Antisense oligodeoxynucleotides for estrogen receptor-beta and alpha attenuate estradiol's modulation of affective and sexual behavior, respectively

Estradiol or diarylpropionitrile decrease anxiety-like behavior of wildtype, but not estrogen receptor beta knockout, mice

Clinical and basic studies demonstrate that estrogen (E-sub-2)-based therapies influence anxiety and mood, but the receptor targets (e.g., a or ss isoform of the estrogen receptor, ER) for these effects requires further investigation. To address the specificity of E2's anxiolytic-like effects through ERss, anxiety, motor, and nociceptive behavior of ovariectomized, wildtype (WT), and ERss knockout (ssERKO) mice was examined. Mice were administered oil vehicle or ER agonists, 17ss-E2 (E2; 0.1 mg/kg; similar affinity for ERa and ERss), and a selective ER modulator, diarylpropionitrile (DPN; 0.1 mg/kg; greater affinity for ERss than ERa). Performance of mice in anxiety (open field, elevated plus maze, elevated zero maze, social interaction), motor activity (activity monitor) and nociception (tailflick, pawlick) measures was compared. Results supported our hypothesis that ERss is important in modulation of anxiety-like behavior by E2 in some tasks. Administration of E2 or DPN to WT, but not ssERKO, mice increased open field central entries, plus maze open arm time, zero maze open quadrant time, and social interaction. This pattern was neither seen in motor activity nor pain threshold measures. Thus, actions of ERss may be important for modulating anxiety-like behavior of mice.

Rapid and estrogen receptor beta mediated actions in the hippocampus mediate some functional effects of estrogen

The steroid hormone, estradiol (E(2)), has numerous targets in the central nervous system, including the hippocampus, which plays a key role in cognition and affective behavior. This review focuses on our evidence from studies in rodents that E(2) has diverse mechanisms in the hippocampus for its functional effects. E(2) has rapid, membrane-mediated effects in the hippocampus to enhance cognitive performance. Administration of E(2) to the hippocampus of rats for 10 min following training enhances performance in a hippocampus-mediated task. Increased cell firing in the hippocampus occurs within this short-time frame. Furthermore, administration of free E(2) or an E(2) conjugate, E(2):bovine serum albumin (BSA), to the hippocampus produces similar performance-enhancing effects in this task, suggesting that E(2) has membrane actions in the hippocampus for these effects. Further evidence that E(2) has rapid, membrane-mediated effects is that co-administration of E(2) and inhibitors of mitogen-activated protein kinase (MAPK), rather than intracellular E(2) receptors (ERs) or protein synthesis, attenuate the enhancing effects of E(2) in this task. Despite these data that demonstrate E(2) can have rapid and/or membrane-mediated effects in the hippocampus, there is clear evidence to suggest that intracellular ERs, particularly the beta (rather than alpha) isoform of ERs, may be important targets for E(2)'s functional effects for hippocampal processes. Administration of ligands that are specific for ERbeta, but not ERalpha, have enhancing effects on hippocampal processes similar to that of E(2) (which has similar affinity for ERalpha and ERbeta). These effects are attenuated when ERbeta expression is knocked down in transgenic models or with central administration of antisense oligonucleotides. Thus, there may be a convergence of E(2)'s actions through rapid, membrane-mediated effects and intracellular ERs in the hippocampus for these functional effects.

Viral vector-mediated delivery of estrogen receptor-alpha to the hippocampus improves spatial learning in estrogen receptor-alpha knockout mice

Estrogen, which influences both classical genomic and rapid membrane-associated signaling cascades, has been implicated in the regulation of hippocampal function, including spatial learning. Gene mutation studies suggest that estrogen effects are mediated by estrogen receptor-alpha (ER-alpha); however, because gonadal steroids influence the organization of the hippocampus during development, it has been difficult to distinguish developmental effects from those specific to adults. In this study we show that lentiviral delivery of the gene encoding ER-alpha to the hippocampus of adult ER-alpha-knockout (ER-alphaKO) mice restores hippocampal responsiveness to estrogen and rescues spatial learning. We propose that constitutive estrogen receptor activity is important for maintaining hippocampus-dependent memory function in adults.

Adult hippocampal cell proliferation is suppressed with estrogen withdrawal after a hormone-simulated pregnancy

Estradiol withdrawal after pregnancy is hypothesized to precipitate depressive symptoms in vulnerable women. A hormone-simulated pregnancy was induced in female rats and the effects of a 'postpartum' drop in estradiol on hippocampal cell proliferation were examined. All groups were ovariectomized or given sham surgery prior to treatment. Rats were randomly assigned to 'postpartum', 'postpartum'+EB (estradiol benzoate), 'postpartum'+DPN (diarylpropionitrile; an ERbeta agonist), 'postpartum'+IMI (imipramine; a tricyclic antidepressant), sham, ovariectomized (OVX), sham+IMI or OVX+IMI groups. All 'postpartum' groups received hormone injections (estradiol and progesterone) over 23 days to simulate pregnancy, while IMI groups also received daily imipramine injections. After day 23, 'postpartum' rats were withdrawn from the hormone-simulated pregnancy (mimicking the postpartum drop in gonadal hormones), while other 'postpartum' treatment groups received daily injections of DPN, EB or IMI. On day 3 'postpartum' all rats were injected with bromodeoxyuridine (BrdU; a DNA synthesis marker) and perfused 24 h later to assess cell proliferation and cell death in the dentate gyrus. 'Postpartum' hormone withdrawal decreased hippocampal cell proliferation in the 'postpartum' and 'postpartum'+EB groups only. Chronic imipramine significantly increased hippocampal cell proliferation in sham+IMI, but not OVX+IMI rats suggesting that imipramine's effects to increase hippocampal cell proliferation in female rats is related to reproductive status. Cell death (pyknotic cells) was decreased only in the 'postpartum' group. Together, these results suggest an important, though complex, role for gonadal hormones in the cellular changes accompanying this model of postpartum depression.

ERalpha, but not ERbeta, mediates the expression of sexual behavior in the female rat

Estrogen has well known effects on sexual behavior, however the role of the estrogen receptors (ER) alpha and beta on sexual behavior remains to be fully determined. This study investigated the individual and co-operative involvement of ERalpha and beta on sexual behaviors in the adult female rat. Subtype selective ER agonists, propyl-pyrazole triol (PPT; ERalpha agonist) and diarylpropionitrile (DPN; ERbeta agonist) were utilized to examine each receptor subtype's contribution, individual and co-operative, for both receptive (lordosis) and proceptive (hopping/darting, 'ear wiggling') female sexual behaviors. Ovariectomized female rats received subcutaneous injections of either: sesame oil (OIL), dimethylsulfoxide (DMSO), estradiol benzoate (EB; 10 microg/0.1 ml OIL), one of three doses of the ERalpha agonist PPT (1.25mg, 2.5mg or 5.0mg/0.1 ml DMSO), one of three doses of the ERbeta agonist DPN (1.25mg, 2.5mg or 5.0mg/0.1 ml DMSO) or a combination dose of PPT and DPN (2.5mg PPT+2.5mg DPN/0.1 ml DMSO) for two consecutive days, 48 and 24h prior to testing followed by a progesterone injection (500 microg/0.1 ml OIL) 4h prior to testing in order to elicit sexual behavior. The ERalpha agonist PPT, but not the ERbeta agonist DPN, elicited both proceptive and receptive behavior. PPT at doses of 2.5 and 5.0mg significantly elicited lordosis and proceptive behavior ('ear wiggling', hopping and darting). Intriguingly, the administration of both agonists together at the 2.5mg dose resulted in reduced levels of proceptivity and receptivity, suggesting that ERbeta modulates ERalpha's ability to elicit receptive and proceptive sexual behavior.

Parity and estrogen-administration alter affective behavior of ovariectomized rats

Evidence from clinical and basic research studies demonstrates that estradiol (E(2)) reduces anxiety and/or depressive behavior; however, this effect is not observed in all studies. One factor that may mitigate differential responses to E(2) may be previous E(2) experience, i.e. parity. To investigate this, performance in tasks that are utilized to assess whether compounds, such as E(2), can alter anxiety-like behavior (elevated plus maze) and have anti-depressant-like effects (forced swim test) were determined. Performance of ovariectomized (ovx), young (3-6 months old) rats that had never had a litter (nulliparous) was compared to that of those that had several litters in their lifetime (multiparous) following 48 h of oil vehicle or E(2) (10 microg) administration. We predicted that E(2) would decrease anxiety-like behavior and increase anti-depressant-like effects of ovx rats and that this pattern may be influenced by parity. Multiparous rats, irrespective of E(2)-priming, had increased open arm time compared to nulliparous rats. Administration of E(2) to ovx, nulliparous or multiparous rats decreased immobility in the forced swim test compared to vehicle-administration. Together, these data suggest that E(2) can alter affective behavior and rats with greater reproductive experience have decreased anxiety-like behavior in the elevated plus maze, irrespective of E(2)-priming.