Neural steroidogenic enzymes and brain function

描述（由申请人提供）：有大量关于外周类固醇合成和分泌的信息，但令人惊讶的是，关于活性神经回路中类固醇实际浓度的信息很少。我们对大脑类固醇的认识存在差距，特别是那些在大脑中合成的类固醇（神经类固醇），阻碍了确定改善人类心理健康和认知的最佳治疗方法的努力。在人类和非人类动物模型中，雌二醇（E2）可通过与海马神经元和GABA能信号相互作用增强记忆功能，但其机制尚不清楚。由于海马体可能在突触末端重新合成E2，因此外周E2浓度的测量几乎不能告诉我们生物活性局部水平。海马E2水平的实时体内测量将具有很大的价值，特别是提供了快速调节类固醇合成酶和E2对记忆功能的快速作用的证据。为了解决这一差距，我们已经开发出测量类固醇水平在自由行为的鸣禽使用体内微透析的能力。我们的研究结果表明，E2和睾酮（T）在鸣禽大脑中的水平波动相对较快，在社会交往中独立于他们的周边水平或水平在相邻的大脑区域;抑制E2流量有明确的行为影响。此外，我们发现，E2的自然波动相反，相对于谷氨酸和谷氨酸的逆向透析迅速降低E2浓度。这些波动是如何以及为什么发生的尚不清楚。我们建议对鸣禽海马进行微透析，以测量类固醇、谷氨酸和GABA，因为鸟类执行基于自然海马的空间和时间记忆密集行为。我们将使用后透析来抑制神经类固醇的合成，并检查空间记忆的表现。我们将结合联合收割机微透析与脑提取程序，以确定具有生物活性的神经雌激素浓度。我们将确定神经递质调节大脑海马切片中类固醇生成酶的机制，以产生我们在体内看到的水平。这些研究的结果将有助于澄清有关类固醇作为神经调质/神经递质的重要概念，并将有助于解决有关雌激素对认知，海马生理学和记忆功能特定方面的作用的争论。影响海马体雌激素信号传导的疗法可以缓解诸如创伤后应激障碍和由精神障碍如抑郁症和精神病引起的认知障碍等疾病。 公共卫生相关性：脑内合成的类固醇促进学习、记忆和其他认知过程，作为兴奋性和抑制性神经回路上的神经调质。我们的研究试图通过记录行为动物大脑中神经类固醇和神经递质的自然变化来理解这些关键的相互作用，然后阐明产生这些变化的机制。这些研究有助于理解基本的大脑功能，并对人类认知和情绪障碍的治疗产生影响。

DESCRIPTION (provided by applicant): There is a wealth of information about peripheral steroid synthesis and secretion, but surprisingly little information about actual concentrations of steroids in active neural circuits. This gap in our knowledge of brain steroids, especially those synthesized in the brain (neurosteroids), hampers efforts to identify optimal treatments to improve human mental health and cognition. Estradiol (E2) can enhance memory function in humans and non-human animal models by interactions with hippocampal glutamatergic and GABAergic signaling, but the mechanisms are poorly understood. Because the hippocampus synthesizes E2 de novo, perhaps at synaptic terminals, measures of peripheral E2 concentrations tell us little about biologically active local levels. Real-time in vivo measures of hippocampal E2 levels would be of great value, especially given evidence for rapid regulation of steroid synthetic enzymes and for rapid actions of E2 on memory function. To address this gap we have developed the ability to measure steroid levels in freely-behaving songbirds using in vivo microdialysis. Our findings show that E2 and testosterone (T) levels in the songbird brain fluctuate relatively rapidly during social interactions independent of their peripheral levels or levels in adjacent brain regions; inhibition of this E2 flux has clear behavioral implications. Further, we find that E2 naturally fluctuates inversely relative to glutamate and retrodialysis of glutamate rapidly reduces E2 concentrations. How and why these fluctuations occur is unknown. We propose performing microdialysis on the songbird hippocampus to measure steroids, glutamate and GABA as the birds perform natural hippocampal-based spatial and temporal memory intensive behaviors. We will use retrodialysis to inhibit neurosteroid synthesis and examine spatial-memory performance. We will combine microdialysis with brain extraction procedures to determine the biologically active neuroestrogen concentrations. We will identify mechanisms whereby neurotransmitters regulate steroidogenic enzymes in hippocampal slices of brain to produce the levels we see in vivo. Results of these studies will help clarify important concepts about steroids as neuromodulators/neurotransmitters and will help resolve debate over the role of estrogens on specific aspects of cognition, hippocampal physiology and memory function. Therapies that impact hippocampal estrogen signaling may provide relief from disorders such as post-traumatic stress and cognitive impairment arising from psychiatric disorders such as depression and psychosis. PUBLIC HEALTH RELEVANCE: Steroids synthesized within the brain facilitate learning, memory and other cognitive processes acting as neuromodulators on excitatory and inhibitory neural circuits. Our research seeks to understand these critical interactions by documenting natural changes in neurosteroids and neurotransmitters in the brains of behaving animals and then elucidating the mechanisms creating these changes. These studies contribute to an understanding of basic brain function with implications for the treatment of human cognitive and mood disorders.