NEUROCALCIN IMMUNOREACTIVITY IN THE RAT MAIN OLFACTORY-BULB

The morphological characteristics and distribution of neurocalcin (NC) -immunoreactive elements were studied in the rat main olfactory bulb ( OB) using a polyclonal antibody and the avidin-biotin immunoperoxidase method. NC-positive elements were abundant in the glomerular layer (G L), where numerous immunostained external tufted cells and periglomeru lar cells were detected. Other less abundant NC-immunolabeled populati ons included middle and internal tufted cells, Van Gehuchten cells, ho rizontal cells, vertical cells of Cajal, deep short-axon cells and gra nule cells. This study demonstrates the presence of NC immunoreactivit y in subsets of different neuronal types in the rat main OB. This calc ium-binding protein has been found in interneurons, and no evidence of immunoreactivity to NC is detected in projecting neurons. Despite the large population of labeled external tufted cells, most of them belon g according to morphological criteria to the local circuit group and s ome others to those with interbulbar and/or intrabulbar connections. T he identification of neuronal subpopulations expressing NC provides a further characterization and shows the existence of biochemical differ ences within morphologically identical neurons. Thus, this marker may be a useful tool in unravelling the circuitries of the rodent OB in bo th normal and experimental conditions. The exact physiological functio n of NC in the olfactory system remains unknown. On the basis of simil arities to recoverin, it could be involved in mechanisms responsible f or sensory adaptation. Additionally, its calcium-binding abilities may contribute to improve the temporal precision of stimuli transmission, or be concerned with general calcium-related events occurring in spec ific interneuronal groups. (C) 1998 Elsevier Science B.V. All rights r eserved.