Structure and chemistry of glucose-producing cells in meningeal tissue of the lamprey

Abstract

The structure of meningeal tissue of sea and brook lampreys was investigated with light and electron microscopy. Glucose and other metabolites were measured in separated meningeal and nervous tissues, and a direct fluorometric method was developed to follow the release of glucose from incubated meningeal tissue. Meningeal tissues around brains and spinal cords of both larval and adult lampreys of both species contain prominent round cells. These cells are the probable source of the glucose produced since they contain considerable glycogen. They also contain lipid droplets, darkly staining mitochondria, membrane-bound granules, and whorled endoplasmic membranes which are related to glycogen deposits. Direct extracellular pathways extend from round cells to the basement membrane covering the brain. Evidence is presented that glucose produced by the meninges can pass into the brain. Furthermore, dyes injected into the meningeal tissue also enter the nearby nervous tissue. Kinetics and stability of meningeal glucose-6-phosphatase, which probably participates in the conversion of glycogen to glucose, were investigated. The enzyme resembles that of mammalian liver and kidney, but differs from β-glycerophosphatase.