Dorsal raphe nucleus melanocortin signaling regulates energy homeostasis

我们最近的研究表明，DRN中GABA能MC 4 R神经元的激活增加， 喂养（Nectow等人，2017年; Reichetta等人，2020），从而表明，相反，MC 4 R神经元位于 PVN、DRN GABA能MC 4 R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中注射α-MSH减少了食物摄入量（Reichetta等人，2020），并减少DRN神经元 活化（Reichetta等人，2020）在过夜禁食的小鼠中。与这些数据一致，DREADD抑制 DRN MC 4 R神经元的释放减少了禁食过夜小鼠的进食（Reichetta等人，2020年），而梦想 DRN MC 4 R神经元的激活增加了过夜喂养小鼠的进食（Reichetta等人，2020年）。此外，委员会认为， α-MSH在DRN切片中的浴式应用导致MC 4 R神经元的超极化（Reichetta等，2020年） 和DRN GABA能神经元中动作电位频率的显著降低（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）报道了MC 4 R的激活 DRN中的神经元不影响摄食，但通过增加能量引起体重减轻 消耗和产热。在这项研究中，作者表明，这些MC 4 R神经元的激活 我们的研究发现，大多数MC 4 R神经元本质上是GABA能的， 并且它们的抑制影响进食，从而表明存在至少两个DRN MC 4 R神经元 亚群，即GABA能与谷氨酸能MC 4 R神经元，在调节 新陈代谢.值得注意的是，我们还发现饮食的DRN中α-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）小鼠相比，提示DRN可能的作用 黑皮质素信号在饮食诱导的肥胖症的发展。基于这些数据，我们假设 DRN中的黑皮质素信号传导在代谢的调节中起作用（Nectow等人，二〇一七年; Reichetta等人，2020）通过2个不同的MC 4 R亚群，GABA能和 能MC 4 R神经元。 在目标1中，我们将确定并比较黑皮质素信号传导在DRN GABA能神经元中的作用与 DRN能神经元通过影响摄食和代谢调节摄食和代谢 遗传GABA能和谷氨酸能MC 4 R神经元。在目标2中，我们将分析POMC（和AgRP）投影 DRN GABA能和谷氨酸能MC 4 R神经元亚群和细胞内信号传导 DRN（和PVN）GABA能和谷氨酸能MC 4 R神经元中的通路。在目标3中，我们将询问角色 DRN黑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逻辑延伸，完成这些研究将揭示 新的机制原则，在中央调节代谢。

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.