CBP-18, A CA-2-BINDING PROTEIN IN RAT-BRAIN - TISSUE DISTRIBUTION ANDLOCALIZATION()

The distribution of a novel calcium-binding protein with a molecular m ass of 18 kDa (CBP-18) in the rat brain was studied by means of bioche mical methods and immunohistochemistry on cryostat-sectioned tissue an d compared with staining patterns of parvalbumin on adjacent sections. The biochemical analysis revealed high levels of CPB-18 in cortex and cerebellum, low levels in the lungs, and undetectable levels in all o ther tissues tested. Immunohistochemically, the polyclonal rabbit-deri ved antibody for CPB-18 showed selective affinity with periglomerular cells and dendrites in the olfactory bulb. Distinct immunostaining of scattered cells and their proximal dendrites was found in the anterior olfactory nuclei and in the perirhinal and entorhinal cortex. Strong staining of neuropil with recognizable but diffusely outlined cells wa s observed in the retrosplenial cortex, central amygdala, hippocampal rudiment, septum, area preoptica, hypothalamus, colliculus superior, a nd parabrachial nuclei. The cerebellum showed strong neuropil staining of both the molecular and the granule cell layer. Less intense neurop il staining and a few scattered cells were found in the neocortex, the remaining basal forebrain, and in the entire brainstem. Immunoreactiv ity was barely detectable or missing in the striatum, the hippocampus, the thalamus, and in the colliculus inferior. Thus, CPB-18 shows a un ique staining pattern in the CNS, different from all other Ca2+-bindin g proteins studied so far.