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，关于活跃神经回路中类固醇实际浓度的信息很少。我们对脑类固醇，特别是那些在大脑中合成的类固醇（神经类固醇）的认识存在差距，这阻碍了我们寻找改善人类心理健康和认知的最佳治疗方法。雌二醇（E2）可以通过与海马谷氨酸能和gaba能信号的相互作用增强人类和非人类动物模型的记忆功能，但其机制尚不清楚。因为海马体可能在突触末端重新合成E2，所以外周E2浓度的测量几乎不能告诉我们生物活性的局部水平。海马体内实时测量E2水平具有重要价值，特别是考虑到类固醇合成酶的快速调节和E2对记忆功能的快速作用的证据。为了解决这一差距，我们已经开发了使用体内微透析来测量自由行为鸣禽体内类固醇水平的能力。我们的研究结果表明，鸣禽大脑中的E2和睾酮(T)水平在社会互动中波动相对较快，与周围或邻近大脑区域的水平无关；E2通量的抑制具有明显的行为学意义。此外，我们发现E2自然地与谷氨酸呈负相关波动，谷氨酸的反透析迅速降低E2浓度。这些波动发生的方式和原因尚不清楚。我们建议对鸣禽的海马体进行微透析，以测量鸟类在进行自然的基于海马体的空间和时间记忆强化行为时的类固醇、谷氨酸和GABA。我们将使用反透析来抑制神经类固醇合成并检查空间记忆性能。我们将结合微透析和脑提取程序来确定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的类固醇生成酶以产生我们在体内看到的水平的机制。这些研究的结果将有助于澄清类固醇作为神经调节剂/神经递质的重要概念，并将有助于解决关于雌激素在认知、海马生理和记忆功能的特定方面的作用的争论。影响海马体雌激素信号的疗法可以缓解创伤后应激障碍和抑郁症和精神病等精神疾病引起的认知障碍。

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.