Analyses on the juxtaglomerular neurons of the olfactory bulb : 2 types of periglomerular cells

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In the olfactory bulb, the first center of the olfaction, the glomerulus is considered as a functional unit and thus to be important in the olfactory information processing. In the present study we examined following three points. (1) Do the periglomerular cells, type 1 and type 2, have axons? We applied multiple fluorescent immunostaining using antibodies of chemical markers for type 1 and 2 periglomerular cells as well as for axon initial segments, such as AnkyrinG, Nav, and βIV-spectrin. The confocal laser scanning observations revealed that large type of tyrosine hydroxylase (TH) positive GABAergic juxtaglomerular neurons, nitric oxide synthase (NOS) positive external tufted cells and short-axon cells expressing NOS, calbindin and parvalbumin (PV). However, most of Analyses on the juxtaglomerular neurons of the olfactory bulb : 2 types of periglomerular cells periglomerular cells did not show the chemically identified axon initial segments, indicating those periglomerular cells are … More anaxonic. (2) As well known TH positive GABAergic juxtaglomerular neurons are one of major groups of neurons generated even in adult period. On the other hand, there two types of TH positive neurons, large and small ones, and as we previously revealed the large type of TH positive neurons show long extending axonal processes to distant glomeruli making the inhibitory association system. In the present study we determined when both types of TH positive neurons are born and whether adult-generated TH positive neurons include both types. BrdU were injected at various developmental stages; prenatal period (E13, E17), neonate (P3) and juvenile or adult (P4w or 8w). This analysis revealed that both large and small TH positive neurons generated during prenatal and neonate periods. But only small type of TH positive neurons are adult-generated neurons. (3) We found particular axon initial segment-like or node of Ranvier-like sites "hot spots" on the dendritic segments of anaxonic PV positive GABAergic neurons in the external plexiform layer. These hot spots expressed chemical markers for axon initial segments and furthermore showed the ultrastructural feature characteristic to axon initial segment, membrane undercoating. Thus these hot spots are supposed to be the spike generating sites. Less