Preoptic histamine signaling in thermoregulation and energy expenditure

描述（由申请人提供）：下丘脑中的组胺信号控制能量消耗、体温调节、睡眠和进食。组胺信号传导被破坏（H1 受体 k.o.、H3 受体 k.o. 和组胺脱羧酶 k.o.）的转基因动物会出现瘦素抵抗性肥胖，这表明正常组胺信号传导对于维持能量稳态的重要性。此外，瘦素缺陷（ob/ob）和瘦素受体缺陷（db/db）肥胖小鼠的下丘脑组胺浓度降低。这些观察结果强调了瘦素下游组胺发挥的关键作用。增加下丘脑组胺浓度的药物对糖尿病、肥胖症和发作性睡病的动物模型有益，并且几种此类药物正在进行临床试验。然而，下丘脑中组胺信号传导增强所激活的细胞机制尚不清楚。先前的研究表明，组胺对体温调节和能量消耗的影响是由于其在视前区/下丘脑前部（PO/AH）的作用。 PO/AH 的电生理学研究揭示了热敏神经元的存在，这些神经元现在被认为是中枢神经系统温度调节系统的关键要素。温敏感 PO/AH 神经元响应温度升高而增加放电率（与温度不敏感神经元相反），并充当稳态条件的积分器。 PO/AH 温度调节神经元投射到下丘脑背内侧或中缝苍白肌头侧。我们将通过这些中心的逆行标记来识别体温调节 PO/AH 神经元。我们的主要假设是组胺影响参与体温调节的 PO/AH 神经元的活动，我们预测这种作用决定了组胺引起的体温和能量消耗的变化。我们还假设 PO/AH 中的组胺信号在瘦素缺陷 (ob/ob) 小鼠（一种众所周知的肥胖模型）中发生改变。初步数据表明，该区域存在 H1、H2 和 H3 受体，组胺有效调节 PO/AH 神经元的突触活动和突触后电导，并对细胞内 Ca 浓度发挥复杂的作用。我们计划通过切片中 PO/AH 神经元的电生理记录来识别热敏感和不敏感神经元，并研究组胺和所涉及的离子电导对其活动的调节（具体目标 1）。所涉及的受体亚型将在 Specific Aim2 中进行研究，该项目将使用药理学工具、电生理学和单细胞 RT-PCR。 Specific Aim3 将研究 PO/AH 中的组胺信号传导对核心体温和能量消耗的影响，该项目将使用遥测、间接量热法和体外定量解偶联蛋白 1、2 和 3 在 mRNA 和蛋白质水平上的表达。具体目标 3 将在 w-t 和 ob/ob 小鼠中进行研究，并对结果进行比较以确定组胺信号传导中可能的差异。公共健康相关性：温度稳态在整个生命过程中受到严格调节且非常稳定，是代谢过程的关键因素。下丘脑中的组胺信号传导是决定能量稳态、体温调节、睡眠和进食的主要因素。因此，这些研究将对理解肥胖和糖尿病等代谢性疾病以及白天过度嗜睡和发作性睡病等睡眠障碍产生影响。

DESCRIPTION (provided by applicant): Histamine signaling in the hypothalamus controls energy expenditure, thermoregulation, sleep and feeding. Transgenic animals in which histamine signaling is disrupted (the H1 receptor k.o., the H3 receptor k.o. and the histamine decarboxylaze k.o.) develop leptin-resistant obesity, indicating the importance of normal histamine signaling for the maintenance of energy homeostasis. Furthermore, leptin-deficient (ob/ob) and leptin receptor- defective (db/db) obese mice display lowered hypothalamic histamine concentrations. These observations underline the key role played by histamine downstream of leptin. Pharmacological agents that increase the hypothalamic concentration of histamine are beneficial in animal models of diabetes, obesity and narcolepsy, and several such drugs are in clinical trials. However, the cellular mechanisms activated by increased histamine signaling in the hypothalamus are not well understood. Previous studies have shown that histamine effects on thermoregulation and energy expenditure are due to its actions in the preoptic area/ anterior hypothalamus (PO/AH). Electrophysiological studies of PO/AH have revealed the existence of thermosensitive neurons that are now considered to be key elements of the thermoregulatory system of the CNS. Warm- sensitive PO/AH neurons increase their firing rate in response to temperature elevation (in contrast to the temperature-insensitive neurons) and function as integrators of homeostatic conditions. PO/AH thermoregulatory neurons project to the dorsomedial hypothalamus or to the rostral raphe pallidus. We will identify thermoregulatory PO/AH neurons by retrograde labeling from these centers. Our primary hypothesis is that histamine affects the activity of PO/AH neurons involved in thermoregulation and we predict that this action determines the changes in body temperature and energy expenditure induced by histamine. We also hypothesize that histamine signaling in the PO/AH is altered in leptin-deficient (ob/ob) mice, a well-known obesity model. Preliminary data indicate that H1, H2 and H3 receptors are present in this region, that histamine potently modulates synaptic activity and postsynaptic conductances in PO/AH neurons and also exerts complex actions on intracellular Ca concentrations. We plan to identify both warm-sensitive and - insensitive neurons by electrophysiological recordings in PO/AH neurons in slices and study the modulation of their activity by histamine and the ion conductances involved (Specific aim1). The receptor subtypes involved will be studied in Specific Aim2 which will use pharmacological tools, electrophysiology, and single cell RT- PCR. The influence of histamine signaling in the PO/AH on core body temperature and energy expenditure will be investigated in Specific Aim3 which will use telemetry, indirect calorimetry and ex-vivo quantification of the expression of uncoupling proteins 1, 2 and 3 at the mRNA and protein levels. Specific aim 3 will be studied both in w-t and ob/ob mice and the results will be compared in order to determine possible differences in histamine signaling. PUBLIC HEALTH RELEVANCE: Temperature homeostasis is strictly regulated and remarkably stable throughout life and is a key factor to metabolic processes. Histamine signaling in the hypothalamus is a major factor in determining energy homeostasis, thermoregulation, sleep and feeding. These studies will therefore have implications for understanding metabolic disorders, such as obesity and diabetes, as well as sleep disorders such as excessive day sleepiness and narcolepsy.