acid on lordosis behavior and luteinizing hormone secretion in the estrogen-primed female rat

We have observed that intracerebroventricular (icv) injection of selective N-methyl-D-aspartic acid (NMDA)-type glutamatergic receptor antagonists inhibits lordosis in ovariectomized (OVX), estrogen-primed rats receiving progesterone or luteinizing hormone-releasing hormone (LHRH). When NMDA was injected into OVX estrogen-primed rats, it induced a significant increase in lordosis. The interaction between LHRH and glutamate was previously explored by us and another groups. The noradrenergic systems have a functional role in the regulation of LHRH release. The purpose of the present study was to explore the interaction between glutamatergic and noradrenergic transmission. The action of prazosin, an alpha1- and alpha2b-noradrenergic antagonist, was studied here by injecting it icv (1.75 and 3.5 microg/6 microL) prior to NMDA administration (1 microg/2 microL) in OVX estrogen-primed Sprague-Dawley rats (240-270 g). Rats manually restrained were injected over a period of 2 min, and tested 1.5 h later. The enhancing effect induced by NMDA on the lordosis/mount ratio at high doses (67.06 +/- 3.28, N = 28) when compared to saline controls (6 and 2 microL, 16.59 +/- 3.20, N = 27) was abolished by prazosin administration (17.04 +/- 5.52, N = 17, and 9.33 +/- 3.21, N = 20, P < 0.001 for both doses). Plasma LH levels decreased significantly only with the higher dose of prazosin (1.99 +/- 0.24 ng/mL, N = 18, compared to saline-NMDA effect, 5.96 +/- 2.01 ng/mL, N = 13, P < 0.05). Behavioral effects seem to be more sensitive to the alpha-blockade than hormonal effects. These findings strongly suggest that the facilitatory effects of NMDA on both lordosis and LH secretion in this model are mediated by alpha-noradrenergic transmission.

Estrogen receptor-alpha and -beta immunoreactive neurons in the brainstem and spinal cord of male and female mice: relationships to monoaminergic, cholinergic, and spinal projection systems

For many populations of estrogen-sensitive neurons it remains unknown how they are associated with central nervous system circuitries that mediate estrogen-induced modulation of behavioral components. With the use of double-labeling immunohistochemistry and tracing techniques, the relationships of estrogen receptor (ER)-alpha- and ER-beta-immunoreactive (IR) neurons in the mouse brainstem and spinal cord to monoaminergic, cholinergic, and spinal projection systems are explored. Similar distributions of ER-IR neurons were present in females and males, with differences in labeling intensity of ER-alpha immunoreactivity among males and estrogen-, and oil-treated females. Barrington's nucleus, the ventrolateral medulla, and the nucleus of the solitary tract contained spinal-projecting ER-alpha-IR neurons, whereas ER-alpha-IR neurons in the periaqueductal gray, parabrachial nucleus, and catecholaminergic A1 cell group received spinal input. Numerous tyrosine hydroxylase (TH)-IR ER-alpha-IR neurons were present in the ventral periaqueductal gray, nucleus of the solitary tract, A1 cell group, and lumbosacral cord. The dorsal raphe nucleus contained ER-alpha-IR and ER-beta-IR neurons that colocalized with serotonin (5HT), and the reticulotegmental nucleus contained 5HT-IR ER-alpha-IR neurons. Fibers IR for vesicular acetylcholine transporter (VAChT), TH, and 5HT were located among ER-alpha-IR neurons in the dorsal horn and spinal autonomic regions. Robust staining for TH and VAChT, but not 5HT, was present among ER-alpha-IR neurons in the lumbosacral lateral collateral pathway. Possible modulatory actions of estrogen on each of these ER-IR populations are discussed in the context of their specific function, including micturition, sexual behavior, ejaculation, cardiovascular and respiratory control, tactile and nociceptive sensory processing, anti-nociception, endocrine regulation, and feeding.

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.

LHRH release depends on Locus Coeruleus noradrenergic inputs to the medial preoptic area and median eminence

We tested the hypothesis that Locus Coeruleus (LC) inputs to the medial preoptic area (MPOA) and median eminence (ME) are essential for gonadotropin release. Proestrus and ovariectomized (OVX) rats were decapitated at 16:00 h. LC electrolytic lesion was performed at 11:00 h during proestrus and 24h before decapitation in OVX rats. Plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured and MPOA and ME were microdissected for LHRH content measurement. In addition, FOS protein in LC and MPOA were studied in proestrus and OVX rats at 12:00, 15:00, and 17:00 h. On proestrus, LC lesion blocked the LH surge and only decreased plasma FSH; in OVX rats the lesion induced only a slight decrease on plasma LH without affecting FSH secretion. An increased content of LHRH in the MPOA and ME of both groups accompanied the decreases of plasma LH. In proestrus, the number of FOS-immunoreactive (FOS-ir) neurons increased from 12:00 to 17:00 h in the LC and MPOA. In OVX rats, there was an increase at 15:00 h in the LC and a decrease at 17:00 h in both areas. The number of FOS-ir neurons was lower in OVX than in proestrus animals. Thus, LC (1) is responsible, at least in part, for gonadotropin release through the activation of LHRH neurons, (2) is more closely related to the positive than the negative feedback, and (3) seems to show an intrinsic cyclic activity which is amplified by ovarian steroids.

Location, development, control, and function of extraadrenal phenylethanolamine N-methyltransferase

Phenylethanolamine N-methyltransferase (PNMT) methylates norepinephrine (NE) to form epinephrine (E). It is present in a high concentration in the adrenal medula but occurs in many other tissues throughout the body. In the brain stem and retina PNMT is present in specific neurons. Cardiac PNMT develops early in the fetal heart and is found in relatively high levels in the adult left atrium. Intrinsic cardiac adrenergic cells are distributed throughout the adult myocardium and contain all the enzymes necessary for E synthesis. The PNMT gene promoter region contains a glucocorticoid response element; however, the initial development of brain and cardiac fetal PNMT is glucocorticoid independent. Rat fetal heart PNMT peaks at embryonic day 11 and becomes sensitive to glucocorticoid induction by day 12. PNMT-containing cells are concentrated in the atrioventricular canal and interventricular septum during cardiac development, areas important in the development of the cardiac conduction system. In the adult rat, cardiac PNMT is inducible by glucocorticoids and synthesizes E. Glucocorticoids are essential for development of the high levels of PNMT in the adrenal, but are less important outside the adrenal. The PNMT gene contains 3 exons and 2 introns. Adrenal PNMT mRNA exists as a single type, but in the heart PNMT mRNA is present as both an intronless and an intron-containing type. In some cardiac tissues, glucocorticoids decrease levels of intron-containing PNMT mRNA and increase intronless PNMT mRNA and PNMT activity. Studies in adrenalectomized animals suggest that extraadrenal PNMT increases blood pressure, blood glucose, and lymphocyte cytokine production. PNMT may also play a role in the regulation of fetal heart rate prior to development of the adrenal medulla.

Mating-activated nitric oxide-producing neurons in specific brain regions in the female rat

Nitric oxide (NO)-containing neurons have been localized in various parts of the central nervous system including the hypothalamus. NO plays an important role in the regulation of reproductive activities including sexual behavior and pituitary hormone secretion. To test the hypothesis that NO-containing neurons in specific brain areas may respond to the stimulus of mating and participate in integrating the tactile information in the hypothalamus, this study used Fos as a marker of neuronal activity. Proestrous rats receiving intromissions (mated group) from males or mounts-without-intromission (mounted group) were sacrificed along with rats taken directly from their home cage (control group) 90 min after the beginning of mating or mounting. NOergic neurons were labeled by histochemical reaction for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d). The presence of activated NO-producing (double-stained NADPH-d/Fos) neurons was quantitatively assessed in several brain areas before and after mating. The results showed that mating-with-intromissions induced a significant increase in the percentage of NADPH-d/Fos colabeled neurons in the medial preoptic area (mPOA) and the magnocellular component of the paraventricular nucleus (PVNm) compared to mounts-without-intromission or control treatment. Both mating and mounting induced Fos expression in NADPH-d-positive cells in the ventromedial nucleus of hypothalamus (VMN). In contrast, the expression of Fos in the NADPH-d-positive neurons in the supraoptic nucleus (SON) and the parvocellular portion of the paraventricular nucleus (PVNp) was not influenced by either mating or mounting although abundant NO-containing neurons were found in the two brain areas. The second experiment of the study examined whether NOergic neurons in these brain areas are influenced directly by estrogen by determining the number of NADPH-d-positive neurons that contained the estrogen receptor alpha (ERalpha), the classical ER. Double labeled NADPH-d/ERalpha neurons were observed in several brain areas including the mPOA and VMN while few, if any, NADPH-d-positive neurons in the SON, PVNm or PVNp contained ERalpha. The results suggest that the activated NOergic neurons in these brain areas may be involved in processing and integrating the mating stimulus. Further investigation is required to determine the physiological role of the mating-activated NOergic activity in specific mating-induced changes in reproductive neuroendocrinology.

A progestin antagonist blocks vaginocervical stimulation-induced fos expression in neurones containing progestin receptors in the rostral medial preoptic area

Vaginocervical stimulation (VCS) has a variety of effects on the brain, physiology and behaviour. Previous work demonstrated that a progestin antagonist blocked neuronal response to VCS (i.e. Fos expression) in the absence of progesterone in some neurones, and suggested that some of the effects of VCS on the brain are mediated by ligand-independent activation of progestin receptors (PRs). Although it had been reported previously that some of the cells in which VCS induces Fos expression also contain PRs, it had not been determined if a progestin antagonist blocked Fos expression in these particular neurones. The purpose of this experiment was to determine if a progestin antagonist decreases Fos expression specifically in cells that also express PRs in the preoptic area and ventromedial hypothalamus. As has been shown previously, VCS increased Fos-immunoreactive (ir) expression in the particular areas studied. In the rostral medial preoptic area, VCS increased Fos expression in cells that coexpressed PRs, as well as in cells that do not. However, in the caudal medial preoptic area, VCS only increased Fos expression in cells that did not coexpress PRs. Injection of the progestin antagonist, RU 486, decreased Fos expression in the rostral, but not caudal medial preoptic area, and it decreased Fos expression only in cells that coexpressed PR-ir. In contrast to a previous report, in the present study, the progestin antagonist did not inhibit VCS-induced Fos expression in the ventromedial hypothalamic area. The results of this experiment suggest that the progestin antagonist inhibits VCS-induced Fos expression in some neurones by blocking PRs, and they provide further support for the idea that VCS influences neuronal response in some cells by ligand-independent activation of PRs in those cells.