The qualitative and quantitative analysis of olfactory glomerulus and nidus in the olfactory bulb

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We investigated immunohistochemically the main olfactory bulbs (MOBs) of 7 mammalian species, focusing on two points: 1) whether nidi, particular spheroidal synaptic regions containing many GABAergic calbindin D28K-immunoreactive (CB-IR) elements we previously reported in the laboratory musk shrew MOBs, are also present in other animals, and 2) whether the compartmental organization of glomeruli and two types of periglomerular cells we proposed in the rat MOBs, are general in the MOBs, of these animals. We used two insectivores, moles and hedgehogs, tree shrews, bats and mice as well as laboratory musk shrews and rats. We found discrete nidi and the nidal layer only in the mole and laboratory shrew MOBs, where observed none or a few olfactory nerves (Ons) extruding from glomeruli. These results suggest that the nidi and related distinctive organization might be specific to only some species of insectivores.On the other hand, we recognized the apparent compartmental organization of glomeruli and two types of periglomerular cells in the MOBs of all of the mammals we examined, indicating these structural features are common to the MOBs of various mammals and thus might be important organizational principles of the MOBs.