title: Nidus and tasseled cell: distinctive neuronal organization of the main olfactory bulb of the laboratory musk shrew (Suncus murinus).
abstract: We revealed the structural features of particular synaptic regions, nidi, and newly found neurons, tasseled cells, in the main olfactory bulb (MOB) of the laboratory musk shrew (Suncus murinus). Nidi were intensely immunoreactive for glutamic acid decarboxylase (GAD) and calbindin D28k (CB), were 30-80 microm in diameter, and were located beneath glomeruli, appearing to make glomerulus-nidus unit-like complexes. In contrast to glomeruli, they contained few or no olfactory nerves. Nidi were distributed throughout the whole MOB and made a distinctive layer, nidal layer. Tasseled cells were located in the mitral cell layer and in the middle of the external plexiform layer (EPL) and extended single primary dendrites to the nidus, where their small tuft-like complicated branches intermingled with processes of perinidal cells surrounding nidi. Primary dendrites of mitral/tufted cells also penetrated nidi but passed to glomeruli. In the outer half of the EPL, columnar structures were seen, where CB- and GAD-positive elements appeared to associate with bundles of cylindrical dendrites of presumed mitral/tufted and tasseled cells. By electron microscopic examinations, nidi were confirmed to be particular synaptic areas where GAD-positive processes made symmetrical synapses to GAD-negative presumed tasseled and mitral/tufted cell dendrites and received asymmetrical synapses from the latter. Retrograde tracings revealed that tasseled cells, in addition to mitral/tufted cells, projected their axons to the lateral olfactory tract, indicating that there were two parallel projection systems in the shrew MOB, which might interact with each other via various types of gamma-aminobutyric acid (GABA)ergic interneurons. The present study clearly showed that the neuronal organization of the shrew MOB was distinctly different from that in rodents.
authors.affiliation: Department of Anatomy and Neurobiology, Graduate School of Medical Sciences, Kyushu University, Higashiku, Fukuoka 812-8582, Japan. kosaka@shs.kyushu-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Kosaka
authors.forename: T
authors.initials: T
authors.lastname: Kosaka
mesh_terms: D000818:Animals; D064026:Calbindins; D048429:Cell Size / Q000502:physiology; D005260:Female; D007150:Immunohistochemistry; D007395:Interneurons / Q000737:chemistry / Q000648:ultrastructure; D008297:Male; D018613:Microscopy, Confocal; D009830:Olfactory Bulb / Q000166:cytology*; D018034:Olfactory Receptor Neurons / Q000737:chemistry / Q000648:ultrastructure*; D064030:S100 Calcium Binding Protein G / Q000032:analysis; D012788:Shrews / Q000033:anatomy & histology*; D005680:gamma-Aminobutyric Acid / Q000032:analysis
chemical_list: D064026:Calbindins; D064030:S100 Calcium Binding Protein G; D005680:gamma-Aminobutyric Acid