Coexpression of neurocalcin with other calcium-binding proteins in the ratmain olfactory bulb

The distribution patterns of four calcium-binding proteins (CaBPs)-calbindi n D-28k (CB), calretinin (CR), neurocalcin (NC), and parvalbumin (PV)-in th e rat main olfactory bulb were compared, and the degrees of colocalization of NC with the other CaBPs were determined by using double immunocytochemic al techniques. All investigated CaBPs were detected in groups of periglomerular cells and Van Gehuchten cells, whereas other cell types expressed some of the investi gated proteins but not all four. Double-labeling techniques demonstrated th e colocalization of NC with CB, CR, or PV in periglomerular cells, whereas each neurochemical group constituted entirely segregated populations in the remaining neuronal types. This is evident in granule cells that demonstrat ed large but segregated populations immunoreactive to either NC or CR. This study provides a further biochemical characterization of interneuronal types in the rat main olfactory bulb. On the basis of the distinct calcium -binding affinities, each neurochemically defined population may have diffe rent responses to calcium influx that would result in the existence of dist inct functional subgroups within morphologically defined neuronal types. Th e expression of the investigated CaBPs in periglomerular cells with both si ngle and colocalized patterns suggests that the local circuits in the glome rular layer are constituted by a complex network of elements with particula r calcium requirements. J. Comp. Neurol. 407:404-414, 1999. (C) 1999 Wiley- Liss, Inc.