Ovariectomy aggravates convulsions and hippocampal gamma-aminobutyric acid inhibition induced by cyclosporin A in rats

GABA System Modifications During Periods of Hormonal Flux Across the Female Lifespan

The female lifespan is marked by periods of dramatic hormonal fluctuation. Changes in the ovarian hormones estradiol and progesterone, in addition to the progesterone metabolite allopregnanolone, are among the most significant and have been shown to have widespread effects on the brain. This review summarizes current understanding of alterations that occur within the GABA system during the major hormonal transition periods of puberty, the ovarian cycle, pregnancy and the postpartum period, as well as reproductive aging. The functional impacts of altered inhibitory activity during these times are also discussed. Lastly, avenues for future research are identified, which, if pursued, can broaden understanding of the GABA system in the female brain and potentially lead to better treatments for women experiencing changes in brain function at each of these hormonal transition periods.

Activation of Estrogen Receptor β in the Lateral Habenula Improves Ovariectomy-Induced Anxiety-Like Behavior in Rats

Background

Loss of estrogen due to menopause or ovarian resection is involved in the development of anxiety, which negatively impacts work productivity and quality of life. Estrogen modulates mood by binding to estrogen receptors in the brain. Estrogen receptor beta (ERβ) is highly expressed in the lateral habenula (LHb), a key site for controlling the activities of dopaminergic neurons in the ventral tegmental area (VTA) and serotoninergic neurons in the dorsal raphe nucleus (DRN) that are known to be involved in anxiety.

Methods

In this study, we examined the role of LHb in the anxiolytic-like effect of estrogen in ovariectomized (OVX) rats. The establishment of OVX anxiety model was validated in behavioral tests, including elevated plus maze (EPM) and mirror chamber maze (MCM) tasks. The expression of c-Fos in the LHb neurons was analyzed by immunohistochemistry, and monoamine neurotransmitter levels in related nuclei were analyzed using high-performance liquid chromatography (HPLC).

Results

Estrogen-treated OVX rats showed a lower degree of anxiety-like behavior than OVX rats. OVX rats showed anxiety-like behavior and low monoamine levels in the DRN and VTA compared with sham operated and estrogen-treated OVX rats. c-Fos expression in the LHb was higher than that in the sham operated and estrogen-treated OVX rats. Intra-LHb injection of the ERβ-selective agonist diarylprepionitrile (DPN) reduced expression of c-Fos (a neuronal activity marker) and anxiety-like behavior in OVX rats, but not in normal rats, as evidenced by increased time spent in EPM open areas and the MCM mirror chamber. These changes coincided with higher levels of serotonin and dopamine in the DRN and higher dopamine levels in the VTA in OVX rats receiving intra-LHb DPN compared with those receiving vehicle injection.

Conclusion

These results suggest that OVX-induced anxiety-like behavior may be associated with increased LHb activity. DPN may inhibit LHb activity to improve anxiety-like behavior in OVX rats by increasing monoamine neurotransmitter levels in the DRN and VTA.

Anti-climacterium effects of pomegranate concentrated solutions in ovariectomized ddY mice

In the present study, the complex anti-climacterium potential of standardized pomegranate concentrated solution (PCS) was investigated using bilateral ovariectomy (OVX) female ddY mice. Changes in body weight and gain during experimental periods, food consumption, serum estradiol levels, total body and abdominal fat densities, abdominal fat pads, and uterus weights were observed, along with the histopathology of abdominal fat pads and uterus for anti-obesity and estrogenic effects. In addition, liver weights, serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) levels, and histopathological inspections were performed to explore the hepato-protective effects. Serum total cholesterol (TC), low density lipoprotein (LDL), high density lipoprotein, and triglyceride (TG) levels were monitored for hypolipidemic effects with total body and femur mean bone mineral density (BMD), right femur wet, dry and ash weights, strength, serum osteocalcin, bone-specific alkaline phosphatase (bALP) contents, and histological and histomorphometrical analyses for anti-osteoporosis activity. As a result of OVX, notable increases in body weight and gains, food consumption, abdominal fat mass densities, weights of abdominal fat pads deposited in the abdominal cavity, and serum AST, ALT, TC, LDL, TG, and osteocalcin levels were observed, along with decreases in the uterus, liver, and femur weights, mean total body and femur BMD, femur strength, serum bALP, and estradiol levels. In addition, marked hypertrophic alterations in adipocytes located in the deposited abdominal fat pads, liver steatosis, uterine disused atrophic changes, and decreases in bone mass and structures of the femur were also observed in OVX control mice with significant increases in bone resorption markers based on histopathological and histomorphometrical analysis. However, these estrogen-deficient climacterium symptoms were significantly (P<0.05 or P<0.01) inhibited after 84 days of continuous treatment with estradiol and PCS (1, 2 and 4 ml/kg), respectively. The present results suggested that PCS was able to effectively inhibit or refine the climacterium symptoms, including obesity, hyperlipidemia, hepatic steatosis, and osteoporosis, induced by OVX in ddY mice.

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.

Female ovarian steroids in epilepsy: a cause or remedy

In this article, we review published preclinical and clinical studies that examine the role of female ovarian steroids (estrogen and progesterone) in epilepsy. Its effects on the reproductive and endocrine system are well known but a large and growing body of evidences indicates that the hormones also exert neuroprotective effects on the central nervous system. Estrogen crosses the blood-brain barrier due to its low molecular weight and lipophilic properties and easily reaches the neuronal tissue. Estrogens and progesterone influence neuronal activity and are important for normal brain functions. It is commonly accepted that estrogens may increase neuronal excitability and thus mediate proconvulsant effects whereas in case of progesterone, various preclinical and clinical studies have proved that progesterone shows anticonvulsant effects. To concise our review we concluded that the effects of estrogens and progesterone on seizures depend on various factors, such as treatment duration and latency prior to the seizure testing, dose, hormonal status, the seizure type/model used and sex.

Long-term effects of ageing and ovariectomy on aversive and recognition memory and DNA damage in the hippocampus of female rats

OBJECTIVE

This study investigated the influence of ageing - in particular the decrease of gonadal hormone levels during the ageing process - on the memory and the levels of DNA damage in the hippocampus of female rats.

METHODS

Three groups of female Wistar rats were investigated: Group I consisted of non-ovariectomised, adult animals (6 months old); Group II consisted of non-ovariectomised, aged animals (18 months old); and Group III consisted of ovariectomised, aged animals (18 months old). The memory of the animals in these groups was examined via novel object recognition and inhibitory avoidance tests. The hippocampus tissue samples of all animals were obtained via biopsy and used to quantify the DNA damage using a Comet Assay.

RESULTS

According to our findings, the process of ageing results in a change during the behavioural tests. To prevent genotoxic damage to the hippocampus caused by the ageing process, lowered hormone levels seem to be part of a protective biochemical mechanism in the body of rats. Animals that were previously submitted to an ovariectomy adapted better to these lower levels of hormones.

CONCLUSION

Our results indicate that ovariectomy can provide beneficial long-term effects on the memory. However, this could be specific to the kind of memory examined, as the aversive memory deficits caused by ageing were not affected by ovariectomy.

Sex and hormonal influences on seizures and epilepsy

Epilepsy is the third most common chronic neurological disorder. Clinical and experimental evidence supports the role of sex and influence of sex hormones on seizures and epilepsy as well as alterations of the endocrine system and levels of sex hormones by epileptiform activity. Conversely, seizures are sensitive to changes in sex hormone levels, which in turn may affect the seizure-induced neuronal damage. The effects of reproductive hormones on neuronal excitability and seizure-induced damage are complex to contradictory and depend on different mechanisms, which have to be accounted for in data interpretation. Both estradiol and progesterone/allopregnanolone may have beneficial effects for patients with epilepsy. Individualized hormonal therapy should be considered as adjunctive treatment in patients with epilepsy to improve seizure control as well as quality of life.

Females, their estrogens, and seizures

Estrogens are essential for normal brain functions. The effects of estrogens on seizures are contradictory. More studies are necessary to determine under which conditions the estrogens have proconvulsant effects and when the estrogens may have beneficial action in patients with epilepsy.

Immunosuppressant neurotoxicity in rat brain models: oxidative stress and cellular metabolism

Coadministration of the calcineurin inhibitor cyclosporine (CsA) and the mTOR inhibitors sirolimus (SRL) or everolimus (RAD) increases the efficacy of immunosuppression after organ transplantation. Neurotoxicity of CsA is a major clinical problem. Our goal was to assess the effects of CsA, SRL, and RAD on brain cell metabolism. The studies included the comparison of immunosuppressant-mediated effects on glucose metabolism, energy production, and reactive oxygen species (ROS) formation in perfused rat brain slices, primary rat astrocytes, and C6 glioma cells. In brain slices and astrocytes, CsA inhibited Krebs cycle metabolism, while activating anaerobic glycolysis, most likely to compensate for the inhibition of mitochondrial energy production. SRL and RAD inhibited cytosolic glycolysis but did not cause changes in mitochondrial energy production. CsA + SRL inhibited Krebs cycle and glycolysis, thus reducing the ability of the cell to compensate for the negative effects of CsA on mitochondrial nucleoside triphosphate synthesis. In contrast to SRL at the concentrations tested, RAD reduced the CsA-induced ROS formation and antagonized CsA-induced effects on glucose and energy metabolism. Surprisingly, in C6 cells, SRL and RAD exposure resulted in high ROS concentrations without significant impairment of cell metabolism. Our results suggested that SRL enhances CsA-induced ROS formation and negative metabolic effects in brain cells, while RAD seems to antagonize the CsA effects. However, the three models showed different metabolic responses when challenged with the study drugs. In contrast to SRL, RAD enhances ROS formation in C6 glioma cells but has only minor effects on normal rat brain tissue.

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

Excitability of the motor cortex during ovulatory and anovulatory cycles: a transcranial magnetic stimulation study

OBJECTIVE

The pathophysiology of catamenial diseases such as epilepsy is unclear. Therefore, we investigated changes in cortical excitability during anovulatory and ovulatory cycles.

PATIENTS AND METHODS

Using transcranial magnetic stimulation (TMS), eight healthy women were investigated during anovulatory and 12 during ovulatory cycles. On days 8, -14, -7 and 2 of the cycle, resting motor threshold (RMT), cortical silent period (CSP), intracortical inhibition (ICI) and intracortical facilitation (ICF) were investigated. Repeated-measures analysis of variance (anova) and nonparametric methods were used for statistical analysis.

RESULTS

A trend was seen for group by phase interaction regarding ICI (F = 2.5, P = 0.10). ICI varied during anovulatory cycles (median: 51.0% on day 8; 45.3% on day -14, 51.0% on day -7, and 28.6% on day 2; P = 0.040), mainly because of an increased inhibition on day 2. ICI was more pronounced in anovulatory cycles on day -14 (P = 0.021), -7 (P = 0.048) and 2 (P = 0.018) compared to ovulatory women who did not show intraindividual changes (P = 0.56). RMT, CSP and ICF showed no significant changes during anovulatory or ovulatory cycles.

CONCLUSIONS

The results suggest fluctuations in cortical excitability during anovulatory cycles, possibly due to the withdrawal of 'excitatory' oestrogens that initiate menses in anovulatory cycles.

Influence of the post-ovariectomy time frame on the experimental anxiety and the behavioural actions of some anxiolytic agents

This study analyzes the long-term effects of ovariectomy on the basal experimental anxiety of rats and the influence of this condition on the anxiolytic properties of diazepam and the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). Rats ovariectomized 3, 6 and 12 weeks previously, were tested in the burying behaviour paradigm and in an automatic activity counter. The highest values of time spent burying were observed in the 12-week group. In general, the 12-week group was more responsive to diazepam than the 3-week group, while 8-OH-DPAT showed similar effects on time spent burying, independently of how long ago the ovariectomy was done. Detection of anxiogenic-like behaviours by the shock-probe burying test in rats after chronic absence of gonadal hormones could help in the understanding of mood changes associated with human menopause.

Estrogen-priming can enhance progesterone's anti-seizure effects in part by increasing hippocampal levels of allopregnanolone

Estrogen can be proconvulsant, while progesterone and its metabolite allopregnanolone typically have anti-seizure effects. We investigated whether estrogen-priming also has anti-seizure effects by altering progesterone's metabolism to allopregnanolone, or levels of brain-derived neurotrophic factor (BDNF), in the hippocampus. Two experiments investigated effects of different estrogen-priming regimen (Experiment 1--10 microg; Experiment 2--2 microg) on pentylenetetrazole (PTZ)-induced seizures and levels of estrogen, progesterone and allopregnanolone in plasma and hippocampus. In Experiment 1, ovariectomized (ovx) rats were administered sesame oil vehicle or 10 microg 17beta-estrogen at hour 0. Forty-four hours later, progesterone (500 microg; s.c.) or vehicle was administered. At hour 47, PTZ (70 mg/kg i.p.) was administered. For Experiment 2, a similar protocol was used except that ovx rats were administered vehicle or 2 microg 17beta-estradiol at hours 0 and 24. Progesterone, alone or in conjunction with either 10 or 2 microg estrogen-priming, tended to increase the latency to, and significantly reduced the number of, tonic seizures and elevated levels of progestins in hippocampus and plasma. Two, but not 10, micrograms of estrogen alone had anti-seizure effects and increased levels of allopregnanolone in the hippocampus. BDNF levels in the hippocampus were increased by estrogen-priming, but reduced by progesterone administration. Thus, estrogen may have anti-seizure effects by enhancing formation of allopregnanolone.

The role of estrogens in seizures and epilepsy: the bad guys or the good guys?

Estrogens influence neuronal activity and are important for normal brain functions. Effects of estrogens on seizures are contradictory. It is commonly accepted that estrogens may increase neuronal excitability and thus mediate proconvulsant effects. However, clinical and animal data show that estrogen may also have no effect or anticonvulsant effects. The action of estrogens on seizures depends on various factors, such as treatment duration and latency prior to the seizure testing, estrogen dose, hormonal status (naïve vs gonadectomized animals), estrogenic substance, the region/neurotransmitter system involved, the seizure type/model used, and sex. Besides the effects on seizure susceptibility, estrogens may also play an important role in seizure-induced damage. Pretreatment with beta-estradiol in ovariectomized female rats has neuroprotective effects on status epilepticus-induced hippocampal damage and prevents the loss of inhibition in the dentate gyrus during the early post-status epilepticus period determined by the in vitro paired pulse paradigm. Several signaling pathways may be involved in the neuroprotective effects of beta-estradiol on status epilepticus-induced hippocampal damage but at least one of these pathways involves interactions with neuropeptide Y.

Seizure susceptibility in intact and ovariectomized female rats treated with the convulsant pilocarpine

Despite numerous neuroendocrinological studies of seizures, the influence of estrogen and progesterone on seizures and epilepsy remains unclear. This may be due to the fact that previous studies have not systematically compared distinct endocrine conditions and included all relevant controls. The goal of the present study was to conduct such a study using pilocarpine as chemoconvulsant. Thus, age and weight-matched, intact or ovariectomized rats were tested to determine incidence of status epilepticus and to study events leading to status. Intact female rats were sampled at each cycle stage (proestrus, estrus, metestrus, or diestrus 2). Convulsant was administered at the same time of day, 10:00-10:30 a.m. Statistical analysis showed that there was a significantly lower incidence of status on the morning of estrus, but differences were attenuated in older animals. Ovariectomized rats were distinct in their rapid progression to status. These results show that the incidence of status in female rats following pilocarpine injection, and the progression to pilocarpine-induced status, are influenced by reproductive state as well as age. The hormonal milieu present specifically on the morning of estrus appears to decrease susceptibility to pilocarpine-induced status, particularly at young ages. In contrast, the chronic absence of reproductive steroids that characterizes the ovariectomized rat leads to a more rapid progression to status. This dissociation between incidence vs. progression provides new insight into the influence of estrogen and progesterone on seizures.

Ovariectomy aggravates nifedipine-induced flushing of tail skin in mice

Flushing is one of the most common vasodilation-related adverse effects associated with Ca(2+) channel antagonist treatment. This symptom is known to occur more frequently in women than men. The present study aimed at investigating the effect of ovariectomy on nifedipine-induced flushing in mice. Ovariectomy markedly increased the tail skin temperature, a parameter of skin flushing, induced by nifedipine at a dose showing no influence on blood pressure. This event was blocked by estradiol replacement. Estrogen withdrawal is, therefore, included in the risk factors for nifedipine-induced flushing and this risk is lessened by estrogen replacement.

Skeletal effects of cyclosporin A are gender related in rats

The immunosuppressive drug cyclosporin A (CsA) is thought to be involved in the pathogenesis of posttransplantation osteoporosis. To evaluate further the skeletal effects of CsA, we treated aged male and female sham-operated and gonadectomized rats with low doses of CsA for 4 months. Here, we show that CsA is antiresorptive and bone-sparing in aged female rats but increases bone resorption and reduces bone mass in aged male rats. However, even in male rats, CsA treatment, at clinically relevant doses, increased bone resorption only transiently and did not result in pronounced long-term cancellous bone loss. The gender-specific skeletal effects of CsA were not modulated by sex hormones or gonadectomy. CsA did not influence sex steroid metabolism in male or female rats. However, endogenous estradiol in sham-operated female rats (and especially, exogenous administration of 17beta-estradiol in ovariectomized rats) markedly diminished blood levels of CsA, probably by increasing hepatic CsA metabolism. Although the mechanism for the gender-specific skeletal effects of CsA is still obscure, our findings may have important implications for clinical therapy with CsA.

Subchronic treatment with cyclosporin A decreases the binding properties of the GABAA receptor in ovariectomized rats

In this study, we investigated the effect of cyclosporin A on the binding properties of the GABAA receptor in the hippocampus, known to be responsible for the induction of seizures, to clarify the mechanism of cyclosporin A-inhibited GABA neurotransmission in ovariectomized rats, as a climacterium model. The effects of single and subchronic treatments with cyclosporin A were examined on [3H]muscimol binding to hippocampal synaptosomal membranes in sham, ovariectomized, and estradiol/ovariectomized rats. A single treatment with cyclosporin A (40 mg/kg, i.p.) failed to change [3H]muscimol binding in the 3 groups, when compared with each corresponding vehicle-treated group. Subchronic treatment with cyclosporin A (40 mg/kg, i.p., once a day for 5 days) significantly decreased the amount of [3H]muscimol binding in ovariectomized rats. However, this inhibitory effect was not observed in sham or estradiol/ovariectomized rats. These results demonstrated that the binding activity of the GABAA receptor was decreased in ovariectomized rats after subchronic cyclosporin A treatment. This study supports the hypothesis that ovariectomy elevates the susceptibility to cyclosporin A-induced convulsions by accelerating the inhibitory actions of cyclosporin A on GABA neurotransmission in the hippocampus.