Brains were quickly removed and placed into ice-cold sectioning solution. A block of brain tissue was glued to the stage of a Campden Vibroslice for slicing while immersed in ice-cold sectioning solution. After a 1 hr recovery period at 35°C in ACSF, slices were used for recordings within ∼8 hr. ACSF was continuously gassed with 95% O2 and 5% CO2 and contained (in mM): 125 NaCl, 2.5 KCl, 2 MgCl2, 2 CaCl2, 1.2 NaH2PO4, 21 NaHCO3, and 1 glucose (except where indicated otherwise). Sectioning solution contained (in mM): 95 NaCl, 1.8 KCl, 1.2 CaCl2, 26 NaHCO3, 1.2 KH2PO4, 7 MgSO4, 50 sucrose,

and 15 glucose. Two types of intracellular (pipette) solutions were used. “High-Cl” pipette solution contained (in mM): 130 KCl, 0.1 EGTA, 10 HEPES, 5 K2ATP, 1 NaCl, 2 MgCl2 (pH 7.3) with KOH. “Low-Cl” pipette PFI-2 nmr solution contained (in mM): 120 K-gluconate, 10 KCl, 0.1 EGTA, 10 HEPES, 5 K2ATP, 1 NaCl, 2 MgCl2 (pH 7.3) with KOH. Liquid junction potential for the low-Cl solution was estimated to be 10 mV and has not been subtracted from the measurements. The low-Cl solution, which mimics the ionic composition in a typical central neuron, was used in all experiments except

those in Figures 3A–3C (where we see more used high-Cl solution) and Figure 1H (where we used ACSF). All AAs used were L-isoforms and glucose was D-(+)-glucose. The concentrations of AAs in the control and “low” AA mixes are given in Table S1 (called “AA mix” and “low AA mix,” respectively). Purity of the AA mix was examined by ion-exchange chromatography followed by ninhydrin analysis (Department of Biochemistry Analytical Facility, University of Cambridge), where threshold for detection was 0.5 μM. No GABA or glutamate contamination was detected and glycine concentration was within 10% of the intended value. Classification of amino acids as essential Casein kinase 1 or nonessential in Figure 3B was based on Gietzen and Rogers (2006). In the upper panel of Figure 3D, we omitted cysteine

because it is toxic and not found in CSF (Choi et al., 1999 and Nishimura et al., 1995), glutamate to avoid excitation through glutamate receptors, and glycine because at high concentrations it may modulate orx/hcrt neurons through glycine receptors (Karnani et al., 2010). In the upper panel of Figure 3D, other AAs listed in Table S1 were present in 100 μM concentration making the total concentration for essential AA mix 1.1 mM, and nonessential AA mix 0.6 mM. In the lower panel of Figure 3D, the concentrations for AAs were from “AA mix” in Table S1. “FA mix” contained (in μM): 5 oleic acid, 5.4 palmitic acid, and 1.8 palmitoleic acid (Oomura et al., 1975 and Wang et al., 2006).