c-fos expression in noradrenergic A2 neurons of the rat during the estrous cycle and after steroid hormone treatments

Kisspeptin Neurons and Estrogen-Estrogen Receptor α Signaling: Unraveling the Mystery of Steroid Feedback System Regulating Mammalian Reproduction

Estrogen produced by ovarian follicles plays a key role in the central mechanisms controlling reproduction via regulation of gonadotropin-releasing hormone (GnRH) release by its negative and positive feedback actions in female mammals. It has been well accepted that estrogen receptor α (ERα) mediates both estrogen feedback actions, but precise targets had remained as a mystery for decades. Ever since the discovery of kisspeptin neurons as afferent ERα-expressing neurons to govern GnRH neurons, the mechanisms mediating estrogen feedback are gradually being unraveled. The present article overviews the role of kisspeptin neurons in the arcuate nucleus (ARC), which are considered to drive pulsatile GnRH/gonadotropin release and folliculogenesis, in mediating the estrogen negative feedback action, and the role of kisspeptin neurons located in the anteroventral periventricular nucleus-periventricular nucleus (AVPV-PeN), which are thought to drive GnRH/luteinizing hormone (LH) surge and consequent ovulation, in mediating the estrogen positive feedback action. This implication has been confirmed by the studies showing that estrogen-bound ERα down- and up-regulates kisspeptin gene (Kiss1) expression in the ARC and AVPV-PeN kisspeptin neurons, respectively. The article also provides the molecular and epigenetic mechanisms regulating Kiss1 expression in kisspeptin neurons by estrogen. Further, afferent ERα-expressing neurons that may regulate kisspeptin release are discussed.

Chronic treatment with estradiol restores depressive-like behaviors in female Wistar rats treated neonatally with clomipramine

Neonatal administration of clomipramine (CMI) induces diverse behavioral and neurochemical alterations in adult male rats that resemble major depression disorder. However, the possible behavioral alterations in adult female rats subjected to neonatal treatment with clomipramine are unknown. Therefore, the aim of this study was to explore the effect of neonatal treatment with CMI on adult female rats in relation to locomotion and behavioral despair during the estrus cycle. Also evaluated was the effect of chronic treatment with E2 on these female CMI rats. We found no effects on spontaneous locomotor activity due to neonatal treatment with CMI, or after 21days of E2 administration. In the FST, neonatal treatment with CMI increased immobility and decreased active swimming and climbing behaviors. Influence of the ovarian cycle was detected only in relation to climbing behavior, as the rats in the MD phase displayed less climbing activity. Chronic E2 administration decreased immobility but increased only swimming in CMI rats. These results suggest that neonatal treatment with CMI induces despair-like behavior in female rats, but that chronic E2 administration generates antidepressant-like behavior by decreasing immobility and increasing swimming, perhaps through interaction with the serotonergic system.

Absence of Female-Typical Pheromone-Induced Hypothalamic Neural Responses and Kisspeptin Neuronal Activity in α-Fetoprotein Knockout Female Mice

Pheromones induce sexually dimorphic neuroendocrine responses, such as LH secretion. However, the neuronal network by which pheromones are converted into signals that will initiate and modulate endocrine changes remains unclear. We asked whether 2 sexually dimorphic populations in the anteroventral periventricular and periventricular nuclei that express kisspeptin and tyrosine hydroxylase (TH) are potential candidates that will transduce the olfactory signal to the neuroendocrine system. Furthermore, we assessed whether this transduction is sensitive to perinatal actions of estradiol by using female mice deficient in α-fetoprotein (AfpKO), which lack the protective actions of Afp against maternal estradiol. Wild-type (WT) and AfpKO male and female mice were exposed to same- versus opposite-sex odors and the expression of Fos (the protein product of the immediate early gene c-Fos) was analyzed along the olfactory projection pathways as well as whether kisspeptin, TH, and GnRH neurons are responsive to opposite-sex odors. Male odors induced a female-typical Fos expression in target forebrain sites of olfactory inputs involved in reproduction in WT, but not in AfpKO females, whereas female odors induced a male-typical Fos expression in males of both genotypes. In WT females, opposite-sex odors induced Fos in kisspeptin and TH neurons, whereas in AfpKO females and WT males, only a lower, but still significant, Fos expression was observed in TH but not in kisspeptin neurons. Finally, opposite-sex odors did not induce any significant Fos expression in GnRH neurons of both sexes or genotypes. Our results strongly suggest a role for fetal estrogen in the sexual differentiation of neural responses to sex-related olfactory cues.

Hindbrain lactate regulates preoptic gonadotropin-releasing hormone (GnRH) neuron GnRH-I protein but not AMPK responses to hypoglycemia in the steroid-primed ovariectomized female rat

Steroid positive-feedback activation of the gonadotropin-releasing hormone (GnRH)-pituitary luteinizing hormone (LH) neuroendocrine axis propagates the pre ovulatory LH surge, a crucial component of female reproduction. Our work shows that this key event is restrained by inhibitory metabolic input from hindbrain A2 noradrenergic neurons. GnRH neurons express the ultra-sensitive energy sensor adenosine 5'-monophosphate-activated protein kinase (AMPK); here, we investigated the hypothesis that GnRH nerve cell AMPK and peptide neurotransmitter responses to insulin-induced hypoglycemia are controlled by hindbrain lack of the oxidizable glycolytic end-product L-lactate. Data show that hypoglycemic inhibition of LH release in steroid-primed ovariectomized female rats was reversed by coincident caudal hindbrain lactate infusion. Western blot analyses of laser-microdissected A2 neurons demonstrate hypoglycemic augmentation [Fos, estrogen receptor-beta (ER-β), phosphoAMPK (pAMPK)] and inhibition (dopamine-beta-hydroxylase, GLUT3, MCT2) of protein expression in these cells, responses that were normalized by insulin plus lactate treatment. Hypoglycemia diminished rostral preoptic GnRH nerve cell GnRH-I protein and pAMPK content; the former, but not the latter response was reversed by lactate. Results implicate caudal hindbrain lactoprivic signaling in hypoglycemia-induced suppression of the LH surge, demonstrating that lactate repletion of that site reverses decrements in A2 catecholamine biosynthetic enzyme and GnRH neuropeptide precursor protein expression. Lack of effect of lactate on hypoglycemic patterns of GnRH AMPK activity suggests that this sensor is uninvolved in metabolic-inhibition of positive-feedback-stimulated hypophysiotropic signaling to pituitary gonadotropes.

Role of dorsal vagal complex A2 noradrenergic neurons in hindbrain glucoprivic inhibition of the luteinizing hormone surge in the steroid-primed ovariectomized female rat: effects of 5-thioglucose on A2 functional biomarker and AMPK activity

Neuro-glucostasis is required for normal expression of the steroid positive-feedback-induced preovulatory pituitary luteinizing hormone (LH) surge, a critical element of female reproduction. Glucoprivic signals from the caudal hindbrain restrain this surge, but the cellular source of this stimulus is unclear. Norepinephrine (NE) exerts well-defined stimulatory effects on the reproductive neuroendocrine axis. Our studies show that medullary A2 noradrenergic neurons are both estrogen- and glucoprivic-sensitive. Here, we investigated the premise that the LH surge is inhibited by A2 cell reactivity to hindbrain glucopenia and diminished preoptic NE neurotransmission. Estradiol- and progesterone-primed ovariectomized (OVX) female rats were injected into the caudal fourth ventricle (CV4) with the glucose anti-metabolite, 5-thioglucose (5TG) or saline (SAL) prior to onset of the LH surge. Pretreatment by intra-CV4 delivery of the selective catecholamine neurotoxin, 6-OHDA, attenuated LH output, but prevented inhibition by 5TG. 5TG modified patterns of steroid feedback-associated Fos staining of A2, but not other medullary catecholamine cell groups. Intra-preoptic administration of the alpha₁-adrenergic receptor agonist, methoxamine, elicited site-specific reversal of hindbrain glucoprivic suppression of gonadotropin-releasing hormone (GnRH) neuron Fos labeling and LH release. Western blotting of laser-microdissected A2 neurons revealed glucoprivic stimulation of Fos, but inhibition of the catecholamine synthetic enzyme, dopamine-β-hydroxylase; 5TG also diminished A2 estrogen receptor (ER)-α and progesterone receptor profiles, but augmented ER-β protein. Intriguingly, A2 AMPK activity was decreased in 5TG-treated rats, despite down-regulation of GLUT3 and no change in MCT2 protein expression. Rostral preoptic GnRH neurons also exhibited decreased AMPK activation simultaneous with apparent reduction of neuropeptide signaling to the pituitary. The present studies demonstrate that hindbrain glucoprivation inhibits the LH surge, in part, by reducing preoptic noradrenergic input, and furthermore implicate A2 neurons as a source of this altered signal. Results also suggest that AMPK sensor deactivation does not supersede the impact of pharmacological inhibition of glucose catabolism on A2 cell function nor afferent signaling of hindbrain glucopenia on GnRH neurons. Further studies are needed to determine if decreased AMPK activation in these cell populations reflect compensatory gain in positive energy balance and/or direct effects of estrogen on AMPK.

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.

Release of norepinephrine in the preoptic area activates anteroventral periventricular nucleus neurons and stimulates the surge of luteinizing hormone

The role of norepinephrine (NE) in regulation of LH is still controversial. We investigated the role played by NE in the positive feedback of estradiol and progesterone. Ovarian-steroid control over NE release in the preoptic area (POA) was determined using microdialysis. Compared with ovariectomized (OVX) rats, estradiol-treated OVX (OVX+E) rats displayed lower release of NE in the morning but increased release coincident with the afternoon surge of LH. OVX rats treated with estradiol and progesterone (OVX+EP) exhibited markedly greater NE release than OVX+E rats, and amplification of the LH surge. The effect of NE on LH secretion was confirmed using reverse microdialysis. The LH surge and c-Fos expression in anteroventral periventricular nucleus neurons were significantly increased in OVX+E rats dialyzed with 100 nm NE in the POA. After Fluoro-Gold injection in the POA, c-Fos expression in Fluoro-Gold/tyrosine hydroxylase-immunoreactive neurons increased during the afternoon in the A2 of both OVX+E and OVX+EP rats, in the locus coeruleus (LC) of OVX+EP rats, but was unchanged in the A1. The selective lesion of LC terminals, by intracerebroventricular N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, reduced the surge of LH in OVX+EP but not in OVX+E rats. Thus, estradiol and progesterone activate A2 and LC neurons, respectively, and this is associated with the increased release of NE in the POA and the magnitude of the LH surge. NE stimulates LH secretion, at least in part, through activation of anteroventral periventricular neurons. These findings contribute to elucidation of the role played by NE during the positive feedback of ovarian steroids.

Chronic estradiol-17β exposure suppresses hypothalamic norepinephrine release and the steroid-induced luteinizing hormone surge: role of nitration of tyrosine hydroxylase

Chronic exposure to estrogens is known to produce a variety of deleterious effects in women including breast and ovarian cancer and anovulation. In female rats, exposure to low levels of estradiol-17β (E2) decreases hypothalamic norepinephrine (NE) to suppress luteinizing hormone (LH) secretion and cause failure of ovulation. We hypothesized that E2 exposure most likely decreases NE release in the medial preoptic area (MPA) of the hypothalamus to produce this effect and that this may be due to E2-induced inflammatory changes in noradrenergic nuclei leading to nitration of an enzyme involved in NE synthesis. To test this, female Sprague Dawley rats were sham implanted or implanted with slow release E2 pellets (20ng/day) for 30, 60 or 90 days (E30, E60 and E90 respectively). At the end of the treatment period, the rats were implanted with a push-pull cannula in the MPA, ovariectomized and steroid primied to induce a LH surge and subjected to push-pull perfusion. Perfusates were analyzed for NE levels using HPLC-EC. Blood samples collected simultaneously were analyzed for LH levels. We measured interleukin-1β (IL-1β) and nitrate levels in brainstem noradrenergic nuclei that innervate the MPA. In control animals, there was a marked increase in NE levels in response to steroid priming at 1600h that was reduced in the E30 group, and completely abolished after 60 and 90 days of E2 exposure. LH profiles were similar to NE release profiles in control and E2-treated animals. We found that IL-1β levels increased in all three (A1, A2 and A6) noradrenergic nuclei with chronic E2 exposure, while nitrate levels increased only in the A6 region. There was an increase in the nitration of the NE synthesizing enzyme in the MPA in this group as well probably contributing to reduced NE synthesis. This could be a possible mechanism by which chronic E2 exposure decreases NE levels in the MPA to suppress the LH surge.

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.

The neuroendocrine physiology of female reproductive aging: An update

The transition into menopause is a complex process that affects fertility and increases the risk for a number of health problems in aging women that include, but are not limited to osteoporosis, heart disease, diabetes mellitus and cognitive dysfunction. Improved nutrition and enhanced access to medical care have increased the average lifespan for women in developed countries, and many will spend more than one-third of their life in a post-menopausal state. Epidemiological studies indicate that a delayed natural menopause confers longevity and decelerates the appearance of much age-related morbidity, suggesting that developing treatments to delay menopause would significantly improve quality of life for women. Although menopause is ultimately defined by ovarian follicular exhaustion, several lines of scientific evidence in humans and animals now suggest that dysregulation of estradiol feedback mechanisms and hypothalamic-pituitary dysfunction contributes to the onset and progression of reproductive senescence, independent of ovarian failure. This article provides a brief update on our current understanding of the role of the hypothalamic-pituitary axis in the onset of and transition into female reproductive senescence.

Estradiol-17beta-responsive A1 and A2 noradrenergic cells of the brain stem project to the bed nucleus of the stria terminalis in the ewe brain: a possible route for regulation of gonadotropin releasing hormone cells

We have studied brain stem cells in the ewe brain that project to the bed nucleus of the stria terminalis (BNST) and determined if these cells are activated by estradiol-17beta. This would predicate an indirect role in the estradiol-17beta regulation of gonadotropin releasing hormone (GnRH) cells, since these receive input from the BNST. Ovariectomized ewes received 50 mug estradiol-17beta benzoate (i.m.) 1 h prior to brain collection, so that activated cells could be identified by Fos immunohistochemistry. Retrograde tracer (FluoroGold; FG), was injected into the three divisions of the BNST and labeled cells were mapped to the A1 and A2 regions and the parabrachial nucleus (PBN) of the brain stem. With FG injection into the dorsal and lateral BNST, all FG-containing cells in the caudal A1 and 45% of those in A2 stained for dopamine-beta-hydroxylase (DBH), indicating noradrenergic type. No FG-labelled cells in the PBN were DBH-positive. In A1 and A2 respectively, 42% and 46% of FG-labelled cells were Fos-positive, with no double-labeling in cells of the PBN. In ewes receiving FG injections into the ventral BNST, estrogen receptor (ER)alpha-immunoreactive nuclei were found in 82% of A1-FG labeled and 38% of A2-FG labeled cells. No FG-labelled cells of the PBN were ERalpha-positive. Anterograde tracing from A1 with microruby injection identified projections to the PBN, BNST and preoptic area (POA). Thus, A1 and A2 noradrenergic neurons project to the BNST in the ewe brain, express ERalpha and are activated by estradiol-17beta. These noradrenergic, estrogen-responsive cells may provide indirect input to GnRH cells, via the BNST.

Monoamines and sexual function in rats bred for increased catatonic reactivity

Body weight, ovary and uterus weight, the nature of estral cycles, and hypothalamus dopamine and noradrenaline levels and plasma testosterone levels were studied in female GC rats, bred for increased catatonic reactivity, at different stages of the estral cycle (estrus, proestrus). The outbred Wistar strain served as controls. On the background of decreased body weight, GC females showed impairments to the morphological cyclical changes in the ovaries and uterus, with a reduction in ovary weight in diestrus (p < 0.01) and a smaller estrogen-dependent increase in uterus weight in estrus as compared with Wistar females. On the background of decreases in dopamine and noradrenaline contents in the hypothalamus, GC rats showed higher levels of these monoamines in estrus and lower levels in diestrus. Plasma testosterone levels in female GC rats were higher in diestrus than in estrus and in Wistar rats.

Ovarian-steroid modulation of locus coeruleus activity in female rats: involvement in luteinising hormone regulation

The noradrenergic nucleus locus coeruleus (LC) has been reported to regulate luteinising hormone (LH) secretion in female rats. Both oestrogen and progestin receptors have been demonstrated in LC neurones, suggesting that these cells are possibly responsive to variations in circulating levels of ovarian steroids. We therefore evaluated changes in the activity of LC neurones during the oestrous cycle and after ovarian-steroid treatment in ovariectomised (OVX) rats, as determined by immunoreactivity to Fos-related antigens (FRA), which comprises all of the known members of the Fos family. Effects of ovarian steroids on the firing rate of LC neurones were also determined in a slice preparation. The number of FRA/tyrosine hydroxylase (TH)-immunoreactive (ir) neurones in the LC increased from 14.00-16.00 h on pro-oestrus, coinciding with the onset of the LH surge and rise in plasma progesterone. FRA immunoreactivity was unaltered during dioestrus. Oestradiol-treated OVX rats (OVX+E) displayed marked reduction in FRA/TH-ir neurones in LC compared to oil-treated OVX rats. Accordingly, oestradiol superfusion significantly reduced the spontaneous firing rate of LC neurones in slices from OVX rats. Compared to OVX+E, oestradiol-treated rats injected with progesterone at 08.00 h (OVX+EP) exhibited higher number of FRA/TH-ir neurones in the LC at 10.00 h and 16.00 h, and great amplification of the LH surge. Bath application of progesterone significantly increased the spontaneous firing rate of OVX+E LC neurones. Our data suggest that ovarian steroids may physiologically modulate the activity of LC neurones in females, with possible implications for LH secretion. Moreover, oestradiol and progesterone appear to exert opposite and complementary effects (i.e. whereas oestradiol inhibits, progesterone, after oestradiol priming, stimulates LC activity).

The role of noradrenaline in the generation of the preovulatory LH surge in the ewe

Increasing plasma estrogen (E) levels during the follicular phase of the estrous cycle trigger the pre-ovulatory surge of gonadotropin-releasing hormone (GnRH)/LH. Noradrenaline (NA)-producing cells of the brain stem are involved in regulating GnRH cells and project to the preoptic area (POA) and bed nucleus of stria terminalis (BnST). Input to GnRH cells may be direct or indirect, via relay neurons in the POA/BnST. To investigate this, we ascertained whether an alpha(1)-adrenergic antagonist would block/delay the LH surge in ovariectomised (OVX), E-treated ewes. E benzoate (EB) (50microg) was injected (i.m.) and Doxazosin (100nmol/h) or vehicle was infused into the third ventricle 2-26h after EB injection. Doxazosin reduced the magnitude of the LH surge, but did not affect timing. To determine if NA is released in the POA/BnST of cyclic ewes, we immunostained dopamine-beta-hydroxylase (DBH) in terminal fields. Reduced numbers of varicosities staining for DBH indicates release of NA. The number of varicosities immunostained for DBH was reduced in the dorsal and lateral BnST during the follicular phase and during the preovulatory LH surge compared to the luteal phase. These data suggest that noradrenergic mechanisms are involved in generation of the GnRH/LH surge via projections to the BnST and relay to GnRH cells. Since Doxasozin reduced the magnitude of the LH surge in the E-treated OVX ewe, and release of NA in cyclic ewes occurred during the follicular phase of the estrous cycle, we speculate that NA is a permissive factor in surge generation. Thus, increased noradrenergic activity is not a trigger mechanism for initiation of the surge.

Estrogen alters c-Fos response to immobilization stress in the brain of ovariectomized rats

Estrogen receptors are widely expressed in the brain, where estrogen modulates central nervous function. In this study, we investigated the effect of estrogen on the emotional stress response in the brain by comparing the CNS patterns of c-Fos expression in response to immobilization stress (IMO) in ovariectomized rats with placebo treatment (OVX + Pla) vs. ovariectomized rats supplemented with 17beta-estradiol (OVX + E2). Increased c-Fos immunoreactive neurons in response to IMO were observed in cerebral cortex, septum, thalamus, hypothalamus, midbrain, pons and medulla oblongata in accordance with previous findings. When OVX + E2/Stress were compared with OVX + Pla/Stress, the numbers of c-Fos immunoreactive cells were significantly lower in the lateral septum, paraventricular hypothalamic nucleus, dorsomedial hypothalamic nucleus, medial amygdaloid nucleus, lateral periaqueductal gray, laterodorsal tegmental nucleus and locus coeruleus, while they were significantly higher in paraventricular thalamic nucleus and nucleus of the solitary tract. These data suggest that neuronal activities in these areas are influenced bidirectionally by systemic estrogen level.

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.

Response of tyrosine hydroxylase and GTP cyclohydrolase I gene expression to estrogen in brain catecholaminergic regions varies with mode of administration

The effect of different dose, mode and duration of estradiol administration was examined in the different brain catecholaminergic areas in ovariectomized (OVX) female rats. We determined changes in mRNA levels of tyrosine hydroxylase (TH), rate-limiting enzyme in catecholamine (CA) biosynthesis of GTP cyclohydrolase I (GTPCH), rate-limiting enzyme in biosynthesis as well as of tetrahydrobiopterin (BH4), and concentration of BH4, which is an essential cofactor for TH, tryptophan hydroxylase and nitric oxide synthase. Short-term administration of estradiol benzoate (EB) by five injections of 15 or 40 microg/kg 12 h apart led to increase in TH and GTPCH mRNA levels in dopaminergic and noradrenergic cell bodies of the ventral tegmental area (VTA), substantia nigra (SN), locus coeruleus (LC) and the nucleus of solitary tract (NTS) depending on dose of administration. Estrogen-elicited alterations in BH4 concentrations were mostly correlated with changes in GTPCH mRNA levels, except in SN. Long-term administration of estradiol by injections (EB: 25 microg/kg, 16 injections 26 h apart; 50 microg/kg, 16 injections 48 h apart) or pellets (0.1 mg 17 beta-estradiol, 14 days) were not very effective in modulating mRNA levels for both genes in most locations except the NTS. Long-term injections of EB elevated GTPCH mRNA levels throughout the NTS and in microvessels. Administration of estradiol by pellets led to decline of TH mRNA in rostral-medial and elevation in caudal parts of the NTS. Thus, estradiol has a complex and differential effect on TH and GTPCH gene expression in a tissue specific manner and depends on the mode of administration.

Interrelationships between Hormones, Behavior, and Affect during Adolescence: Understanding Hormonal, Physical, and Brain Changes Occurring in Association with Pubertal Activation of the Reproductive Axis. Introduction to Part III

This paper summarizes the goals of this section and considers current knowledge about the association between hormonal changes that occur over pubertal development and the changes in behavior and brain function over the adolescent period. It reviews the cascade of neural and hormonal changes that occur with puberty; discusses mechanisms by which these changes can affect higher-order brain processes; reviews the current limited state of knowledge about links between puberty and changes in affect regulation in the adolescent period; identifies hurdles that have made progress in our understanding of these relationships difficult; and suggests areas for future investigation that will allow us to obtain a much more comprehensive understanding of these interrelationships. This overview of the physiological processes occurring at puberty indicates that puberty (1) encompasses changes in a number of neural systems; (2) results in altered secretion of a number of hormones; (3) involves hormones that are secreted in a pulsatile manner so that collection of a single blood sample does not clearly delineate hormone profiles; and (4) shows considerable individual variation in the rate of progression and in hormone secretion during progression. The important role that gonadal steroid hormones play throughout development and adulthood in regulating plastic changes in neuronal structure and function is noted, highlighting the need for further studies to determine the extent to which the dramatic increases in circulating steroid hormones at puberty modulate brain circuits that underlie changes in social behaviors, risk-taking behaviors, and cognitive function at adolescence.

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.

Oestradiol-dependent and -independent modulation of tyrosine hydroxylase mRNA levels in subpopulations of A1 and A2 neurones with oestrogen receptor (ER)alpha and ER beta gene expression

Oestradiol (E2) induces luteinizing hormone-releasing hormone (LHRH) hypersecretion, thereby triggering LH surge release in ovariectomized (OVX) rats. Neural signals responsible for the surge are marked by a morning increase in LHRH gene expression and an afternoon increase in LHRH release. Evidence suggests that subpopulations of noradrenergic neurones may be responsible for one or both of these signals. To further investigate this issue, we examined effects of E2 on the activity of A1 and A2 noradrenergic neurones, as reflected in changes in tyrosine hydroxylase (TH) mRNA expression, on the day of LH surge release. We then used dual-label in situ hybridization to determine whether E2-induced changes occurred primarily in A1 and A2 subdivisions wherein most noradrenergic neurones expressed oestrogen receptor (ER)alpha and/or ER beta mRNA. We found that in all subdivisions, levels of TH mRNA were higher in E2- than oil-treated rats at 12.00 h. These differences resulted from a decline in TH mRNA expression in oil-treated rats, as well as a rise in levels in E2-treated rats between 10.00 h and 12.00 h. During the afternoon, TH mRNA expression in most A1 and A2 subdivisions peaked at 14.00 h when LH surge release began. However, in all but the middle and caudal A2 subdivisons, levels were similar in E2-treated and control rats at this time. This was attributable to a widespread increase in TH mRNA expression between 12.00 h and 14.00 h in OVX rats. There was no evidence that E2 induced changes in TH mRNA expression preferentially in regions wherein most neurones contained ER alpha or ER beta mRNA. Our findings suggest that E2 activation of middle and caudal A2 neurones, in conjunction with the widespread E2-independent activation of noradrenergic neurones in other subdivisions, may play a role in the induction of LH surge release.

Estradiol stimulates gene expression of norepinephrine biosynthetic enzymes in rat locus coeruleus

Gender-specific differences in susceptibility to a number of disorders related to catecholaminergic systems, including depression and hypertension, have been postulated to be mediated, at least in part, by estrogens. In this study, we examined if estrogens may regulate gene expression of norepinephrine biosynthetic enzymes. Administration of five injections of 15 or 40 microg/kg estradiol benzoate to ovariectomized (OVX) female rats elicited a dose-dependent elevation in mRNA levels of tyrosine hydroxylase (TH) in locus coeruleus, to as great as 3-fold over control. Dopamine beta-hydroxylase (DBH) mRNA levels were also similarly increased. To examine the mechanism, PC12 cells were cotransfected with luciferase reporter constructs under control of DBH or TH promoters [pDBH/Luc(-2,236/+21) or pTH/Luc(-272/+27 or -773/+27)] with an expression vector for estradiol receptor alpha. The cells were treated with 17beta-estradiol (E(2)) for 12-36 h. E(2) triggered a several fold increase in luciferase activity under control of the DBH promoter in a dose-dependent fashion. Omission of estrogen receptor alpha or addition of the estrogen receptor antagonist ICI 182,780 prevented the DBH promoter-driven increase in luciferase. When E(2) was given with 0.2 mM CPT-cAMP, reporter activity with pDBH/Luc(-2,236/+21) was increased greater than with either treatment alone. In contrast, addition of E(2) to cells transfected with pTH/Luc(-272/+27) elicited no change in basal luciferase activity nor in the response to 0.2 mM CPT-cAMP. These findings are the first to reveal that estrogen can stimulate DBH gene expression. Differing mechanisms may underlie the regulation of TH and DBH gene expression by estrogens.

Vaginocervical stimulation-induced release of classical neurotransmitters and nitric oxide in the nucleus of the solitary tract varies as a function of the oestrus cycle

The effects of vaginocervical stimulation (VCS) on glutamate (GLU), aspartate (ASP), gamma-aminobutyric acid (GABA), noradrenaline (NA), arginine (ARG) and nitric oxide (NO) (citrulline) release in the nucleus of the solitary tract (nTS) were measured in anaesthetised female rats as a function of the oestrus cycle. During pro-oestrus/oestrus (P/E), but not during met-oestrus/di-oestrus (M/D), VCS significantly increased concentrations of NA, ASP, GLU, NO (citrulline) and GABA, but not ARG. Basal NA concentrations were also increased in P/E. These effects were prevented by bilateral section of either the vagus nerve or pelvic and hypogastric nerves. Vagotomy also significantly decreased basal NO concentrations in M/D and P/E while pelvic and hypogastric nerve section significantly increased GABA concentrations. Our results therefore confirm that the nTS is a relay structure for the visceral afferents sending information from the uterus into the central nervous system. The ability of VCS to trigger classical transmitter release and NO in the female is influenced by the stage of the oestrous cycle and is routed both via the vagus and pelvic/hypogastric nerves.

Mating induces gonadotropin-releasing hormone neuronal activation in anosmic female ferrets

In females of both spontaneously and induced ovulating species, pheromones from male conspecifics can directly stimulate GnRH neuronal activity, thereby inducing pituitary LH secretion and stimulating the onset of estrus. However, whether pheromones contribute to the steroid- or mating-induced preovulatory activation of GnRH neurons is less clear. Previous studies in the ferret, an induced ovulator, raised the possibility that olfactory cues contribute to the ability of genital-somatosensory stimulation to activate GnRH neurons in the mediobasal hypothalamus (MBH). In the present study the percentage of GnRH neurons colabeled with Fos-immunoreactivity (IR), used as a marker for neuronal activation, was investigated in the MBH of mated gonadectomized, estradiol-treated female ferrets in which both nares were occluded. In addition, the percentage of GnRH neurons colabeled with Fos-IR was examined in the MBH of gonadectomized, estradiol-treated female ferrets exposed to male bedding. Bilateral nares occlusion successfully blocked mating or odor-induced increments in Fos-IR in central olfactory regions, including the cortical and medial amygdala. By contrast, the percentage of GnRH neurons expressing Fos-IR did not differ between mated nares- and sham-occluded females. Exposure to male bedding alone failed to induce Fos-IR in MBH GnRH neurons. Thus, the mating-induced preovulatory activation of GnRH neurons in the female ferret's MBH appears to rely solely on genital-somatosensory as opposed to olfactory inputs.

Estradiol induces a phasic Fos response in the hippocampal CA1 and CA3 regions of adult female rats

Previous studies have shown that estradiol induces structural and functional changes in hippocampal CA1 pyramidal cells of the adult female rat. Estradiol increases the density of dendritic spines and axospinous synapses on CA1 pyramidal cells, and increases these cells' sensitivity to NMDA receptor-mediated synaptic input. Curiously, while estradiol effects are observed in CA1 pyramidal cells, the majority of the evidence indicates that these cells lack genomic estradiol receptors. In contrast, genomic estradiol receptors are expressed in at least some hippocampal interneurons in CA1. The goal of the present study was to determine which hippocampal neuronal populations are activated by estradiol, as determined by induction of c-Fos immunoreactivity, as well as the time-course of this activation. We quantified c-Fos expression in each of the major subdivisions of the hippocampus in adult female rats at various time points during the same estradiol treatment regimen known to regulate dendritic spines and synapses on CA1 pyramidal cells. Our results show a phasic estradiol-induced c-Fos response in the pyramidal cell layers of both CA1 and CA3. c-Fos was induced within 2 h of treatment, decreased at 6 and 12 h, and subsequently increased again at 24 h after treatment with estradiol. Double labeling for c-Fos and GAD 65 or GAD 67 suggests that c-Fos is induced primarily in principal cells, though a small proportion of GABAergic cells is also labeled. These estradiol-induced changes in c-Fos expression may reflect phasic neuronal activation and coupling to gene expression, which could be involved in estradiol's effects on excitatory synaptic connectivity in the hippocampus.

Expression of estrogen receptor-alpha and c-Fos in adrenergic neurons of the female rat during the steroid-induced LH surge

Epinephrine is an important neurotransmitter that is synthesized in relatively few neurons of the medullary regions C1-C3. Epinephrine is involved, among others in the control of most neuroendocrine systems, such as corticotropin releasing hormone-, gonadotropin releasing hormone- and oxytocin/vasopressin-containing neurons as part of complex feedback loop systems that often include interactions with the gonadal or adrenal steroid hormones. In order to determine if the interactions between gonadal steroid hormones with the adrenergic neurons are direct or involve steroid-receptive interneurons that in turn innervate the adrenergic neurons, dual immunohistochemistry was applied to identify if estrogen receptor-alpha (ERalpha) protein was expressed by adrenergic, phenylethanolamine-N-methyl transferase (PNMT)-positive neurons and if estradiol can activate these neurons as determined by the transient expression of the transcription factor c-Fos. The results show that an average of 22% of all PNMT neurons in the C1 region, 38% in C2 and 42% in the C3 region express estrogen receptor-alpha protein with the highest numbers of dual labeled neurons in the central levels of the C1-C3 regions. Overall, the percentages of dual labeled PNMT/ERalpha neurons did not change during the steroid-induced LH surge. In contrast, the percentage of c-Fos expressing PNMT neurons changed significantly during the LH surge. Thus, c-Fos immunoreactivity was highest in all three regions at 1200 h with 69% of the PNMT neurons in C1, 60% in C2 and 79% in C3 co-expressing c-Fos. C-Fos expression was lowest before and after the surge with 39% of the PNMT neurons in the C2 region containing c-Fos at 0800 h, 52% c-Fos-positive PNMT neurons in C1 and 54% in area C3. The results show that many adrenergic neurons are direct targets for estradiol and that most PNMT neurons in the brainstem are activated during the initiation of the steroid-induced LH surge which suggests that epinephrine is one of the triggers that stimulates GnRH release during the surge.

c-Fos gene expression pattern in the hypothalamus and the preoptic area of defeminized rats

The object of the present study was to determine the c-fos gene expression pattern in the hypothalamus (HYP) and the preoptic area (POA) after estradiol and testosterone priming during the critical period of sexual differentiation of the rat brain. Three-day-old female rats were injected s.c. with a single dose of 17beta-estradiol (200 microg), testosterone enantate (200 microg) or vehicle (corn oil). HYP and POA were dissected 2 h, 24 h and 14 days after treatments and on the day of vaginal opening (VO). Other animals, previously treated as above, were acutely injected with 17beta-estradiol (5 microg) on the day of VO; HYP and POA were obtained 3 h later. Total RNA was extracted and processed for semiquantitative RT-PCR. We observed that c-fos gene expression was markedly increased in POA of the animals treated with estradiol or testosterone 2 h after treatments, while a non-significant increase in c-fos gene expression was observed in the HYP of these animals. We found a significant increase in c-fos expression in HYP and POA on the day of VO in both estradiol and testosterone defeminized rats. Interestingly, the acute estradiol administration on the day of VO did not induce c-fos gene expression in either HYP or POA of defeminized animals, instead a diminution in its expression was observed in animals treated with testosterone in POA. The overall results suggest that estradiol and testosterone imprinting during critical postnatal period of sexual differentiation of the brain permanently modifies the regulation of c-fos gene expression.

Molecular activation of noradrenergic neurons in the rabbit brainstem after coitus

Our previous studies indicate that coitus in female rabbits induces a gonadotropin-releasing hormone (GnRH) surge that is preceded by an increase in hypothalamic norepinephrine (NE) release. The additional findings of an enhanced tyrosine hydroxylase (TH) mRNA expression in the female brainstem after coitus, in addition to the appropriate topographic distribution of TH and dopamine-beta-hydroxylase (DBH), lead us to hypothesize that coital signals are relayed to hypothalamic GnRH-secreting neurons via brainstem NE-containing perikarya. Here we analyzed coitally activated areas in the brainstem by in situ hybridization of the oncogene c-fos, as well as the expression of TH mRNA at 0, 30 and 60 min postcoitus using specific 35S-labeled probes for c-fos and TH. To establish the identity of activated brainstem neurons, we immunocytochemically double-labeled cells with specific antibodies against Fos protein and DBH at 90 min postcoitus. Both c-fos and TH mRNAs were present at 0 min (control) in the A1, A2 and A6 brainstem-noradrenergic areas. At 30 min after coitus the expression of both genes significantly increased (P<0.01) in the A1 and A2 areas. By 60 min postcoitus the expression of c-fos mRNA decreased to control levels, while that of TH mRNA remained stimulated. Double-labeling of Fos and DBH indicated that the number of dual-labeled neurons increased (P<0.05) over control levels only in the A1 and A2 areas (not in A6) at 90 min postcoitus. These findings support the hypothesis that coitus activates transcriptional/translational events within brainstem NE neurons that culminate in the release of hypothalamic NE and hence a GnRH surge.

Kainate receptor subunit-positive gonadotropin-releasing hormone neurons express c-Fos during the steroid-induced luteinizing hormone surge in the female rat

During the preovulatory and estradiol-progesterone-induced GnRH-LH surge, a subpopulation of GnRH neurons transiently expresses the transcription factor c-fos, which is a useful marker of cell activation. To further characterize this subpopulation of GnRH neurons, multiple immunohistochemical procedures were applied to visualize GnRH, c-Fos, KA2, GluR5, GluR6, and GluR7 receptor subunits during different phases of the estrogen-progesterone-induced LH surge. The results show that the LH surge begins at 1400 h and peaks at 1600 h before returning to baseline late in the evening. At 1400 h, about 50% of the GnRH neurons contained c-Fos, and this percentage remained high at 65% at 1600 and 2000 h. During the surge, 50% of the c-Fos-positive GnRH neurons contained KA2 receptor subunit protein at 1400 h, 65% of the c-Fos-positive GnRH neurons expressed the KA2 subunit at 1600 h, and 50% of the c-Fos-positive GnRH neurons expressed the KA2 subunit at 2000 h. As KA2 subunits require other kainate-preferring subunits to form functional receptor channels, we examined GnRH neurons for the presence of GluR5, GluR6, and GluR7 messenger RNA (mRNA) and protein. The results show that the KA2-containing GnRH neurons also contain GluR5 receptor subunit mRNA and protein, and that these GnRH neurons are c-Fos positive during the steroid-induced LH surge. To determine whether administration of kainate is sufficient to induce c-Fos in GnRH neurons, steroid-primed animals received iv injections of subseizure-inducing amounts of kainic acid and were processed for immunohistochemistry and in situ hybridization. The results show that kainic acid causes a significant increase in circulating LH; however, it does not induce c-Fos in GnRH neurons, nor does it cause an increase in GnRH mRNA. Together, the results suggest that a large subset of GnRH neurons expresses KA2 as well as GluR5 receptor subunits, which would allow the formation of functional glutamate receptor channels, and that this subset of GnRH neurons is activated during the steroid-induced LH surge.

Oestrogen receptors in the brainstem of the female sheep: relationship to noradrenergic cells and cells projecting to the medial preoptic area

Oestrogen regulates the secretion of gonadotropin releasing hormone (GnRH) and this could be mediated by noradrenergic systems originating in the brainstem. Whilst it is known that noradrenergic cells possess oestrogen receptors (ER), it is not known whether ER-immunoreactive (-ir) cells in the brainstem project to the regions of the hypothalamus in which GnRH neurons are found. We have used dual-label immunocytochemistry to determine the extent to which ER-alpha is found in noradrenergic cells in the brainstem of the ovariectomized (OVX) ewe. Noradrenergic/adrenergic cells were identified by immunostaining for dopamine beta-hydroxylase (DBH). Cells that stained for both DBH and ER were found in both the A1 and A2 cell groups, with the highest levels found in the most caudal regions. In the A1 group, at the most caudal extent, 73% of ER-ir cells were DBH-positive and 19% of DBH-ir cells were ER-positive. The degree of co-localization decreased in a linear manner towards the rostral brainstem. In the caudal half of A2, 9-14% of ER-ir cells were DBH-positive and 20-25% of DBH cells were ER-positive. Less than 2% of DBH-ir cells in the A5 group were dual-labelled and none of the cells in the A6 and A7 groups were ER-positive. The retrograde tracer FluoroGold was injected into the preoptic area of nine OVX ewes and labelled cells were examined in the brainstem to determine the extent of co-localization of ER. Only injections in the rostroventral part of the medial preoptic area near to the organum vasculosum of the lamina terminalis resulted in the labelling of cells in the brainstem. One ewe with very strong labelling of the brainstem was selected for detailed mapping. In the ventrolateral medulla, half the ER-ir cells in the most caudal regions were retrogradely labelled. Almost all the ER-ir cells in the mid-region of the ventrolateral medulla were retrogradely labelled but no co-localization of retrograde tracer and ER was observed rostral to obex. There were many ER-ir cells and retrogradely-labelled cells in the nucleus of the solitary tract but only a few double-labelled cells. Similarly, numerous ER-ir cells and retrogradely labelled cells were observed around the lateral edges of the caudal fourth ventricle and across to the lateral parabrachial nucleus but there were few double-labelled cells. These results suggest differential regulation of noradrenergic cells by oestrogen, with a direct action of the hormone confined to the cells in the most caudal region of the A1 and A2 cell groups. The cells of the caudal ventrolateral medulla which contain ER-ir cells that project to the preoptic area may be important in the mediation by noradrenaline of the actions of oestrogen on GnRH secretion in the ewe.

Neonatal handling induces anovulatory estrous cycles in rats

Since previous work has shown that stimulation early in life decreases sexual receptiveness as measured by the female lordosis quotient, we suggested that neonatal handling could affect the function of the hypothalamus-pituitary-gonadal axis. The effects of neonatal handling on the estrous cycle and ovulation were analyzed in adult rats. Two groups of animals were studied: intact (no manipulation, N = 10) and handled (N = 11). Pups were either handled daily for 1 min during the first 10 days of life or left undisturbed. At the age of 90 days, a vaginal smear was collected daily at 9:00 a.m. and analyzed for 29 days; at 9:00 a.m. on the day of estrus, animals were anesthetized with thiopental (40 mg/kg, ip), the ovaries were removed and the oviduct was dissected and squashed between 2 glass slides. The number of oocytes of both oviductal ampullae was counted under the microscope. The average numbers for each phase of the cycle (diestrus I, diestrus II, proestrus and estrus) during the period analyzed were compared between the two groups. There were no significant differences between intact and handled females during any of the phases. However, the number of handled females that showed anovulatory cycles (8 out of 11) was significantly higher than in the intact group (none out of 10). Neonatal stimulation may affect not only the hypothalamus-pituitary-adrenal axis, as previously demonstrated, but also the hypothalamus-pituitary-gonadal axis in female rats.

Identification and characterization of estrogen receptor alpha-containing neurons projecting to the vicinity of the gonadotropin-releasing hormone perikarya in the rostral preoptic area of the rat

Gonadal steroids exert a powerful regulatory influence upon the functioning of gonadotropin-releasing hormone (GnRH) neurons despite the apparent absence of gonadal steroid receptors in these cells. By using retrograde-tracing techniques combined with dual-labeling immunocytochemistry, we show here that distinct populations of estrogen receptor alpha (ERalpha)-containing neurons located in the hypothalamus and caudal brainstem project to the vicinity of the GnRH perikarya located in the rostral preoptic area (rPOA). The strongest estrogen-receptive afferent projection to this area originated from neurons located in the anteroventral periventricular and medial preoptic nuclei of the preoptic area. Approximately 50% of arcuate nucleus neurons projecting to the rPOA were demonstrated to synthesize either neuropeptide Y or beta-endorphin, but little evidence was found for ERalpha immunoreactivity in either of these specific subpopulations. Over 80% of all tyrosine hydroxylase-expressing neurons in the arcuate nucleus expressed ERalpha, but none projected to the rPOA. In the caudal brainstem, the A1 and A2 norepinephrine neurons comprised nearly all of the retrogradely labeled neurons. However, only the A2 afferents expressed ERalpha immunoreactivity, whereas the A1 afferents coexpressed neuropeptide Y. These observations, combined with the anterograde labeling data of others, provide neuroanatomical evidence for the existence of specific estrogen-receptive neuronal cell populations that project to the rPOA and may be involved in the estrogen-dependent transsynaptic regulation of GnRH neurons in the rat.

Effects of 17beta-estradiol on the baroreflex control of sympathetic activity in conscious ovariectomized rats

The effects of chronic treatment with 17beta-estradiol on baroreflex control of sympathetic activity were examined in conscious unrestrained ovariectomized rats. Baroreflex function was evaluated by logistic sigmoidal analysis of the relationships between changes in mean arterial pressure (MABP) and changes in heart rate (HR) and splanchnic nerve activity (SNA) when MABP was rapidly increased to 150 mmHg by intravenous phenylephrine after its reduction to 50 mmHg by intravenous nitroprusside. These baroreflex function curves were similar in vehicle- and estradiol-treated rats. However, after a 30-min infusion of vasopressin in vehicle-treated rats, the curve for HR was shifted downward, and the upper plateau and maximum gain for the SNA curve were reduced. These effects were abolished by estradiol. A 30-min phenylephrine infusion had no effect on the baroreflex curves. Thus estrogen can modulate the action of vasopressin on baroreflex control of sympathetic outflow and thereby participate in cardiovascular regulation.

Fluctuating estrogen and progesterone receptor expression in brainstem norepinephrine neurons through the rat estrous cycle

Norepinephrine (NE) neurons within the nucleus tractus solitarii (NTS; A2 neurons) and ventrolateral medulla (A1 neurons) represent gonadal steroid-dependent components of several neural networks regulating reproduction. Previous studies have shown that both A1 and A2 neurons express estrogen receptors (ERs). Using double labeling immunocytochemistry we report here that substantial numbers of NE neurons located within the NTS express progesterone receptor (PR) immunoreactivity, whereas few PRs are found in ventrolateral medulla. The evaluation of ERa and PR immunoreactivity in NE neurons through the estrous cycle revealed a fluctuating pattern of expression for both receptors within the NTS. The percentage of A2 neurons expressing PR immunoreactivity was low on metestrus and diestrus (3-7%), but increased significantly to approximately 24% on proestrous morning and remained at intermediate levels until estrus. The pattern of ERalpha immunoreactivity in A2 neurons was more variable, but a similar increment from 11% to 40% of NE neurons expressing ERa was found from diestrus to proestrus. Experiments in ovariectomized, estrogen-treated and estrogen-plus progesterone-treated rats revealed that PR immunoreactivity in A2 neurons was induced strongly by estrogen treatment, whereas progesterone had no significant effect. The numbers of ERalpha-positive NE neurons were not influenced by steroid treatment. These observations provide direct evidence for PRs in NE neurons of the brainstem and show that cyclical patterns of gonadal steroid receptor expression exist in A2, but not A1, neurons through the rat estrous cycle. The expression of PR in A2 neurons appears to be driven principally by circulating estrogen concentrations. The fluctuating levels of ERalpha and PR expression in these brainstem NE neurons may help generate cyclical patterns of biosynthetic and electrical activity within reproductive neural networks.

Identification of alpha1B adrenergic receptor protein in gonadotropin releasing hormone neurones of the female rat

Noradrenaline is an important neurotransmitter which regulates GnRH release from the median eminence in the female rat during both basal GnRH secretion and the preovulatory or steroid hormone-induced GnRH-mediated LH surge. However, it is not clear at which sites in the brain this predominantly stimulatory influence is exerted nor is it known which adrenergic receptor subtype(s) mediate(s) the effects of noradrenaline. In order to determine if the GnRH neurones in the septum-diagonal band-preoptic area and/or their axon terminals in the median eminence are direct targets for noradrenaline, immunohistochemical triple-labelling studies were conducted to localize simultaneously GnRH peptide, dopamine-beta-hydroxylase and alpha1B adrenergic receptor protein. The results show that about 80% of all GnRH neurones examined contained patches of immunoreactive alpha1B adrenergic receptor protein at or near the plasma membrane and that some of these alpha1B adrenergic receptors were adjacent to dopamine-beta-hydroxylase containing axons. The GnRH neurones which did not contain alpha1B adrenergic receptors were preferentially located in the rostral portion of the septum and diagonal band while all GnRH neurones in the caudal septum, diagonal band and in the preoptic area expressed alpha1B adrenergic receptors. In the median eminence, a few alpha1B adrenergic receptor patches were seen in the external layer and these receptors were only rarely observed to be associated with GnRH containing axon terminals. The results suggest that the effects of noradrenaline on GnRH release are, at least in part, mediated by the activation of alpha1B adrenergic receptors which are located on most GnRH perikarya while the median eminence is not a likely site at which GnRH release is regulated by alpha1B adrenergic receptors.

CNS location of uterine-related neurons revealed by trans-synaptic tracing with pseudorabies virus and their relation to estrogen receptor-immunoreactive neurons

Retrograde, transneuronal tracing with Bartha's strain of pseudorabies virus was used in rats to identify spinal cord, brainstem and hypothalamic loci of uterine-related neurons that could function in the regulation of uterine activity. Based on the premise that estrogen might influence such uterine-related neurons, the existence of estrogen receptors in neurons in these same loci was examined. Viral injections were made into the uterine cervix, body and cervical end of the uterine horns, and the rats allowed to survive for four to six days. After four days, mainly the spinal cord, medulla and pons contained virus-infected neurons. After longer survival times, progressively higher levels of the neuraxis contained viral-labeled neurons, so that by six days hypothalamic uterine-related neurons were identified. First-order virus-infected neurons were visualized by immunohistochemistry in the pelvic paracervical parasympathetic ganglia and in inferior mesenteric sympathetic ganglia. Preganglionic and putative interneurons were labeled in the lumbosacral spinal cord and thoracic spinal cord mainly in the lateral horn area (sacral parasympathetic nucleus and intermediolateral nucleus), lateral aspect of the dorsal horn, intermediate gray, lamina X and dorsal gray commissural area. In the brainstem, labeling was most evident and consistent in the nucleus tractus solitarius, ventrolateral medulla, raphe magnus and pallidus nuclei, parapyramidal area, A5 cell group, Barrington's nucleus of the pons and periaqueductal gray of the midbrain. In the hypothalamus, virus-infected neurons were most marked in the paraventricular nucleus, with fewer in the medial preoptic area and ventromedial hypothalamic nucleus. Estrogen receptor-immunoreactive neurons were most often present among the virus-labeled uterine-related neurons of the spinal cord, nucleus tractus solitarius, ventrolateral medulla, periaqueductal gray, medial preoptic area and ventromedial hypothalamic nucleus. These results identify a multisynaptic pathway of neurons whose eventual output is involved in uterine functions, whose distribution is similar to that revealed by pseudorabies virus tracing from other visceral organs, and which are often mixed among estrogen-responsive neurons.

Estrogen receptor expression in brainstem noradrenergic neurons of the sheep

Noradrenergic neurons are implicated in the estrogen-dependent neural regulation of luteinizing hormone secretion in a variety of mammalian species. The current study has used immunocytochemical methods to determine whether estrogen receptors (ER) are expressed within the brainstem of the ewe and to establish their relationship to noradrenergic neurons. Using a monoclonal mouse antiserum directed against the N-terminal of ERa, four distinct populations of ER alpha-immunoreactive cells were identified in ovine medulla and pons. The largest population was found in the superficial laminae of the spinal nucleus of the trigeminal nerve, followed by the nucleus tractus solitarius, lateral area postrema, and ventrolateral medulla. Double-labelling immunocytochemistry using antisera directed against the ER alpha and dopamine-beta-hydroxylase revealed that noradrenergic neurons expressing ER immunoreactivity were only found in ventrolateral medulla (A1 cell group) and nucleus tractus solitarius (A2 cell group). No double-labelled cells were identified in the A5, A6, or A7 noradrenergic cell groups. ERs were expressed with a clear rostrocaudal topography within the A1 and A2 populations, with 80-90% of noradrenergic neurons expressing ERA alpha in the caudalmost medulla as compared with less than 5% rostral to the obex. Our findings demonstrate that, as in the rat, the ovine A1 and A2 neurons express ERs in a defined topographical manner, while, dissimilar to the rat, ER alpha is not synthesized by noradrenergic neurons in the other cell groups. These observations indicate that A1 and A2 noradrenergic neurons in the ovine brainstem are likely to be influenced by circulating estrogens and lay the neuroanatomical foundations for investigating the functional role of these cell populations within the gonadotropin-releasing hormone neuron network of the sheep.

Sex hormones enhance the impact of male sensory cues on both primary and association cortical components of visual and olfactory processing pathways as well as in limbic and hypothalamic regions in female sheep

Differential activation of neural substrates was investigated in female sheep exposed to a male when they were in oestrus, and sexually receptive and attracted to males, as opposed to anoestrus when they were not. Changes in neuronal activation were visualized in ovariectomized, hormone-treated ewes by quantifying changes in cellular expression of c-fos messenger RNA by in situ hybridization histochemistry. Results showed that, while oestrus induction had no significant effects on c-fos expression per se, a 5-min exposure to a male significantly increased it in a number of primary and association cortical regions (the mitral and granule cell layers of the olfactory bulb, visual, somatosensory, orbitofrontal, piriform, cingulate and temporal cortices), the limbic system (CA1 region of the hippocampus, subiculum, lateral septum, lateral and basolateral amygdala, bed nucleus of the stria terminalis) and hypothalamus (mediobasal hypothalamus, medial preoptic area and paraventricular nucleus) as well as the nucleus accumbens and mediodorsal thalamus. Intromissions did not contribute significantly to these c-fos changes however. In anoestrus females, exposure to a male only produced a small significant increase in c-fos messenger RNA expression in the temporal cortex inspite of receiving similar amounts of visual and olfactory cues from him and a number of mating attempts. These results clearly demonstrate that changes in sexual motivation markedly alter the neural processing of sensory cues from males. They also show that the hormonal induction of sexual attraction to males cues and the resultant stimulation of sexual behaviour is due not only to altered responsiveness of oestrogen-sensitive brain regions involved in mediating behavioural responses towards the male, but also to changes in primary and secondary/tertiary somatosensory, olfactory and visual processing regions which relay sensory information to them.

Effects of estrogen on basal forebrain cholinergic neurons vary as a function of dose and duration of treatment

Studies suggest that estrogen replacement can influence learning and memory processes via effects on cholinergic neurons located in specific regions of the basal forebrain. In the present study, immunocytochemical techniques were used to examine the effects of estrogen on basal forebrain cholinergic neurons as a function of the dose and duration of estrogen treatment. Ovariectomized rats received 2, 10, 25, or 100 microg estradiol every other day for a period of 1, 2, or 4 weeks. Sections through the basal forebrain were then processed for the detection of choline acetyltransferase (ChAT) or the low-affinity nerve growth factor receptor (p75NGFR), and the number of immunoreactive cells in the medial septum (MS), the horizontal limb of the diagonal band of Broca (HDB) and the nucleus basalis magnocellularis (NBM) were counted. The effects of dose and duration of estrogen treatment were evaluated by analysis of variance and individual group means were compared with ovariectomized controls using a two-tailed Dunnets test. Administration of 2, 10, or 25 microg estradiol for 1 week produced a dose-related increase in the number of ChAT-like immunoreactive (IR) cells detected in the MS. Likewise treatment with 10 microg estradiol for 1 week, or with 2 microg estradiol for 2 weeks resulted in a significant increase in the number of ChAT-IR cells detected in the NBM. These effects were not observed following treatment with higher doses of estradiol. Nor were they maintained following repeated administration of estradiol for longer periods of time. In contrast, repeated administration of estradiol for 2 or 4 weeks resulted in significant decreases in the number of p75NGFR-IR cells detected in the MS, with the greatest effects observed following treatment with the higher doses of estradiol for longer periods of time. These findings demonstrate that (1) estrogen replacement produces regionally selective effects on basal forebrain cholinergic neurons which vary as a function of both the dose and duration of estrogen treatment, and (2) estrogen has both short-term and longer-term effects on basal forebrain cholinergic neurons, each of which may contribute to the effects of estrogen on learning and memory process and the development of age- and disease-related cognitive decline.

Luteinizing hormone pulsatility is altered in essential hypertension

The aim of this investigation was to study the pattern of luteinizing hormone (LH) secretion in men with mild and moderate hypertension. LH pulsatility was evaluated for 8 h in 14 male patients, subdivided into 2 groups; group A, consisting of 8 patients, whose systolic blood pressure ranged between 180 and 160 mm Hg and whose diastolic blood pressure was between 115 and 105 mm Hg; and group B, 6 patients whose systolic blood pressure ranged between 220 and 180 mm Hg and whose diastolic blood pressure was between 104 and 95 mm Hg. Seven healthy males were evaluated as controls (group C). The major changes of LH pulsatility in group A included an increased peak width, increased peak amplitude, and increased peak area. In group B the changes followed the same pattern as in group A, but were more pronounced. The number of LH peaks was reduced, the peak width was increased, and both peak amplitude and peak area were increased as compared to the control group. The pattern of LH pulsatility is altered in essential hypertension and the main feature is represented by the prolonged duration of LH peaks and their greater amplitude. The altered pattern of LH secretion is likely to reflect a primary hypothalamic derangement with the gonadotropin releasing hormone (Gn-RH) secreting neurons remaining synchronized for longer times and secreting larger Gn-RH masses than in normal subjects. Since the nuclei of the brain stem (A1-A6) involved in the control of Gn-RH secretion respond to blood pressure changes, the altered activity of monoaminergic neurons may be the link between hypertension and changes of LH pulsatility.

Differential expression of estrogen receptor and neuropeptide Y by brainstem A1 and A2 noradrenaline neurons

The release of noradrenaline and neuropeptide Y appears to be regulated by estrogen in a co-ordinated fashion within specific brain regions. The present study has used double and triple-labelling immunocytochemical procedures to determine the patterns of nuclear estrogen receptor and neuropeptide Y expression by brainstem A1 and A2 noradrenergic neurons in the female rat. Estrogen receptor-immunoreactive cells were detected within the ventrolateral medulla, nucleus tractus solitarius, area postrema and, in the very caudal medulla, the reticular nuclei and spinal nucleus of the trigeminal nerve. Cells double labelled for the estrogen receptor and dopamine-beta-hydroxylase were identified in largest numbers (up to seven double-labelled cells per 30-microm-thick coronal section) in the caudal-most medulla, where approximately 30% of A1 and 60% of A2 neurons were immunoreactive for the estrogen receptor. These percentages reduced in a linear fashion in more rostral sections and at the level of the area postrema, no co-expression was evident in the ventrolateral medulla and only 10% of A2 neurons displayed estrogen receptor immunoreactivity. Fluorescence double-labelling studies undertaken in colchicine-treated rats revealed that 50% and 90-100% of tyrosine hydroxylase-immunoreactive cells were positive for neuropeptide Y in the rostral ventrolateral medulla and nucleus tractus solitarius (up to 15 double-labelled cells per section), respectively. This pattern of co-expression also showed a rostrocaudal bias, but in the opposite direction, such that none of the caudal-most A1 and only 10% of caudal A2 neurons were immunoreactive for neuropeptide Y. Triple-labelling experiments revealed the presence of a total of only three triple-labelled cells in the ventrolateral medulla and none in the nucleus tractus solitarius of four rats. Double-labelling studies examining estrogen receptor and neuropeptide Y co-expression similarly found only three double-labelled cells in the ventrolateral medulla. These findings provide immunocytochemical evidence for a clear rostrocaudal topography in nuclear estrogen receptor synthesis by A1 and A2 neurons and show a reverse rostrocaudal bias in neuropeptide Y expression by these cells. The absence of any substantial neuropeptide Y and estrogen receptor co-expression in A1 and A2 neurons indicates that these two proteins are very likely to be differentially expressed by brainstem noradrenergic neurons. Such observations provide further evidence for the biosynthetic and functional heterogeneity of brainstem noradrenergic cells and suggest that A1 and A2 neurons transmitting information on estrogen status within the brain are unlikely to utilize neuropeptide Y as a co-transmitter.

Estrogen uncouples noradrenergic activation of Fos expression in the female rat preoptic area

The preoptic area of the rat brain is a site at which gonadal steroids act to regulate sexual behaviour and gonadotrophin secretion. The expression of the immediate-early gene product, Fos, in the preoptic area was investigated in conscious ovariectomised, vehicle and estrogen-treated animals which had received an intracerebroventricular (i.c.v.) infusion of noradrenaline, and also in anaesthetised proestrous and ovariectomised rats following electrical stimulation of the brainstem A1 or A2 noradrenergic cell groups. In ovariectomised oil-treated rats, a third ventricular infusion of noradrenaline (45 micrograms) resulted in a significant (P < 0.05) increase in the numbers of Fos-immunoreactive cell nuclei throughout the preoptic area, compared to vehicle controls. In contrast, Fos expression in animals which had received estrogen replacement showed no change in response to i.c.v. noradrenaline compared with saline-treated controls. In anaesthetised, ovariectomised animals electrical stimulation of the A1 cell group resulted in a significant increase (P < 0.05) in Fos-like immunoreactivity compared with sham controls, specifically within the ventral preoptic area whilst stimulation of the A2 cell group had no significant effect. In anaesthetised, proestrous rats receiving electrical stimulation no significant changes in Fos-like immunoreactivity were detected within the preoptic area after either A1 or A2 stimulation compared with paired controls. These results show that noradrenaline-induced Fos expression in the preoptic area is dependent on estrogen status and suggest that the estrogenic regulation of reproductive functions may thus involve altered responses to noradrenaline in sub-populations of preoptic neurones.

Changing patterns of Fos expression in brainstem catecholaminergic neurons during the rat oestrous cycle

Brainstem catecholaminergic neurons are believed to play an important role in the activation of luteinising hormone-releasing hormone (LHRH) neurons on the afternoon of proestrus which results in the luteinising hormone (LH) surge. To examine the respective roles of brainstem A1 and A2 neurons and the adjoining C1 and C2 adrenergic cells at this time, we have examined the patterns of Fos-immunoreactivity within tyrosine hydroxylase (TH) and phenylethanolamine-N-methyl transferase (PNMT) neurons during diestrus and proestrus. Initial studies demonstrated that the LH surge commenced at approximately 15:00 h in proestrous animals and that peak plasma levels of LH were observed between 16:00 and 17:00 h. Groups of cycling female rats (n = 6) were then perfused between 09:00 and 11:00 (diestrus early) and 18:00 to 19:30 h (diestrus late) on diestrus and at the same times on proestrus (proestrus early and proestrus late). Double-labelling immunocytochemistry revealed little Fos expression by adrenergic neurons of the C1 or C2 cell groups and this did not change significantly between any of the experimental groups. Analysis of the A2 region was divided into rostral, middle and caudal divisions and all regions showed a significant (P < 0.01) increase in the number of Fos-expressing TH neurons (up to 35% of TH cells) in proestrus early animals compared with diestrus and proestrus late rats. In the A1 region, a significant increase in the number of TH neurons expressing Fos (approximately 33%) was detected in both proestrus early (P < 0.05) and diestrus early (P < 0.01) rats compared with animals perfused in the late afternoon (approximately 12%).(ABSTRACT TRUNCATED AT 250 WORDS)

A sensitive double immunostaining protocol for Fos-immunoreactive neurons

Immunostaining of Fos, the nuclear protein encoded by the immediate early gene c-fos, is widely used to reveal the functional activation of neurons. The chemical identity of cells that express c-fos can be investigated with double immunohistochemistry. We report the usefulness of a sequential two-color avidin-biotin-immunoperoxidase method that provides a highly sensitive double immunostaining and allows long-term storage of the sections. In this protocol, metal intensification of diaminobenzidine (int-DAB) resulted in dark brown/black Fos immunostaining of the neuronal nucleus. The use of alpha-naphthol/pyronin reaction product yielded pink immunostaining of a second antigen in the cytoplasm. This combination produced higher contrast than that produced by int-DAB Fos immunostaining combined with conventional DAB light brown cytoplasmic staining. The sensitivity of the use of int-DAB and alpha-naphthol/pyronin was verified in different experimental paradigms, combining the immunocytochemical detection of Fos with that of the p75 nerve growth factor receptor, or parvalbumin, or calbindin D28k.

Analysis of brainstem A1 and A2 noradrenergic inputs to the preoptic area using microdialysis in the rat

Noradrenergic inputs to the preoptic area (POA) are involved in regulating a variety of homeostatic functions. However, the accurate measurement of endogenous noradrenaline (NA) release in the POA has been difficult to achieve and consequently little has been done to characterise the different noradrenergic pathways. By combining the technique of intracranial microdialysis with tissue pre-loading of [3H]NA we have developed a sensitive index of NA release in the POA [8]. Using this method we have now examined and compared the effects of electrical stimulation of the brainstem A1 and A2 cell groups on NA release in the POA. Anaesthetised proestrus rats were implanted with microdialysis probes either unilaterally or bilaterally in the POA and stimulating electrodes positioned in either the A1 or A2 regions. Electrical stimulation (10 Hz, 10s on/off for 20 min) of the A1 region resulted in repeatable, calcium-dependent increases in radioactivity outflow from the ipsilateral POA (P < 0.01). A1-evoked release was twice as large as that observed after equivalent 10 Hz electrical stimulation of the A2 region (P < 0.05). In experiments using bilateral POA microdialysis and A1 stimulation, a significant increase in release from the contralateral POA, amounting to approximately 80% of that observed in the ipsilateral POA, was observed. Experiments involving the blockade of A1-stimulated release in the ipsilateral POA by perfusion with a calcium-free medium demonstrated that increases in radioactivity measured in the contralateral POA were not originating from the ipsilateral POA.(ABSTRACT TRUNCATED AT 250 WORDS)

Origin of noradrenergic projections to GnRH perikarya-containing areas in the medial septum-diagonal band and preoptic area

The purpose of the present study was to identify the sites of origin of the noradrenergic fibers that project to areas containing gonadotropin-releasing hormone (GnRH) perikarya since norepinephrine (NE) is known to influence the activity of GnRH neurons. Fluorescent retrograde tracers were used in combination with immunohistochemistry for dopamine-beta-hydroxylase (DBH) and GnRH. Small volumes of either Fluoro-gold (FG) or Fluoro-Ruby (FR) were pressure injected into areas that contain the largest number of GnRH cell bodies, i.e., the medical septum-diagonal band complex or preoptic area. Retrogradely labeled neurons were observed ipsilaterally in the following noradrenergic cell groups: A2 (in the nucleus tractus solitarii), A1 (in the ventrolateral medulla) and locus coeruleus. Approximately 8% of all DBH-positive neurons within the A2-cell group were retrogradely labeled, while 12% of DBH-ir neurons in the A1-group were double-labeled. Only a few retrogradely labeled DBH-ir neurons were observed in the locus coeruleus (< 1%). Double-labeled neurons were not organized into discrete cell groups, but were dispersed among other NE-neurons within the A2- and A1-cell groups. The highest concentrations of double-labeled neurons were located in the central one-third of both the A2 and A1 cell groups. The results suggest that most noradrenergic terminals in the region of the GnRH perikarya in the medial septum-diagonal band/rostral preoptic area originate from ipsilateral neurons in areas A1 and A2.(ABSTRACT TRUNCATED AT 250 WORDS)