Estrogen Protects Neurotransmission Transcriptome During Status Epilepticus.

Women with epilepsy commonly have premature onset of menopause. The decrease in estrogen levels is associated with increased occurrence of neurodegenerative processes and cognitive decline. Previously, we found that estradiol (E2) replacement in ovariectomized (OVX) female rats significantly reduced the seizure-related damage in the sensitive hilar region of hippocampal dentate gyrus (DG). However, the complex mechanisms by which E2 empowers the genomic fabrics of neurotransmission to resist damaging effects of status epilepticus (SE) are still unclear. We determined the protective effects of the estradiol replacement against kainic acid-induced SE-associated transcriptomic alterations in the DG of OVX rats. Without E2 replacement, SE altered expression of 44% of the DG genes. SE affected all major functional pathways, including apoptosis (61%), Alzheimer's disease (47%), cell cycle (59%), long-term potentiation (62%), and depression (55%), as well as synaptic vesicle cycle (62%), glutamatergic (53%), GABAergic (49%), cholinergic (52%), dopaminergic (55%), and serotonergic (49%) neurotransmission. However, in rats with E2 replacement the percentage of significantly affected genes after SE was reduced to the average 11% (from 8% for apoptosis to 32% for GABAergic synapse). Interestingly, while SE down-regulated most of the synaptic receptor genes in oil-injected females it had little effect on these receptors after E2-replacement. Our novel Pathway Protection analysis indicated that the E2-replacement prevented SE-related damage from 50% for GABA to 75% for dopaminergic transmission. The 15% synergistic expression between genes involved in estrogen signaling (ESG) and neurotransmission explains why low E2 levels result in down-regulation of neurotransmission. Interestingly, in animals with E2-replacement, SE switched 131 synergistically expressed ESG-neurotransmission gene pairs into antagonistically expressed gene pairs. Thus, the ESG pathway acts like a buffer against SE-induced alteration of neurotransmission that may contribute to the E2-mediated maintenance of brain function after the SE injury in postmenopausal women. We also show that the long-term potentiation is lost in OVX rats following SE but not in those with E2 replacement. The electrophysiological findings in OVX female rats with SE are corroborated by the high percentage of long-term potentiation regulated genes (62%) in oil-injected while only 13% of genes were regulated following SE in E2-replaced rats.

Anti-seizure medications and estradiol for neuroprotection in epilepsy: the 2013 update.

Current epilepsy therapy is still symptomatic using anti-seizure, rather than anti-epileptic, medications. This therapy may control the seizure activity but does not prevent or even cure epilepsy. Treatment strategies that could interfere with the process leading to epilepsy (epileptogenesis) would have significant benefits over the current approaches. Neuronal damage contributing to remodeling of the neuronal networks (such as in the hippocampus during temporal lobe epilepsy) is one of the significant components of ongoing epileptogenesis. Thus, treatment strategies alleviating seizure-induced neuronal damage and network reorganization may become powerful tools fighting the deteriorating process of epileptogenesis. Current anti-seizure medications, especially valproic acid, have some neuroprotective potential. Similarly, there is some hope of neuroprotection with newer anti-seizure drugs such as retigabine and levetiracetam. However, the neuroprotective potential of anti-seizure medications is frequently weak or masked by negative side effects associated with long-term treatment, therefore exceeding the benefits.. Thus, the attention is shifted to different compounds with already established neuroprotective potential. Among steroid hormones under investigation, two groups appear interesting: ß-estradiol and selective estrogen receptor modulators - SERM. In low doses, ß-estradiol has neuroprotective potency in neurodegenerative diseases. However, its use for seizure-induced neuroprotection is confounded by a common perception of proconvulsant features of estrogens. Here we review that both features, effects on neuronal excitability and neuroprotection, apply under specific conditions and may be separated by individualized therapy taking into account the dosage paradigm, timing, sex and age of the subjects and their gonadal hormone status (including progesterone: opposed vs. unopposed estrogen). Several studies have demonstrated that ß-estradiol has indeed potency to protect neurons from seizure-induced damage. Additional studies are required to determine exact mechanisms of ß-estradiol and SERMs in seizure-induced neuroprotection for truly individualized and effective therapy. The article presents some promising patents on anti-seizure medications.

ß-Estradiol unmasks metabotropic receptor-mediated metaplasticity of NMDA receptor transmission in the female rat dentate gyrus.

Loss of estrogen in women following menopause is associated with increased risk for cognitive decline, dementia and depression, all of which can be prevented by estradiol replacement. The dentate gyrus plays an important role in cognition, learning and memory. The gatekeeping function of the dentate gyrus to filter incoming activity into the hippocampus is modulated by estradiol in a frequency-dependent manner and involves activation of metabotropic glutamate receptors (mGluR). In the present study, we investigated whether estradiol (EB) modulates the metaplastic effect of inducing synaptic long-term potentiation (LTP) on subsequent propensity for expression of LTP in the dentate gyrus. At medial perforant path-dentate granule cell synapses in hippocampal slices of ovariectomized female rats, EB replacement was critical for an initial induction of LTP to enhance the magnitude of subsequent LTP elicited by a second high-frequency stimulation, metaplasticity, which was not present in slices from oil-treated control animals. EB enhanced expression of group I mGluRs, and the metaplastic effect of EB on LTP required activation of group I mGluRs that led to Src-family tyrosine kinase-mediated phosphorylation of NR2B subunits of N-methyl-d-aspartate receptors (NMDAR) that enhanced the magnitude of NMDAR-dependent LTP. Our data show that EB effects on LTP in the hippocampal dentate gyrus require activation of group I mGluRs, which in turn leads to functional metaplastic regulation of NR2B subunit-containing NMDARs, as opposed to direct effects of EB on NMDARs.

Effects of lesions of the bed nucleus of the stria terminalis, lateral hypothalamus, or insular cortex on conditioned taste aversion and conditioned odor aversion.

The effects of permanent forebrain lesions on conditioned taste aversions (CTAs) and conditioned odor aversions (COAs) were examined in 3 experiments. In Experiment 1, lesions of the bed nucleus of the stria terminalis had no influence on CTA or COA acquisition. Although lesions of the lateral hypothalamus induced severe hypodipsia in Experiment 2, they did not prevent the acquisition of CTAs or COAs. Finally, in Experiment 3, lesions of the insular cortex retarded CTA acquisition but had no influence on COA acquisition. The implications of these findings are discussed with regard to the forebrain influence on parabrachial nucleus function during CTA acquisition.