Localization of glucokinase-like immunoreactivity in the rat lower brain stem: For possible location of brain glucose-sensing mechanisms

Pancreatic glucokinase (GK) is considered an important element of the gluco se-sensing unit in pancreatic P-cells. It is possible that the brain uses s imilar glucose-sensing units, and we employed GK immunohistochemistry and c onfocal microscopy to examine the anatomical distribution of GK-like immuno reactivities in the rat brain. We found strong GK-like immunoreactivities i n the ependymocytes, endothelial cells, and many serotonergic neurons. In t he ependymocytes, the GK-like immunoreactivity was located in the cytoplasm ic area, but not in the nucleus. The GK-positive ependymocytes were found t o have glucose transporter-2 (GLUT2)-like immunoreactivities on the cilia. In addition, the ependymocytes had GLUT1-like immunoreactivity on the cilia and GLUT4-like immunoreactivity densely in the cytoplasmic area and slight ly in the plasma membrane. In serotonergic neurons, GK-like immunoreactivit y was found in the cytoplasm and their processes. The present results raise the possibility that these GK-like immunopositive cells comprise a part of a vast glucose-sensing mechanism in the brain.