Karyn M. Frick, PhD - US grants

DESCRIPTION Age-related spatial memory decline occurs earlier in female mice relative to males. Although this sex difference coincides with the age- related cessation of regular estrous cycling (at 17 months of age), levels of ovarian hormones have been directly measure din the context of memory decline in aging. Therefore, it is unknown whether loss of these hormones contributes to sex differences in spatial memory decline. The proposed studies re designed to determine: 1) the age at which sex differences in spatial memory begin to emerge, 2) whether the onset of these six differences is related to age-related ovarian hormone decline, 3) whether neuroanatomical markers that are affected by age and ovarian hormones differentially decline in males and females, and 4) whether treatment of middle-aged females with hormone replacement will ameliorate their spatial memory deficit. In Experiment 1, designed to address questions 1-3, the spatial memory of male and female mice at 4 ages (5, 11, 14, and 17 months) will be measured in a 1-day water maze tasks, immediately after which the mice will be perfused and their brains removed for measurement of synapse and cholinergic neuron number. Blood will be collected for measurement of ovarian hormone levels. In Experiment 2, which will address question 4, ovariectomized 17 month-old female mice will be given hormone replacement and their spatial memory will be tested as in Experiment 1. The results of this study will provide insights into the mechanisms of, and possible treatments for, cognitive decline in menopausal women.

[unreadable] DESCRIPTION (provided by applicant): The main objective of the proposed research is to understand the mechanisms by which estrogenic modulation of the cholinergic system facilitates spatial memory. The proposed studies uniquely address these issues in a series of three experiments using drug injections, a recently developed mouse cholinergic immunotoxin, and a knockout mouse lacking estrogen receptor alpha (ERa). The specific aims are as follows: 1) To determine whether estrogen facilitates spatial memory retention in mice through modulation of cholinergic function, 2) To examine whether destruction of basal forebrain cholinergic afferents to neocortex and hippocampus by a new mouse immunotoxin affects estrogenic modulation of spatial memory, and 3) To investigate whether estrogen modulates cholinergic function and spatial memory via activation of the ERa receptor. Ovariectomized female mice will receive one session of training in a spatial water maze task requiring them to use extramaze cues to locate a hidden escape platform. Immediately afterward, they wilt be injected with estrogen, scopolamine, or a combination of both. Twenty-four hours later, mice will receive a retention test. One week later, the mice will again be injected with estrogen and scopolamine and then sacraficed 24 hours later for analysis of choline acetyltransferase (CHAT) activity in the hippocampus and frontoparietal cortex. In Experiment 1, we will examine the ability of post-training estrogen injections to enhance spatial memory and augment cholinergic function in the presence of the cholinergic antagonist scopolamine. Because we hypothesize that the locus of estrogenic-cholinergic interaction is the basal forebrain, Experiment 2 will test the ability of estrogen to enhance memory using mice in whom basal forebrain cholinergic neurons were selectively destroyed using the toxin saporin, which is linked to antibodies raised against the mouse low-affinity nerve growth factor receptor, p75. Finally, in Experiment 3 we will examine whether estrogen modulates spatial memory and cholinergic function via activation of the ERa receptor. Findings from the proposed studies will lay a foundation to elucidate the mechanisms by which estrogen influences cholinergic modulation of memory. If estrogen improves memory by modulating basal forebrain cholinergic function, then this work may have significant implications for the treatment of Alzheimer's disease, for which anticholinesterases are largely ineffective.

[unreadable] DESCRIPTION (provided by applicant): The recent controversial Women's Health Initiative Memory Study (WHIMS) implies that long-term treatment with estrogen and progestin significantly increases the risk of cognitive decline and dementia in menopausal women. These data sharply contrast with studies in women and rodents that have demonstrated a clear ability of estrogen to alleviate age- and hormone-related memory loss. The WHIMS finding that progestin is detrimental to memory is even more surprising because estrogen and progesterone treatment have been shown to be beneficial to memory in laboratory animals. The proposed studies were designed to clarify whether progesterone attenuates the beneficial effects of estrogen and to identify the neural mechanisms underlying the effects of estrogen and progesterone on memory consolidation. Because adverse side effects of hormone replacement such as increased risks of breast cancer and stroke make it impractical to conduct these studies in women, the proposed studies will utilize a female mouse model. The specific aims are as follows: 1) To pinpoint if estrogen and progesterone, alone or in combination, enhance memory consolidation and alter MAP kinase signaling in the hippocampus in young and aging females, 2) To determine if the mnemonic and hippocampal response to estrogen and progesterone is influenced by environmental factors, and 3) To compare the mnemonic and neural effects of estrogen and progesterone treatments that vary in duration (short- vs. long-term) and type (sustained vs. cyclic). To achieve these aims, ovariectomized female C57BL/6 mice (4, 17, and 24 months old) will be used in a series of nine experiments. Spatial memory will be tested in a spatial water maze task and non-spatial memory will be tested in an object recognition task. The goal of this research is to clarify the findings of WHIMS, a study which has greatly impacted the treatment of millions of menopausal women. WHIMS was a limited study, focusing on an older, highly educated population receiving treatment that was not cyclic and included a detrimental type of progestin. Establishing how factors such as age at treatment, degree of cognitive stimulation, type of progestin, and type of treatment (i.e., cyclic vs. sustained) influence the mnemonic and neural response to hormones will be critical to future use of hormone replacement. Our mouse model will enable a more controlled study of these factors than is possible with women. Elucidation of these issues may ultimately lead to the development of safer and more effective treatments to prevent cognitive decline and dementia in women [unreadable] [unreadable]

Memory deficits plague patients with numerous mental disorders, yet a fundamental lack of knowledge about the neural mechanisms regulating memory formation has hampered the development of therapies to reduce this memory dysfunction. The sex steroid hormone 17?-estradiol (E2) is a potent modulator of hippocampal synaptic plasticity and memory, and likely contributes to sex differences in the prevalence, progression, and severity of many psychiatric and neurodegenerative diseases. However, the neural mechanisms through which E2 regulates memory are poorly understood. Thus, there is an urgent need to identify molecular mechanisms through which E2 regulates learning and memory processes in both sexes. Our long-term goal is to pinpoint the key neural mechanisms through which estrogens regulate hippocampal memory formation in males and females. The overall objective of this application, which is the next step toward attainment of our goal, is to determine the extent to which canonical Wnt signaling and BDNF contribute to the memory enhancing effects of E2. Our central hypothesis is that E2 enhances memory by promoting Wnt signaling, which then epigenetically regulates the transcription and translation of BDNF. These hypotheses were formulated on the basis of published data indicating that Wnt signaling increases BDNF expression6, and our own published data showing that canonical Wnt signaling is necessary for hippocampal memory consolidation in male mice7, histone acetylation is necessary for E2 to enhance hippocampal memory consolidation in female mice8, and that E2 increases hippocampal BDNF protein and H3 acetylation at Bdnf promoters in female mice7. Guided by our strong preliminary data, our hypothesis will be tested in three specific aims designed to: 1) determine the extent to which estrogenic regulation of canonical Wnt signaling facilitates hippocampal memory consolidation, 2) establish the extent to which canonical Wnt signaling and BDNF interact to regulate hippocampal memory consolidation, and 3) identify the molecular mechanisms through which E2 mediates BDNF expression and memory formation. This research is innovative because it utilizes a hypothesis-driven approach that integrates behavioral and biochemical analyses to identify mechanistic relationships among modulatory pathways that regulate hippocampal memory formation in both males and females. The proposed research is significant because it is the first step in a continuum of research designed to provide foundational knowledge about the molecular mechanisms through which E2 regulates memory formation. This work will provide sorely needed insights about estrogenic regulation of memory formation in both sexes that could lead to the generation of novel therapies specifically tailored to reduce memory dysfunction in patients of each sex. Such therapeutic advances would greatly improve the quality of life for millions of patients and their families.