Protein tyrosine phosphatase receptor type Q in cerebrospinal fluid reflects ependymal cell dysfunction and is a potential biomarker for adult chronic hydrocephalus.

BACKGROUND AND PURPOSE: Protein tyrosine phosphatase receptor type Q (PTPRQ) was extracted from the cerebrospinal fluid (CSF) of patients with probable idiopathic normal-pressure hydrocephalus (iNPH) by proteome analysis. We aimed to assess the feasibility of using CSF PTPRQ concentrations for the additional diagnostic criterion of iNPH in Japanese and Finnish populations. METHODS: We compared PTPRQ concentrations among patients with probable iNPH and neurologically healthy individuals (normal control [NC] group), patients with normal-pressure hydrocephalus (NPH) of acquired and congenital/developmental aetiologies, patients with Alzheimer's disease and patients with Parkinson's disease in a Japanese analysis cohort. A corresponding iNPH group and NC group in a Finnish cohort was used for validation. Patients in the Finnish cohort who underwent biopsy were classified into two groups based on amyloid and/or tau deposition. We measured PTPRQ expression levels in autopsied brain specimens of iNPH patients and the NC group. RESULTS: Cerebrospinal fluid PTPRQ concentrations in the patients with NPH of idiopathic, acquired and congenital/developmental aetiologies were significantly higher than those in the NC group and those with Parkinson's disease, but iNPH showed no significant differences when compared with those in the Alzheimer's disease group. For the patients with iNPH, the area under the receiver-operating characteristic curve was 0.860 in the Japanese iNPH and 0.849 in the Finnish iNPH cohorts. Immunostaining and in situ hybridization revealed PTPRQ expression in the ependymal cells and choroid plexus. It is highly possible that the elevated PTPRQ levels in the CSF are related to ependymal dysfunction from ventricular expansion. CONCLUSIONS: Cerebrospinal fluid PTPRQ levels indicated the validity of this assay for auxiliary diagnosis of adult chronic hydrocephalus.

Protein kinase C -activating isophthalate derivatives mitigate Alzheimer's disease-related cellular alterations.

Abnormal protein kinase C (PKC) function contributes to many pathophysiological processes relevant for Alzheimer's disease (AD), such as amyloid precursor protein (APP) processing. Phorbol esters and other PKC activators have been demonstrated to enhance the secretion of soluble APPα (sAPPα), reduce the levels of ß-amyloid (Aß), induce synaptogenesis, and promote neuroprotection. We have previously described isophthalate derivatives as a structurally simple family of PKC activators. Here, we characterised the effects of isophthalate derivatives HMI-1a3 and HMI-1b11 on neuronal viability, neuroinflammatory response, processing of APP and dendritic spine density and morphology in in vitro. HMI-1a3 increased the viability of embryonic primary cortical neurons and decreased the production of the pro-inflammatory mediator TNFα, but not that of nitric oxide, in mouse neuron-BV2 microglia co-cultures upon LPS- and IFN-γ-induced neuroinflammation. Furthermore, both HMI-1a3 and HMI-1b11 increased the levels of sAPPα relative to total sAPP and the ratio of Aß42/Aß40 in human SH-SY5Y neuroblastoma cells. Finally, bryostatin-1, but not HMI-1a3, increased the number of mushroom spines in proportion to total spine density in mature mouse hippocampal neuron cultures. These results suggest that the PKC activator HMI-1a3 exerts neuroprotective functions in the in vitro models relevant for AD by reducing the production of TNFα and increasing the secretion of neuroprotective sAPPα.

Polypyrrole-coated electrodes show thickness-dependent stability in different conditions during 42-day follow-up in vitro.

Electroconductive polypyrrole/dodecylbenzenesulphonate (PPy/DBS) has been proposed as novel electrode coating for biomedical applications. However, as yet, little is known about its long-term stability in moist conditions. This study compares the stability of PPy/DBS-coated platinum electrodes that are either dry-stored, incubated, or both incubated and electrically stimulated. The electrical and material properties of three different coating thicknesses were monitored for 42 days. Initially, the PPy/DBS-coating decreased the low frequency impedance of the platinum electrodes by 52% to 79%. The dry-stored electrodes remained stable during the follow-up, whereas the properties of all the incubated electrodes were altered in three stages with thickness-dependent duration: stabilization, stable, and degradation. The coated electrodes would be applicable for short-term, low-frequency in vitro measurements of up to 14 days without electrical stimulation, and up to 7 days with stimulation. The coating thickness is bound to other coating properties, and should therefore be selected according to the specific target application. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2202-2213, 2018.

Functional screening of Alzheimer risk loci identifies PTK2B as an in vivo modulator and early marker of Tau pathology.

A recent genome-wide association meta-analysis for Alzheimer's disease (AD) identified 19 risk loci (in addition to APOE) in which the functional genes are unknown. Using Drosophila, we screened 296 constructs targeting orthologs of 54 candidate risk genes within these loci for their ability to modify Tau neurotoxicity by quantifying the size of >6000 eyes. Besides Drosophila Amph (ortholog of BIN1), which we previously implicated in Tau pathology, we identified p130CAS (CASS4), Eph (EPHA1), Fak (PTK2B) and Rab3-GEF (MADD) as Tau toxicity modulators. Of these, the focal adhesion kinase Fak behaved as a strong Tau toxicity suppressor in both the eye and an independent focal adhesion-related wing blister assay. Accordingly, the human Tau and PTK2B proteins biochemically interacted in vitro and PTK2B co-localized with hyperphosphorylated and oligomeric Tau in progressive pathological stages in the brains of AD patients and transgenic Tau mice. These data indicate that PTK2B acts as an early marker and in vivo modulator of Tau toxicity.

Lake eutrophication and brownification downgrade availability and transfer of essential fatty acids for human consumption.

Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammals and humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiological processes and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levels obtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluated how the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs (brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changes can be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributed species and commonly consumed by humans. Data from 713 lakes showed statistically significant differences in the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations and content of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA and DHA content of phytoplankton biomass (mgHUFAg-1) was significantly lower in the eutrophic lakes than in the oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA content in the muscle of piscivorous perch and phytoplankton DHA content (r=0.85) as well with the contribution of DHA-synthesizing phytoplankton taxa (r=0.83). Among all DHA-synthesizing phytoplankton this correlation was the strongest with the dinoflagellates (r=0.74) and chrysophytes (r=0.70). Accordingly, the EPA+DHA content of perch muscle decreased with increasing total phosphorus (r2=0.80) and dissolved organic carbon concentration (r2=0.83) in the lakes. Our results suggest that although eutrophication generally increase biomass production across different trophic levels, the high proportion of low-quality primary producers reduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophication and brownification decrease the nutritional quality of fish for human consumers.

Uniform and electrically conductive biopolymer-doped polypyrrole coating for fibrous PLA.

Three-dimensional, fibrous scaffolds can be easily fabricated from polylactide (PLA) using melt spinning and textile techniques. However, the surface properties of PLA scaffolds are not ideal for tissue engineering purposes. Furthermore, electrically conducting scaffolds are required to deliver electrical stimulation to cells. In this study, uniform, electrically conducting polypyrrole (PPy) coatings were fabricated on biodegradable PLA fibers. Biopolymer dopants-hyaluronic acid (HA) and chondroitin sulfate (CS)-were compared, and a PPy/CS composition was analyzed further. The effect of the oxidative polymerization conditions on the PLA fibers and CS counterion was studied. Furthermore, the initial molecular weight of CS and its degree of polymerization were determined. Our experiments showed that the molecular weight of CS decreases under oxidizing conditions but that the decay is not significant with the short polymerization process we used. The coating process was transferred to nonwoven PLA fabrics, and the stability of PPy/CS coating was studied during in vitro incubation in phosphate buffer solution at physiological temperature. The conductivity and surface roughness of the coating decayed during the 20-day incubation. The mechanical strength, however, remained at the initial level. Thus, the fabricated structures are suitable for short-term electrical stimulation adequate to promote cell functions in specific cases. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1721-1729, 2016.

Adjustment of apnea-hypopnea index with severity of obstruction events enhances detection of sleep apnea patients with the highest risk of severe health consequences.

INTRODUCTION: Presently, the severity of obstructive sleep apnea (OSA) is estimated based on the apnea-hypopnea index (AHI). Unfortunately, AHI does not provide information on the severity of individual obstruction events. Previously, the severity of individual obstruction events has been suggested to be related to the outcome of the disease. In this study, we incorporate this information into AHI and test whether this novel approach would aid in discriminating patients with the highest risk. We hypothesize that the introduced adjusted AHI parameter provides a valuable supplement to AHI in the diagnosis of the severity of OSA. METHODS: This hypothesis was tested by means of retrospective follow-up (mean ± sd follow-up time 198.2 ± 24.7 months) of 1,068 men originally referred to night polygraphy due to suspected OSA. After exclusion of the 264 patients using CPAP, the remaining 804 patients were divided into normal (AHI < 5) and OSA (AHI ≥ 5) categories based on conventional AHI and adjusted AHI. For a more detailed analysis, the patients were divided into normal, mild, moderate, and severe OSA categories based on conventional AHI and adjusted AHI. Subsequently, the mortality and cardiovascular morbidity in these groups were determined. RESULTS: Use of the severity of individual obstruction events for adjustment of AHI led to a significant rearrangement of patients between severity categories. Due to this rearrangement, the number of deceased patients diagnosed to have OSA was increased when adjusted AHI was used as the diagnostic index. Importantly, risk ratios of all-cause mortality and cardiovascular morbidity were higher in moderate and severe OSA groups formed based on the adjusted AHI parameter than in those formed based on conventional AHI. CONCLUSIONS: The adjusted AHI parameter was found to give valuable supplementary information to AHI and to potentially improve the recognition of OSA patients with the highest risk of mortality or cardiovascular morbidity.

Genome-wide haplotype association study identifies the FRMD4A gene as a risk locus for Alzheimer's disease.

Recently, several genome-wide association studies (GWASs) have led to the discovery of nine new loci of genetic susceptibility in Alzheimer's disease (AD). However, the landscape of the AD genetic susceptibility is far away to be complete and in addition to single-SNP (single-nucleotide polymorphism) analyses as performed in conventional GWAS, complementary strategies need to be applied to overcome limitations inherent to this type of approaches. We performed a genome-wide haplotype association (GWHA) study in the EADI1 study (n=2025 AD cases and 5328 controls) by applying a sliding-windows approach. After exclusion of loci already known to be involved in AD (APOE, BIN1 and CR1), 91 regions with suggestive haplotype effects were identified. In a second step, we attempted to replicate the best suggestive haplotype associations in the GERAD1 consortium (2820 AD cases and 6356 controls) and observed that 9 of them showed nominal association. In a third step, we tested relevant haplotype associations in a combined analysis of five additional case-control studies (5093 AD cases and 4061 controls). We consistently replicated the association of a haplotype within FRMD4A on Chr.10p13 in all the data set analyzed (OR: 1.68; 95% CI: (1.43-1.96); P=1.1 × 10(-10)). We finally searched for association between SNPs within the FRMD4A locus and Aß plasma concentrations in three independent non-demented populations (n=2579). We reported that polymorphisms were associated with plasma Aß42/Aß40 ratio (best signal, P=5.4 × 10(-7)). In conclusion, combining both GWHA study and a conservative three-stage replication approach, we characterised FRMD4A as a new genetic risk factor of AD.

CSF biomarkers for Alzheimer disease correlate with cortical brain biopsy findings.

OBJECTIVE: To assess the relationship between Alzheimer disease (AD)-related pathologic changes in frontal cortical brain biopsy and AD biomarkers in ventricular vs lumbar CSF, and to evaluate the relationships of AD biomarkers in CSF and cortical biopsy with the final clinical diagnosis of AD. METHODS: In 182 patients with presumed normal pressure hydrocephalus (152 with known APOE carrier status), Aß plaques and tau in the cortical brain biopsies were correlated with the ventricular and lumbar CSF Aß42, total tau, and p-tau levels measured by ELISA. In a median follow-up of 2.0 years, 51 patients developed AD dementia. RESULTS: The patients with Aß plaques in the cortical biopsy had lower (p = 0.009) CSF Aß42 levels than those with no Aß plaques. The patients with tau in the cortical biopsy had lower (p = 0.014) Aß42 but higher (p = 0.015) p-tau 181 in CSF as compared to those with no tau in the cortical biopsy. The patients with amyloid + tau + biopsies had the lowest Aß42 and highest tau and p-tau 181 levels in CSF. The Aß42 levels were lower and the tau and p-tau 181 higher in the ventricular vs corresponding lumbar CSF samples. In multivariate analysis, the presence of cortical Aß was independently predicted by the APOE ε4 carrier status and age but not by CSF Aß42 or tau levels. CONCLUSIONS: Amyloid plaques and hyperphosphorylated tau in cortical brain biopsies are reflected by low CSF Aß42 and high CSF tau and p-tau levels, respectively.

APOE and Alzheimer disease: a major gene with semi-dominant inheritance.

Apolipoprotein E (APOE) dependent lifetime risks (LTRs) for Alzheimer Disease (AD) are currently not accurately known and odds ratios alone are insufficient to assess these risks. We calculated AD LTR in 7351 cases and 10 132 controls from Caucasian ancestry using Rochester (USA) incidence data. At the age of 85 the LTR of AD without reference to APOE genotype was 11% in males and 14% in females. At the same age, this risk ranged from 51% for APOE44 male carriers to 60% for APOE44 female carriers, and from 23% for APOE34 male carriers to 30% for APOE34 female carriers, consistent with semi-dominant inheritance of a moderately penetrant gene. Using PAQUID (France) incidence data, estimates were globally similar except that at age 85 the LTRs reached 68 and 35% for APOE 44 and APOE 34 female carriers, respectively. These risks are more similar to those of major genes in Mendelian diseases, such as BRCA1 in breast cancer, than those of low-risk common alleles identified by recent GWAS in complex diseases. In addition, stratification of our data by age groups clearly demonstrates that APOE4 is a risk factor not only for late-onset but for early-onset AD as well. Together, these results urge a reappraisal of the impact of APOE in Alzheimer disease.

Low-loss silicon slot waveguides and couplers fabricated with optical lithography and atomic layer deposition.

We demonstrate low-loss silicon slot waveguides patterned with 248 nm deep-UV lithography and filled with atomic layer deposited aluminum oxide. Propagation losses less than 5 dB/cm are achieved with the waveguides. The devices are fabricated using low-temperature CMOS compatible processes. We also demonstrate simple, compact and efficient strip-to-slot waveguide couplers. With a coupler as short as 10 µm, coupling loss is less than 0.15 dB. The low-index and low-nonlinearity filling material allows nonlinearities nearly two orders of magnitude smaller than in silicon waveguides. Therefore, these waveguides are a good candidate for linear photonic devices on the silicon platform, and for distortion-free signal transmission channels between different parts of a silicon all-optical chip. The low-nonlinearity slot waveguides and robust couplers also facilitate a 50-fold local change of the waveguide nonlinearity within the chip by a simple mask design.

Brain pathology in three subjects from the same pedigree with presenilin-1 (PSEN1) P264L mutation.

AIMS: Our goal was to assess pathological lesions with respect to type and distribution and to compare these results with the clinical presentation including symptoms and mode of progression in three members of the same pedigree with a P264L presenilin-1 gene mutation. METHODS: We used immunohistochemistry and a tissue microarray technique applied to post mortem brain tissue samples. RESULTS: All three subjects were demented, one subject displayed spastic paraparesis and two had Parkinsonism. All three cases displayed abundant cotton wool plaques composed of amyloid-beta42 but also containing other proteins, for example, hyperphosphorylated tau and in one case TAR DNA binding protein 43. The distribution of the pathology varied and seemed to some extent to be related to the clinical phenotype. An association was detected between neocortical/thalamic involvement and psychiatric symptoms, between striatal/amygdaloid involvement and Parkinsonism, and between brainstem involvement and spastic paraparesis. CONCLUSIONS: Subjects from the same pedigree carrying the same mutation display a clear variability in the type and distribution of pathology as well as in their clinical symptoms. These results emphasize that still unknown factors significantly alter the pathological and clinical phenotypes in genetically predetermined disease.

Combined risk effects of IDE and NEP gene variants on Alzheimer disease.

Polymorphisms in genes encoding amyloid beta-peptide (A beta)-degrading enzymes neprilysin (NEP) and insulin-degrading enzyme (IDE) individually affect the susceptibility to Alzheimer disease (AD) among the Finnish population. Here we show that a combination of risk genotypes for NEP and IDE genes leads to a higher susceptibility to AD. Individuals with the combination of risk genotypes for NEP and IDE conferred a threefold higher susceptibility to AD when compared with individuals not carrying these genotypes. Although no significant interaction was observed between NEP and IDE genes, these data suggest that NEP and IDE exhibit an additive risk effect in AD.

Genetic study between SIRT1, PPARD, PGC-1alpha genes and Alzheimer's disease.

Single nucleotide polymorphisms (SNPs) in three diabetes-related genes (SIRT1, PPARD, PGC-1alpha) were investigated with a case-control approach. To examine the genetic association of those genes with Alzheimer's disease (AD) risk, we used the TaqMan technique to genotype five SNP sites for SIRT1, six for PPARD and eight for the PGC-1alpha gene, in 326 Finnish AD cases and 463 controls and conducted a single allele and genotypic distribution comparison as well as estimated haplotype frequencies between cases and controls. No significant differences in AD risk were found in single SNP and haplotype analyses for any of the three genes between 326 cases and 463 controls. However, in a subgroup of women older than 65 years, the frequencies of three SNPs in the SIRT1 gene were significantly different between AD and controls. We conclude that there is no real association with SNPs available in the present study between SIRT1, PPARD or PGC-1alpha genes and AD risk in the Finnish population.

Genetic study evaluating LDLR polymorphisms and Alzheimer's disease.

We genotyped SNPs rs11668477, rs12983082, rs11669576, rs2738444, rs5925 and rs1433099 in 405 Finnish AD cases and 463 controls and conducted a single allele and genotypic distribution comparison and estimated the haplotype frequencies between cases and controls and evaluated the level of biomarkers in haplotype carriers. We observed that T allele of rs2738444 was overrepresented in AD women with p=0.014 (Bonferroni corrected p=0.252). A specific haplotype block consisting of SNPs rs11669576, rs2738444 and rs5925 was identified and in women the haplotype GTT was overrepresented in AD cases when compared to controls with p=0.008. We measured CSF Abeta(42), tau and phosphorylated tau (ptau) levels in a subgroup of cases and controls and found that some genotypes were associated with increased levels of tau and ptau or a decreased Abeta(42) level in women. The specific risk haplotype GTT was associated with an increased level of tau and ptau in both men and women. Our findings suggest that LDLR gene may be associated with AD risk and its CSF biomarkers, especially in women.

Study on the association between SOAT1 polymorphisms, Alzheimer's disease risk and the level of CSF biomarkers.

BACKGROUND: In Alzheimer's disease (AD) the beta-amyloid precursor protein is excessively cleaved into Abeta(42), causing the abundant amyloid plaque loads in affected brain areas. Sterol O-acyltransferase 1 (SOAT1) has been found to regulate the production of beta-amyloid precursor protein. METHODS: We genotyped 4 SOAT1 single nucleotide polymorphism (SNP) sites (rs2247071, rs2862616, rs3753526 and rs1044925) in 410 Finnish AD cases and 455 controls and conducted a single allele and genotypic distribution comparison as well as estimating the haplotype frequencies between cases and controls and the level of biomarkers in genotype and haplotype carriers. RESULTS: The CC genotype of rs2247071 was overrepresented in the AD cases (OR = 1.38, 95% CI = 1.01-1.89, p = 0.043, Bonferroni corrected p = 0.172 with 4 tests) independent of gender, age and APOE epsilon4 allele carrier status. We did not find any significant differences between Abeta(42), tau or ptau levels in different allele, genotype or haplotype carrier cases. CONCLUSION: Our findings suggest that SOAT1 gene may possibly be only a minor risk factor in AD.

The association study between DHCR24 polymorphisms and Alzheimer's disease.

DHCR24 gene in chromosome 1 encodes seladin 1, a cholesterol synthesizing enzyme. Seladin 1 protects neurons from Abeta(42) mediated toxicity and participates in regulation of Abeta(42) formation by organizing the placement of APP cleaving beta-secretase in cholesterol-rich detergent-resistant membrane domains (DRMs). In Alzheimer's disease (AD) the level of seladin 1 in affected neurons is reduced, DRMs are disorganized and Abeta(42) formation is increased. To examine genetic association of the DHCR24 with AD, we genotyped four single nucleotide polymorphism (SNP) sites (rs638944, rs600491, rs718265, and rs7374) in 414 Finnish AD cases and 459 controls and calculated the allelic and genotypic distribution of both cases and controls. The single locus association analysis indicated that men carrying the T allele of rs600491 had an increased risk of AD (OR 1.7 95% CI 1.2-2.4; P = 0.004, Bonferroni corrected P = 0.048 with 12 tests). We estimated haplotypes of SNPs rs638944 and rs600491 between cases and controls and found overall distribution of haplotypes highly significant (P < 0.001). There was a common protective haplotype TC with frequency of 0.22 in cases and 0.30 in controls (P < 0.001) and a risk haplotype GC with frequency of 0.10 in cases and 0.05 in controls (P < 0.001). We also measured CSF Abeta(42), tau and phosphorylated tau (ptau) levels in a subgroup of AD cases (n = 44) and controls (n = 10) and found that AD cases that carry rs718265 GG had lower levels of Abeta(42) than other genotype carriers. Our findings indicate that DHCR24 gene may be associated with AD risk.

Aromatase enzyme and Alzheimer's disease.

Aromatase enzyme encoded by CYP19 gene is responsible for the formation of estrone and estradiol from C19 androgens, androstenedione and testosterone. Several lines of evidence suggest an important role for the estrogens as well as androgens in the key pathogenic processes of Alzheimer's disease (AD) such as amyloid beta (Abeta) production, hyperphosporylation of tau protein, oxidative stress and apoptosis. Moreover, epidemiological studies suggest a neuroprotective role for estrogen in AD for which reason estrogen replacement therapies have been extensively studied as a way to improve the cognition and to lower the risk of AD. Aromatase enzyme is a key player in this context as it controls estrogen biosynthesis and, therefore, it may exert neuroprotective effects via increasing the local estrogen levels in injured neurons. Consistent with this idea, brain injury in mice and rats rapidly up-regulates aromatase enzyme expression in glial cells at the injury site suggesting that aromatase may be involved in protection of injured neurons through increased estrogen levels. Additional support for the role of aromatase in AD originates from the recent genetic studies, which have shown that single nucleotide polymorphisms in CYP19 gene are independently or in synergy with other AD risk genes increasing the susceptibility for AD. These genetic findings suggest that CYP19 gene encompasses functional alterations, which may affect stability, expression or activity of the aromatase enzyme. Characterization of these novel alternations may ultimately reveal new avenues to understand and design new therapeutic approaches to AD.

Effects of estradiol on spatial learning, hippocampal cytochrome P450 19, and estrogen alpha and beta mRNA levels in ovariectomized female mice.

The brain is an important target organ for peripherally synthesized estrogen but it also has its own steroid biosynthesis producing estrogen from testosterone catalyzed by the aromatase enzyme. This study examined the effects of estrogen treatment in two spatial memory tasks, one-arm-baited radial arm maze and a position discrimination task in the T-maze in ovariectomized female mice. Hippocampal cytochrome P450 19 (encoding aromatase), and estrogen receptor alpha and beta gene expressions were also measured using real time quantitative polymerase chain reaction analysis. Estrogen (17beta-estradiol) was administered either tonically via s.c. minipellets or phasically via daily i.p. injections. In ovariectomized mice, the tonic estrogen decreased the number of reference memory errors in radial arm maze. Tonic estrogen treatment also up-regulated the expression of cytochrome P450 19 and estrogen receptors. In contrast, estrogen injections decreased the expression of cytochrome P450 19 and estrogen receptor alpha genes. The number of reference memory errors correlated negatively with estrogen receptor alpha expression. These findings indicate that peripheral estrogen levels affect neuronal estrogen synthesis by regulating the cytochrome P450 19 gene expression and also influence estrogen receptor alpha expression. The results also suggest that tonic rather than cyclic estrogen treatment might be more beneficial for cognitive functions.