Further, we demonstrate that one of these afferent neuron subtypes can sense leptin and robustly decrease feeding, even after an overnight fast. Another afferent neuron subtype in the arcuate region likely corresponds to a missing link in leptin’s control of metabolism. Together, these preliminary findings raise the possibility that leptin acts through distinct AgRP neuron afferents to decrease appetite and increase metabolism. Building on these discoveries, we aim to define afferents to AgRP neurons molecularly, anatomically, and functionally, from across the brain. We will also investigate the two novel, leptin receptor-expressing afferents to AgRP neurons identified by our pilot study. Specifically, we will determine both their control of appetite and metabolism and role in coupling leptin signaling to energy balance. Overall, our proposed studies will demonstrate a powerful, new approach to identifying synaptically connected neurons and define the cells, circuits, and signals that control appetite and metabolism through AgRP neurons.
Can high-throughput RNA sequencing reveal the neural circuitry that controls appetite and body weight?
Identifying neurons which are synaptically connected is a fundamental challenge in neuroscience, particularly in the hypothalamus, a complex and heterogeneous region which controls energy balance and other homeostatic functions through largely unknown synaptic circuits. Notably, one population of neurons in the arcuate nucleus of the hypothalamus, AgRP (Agouti-related peptide) neurons, also known as the “hunger neurons,” vitally controls feeding and metabolism and is among the best characterized neurons in the hypothalamus. Yet, across the 18 regions of the hypothalamus that provide synaptic input to AgRP neurons, only a few afferent neuron populations and their functional roles are known. This has greatly limited knowledge of how AgRP neurons stay informed about external and internal cues that predict energy supply and demand, such as environmental temperature and satiety signals including the adipose-derived hormone leptin and the hormone glucagon-like peptide 1 (GLP1). Thus, there is much to learn about the upstream circuits which control of AgRP neurons: their nature, organization, and signaling pathways, and how they can be targeted to treat obesity, cachexia, and metabolic disease. To address this critical gap in knowledge, we developed a method which leverages rabies-based connectomics with single-cell transcriptomics and used this method to identify AgRP neuron afferents from the mediobasal hypothalamus. Our preliminary studies suggest 17 neuron subtypes that input to AgRP neurons, including 14 sources of input not previously reported.