Vivaria housing conditions expose sex differences in brain oxidation, microglial activation, and immune system states in aged hAPOE4 mice.

Apolipoprotein E ε4 allele (APOE4) is the predominant genetic risk factor for late-onset Alzheimer's disease (AD). APOE4 mouse models have provided advances in the understanding of disease pathogenesis, but unaccounted variables like rodent housing status may hinder translational outcomes. Non-sterile aspects like food and bedding can be major sources of changes in rodent microflora. Alterations in intestinal microbial ecology can cause mucosal barrier impairment and increase pro-inflammatory signals. The present study examined the role of sterile and non-sterile food and housing on redox indicators and the immune status of humanized-APOE4 knock-in mice (hAPOe4). hAPOE4 mice were housed under sterile conditions until 22 months of age, followed by the transfer of a cohort of mice to non-sterile housing for 2 months. At 24 months of age, the redox/immunologic status was evaluated by flow cytometry/ELISA. hAPOE4 females housed under non-sterile conditions exhibited: (1) higher neuronal and microglial oxygen radical production and (2) lower CD68+ microglia (brain) and CD8+ T cells (periphery) compared to sterile-housed mice. In contrast, hAPOE4 males in non-sterile housing exhibited: (1) higher MHCII+ microglia and CD11b+CD4+ T cells (brain) and (2) higher CD11b+CD4+ T cells and levels of lipopolysaccharide-binding protein and inflammatory cytokines in the periphery relative to sterile-housed mice. This study demonstrated that sterile vs. non-sterile housing conditions are associated with the activation of redox and immune responses in the brain and periphery in a sex-dependent manner. Therefore, housing status may contribute to variable outcomes in both the brain and periphery.

Two separate, large cohorts reveal potential modifiers of age-associated variation in visual reaction time performance.

To identify potential factors influencing age-related cognitive decline and disease, we created MindCrowd. MindCrowd is a cross-sectional web-based assessment of simple visual (sv) reaction time (RT) and paired-associate learning (PAL). svRT and PAL results were combined with 22 survey questions. Analysis of svRT revealed education and stroke as potential modifiers of changes in processing speed and memory from younger to older ages (ntotal = 75,666, nwomen = 47,700, nmen = 27,966; ages 18-85 years old, mean (M)Age = 46.54, standard deviation (SD)Age = 18.40). To complement this work, we evaluated complex visual recognition reaction time (cvrRT) in the UK Biobank (ntotal = 158,249 nwomen = 89,333 nmen = 68,916; ages 40-70 years old, MAge = 55.81, SDAge = 7.72). Similarities between the UK Biobank and MindCrowd were assessed using a subset of MindCrowd (UKBb MindCrowd) selected to mirror the UK Biobank demographics (ntotal = 39,795, nwomen = 29,640, nmen = 10,155; ages 40-70 years old, MAge = 56.59, SDAge = 8.16). An identical linear model (LM) was used to assess both cohorts. Analyses revealed similarities between MindCrowd and the UK Biobank across most results. Divergent findings from the UK Biobank included (1) a first-degree family history of Alzheimer's disease (FHAD) was associated with longer cvrRT. (2) Men with the least education were associated with longer cvrRTs comparable to women across all educational attainment levels. Divergent findings from UKBb MindCrowd included more education being associated with shorter svRTs and a history of smoking with longer svRTs from younger to older ages.

Smoking is associated with impaired verbal learning and memory performance in women more than men.

Vascular contributions to cognitive impairment and dementia (VCID) include structural and functional blood vessel injuries linked to poor neurocognitive outcomes. Smoking might indirectly increase the likelihood of cognitive impairment by exacerbating vascular disease risks. Sex disparities in VCID have been reported, however, few studies have assessed the sex-specific relationships between smoking and memory performance and with contradictory results. We investigated the associations between sex, smoking, and cardiovascular disease with verbal learning and memory function. Using MindCrowd, an observational web-based cohort of ~ 70,000 people aged 18-85, we investigated whether sex modifies the relationship between smoking and cardiovascular disease with verbal memory performance. We found significant interactions in that smoking is associated with verbal learning performance more in women and cardiovascular disease more in men across a wide age range. These results suggest that smoking and cardiovascular disease may impact verbal learning and memory throughout adulthood differently for men and women.

Precision hormone therapy: identification of positive responders.

Since the introduction of menopausal hormone therapy (MHT) in the 1940s, randomized clinical trials and observational studies have been performed to determine the benefits and risks of MHT. However, MHT therapeutic impact remains under debate as multiple factors including genetic biomarkers and medical history contribute to inter-individual variations in neurodegenerative diseases. Herein, we review the characteristics of women who participated in clinical studies and methodological approaches for study analyses to assess the critical variables influencing an association between MHT and risk of neurodegenerative diseases. Outcomes of the review indicated that: (1) observational studies assessed outcomes of MHT in symptomatic women whereas MHT clinical trials were conducted in asymptomatic postmenopausal women not treated for menopausal symptoms, (2) in asymptomatic postmenopausal women, late MHT intervention was of no benefit, (3) different MHT treatments and regimens between observational studies and clinical trials may impact outcomes, and (4) observational studies may provide greater predictive validity for long-term neurological health outcomes as MHT was introduced in symptomatic women and administered over a long period of time. Going forward, achieving precision hormone therapy will require a priori identification of symptomatic women appropriate for MHT and the type and dose of MHT appropriate for their genetic profile and health risks.

Open-Label Allopregnanolone Treatment of Men with Fragile X-Associated Tremor/Ataxia Syndrome.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder affecting approximately 45% of male and 16% of female carriers of the FMR1 premutation over the age of 50 years. Currently, no effective treatment is available. We performed an open-label intervention study to assess whether allopregnanolone, a neurosteroid promoting regeneration and repair, can improve clinical symptoms, brain activity, and magnetic resonance imaging (MRI) measurements in patients with FXTAS. Six patients underwent weekly intravenous infusions of allopregnanolone (2-6 mg over 30 min) for 12 weeks. All patients completed baseline and follow-up studies, though MRI scans were not collected from 1 patient because of MRI contraindications. The MRI scans from previous visits, along with scans from 8 age-matched male controls, were also included to establish patients' baseline condition as a reference. Functional outcomes included quantitative measurements of tremor and ataxia and neuropsychological evaluations. Brain activity consisted of event-related potential N400 word repetition effect during a semantic memory processing task. Structural MRI outcomes comprised volumes of the hippocampus, amygdala, and fluid-attenuated inversion recovery hyperintensities, and microstructural integrity of the corpus callosum. The results of the study showed that allopregnanolone infusions were well tolerated in all subjects. Before treatment, the patients disclosed impairment in executive function, verbal fluency and learning, and progressive deterioration of all MRI measurements. After treatment, the patients demonstrated improvement in executive functioning, episodic memory and learning, and increased N400 repetition effect amplitude. Although MRI changes were not significant as a group, both improved and deteriorated MRI measurements occurred in individual patients in contrast to uniform deterioration before the treatment. Significant correlations between baseline MRI measurements and changes in neuropsychological test scores indicated the effects of allopregnanolone on improving executive function, learning, and memory for patients with relatively preserved hippocampus and corpus callosum, while reducing psychological symptoms for patients with small hippocampi and amygdalae. The findings show the promise of allopregnanolone in improving cognitive functioning in patients with FXTAS and in partially alleviating some aspects of neurodegeneration. Further studies are needed to verify the efficacy of allopregnanolone for treating FXTAS.

Estrogen, astrocytes and the neuroendocrine control of metabolism.

Obesity, and its associated comorbidities such as type 2 diabetes, cardiovascular diseases, and certain cancers, represent major health challenges. Importantly, there is a sexual dimorphism with respect to the prevalence of obesity and its associated metabolic diseases, implicating a role for gonadal hormones. Specifically, estrogens have been demonstrated to regulate metabolism perhaps by acting as a leptin mimetic in the central nervous system (CNS). CNS estrogen receptors (ERs) include ER alpha (ERα) and ER beta (ERß), which are found in nuclear, cytoplasmic and membrane sites throughout the brain. Additionally, estrogens can bind to and activate a G protein-coupled estrogen receptor (GPER), which is a membrane-associated ER. ERs are expressed on neurons as well as glia, which are known to play a major role in providing nutrient supply for neurons and have recently received increasing attention for their potentially important involvement in the CNS regulation of systemic metabolism and energy balance. This brief overview summarizes data focusing on the potential role of astrocytic estrogen action as a key component of estrogenic modulation responsible for mediating the sexual dimorphism in body weight regulation and obesity.

Selective oestrogen receptor modulators differentially potentiate brain mitochondrial function.

The mitochondrial energy-transducing capacity of the brain is important for long-term neurological health and is influenced by endocrine hormone responsiveness. The present study aimed to determine the role of oestrogen receptor (ER) subtypes in regulating mitochondrial function using selective agonists for ERα (propylpyrazoletriol; PPT) and ERß (diarylpropionitrile; DPN). Ovariectomised female rats were treated with 17ß-oestradiol (E(2) ), PPT, DPN or vehicle control. Both ER selective agonists significantly increased the mitochondrial respiratory control ratio and cytochrome oxidase (COX) activity relative to vehicle. Western blots of purified whole brain mitochondria detected ERα and, to a greater extent, ERß localisation. Pre-treatment with DPN, an ERß agonist, significantly increased ERß association with mitochondria. In the hippocampus, DPN activated mitochondrial DNA-encoded COX I expression, whereas PPT was ineffective, indicating that mechanistically ERß, and not ERα, activated mitochondrial transcriptional machinery. Both selective ER agonists increased protein expression of nuclear DNA-encoded COX IV, suggesting that activation of ERß or ERα is sufficient. Selective ER agonists up-regulated a panel of bioenergetic enzymes and antioxidant defence proteins. Up-regulated proteins included pyruvate dehydrogenase, ATP synthase, manganese superoxide dismutase and peroxiredoxin V. In vitro, whole cell metabolism was assessed in live primary cultured hippocampal neurones and mixed glia. The results of analyses conducted in vitro were consistent with data obtained in vivo. Furthermore, lipid peroxides, accumulated as a result of hormone deprivation, were significantly reduced by E(2) , PPT and DPN. These findings suggest that the activation of both ERα and ERß is differentially required to potentiate mitochondrial function in brain. As active components in hormone therapy, synthetically designed oestrogens as well as natural phyto-oestrogen cocktails can be tailored to improve brain mitochondrial endpoints.

17beta-Estradiol potentiates field excitatory postsynaptic potentials within each subfield of the hippocampus with greatest potentiation of the associational/commissural afferents of CA3.

We sought to determine the impact of 17beta-estradiol throughout the hippocampal trisynaptic pathway and to investigate the afferent fiber systems within CA1 and CA3 in detail. To achieve this objective, we utilized multielectrode arrays to simultaneously record the field excitatory postsynaptic potentials from the CA1, dentate gyrus, and CA3 of rat hippocampal slices in the presence or absence of 100 pM 17beta-estradiol. We confirmed our earlier findings in CA1, where 17beta-estradiol significantly increased field excitatory postsynaptic potentials amplitude (20%+/-3%) and slope (22%+/-7%). 17beta-Estradiol significantly potentiated the field excitatory postsynaptic potentials in dentate gyrus, amplitude (15%+/-4%) and slope (17%+/-5), and in CA3, amplitude (15%+/-4%) and slope (19%+/-5%). Using a high-density multielectrode array, we sought to determine the source of potentiation in CA1 and CA3 by determining the impact of 17beta-estradiol on the apical afferents and the basal afferents within CA1 and on the mossy fibers and the associational/commissural fibers within CA3. In CA1, 17beta-estradiol induced a modest increase in the amplitude (7%+/-2%) and slope (9%+/-3%) following apical stimulation with similar magnitude of increase following basal stimulation amplitude (10%+/-2%) and slope (12%+/-3%). In CA3, 17beta-estradiol augmented the mossy fiber amplitude (15%+/-3%) and slope (18%+/-6%) and the associational/commissural fiber amplitude (31%+/-13%) and slope (40%+/-15%). These results indicate that 17beta-estradiol potentiated synaptic transmission in each subfield of the hippocampal slice, with the greatest magnitude of potentiation at the associational/commissural fibers in CA3. 17beta-Estradiol regulation of CA3 responses provides a novel site of 17beta-estradiol action that corresponds to the density of estrogen receptors within the hippocampus. The implications of 17beta-estradiol potentiation of the field potential in each of the hippocampal subfields and in particular CA3 associational/commissural fibers for memory function and clinical assessment are discussed.

17Beta-estradiol induced Ca2+ influx via L-type calcium channels activates the Src/ERK/cyclic-AMP response element binding protein signal pathway and BCL-2 expression in rat hippocampal neurons: a potential initiation mechanism for estrogen-induced neuroprotection.

Our group and others have demonstrated that 17beta-estradiol (E2) induces neurotrophic and neuroprotective responses in hippocampal and cortical neurons which are dependent upon the Src/extracellular signal-regulated kinase (ERK) signaling pathways. The purpose of this study was to determine the upstream mechanism(s) that initiates the signaling cascade leading to E2-inducible neuroprotection. We tested the hypothesis that E2 activates rapid Ca(2+) influx in hippocampal neurons, which would lead to activation of the Src/ERK signaling cascade and up-regulation of Bcl-2 protein expression. Using fura-2 ratiometric Ca(2+) imaging, we demonstrated that E2 induced a rapid rise of intracellular Ca(2+) concentration ([Ca(2+)](i)) within minutes of exposure which was blocked by an L-type Ca(2+) channel antagonist. Inhibition of L-type Ca(2+) channels resulted in a loss of E2 activation of the Src/ERK cascade, activation of cyclic-AMP response element binding protein (CREB) and subsequent increase in Bcl-2. Real-time intracellular Ca(2+) imaging combined with pERK immunofluorescence, demonstrated that E2 induced [Ca(2+)](i) was coincident with ERK activation in the same neuron. Small interfering RNA knockdown of CREB resulted in a loss of E2 activation of CREB and subsequent E2-induced increase of Bcl-2 expression. We further demonstrated the presence of specific membrane E2 binding sites in hippocampal neurons. Together, these data indicate that E2-induced Ca(2+) influx via the L-type Ca(2+) channel is required for E2 activation of the Src/ERK/CREB/Bcl-2 signaling. Implications of these data for understanding estrogen action in brain and use of estrogen therapy for prevention of neurodegenerative disease are discussed.

17beta-estradiol induces Ca2+ influx, dendritic and nuclear Ca2+ rise and subsequent cyclic AMP response element-binding protein activation in hippocampal neurons: a potential initiation mechanism for estrogen neurotrophism.

Previous studies from our laboratory have shown that 17beta-estradiol (E2) promotes neurite outgrowth in hippocampal and cortical neurons. The neurotrophic effect of E2 seen in vitro has also been observed in vivo by other investigators who found that E2 enhances the density of dendritic spines involved in neuronal synaptic connection. To investigate the rapid upstream mechanisms initiating the E2 neurotrophic effect, we tested the hypothesis that E2 would directly activate Ca2+ influx in primary hippocampal neurons, which would result in activation of the transcription factor, cyclic AMP response element-binding protein (CREB), and regulate E2 enhancement of neurite outgrowth. Using fura-2 ratiometric and fluo-3 Ca2+ imaging, we demonstrated that E2 induced a significant rise in intracellular Ca2+ concentration ([Ca2+]i) through E2-induced Ca2+ influx. Interestingly, the rise in [Ca2+]i occurred not only in the cytoplasm, but also in the nucleus and dendrites of hippocampal neurons. Since CREB is activated by Ca2+-dependent kinases and is required for certain aspects of synaptic plasticity, we investigated whether E2 would lead to activation of CREB. Western immunoblotting and immunocytochemical analyses revealed that E2 induced rapid CREB activation consistent with rapid intracellular Ca2+ signaling, which was dependent on the influx of extracellular Ca2+. E2-induced increase in dendritic spine marker protein spinophilin was abolished following treatment with a small interfering RNA against CREB, indicating that E2-induced neurotrophic effect requires the upstream CREB activation. Results of these analyses indicate that E2-induced neurotrophic responses are mediated by a Ca2+ signaling cascade that is dependent upon extracellular Ca2+ and CREB activation. These data provide insights into the initiating mechanisms required to activate the estrogen neurotrophic response and provide a mechanistic framework for determining the neurotrophic efficacy of existing and emerging estrogen therapies for the brain.

Regulation and mechanism of L-type calcium channel activation via V1a vasopressin receptor activation in cultured cortical neurons.

We have sought to elucidate the biochemical mechanisms that underlie the memory enhancing properties of the neural peptide vasopressin. Toward that goal we have investigated vasopressin induction of calcium signaling cascades, long held to be involved in long-term memory function, in neurons derived from the cerebral cortex, a brain region associated with long-term memory. Our previous studies demonstrated that in cultured cortical neurons, V1a vasopressin receptor (V1aR) activation resulted in a sustained rise in intracellular calcium concentration that was dependent on calcium influx (Son & Brinton, 1998). To investigate the mechanism of V1aR-induced calcium influx, we investigated V1aR activation of the calcium channel subtype(s) in cortical neurons cultured from Sprague-Dawley rat embryonic day 18 fetuses. The results of these analyses demonstrated that the L-type calcium channel blocker nifedipine blocked 250 nM V1 vasopressin receptor agonist (V1 agonist)-induced calcium influx. Intracellular calcium imaging analyses using fura-2AM demonstrated that blockade of L-type calcium channels prevented the 250 nM V1 agonist-induced rise in intracellular calcium concentration. These results indicate that the influx of extracellular calcium via L-type calcium channels is an essential step in the initiation of the V1 agonist-induced rise in intracellular calcium concentration. To determine the mechanism of V1aR activation of L-type calcium channels, regulatory components of the phosphatidylinositol signaling pathway were investigated. The results of these analyses demonstrated that V1 agonist-induced calcium influx was blocked by both a phospholipase C inhibitor (U-73122) and a protein kinase C inhibitor (bisindolylmaleimide I). Further analysis of V1aR activation of protein kinase C (PKC) demonstrated that V1 agonist induced PKC activity within 1 min of exposure in cultured cortical neurons. These data indicate that in cultured cortical neurons, V1aR activation regulates the influx of extracellular calcium via L-type calcium channel activation through a protein kinase-C-dependent mechanism. The results of these studies provide biochemical mechanisms by which vasopressin could enhance memory function. Those mechanisms include a complex cascade that is initiated by activation of the phosphatidylinositol pathway, activation of protein kinase C, followed by phosphorylation of L-type calcium channels to initiate the influx of extracellular calcium to activate a cascade of calcium-dependent release of intracellular calcium.

Cellular and molecular mechanisms of estrogen regulation of memory function and neuroprotection against Alzheimer's disease: recent insights and remaining challenges.

This review focuses on recent advances in our knowledge of estrogen action in the brain. The greatest amount of attention was devoted to those studies that impact our understanding of estrogen regulation of memory function and prevention of degenerative diseases associated with memory systems, such as Alzheimer's disease. A review of recent advances in our understanding of estrogen receptors, both nuclear and membrane, is also presented. Finally, these data are considered in regard to their relevancy to the use of estrogen replacement therapy for cognitive health throughout menopause and the development of an estrogen replacement therapy designed for the unique requirements of the brain.

Vasopressin-induced neurotrophism in cultured neurons of the cerebral cortex: dependency on calcium signaling and protein kinase C activity.

Neuronal process outgrowth has been postulated to be one of the fundamental steps involved in neuronal development. To test whether vasopressin can influence neuronal development by acting on the outgrowth of neuronal processes, we determined the neurotrophic action of the memory-enhancing peptide, vasopressin, in neurons derived from the cerebral cortex, a site of integrative cognitive function and long-term memory. Exposure to V(1) receptor agonist significantly increased multiple features of nerve cell morphology, including neurite length, number of branches, branch length, number of branch bifurcation points and number of microspikes. The dose-response profile of V(1) receptor agonist-induced neurotrophism exhibited a biphasic function, with lower concentrations inducing a significant increase while higher concentrations generally induced no significant effect. The neurotrophic effect of V(1) receptor activation did not require growth factors present in serum. Analysis of the regional selectivity of the vasopressin-induced neurotrophic effect revealed significant V(1) receptor agonist-induced neurotrophism in occipital and parietal neurons, whereas frontal and temporal neurons were unresponsive. Results of experiments to determine the mechanism of vasopressin-induced neurotrophism demonstrated that vasopressin-induced neurotrophism is dependent on V(1)a receptor activation, requires L-type calcium channel activation and activation of both pathways of the phosphatidylinositol signaling cascade, inositol trisphosphate and protein kinase C. These studies are the first to describe a functional cellular response for vasopressin in the cerebral cortex. The findings are discussed with respect to their implications for understanding the role of vasopressin-induced neurotrophism, the associated signaling pathways required for this response, and the ability of vasopressin to enhance memory function.

Spatial, cellular and temporal basis of vasopressin potentiation of norepinephrine-induced cAMP formation.

This study investigated the spatial distribution of vasopressin V(1) and beta(1)-adrenoceptors within hippocampal subfields and lamina in an attempt to localize the site(s) of interaction between these two receptor systems. In addition, the cell types, neuronal and glial, in which the vasopressin-induced neuromodulation occurs, were identified. Lastly, the temporal constraints of the potentiation induced by vasopressin were investigated. Results of these analyses demonstrated multiple sites within the hippocampus where the interaction between vasopressin and norephinephrine could occur. Moreover, vasopressin-induced potentiation of adrenergic stimulated cyclase occurred in both hippocampal neurons and glia whereas it did not occur in undifferentiated neurons. Analysis of the temporal constraints of vasopressin-induced potentiation revealed that pre-activation of the vasopressin V(1) receptor for 1 min yielded greater potentiation than simultaneous exposure to vasopressin and norepinephrine. These data provide insights into the spatial and temporal characteristics for the interaction between the vasopressin receptor and adrenoceptor systems and provide a cellular and biochemical rationale for the behavioral findings of Kovács and De Wied.

Vasopressin and oxytocin receptor mRNA expression during rat telencephalon development.

We investigated the developmental expression of vasopressin and oxytocin receptor and peptide mRNA using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot hybridization. Messenger RNAs for both vasopressin receptor subtypes V(1)a and V(2)were present in the telencephalon from embryonic day 12 to day 20. Both V(1)a and V(2)receptor mRNA increased on day 13 and then remained stable from embryonic day 13 to day 20. Messenger RNA for the vasopressin peptide was also detected in the telencephalon from day 12 to day 20, indicating that vasopressin could be synthesized within the rat cerebral cortex during rat embryonic development. Oxytocin receptor mRNA expression was also present in the telencephalon, but expression levels varied considerably from day 12 to day 20. No oxytocin mRNA expression was detected during rat telencephalon development. Temporal patterns of vasopressin receptor and vasopressin peptide mRNA expression along with oxytocin receptor mRNA suggest a temporal role for vasopressin- and oxytocin-mediated actions during rat telencephalon development.

The estrogen replacement therapy of the Women's Health Initiative promotes the cellular mechanisms of memory and neuronal survival in neurons vulnerable to Alzheimer's disease.

OBJECTIVES: The current study investigated the neurotrophic and neuroprotective action of the complex formulation of conjugated equine estrogens (CEEs), the most frequently prescribed estrogen replacement therapy in the United States and the estrogen replacement therapy of the Women's Health Initiative. METHODS: Videomicroscopic, morphologic and biochemical analyses were conducted in primary cultures of hippocampal neurons to determine the neurotrophic and neuroprotective properties of CEEs. RESULTS: Results of these analyses demonstrated that CEEs significantly increased hippocampal neuronal outgrowth, a cellular marker of memory formation. Dose response analyses indicated that the lowest effective concentration of CEEs exerted the maximal neurotrophic effect. Results of neuroprotection studies demonstrated that CEES induced highly significant neuroprotection against beta amyloid(25-35), hydrogen peroxide and glutamate-induced toxicity. CONCLUSIONS: CEEs induced cellular markers of memory function in neurons critical to memory and vulnerable to negative effects of aging and Alzheimer's disease. In addition, CEEs significantly and potently protected neurons against toxic insults associated with Alzheimer's disease. Because CEEs are the estrogen replacement therapy of the Women's Health Initiative, results of the current study could provide cellular mechanisms for effects of CEEs on cognitive function and risk of Alzheimer's disease derived from this prospective clinical trial.

A women's health issue: Alzheimer's disease and strategies for maintaining cognitive health.

Data indicate that women are two to three times as likely as men to develop Alzheimer's disease, making this neurodegenerative condition a women's health issue. The challenge of an aging population and women's vulnerability to Alzheimer's disease is reviewed. Strategies to prevent Alzheimer's disease in women are discussed. These strategies include cognitive challenge and exercise, estrogen replacement therapy, anti-inflammatory agents, and antioxidants. Each of these strategies has been associated with a decreased risk of Alzheimer's disease and could have a profound impact on the incidence of Alzheimer's disease in the most vulnerable segment of the population, postmenopausal women.

In vivo and in vitro hyperbaric studies in mice suggest novel sites of action for ethanol.

The present study uses increased atmospheric pressure as an ethanol antagonist to test the hypothesis that allosteric coupling pathways in the GABA(A) receptor complex represent initial sites of action for ethanol. This was accomplished using behavioral and in vitro measures to determine the effects of pressure on ethanol and other GABAergic drugs in C57BL/6 and LS mice. Behaviorally, exposure to 12 times normal atmospheric pressure (ATA) of a helium-oxygen gas mixture (heliox) antagonized loss of righting reflex (LORR) induced by the allosteric modulators ethanol and pentobarbital, but did not antagonize LORR induced by the direct GABA agonist 4,5,6,7-tetrahydroisoxazolo-pyridin-3-ol (THIP). Similarly, exposure to 12 ATA heliox antagonized the anticonvulsant effects verses isoniazid of ethanol, diazepam and pentobarbital. Biochemically, exposure to 12 ATA heliox antagonized potentiation of GABA-activated 36Cl-uptake by ethanol, flunitrazepam and pentobarbital in LS mouse brain preparations, but did not alter GABA-activated 36Cl- uptake per se. In contrast to its antagonist effect versus other allosteric modulators, pressure did not antagonize these behavioral or in vitro effects induced by the neuroactive steroid, 3alpha-hydroxy-5beta-pregnan-20-one (3alpha,5beta-P). These findings add to evidence that pressure directly and selectively antagonizes drug effects mediated through allosteric coupling pathways. The results fit predictions, and thus support the hypothesis that allosteric coupling pathways in GABA(A) receptors represent initial sites of action for ethanol. Collectively, the results suggest that there may be common physicochemical and underlying structural characteristics that define ethanol sensitive regions of receptor proteins and/or their associated membranes that can be identified by pressure within (e.g., GABA(A)) and possibly across (e.g., GABA(A), NMDA, 5HT3) receptors.

17beta-estradiol enhances NMDA receptor-mediated EPSPs and long-term potentiation.

Gonadal steroid hormones influence CNS functioning through a variety of different mechanisms. To test the hypothesis that estrogen modulates synaptic plasticity in the hippocampus, in vitro hippocampal slices from 2-mo-old Sprague-Dawley male rats were used to determine the effect of 17beta-estradiol on both N-methyl-D-aspartate (NMDA) receptor-mediated excitatory postsynaptic potentials (EPSPs) through intracellular recordings and long-term potentiation (LTP) through extracellular recordings. Intracellular EPSPs and extracellular field EPSPs (fEPSPs) were recorded from CA1 pyramidal cells by stimulating Schaffer collateral fibers. In intracellular experiments, slices were perfused with medium containing bicuculline (5 microM) and low Mg2+ (0.1 mM) to enhance the NMDA receptor-mediated currents and 6, 7-dinitroquinoxaline-2,3-dione (DNQX) (10 microM) to block the alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprianate (AMPA) receptor-mediated component. The effects of 17beta-estradiol on NMDA receptor-mediated activity were excitatory; concentrations >10 nM induced seizure activity, and lower concentrations (1 nM) markedly increased the amplitude of NMDA-mediated EPSPs (both the first and second responses increased during paired pulse stimulation by 180 and 197%, respectively). In extracellular experiments, slices perfused with 17beta-estradiol (100 pM) exhibited a pronounced, persisting, and significant enhancement of LTP of both the fEPSP slope (192%) and fEPSP amplitude (177%) compared with control slices (fEPSP slope = 155%; fEPSP amplitude = 156%) 30 min after high-frequency stimulation. These data demonstrate that estrogen enhances NMDA receptor-mediated currents and promotes an enhancement of LTP magnitude.

Vasopressin-induction of the immediate early gene, NGFI-A, in cultured hippocampal glial cells.

Our earlier autoradiographic work had documented a wide distribution of vasopressin receptors in the hippocampus [R.E. Brinton, K.W. Gee, J.K. Wamsley, T.P. Davis, H.I. Yamamura, Regional distribution of putative vasopressin receptors in rat brain and pituitary by quantitative autoradiography, in: Proc. Natl. Acad. Sci. USA, 81 (1984) pp. 7248-7252; C. Chen, R.D. Brinton, T.J. Shors, R.F. Thompson, [Arg 8]-Vasopressin-induction of long lasting potentiation of synaptic transmission in the dentate gyrus, Hippocampus 3 (1993) 193-203.] which suggested the possibility that receptors for vasopressin were present in both neurons and glia. In the periphery, vasopressin is a potent mitogen in select proliferative cell types [E. Rozengurt, A. Legg, P. Pettican, Vasopressin stimulation of mouse 3T3 cell growth, Proc. Natl. Acad. Sci. USA, 76 (1979) pp. 1284-1287.] which also suggested a possible association between vasopressin receptor activation and the proliferative capacity of astrocytes. We therefore investigated whether vasopressin would induce the expression of the immediate early response gene, NGFI-A (also known as zif/268, ZENK, egr-1, krox 24), which is associated with initiation of mitogenesis [M. Sheng, M.E. Greenberg, The regulation and function of c-fos and other immediate early genes in the nervous system, Neuron, 4 (1990) pp. 477-485.]. Cultured hippocampal glial cells were exposed to vasopressin or a selective V1 vasopressin receptor agonist and in situ hybridization for NGFI-A mRNA was conducted. Results of these experiments demonstrated that vasopressin induced a highly significant dose-dependent increase in the number of cells expressing NGFI-A. Studies to determine the receptor subtype mediating vasopressin induction of NGFI-A were conducted utilizing the specific V1 agonist, [Phe2, Ile3, Orn8]-vasopressin. The V1 receptor agonist induced a highly significant dose dependent increase in the number of grains per NGFI-A positive cell. Time course analysis demonstrated that V1 agonist induction of NGFI-A occurred within 5 min, was maximally induced at 15 min of exposure and exhibited a gradual decline within 30 min of exposure which continued to decline over the 60 min time course. Glial cell responsivity was selective in that vasopressin and V1 agonist induction of NGFI-A occurred in a subpopulation of glial cells. Within a sea of glial cells, vasopressin and V1 agonist would induce islands of NGFI-A positive cells. Results of combined immunocytochemical labeling for the astrocyte specific marker, GFAP, and in situ hybridization for NGFI-A demonstrated that V1 agonist-induced NGFI-A expression occurred in GFAP positive cells. We observed no evidence for V1 agonist induction of NGFI-A in neurons. Collectively, these data document that vasopressin, acting via V1 vasopressin receptors, induces a highly significant increase in NGFI-A expression in select GFAP positive hippocampal astrocytes. To our knowledge, these data are the first report of a vasopressin mediated response in hippocampal glial cells. The potential functional significance of these findings is discussed.