17beta-estradiol inhibits excitatory amino acid-induced activity of neurons of the nucleus tractus solitarius

Sex-steroid-dependent plasticity of brain-stem autonomic circuits

In the central nervous system (CNS), nuclei of the brain stem play a critical role in the integration of peripheral sensory information and the regulation of autonomic output in mammalian physiology. The nucleus tractus solitarius of the brain stem acts as a relay center that receives peripheral sensory input from vagal afferents of the nodose ganglia, integrates information from within the brain stem and higher central centers, and then transmits autonomic efferent output through downstream premotor nuclei, such as the nucleus ambiguus, the dorsal motor nucleus of the vagus, and the rostral ventral lateral medulla. Although there is mounting evidence that sex and sex hormones modulate autonomic physiology at the level of the CNS, the mechanisms and neurocircuitry involved in producing these functional consequences are poorly understood. Of particular interest in this review is the role of estrogen, progesterone, and 5α-reductase-dependent neurosteroid metabolites of progesterone (e.g., allopregnanolone) in the modulation of neurotransmission within brain-stem autonomic neurocircuits. This review will discuss our understanding of the actions and mechanisms of estrogen, progesterone, and neurosteroids at the cellular level of brain-stem nuclei. Understanding the complex interaction between sex hormones and neural signaling plasticity of the autonomic nervous system is essential to elucidating the role of sex in overall physiology and disease.

Sex differences in GABAergic neurotransmission to rat DMV neurons

Functional gastrointestinal disorders, including delayed gastric emptying and decreased gastric motility, are more prevalent in women, suggesting a potential role for circulating gonadal hormones, including estrogen. Gastric motility is tuned by the vagal inputs arising from the dorsal motor nucleus of the vagus (DMV), which is itself controlled by tonic GABAergic inputs. Estrogen increases GABA functions in various central nervous system areas; however, the effect of the estrus cycle in modulating GABAergic inputs onto DMV neurons, hence vagal control of gastric motility, has not been investigated. The aim of the present study was to test the hypothesis that GABAergic tone to DMV neurons, hence the vagal output to the stomach, varies according to sex and the estrus cycle. Experiments were performed on age-matched Sprague-Dawley male and virgin female rats; females were subdivided according to the high-estrogen (HE) or low-estrogen (LE) period of their cycle. Whole-cell patch-clamp recordings were made from gastric-projecting DMV neurons, and the response to perfusion with the GABA_A receptor antagonist bicuculline was examined. The response of corpus and antrum tone and motility to bicuculline microinjected in the dorsal vagal complex, recorded via strain gauges sewn to the anterior gastric surface, was also assessed. Bicuculline increased the firing rate of DMV neurons, as well as gastric tone and motility, to a larger extent in HE compared with LE or male rats, suggesting a higher GABAergic tone in HE female rats. Taken together, the data support the hypothesis that GABAergic tone to DMV neurons varies according to sex and estrus cycle.NEW & NOTEWORTHY GABAergic neurotransmission to the dorsal motor nucleus of the vagus (DMV) plays a pivotal role in the modulation of gastric tone and motility. Gastric motility is reduced in women and may contribute to the higher incidence of functional gastrointestinal disorders. In the present study, we report that GABAergic tone to rat DMV neurons, hence vagal output to the stomach, varies according to sex and estrus cycle, and the GABAergic tone is increased during the high-estrogen period of the estrus cycle.

Desogestrel enhances ventilation in ondine patients: Animal data involving serotoninergic systems

Congenital central hypoventilation syndrome (CCHS) is a neurorespiratory disease characterized by life-threatening sleep-related hypoventilation involving an alteration of CO2/H(+) chemosensitivity. Incidental findings have suggested that desogestrel may allow recovery of the ventilatory response to CO2. The effects of desogestrel on resting ventilation have not been reported. This study was designed to test the hypothesis that desogestrel strengthens baseline ventilation by analyzing the ventilation of CCHS patients. Rodent models were used in order to determine the mechanisms involved. Ventilation in CCHS patients was measured with a pneumotachometer. In mice, ventilatory neural activity was recorded from ex vivo medullary-spinal cord preparations, ventilation was measured by plethysmography and c-fos expression was studied in medullary respiratory nuclei. Desogestrel increased baseline respiratory frequency of CCHS patients leading to a decrease in their PETCO2. In medullary spinal-cord preparations or in vivo mice, the metabolite of desogestrel, etonogestrel, induced an increase in respiratory frequency that necessitated the functioning of serotoninergic systems, and modulated GABAA and NMDA ventilatory regulations. c-FOS analysis showed the involvement of medullary respiratory groups of cell including serotoninergic neurons of the raphe pallidus and raphe obscurus nuclei that seem to play a key role. Thus, desogestrel may improve resting ventilation in CCHS patients by a stimulant effect on baseline respiratory frequency. Our data open up clinical perspectives based on the combination of this progestin with serotoninergic drugs to enhance ventilation in CCHS patients.

Ventilatory, metabolic, and thermal responses to hypercapnia in female rats: effects of estrous cycle, ovariectomy, and hormonal replacement

The aim of this study was to examine how estrous cycle, ovariectomy, and hormonal replacement affect the respiratory [ventilation (V̇e), tidal volume, and respiratory frequency], metabolic (V̇o2), and thermoregulatory (body temperature) responses to hypercapnia (7% CO2) in female Wistar rats. The parameters were measured in rats during different phases of the estrous cycle, and also in ovariectomized (OVX) rats supplemented with 17β-estradiol (OVX+E2), with a combination of E2 and progesterone (OVX+E2P), or with corn oil (OVX+O, vehicle). All experiments were conducted on day 8 after ovariectomy. The intact animals did not present alterations during normocapnia or under hypercapnia in V̇e, tidal volume, respiratory frequency, V̇o2, and V̇e/V̇o2 in the different phases of the estrous cycle. However, body temperature was higher in female rats on estrus. Hormonal replacement did not change the ventilatory, thermoregulatory, or metabolic parameters during hypercapnia, compared with the OVX animals. Nevertheless, OVX+E2, OVX+E2P, and OVX+O presented lower hypercapnic ventilatory responses compared with intact females on the day of estrus. Also, rats in estrus showed higher V̇e and V̇e/V̇o2 during hypercapnia than OVX animals. The data suggest that other gonadal factors, besides E2 and P, are possibly involved in these responses.

Yes! Sex matters: sex, the brain and blood pressure

The role of the brain in hypertension between the sexes is known to be important especially with regards to the effects of circulating sex hormones. A number of different brain regions important for regulation of sympathetic outflow and blood pressure express estrogen receptors (ERα and ERβ). Estradiol, acting predominantly via the ERα, inhibits angiotensin II activation of the area postrema and subfornical organ neurons and inhibits reactive oxygen generation that is required for the development of Angiotensin II-induced neurogenic hypertension. Estradiol activation of ERβ within the paraventricular nucleus and the rostral ventral lateral medulla inhibits these neurons and inhibits angiotensin II, or aldosterone induced increases in sympathetic outflow and hypertension. Understanding the cellular and molecular mechanisms underlying ERα and ERβ actions within key brain regions regulating blood pressure will be essential for the development of "next generation" selective estrogen receptor modulators (SERMS) that can be used clinically for the treatment of neurogenic hypertension.

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.

The failure of mitochondria leads to neurodegeneration: Do mitochondria need a jump start?

Mitochondria are the power engine generating biochemical energy in the cell. Mitochondrial dysfunction and bioenergy deficiency is closely linked to the pathogenesis of neurodegenerative disorders. Mitochondria play a variety of roles by integrating extracellular signals and executing important intracellular events in neuronal survival and death. In this context, the regulation of mitochondrial function via therapeutic approaches may exert some salutary and neuroprotective mechanisms. Understanding the relationship of mitochondria-dependent pathogenesis may provide important pharmacological utility in the treatment of neurodegenerative conditions such as Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease and Parkinson's disease. Indeed, the modulation of mitochondrial pathways is rapidly emerging as a novel therapeutic target. This review focuses on how mitochondria are involved in neurodegeneration and what therapeutics are available to target mitochondrial pathways.

Estrous cycle-dependent neurovascular dysfunction induced by angiotensin II in the mouse neocortex

Female mice are protected from the cerebrovascular dysfunction induced by angiotensin II (Ang II), an effect attributed to estrogen. We examined whether such cerebrovascular protection from Ang II is related to the estrous cycle. Cerebral blood flow was monitored by laser-Doppler flowmetry in anesthetized (urethane-chloralose) C57BL/6 female mice equipped with a cranial window. The phase of the estrous cycle was determined by vaginal smear cytology and plasma estrogen measurement. Ang II (0.25 microg/kg per minute, IV, 30 to 45 minutes) elevated arterial pressure (15 to 20 mm Hg) equally across the estrous cycle. However, in proestrus and estrus, phases in which estrogen is relatively high, Ang II did not impair the increase in the cerebral blood flow induced by neural activity or by endothelium-dependent vasodilators (P>0.05 from vehicle). In contrast, in diestrus (lower estrogen), Ang II induced a marked cerebrovascular dysfunction comparable to that of male mice. For example, the cerebral blood flow responses to whisker stimulation and to the endothelium-dependent vasodilator acetylcholine were attenuated by 41+/-12% and 49+/-12%, respectively (P<0.05; n=6 per group). The protection from the cerebrovascular effects of Ang II in proestrus was abolished by the estrogen receptor inhibitor ICI182,780. Ang II also increased production of free radicals in cerebral blood vessels in diestrus (+116+/-13%; P<0.05) but not in proestrus and estrus (P>0.05 from control). Topical treatment with ICI182,780 reestablished Ang II-induced oxidative stress in proestrus (P>0.05 from diestrus). We conclude that the protection from the neurovascular dysfunction induced by acute administration of Ang II in females depends on the estrous cycle and may underlie the increased propensity to cerebrovascular damage associated with low estrogen states.

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.

Estrogen attenuates glutamate-induced cell death by inhibiting Ca2+ influx through L-type voltage-gated Ca2+ channels

Estrogen-mediated neuroprotection is observed in neurodegenerative disease and neurotrauma models; however, determining a mechanism for these effects has been difficult. We propose that estrogen may limit cell death in the nervous system tissue by inhibiting increases in intracellular free Ca(2+). Here, we present data using VSC 4.1 cell line, a ventral spinal motoneuron and neuroblastoma hybrid cell line. Treatment with 1 mM glutamate for 24 h induced apoptosis. When cells were pre-treated with 100 nM 17beta-estradiol (estrogen) for 1 h and then co-treated with glutamate, apoptotic death was significantly attenuated. Estrogen also prevented glutamate-mediated changes in resting membrane potential and membrane capacitance. Treatment with either 17 alpha-estradiol or cell impermeable estrogen did not mimic the findings seen with estrogen. Glutamate treatment significantly increased both intracellular free Ca(2+) and the activities of downstream proteases such as calpain and caspase-3. Estrogen attenuated both the increases in intracellular free Ca(2+) and protease activities. In order to determine the pathway responsible for estrogen-mediated inhibition of these increases in intracellular free Ca(2+), cells were treated with several Ca(2+) entry inhibitors, but only the L-type Ca(2+) channel blocker nifedipine demonstrated cytoprotective effects comparable to estrogen. To expand these findings, cells were treated with the L-type Ca(2+) channel agonist FPL 64176, which increased both cell death and intracellular free Ca(2+), and estrogen inhibited both effects. From these observations, we conclude that estrogen limits glutamate-induced cell death in VSC 4.1 cells through effects on L-type Ca(2+) channels, inhibiting Ca(2+) influx as well as activation of the pro-apoptotic proteases calpain and caspase-3.

Effects of 17beta-estradiol on neuronal cell excitability and neurotransmission in the suprachiasmatic nucleus of rat

17beta-Estradiol receptors have been found in several brain nuclei including the suprachiasmatic nucleus (SCN) of mammalian species. The SCN is believed to act as brain clock regulating circadian and circannual biological rhythms, such as body temperature, sleep, and mood. Here, we examined whether 17beta-estradiol (E2) could affect cell excitability and synaptic transmission in the SCN. Bath application of E2 (0.03-3 microM) increased the spontaneous firing frequency and depolarized cell membrane of the SCN neurons significantly. Furthermore, E2 (0.03-3 microM) increased (by about 25-150% of control) frequency of the miniature excitatory postsynaptic currents. Amplitude of the evoked excitatory postsynaptic currents was enhanced (by about 32% of control) after exposure to 1 microM E2. The paired-pulse ratio was reduced by E2. These effects were prevented by the estrogen receptor antagonist, ICI 182780. Exposure to the biologically inactive 17alpha-estradiol did not cause any significant changes in the parameters mentioned above. These findings are in favor of an implication of estrogen in modulation of neuronal activity in SCN and possibly regulating circadian rhythms.

Mitochondrial nuclear receptors and transcription factors: who's minding the cell?

Mitochondria are power organelles generating biochemical energy, ATP, in the cell. Mitochondria play a variety of roles, including integrating extracellular signals and executing critical intracellular events, such as neuronal cell survival and death. Increasing evidence suggests that a cross-talk mechanism between mitochondria and the nucleus is closely related to neuronal function and activity. Nuclear receptors (estrogen receptors, thyroid (T3) hormone receptor, peroxisome proliferators-activated receptor gamma2) and transcription factors (cAMP response binding protein, p53) have been found to target mitochondria and exert prosurvival and prodeath pathways. In this context, the regulation of mitochondrial function via the translocation of nuclear receptors and transcription factors may underlie some of the mechanisms involved in neuronal survival and death. Understanding the function of nuclear receptors and transcription factors in the mitochondria may provide important pharmacological utility in the treatment of neurodegenerative conditions. Thus, the modulation of signaling pathways via mitochondria-targeting nuclear receptors and transcription factors is rapidly emerging as a novel therapeutic target.

Estrogen receptors: their roles in regulation of vasopressin release for maintenance of fluid and electrolyte homeostasis

Long standing interest in the impact of gonadal steroid hormones on fluid and electrolyte balance has led to a body of literature filled with conflicting reports about gender differences, the effects of gonadectomy, hormone replacement, and reproductive cycles on plasma vasopressin (VP), VP secretion, and VP gene expression. This reflects the complexity of gonadal steroid hormone actions in the body resulting from multiple sites of action that impact fluid and electrolyte balance (e.g. VP target organs, afferent pathways regulating the VP neurons, and the VP secreting neurons themselves). It also reflects involvement of multiple types of estrogen receptors (ER) in these diverse sites including ERs that act as transcription factors regulating gene expression (i.e. the classic ERalpha as well as the more recently discovered ERbeta) and potentially G-protein coupled, membrane localized ERs that mediate rapid non-genomic actions of estrogen. Furthermore, altered expression of these receptors in physiologically diverse conditions of fluid and electrolyte balance contributes to the difficulty of using simplistic approaches such as gender comparisons, gonadectomy, and hormone replacement to assess the role of gonadal steroids in regulation of VP secretion for maintenance of fluid and electrolyte homeostasis. This review catalogs these inconsistencies and provides a frame work for understanding them by describing: (1) the effect of gonadal steroids on target organ responsiveness to VP; (2) the expression of multiple types of estrogen receptors in the VP neurons and in brain regions monitoring feedback signals from the periphery; and (3) the impact of dehydration and hyponatremia on expression of these receptors.

Membrane and synaptic properties of nucleus tractus solitarius neurons projecting to the caudal ventrolateral medulla

Projections from the nucleus of tractus solitarius (NTS) to the caudal ventrolateral medulla (CVLM) are important in mediating autonomic reflexes. However, little is known about the cellular properties of the CVLM-projecting NTS neurons. In this study, the CVLM-projecting NTS neurons were retrogradely labeled by fluorescent microspheres injected into the CVLM. Whole cell voltage- and current-clamp recordings were performed on labeled NTS neurons in coronal brainstem slices. Compared with unlabeled neurons, the labeled NTS neurons had more depolarized resting membrane potentials, larger input resistance, and higher firing activity in response to depolarizing currents. Bath application of an ionotropic glutamate receptor antagonist kynurenic acid and a non-NMDA receptor antagonist CNQX significantly decreased the firing activity in the majority of labeled NTS neurons. In contrast, an NMDA receptor antagonist AP5 failed to alter the firing activity in labeled neurons tested. While the glycine receptor antagonist strychnine had no effect on the firing activity, blockade of GABA(A)receptors with bicuculline significantly increased the firing rate in the majority of labeled NTS neurons. Furthermore, CNQX blocked the majority of spontaneous excitatory postsynaptic currents (EPSCs) and evoked EPSCs elicited by stimulation of the tractus solitarius. The residual spontaneous and evoked EPSCs were abolished by the nicotinic receptor antagonist mecamylamine and the purinergic P2X receptor antagonist iso-PPADS. Finally, while bicuculline completely blocked the miniature inhibitory postsynaptic currents (IPSCs), the spontaneous and evoked IPSCs were abolished by a combination of bicuculline and strychnine in labeled NTS neurons. Collectively, these data suggest that the CVLM-projecting neurons are a population of neurons with distinctive membrane properties.

17beta-estradiol attenuates excitatory neurotransmission and enhances the excitability of rat parabrachial neurons in vitro

The steroid hormone 17beta-estradiol and its respective receptors have been found in several cardiovascular nuclei in the central nervous system including the parabrachial nucleus. In a previous study, we provided evidence that 17beta-estradiol attenuated an outward potassium conductance in parabrachial neurons of male rats, using an in vitro slice preparation. In this study we sought to enhance the comprehensive information provided previously on estradiol's postsynaptic effects in the parabrachial nucleus by directly examining whether 17beta-estradiol application will modulate excitatory synaptic neurotransmission. Using a pontine slice preparation and whole-cell patch-clamp recording, bath application of either 17beta-estradiol (20-100 muM) or BSA-17beta-estradiol (50 muM) decreased the amplitude of evoked excitatory postsynaptic currents (from 30-60% of control) recorded from neurons in the parabrachial nucleus. The paired pulse ratio was not significantly affected and suggests a post-synaptic site of action. The inhibitory effect on the synaptic current was relatively long-lasting (non-reversible) and was blocked by the selective estrogen receptor antagonist, ICI 182,780. Furthermore, 17beta-estradiol reduced the maximum current elicited by a ramp protocol, increased the input resistance measured between resting membrane potential and action potential threshold and caused an increase in the firing frequency of the cells under current-clamp. In summary, 17beta-estradiol caused 3 effects: first, a depolarization; second, a reduction in evoked excitatory postsynaptic potentials; and third, an enhancement of action potential firing frequency in neurons of the parabrachial nucleus. These observations are consistent with our previous findings and support a role for estrogen in modulating neurotransmission in this nucleus.

Pain activates cortical areas in the preterm newborn brain

To study the patterns of supraspinal pain processing in neonates, we hypothesized that acute pain causes haemodynamic changes associated with activation of the primary somatosensory cortex. Forty preterm neonates at 28-36 weeks of gestation (mean=32.0) and at 25-42 h (mean=30.7) of age were studied following standardized tactile (skin disinfection) and painful (venipuncture) stimuli. Changes in regional cerebral haemodynamics were monitored by near infrared spectroscopy (NIRS) over both somatosensory cortices in 29 newborns, and over the contralateral somatosensory and occipital areas in 11 newborns. Heart rate (HR) and peripheral oxygen saturation (SaO2) were recorded simultaneously with NIRS parameters: oxygenated [HbO2], deoxygenated, and total hemoglobin. Tactile stimulation produced no changes in HR or SaO2. HR increased in the first 20s (p<0.001), while SaO2 decreased during the 40s after venipuncture (p<0.0001). Following tactile or painful stimulation, [HbO2] increased bilaterally regardless of which hand was stimulated (p<0.0001). Pain-induced [HbO2] increases in the contralateral somatosensory cortex (p<0.05) were not mirrored in the occipital cortex (p>0.1). Pain-related [HbO2] increases were more pronounced in male neonates (p<0.05 on left, p<0.001 on right), inversely correlated with gestational age (r=-0.53 on left, p<0.01; r=-0.42 on right, p<0.05) and directly correlated with postnatal age (r=0.75 on left, p<0.0001; r=0.67 on right, p<0.0001). Painful and tactile stimuli elicit specific haemodynamic responses in the somatosensory cortex, implying conscious sensory perception in preterm neonates. Somatosensory cortical activation occurs bilaterally following unilateral stimulation and these changes are more pronounced in male neonates or preterm neonates at lower gestational ages.

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.

Estrogen prevents glutamate-induced apoptosis in C6 glioma cells by a receptor-mediated mechanism

Estrogen-mediated neuroprotection is well established; however, no single mechanism of action for this effect has yet been established. As glial cells are integral for both the intact and injured nervous system, we hypothesized that estrogen-mediated neuroprotection may partly be attributed to attenuation of glial cell apoptosis, allowing them to protect neurons following injury. To assess the protective effects of estrogen on glia, C6 rat glioma cells were treated for 24 h with 500 microM glutamate. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and apoptosis was confirmed by cell morphology and DNA fragmentation. Pretreatment with 10 nM 17beta-estradiol (estrogen) increased cell viability and attenuated apoptosis. Treatment with the stereoisomer 17alpha-estradiol, or estrogen plus estrogen receptor antagonist ICI 182,780, was significantly less effective, indicating that cytoprotection was receptor-mediated. Estrogen treatment upregulated expression of estrogen receptor alpha. Cell impermeable bovine serum albumin-conjugated estrogen was also protective, indicating activation of estrogen receptors on the cell membrane. Intracellular free [Ca2+] was increased after glutamate treatment. This increase was attenuated in cells pretreated with estrogen. Glutamate increased the activity of pro-apoptotic proteases, such as calpain and caspase-3, and these protease activities were significantly attenuated by estrogen. The mechanism by which estrogen decreased intracellular Ca2+ was examined by assaying cell viability after using inhibitors that either blocked extracellular Ca2+ influx or prevented the release of intracellular Ca2+ stores. While several inhibitors increased cell viability in glutamate-treated cells, none were as protective as estrogen, and estrogen co-treatment significantly increased cell viability. These findings indicate that estrogen-mediated cytoprotection may be related to effects on Ca2+ entry but that these effects are not limited to any one of these Ca2+ entry points alone.

A human experimental capsaicin model for trigeminal sensitization. Gender-specific differences

Migraine is much more common in women (18%) than in men (6%). Menstrual migraine in female migraineurs also varies from 7 to 19%. The main goals of the present study were (1) to investigate gender specific differences in an experimental capsaicin model of trigeminal sensitization (a proposed mechanism of migraine) and (2) to explore the influence of menstrual cycle phases. Twenty-eight healthy female and male volunteers were studied. Capsaicin (100 microg/0.1 ml) was injected intradermally to the forehead. Pain intensity and distribution together with the visual flare and allodynic area (central sensitization) were assessed for females (during their menstrual and luteal phases) and for males. Pain area significantly changed across the menstrual cycle with 19.2+/-2.0 cm x min at menstrual and 16.4+/-0.9 cm x min at luteal phase (P<0.001). The area was significantly larger in both phases for females compared to males (14.2+/-1.3 cm x min, P<0.0001). Flare area at menstrual phase (69.2+/-4.2 cm(2)) was significantly (P<0.0001) larger than luteal phase (58.6+/-2.1 cm(2)). Females, in both phases, showed larger flare area compared to males (44.9+/-3.6 cm(2), P<0.0001). Area of brush-evoked allodynia was also larger at the menstrual phase compared to the luteal phase (P<0.0001) and males (P<0.0001). A significant difference was found in the capsaicin-evoked pain distribution with a greater response in menstrual phase compared to the luteal phase (P<0.01) and men (P<0.0001). Capsaicin induced trigeminal sensitization and evoked gender specific sensory and vaso-motor responses, with menstruating females generally showing the strongest manifestations. The model may be further applied to explore mechanisms of human trigeminal sensitization.

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.

Stress-induced reductions of sensory reactivity in female rats depend on ovarian hormones and the application of a painful stressor

The current experiments occurred in the context of disputes in the literature concerning whether inescapable stress causes differential changes in sensory reactivity, which could lead to differences in many learning procedures. We tested rats for differences in sensitivity and responsivity to acoustic stimuli through the use of the acoustic startle response (ASR) 2 h after stressor exposure and ambulatory activity 24 h later in the open field. Stressed females showed reduced responsivity to acoustic stimuli with no apparent shift in stimulus sensitivity. Males did not show differences in either reactivity index following stressor exposure. Reduced responsivity did not occur if females had been OVX (OVX alone did not effect stimulus responsivity or sensitivity). All groups that experienced tailshock stress also had reduced open field activity 24 h later. Restraint for 2 h did not reduce stimulus responsivity in the ASR or open field activity in female rats. Acute reductions in ASRs after a painful stressor appear to be a feature specific to females, with an apparent role of ovarian hormones as a modulator of the effect. Possible hormone and/or immunological mechanisms of these sex-specific effects are discussed. Understanding the mechanisms of this stressor-induced reduction in sensory reactivity could advance our knowledge of how individual differences in ovarian hormone levels influence the physical and psychological processes by which females acutely respond and later recover from traumatic events.