Project Summary: Amylin signaling decreases food intake and gastric emptying in both humans and rats via activation of CNS amylin receptors (calcitonin receptor, CTR; heterodimerized with a receptor activating modified protein, RAMP1-3) making it a potential target for the development of novel pharmacotherapies to treat obesity. Despite the distributed nature of CNS amylin receptors, research on the role of amylin signaling in the control of energy balance has been largely focused on hypothalamic and hindbrain nuclei, leaving other nuclei with abundant CTR expression such as the mesopontine laterodorsal tegmental nucleus (LDTg) understudied. Recent work from our lab showed that LDTg CTR signaling reduces food intake. Additionally, in the absence of endogenous LDTg CTR signaling, rats show increased food intake and body weight gain. However, the mechanism by which CTR signaling in the LDTg modulates energy balance, as well as the downstream nuclei targeted by LDTg CTR expressing neurons (LDTgCTR) has not been explored. The LDTg is known to modulate dopamine signaling to regulate motivated behavior via direct projections to the ventral tegmental area (VTA) and our preliminary data shows that several LDTgCTR neurons send direct projections to the VTA. Consequently, we will use chemogenetics to activate LDTgCTR neurons that project to the VTA and evaluate the effect of this manipulation on feeding and motivation to obtain palatable food rewards (Aim 1). We will also use a dual AAV approach to projection-specifically knockdown CTR expression in LDTg neurons that project to the VTA and evaluate the role of these neuron’s endogenous CTR activity in the regulation of energy balance and palatable food reward seeking motivation (Aim 2). Lastly, we will use fiber photometry to monitor the activity of LDTgCTR neurons in lean and obese animals in response to food availability at different energetic states. Then, we will determine how diet-induced obesity affects the ability of LDTgCTR neurons to modulate downstream VTA dopaminergic (VTATH) neurons (Aim 3). Altogether, we hypothesize that this novel mesopontine-limbic signaling pathway will have the ability to reduce food intake and body weight without inducing symptoms of malaise, via modulation of downstream VTATH neurons. Consequently, the proposed work will functionally characterize a promising target for the development of effective obesity pharmacotherapies.