INOSITOL 1,4,5-TRISPHOSPHATE RECEPTORS - IMMUNOCYTOCHEMICAL LOCALIZATION IN THE DORSAL COCHLEAR NUCLEUS

In the cochlear nucleus of mammals, the relatively homogeneous respons es of auditory nerve fibers are transformed into a variety of differen t response patterns by the different classes of resident neurons. The spectrum of these responses is hypothesized to depend on the types and distribution of receptors, ion channels, G proteins, and second messe ngers that form the signaling capabilities in each cell class. In the present study, we examined the immunocytochemical distribution of the inositol 1,4,5-trisphosphate (IP3) receptor in the dorsal cochlear nuc leus to better understand how this second messenger might be involved in shaping the neural signals evoked by sound. Affinity-purified polyc lonal antibodies directed against the IP3 receptor labeled a homogeneo us population of neurons in the dorsal cochlear nucleus of rats, guine a pigs, mustache bats, cats, New World owl monkeys, rhesus monkeys, an d humans. These cells were all darkly immunostained except in the huma n where the labeling was less intense. Immunoblots of dorsal cochlear nucleus tissue from the rat revealed a single band of protein of molec ular weight similar to 260 kD, which is the same size as the purified receptor, indicating that our antibodies reacted specifically with the IP3 receptor. These immunolabeled neurons were identified as cartwhee l cells on the basis of shared characteristics across species, includi ng cell body size and distribution, the presence of a highly invaginat ed nucleus, and a well-developed system of cisternae. Reaction product was localized along the membranes of rough and smooth endoplasmic ret iculum, subsurface cisternae, and the nuclear envelope, This label was distributed throughout the cartwheel cell body and dendritic shafts b ut not within dendritic spines, axons, or axon terminals. The regular pattern of immunolabeling across mammals suggests that IP3 and cartwhe el cells are conserved in evolution and that both play an important bu t as yet unknown role in hearing. (C) 1995 Wiley-Liss, Inc.