Immunocytochemical localization of glycogen phosphorylase kinase in rat brain sections and in glial and neuronal primary cultures

The physiological function of brain glycogen and the role of phosphorylase kinase as a regulatory enzyme in the cascade of reactions associated with g lycogenolysis in the brain have not been fully elucidated. As a first step toward elucidating such a function, we studied the localization of phosphor ylase kinase in glial and neuronal primary cell cultures, and in adult rat brain slices, using a rabbit polyclonal antibody against skeletal muscle gl ycogen phosphorylase kinase. Immunocytochemical examination of rat astrogli a-rich primary cultures revealed that a large number of cells were positive for glycogen phosphorylase kinase immunoreactivity. These cells were also positive for vimentin, a marker for immature glia, while they were negative for glial fibrillary acidic protein, a marker for mature astroglia, and fo r galactocerebroside, an oligodendroglial marker. Neurons in rat neuron-ric h primary cultures did not show any kinase-positive staining. In paraformal dehyde-fixed adult rat brain sections, phosphorylase kinase immunoreactivit y was detected in glial-like cells throughout the brain, with relatively hi gh staining found in the cerebral cortex, the cerebellum, and the medulla o blongata. Phosphorylase kinase immunoreactivity could not be detected in ne urons, with the exception of a group of large neurons in the brain stem, mo st likely belonging to the mesencephalic trigeminal nucleus. Phosphorylase kinase was also localized in the choroid plexus and to a lesser degree in t he ependymal cells lining the ventricles. Phosphorylase kinase thus appears to have the same cellular distribution in nervous tissue as its substrates , i.e. glycogen phosphorylase and glycogen, which suggests that the physiol ogical role of brain phosphorylase kinase is the mobilization of glycogen s tores to fuel the increased metabolic demands of neurons and astrocytes.