Expression pattern of αCaMKII in the mouse main olfactory bulb

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Abstract
Multifunctional Ca2+/calmodulin‐dependent protein kinase II (CaMKII) is highly enriched at synapses and has been implicated in regulating the formation and function of several sensory systems, including the visual and the somatosensory systems. Although there is evidence for CaMKII expression in the olfactory system, the cellular localization of CaMKII has not been well studied and its function remains unknown. In this study, we examined the normal expression patterns of the predominant αCaMKII in the mouse main olfactory bulb. We showed that αCaMKII expression levels were high in the olfactory bulb and were developmentally regulated. Immunoreactivity to αCaMKII was heavy in the external plexiform layer and the granule cell layer but minimal in the olfactory nerve layer and the glomerular layer. At the cellular level, αCaMKII was selectively expressed in the γ‐aminobutyric acid (GABA)ergic granule cells but not in the GABAergic periglomerular cells. Unexpectedly, αCaMKII was not detected in the glutamatergic mitral/tufted cells. At the ultrastructural level, αCaMKII immunoreactivity was positive in granule cell spines and dendrites, but negative in mitral/tufted cell dendrites. In contrast, in the piriform cortex, as in the majority of cortical regions, αCaMKII was expressed in the glutamatergic neurons but not in the GABAergic neurons. Our results set the stage for ongoing investigations of the roles of CaMKII in the formation and function of the olfactory system. J. Comp. Neurol. 443:226–236, 2002.