CALCIUM-BINDING PROTEINS IN THE PERIGLOMERULAR REGION OF TYPICAL AND ATYPICAL OLFACTORY GLOMERULI

The distribution of chemically identified neuronal populations was stu died in the glomerular layer of the rat olfactory bulb using calcium-b inding protein immunocytochemistry combined with acetylcholinesterase histochemistry. Four calcium-binding proteins (calbindin D-28k, parval bumin, calretinin, and neurocalcin) were analyzed in the periglomerula r region of two different glomerular subsets: typical and atypical glo meruli. Atypical glomeruli were clearly distinguishable from typical o nes by their dense network of acetylcholinesterase-positive centrifuga l fibers. Each calcium-binding protein studied showed a specific distr ibution pattern in the rat olfactory bulb. Calbindin D-28k-, calretini n-, and neurocalcin-immunoreactive neurons were specially abundant in the glomerular layer. These three calcium-binding proteins had their m ain expression in neuronal subpopulations directly involved in the glo merular circuitries of the rat olfactory bulb. Specific populations of periglomerular cells were stained for calbindin D-28k, parvalbumin, c alretinin, or neurocalcin, whereas external tufted cells were only imm unoreactive to neurocalcin. Both neuronal types, periglomerular cells and external tufted cells, were found in the periglomerular region of both glomerular subsets. Nevertheless, a homogeneous distribution of c albindin D-28k- or calretinin-immunopositive periglomerular cells were found between typical and atypical glomeruli, whereas the neurocalcin -immunostained external tufted cells were statistically more abundant in typical glomeruli than in atypical ones (P < 0.001). These data sug gest that some neuronal subpopulations are related with general proper ties of the glomerular physiology, and they have a homogeneous distrib ution in different subsets of glomeruli, whereas other chemically iden tified populations are related with a finer tuning of the olfactory pr ocessing, and they are segregately distributed in relation to particul ar glomerular subsets. In addition, this work adds new differences in the cellular composition of typical and atypical glomeruli.