Expression of lactate dehydrogenase-A and -B messenger ribonucleic acids in chick glycogen body

Department of Veterinary Anatomy, Faculty of Agriculture, Tottori University, Japan. imagawat@muses.tottori-u.ac.jp

Glucose is a main metabolic substrate in the central nervous system (CNS). Recently, lactate has attracted renewed attention because it plays an important role in the CNS as a metabolic substrate between neurons and astrocytes. Lactate and lactate dehydrogenase (LDH), a key enzyme for lactate and pyruvate interconversion, have been investigated. The glycogen body (GB) is a gelatinous tissue in the dorsal area of the lumbosacral spinal cord in birds. It is composed of uniform cells with high glycogen storage and is thought to be in the astroglia lineage. In this article, we investigated the LDH enzyme activity in embryo GB (embryonic d 12, 14, 16, 17, and 18) and chickens. To detect the subtype of the LDH, mRNA expressions in GB were investigated and compared with those of cerebral cortex and spinal cord. By histochemical observations, LDH enzyme activity was detected in the cytoplasm of GB cells of all embryonic periods after embryonic d 12. In biochemical analysis, the enzymatic activities of the GB were higher than in the cerebral cortex. In the GB the subtype of LDH mRNA was LDM-B only, and in the cerebral cortex and spinal cord, the subtype of LDH mRNA was predominantly LDH-B, and a small amount of LDH-A was found in the chicken and embryo. The LDH-B mRNA expression in GB was detected during all periods of the study (after embryonic d 12). These observations suggest that GB expressed only LDH-B and that GB cells are not lactate-producing cells, like astrocyte, but rather are lactate-consuming cells, similar to neurons in CNS.