DIFFERENTIAL DISTRIBUTION AND SUBCELLULAR-LOCALIZATION OF RYANODINE RECEPTOR ISOFORMS IN THE CHICKEN CEREBELLUM DURING DEVELOPMENT

The distribution of ryanodine receptor (RyR) isoforms was examined usi ng isoform-specific monoclonal antibodies in the developing chicken br ain, from E18 through adulthood, using light and electron microscopic immunocytochemistry. Monoclonal antibody 110F is specific for the alph a-skeletal muscle form of RyR, while monoclonal antibody 110E recogniz es both the beta-skeletal muscle and cardiac isoforms, but does not di stinguish between the two. Significant differences in the distribution of the alpha- and beta/cardiac forms were observed. Labeling for the alpha-form was restricted to cerebellar Purkinje neurons while the bet a/cardiac form was observed in neurons throughout the brain. A major f inding was the presence of labeling for the beta/cardiac in presynapti c terminals of the parallel fibers in the molecular layer and the mess y fiber terminals in the granular layer glomeruli in late development and during adulthood. Labeling for the beta/cardiac, but not the alpha -form, underwent a major redistribution in the cerebellum during the c ourse of development. At 1 day of age, beta/cardiac labeling was prese nt mainly in Purkinje neurons. From 1 day to 4 weeks, immunolabeling f or the beta/cardiac form gradually disappeared from Purkinje neurons, but increased in granule cells. Within the molecular layer, the labeli ng pattern changed from being primarily within Purkinje dendrites to a more diffuse pattern. Electron microscopic examination of the cerebel lar molecular layer of 2-week-old chicks revealed that beta/cardiac-la beling was mainly present in the axons and presynaptic processes of th e parallel fibers. No developmental changes were observed in other bra in regions. This study represents the first demonstration of ryanodine receptor immunoreactivity in presynaptic boutons and suggests that th e ryanodine receptor may modulate neurotransmitter release through loc al regulation of intracellular calcium in the parallel fiber synapse. (C) 1997 Elsevier Science B.V.