Distribution of Glucose Transporter - 3 and Hexokinase I in the Developing Mouse Brain. • 421

Abstract

Glucose is transported into neurons by a facilitative glucose transporter - 3 (Glut 3) isoform and is phosphorylated into glucose-6-phosphate by hexokinase I. Employing the 2d, 14d, and 60d old rostrocaudal floating microtome murine brain sections (n=3 each) and immunohistochemical analysis we examined the distribution of Glut 3 and hexokinase I. An age-dependent increase in Glut 3 immunoreactivity was uniformly noted in all regions. Overall Glut 3 was present in the neuropil, neuronal processes, and nerve fiber bundles in most regions examined with the exception of a neuronal cellular distribution in the cerebellar granular layer. Prominent axonal Glut 3 labeling was noted in circumventricular regions lacking a blood-brain barrier and the periventricular hypothalamic region. In the 2d old, Glut 3 positive cells and processes were also noted in the dorsomedial subnuclei of the suprachiasmatic nucleus. In contrast, hexokinase I was observed intracellularly with a perinuclear distribution in all areas, including the cerebellar Purkinje cells and dendrites that extend into the molecular layer, the laminar zone between the brain parenchymal and ependymal cells of the third ventricle, and the choroid plexus. We conclude that 1] Glut 3 immunoreactivity increases with age while hexokinase I labeling remains unchanged, 2] Glut 3 is expressed in neuronal cellular processes, being most prominent in regions that are exposed to circulating factors and peripheral stimuli, while hexokinase I is noted intracellularly in neurons and non-neuronal cells. We speculate that Glut 3 mediates glucose transport necessary to fuel neurotransmission in response to perturbations in the metabolic/hormonal mileu, while hexokinase I phosphorylates glucose in brain cells not limited to expressing Glut 3.