Restoration of Estradiol Effects on Learning by Cholinergic Enhancement

描述（由申请人提供）：本项目的目的是提供以下原理的证明：通过用胆碱酯酶抑制剂治疗，从而增强脑中的胆碱能活性，雌二醇介导的认知功能增强可以在（a）具有胆碱能损伤的年轻大鼠和（B）经历长期卵巢功能丧失的老年大鼠中恢复。我们假设，引起雌二醇对绝经后认知能力的积极影响的关键时期是由基底前脑胆碱能投射的功能定义的（即，当胆碱能系统显著受损时，反应性丧失）。基于此，我们预测，增强胆碱能系统抑制（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性，即使在卵巢功能长期丧失之后。用选择性免疫毒素192 IgG-saporin（SAP）和本实验室建立的方法，对去卵巢幼鼠的内侧隔和斜角带胆碱能神经元进行选择性损伤。这些大鼠将用特定剂量的多奈哌齐或加兰他敏（常用于治疗阿尔茨海默病的胆碱酯酶抑制剂）治疗，有和没有雌二醇，然后使用体内微透析和行为训练进行研究。还将评估在3月龄时切除卵巢，然后在12月龄时用多奈哌齐或加兰他敏（有或无雌二醇）治疗的老年大鼠。所有大鼠将接受两项认知任务的训练，即延迟位置匹配（delayed matching to position，OMT）T迷宫任务和神经联想（CA）操作性条件反射任务。体内微透析将用于测量对海马中乙酰胆碱释放的影响。还将测量海马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，作为胆碱能去神经支配程度的指标。我们的预测是，在大鼠胆碱能损伤，并在老年大鼠，雌二醇的影响将恢复治疗与胆碱酯酶抑制剂，这些影响将与乙酰胆碱酯酶抑制和海马体中的乙酰胆碱释放。这将提供证据的原则，增强胆碱能活性的大脑中可以恢复雌二醇的能力，以提高认知能力，在年轻的大鼠与受损的基底前脑胆碱能功能，并在老年大鼠经历了长期的卵巢功能丧失。人类和动物数据都表明，激素治疗相对于绝经的时间对于确定治疗是否对大脑衰老和认知产生有益影响至关重要。我们假设，引起雌二醇对绝经后认知能力的积极影响的关键时期是由基底前脑胆碱能投射的功能定义的（即，当胆碱能系统显著受损时，反应性丧失）。基于这一假设，我们预测，增强胆碱能系统抑制（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疗法对（a）具有胆碱能损伤的年轻大鼠和（B）经历了卵巢功能长期丧失的老年大鼠的认知表现的有益作用。这个试点项目将为这一假设提供主要证据。积极的结果将确定一种机制来解释为什么绝经后激素治疗的时机是至关重要的，并将提供一个可行的策略，恢复激素治疗的有效性，绝经后妇女谁没有使用激素治疗多年。

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.