Aging Female Brain Research Articles

P3‐324: Beta‐amyloid neurotoxicity and neuroprotective role of 17β estradiol in aging rat brain synaptosomes

Alzheimer's disease (AD) is the most common form of dementia in the elderly. AD is characterized by the presence of amyloid plaques which are formed from deposits of beta-amyloid protein (Aβ). Accumulation of oligomeric Aβ in the brain contributes to neuronal dysfunction and ultimately leads to neurodegeneration. During aging the brain experiences structural, molecular, and functional alterations. These changes increase during menopausal condition in females when the level of estradiol is decreased. The aim of the present study was to determine the effect of neuropeptide, neurokinin B (NKB) and beta-amyloid fragment Aβ (25-35) on 17β estradiol (E2) treated aging female rat brain of 3 months (young), 12 months (adult) and 24 months (old) age groups. The aged rats (12 and 24 months old) (n= 8 for each group) were given subcutaneous injection of 17 b -estradiol (0.1 μg/g body weight) daily for one month. After 30 days of hormone treatment, experimental animals of all the groups were sacrificed and brains were isolated for further study. Aging brain function were assayed by measuring the activities of antioxidant enzymes, monoamine oxidase (MAO), membrane bound ATPases, intracellular calcium levels and lipid peroxidation in presence of neuropeptides. The results obtained in the present work revealed that i ncreased activities of antioxidant enzymes, membrane bound ATPases and decrease in level of calcium levels, MAO actiivty and lipid peroxidation in presence of NKB and combined NKB and Aβ in vivo estradiol (E2) treated ageing rat brain. NKB treatment reversed the beneficial in preventing some of the age related changes in the brain. An in vitro incubation of E2 treated synaptosomes with Aβ showed toxic effects on all the parameters, while NKB showed stimulating effects and the combined NKB and Aβ showed a partial effects as compared to Aβ (25-35) and NKB alone. Present study elucidates an antioxidant, neuromodulatory and neuroprotective role of tachykinin peptide NKB against the beta amyloid induced toxicity in E2 treated female rats. NKB treatment reversed the beneficial in preventing some of the age related changes in the brain.

Abstract 203: Chronic and Acute Estrogen Replacement Therapy Has Different Effects in Aged Animals After Experimental Stroke

Introduction: The effect of estrogen replacement therapy (ERT) on stroke incidence and severity has been extensively debated. Clinical trials of ERT demonstrated an increased risk of stroke in treated women, but study participants were well past menopause when therapy was initiated. It has been suggested that detrimental effects of ERT may be unmasked after prolonged periods of hypoestrogenicity. To date, very few studies have examined the effect of ERT in aged animals although the timing of replacement may be critical to the neuroprotective effects of ERT. Hypothesis: We hypothesized that chronic estrogen replacement (CER) initiated in late middle age, would decrease infarct size after an induced stroke whereas acute estrogen replacement (AER) would have no beneficial effects in the aged female brain. Methods: CER was administered to aged C57BL6 mice from 17 to 20 months of age, and AER was initiated at 20 months of age. Both CER and AER treated mice were subjected to 90-minute middle cerebral artery occlusion (MCAO) at 20.5 months of age. Stroke outcomes at 24 hours of MCAO were measured. Protein levels of nuclear factor κB (NFκB), estrogen receptor α (ERα) and serum levels of pro-inflammatory cytokines were also examined. Results: Female mice that received CER showed improved stroke outcomes after MCAO (total infarct: CER vs. vehicle 34.7±2.4% vs. 58.2±2.6%; n=9/gp, p <0.05); whereas females that had AER did not. CER females exhibited diminished levels of NFκB translocation compared to AER females after stroke. AER females demonstrated both an increase in nuclear NFκB and enhanced expression of pro-inflammatory cytokines. The differential NFκB translocation was related to corresponding changes in ERα expression. Aged males benefited from ERT regardless of the timing of initiation of ERT, and had significantly reduced expression of pro-inflammatory markers after stroke compared to age-matched females. Conclusions: AER worsened stroke outcomes whereas CER was protective in aged females. A pro-inflammatory milieu emerges with age in females which was attenuated by CER treatment. Interestingly both AER and CER reduced stroke injury in aged males, suggesting sexually dimorphic effects on inflammation.

Physiological and biochemical effects of 17β estradiol in aging female rat brain

Aging in females and males is considered as the end of natural protection against age related diseases like osteoporosis, coronary heart disease, diabetes, Alzheimer's disease and Parkinson's disease. These changes increase during menopausal condition in females when the level of estradiol is decreased. The objective of this study was to observe the changes in activities of monoamine oxidase, glucose transporter-4 levels, membrane fluidity, lipid peroxidation levels and lipofuscin accumulation occurring in brains of female rats of 3 months (young), 12 months (adult) and 24 months (old) age groups, and to see whether these changes are restored to normal levels after exogenous administration of estradiol (0.1 μg/g body weight for 1 month). The results obtained in the present work revealed that normal aging was associated with significant increases in the activity of monoamine oxidase, lipid peroxidation levels and lipofuscin accumulation in the brains of aging female rats, and a decrease in glucose transporter-4 level and membrane fluidity. Our data showed that estradiol treatment significantly decreased monoamine oxidase activity, lipid peroxidation and lipofuscin accumulation in brain regions of aging rats, and a reversal of glucose transporter-4 levels and membrane fluidity was achieved, therefore it can be concluded from the present findings that estradiol's beneficial effects seemed to arise from its antilipofuscin, antioxidant and antilipidperoxidative effects, implying an overall anti-aging action. The results of this study will be useful for pharmacological modification of the aging process and applying new strategies for control of age related disorders.

Frontiers proposal. National Institute on Aging “bench to bedside: estrogen as a case study”

On 28-29 September 2004, the National Institute on Aging (NIA) convened scientists for a workshop on the aging female brain focused on translating into clinical practice discoveries concerning estrogens and progestogens. Workshop objectives were to examine effects of estrogen and progestogen on brain and cognitive function in relation to aging, to examine consistencies and apparent discrepancies between Women's Health Initiative Memory Study findings and other research on cognitive function, to determine whether additional hormone interventions could be developed in this area, and to offer advice on design of clinical trials for other interventions that might ameliorate cognitive aging. Following the workshop, participants joined by other interested scientists organized into regional work groups to continue the dialogue begun in Bethesda and to propose recommendations for NIA. The resulting recommendations, referred to as the "Frontiers Proposal for Estrogen and Cognitive Aging", acknowledge the persistence of critical gaps in our understanding of how decline in ovarian steroid secretion during reproductive aging and use of ovarian steroid hormone therapy affect normal brain function and risk for late-life neurodegenerative disorders such as Alzheimer's disease. There is a pressing need for preclinical, human, and integrated studies on the relationship between the menopausal transition and midlife exposures to estrogens, progestogens and related compounds, and risks for age-associated cognitive disorders. Research is also needed on better predictors of adverse cognitive outcomes, valid biomarkers for risks associated with hormone therapy use, enhanced tools for monitoring brain function and disease progression, and novel forms of therapy for improving long-term cognitive outcomes.

Sex-dependent differences in aged rat brain mitochondrial function and oxidative stress

Females show lower incidences of several neurodegenerative diseases related to oxidative stress and mitochondrial dysfunction than males. In addition, female rats show more differentiated mitochondria than males in several tissues. The aim of this work was to investigate the existence of sex-dependent differences in brain mitochondrial bioenergetics and oxidative balance in aged rats. Results showed that aged female rat brain had a lower mitochondria content than aged male brain but with a greater differentiation degree given the higher mitochondrial protein content and mitochondrial complex activities in females. Female rat brain also showed a better oxidative balance than that of males, reflected by the fact that higher mitochondrial respiratory chain function is accompanied by a similar ROS production and greater antioxidant enzyme activities, which could be responsible for the lesser oxidative damage observed in proteins and lipids in this sex. Interestingly, levels of UCP4 and UCP5—proteins related to a decrease in ROS production—were also higher in females. In conclusion, aged female rat brain had more differentiated mitochondria than male brain and showed a better control of oxidative stress balance, which could be due, in part, to the neuroprotective effect of UCPs.

Motherhood mitigates aging-related decrements in learning and memory and positively affects brain aging in the rat

The current work examined spatial learning and memory (i.e., latencies to find a baited food well) in age-matched nulliparous, primiparous and multiparous (NULL, PRIM and MULT, zero, one or two pregnancies and lactations, respectively). We tested at 6, 12, 18 and 24 months of age in a dry land version of the Morris water maze (Main task), and at 12, 18 and 24 months in the same task in which the original location of the baited well was changed (Reversal task). We show that PRIM/MULT rats, compared to the age-matched NULL females, learned the spatial tasks significantly better and exhibited attenuated memory decline, up to 24 months of age. Furthermore, at the conclusion of behavioral testing, we investigated levels of these animals’ hippocampal (CA1 and dentate gyrus) immunoreactive amyloid precursor protein (APP), a marker of neurodegeneration and age-related cognitive loss. MULTs had significantly reduced APP in both CA1 and DG, relative to PRIMs and NULLs, and PRIMs had a trend ( p < 0.06) toward a reduction in APP compared to NULLs in DG. Further, level of APP was negatively correlated with performance in the two tasks (viz., more APP, worse maze performance). Reproduction, therefore, with its attendant natural endocrine and postpartum sensory experiences, may facilitate lifelong learning and memory, and may mitigate markers of neural aging, in the rat. Combining natural hormonal exposure with subsequent substantial experience with stimuli from the offspring may preserve the aged parous female brain relative to that of NULL females.

Reductions in spontaneous locomotor activity in aged male, but not female, rats in a model of early Parkinson's disease

The excessive loss of dopamine (DA) neurons that occurs with Parkinson's disease is usually confined to older individuals. While 6-hydroxydopamine (6-OHDA) is often used in animal models of DA neuron degeneration, there have been relatively few studies that have examined the effects of 6-OHDA in older animals. In the present study, we compared the effects of a bilateral, partial lesion with 6-OHDA in young (4 months), middle-aged (14 months), and aged (24 months) Fischer-344 rats of both sexes. Animals were given a single injection of vehicle or 100 μg 6-OHDA into the right lateral ventricle. Four weeks later, spontaneous locomotor activity was monitored. Microdialysis experiments were carried out 1 to 3 days later. The 6-OHDA treatments had no effect on horizontal activity or total distance traveled in young adults. However, with aged rats, there was a decrease in both measures in the vehicle-treated control rats compared to young adult controls, and a further decrease in the lesioned aged male rats. The 6-OHDA treatments led to significant decreases in both potassium- and amphetamine-evoked overflow of DA from the striatum in all groups. Thus, partial bilateral lesions of the nigrostriatal DA system led to decreases in evoked release of DA in the striatum of male and female rats of all three ages, but to changes in spontaneous activity only in the aged males. These results indicate that there are both age and sex differences in the brain's response to 6-OHDA, and imply that compensatory or neuroprotective mechanisms in the young brain and aged female brain are more efficient than in the aged male brain.

Progesterone counteracts estrogen-induced increases in neurotrophins in the aged female rat brain

Neurotrophin alterations have been associated with normal aging and age-related neurodegenerative disease, as well as cognitive status. Estrogen influences expression of mRNA and protein of neurotrophins and their receptors, and affects cognitive performance in young ovariectomized (Ovx) rats. The current investigation evaluated whether estrogen or estrogen plus progesterone affects neurotrophin protein levels in cognitive brain regions in the aged Ovx rat. While estrogen treatment increased BDNF, NGF, and NT3 levels in entorhinal cortex, progesterone abated the effects of estrogen resulting in neurotrophin levels comparable to aged Ovx rats not given hormone. Our findings suggest that the aged female brain is responsive to estrogen in cognitive brain regions, and that progesterone can reverse these estrogen effects.

In vivo imaging of muscarinic receptors in the aging female brain with ( R, R)[ 123I]-I-QNB and single photon emission tomography

The effect of age on brain muscarinic receptor density is unclear. Some in vivo neuroimaging studies have reported a large age-related reduction in muscarinic receptor density; however, others have reported increases or no change. The variability in these results most likely arises because of the heterogeneity of the populations studied, differences in quantification methods employed, and a paucity of subtype selective ligands. Thus, we used the m 1/m 4 selective probe ( R, R)[ 123I]-I-QNB to investigate age-related differences in brain muscarinic receptors in healthy females. We included 10 younger subjects (age range 26–37) and 22 older women (age range 57–82 years). The older women had significantly lower ( R, R)[ 123I]-I-QNB binding in widespread brain regions including cerebral cortex and hippocampus. Across all subjects, regional binding was significantly negatively correlated with age. Thus, in this population of healthy women, there was an age-related reduction in muscarinic receptor density. This may contribute to age-related differences in cognitive function and risk for Alzheimer's disease.

Regional heterogeneity of serotonin 1A receptor inactivation and turnover in the aging female rat brain following EEDQ

The turnover of serotonin 1A (5-HT 1A) receptors was investigated in several brain regions of young adult (3 months) and old (22 months) female Fischer 344 rats following irreversible inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). Equilibrium binding analyses for the 5-HT 1A receptor binding site incorporated [ 3H]8-hydroxy-2-(di- N-propylamino)tetralin ([ 3H]8-OH-DPAT) and were conducted in the frontal cortex, amygdala and hippocampus at 1, 2, 7 and 14 days after treatment with EEDQ (6.0 mg/kg, s.c.) or vehicle. The pattern of 5-HT 1A receptor recovery following EEDQ treatment was found to be age- and region-dependent. For example, in the hippocampus, receptor recovery occurred at a faster rate in the old rats compared to young adult rats. While a significant decrease in affinity for the 5-HT 1A receptor was found in the frontal cortex and amygdala in young adult and old rats following EEDQ, B MAX values for [ 3H]8-OH-DPAT binding in these brain regions were unaltered by EEDQ across age groups. In the frontal cortex and amygdala, significant age-dependent decreases in affinity for the 5-HT 1A receptor were revealed at day 1 following EEDQ administration. The significance of the present findings is discussed in terms of aging and a regionally-defined sensitivity of 5-HT 1A receptors to the irreversible inactivator EEDQ.

Amplification of exons 4 and 5 of androgen receptor gene by testosterone in aged female mouse brain cortex.

We have investigated the effect of testosterone on the amplification of androgen receptor (AR) gene in the brain cortex of aging female mice. For this purpose, high molecular weight (HMW) DNA purified from the brain cortex of intact, gonadectomized, testosterone- and estradiol-treated adult and old female mice was digested with different restriction enzymes and used for Southern hybridization with 32P-labeled AR cDNA fragments representing different domains of AR. The results reveal that only exons 4 and 5 corresponding to amino-terminal part of the hormone binding domain of AR are amplified in testosterone-treated old female but not in adult mice. Densitometric analysis further shows that testosterone increases the copy number of exons 4 and 5 of mouse AR gene by four-fold. Reprobing of slot blots with estrogen receptor and cathepsin D cDNA as probes supports the observation that amplification occurs only in AR gene. The tissue specificity is also confirmed when the slot blot hybridization of mouse liver HMW DNA with AR cDNA fails to show similar amplification. As the restriction map analysis of Southern blots does not show restriction fragment length polymorphism, the possibility of structural rearrangement leading to amplification of AR gene is ruled out. Thus our results suggest that the in vivo induction of mouse AR gene amplification by testosterone is tissue- and age-specific, and might contribute to the progress of genetic instability in the brain of aged female mice.

Aging female brain: is there a change of adaptive stress?

Aging female brain: is there a change of adaptive stress?

Increases of glial fibrillary acidic protein in the aging female mouse brain.

Age-related increases of the astrocyte marker, glial fibrillary acidic protein (GFAP), were further resolved by in situ hybridization and immunocytochemistry in female C57BL/6J mice. The age groups represented the major stages of reproductive aging: young (5 months), middle-age (18 months), and old (23 and 26 months). GFAP mRNA and protein showed generalized increases in old mice. Major white fiber tracts, such as the corpus callosum, fimbria, stria terminalis, and optic tract, showed increased GFAP immunostaining and mRNA. Gray matter showed robust > or = twofold increases in GFAP mRNA with age, especially in the thalamus and hypothalamus, areas that expressed little GFAP in the young. These generalized age-related increases of GFAP in many brain regions imply the existence of a widespread stimulus for increased activity of astrocytes during aging.