Restoration of Estradiol Effects on Learning by Cholinergic Enhancement

描述(申请人提供)：该项目的目标是提供原理证据，证明雌激素介导的认知功能增强可以在(A)胆碱能受损的年轻大鼠和(B)长期失去卵巢功能的老年大鼠中恢复，方法是用胆碱酯酶抑制剂治疗，从而增强大脑中的胆碱能活性。我们假设，绝经后雌激素对认知功能产生积极影响的关键时期是由基底前脑胆碱能投射的功能决定的(即，当胆碱能系统严重受损时，失去反应性)。基于此，我们预测，从药理上增强胆碱能系统(例如，通过使用胆碱酯酶抑制剂)将重新打开机会之窗并恢复反应，即使在卵巢功能长期丧失后也是如此。用选择性免疫毒素192Ig G-Saporin(SAP)和本实验室建立的方法，在去卵巢的幼年大鼠上选择性损毁Broca内侧隔和斜角带的胆碱能神经元。这些大鼠将接受特定剂量的多奈哌齐或加兰他明(治疗阿尔茨海默病的常用胆碱酯酶抑制剂)的治疗，并同时使用和不使用雌二醇，然后使用活体微透析和行为训练进行研究。老年大鼠在3个月龄时切除卵巢，然后在12个月龄时接受多奈哌齐或加兰他明加和不加雌二醇的治疗，也将进行评估。所有大鼠将接受两项认知任务的训练，一项是延迟匹配定位(DMP)T迷宫任务，另一项是结构联想(CA)操作条件反射任务。体内微透析将被用来测量对海马乙酰胆碱释放的影响。海马区和额叶皮质中胆碱乙酰转移酶和乙酰胆碱酯酶活性的水平也将被测量为胆碱能去神经程度的指标。我们的预测是，在胆碱能损伤的大鼠和老年大鼠中，雌二醇的作用将通过胆碱酯酶抑制剂的治疗而恢复，这些作用将与AChE抑制和海马乙酰胆碱释放有关。这将为增强大脑胆碱能活动可以恢复雌二醇提高认知能力的原理提供证据，无论是在基底前脑胆碱能功能受损的年轻大鼠，还是在卵巢功能长期丧失的老年大鼠。公共卫生相关性人类和动物的数据都表明，激素治疗相对于更年期的时机对于确定治疗是否会对大脑老化和认知产生有益影响至关重要。我们假设，绝经后雌激素对认知功能产生积极影响的关键时期是由基底前脑胆碱能投射的功能决定的(即，当胆碱能系统严重受损时，失去反应性)。基于这一假设，我们预测，从药理上增强胆碱能系统(例如，通过使用胆碱酯酶抑制剂)将重新打开机会之窗，并恢复激素治疗对认知功能的有益影响：(A)患有胆碱能损害的年轻大鼠，(B)经历了长期卵巢功能丧失的老年大鼠。这一试点项目将为这一假设提供原则证明。积极的结果将确定一种机制，解释为什么绝经后激素治疗的时机至关重要，并将为恢复绝经后多年未使用激素治疗的妇女的激素治疗有效性提供一种可行的策略。

DESCRIPTION (provided by applicant): The goal of this project is to provide proof of principle that estradiol-mediated enhancement of cognitive function can be restored (a) in young rats with cholinergic lesions, and (b) in aged rats that have undergone long-term loss of ovarian function, by treating with a cholinesterase inhibitor and thereby enhancing cholinergic activity in the brain. We hypothesize that the critical period for eliciting positive effects of estradiol on cognitive performance post menopause is defined by the functionality of basal forebrain cholinergic projections (i.e., responsiveness is lost when the cholinergic system becomes significantly impaired). Based on this, we predict that enhancing the cholinergic system pharmacologically (e.g., via the use of cholinesterase inhibitors) will re-open the window of opportunity and restore responsiveness, even after prolonged loss of ovarian function. Selective lesions of cholinergic neurons in the medial septum and diagonal band of Broca will be produced in young ovariectomized rats using the selective immunotoxin 192IgG-saporin (SAP) and methods established in our laboratory. These rats will be treated with specific doses of donepezil or galantamine (cholinesterase inhibitors commonly used in the treatment of Alzheimer's disease), with and without estradiol, and then studied using in vivo microdialysis and behavioral training. Aged rats that are ovariectomized at 3 month of age, and then treated at 12 months of age with donepezil or galantamine with and without estradiol, will also be evaluated. All rats will be trained on two cognitive tasks, a delayed matching-to-position (DMP) T-maze task, and a configural association (CA) operant conditioning task. In vivo microdialysis will be used to measure effects on acetylcholine release in the hippocampus. Levels of choline acetyltransferase and acetylcholinesterase activities in the hippocampus and frontal cortex also will be measured as indices of the degree of cholinergic denervation. Our prediction is that in rats with cholinergic lesions, and in aged rats, effects of estradiol will be restored by treatment with the cholinesterase inhibitors, and that these effects will correlate with AChE inhibition and with acetylcholine release in the hippocampus. This would provide proof of principle that enhancing cholinergic activity in the brain can reinstate the ability of estradiol to enhance cognitive performance both in young rats with impaired basal forebrain cholinergic function, and in aged rats that have undergone long-term loss of ovarian function. PUBLIC HEALTH RELEVANCE Both human and animal data suggest that the timing of hormone therapy relative to menopause is critical for determining whether therapy will have a beneficial effect on brain aging and cognition. We hypothesize that the critical period for eliciting positive effects of estradiol on cognitive performance post menopause is defined by the functionality of basal forebrain cholinergic projections (i.e., responsiveness is lost when the cholinergic system becomes significantly impaired). Based on this hypothesis, we predict that enhancing the cholinergic system pharmacologically (e.g., via the use of a cholinesterase inhibitor) will re-open the window of opportunity and restore beneficial effects of hormone therapy on cognitive performance (a) in young rats with cholinergic lesions, and (b) in aged rats that have undergone long-term loss of ovarian function. This pilot project will provide proof of principal for this hypothesis. Positive results would identify a mechanism to explain why the timing of hormone therapy post menopause is critical, and would provide a viable strategy for restoring the effectiveness of hormone therapy in postmenopausal women who have not used hormone therapy for many years.