The VMN is a key site for regulating energy balance. We previously found several subtypes of VMN glucosensing neurons which respond to physiologic changes in extracellular glucose. Glucose responsive (GR) and glucose sensitive (GS) neurons were directly inhibited or excited, respectively, when extracellular glucose levels were decreased from 2.5 to 0.1 mM. In contrast, other VMN neurons (PED neurons) were presynaptically excited when extracellular glucose was decreased from 2.5 to 0.1 mM (Song et al., SFN Abst.26: 2219, 2000). It is not known whether these glucosensing neurons are uniquely sensitive to changes in glucose or whether they respond to other energy substrates used by the brain. Recent evidence indicates that the brain derives a significant portion of its energy from lactate. Thus, this study was performed to determine whether lactate could reverse the effects of decreasing extracellular glucose on VMN glucosensing neurons. 350 μm slices were sectioned through the VMN of the brains of 14-21 d Sp...