Dorsal raphe nucleus melanocortin signaling regulates energy homeostasis

我们最近的研究表明，DRN中GABA能MC4R神经元的激活增加 摄食(Nectow等人，2017；布鲁塞尔等人，2020)，因此表明与位于 PVN、DRN GABA能MC4R神经元被其配体α-MSH抑制。为了支持这一点，我们观察到 在DRN内注射α-MSH减少了食物摄入量(布鲁塞尔等人，2020)，并减少了DRN神经元 在隔夜禁食小鼠中的激活(布鲁塞尔等人，2020年)。与这些数据一致，DREADD抑制 DRN MC4R神经元减少了过夜禁食小鼠的进食(布鲁塞尔等人，2020)，而DREADD DRN MC4R神经元的激活增加了过夜喂养小鼠的摄食(布鲁塞尔等人，2020年)。此外， 在DRN切片上应用α-MSH可导致MC4R神经元超极化(布鲁塞尔等人，2020) DRN GABAerigic神经元的动作电位频率显著降低(Nectow等人，2017年)。 然而，与我们公布的数据相反，最近的一项研究(han等人，2021年)报告了MC4R的激活 背根神经节中的神经元不影响摄食，但通过增加能量而导致体重减轻 支出和生热作用。而在这项研究中，作者表明，这些MC4R神经元的激活 诱导谷氨酸释放，我们的研究发现，大多数MC4R神经元本质上是GABA能的 它们的抑制影响了摄食，因此表明至少存在两个DRN MC4R神经元 亚群，即GABA能与谷氨酸能MC4R神经元，具有不同的调节作用 新陈代谢。值得注意的是，我们还发现饮食中DRN中的a-MSH免疫反应性显著增加。 诱导肥胖(DIO)小鼠与标准饲料喂养(SD)小鼠的比较，提示DRN可能发挥作用 黑素皮质素信号在饮食诱导的肥胖发展中的作用。因此，根据这些数据，我们假设 DRN中的黑素皮质素信号在新陈代谢调节中发挥作用(Nectow等人，2017； Bruschetta等人，2020)通过两个不同的MC4R亚群的活动，GABA和 谷氨酸能MC4R神经元。 在目标1中，我们将确定和比较黑素皮质素信号在DRN GABA能神经元中的作用 DRN谷氨酸能神经元影响摄食和代谢的药理作用及机制 遗传的GABA能和谷氨酸能的MC4R神经元。在目标2中，我们将分析POMC(和AgRP)预测 对DRN GABA能和谷氨酸能MC4R神经元亚群及细胞内信号传导的影响 DRN(和PVN)GABA能和谷氨酸能MC4R神经元的通路。在《目标3》中，我们将询问这个角色 DRN黑素皮质素信号在饮食诱导的肥胖中的作用。 拟议的研究是我们初步数据的合乎逻辑的扩展，它们的完成将揭示一个 新陈代谢中枢调节的新机制原理。

Our recent studies have demonstrated that that activation of GABAergic MC4R neurons in the DRN increases feeding (Nectow et al., 2017; Bruschetta et al., 2020), thus suggesting that contrary to MC4R neurons located in the PVN, DRN GABAergic MC4R neurons are inhibited by its ligand, a-MSH. In support of this, we have observed that injection of a-MSH in the DRN reduces food intake (Bruschetta et al., 2020) and reduces DRN neuronal activation (Bruschetta et al., 2020) in overnight fasted mice. In agreement with these data, DREADD inhibition of DRN MC4R neurons reduces feeding in overnight fasted mice (Bruschetta et al., 2020) while DREADD activation of DRN MC4R neurons increases feeding in overnight fed mice (Bruschetta et al., 2020). Furthermore, bath application of a-MSH in DRN slice leads to hyperpolarization of MC4R neurons (Bruschetta et al., 2020) and a significant decreased of frequency of action potentials in DRN GABAerigic neurons (Nectow et al., 2017). Contrary to our published data, however, a recent study (Han et al., 2021) has reported that activation of MC4R neurons in the DRN does not affect feeding while induce decreased body weight by increasing energy expenditure and thermogenesis. While in this study the authors showed that activation of these MC4R neurons induced glutamate release, our studies found that the majority of the MC4R neurons are GABAergic in nature and their inhibition affects feeding, thus suggesting the existence of at least two DRN MC4R neuronal subpopulations, i.e. GABAergic vs glutamatergic MC4R neurons, with distinct roles in the regulation of metabolism. Notably, we have also found a significant increase in a-MSH immunoreactivity in the DRN of diet- induced obese (DIO) mice compared to standard chow-fed (SD) mice, suggesting a possible role for DRN melanocortin signaling in the development of diet-induced obesity. Thus, based on these data, we hypothesize that melanocortin signaling in the DRN plays a role in the regulation of metabolism (Nectow et al., 2017; Bruschetta et al., 2020) through the activity of 2 distinct MC4R subpopulations, GABAergic and glutamatergic MC4R neurons. In Aim 1 we will determine and compare the role of melanocortin signaling in DRN GABAergic neurons versus DRN glutamatergic neurons in the regulation of feeding and metabolism by affecting pharmacologically and genetically GABAergic and glutamatergic MC4R neurons. In Aim 2 we will profile POMC (and AgRP) projections to the DRN GABAergic and glutamatergic MC4R neuronal subpopulations and the intracellular signaling pathways in DRN (and PVN) GABAergic and glutamatergic MC4R neurons. In Aim 3 we will interrogate the role of DRN melanocortin signaling in diet-induced obesity. The proposed studies are a logical extension of our preliminary data and, their completion will unmask a novel mechanistic principle in the central regulation of metabolism.