PROJECT SUMMARY With support from this program, we reported in 2016 that across multiple rodent models of type 2 diabetes (T2D), remission of hyperglycemia lasting for weeks or months can be achieved with a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1). In the years since, our investigation into mechanisms underlying this effect has consistently shown that in addition to sustained glucose lowering, FGF1 also induces a potent but transient anorexic response. In a primate model, this effect is sufficiently intense as to suspend ongoing efforts to translate FGF1-based diabetes therapy to the clinic. Studies in this proposal will clarify mechanisms underlying both the anorexic response and sustained glucose lowering induced by the central action of FGF1, with a focus on neurons in the hypothalamic arcuate nucleus (ARC) that express agouti-related peptide (AgRP neurons). Inhibition of these neurons by FGF1 is implicated in both the feeding and glucose-lowering effects of FGF1, although distinct projections and signaling molecules appear to mediate these divergent effects. Thus, whereas diabetes remission induced by icv FGF1 injection is blocked by Mc4r deletion or blockade, these interventions have no impact on FGF1-induced anorexia. Instead, we hypothesize that the anorexic response involves activation of neurons in the parabrachial nucleus that express calcitonin gene-related peptide (PBNCGRP neurons) via a melanocortin-independent mechanism. These neurons are 1) highly anorexigenic, 2) tonically inhibited by GABAergic projections from AgRP neurons, and 3) robustly activated following icv FGF1 injection. SA1 investigates the hypothesis that FGF1-induced anorexia results from PBNCGRP neuron activation secondary to reduced GABAergic input from AgRP neurons. We will also determine if FGF1-induced PBNCGRP neuron activation can be blocked by pharmacological intervention with a GABA receptor agonist, while having no effect on the associated remission of hyperglycemia. A second goal of this proposal is to delineate the mechanism(s) underlying prolonged inhibition of AgRP neurons by FGF1. Perineuronal nets (PNNs) are extracellular matrix specializations that enmesh most AgRP neurons, and loss of these PNNs is hypothesized to contribute to diabetes-associated AgRP neuron activation. Since these PNNs are rapidly reformed following icv FGF1 injection, SA 2 tests the hypothesis that sustained inhibition of AgRP neurons by FGF1 requires reassembly of the PNNs that enmesh them. 1