Sex differences in androgen and estrogen receptor expression in rat substantia nigra during development: an immunohistochemical study

Effects of chronic insecticide exposure on neuronal network development in vitro in rat cortical cultures

Developmental exposure to carbamates, organophosphates, and pyrethroids has been associated with impaired neurodevelopmental outcomes. Sex-specific differences following chronic insecticide exposure are rather common in vivo. Therefore, we assessed the chronic effects of in vitro exposure to different carbamates (carbaryl, methomyl and aldicarb), organophosphates [chlorpyrifos (CPF), chlorpyrifos-oxon (CPO), and 3,5,6,trichloropyridinol (TCP)], and pyrethroids [permethrin, alpha-cypermethrin and 3-phenoxy benzoic acid (3-PBA)] on neuronal network development in sex-separated rat primary cortical cultures using micro-electrode array (MEA) recordings. Our results indicate that exposure for 1 week to carbaryl inhibited neurodevelopment in male cultures, while a hyperexcitation was observed in female cultures. Methomyl and aldicarb evoked a hyperexcitation after 2 weeks of exposure, which was more pronounced in female cultures. In contrast to acute MEA results, exposure to ≥ 10 µM CPF caused hyperexcitation in both sexes after 10 days. Interestingly, exposure to 10 µM CPO induced a clear hyperexcitation after 10 days of exposure in male but not female cultures. Exposure to 100 µM CPO strongly inhibited neuronal development. Exposure to the type I pyrethroid permethrin resulted in a hyperexcitation at 10 µM and a decrease in neuronal development at 100 µM. In comparison, exposure to ≥ 10 µM of the type II pyrethroid alpha-cypermethrin decreased neuronal development. In female but not in male cultures, exposure to 1 and 10 µM permethrin changed (network) burst patterns, with female cultures having shorter (network) bursts with fewer spikes per (network) burst. Together, these results show that MEA recordings are suitable for measuring sex-specific developmental neurotoxicity in vitro. Additionally, pyrethroid exposure induced effects on neuronal network development at human-relevant concentrations. Finally, chronic exposure has different effects on neuronal functioning compared to acute exposure, highlighting the value of both exposure paradigms.

Maternal immune activation and estrogen receptor modulation induce sex-specific dopamine-related behavioural and molecular alterations in adult rat offspring

Dopamine dysregulation contributes to psychosis and cognitive deficits in schizophrenia that can be modelled in rodents by inducing maternal immune activation (MIA). The selective estrogen receptor (ER) modulator, raloxifene, can improve psychosis and cognition in men and women with schizophrenia. However, few studies have examined how raloxifene may exert its therapeutic effects in mammalian brain in both sexes during young adulthood (age relevant to most prevalent age at diagnosis). Here, we tested the extent to which raloxifene alters dopamine-related behaviours and brain transcripts in young adult rats, both control and MIA-exposed females and males. We found that raloxifene increased amphetamine (AMPH)-induced locomotor activity in female controls, and in contrast, raloxifene reduced AMPH-induced locomotor activity in male MIA offspring. We did not detect overt prepulse inhibition (PPI) deficits in female or male MIA offspring, yet raloxifene enhanced PPI in male MIA offspring. Whereas, raloxifene ameliorated increased startle responsivity in female MIA offspring. In the substantia nigra (SN), we found reduced Drd2s mRNA in raloxifene-treated female offspring with or without MIA, and increased Comt mRNA in placebo-treated male MIA offspring relative to placebo-treated controls. These data demonstrate an underlying dopamine dysregulation in MIA animals that can become more apparent with raloxifene treatment, and may involve selective alterations in dopamine receptor levels and dopamine breakdown processes in the SN. Our findings support sex-specific, differential behavioural responses to ER modulation in MIA compared to control offspring, with beneficial effects of raloxifene treatment on dopamine-related behaviours relevant to schizophrenia found in male MIA offspring only.

Neuroprotective and neurotoxic outcomes of androgens and estrogens in an oxidative stress environment

BACKGROUND

The role of sex hormones on cellular function is unclear. Studies show androgens and estrogens are protective in the CNS, whereas other studies found no effects or damaging effects. Furthermore, sex differences have been observed in multiple oxidative stress-associated CNS disorders, such as Alzheimer's disease, depression, and Parkinson's disease. The goal of this study is to examine the relationship between sex hormones (i.e., androgens and estrogens) and oxidative stress on cell viability.

METHODS

N27 and PC12 neuronal and C6 glial phenotypic cell lines were used. N27 cells are female rat derived, whereas PC12 cells and C6 cells are male rat derived. These cells express estrogen receptors and the membrane-associated androgen receptor variant, AR45, but not the full-length androgen receptor. N27, PC12, and C6 cells were exposed to sex hormones either before or after an oxidative stressor to examine neuroprotective and neurotoxic properties, respectively. Estrogen receptor and androgen receptor inhibitors were used to determine the mechanisms mediating hormone-oxidative stress interactions on cell viability. Since the presence of AR45 in the human brain tissue was unknown, we examined the postmortem brain tissue from men and women for AR45 protein expression.

RESULTS

Neither androgens nor estrogens were protective against subsequent oxidative stress insults in glial cells. However, these hormones exhibited neuroprotective properties in neuronal N27 and PC12 cells via the estrogen receptor. Interestingly, a window of opportunity exists for sex hormone neuroprotection, wherein temporary hormone deprivation blocked neuroprotection by sex hormones. However, if sex hormones are applied following an oxidative stressor, they exacerbated oxidative stress-induced cell loss in neuronal and glial cells.

CONCLUSIONS

Sex hormone action on cell viability is dependent on the cellular environment. In healthy neuronal cells, sex hormones are protective against oxidative stress insults via the estrogen receptor, regardless of sex chromosome complement (XX, XY). However, in unhealthy (e.g., high oxidative stress) cells, sex hormones exacerbated oxidative stress-induced cell loss, regardless of cell type or sex chromosome complement. The non-genomic AR45 receptor, which is present in humans, mediated androgen's damaging effects, but it is unknown which receptor mediated estrogen's damaging effects. These differential effects of sex hormones that are dependent on the cellular environment, receptor profile, and cell type may mediate the observed sex differences in oxidative stress-associated CNS disorders.

Effects of Oxidative Stress and Testosterone on Pro-Inflammatory Signaling in a Female Rat Dopaminergic Neuronal Cell Line

Parkinson's disease, a progressive neurodegenerative disorder, is associated with oxidative stress and neuroinflammation. These pathological markers can contribute to the loss of dopamine neurons in the midbrain. Interestingly, men have a 2-fold increased incidence for Parkinson's disease than women. Although the mechanisms underlying this sex difference remain elusive, we propose that the primary male sex hormone, testosterone, is involved. Our previous studies show that testosterone, through a putative membrane androgen receptor, can increase oxidative stress-induced neurotoxicity in dopamine neurons. Based on these results, this study examines the role of nuclear factor κ B (NF-κB), cyclooxygenase-2 (COX2), and apoptosis in the deleterious effects of androgens in an oxidative stress environment. We hypothesize, under oxidative stress environment, testosterone via a putative membrane androgen receptor will exacerbate oxidative stress-induced NF-κB/COX2 signaling in N27 dopaminergic neurons, leading to apoptosis. Our data show that testosterone increased the expression of COX2 and apoptosis in dopamine neurons. Inhibiting the NF-κB and COX2 pathway with CAPE and ibuprofen, respectively, blocked testosterone's negative effects on cell viability, indicating that NF-κB/COX2 cascade plays a role in the negative interaction between testosterone and oxidative stress on neuroinflammation. These data further support the role of testosterone mediating the loss of dopamine neurons under oxidative stress conditions, which may be a key mechanism contributing to the increased incidence of Parkinson's disease in men compared with women.

Oestradiol Regulates Neuropeptide Y Release and Gene Coupling with the GABAergic and Glutamatergic Synapses in the Adult Female Rat Dentate Gyrus

Neuropeptide Y (NPY) is an endogenous modulator of neuronal activity affecting both GABAergic and glutamatergic transmission. Previously, we found that oestradiol modifies the number of NPY immunoreactive neurones in the hippocampal dentate gyrus. In the present study, we investigated which oestrogen receptor type is responsible for these changes in the number of NPY-positive neurones. Furthermore, we determined the effects of oestrogen receptor activation on NPY release. Finally, we examined the contribution of oestrogen toward the remodelling of the GABAergic and glutamatergic gene networks in terms of coupling with Npy gene expression in ovariectomised rats. We found that activation of either oestrogen receptor type (ERα or ERβ) increases the number of NPY-immunopositive neurones and enhances NPY release in the dentate gyrus. We also found that, compared to oestrogen-lacking ovariectomised rats, oestrogen replacement increases the probability of synergistic/antagonistic coupling between the Npy and GABAergic synapse genes, whereas the glutamatergic synapse genes are less likely to be coupled with Npy under similar conditions. The data together suggest that oestrogens play a critical role in the regulation of NPY system activity and are also involved in the coupling/uncoupling of the Npy gene with the GABAergic and glutamatergic synapses in the female rat dentate gyrus.

Development and regulation of chloride homeostasis in the central nervous system

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter of the mature central nervous system (CNS). The developmental switch of GABAergic transmission from excitation to inhibition is induced by changes in Cl⁻ gradients, which are generated by cation-Cl⁻ co-transporters. An accumulation of Cl⁻ by the Na⁺-K⁺-2Cl⁻ co-transporter (NKCC1) increases the intracellular Cl⁻ concentration ([Cl⁻]_i) such that GABA depolarizes neuronal precursors and immature neurons. The subsequent ontogenetic switch, i.e., upregulation of the Cl⁻-extruder KCC2, which is a neuron-specific K⁺-Cl⁻ co-transporter, with or without downregulation of NKCC1, results in low [Cl⁻]_i levels and the hyperpolarizing action of GABA in mature neurons. Development of Cl⁻ homeostasis depends on developmental changes in NKCC1 and KCC2 expression. Generally, developmental shifts (decreases) in [Cl⁻]_i parallel the maturation of the nervous system, e.g., early in the spinal cord, hypothalamus and thalamus, followed by the limbic system, and last in the neocortex. There are several regulators of KCC2 and/or NKCC1 expression, including brain-derived neurotrophic factor (BDNF), insulin-like growth factor (IGF), and cystic fibrosis transmembrane conductance regulator (CFTR). Therefore, regionally different expression of these regulators may also contribute to the regional developmental shifts of Cl⁻ homeostasis. KCC2 and NKCC1 functions are also regulated by phosphorylation by enzymes such as PKC, Src-family tyrosine kinases, and WNK1–4 and their downstream effectors STE20/SPS1-related proline/alanine-rich kinase (SPAK)-oxidative stress responsive kinase-1 (OSR1). In addition, activation of these kinases is modulated by humoral factors such as estrogen and taurine. Because these transporters use the electrochemical driving force of Na⁺ and K⁺ ions, topographical interaction with the Na⁺-K⁺ ATPase and its modulators such as creatine kinase (CK) should modulate functions of Cl⁻ transporters. Therefore, regional developmental regulation of these regulators and modulators of Cl⁻ transporters may also play a pivotal role in the development of Cl⁻ homeostasis.

Axon diameter and axonal transport: In vivo and in vitro effects of androgens

Testosterone is a sex hormone involved in brain maturation via multiple molecular mechanisms. Previous human studies described age-related changes in the overall volume and structural properties of white matter during male puberty. Based on this work, we have proposed that testosterone may induce a radial growth of the axon and, possibly, modulate axonal transport. In order to determine whether this is the case we have used two different experimental approaches. With electron microscopy, we have evaluated sex differences in the structural properties of axons in the corpus callosum (splenium) of young rats, and tested consequences of castration carried out after weaning. Then we examined in vitro the effect of the non-aromatizable androgen Mibolerone on the structure and bidirectional transport of wheat-germ agglutinin vesicles in the axons of cultured sympathetic neurons. With electron microscopy, we found robust sex differences in axonal diameter (males>females) and g ratio (males>females). Removal of endogenous testosterone by castration was associated with lower axon diameter and lower g ratio in castrated (vs. intact) males. In vitro, Mibolerone influenced the axonal transport in a time- and dose-dependent manner, and increased the axon caliber as compared with vehicle-treated neurons. These findings are consistent with the role of testosterone in shaping the axon by regulating its radial growth, as predicted by the initial human studies.

Testosterone attenuates and the selective estrogen receptor modulator, raloxifene, potentiates amphetamine-induced locomotion in male rats

Although sex steroids are known to modulate brain dopamine, it is still unclear how testosterone modifies locomotor behaviour controlled, at least in part, by striatal dopamine in adolescent males. Our previous work suggests that increasing testosterone during adolescence may bias midbrain neurons to synthesise more dopamine. We hypothesised that baseline and amphetamine-induced locomotion would differ in adult males depending on testosterone exposure during adolescence. We hypothesised that concomitant stimulation of estrogen receptor signaling, through a selective estrogen receptor modulator (SERM), raloxifene, can counter testosterone effects on locomotion. Male Sprague-Dawley rats at postnatal day 45 were gonadectomised (G) or sham-operated (S) prior to the typical adolescent testosterone increase. Gonadectomised rats were either given testosterone replacement (T) or blank implants (B) for six weeks and sham-operated (i.e. intact or endogenous testosterone group) were given blank implants. Subgroups of sham-operated, gonadectomised and gonadectomised/testosterone-replaced rats were treated with raloxifene (R, 5mg/kg) or vehicle (V), daily for the final four weeks. There were six groups (SBV, GBV, GTV, SBR, GBR, GTR). Saline and amphetamine-induced (1.25mg/kg) locomotion in the open field was measured at PND85. Gonadectomy increased amphetamine-induced locomotion compared to rats with endogenous or with exogenous testosterone. Raloxifene increased amphetamine-induced locomotion in rats with either endogenous or exogenous testosterone. Amphetamine-induced locomotion was negatively correlated with testosterone and this relationship was abolished by raloxifene. Lack of testosterone during adolescence potentiates and testosterone exposure during adolescence attenuates amphetamine-induced locomotion. Treatment with raloxifene appears to potentiate amphetamine-induced locomotion and to have an opposite effect to that of testosterone in male rats.

Regional specific regulation of steroid receptor coactivator-1 immunoreactivity by orchidectomy in the brain of adult male mice

Androgens including testosterone and dihydrotestosterone play important roles on brain structure and function, either directly through androgen receptor or indirectly through estrogen receptors, which need coactivators for their transcription activation. Steroid receptor coactivator-1 (SRC-1) has been shown to be multifunctional potentials in the brain, but how it is regulated by androgens in the brain remains unclear. In this study, we explored the effect of orchidectomy (ORX) on the expression of SRC-1 in the adult male mice using nickel-intensified immunohistochemistry. The results showed that ORX induced dramatic decrease of SRC-1 immunoreactivity in the olfactory tubercle, piriform cortex, ventral pallidum, most parts of the septal area, hippocampus, substantia nigra (compact part), pontine nuclei and nucleus of the trapezoid body (p<0.01). Significant decrease of SRC-1 was noticed in the dorsal and lateral septal nucleus, medial preoptical area, dorsomedial and ventromedial hypothalamic nucleus and superior paraolivary nucleus (p<0.05). Whereas in other regions examined, levels of SRC-1 immunoreactivity were not obviously changed by ORX (p>0.05). The above results demonstrated ORX downregulation of SRC-1 in specific regions that have been involved in sense of smell, learning and memory, cognition, neuroendocrine, reproduction and motor control, indicating that SRC-1 play pivotal role in the mediating circulating androgenic regulation on these important brain functions. It also indicates that SRC-1 may serve as a novel target for the central disorders caused by the age-related decrease of circulating androgens.

Distribution of androgen and oestrogen receptors-α in the seminal vesicle-related spinal neurones in male rats

The seminal vesicles are male accessory sex glands that contribute much of the seminal fluid volume. Previous studies have suggested that the majority of autonomic innervations to the rat seminal vesicles originate from the bilateral major pelvic ganglia. Many preganglionic autonomic neurones innervating the pelvic ganglion were expressed androgen receptors (AR) or oestrogen receptor (ER)-α immunoreactivity. However, direct neuroanatomic data regarding the distribution of AR and ER-α in seminal vesicle related-spinal neurones are lacking. In the present study, a nonvirulent pseudorabies virus (PRV-152 strain) was used in a retrograde tracing experiment. Four days after PRV injection into the seminal vesicles of male rats, spinal cord sections were prepared. Double- and triple-fluorescence techniques using AR and ER-α with choline acetyltransferase (ChAT) and PRV were used to investigate the AR and ER-α distribution in the seminal vesicles related spinal neurones in male rats. In lamina X, 14% of the PRV-labelled neurones in the L1-L4 segments and 43% in the L5-S1 segments were double-labelled with AR. In the L1-L4 segments, 6% of PRV-labelled neurones and 26% in the L5-S1 segments were double-labelled with ER-α. In the intermedial cell column area, 10% of PRV-labelled neurones in the L1-L4 segments and 47% of PRV-labelled neurones in the L5-S1 segments were double-labelled with AR. Up to 16% of PRV-labelled neurones in the L5-S1 segments were double-labelled with ER-α. No PRV-labelled neurones in the L1-L4 segments were double-labelled with ER-α. However, for the AR and ER-α/PRV/ChAT triple-fluorescence experiments, very few seminal vesicle preganglionic neurones expressed AR or ER-α. Our data suggests that many spinal interneurones but not preganglionic neurones involved in the seminal vesicle control in male rats were double-labelled with AR or ER-α, and they were mainly located at the parasympathetic level in the spinal cord.

Rapamycin has age-, treatment paradigm-, and model-specific anticonvulsant effects and modulates neuropeptide Y expression in rats

PURPOSE

  Rapamycin (RAP) has certain antiepileptogenic features. However, it is unclear whether these effects can be explained by the anticonvulsant action of RAP, which has not been studied. To address this question, we tested potential anticonvulsant effects of RAP in immature and adult rats using different seizure models and treatment paradigms. In addition, we studied changes in the expression of neuropeptide Y (NPY) induced by RAP, which may serve as an indirect target of the RAP action.

METHODS

  A complex approach was adopted to evaluate the anticonvulsant potential of RAP: We used flurothyl-, pentylenetetrazole (PTZ)-, N-methyl-D-aspartate (NMDA)-, and kainic acid (KA)-induced seizures to test the effects of RAP using different pretreatment protocols in immature and adult rats. We also evaluated expression of NPY within the primary motor cortex, hippocampal CA1, and dentate gyrus (DG) after different pretreatments with RAP in immature rats.

KEY FINDINGS

  We found the following: (1) RAP administered with short-term pretreatment paradigms has a weak anticonvulsant potential in the seizure models with compromised inhibition. (2) Lack of RAP efficacy correlates with decreased NPY expression in the cortex, CA1, and DG. Specifically in immature rats, a single dose of RAP (3 mg/kg) 4 or 24 h before seizure testing had anticonvulsant effects against PTZ-induced seizures. In the flurothyl seizure model only the 4-h pretreatment with RAP was anticonvulsant in the both age groups. Short-term pretreatments with RAP had no effects against NMDA- and KA-induced seizures tested in immature rats. Long-term pretreatments with RAP over 8 days did not show beneficial effect in all tested seizure models in developing rats. Moreover, the long-term pretreatment with RAP had a slight proconvulsant effect on KA-induced seizures. In immature rats, any lack of anticonvulsant effect (including proconvulsant effect of multiple doses of RAP) was associated with downregulation of NPY expression in the cortex and DG. In immature animals, after a single dose of RAP with 24 h delay, we found a decrease of NPY expression in DG, and CA1 as well.

SIGNIFICANCE

  Our data show weak age-, treatment paradigm-, and model-specific anticonvulsant effects of RAP as well as loss of those effects after long-term RAP pretreatment associated with downregulation of NPY expression. These findings suggest that RAP is a poor anticonvulsant and may have beneficial effects only against epileptogenesis. In addition, our data present new insights into mechanisms of RAP action on seizures indicating a possible connection between mammalian target of rapamycin (mTOR) signaling and NPY system.

Testosterone regulation of sex steroid-related mRNAs and dopamine-related mRNAs in adolescent male rat substantia nigra

BACKGROUND

Increased risk of schizophrenia in adolescent males indicates that a link between the development of dopamine-related psychopathology and testosterone-driven brain changes may exist. However, contradictions as to whether testosterone increases or decreases dopamine neurotransmission are found and most studies address this in adult animals. Testosterone-dependent actions in neurons are direct via activation of androgen receptors (AR) or indirect by conversion to 17β-estradiol and activation of estrogen receptors (ER). How midbrain dopamine neurons respond to sex steroids depends on the presence of sex steroid receptor(s) and the level of steroid conversion enzymes (aromatase and 5α-reductase). We investigated whether gonadectomy and sex steroid replacement could influence dopamine levels by changing tyrosine hydroxylase (TH) protein and mRNA and/or dopamine breakdown enzyme mRNA levels [catechol-O-methyl transferase (COMT) and monoamine oxygenase (MAO) A and B] in the adolescent male rat substantia nigra. We hypothesized that adolescent testosterone would regulate sex steroid signaling through regulation of ER and AR mRNAs and through modulation of aromatase and 5α-reductase mRNA levels.

RESULTS

We find ERα and AR in midbrain dopamine neurons in adolescent male rats, indicating that dopamine neurons are poised to respond to circulating sex steroids. We report that androgens (T and DHT) increase TH protein and increase COMT, MAOA and MAOB mRNAs in the adolescent male rat substantia nigra. We report that all three sex steroids increase AR mRNA. Differential action on ER pathways, with ERα mRNA down-regulation and ERβ mRNA up-regulation by testosterone was found. 5α reductase-1 mRNA was increased by AR activation, and aromatase mRNA was decreased by gonadectomy.

CONCLUSIONS

We conclude that increased testosterone at adolescence can shift the balance of sex steroid signaling to favor androgenic responses through promoting conversion of T to DHT and increasing AR mRNA. Further, testosterone may increase local dopamine synthesis and metabolism, thereby changing dopamine regulation within the substantia nigra. We show that testosterone action through both AR and ERs modulates synthesis of sex steroid receptor by altering AR and ER mRNA levels in normal adolescent male substantia nigra. Increased sex steroids in the brain at adolescence may alter substantia nigra dopamine pathways, increasing vulnerability for the development of psychopathology.

Sexual differentiation of the brain and ADHD: what is a sex difference in prevalence telling us?

Sexual differentiation of the brain is a function of various processes that prepare the organism for successful reproduction in adulthood. Release of gonadal steroids during both the perinatal and the pubertal stages of development organizes many sex differences, producing changes in brain excitability and morphology that endure across the lifespan. To achieve these sexual dimorphisms, gonadal steroids capitalize on a number of distinct mechanisms across brain regions. Comparison of the developing male and female brain provides insight into the mechanisms through which synaptic connections are made, and circuits are organized that mediate sexually dimorphic behaviors. The prevalence of most psychiatric and neurological disorders differ in males versus females, including disorders of attention, activity and impulse control. While there is a strong male bias in incidence of attention deficit and hyperactivity disorders, the source of that bias remains controversial. By elucidating the biological underpinnings of male versus female brain development, we gain a greater understanding of how hormones and genes do and do not contribute to the differential vulnerability in one sex versus the other.

Gender segregation in gene expression and vulnerability to oxidative stress induced injury in ventral mesencephalic cultures of dopamine neurons

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNC). Most epidemiologic studies have demonstrated that PD has a higher prevalence in males than in females. Both hormones and genetic factors have been considered to be contributors to this phenomenon. In the present study, we used primary cultures of ventral mesencephalic (VM) neurons from E13.5 Balb/C mice to investigate whether there were any gender differences in gene expression and cell sensitivity to oxidative stress in sex segregated cultures. We also investigated the role of SRY, the sex-determining region on the Y chromosome, and the female hormone estrogen in the gender dimorphism. We measured the expression levels of genes that previously were thought to be related to PD or DA neuron development and functions by real-time PCR, and found six of them, ATP13A2, ERβ, MAO-A, D2, DAT, and Pitx3, showing significantly differential expression between males and females in the normal physiological state or under stress conditions. Furthermore, we demonstrated that male VM neurons are more vulnerable than female neurons to rotenone-induced cytotoxicity and that 17β-estrogen has a moderate protective effect in both male and female VM neurons. Moreover, we document that SRY can upregulate monoamine oxidase A and downregulate estrogen receptor-β, and SRY-overexpressing N2A cells enhance the resistance to oxidative stress-induced cell injury. Our results suggest that gender indeed influences several PD-related gene expressions in VM neurons, and SRY and estrogen are involved in the different responses to oxidative stress in culture.

Differential expression of estrogen receptors in two hippocampal regions during the estrous cycle of the rat

In the hippocampus, estrogens increase dendritic arborization, long-term potentiation, neuroprotection, and participate in many functions related with learning, memory, and affective behaviors. The presence of both estrogen receptors alpha (ERα) and beta (ERβ) isoforms has been described in the hippocampus where they play different physiological roles. The aim of this study was to investigate, by using both techniques immunohistochemistry and Western Blot, the expression pattern of ERα and ERβ in the hippocampus of the rat along the estrous cycle. Western blot analysis was used to confirm the specificity of the antibodies used against ERα and ERβ and its relative content in the hippocampus. Results from immunohistochemical studies indicate that ERβ expression increased more than the ERα in CA1 and CA3 regions during all phases of the estrous cycle. ERβ immunoreactivity was mainly located in the nucleus and predominantly expressed in CA1 during estrous and metestrus, and in CA3 during diestrus. ERα was more abundant during estrous in comparison to other phases of the cycle in CA1 region, while it was more abundant during metestrus in CA3. Interestingly, the immunolocalization of ERα subtype was both cytoplasmic and nuclear. The overall results indicate that there is a differential expression, cellular localization, and distribution of both ER subtypes in CA1 and CA3 regions, suggesting different roles for these two receptors in the hippocampus along the estrous cycle.

GABAergic neuron deficit as an idiopathic generalized epilepsy mechanism: the role of BRD2 haploinsufficiency in juvenile myoclonic epilepsy

Idiopathic generalized epilepsy (IGE) syndromes represent about 30% of all epilepsies. They have strong, but elusive, genetic components and sex-specific seizure expression. Multiple linkage and population association studies have connected the bromodomain-containing gene BRD2 to forms of IGE. In mice, a null mutation at the homologous Brd2 locus results in embryonic lethality while heterozygous Brd2+/− mice are viable and overtly normal. However, using the flurothyl model, we now show, that compared to the Brd2+/+ littermates, Brd2+/− males have a decreased clonic, and females a decreased tonic-clonic, seizure threshold. Additionally, long-term EEG/video recordings captured spontaneous seizures in three out of five recorded Brd2+/− female mice. Anatomical analysis of specific regions of the brain further revealed significant differences in Brd2+/− vs +/+ mice. Specifically, there were decreases in the numbers of GABAergic (parvalbumin- or GAD67-immunopositive) neurons along the basal ganglia pathway, i.e., in the neocortex and striatum of Brd2+/− mice, compared to Brd2+/+ mice. There were also fewer GABAergic neurons in the substantia nigra reticulata (SNR), yet there was a minor, possibly compensatory increase in the GABA producing enzyme GAD67 in these SNR cells. Further, GAD67 expression in the superior colliculus and ventral medial thalamic nucleus, the main SNR outputs, was significantly decreased in Brd2+/− mice, further supporting GABA downregulation. Our data show that the non-channel-encoding, developmentally critical Brd2 gene is associated with i) sex-specific increases in seizure susceptibility, ii) the development of spontaneous seizures, and iii) seizure-related anatomical changes in the GABA system, supporting BRD2's involvement in human IGE.

Neonatal androgen-dependent sex differences in lumbar spinal cord dopamine concentrations and the number of A11 diencephalospinal dopamine neurons

A(11) diencephalospinal dopamine (DA) neurons provide the major source of DA innervation to the spinal cord. DA in the dorsal and ventral horns modulates sensory, motor, nociceptive, and sexual functions. Previous studies from our laboratory revealed a sex difference in the density of DA innervation in the lumbar spinal cord. The purpose of this study was to determine whether sex differences in spinal cord DA are androgen dependent, influenced by adult or perinatal androgens, and whether a sex difference in the number of lumbar-projecting A(11) neurons exists. Adult male mice have significantly higher DA concentrations in the lumbar spinal cord than either females or males carrying the testicular feminization mutation (tfm) in the androgen receptor (AR) gene, suggesting an AR-dependent origin. Spinal cord DA concentrations are not changed following orchidectomy in adult male mice or testosterone administration to ovariectomized adult female mice. Administration of exogenous testosterone to postnatal day 2 female mice results in DA concentrations in the adult lumbar spinal cord comparable to those of males. Male mice display significantly more lumbar-projecting A(11) DA neurons than females, particularly in the caudal portion of the A(11) cell body region, as determined by retrograde tract tracing and immunohistochemistry directed toward tyrosine hydroxylase. These results reveal an AR-dependent sex difference in both the number of lumbar-projecting A(11) DA neurons and the lumbar spinal cord DA concentrations, organized by the presence of androgens early in life. The AR-dependent sex difference suggests that this system serves a sexually dimorphic function in the lumbar spinal cord.

Update on the role of substantia nigra pars reticulata in the regulation of seizures

The substantia nigra pars reticulata (SNR) represents an endogenous seizure suppressing system, which may be targeted to develop treatments for generalized or multifocal epilepsies. This review summarizes the region-, age-, and sex-specific features of the SNR-based seizure-controlling network.

Spatiotemporal expression of androgen receptors in the female rat brain during the oestrous cycle and the impact of exogenous androgen administration: a comparison with gonadally intact males

Little is known about the regulation and cellular distribution of androgen receptors (ARs) in female rodent brains at various stages of the oestrous cycle. This information is critical for further studies of androgen signalling in the regulation of brain function under physiological and pathophysiological conditions. In this report, we show that the distribution of AR immunoreactivity in the female rat brain is consistent with reported AR mRNA hybridisation signals in the male brain, except for the dentate gyrus of the hippocampus. Immunohistochemical and Western blot analyses performed herein revealed that the onset of region-specific changes in AR proteins was strongly correlated with circulating and ovarian levels of estradiol and testosterone across the oestrous cycle. During the metestrus and diestrus stages, however, the highest levels of AR expression were abolished by chronic dihydrotestosterone (DHT) treatment. This demonstrates that fluctuations in endogenous androgens are required for the regulation of AR expression in the female rat brain. Colocalisation studies revealed that: (1) anatomical variations in AR protein localisation existed between female and male brains, (2) AR immunoreactivity was both neuronal and non-neuronal, and (3) AR protein expression was lower in female rat brains at all stages of the oestrous cycle compared to age-matched males. Our results indicate the presence of regional sex differences in AR expression and changes in the proportion of AR between different subcellular compartments. Furthermore, DHT was found to down-regulate the level of AR in the subcellular compartment in females in a region-specific manner. As a whole, the present study provides the first step toward understanding the dynamics of AR expression and regulation in the brain during normal physiological conditions and for differences in neuronal androgen effects based on sex.

Androgen receptor in the neural tube of the mouse and chicken embryo

Androgen effects, mediated by the androgen receptor, regulate important cellular processes such as growth, proliferation, and differentiation. The presence of androgen receptor has been described in structures of the central nervous system, mainly in advanced fetuses, newborns, and adult animals. This study describes the presence and location of androgen receptor in early developmental stages of the nervous system. The androgen receptor mRNA was evidenced through reverse transcriptase-PCR and the androgen receptor protein by immunohistochemistry and western blot techniques in the cerebral vesicles of 9.5-day mouse embryos and chicken embryos at stages 8-17 of Hamburger and Hamilton. The androgen receptor protein was located in the nucleus of neuroepithelial cells throughout the neural tube.

Metabolic environment in substantia nigra reticulata is critical for the expression and control of hypoglycemia-induced seizures

Seizures represent a common and serious complication of hypoglycemia. Here we studied mechanisms of control of hypoglycemic seizures induced by insulin injection in fasted and nonfasted rats. We demonstrate that fasting predisposes rats to more rapid and consistent development of hypoglycemic seizures. However, the fasting-induced decrease in baseline blood glucose concentration cannot account for the earlier onset of seizures in fasted versus nonfasted rats. Data obtained with c-Fos immunohistochemistry and [14C]2-deoxyglucose uptake implicate a prominent involvement of the substantia nigra reticulata (SNR) among other structures in the hypoglycemic seizure control. This is supported by data showing that fasting decreases the SNR expression of K(ATP) channels, which link metabolism with activity, and is further confirmed with microinfusions of K(ATP) channel agonist and antagonist. Data obtained with whole-cell and perforated patch recordings from SNR neurons in slices in vitro demonstrate that both presynaptic and postsynaptic K(ATP) channels participate in the failure of the SNR to control hypoglycemic seizures. The results suggest that fasting and insulin-induced hypoglycemia can lead to impairment in the function of the SNR, leading thus to hypoglycemic seizures.

Sexually dimorphic expression of KCC2 and GABA function

GABA(A) receptors have an age-adapted function in the brain. During early development, they mediate depolarizing effects, which result in activation of calcium-sensitive signaling processes that are important for the differentiation of the brain. In more mature stages of development and in adults, GABA(A) receptors acquire their classical hyperpolarizing signaling. The switch from depolarizing to hyperpolarizing GABA(A)-ergic signaling is triggered through the developmental shift in the balance of chloride cotransporters that either increase (i.e. NKCC1) or decrease (i.e. KCC2) intracellular chloride. The maturation of GABA(A) signaling follows sex-specific patterns, which correlate with the developmental expression profiles of chloride cotransporters. This has first been demonstrated in the substantia nigra, where the switch occurs earlier in females than in males. As a result, there are sensitive periods during development when drugs or conditions that activate GABA(A) receptors mediate different transcriptional effects in males and females. Furthermore, neurons with depolarizing or hyperpolarizing GABA(A)-ergic signaling respond differently to neurotrophic factors like estrogens. Consequently, during sensitive developmental periods, GABA(A) receptors may act as broadcasters of sexually differentiating signals, promoting gender-appropriate brain development. This has particular implications in epilepsy, where both the pathophysiology and treatment of epileptic seizures involve GABA(A) receptor activation. It is important therefore to study separately the effects of these factors not only on the course of epilepsy but also design new treatments that may not necessarily disturb the gender-appropriate brain development.

Antiseizure effects of 5*-androstane-3*,7beta-diol may be independent of actions at estrogen receptor beta

Testosterone (T), the principal androgen secreted by the testes, can have antiseizure effects; however, the mechanism(s) underlying this action is not well understood. T is metabolized to dihydrotestosterone (DHT) by the enzyme 5*-reductase. DHT is then converted to 5*-androstane-3*,17beta-diol (3*-diol) by the enzyme 3*-hydroxysteroid dehydrogenase. T and DHT bind with high affinity to intracellular androgen receptors; however, 3*-diol does not. The mnemonic effects of 3*-diol are mediated in part through the beta isoform of estrogen receptors (ERbeta) in the hippocampus. As such, we investigated whether 3*-diol has antiseizure effects in mice that require action at ERbeta. 3*-Diol (2 mg/kg subcutaneously) was administered to wild-type C57/B6 mice and heterozygous and homozygous ERbeta knockout (betaERKO) mice 1 hour prior to administration of pentylenetetrazol (PTZ; 85 mg/kg intraperitoneally). Mice administered 3*-diol had significantly longer latencies to clonic seizure and death and lower seizure scores than did mice administered vehicle. This pattern of effects was observed in wild-type or betaERKO mice. Thus, for these mice, the antiseizure effects of 3*-diol for the chemoconvulsant PTZ occur independent of actions at ERbeta.

The visceromotor response to colorectal distention fluctuates with the estrous cycle in rats

The existence of a sex difference in several chronic pain syndromes and the fluctuation of symptoms during the menstrual cycle strongly suggest sex hormones are involved in pain processing. The mechanisms underlying these changes are not well understood. Using the colorectal distention model in the rat, we previously reported a sex difference in the response to distention [Ji Y, Murphy AZ, Traub RJ (2006) Sex differences in morphine induced analgesia of visceral pain are supraspinally and peripherally mediated. Am J Physiol Regul Integr Comp Physiol 291:R307-R314] and that ovariectomy decreased the responses to distention while estrogen replacement reversed the decrease [Ji Y, Murphy AZ, Traub RJ (2003) Estrogen modulates the visceromotor reflex and responses of spinal dorsal horn neurons to colorectal stimulation in the rat. J Neurosci 23:3908-3915], suggesting estrogen increases visceral nociception. In the present study we tested the hypothesis that the visceromotor response to colorectal distention fluctuates with the estrous cycle. Three measurements (vaginal smears, uterine tube weight and plasma estrogen concentration) were used to determine the estrous phase. Comparison of the visceromotor response threshold and magnitude was made between proestrus and metestrus/diestrus. Our experiment demonstrated that the distention threshold was significantly lower in proestrus (median: 15 mm Hg) as compared with metestrus/diestrus (median: 25 mm Hg); and the magnitude of the visceromotor response to graded intensities of colorectal distentions (20, 40, 60, 80 mm Hg) was significantly higher in proestrus. The results indicate that the visceromotor response fluctuates with estrous phase, providing evidence for endogenous estrogen modulation of visceral nociceptive processing that could contribute to sex differences.

Tearful relationships? Sex, hormones, the lacrimal gland, and aqueous-deficient dry eye

Sex and the endocrine system exert a significant influence on the physiology and pathophysiology of the lacrimal gland. The purpose of this article is to briefly review the nature and magnitude of these interactions between sex, hormones and lacrimal tissue, and to address how they may relate to the pathogenesis of aqueous-deficient dry eye. Towards this end, this article has a 3-fold approach: first, to summarize the influence of androgens, estrogens, glucocorticoids, mineralocorticoids, retinoic acid, prolactin, alpha-melanocyte stimulating hormone, adrenocorticotropic hormone, luteinizing hormone, follicle-stimulating hormone, growth hormone, thyroid-stimulating hormone, arginine vasopressin, oxytocin, thyroxine, parathyroid hormone, insulin, glucagon, melatonin, human chorionic gonadotropin and cholecystokinin on the structure and function of the lacrimal gland; second, to discuss the mechanism of action of each hormone on lacrimal tissue; and third, to discuss the clinical relevance of the endocrine-lacrimal gland interrelationship, with a particular focus on each hormone's role (i.e. if relevant) in the development of aqueous-tear deficiency.

Distribution and localization patterns of estrogen receptor-beta and insulin-like growth factor-1 receptors in neurons and glial cells of the female rat substantia nigra: localization of ERbeta and IGF-1R in substantia nigra

Although several studies have focused on the neuroprotective effects of estrogen (E2) on stroke, there have been tantalizing reports on the potential neuroprotective role of E2 in degenerative neuronal diseases such as Alzheimer's and Parkinson's (PD). In animal models of PD, E2 protects the nigrostriatal dopaminergic (DA) system against neurotoxins. However, little is known about the cellular and molecular mechanism(s) involved by which E2 elicits its neuroprotective effects on the nigrostriatal DA system. A preferred mechanism for neuroprotection is the interaction of E2 with specific neuroprotective growth factors and receptors. One such neuroprotective factor/receptor system is insulin-like growth factor-1 (IGF-1). E2 neuroprotective effects in the substantia nigra (SN) DA system have been shown to be dependent on IGF-1. To determine whether E2 also interacts with the IGF-1 receptor (IGF-1R) and to determine the cellular localization of estrogen receptor (ER) and IGF-1R, we compared the distribution of ER and IGF-1R in the SN. Stereological measurements revealed that 40% of the subpopulation of tyrosine hydroxylase-immunoreactive (TH-ir) SN pars compacta (SNpc) DA neurons are immunoreactive for estrogen receptor-beta (ERbeta). No immunolabeling for ERalpha was observed. In situ hybridization and immunocytochemistry studies confirmed the expression of IGF-1R mRNA and revealed that almost all TH-ir SNpc DA neurons were immunoreactive for IGF-1R, respectively. Moreover, one-third of glial fibrillary acidic protein (GFAP-ir) cells in the SN were ERbeta-ir, and 67% of GFAP-ir cells expressed IGF-1R-ir. Therefore, the localization of ERbeta and IGF-1R on SNpc DA neurons and astrocytes suggests a modulatory role of E2 on IGF-1R, and this modulation may affect neuroprotection.

Beta-estradiol increases dentate gyrus inhibition in female rats via augmentation of hilar neuropeptide Y

The dentate gyrus filters incoming activity into the hippocampus proper. It plays a role in learning and memory and in pathological states such as epilepsy. Some of hilar interneurons of the dentate gyrus express neuropeptide Y (NPY), which modulates granule cell activity. A subpopulation of the NPY-expressing inhibitory interneurons is sensitive to seizure-induced damage. Pretreatment with beta-estradiol in ovariectomized rats protects hilar interneurons against seizure-induced injury, including the NPY-containing damage-sensitive subpopulation. Here, we demonstrate that beta-estradiol enhances NPY expression within the hilar interneurons. In vitro paired-pulse stimulation of the mixed perforant path revealed beta-estradiol-induced augmentation of granule cell network inhibition, which at interstimulus intervals between 200 and 300 ms (corresponding to approximately 3-5 Hz) was NPY sensitive and involved Y1 receptors, whereas it was insensitive to GABA(B) or metabotropic glutamate receptor antagonists. Additionally, beta-estradiol pretreatment attenuated propagation of low-frequency (3.3 or 5 Hz) burst activity through the dentate gyrus. Scavenging endogenous NPY by intracerebroventricular administration of anti-NPY antibody accelerated kainic acid-induced seizure onset and increased seizure-induced neuronal damage in the hilus compared with rats treated with beta-estradiol alone. Together, we show that beta-estradiol upregulates hilar NPY and that this leads to enhancement in dentate gyrus inhibition of incoming frequencies between 3 and 5 Hz. Such frequencies are similar to the discharge frequencies recorded during seizure initiation in some patients with epilepsy. Thus, beta-estradiol-induced NPY-sensitive filtering of 3-5 Hz frequencies may be an important regulator of incoming seizure activity, but it could also serve a physiological purpose in modulating information flow into the hippocampus proper.

Neuroprotection by estrogen against MPP+-induced dopamine neuron death is mediated by ERalpha in primary cultures of mouse mesencephalon

Estrogen involvement in neuroprotection is now widely accepted, although the specific molecular and cellular mechanisms of estrogen action in neuroprotection remain unclear. This study examines estrogenic effects in a mixed population of cells in attempts to identify the contributing cells that result in estrogen-mediated neuroprotection. Utilizing primary mesencephalic neurons, we found expression of both estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) with a predominance of ERalpha on both dopamine neurons and astrocytes. We also found that 17beta-estradiol protects dopamine neurons from injury induced by the complex I inhibitor, 1-methyl-4-phenyl pyridinium (MPP(+)) in a time- and ER-dependent manner. At least 4 h of estrogen pre-treatment was required to elicit protection, an effect that was blocked by the ER antagonist, ICI 182,780. Moreover, ERalpha mediated the protection afforded by estrogen since only the ERalpha agonist, HPTE, but not the ERbeta agonist, DPN, protected against dopamine cell loss. Since glial cells were shown to express significant levels of ERalpha, we investigated a possible indirect mechanism of estrogen-mediated neuroprotection through glial cell interaction. Removal of glial cells from the cultures by application of the mitotic inhibitor, 5-fluoro-2'-deoxyuridine, significantly reduced the neuroprotective effects of estrogen. These data indicate that neuroprotection provided by estrogen against MPP(+) toxicity is mediated by ERalpha and involves an interplay among at least two cell types.

Estrogen and the development and protection of nigrostriatal dopaminergic neurons: concerted action of a multitude of signals, protective molecules, and growth factors

The nigrostriatal dopamine system comprises the dopaminergic neurons located in the ventral midbrain, their axonal connections to the forebrain, and their direct cellular target cells in the striatal complex, i.e. GABAergic neurons. The major function of the nigrostriatal dopaminergic unit is the coordination and fine tuning of motor functions at the extrapyramidal level. Numerous biologically active factors including different types of growth factors (neurotrophins, members of the TGFbeta family, IGFs) and peptide/steroid hormones have been identified in the past to be implicated in the regulation of developmental aspects of this neural system. Some of these developmentally active determinants have in addition been found to play a crucial role in the mediation of neuroprotection concerning dopaminergic neurons. Estrogen was identified as such a compound interfering with embryonic neuronal differentiation and cell survival. The physiological mechanisms underlying these effects are very complex and include interactions with other developmental signals (growth factors), inflammatory processes as well as apoptotic events, but also require the activation of nonneuronal cells such as astrocytes. It appears that estrogen is assuming control over or at least influences a multitude of developmental and protective cellular mechanisms rather than taking over the part of a singular protagonist.

Sex-specific densities of estrogen receptors alpha and beta in the subnuclei of the nucleus tractus solitarius, hypoglossal nucleus and dorsal vagal motor nucleus weanling rats

In rats ventilatory responses to N-methyl-d-aspartate (NMDA) receptor modulation are sexually dimorphic and may be altered by manipulating brain levels of estrogen receptors. Here we used image analysis and immunohistochemistry in weanling male and female rats to quantitate areas and densities of ER alpha and ER beta-positive neurons within medullary regions associated with cardiopulmonary regulation including the hypoglossal nucleus, subnuclei of the nucleus of the solitary tract (NTS), and the dorsal motor nucleus of the vagus. Weanling rats were selected because ventilation, metabolic rate, and body and brain weights are comparable at this age and there are no large fluctuations in plasma hormone levels. Females, relative to males, had smaller areas in the A2 region and parts of the NTS. Counts and densities for ER alpha were greater in females than males in almost all regions studied. In contrast sex differences in ER beta were found in fewer nuclei, but in those higher counts and densities were noted in females. In general, ER beta-positive neurons in the brainstem regions examined were less prevalent than ER alpha neurons. Thus, in weanling rats sex affected ER alpha and ER beta neuronal densities in brainstem regions associated with cardiopulmonary regulation that may be responsible for sex differences in control of breathing.

Prenatal exposure to betamethasone decreases anxiety in developing rats: hippocampal neuropeptide y as a target molecule

Repeated antenatal administration of betamethasone is frequently used as a life-saving treatment in obstetrics. However, limited information is available about the outcome of this therapy in children. The initial prospective studies indicate that there are behavioral impairments in children exposed to repeated courses of prenatal betamethasone during the third trimester of pregnancy. In this study, pregnant rats received two betamethasone injections on day 15 of gestation. Using immunohistochemistry, the expression of a powerful anxiolytic molecule neuropeptide Y (NPY) was determined on postnatal day (PN) 20 in the hippocampus and basolateral amygdala (structures related to anxiety and fear) of the offspring. Prenatal betamethasone exposure induced significant increases in NPY expression in the hippocampus but not in the amygdala. Indeed, behavioral tests in the offspring, between PN20 and PN22 in the open field, on the horizontal bar, and in the elevated plus maze, indicated decreases in anxiety, without impairments in motor performance or total activity. Decreased body weight in betamethasone-exposed rats confirmed long-lasting effects of prenatal exposure. Thus, prenatal betamethasone treatment consistently increases hippocampal NPY, with decreases in anxiety-related behaviors and hippocampal role in anxiety in rats. Animal models may assist in differentiation between pathways of the desired main effect of the antenatal corticosteroid treatment and pathways of unwanted side effects. This differentiation can lead to specific therapeutic interventions directed against the side effects without eliminating the beneficial main effect of the corticosteroid treatment.

Estrogen receptors and human disease

Estrogens influence many physiological processes in mammals, including but not limited to reproduction, cardiovascular health, bone integrity, cognition, and behavior. Given this widespread role for estrogen in human physiology, it is not surprising that estrogen is also implicated in the development or progression of numerous diseases, which include but are not limited to various types of cancer (breast, ovarian, colorectal, prostate, endometrial), osteoporosis, neurodegenerative diseases, cardiovascular disease, insulin resistance, lupus erythematosus, endometriosis, and obesity. In many of these diseases, estrogen mediates its effects through the estrogen receptor (ER), which serves as the basis for many therapeutic interventions. This Review will describe diseases in which estrogen, through the ER, plays a role in the development or severity of disease.

Sex-dependent maturation of GABAA receptor-mediated synaptic events in rat substantia nigra reticulata

The substantia nigra pars reticulata (SNR) plays important roles in movement and, in an age- and sex-dependent manner, in seizure control. GABAergic synaptic transmission is critical in both normal development and seizures. In many neuronal types it is excitatory early in development and later switches to the mature hyperpolarizing type. We assessed the time course of the switch of GABAA receptor-mediated postsynaptic currents (PSCs) in anterior SNR neurons of male and female developing rats using the gramicidin perforated patch clamp technique. The switch occurred in males around postnatal day (PN) 17 and in females around PN10. This sex dimorphism may play a role in several other recognized sex differences in the development of SNR and in its regulatory role in seizures.

Estrogen receptor beta in health and disease

Estrogens, acting through its two receptors, ESR1 (hereafter designated ER alpha) and ESR2 (hereafter designated ER beta), have diverse physiological effects in the reproductive system, bone, cardiovascular system, hematopoiesis, and central and peripheral nervous systems. Mice with inactivated ER alpha, ER beta, or both show a number of interesting phenotypes, including incompletely differentiated epithelium in tissues under steroidal control (prostate, ovary, mammary, and salivary glands) and defective ovulation reminiscent of polycystic ovarian syndrome in humans (in ER beta-/- mice), and obesity, insulin resistance, and complete infertility (both in male and female ER alpha-/- mice). Estrogen agonists and antagonists are frequently prescribed drugs with indications that include postmenopausal syndrome (agonists) and breast cancer (antagonists). Because the two estrogen receptors (ERs) have different physiological functions and have ligand binding pockets that differ enough to be selective in their ligand binding, opportunities now exist for development of novel ER subtype-specific selective-ER modulators.

Effects of 17β-estradiol on the spontaneous activity of substantia nigra neurons: Evidence for a non-genomic mechanism

Clinical and experimental evidence suggests that female sex hormones (estradiol and progesterone) affect structures in the central nervous system that are involved in the control of movement. Using conventional electrophysiological techniques to record extracellular action potentials in the substantia nigra of urethane-anesthetized rats, it was found that microiontophoretic applications of 17beta-estradiol were able to modify the spontaneous activity of nigral neurons. 17beta-estradiol produced significant changes in the firing frequency (excitation and inhibition) and increased the rhythmicity of the majority of cells studied. These changes appear to be influenced by the sex and the hormonal status of the animal. Effects are of short latency and are not blocked by the administration of tamoxifen. We conclude that estradiol produces changes in the firing rate and discharge pattern of nigral cells in the urethane-anesthetized rat via a non-genomic mechanism.

Long-term cosequences of intrahippocampal kainate injection in the Proechimys guyannensis rodent

The Proechimys guyannensis (PG), a spiny rodent specie living in the Amazonian region has been recently studied as an animal model of anti-convulsant mechanisms. The PG was found to be resistant to the administration of the muscarinic cholinergic agonist pilocarpine or the amygdala kindling development. This study examined the susceptibility of this animal species to the intrahippocampal kainic acid (KA) injection. Electrographic, behavioral and neuropathological changes induced by intrahippocampal KA injections were analyzed. PG showed to be extremely sensitive to the acute effects of the KA injection. Although the EEG findings in PG rodents were similar to those typically obtained in Wistar rats the pattern of electrographic activity in PG animals was longer than in Wistar rats. Neuropathological examinations of PG brains that survived KA-induced SE revealed severe cell loss in CA1/CA3 areas of the hippocampus, an extensive cell dispersion in the hilus of DG at the injected site with mossy fiber sprouting in the dentate gyrus supragranular layer. None of PG animals presented spontaneous seizures during the 120 days of observation. These findings confirm our previous observation on the resistance of this animal specie to experimental models of limbic epilepsy.

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.

GABA receptors as broadcasters of sexually differentiating signals in the brain

Epileptic seizures are more common in males than in females. One of the areas that has recently been implicated in the higher susceptibility of males to seizures is the substantia nigra reticulata (SNR). Several studies support the existence of phenotypic differences between male and female infantile SNR neurons, and particularly in several aspects of the GABAergic system, including its ability to control seizures. We have recently found that at postnatal day 14-17 (PN14-17) rats, which are equivalent to infants, activation of GABA(A) receptors has different physiological effects in male and female SNR neurons. This is likely due to the differences in the expression of the neuronal-specific potassium-chloride co-transporter KCC2, which regulates the intracellular chloride concentration. In male PN14-17 SNR neurons, GABA(A)-receptor activation with muscimol causes depolarization and increments in intracellular calcium concentration and the expression of calcium regulated genes, such as KCC2. Blockade of L-type voltage-sensitive calcium channels (L-VSCC) by nifedipine decreases KCC2 mRNA expression. However, in PN14-17 females, muscimol hyperpolarizes the SNR neurons, does not increase intracellular calcium, and decreases KCC2 mRNA expression. In PN15 females, nifedipine has no effect on KCC2 mRNA expression in the SNR. This sexually dimorphic function of GABA(A) receptors also creates divergent patterns of estradiol signaling. In male PN15 rats, estradiol decreases KCC2 mRNA expression in SNR neurons. Pretreatment with the GABA(A)-receptor antagonist bicuculline or with nifedipine, prevents the appearance of estradiol-mediated downregulation of KCC2 mRNA expression. In contrast, in PN15 females, estradiol does not influence KCC2 expression. These findings show that, in infantile rats, drugs or conditions that modulate the activity of GABA(A) receptors or L-VSCCs have different effects on the differentiation of the SNR. As a result, they have the potency of causing long-term changes in the function of the SNR in the control of seizures, movement, and the susceptibility to and course of epilepsy and movement disorders.

Seizures in the Developing Brain

PURPOSE

Development and sex hormones are important determinants of seizure susceptibility. Seizures develop in the immature brain more readily than in the mature brain. Male children experience a higher incidence of epilepsy or unprovoked seizures than do female children. Sex-specific differences in the development of seizure-suppressing neuronal networks may account, at least in part, for this increased age- and sex-related susceptibility to seizures. The control of seizures can be influenced by the substantia nigra pars reticulata (SNR) in an age- and sex-specific manner. In the adult male rat SNR, two topographically discrete regions (SNRanterior and SNRposterior) mediate distinct effects on seizures, by using divergent output networks in response to localized infusions of gamma-aminobutyric acid (GABA)A agents, such as muscimol. The GABAA-sensitive "anticonvulsant" region is located in the SNRanterior, whereas the GABAA-sensitive "proconvulsant region is in the SNRposterior. In immature postnatal day (PN)15-21 male rats, the SNR is not topographically segregated, and GABAAergic drug infusions produce similar effects when applied in the SNRanterior or SNRposterior. Only a GABAA-sensitive proconvulsant network is evident. By contrast, female SNR does not contain any region that mediates muscimol-related proconvulsant effects. As with the adult, immature female rats do not develop a proconvulsant SNR region at any age.

METHODS

We measured the effects of SNR muscimol infusions on seizures in male rats castrated at birth to better understand the effects of testosterone on the formation of age- and sex-specific features of the SNR.

RESULTS

Neonatal castration permanently alters the maturation of the muscimol-sensitive SNR effect on seizures. The SNR of neonatally castrated rats develops functionally like the "female" SNR. The "proconvulsant" SNR region does not develop in the absence of testosterone in the immediate postnatal period. The "male" type of SNR effects can be induced in neonatally castrated rats by restoration of testosterone levels or in female rats by artificially increasing testosterone levels. Dihydrotestosterone and estrogen, produced by the reduction and aromatization of testosterone, respectively, are the direct mediators of testosterone actions. At PN0, only beta estrogen receptors are equally expressed in the SNRs of males and females and may be responsible for testosterone-mediated effects in both sexes.

CONCLUSIONS

The phenotype of SNR GABAergic neurons, as characterized by GABAA-receptor subunit composition, by muscimol-induced electrophysiologic responses, and by connectivity of output networks each may be altered by the presence of testosterone. Higher KCC2 messenger RNA (mRNA) expression in female PN15 SNR neurons compared with males may be responsible for sex-related differences in muscimol-induced electrophysiologic responses. In summary, a growing body of compelling evidence identifying sex-related differences in the SNR implicates postnatal testosterone as a critical factor in the development of pro- or anticonvulsant circuits. The recognition of sex- and age-related features in the SNR holds the promise that these findings can be translated into the development of specific and effective treatments for seizure disorders.

Tyrosine hydroxylase expression is affected by sexual vigor and social environment in male Cnemidophorus inornatus

Although the distribution of catecholamine-synthesizing cells has been described for a variety of taxa, less is known about the functional significance of particular populations in nonmammalian species, especially reptiles. To understand the role of these populations in the display of social behaviors in lizards, we studied the interactive effects of sexual vigor (sexually vigorous vs. sluggish) and social condition (housing in isolation vs. with females) on the number and somal areas of cells expressing tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine synthesis, in male whiptail lizards, Cnemidophorus inornatus. We found that, regardless of social condition, sexually vigorous males had more TH-immunoreactive (TH-ir) cells in the dorsal hypothalamus (DH) relative to sluggish males. Sexually vigorous males also had more TH-ir cells in the substantia nigra pars compacta (SNpc), but this difference was significant only among males housed with females. Sexually vigorous males that had been housed with females had smaller TH-ir cells in the preoptic area (POA) than vigorous males housed in isolation. On the other hand, no significant differences were found in the anterior hypothalamus. These results highlight the regional heterogeneity in the plasticity of TH expression and suggest that, just as in other species, the DH, SNpc, and POA might be involved in the expression of social behaviors and in behavioral plasticity following social experiences in lizards.

Role of sex hormones in the sexually dimorphic expression of KCC2 in rat substantia nigra

KCC2 is a neuronal-specific potassium chloride cotransporter. The level of KCC2 expression is a factor determining whether GABA(A) receptor agonists depolarize or hyperpolarize neurons. Substantia nigra reticulata (SNR) neurons of male postnatal day 15 (PN15) rats have low KCC2 mRNA expression and respond to GABA(A) receptor activation with depolarization and activation of calcium-regulated gene expression. Female PN15 SNR neurons have high KCC2 mRNA expression and GABA(A) receptor agonists cannot activate calcium-dependent signaling processes. We investigate whether sex hormones regulate KCC2 mRNA expression in PN15 rat SNR. Using in situ hybridization, we studied the effects of acute (4 h) or prolonged (52 h) subcutaneous (s.c.) administration of testosterone (100 microg), dihydrotestosterone (180 microg) or 17beta-estradiol benzoate (5 microg) on KCC2 mRNA expression in male and female PN15 rat SNR. Different doses of estradiol (1 and 10 microg s.c., 4 h) were also acutely administered in female PN15 rats. Controls received oil injections. Separate groups of PN15 male rats were pretreated with antagonists of L-type voltage-sensitive calcium channels (L-VSCCs) [nifedipine, 100 mg/kg s.c.] or GABA(A) receptors [bicuculline, 2 mg/kg intraperitoneally (i.p.)] or their vehicles, 30 min before estradiol (5 microg s.c., 4 h). Testosterone and dihydrotestosterone upregulated KCC2 mRNA in both sexes. Estradiol downregulated KCC2 mRNA in males but not in females. Both acute and prolonged hormonal administration had similar effects. In male PN15 SNR, nifedipine and bicuculline decreased KCC2 mRNA acutely and prevented further downregulation of KCC2 mRNA by estradiol. Estradiol therefore downregulates KCC2 mRNA in male PN15 SNR, by interacting with the GABA(A) receptor and L-VSCC signaling pathway.

Distribution of estrogen receptor alpha and beta immunoreactive profiles in the postnatal rat brain

The present study was conducted to identify the localization and possible contribution of the two estrogen receptor (ER) subtypes in the rat brain at postnatal (P) days 3, 7 and 14. Evaluation of the distribution of ERalpha and ERbeta immunoreactive (ir) nuclei did not reveal gender differences at the developmental point times examined. With the exception of the cerebral cortex, the pattern of staining for these ERs was unchanged across the postnatal ages examined. The distribution of ERalpha-ir nuclei was wider than ERbeta-ir during brain development. From P3, ERbeta and ERalpha-ir nuclei were found in different regions of the cerebral cortex, basal forebrain, amygdala, thalamus, hypothalamus, mesencephalon, pons, cerebellum and medulla oblongata. In addition, ERalpha-ir nuclei were exclusively detected in the hippocampal subfields, epithalamus and in several circumventricular organs. ERalpha and ERbeta dual immunofluorescence revealed positive nuclei in the medial part of the bed nucleus of the stria terminalis, periventricular preoptic nucleus and in caudal aspects of the ventrolateral part of the ventromedial hypothalamic nucleus. Although the functional significance of the dual expression of both ERs within the same nuclei remains unknown, it is possible that ERs play different roles in gene regulation within the same cell. The presence of ERs in diverse brain regions through early postnatal periods supports a potential role for estrogens in neural differentiation.

Sex differences in GABA(A)ergic system in rat substantia nigra pars reticulata

The substantia nigra pars reticulata (SNR) is involved in the control of movement disorders including seizures through its GABAergic neurons. Microinfusions of muscimol (a GABA(A) receptor agonist) produce specific effects on seizures depending on sex, infusion site (SNR(anterior) or SNR(posterior)) and age. To assess whether these effects are due to sex differences in GABAergic indices within the SNR we analyzed the expression of alpha(1) subunit mRNA of the GABA(A) receptor and the levels of GABA immunoreactivity (IR) of male and female rats at postnatal day 15 (PN15) and PN30. In each age, within the same SNR region, expression of alpha(1) subunit mRNA and intensity of GABA IR per neuron was higher in females compared to males. At PN15, in both sexes, there were no regional differences in expression of alpha(1) subunit mRNA and intensity of GABA IR. However, at PN30 in both sexes, expression of alpha(1) subunit mRNA and intensity of GABA IR per cell was higher in SNR(anterior) than in SNR(posterior). These results demonstrate that expression of alpha(1) subunit mRNA for GABA(A) receptor and levels of GABA IR in the SNR are sex- and site-specific, which may contribute to sex-, regional- and age-related differences in the expression of movement disorders and seizures.

Testosterone regulates androgen and estrogen receptor immunoreactivity in rat substantia nigra pars reticulata

At postnatal day (PN)1, there are sex differences in gonadal receptor expression in the rat substantia nigra pars reticulata (SNR). Male pups have lower levels of androgen receptor (AR) and estrogen receptor (ER)beta immunoreactivity (IR) compared to female pups, while ERalpha IR is equally expressed in the two sexes. To test whether these differences are due to sex differences in testosterone exposure, we injected female pups with testosterone propionate (TP) on the day of birth and analyzed the levels of AR and ER IR at PN1. TP-treated females have lower levels of AR and ERbeta IR than control, while there are no differences in the levels of ERalpha IR. TP treatment did not affect the number of AR and ER expressing cells. The regulation of SNR AR and ERbeta IR by testosterone may be important for the development of sex-specific functional systems involved in motor control.