Nuclear microprobe analysis of transmembrane ion flux in rat brain

Maintenance of euglycemia is crucial because glucose is the sole nutrient that can be utilized by the brain, retina, and germinal epithelium in sufficient quantities to provide required levels of energy. Since carbohydrate reserves in neural tissue are limited, normal nerve cell function depends upon a continuous glucose supply. Neurons located in select brain sites, including the hindbrain nucleus tractus solitarius/area postrema complex (NTS/AP), exhibit unique electrophysiological and/or genomic responses to glucopenia, suggesting that regulatory signaling of this substrate fuel deficit originates within these select loci. Fundamental questions concerning the identification of monitored metabolic variables and the molecular mechanisms by which local sensor cells transduce energetic distributions into neural signals remain unresolved. The combination of microscopic particle induced x-ray emission (muPIXE) and scanning transmission ion microscopy (STIM) can permit quantitative multielemental mapping of the brain, at the single cell level, with part-per-million sensitivity while simultaneously providing structural information. Over the past year, the authors have investigated methods for utilization of muPIXE and STIM in conjunction with established neuroanatomical and pharmacological approaches in a novel strategy to characterize electrolytic indices of neuronal function. Micrometer-scale resolution of discrete brain sites is expected to yield critical information on intracellular levels of ions that regulate membrane potential and synaptic firing. This paper presents results on regional mapping for effects of metabolic manipulations deficits on the transmembrane flux of sodium, potassium, chlorine, and calcium ions. This research will significantly advance the current understanding of the cellular and molecular bases linking neuronal energetics with homeostatic regulation of metabolic substrate availability.