Distribution of ryanodine receptors in the chicken central nervous system

The ryanodine receptor (RR), an intracellular calcium release channel, has been identified in the nervous system but its contributions to neuronal function are unknown. We have utilized immunohistochemical techniques to establish the distribution of RRs in the central nervous system (CNS) of the chick as a step toward elucidating the function of RRs in this system. RR immunoreactivity is observed throughout the brain, most prominently in large neurons. The strongest immunoreactivity is found in cerebellar Purkinje neurons, but nuclei in the motor, visual and vestibular systems are also intensely labeled, and immunoreactive neurons are observed the olfactory bulb and the hippocampus. In these neurons, labeling is prominent in cell bodies, dendrites and axons, but is not observed in the dendritic spines or in plasma membranes. The neuronal RRs bind [3H]ryanodine with high affinity and this activity is regulated by calcium, caffeine, MgCl2/ATP and ionic strength. Multiple forms of the RRs are found in the chicken CNS. Immunoprecipitation and localization studies using RR isoform specific monoclonal antibodies reveal major differences in their distribution. The predominant species in the cerebellum is similar to the skeletal muscle isoform while there is a lower level of expression of either the cardiac or beta skeletal isoforms. In the remainder of the brain, the predominant isoform is similar to the cardiac or beta skeletal muscle isoforms. The broad distribution of RRs in the CNS suggests that calcium release events mediated by these proteins may have a functional role in a diverse array of neurons. Moreover within the populations of neurons expressing RR's, the presence of specific RR isoforms may correlate with specialization in the calcium release events mediated by these proteins.