Imaging Brain Signal Transduction In Vivo With Radiolabeled Arachidonic Acid

由于缺乏血清素再吸收转运蛋白而导致花生四烯酸调节。携带突触前5-羟色胺再摄取转运蛋白（5-HTT）启动子的短（S）等位基因的人与携带长（L）等位基因的人相比，细胞外5-羟色胺（5-HT）增加，患神经精神疾病（包括BD）的风险增加。杂合子5-HTT敲除小鼠（5-HTT-/+）也具有升高的突触5-HT并显示抑郁样行为。它被认为是携带5-HTT的S启动子等位基因的人的模型。我们证明了与野生型5-HTT+/+小鼠相比，5-HTT-/+和纯合5-HTT-/-小鼠中从血浆到不同脑区域的基线AA掺入增加了20-70%。敲除小鼠脑细胞质磷脂酶A2（cPLA 2）活性升高，我们解释为对cPLA 2偶联的5-HT 2A/2C受体的紧张刺激的反应。5-HTT敲除对5-HT 2A/2C激动剂（+/-）2，5-二甲氧基-4-碘苯基-2-氨基丙烷（DOI）的行为和AA信号传导反应与DOI作为部分激动剂的功能一致。因此，神经发育期间5-HTT功能降低会导致小鼠成年期AA信号传导和行为异常（参考文献1）。 在未麻醉大鼠中，急性而非慢性给予多奈哌齐可增加毒蕈碱受体介导的脑信号传导，涉及花生四烯酸。 阿尔茨海默病的记忆改变被归因于胆碱能传递的缺陷。多奈哌齐是一种乙酰胆碱酯酶（AChE）抑制剂，用于治疗该病。据认为，它通过增加突触乙酰胆碱（ACh）发挥作用，从而刺激突触后毒蕈碱M1、3、5受体，这些受体可与cPLA 2和（AA）释放偶联。然而，一些临床试验表明多奈哌齐对阿尔茨海默病进展没有显著影响。我们发现，清醒大鼠对多奈哌齐的AA信号反应表现出脱敏，这可能解释了为什么多奈哌齐可能不会影响阿尔茨海默病的进展。直接M1，3，5激动剂的临床试验可能仍然值得（参考文献2）。 慢性D-安非他明抑制大鼠脑中花生四烯酸代谢的成像标记。从精神兴奋剂如安非他明和可卡因中戒断，会抑制或逆转突触多巴胺再摄取转运蛋白，通常会导致抑郁症。大鼠在1天后退出慢性苯丙胺表现出减少基线（AA）纳入到核丘脑和纹状体，减少AA反应的D2样受体激动剂，quinpirole。这些减少可能是安非他明成瘾后抑郁症的基础，这在大鼠和人类中已有报道（参考文献3）。 阿朴吗啡通过多巴胺D2样受体刺激花生四烯酸信号传导。 阿扑吗啡是一种混合多巴胺D1/D2受体激动剂，用于治疗帕金森病患者。在清醒的大鼠中，急性阿扑吗啡仅通过D2受体在具有多巴胺受体的脑区域中激发了强烈的（AA）信号，因为该信号可以通过预先给予雷氯必利（一种D2/D3受体拮抗剂）来阻断（参考文献4）。该研究支持我们批准的临床方案，其中注射阿扑吗啡以利用正电子发射断层扫描成像多巴胺信号（参考文献4）。 急性尼古丁降低未麻醉大鼠脑花生四烯酸信号传导。 尼古丁可以改善记忆力和注意力，但很容易上瘾。在脑中，它主要与常见的高亲和力突触前胆碱能α 4 β 2受体结合，后者调节可激活与cPLA 2偶联的突触后受体的其他神经递质的释放。α 4 β 2受体在10-15分钟内发生脱敏，这可能与尼古丁成瘾有关。我们还证明了在体内的信号脱敏。尼古丁剂量相当于吸1支香烟（0.1 mg/kg，s.c.），与生理盐水相比，在注射后2分钟降低了大鼠脑中的花生四烯酸（AA）信号，但在注射后10分钟没有降低，这与快速脱敏一致。2 min信号被α 4 β 2拮抗剂美加明阻断（参考文献5）。 细胞内和细胞外钙离子影响磷脂酶A2介导的脑磷脂脂肪酸释放。 我们写了一篇关于钙非依赖性PLA 2（iPLA 2）在神经传递过程中从膜磷脂释放n-3多不饱和脂肪酸二十二碳六烯酸（DHA，22：6 n-3）的调控的重要评论。我们指出，虽然当细胞外钙通过离子型神经受体进入细胞时，DHA不太可能释放，但它应该在G蛋白偶联受体活化后释放，继发于细胞内内质网的钙释放（参考文献6）。

UPREGULATED ARACHIDONIC ACID DUE TO DEFICIENT SEROTONIN REUPTAKE TRANSPORTER. Humans carrying the short (S) compared with the long (L) allele of the presynaptic serotonin reuptake transporter (5-HTT) promoter have increased extracellular serotonin (5-HT) and are at increased risks for neuropsychiatric diseases including BD. The heterozygous 5-HTT knockout mouse (5-HTT-/+), also has elevated synaptic 5-HT and shows depressive-like behaviors. It is considered a model for humans carrying the S promoter allele of the 5-HTT. We demonstrated 20-70% increases in baseline AA incorporation from plasma into different brain regions, in 5-HTT-/+ and homozygous 5-HTT-/- mice compared with wild type 5-HTT+/+ mice. The knockout mice had an elevated brain cytosolic phospholipase A2(cPLA2) activity, which we interpreted as a response to tonic stimulation of cPLA2-coupled 5-HT2A/2C receptors. Behavioral and AA signaling responses in the 5-HTT knockouts to the 5-HT2A/2C agonist, (+/-)2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI), were consistent with DOI's function as a partial agonist. Thus, reduced 5-HTT function during neurodevelopment produces abnormal AA signaling and behavior during adulthood in the mouse (Ref. 1). ACUTE BUT NOT CHRONIC DONEPEZIL ADMINISTRATION INCREASES MUSCARINIC RECEPTOR-MEDIATED BRAIN SIGNALING INVOLVING ARACHIDONIC ACID IN UNANESTHETIZED RATS. Memory changes in Alzheimer disease have been ascribed to a deficit in cholinergic transmission. Donepezil, an acetylcholinesterase (AChE) inhibitor, is used to treat the disease. It is thought to act by increasing synaptic acetylcholine (ACh), thus stimulating post-synaptic muscarinic M1,3,5 receptors that can be coupled to cPLA2 and (AA) release. However, some clinical trials indicate no significant Donepezil effect on Alzheimer disease progression. We found that the AA signaling response to Donepezil in awake rats showed desensitization, which may explain why Donepezil may not affect Alzheimer disease progression. Clinical trials with direct M1,3,5 agonists may still be worthwhile (Ref. 2). CHRONIC D-AMPHETAMINE DEPRESSES AN IMAGING MARKER OF ARACHIDONIC ACID METABOLISM IN RAT BRAIN. Withdrawal from psychostimulants such as amphetamine and cocaine, which inhibit or reverse the synaptic dopamine reuptake transporter, often causes depression. Rats at 1 day after withdrawal from chronic amphetamine showed reduced baseline (AA) incorporation into the nucleus accumbens and striatum, and reduced AA responses to the D2-like receptor agonist, quinpirole. These reductions may underlie post-depression following amphetamine addiction, which has been reported in rats and humans (Ref. 3). APOMORPHINE STIMULATES ARACHIDONIC ACID SIGNALING VIA DOPAMINE D2-LIKE RECEPTORS. Apomorphine, a mixed dopamine D1/D2 receptor agonist, is used to treat patients with Parkinson disease. In awake rats, acute apomorphine provoked a robust (AA) signal in brain regions with dopamine receptors solely through the D2 receptors, as the signal could be blocked by pre-administration of raclopride, a D2/D3 receptor antagonist (Ref. 4) This study supports our approved clinical protocol in which apomorphine is injected to image dopamine signaling with positron emission tomography (Ref. 4). ACUTE NICOTINE REDUCES BRAIN ARACHIDONIC ACID SIGNALING IN UNANESTHETIZED RATS. Nicotine can improve memory and attention, but is highly addictive. In brain, it binds primarily to the common high-affinity presynaptic cholinergic alpha4beta2 receptors, which modulate release of other neurotransmitters that can activate post-synaptic receptors coupled to cPLA2. Alpha4beta2 receptors undergo desensitization within 10-15 min, which may be related to nicotine addiction. We also demonstrated desensitization of signaling in vivo. Nicotine at a dose equivalent to smoking 1 cigarette (0.1 mg/kg, s.c.), compared to saline, decreased the arachidonic acid (AA) signal in rat brain at 2 min but not at 10 min after injection, consistent with rapid desensitization. The 2 min signal was blocked by the alpha4beta2 antagonist mecamylamine (Ref. 5). INTRACELLULAR- AND EXTRACELLULAR-DERIVED CALCIUM INFLUENCE PHOSPHOLIPASE A2-MEDIATED FATTY ACID RELEASE FROM BRAIN PHOSPHOLIPIDS. We wrote a critical review regarding regulation by calcium-independent PLA2 (iPLA2) release of the n-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA, 22:6n-3), from membrane phospholipid during neurotransmission. We indicated that while DHA is not likely released when extracellular calcium is allowed into the cell through ionotropic neuroreceptors, it should be released following activation of G-protein coupled receptors secondary to calcium release from the intracellular endoplasmic reticulum (Ref. 6).