Sex differences in the effects of gonadectomy and acute swim stress on GABAA receptor binding in mouse forebrain membranes

Progesterone and contraceptive progestin actions on the brain: A systematic review of animal studies and comparison to human neuroimaging studies

In this review we systematically summarize the effects of progesterone and synthetic progestins on neurogenesis, synaptogenesis, myelination and six neurotransmitter systems. Several parallels between progesterone and older generation progestin actions emerged, suggesting actions via progesterone receptors. However, existing results suggest a general lack of knowledge regarding the effects of currently used progestins in hormonal contraception regarding these cellular and molecular brain parameters. Human neuroimaging studies were reviewed with a focus on randomized placebo-controlled trials and cross-sectional studies controlling for progestin type. The prefrontal cortex, amygdala, salience network and hippocampus were identified as regions of interest for future preclinical studies. This review proposes a series of experiments to elucidate the cellular and molecular actions of contraceptive progestins in these areas and link these actions to behavioral markers of emotional and cognitive functioning. Emotional effects of contraceptive progestins appear to be related to 1) alterations in the serotonergic system, 2) direct/indirect modulations of inhibitory GABA-ergic signalling via effects on the allopregnanolone content of the brain, which differ between androgenic and anti-androgenic progestins. Cognitive effects of combined oral contraceptives appear to depend on the ethinylestradiol dose.

A prominent environmental endocrine disruptor, 4-nonylphenol, promotes endometriosis development via plasmacytoid dendritic cells

Endometriosis is an estrogen-dependent chronic inflammatory disease and is associated etiologically with environmental endocrine disruptor (EED) exposure. 4-nonylphenol (NP), a widely found EED, has weak estrogenic activity and modulates plasmacytoid dendritic cell (pDC) function in vitro and in vivo. We aimed to elucidate the immunomodulatory effect of NP on the development of endometriosis, particularly focusing on pDCs. This study established a surgically induced endometriosis murine model (C57BL/6) under conditions of NP treatment that are relevant to the level and route of human exposure. Multi-parametric flow cytometry was used for analysis of infiltrated immune cell subsets in lesions. The results showed that NP exposure significantly promoted endometriotic lesion growth, survival and angiogenesis development of lesions as well as pDC accumulation in the lesions in mice. Adoptive transfer of NP-conditioned pDCs into mice significantly enhanced lesion development and local pDC infiltration, whereas NP-conditioned conventional dendritic cells did not affect lesion growth. In vitro functional analysis showed that NP-conditioned pDCs in lesions expressed high levels of CD36, a scavenger receptor and NP-conditioned splenic pDCs secreted an enhanced level of IL-10 in response to apoptotic cell recognition in a CD36-dependent manner. Furthermore, we observed that local treatment with blocking antibodies against IL-10 and CD36 on the day of surgery significantly inhibited lesion development. NP exposure also altered the estrous cycle in mice. The results suggest that chronic and low-dose exposure to NP enhances endometriotic lesion growth by altering pDC homeostasis and function. This study has important implications for understanding the environment-innate immunity interaction in human endometriosis.

Long-term oral administration of a novel estrogen receptor beta agonist enhances memory and alleviates drug-induced vasodilation in young ovariectomized mice

Development of estrogen therapies targeting the β (ERβ) but not α (ERα) estrogen receptor is critically needed for the treatment of negative menopausal symptoms, as ERα activation increases health risks like cancer. Here, we determined the effects of long-term oral treatment with EGX358, a novel highly selective ERβ agonist, on memory, vasodilation, and affect in young ovariectomized mice. Mice were orally gavaged daily for 9 weeks with vehicle, 17β-estradiol (E₂), the ERβ agonist diarylpropionitrile (DPN), or EGX358 at doses that enhance memory when delivered acutely. Tail skin temperature was recorded as a proxy for vasodilation following injection of vehicle or senktide, a tachykinin receptor 3 agonist used to model hot flashes. Anxiety-like behavior was assessed in the open field (OF) and elevated plus maze (EPM), and depression-like behavior was measured in the tail suspension (TST) and forced swim tests (FST). Finally, memory was assessed in object recognition (OR) and object placement (OP) tasks. E₂, DPN, and EGX358 reduced senktide-mediated increases in tail skin temperature compared to vehicle. All three treatments also enhanced memory in the OR and OP tasks, whereas vehicle did not. Although E₂ increased time spent in the center of the OF, no other treatment effects were observed in the OF, EPM, TST, or FST. These data suggest that long-term ERβ activation can reduce hot flash-like symptoms and enhance spatial and object recognition memories in ovariectomized mice. Thus, the highly selective ERβ agonist EGX358 may be a promising avenue for reducing menopause-related hot flashes and memory dysfunction.

Differential effects of progesterone on social recognition and the avoidance of pathogen threat by female mice

Although pathogen threat affects social and sexual responses across species, relatively little is known about the underlying neuroendocrine mechanisms. Progesterone has been speculated to be involved in the mediation of pathogen disgust in women, though with mixed experimental support. Here we considered the effects of acute progesterone on the disgust-like avoidance responses of female mice to pathogen threat. Estrous female mice discriminated and avoided the urinary and associated odors of males subclinically infected with the murine nematode parasite, Heligmosomoides polygyrus. These avoidance responses were not significantly affected by pre-treatment with progesterone. Likewise, brief (1 min) exposure to the odors of infected males attenuated the subsequent responses of females to the odors of the normally preferred unfamiliar males and enhanced their preferences for familiar males. Neither progesterone nor allopregnanolone, a central neurosteroid metabolite of progesterone, had any significant effects on the avoidance of unfamiliar males elicited by pre-exposure to a parasitized male. Progesterone and allopregnanolone, did, however, significantly attenuate the typical preferences of estrous females for unfamiliar uninfected males, suggestive of effects on social recognition. These findings with mice indicate that progesterone may have minimal effects on the responses to specific parasite threat and the expression of pathogen disgust but may influence more general social recognition and preferences.

Ovarian Cycle Stages Modulate Alzheimer-Related Cognitive and Brain Network Alterations in Female Mice

Alzheimer’s disease (AD) begins several decades before the onset of clinical symptoms, at a time when women may still undergo reproductive cycling. Whether ovarian functions alter substrates of AD pathogenesis is unknown. Here we show that ovarian cycle stages significantly modulate AD-related alterations in neural network patterns, cognitive impairments, and pathogenic protein production in the hAPP-J20 mouse model of AD. Female hAPP mice spent more time in estrogen-dominant cycle stages and these ovarian stages worsened AD-related network dysfunction and cognitive impairments. In contrast, progesterone-dominant stages and gonadectomy attenuated these AD-related deficits. Further studies revealed a direct role for estradiol in stimulating neural network excitability and susceptibility to seizures in hAPP mice and increasing amyloid beta levels. Understanding dynamic effects of the ovarian cycle on the female nervous system in disease, including AD, is of critical importance and may differ from effects on a healthy brain. The pattern of ovarian cycle effects on disease-related networks, cognition, and pathogenic protein expression may be relevant to young women at risk for AD.

Characterising Pre-pubertal Resistance to Death from Endotoxemia

Sepsis is a common and deadly syndrome in which a dysregulated host response to infection causes organ failure and death. The current lack of treatment options suggests that a new approach to studying sepsis is needed. Pre-pubertal children show a relative resistance to death from severe infections and sepsis. To explore this phenomenon experimentally, we used an endotoxemia model of sepsis in mice. Following intra-peritoneal injection of endotoxin, pre-pubertal mice showed greater survival than post-pubertal mice (76.3% vs. 28.6%), despite exhibiting a similar degree of inflammation after two hours. Age-associated differences in the inflammatory response only became evident at twenty hours, when post-pubertal mice showed prolonged elevation of serum cytokines and differential recruitment of peritoneal immune cells. Mechanistically, prevention of puberty by hormonal blockade or acceleration of puberty by oestrogen treatment led to increased or decreased survival from endotoxemia, respectively. Additionally, the adoptive transfer of pre-pubertal peritoneal cells improved the survival of post-pubertal recipient mice, while post-pubertal peritoneal cells or vehicle did not. These data establish a model for studying childhood resistance to mortality from endotoxemia, demonstrate that oestrogen is responsible for an increased susceptibility to mortality after puberty, and identify peritoneal cells as mediators of pre-pubertal resistance.

Sodium Valproate Enhances the Urethane-Induced Lung Adenomas and Suppresses Malignization of Adenomas in Ovariectomized Female Mice

In the present study, the possible effect of sodium valproate (NaVP) on urethane-induced lung tumors in female mice has been evaluated. BALB/c mice (n = 60; 4-6 weeks old, females) were used in the following groups: (1) urethane-treated; (2) urethane-NaVP-treated; (3) only NaVP-treated; (4) control. In the same groups, ovariectomized female mice (n = 60) were investigated. Urethane was given intraperitoneally, with a total dose of 50 mg/mouse. In NaVP-treated mice groups, 0.4% aqueous solution of NaVP was offered to mice ad libitum. The duration of the experiment was 6 months. The number of tumors per mouse in ovariectomized mice and in those treated with urethane and NaVP was significantly higher than in mice treated with urethane only (8.29 ± 0.58 versus 6.0 ± 0.63, p < 0.02). No significant difference in the number of tumors per mouse was revealed while comparing the nonovariectomized urethane- and urethane-NaVP-treated groups (p = 0.13). A significant decrease of adenocarcinoma number in ovariectomized mice treated with a urethane-NaVP as compared with ovariectomized mice treated with urethane only was found (p = 0.031). NaVP together with low estrogen may have a protective effect on the malignization of adenomas in ovariectomized mice.

The effect of age on the discriminative stimulus effects of ethanol and its GABA(A) receptor mediation in cynomolgus monkeys

RATIONALE

Excessive alcohol consumption is less common among aged compared to young adults, with aged adults showing greater sensitivity to many behavioral effects of ethanol.

OBJECTIVES

This study compared the discriminative stimulus effects of ethanol in young and middle-aged adult cynomolgus monkeys (Macaca fascicularis) and its γ-aminobutyric acid (GABA)(A) receptor mediation.

METHODS

Two male and two female monkeys trained to discriminate ethanol (1.0 g/kg, i.g.; 60-min pre-treatment interval) from water at 5-6 years of age (Grant et al. in Psychopharmacology 152:181-188, 2000) were re-trained in the current study more than a decade later (19.3 ± 1.0 years of age) for a within-subjects comparison. Also, four experimentally naïve middle-aged (mean ± SEM, 17.0 ± 1.5 years of age) female monkeys were trained to discriminate ethanol for between-subjects comparison with published data from young adult naïve monkeys.

RESULTS

Two of the naïve middle-aged monkeys attained criterion performance, with weak stimulus control and few discrimination tests, despite greater blood-ethanol concentration 60 min after 1.0 g/kg ethanol in middle-aged compared to young adult female monkeys (Green et al. in Alcohol Clin Exp Res 23:611-616, 1999). The efficacy of the GABA(A) receptor positive modulators pentobarbital, midazolam, allopregnanolone, pregnanolone, and androsterone to substitute for the discriminative stimulus effects of 1.0 g/kg ethanol was maintained from young adulthood to middle age.

CONCLUSIONS

The data suggest that 1.0 g/kg ethanol is a weak discriminative stimulus in naive middle-aged monkeys. Nevertheless, the GABA(A) receptor mechanisms mediating the discriminative stimulus effects of ethanol, when learned as a young adult, appear stable across one third of the primate lifespan.

Stress and GABA receptors

GABA(A) receptors are sensitive to subtle changes in the environment in both early-life and adulthood. These neurochemical responses to stress in adulthood are sex-dependent. Acute stress induces rapid changes in GABA(A) receptors in experimental animals, with the direction of the changes varying according to the sex of the animals and the stress-paradigm studied. These rapid alterations are of particular interest as they provide an example of fast neurotransmitter system plasticity that may be mediated by stress-induced increases in neurosteroids, perhaps via effects on phosphorylation and/or receptor trafficking. Interestingly, some studies have also provided evidence for long-lasting changes in GABA(A) receptors as a result of exposure to stressors in early-life. The short- and long-term stress sensitivity of the GABAergic system implicates GABA(A) receptors in the non-genetic etiology of psychiatric illnesses such as depression and schizophrenia in which stress may be an important factor.

The effects of acute 17beta-estradiol treatment on gene expression in the young female mouse hippocampus

Previous studies have demonstrated that treatment with 17beta-estradiol (E(2)) improves both spatial and nonspatial memory in young female mice. Still unclear, however, are the molecular mechanisms underlying the beneficial effects of E(2) on memory. We have previously demonstrated that a single post-training intraperitoneal (i.p.) injection of 0.2 mg/kg E(2) can enhance hippocampal-dependent spatial and object memory consolidation (e.g., Gresack & Frick, 2006b). Therefore, in the present study, we performed a microarray analysis on the dorsal hippocampi of 4-month-old female mice injected i.p. with vehicle or 0.2 mg/kg E(2). Genes were considered differentially expressed following E(2) treatment if they showed a greater than 2-fold change in RNA expression levels compared to controls. Overall, out of a total of approximately 25,000 genes represented on the array, 204 genes showed altered mRNA expression levels upon E(2) treatment, with 111 up-regulated and 93 down-regulated. Of these, 17 of the up-regulated and 6 of the down-regulated genes are known to be involved in learning and memory. mRNA expression changes in 5 of the genes were confirmed by real-time quantitative PCR analysis, and protein changes in these same genes were confirmed by Western blot analysis: Hsp70, a heat shock protein known to be estrogen responsive; Igfbp2, an IGF-I binding protein; Actn4, an actin binding protein involved in protein trafficking; Tubb2a, the major component of microtubules; and Snap25, a synaptosome-specific protein required for neurotransmitter release. The types of genes altered indicate that E(2) may induce changes in the structural mechanics of cells within the dorsal hippocampus that could be conducive to promoting memory consolidation.

Differential effects of acute progesterone administration on spatial and object memory in middle-aged and aged female C57BL/6 mice

The present study examined the effects of acute progesterone administration on hippocampal-dependent memory consolidation in ovariectomized middle-aged (16 months old) and aged (22 months old) female mice. Spatial memory was tested in a 2-day Morris water-maze task and object memory was tested using an object recognition task with 24- and 48-h delays. Immediately after water-maze training, mice received i.p. injections of vehicle, or 5.0, 10.0, or 20.0 mg/kg of water-soluble progesterone. Twenty-four hours later, retention of the platform location was tested. No overnight forgetting of the platform location was observed in middle-aged vehicle-treated mice. Acute progesterone administration had no effect on spatial memory in middle-aged mice. However, aged vehicle-treated mice demonstrated impaired memory for the platform location on Day 2 relative to Day 1. Twenty mg/kg, but not 5 or 10 mg/kg, progesterone reversed these deficits, suggesting that 20 mg/kg progesterone can improve spatial memory in aged females. In the object recognition task, mice explored two identical objects and then immediately received vehicle or progesterone injections. In middle-aged mice, 10 and 20 mg/kg progesterone enhanced object memory consolidation, relative to chance, after 24-h, but all doses were ineffective after 48-h. In aged mice, 10 mg/kg progesterone enhanced object memory consolidation, relative to chance, after 24 h, whereas both 5 and 10 mg/kg progesterone enhanced memory after 48 h. Together, these results indicate that acute progesterone differentially enhances hippocampal-dependent memory in middle-aged and aged females.

Post-training estrogen enhances spatial and object memory consolidation in female mice

The present study was designed to determine if post-training injections of a water-soluble form of 17beta-estradiol could enhance spatial and object memory consolidation in young female mice. Young ovariectomized female mice were trained in Morris water maze and object recognition tasks, injected with 0.1, 0.2, or 0.4 mg/kg cyclodextrin-encapsulated 17beta-estradiol or cyclodextrin-conjugated vehicle, and then re-tested after a delay. In the water maze, mice were trained in eight consecutive trials, injected, and memory for the platform location was re-tested after 24 h. All mice learned to find the platform on Day 1, but only mice receiving 0.2 mg/kg estradiol remembered the platform location on Day 2. In the object recognition task, mice were first presented with two identical objects, injected, and then presented with a familiar and novel object after a 24- or 48-h delay. For both delays, the 0.2 and 0.4 mg/kg doses enhanced memory for the familiar object. These data demonstrate that a 0.2 mg/kg dose of estradiol can enhance multiple types of memory consolidation in female mice, and suggest a narrower effective dose range for spatial memory than for object memory.

Action by and sensitivity to neuroactive steroids in menstrual cycle related CNS disorders

Neuroactive steroids are a large group of substances having effect in the brain and on brain function. The steroids most studied are allopregnanolone (ALLO), tetrahydrodesoxycorticosterone (THDOC), pregnenolone sulfate (PS) dihydroepiandrosteronesulfate (DHEAS), and estradiol (E2). ALLO and THDOC are called gamma-aminobutyric acid (GABA) steroids as they are positive modulators of the GABAA receptor in a similar way as benzodiazepines, barbiturates, and alcohol. GABA steroids not only have similar behavioral effects as benzodiazepines and barbiturates but, possibly, also similar adverse effects as well. This review aims to elucidate the possible role that neuroactive steroids play in the development of mood disorders in women. One of the most clear-cut examples of the interaction between mood, neuroactive steroids, and the GABA system is premenstrual dysphoric disorder (PMDD), which is a cluster of negative mood symptoms occurring during the luteal phase of the menstrual cycle in 2-6% of reproductive women. Furthermore, certain women also experience adverse mood effects during sequential progestin addition to postmenopausal estrogen treatment, which is why the role of neuroactive steroids in postmenopausal women is also addressed in this review.

Effects of estrogen and progesterone on spatial memory consolidation in aged females

Interpretation of data illustrating that estrogen, with or without progestin, is detrimental to memory in post-menopausal women is complicated by the fact that little is known about the effects of progestins on memory. The present study examined if estrogen, alone or with progesterone, affects spatial memory consolidation in ovariectomized aged female mice. Mice received eight training trials in a spatial Morris water maze followed immediately by injection of water-soluble 17beta-estradiol (E(2); 0.2 mg/kg) or vehicle. Mice were re-tested 24 h later. All mice learned to find the platform on Day 1. On Day 2, the performance of control, but not E(2) mice, deteriorated, suggesting that E(2) enhanced memory for the platform location. In a second experiment, mice were injected with E(2) and 10 or 20 mg/kg water-soluble progesterone. The 10 mg/kg dose of progesterone did not affect estrogen's ability to enhance spatial memory consolidation, but 20 mg/kg blocked this effect. These data indicate that estrogen can improve spatial memory consolidation in aged females and that this effect can be attenuated by progesterone.

Effect of acute versus chronic theophylline administration on acute restraint stress-induced increase of pentylenetetrazol seizure threshold in mice

Various stressful paradigms were found to induce anticonvulsant effects in different seizure models. Methylxanthines, such as theophylline might contribute to the reduction of restraint-induced stress. Therefore, in this study the influence of acute restraint stress on pentylenetetrazol (PTZ) seizure thresholds as well as the effect of acute and chronic theophylline pretreatment on stress-induced modulation of the seizure threshold were assessed in mice. The onset of the three consecutive seizure phases: myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hind limb extension (THE) was delayed after exposure to a 2 h restraint stress by 34%, 23% and 24%, respectively. In nonstressed mice, acute theophylline injection (100 mg/kg, i.p.) decreased the threshold only for THE. However, in stressed animals, the pretreatment with the methylxanthine significantly enhanced the dose of the convulsant producing the same seizure phase. In nonstressed mice, long-term theophylline treatment (50 mg/kg, twice daily for 14 days) increased PTZ threshold for all three seizure phases. In contrast, in chronically treated with theophylline mice exposed to restraint stress, significant decrease in the PTZ threshold for all seizure phases compared to control stressed animals have been observed. These results suggest that, depending on the treatment regimen (acute versus chronic), theophylline specifically and differentially modulates the anticonvulsant effect of restraint stress in mice.

Gonadal steroids regulate GABAA receptor subunit mRNA expression in NT2-N neurons

Changes in gonadal steroid hormone levels during the menstrual cycle affect seizure frequency in women with catamenial epilepsy. Since GABA(A) receptors (GABARs) contribute to the prevention and termination of seizures by reducing neuronal excitability, we hypothesized that fluctuating gonadal steroid levels might affect GABAR subunit expression, which could alter inhibitory tone leading to increased seizure activity. To address this question in a simplified environment in vitro, we examined the effects of gonadal steroids on NT2-N neuronal cells. We have previously shown that NT2-N cells express functional GABARs, and that the expression pattern of GABAR subunits is regulated by chronic benzodiazepine exposure and hypoxia. NT2-N neurons were exposed to progesterone (0.1 microM), beta-estradiol (3 nM), or vehicle (DMSO) for 2 days or 7 days prior to RNA harvesting. GABAR subunit mRNA levels were assessed by semiquantitative RT-PCR normalized to actin levels. Progesterone exposure for 7 days increased alpha2 and gamma3 and decreased alpha5 subunit mRNAs, while beta-estradiol caused significant increases in alpha3, beta3 and epsilon expression. Further analysis revealed differential regulation of alpha4, alpha5, epsilon and pi subunit expression. Plots of relative PCR density in progesterone-treated cells for alpha2 vs. alpha5, alpha5 vs. gamma3 and alpha2 vs. gamma3 showed correlation between samples, suggesting coordinate regulation. Both progesterone and estrogen nuclear receptor mRNAs were detected by RT-PCR, and 2 days but not 7 days estrogen exposure upregulated progesterone receptor mRNA. Gonadal steroid fluctuations regulate GABA(A) receptor subunit expression in NT2-N cells. Such changes, if observed in vivo, could affect seizure frequency.

Environmental enrichment reduces the mnemonic and neural benefits of estrogen

The degree to which memory is enhanced by estrogen replacement in postmenopausal women may depend on environmental factors such as education. The present study utilized an animal model of environmental enrichment to determine whether environmental factors influence the mnemonic and neural response to estrogen. Female mice were raised in standard (SC) or enriched (EC) conditions from weaning until adulthood (7 months). All mice were ovariectomized at 10 weeks, and tested in object recognition and water-escape motivated radial arm maze (WRAM) tasks at 6 months. Each day at the completion of training, mice received injections of 0.1 mg/kg cyclodextrin-encapsulated 17-beta-estradiol (E2), 0.2 mg/kg E2, or cyclodextrin vehicle (VEH). At the completion of behavioral testing, hippocampal levels of the presynaptic protein synaptophysin and of brain-derived neurotrophic factor (BDNF) were measured. Enrichment effects were evident in VEH-treated mice; relative to SC-VEH females, EC-VEH females committed fewer working memory errors in the WRAM and exhibited increased hippocampal synaptophysin levels. Estrogen effects depended on environmental conditions. E2 (0.2 mg/kg) improved object memory only in SC females. The same dose improved working memory in SC females, but somewhat impaired working memory in EC females. Furthermore, both doses reduced hippocampal synaptophysin levels in EC, but not SC, females. In contrast, E2 reduced hippocampal BDNF levels in SC, but not EC, females. This study is the first to compare the effects of estrogen on memory and hippocampal function in enriched and non-enriched female mice. The results suggest that: (1) estrogen benefits object and working memory more in mice raised in non-enriched environments than in those raised in enriched environments, and (2) the changes induced by estrogen and/or enrichment may be associated with alterations in hippocampal synaptic plasticity.

Alterations in GABAergic function following forced swimming stress

Forced swimming induces alterations in the GABA brain concentration and could change the sensitivity of the GABA/benzodiazepine receptor-chloride ionophore complex to benzodiazepines. This change in sensitivity could be explained by the allopregnanolone release that takes place during stress. The current study was carried out to determine whether forced swimming is able to modify the anti-anxiety effect of diazepam and to explore the possible relation of this change to allopregnanolone, the GABA concentration or/and the GABA/benzodiazepine receptor density. Unstressed and stressed mice, injected with the vehicle or diazepam, were evaluated in the exploratory behavior test. Diazepam induced clear anxiolytic actions at all doses in unstressed animals, but such an effect was not observed in stressed animals. The injection of allopregnanolone 24 h before the anxiety test blocked the effect of this benzodiazepine. Forced swimming decreased GABA concentrations in the hippocampus and the thalamus-hypothalamus region, besides decreasing the [(3)H]flunitrazepam labeling in both the hypothalamus and amygdala. These results show that forced swimming abolishes the anti-anxiety effect of diazepam.

Differential contribution of cholecystokinin receptors to stress-induced modulation of seizure and nociception thresholds in mice

Recent evidence suggest that endogenous cholecystokinin (CCK) has important roles in central responses to stress. CCK receptors are known as functional modulators of opioidergic system with a tonic antiopioid effect in nociceptive pathways. In contrast, CCK receptor ligands are known to induce anticonvulsant effects similar to endogenous opioids. It is not clear whether endogenous CCK may play a role in the anticonvulsant effects of stress, especially in those stressful paradigms that are associated with strong activation of opioid pathways. The present study examined the role of endogenous CCK receptors in acute stress-induced modulation of seizure (clonic seizures induced by pentylenetetrazole) and nociception (tail-flick) thresholds. Acute restraint stress (for 2 h) and prolonged intermittent footshock stress (30 min) both induced opioid-dependent anticonvulsant and antinociceptive effects. While CCK receptor antagonist proglumide (10, 20, or 40 mg/kg) had no effect on seizure or nociception threshold by itself, it inhibited the anticonvulsant effects of both these types of stress while potentiating their antinociceptive effects. Moreover, proglumide exerted a similar inhibition of the anticonvulsant effect and potentiation of the antinociceptive effect of acute morphine at 1 mg/kg. In contrast, brief and continuous footshock stress (3 min) that induced a nonopioid type of antinociception did not increase the seizure threshold. Proglumide pretreatment did not alter any of these effects of brief footshock stress paradigm. The present data suggest that CCK receptors specifically and differentially modulate the opioid-mediated anticonvulsant and antinociceptive effects of acute stress.

Estradiol and the addition of progesterone increase the sensitivity to a neurosteroid in postmenopausal women

The aim of this study was to compare the pharmacodynamic response to a neuroactive steroid, pregnanolone, before and during different hormonal settings of postmenopausal hormone replacement therapy (HRT), using natural progesterone. A second aim was to investigate whether the response to pregnanolone was associated with cyclicity in negative mood symptoms during treatment. Twenty six postmenopausal women with climacteric symptoms were administered HRT in a randomized, double blinded, placebo-controlled, crossover study. The women received 2 mg oral estradiol (E(2)) continuously during two 28-day cycles and 800 mg of vaginal progesterone or placebo sequentially for the last 14 days of each treatment cycle. Pharmacodynamic response to pregnanolone was assessed before treatment, and during the last week of each treatment cycle, by comparing the effects of intravenous pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one) on saccadic eye velocity (SEV), saccade acceleration, saccade latency and self-rated sedation. Throughout the study daily symptom rating scales were kept. According to the daily symptom rating scales, patients were divided into two groups; one group who displayed a significant variance in negative mood symptoms during HRT (cyclicity) and one group with no cyclical changes in negative mood symptoms during treatment. During treatment with either E(2) alone or E(2)+progesterone the response in saccadic eye movement parameters and in self-rated sedation to pregnanolone was enhanced compared to pretreatment values. The SEV, saccade acceleration and sedation responses to pregnanolone was also increased in women expressing cyclicity in negative mood symptoms compared to women with no cyclical changes in negative mood during HRT. In conclusion, during treatment with either E(2) alone, or E(2)+progesterone, pregnanolone sensitivity was increased. Women expressing cyclicity in negative mood symptoms were more sensitive to pregnanolone than women without symptom cyclicity during HRT.

Sex differences in drug- and non-drug-induced analgesia

Historically, biomedical research has been conducted almost exclusively with male subjects. A growing number of studies now demonstrate sex differences in analgesia produced both by drugs and by environmental stimuli. This review summarizes the current literature on sex differences in analgesia produced by opioids, cholinergics and other drugs, and by stress, exercise and other environmental manipulations. A brief overview of the physiological mechanisms underlying sex differences in analgesia is provided, as well as suggestions for future research. It is not yet known whether the development of sex-specific analgesia treatment guidelines is warranted.

Effects of pre- and postnatal corticosterone exposure on the rat hippocampal GABA system

Several lines of evidence have implicated prenatal stress and the hippocampal GABA system in the pathophysiology of schizophrenia, and prenatal stress is believed to increase the risk for schizophrenia through alterations of this neurotransmitter. To explore this hypothesis, we treated male rats pre- and/or postnatally (P48 and P60) with either corticosterone (CORT) or vehicle to establish three study groups: VVV, receiving vehicle at all three time points; VCC, receiving vehicle prenatally and CORT at both postnatal timepoints; and CCC, receiving CORT at all three timepoints. Animals were sacrificed at either 24 h or 5 days after final injection and examined for mRNA levels of GAD65, GAD67, and the GABA(A) receptor subunits alpha2 and gamma2. At 24 h, GAD65 mRNA was decreased in CA1, CA2, CA4, and dentate gyrus (DG) of VCC rats; this effect was either decreased or reversed in CCC-treated animals. No effect was detected in GAD67 mRNA at 24 h. At 5 days, CORT treatment increased GAD67 mRNA levels in CA1, CA3, and DG. Prenatal treatment with CORT was associated with increased responsiveness only in CA3 and DG. For the GABAA receptor, alpha2 subunit mRNA did not show any change in response to CORT treatment, while that for the gamma2 subunit was decreased in CA2 of both VCC- and CCC-treated animals. Consistent with gamma2 subunit mRNA decreases, benzodiazepine (BZ) receptor binding activity was decreased in CA2 with CORT treatment. Prenatal CORT exposure neither increased nor decreased this effect. These results demonstrate that CORT administration is associated with a complex regulation of mRNA expression for pre- and postnatal aspects of the hippocampal GABA system. Under these conditions, prenatal exposure to CORT may sensitize some of these effects, but does not fundamentally alter the nature of this response.

The involvement of endogenous opioids and nitricoxidergic pathway in the anticonvulsant effects of foot-shock stress in mice

The involvement of endogenous opioids and nitric oxide (NO) in the anticonvulsant effects of stress against pentylenetetrazole (PTZ)- or electroconvulsive shock-induced seizures was assessed in mice. The prolonged and intermittent foot-shock stress, which induced opioid-mediated analgesia, had significant protective effects against both seizure types which was reversible by naloxone (0.3, 1 or 2 mg/kg), while brief and continuous foot-shock did not alter the seizure susceptibility. Pre-treatment with non-specific nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME, 1, 2, 5, 10 or 30 mg/kg), but not with specific inducible NOS (iNOS) inhibitor, aminoguanidine (50 or 100 mg/kg), blocked the stress-induced anticonvulsant effects. The lower doses of naloxone (0.3 mg/kg) and L-NAME (2 mg/kg) showed additive effects in blocking the stress-induced anticonvulsant properties. L-arginine at a per se non-effective dose of 20 mg/kg potentiated the stress-induced anticonvulsant properties, an effect which was inhibited by L-NAME but not by aminoguanidine. Furthermore, a low dose of morphine (0.5 mg/kg) showed potentiation with stress in increasing PTZ seizure threshold. This potentiation was reversed by either naloxone or L-NAME at low doses but not by aminoguanidine. Taken together, these results show that NO synthesis, through constitutive but not iNOS, is involved in opioid-dependent stress-induced anticonvulsant effects against electrical and PTZ-induced convulsions.

Swim stress alters the behavioural response of mice to GABA-related and some GABA-unrelated convulsants

To elucidate the relationship between stress and seizures, the effect of a single swim stress on the convulsive signs and death produced by several GABA-related and GABA-unrelated convulsants, and the effect of repeated swim stress on picrotoxin-induced convulsions was studied. Mice were subjected to swim stress (10 min swimming at 18-19 degrees C), and the i.v. infusion of convulsants started 15 min thereafter. The latency to the onset of several convulsant signs and death was measured, and the doses of convulsants producing convulsions and death were calculated. Additional experiments included mice swimming at room temperature, and those which were stressed repeatedly (twice a day for four consecutive days, plus one stressful procedure on the fifth day). Swim stress increased the dose needed to produce convulsant signs and death after bicuculline, picrotoxin, pentylenetetrazole, strychnine and 4-aminopyridine, while kainic acid-induced convulsions were not affected. Using picrotoxin infusion, the effect of swimming in room temperature water was less than the effect of swimming in 18-19 degrees C water. In addition, the effect of repeated stress was less than the effect of acute stress on picrotoxin-induced convulsions. The results demonstrate that acute swim stress lowers the convulsive potency of GABA-related and some GABA-unrelated convulsants. Repeatedly stressed animals develop tolerance to anticonvulsive effect of swim stress.

Anticonvulsive effect of swim stress in mice

To explore the possible involvement of glucocorticoids in the previously observed anticonvulsive effect of swim stress, mice were, prior to administration of convulsants, subjected to treatments that diminish or enhance plasma corticosterone levels. Aminoglutethimide, the inhibitor of steroid synthesis, failed to modify convulsant doses of picrotoxin, but enhanced threshold doses of pentylenetetrazole producing myoclonus and death, both in unstressed and stressed animals. The same drug prevented the effect of stress on pentylenetetrazole-induced running bouncing clonus (RB clonus) and abolished the appearance of tonic hindlimb extension (THE). Doses of kainic acid producing convulsions and death were not affected by stress, but they were enhanced by aminoglutethimide. Corticosterone administration could not imitate the effect of swim stress. Finasteride, a 5 alpha-reductase inhibitor, did not interfere with the effect of stress on picrotoxin-induced convulsions. Swim stress failed to modify the binding of the convulsant t[3H]-butylbicycloorthobenzoate [3H]TBOB, to washed mouse forebrain membranes. The results confirmed an anticonvulsant effect of swim stress against convulsions produced by GABA-related convulsants, but they do not support the hypothesis suggesting the involvement of glucocorticoids or neurosteroids in this effect.

Brief predator odour exposure activates the HPA axis independent of locomotor changes

Although predator exposure has been proposed to elicit both behavioural responses and neuroendocrine effects in rodents, results of an increasing number studies have failed to consistently detect both of these alterations. We provide a detailed multivariate quantitative assessment of locomotor activity levels and plasma levels of adrenocorticotrophic hormone (ACTH) and corticosterone of male and female laboratory rats following brief (5 min) exposure to a predator odour, (2-propylthietane, the main constituent of weasel anal gland secretion). We show that there is a clear distinction between the behavioural and neuroendocrine responses, with predator odour inducing significant increases in corticosterone and ACTH levels without any significant accompanying changes in various locomotor activity measures.

Influence of the oestrous cycle on L-glutamate and L-aspartate transport in rat brain synaptosomes

Oestrous cycle and sex differences in sodium-dependent transport of L-[3H]glutamate and L-[3H]aspartate were investigated employing well washed synaptosomes prepared from rat brain cortex. Transport was best analysed on the basis of two components, a high and low affinity transport site. Oestrous cycle and sex differences were observed for both substrates. The high affinity transporter displayed highest affinity for glutamate transport in synaptosomes from female rats during proestrous and oestrous. This differed significantly from glutamate transport during dioestrous and in male rats. High affinity aspartate transport displayed highest affinity during oestrous and differed significantly from transport during dioestrous. Maximal velocity of high affinity glutamate transport was higher in synaptosomes from females during dioestrous compared with oestrous and lower in synaptosomes from male rats when compared with female rats in dioestrous and metoestrous. The low affinity sodium-dependent glutamate transporter displayed a 10-fold higher affinity for glutamate during proestrous than during the other three phases of oestrous and in male rats. Exogenously applied oestradiol and progesterone to synaptosomes from male rats showed no effect on glutamate or aspartate transport. No acute effect of oestradiol or progesterone on glutamate currents in oocytes expressing EAAT1 or EAAT2 subtype of glutamate transporter was observed. These results suggest hormonal regulation of high and low affinity sodium-dependent excitatory amino acid transporters over the four day oestrous cycle in synaptosomes from rat cortex. This regulation is unlikely to be due to a direct effect of oestradiol or progesterone on glutamate transporters.