Origin and Migration of Interneurons of the Olfactory Bulb in the Musk Shrew, Suncus murinus.

Abstract

The olfactory bulb of the musk shrew, Suncus murinus, is characterized by the presence of various interneurons. Our previous report (Kakuta et al., 2001) demonstrated that positive immunoreactions for calretinin were observed in periglomerular and perinidal cells in the glomerular layer, small ovoid neurons in the external plexiform layer, and granule cells in the granule cell layer of the olfactory bulb in the musk shrew aged 1 to 5 weeks, in addition to calretinin-immunoreactive bipolar cells distributed in the anterior subependymal layer and in each layer of the olfactory bulb. To examine the origin and migration of interneurons of the olfactory bulb, we labeled generated cells by injecting 28-day-old musk shrews with 5-bromo-2'-deoxyuridine (BrdU), and detected the labeled progeny cells that survived after several intervals. BrdU-labeled cells originated in the subependymal layer around the anterior horn of the lateral ventricle, and rostrally migrated in the subependymal layer from the anterior wall of the lateral ventricle into the center of the olfactory bulb, where they radially migrated into the granule cell layer, external plexiform layer, and glomerular layer. It took 2 days to migrate rostrally in the subependymal layer from the anterior lateral ventricle to the center of the olfactory bulb, and 2 to 6 days to migrate radially from the bulbar subependymal layer into the three layers mentioned. The rate of rostralward migration of the labeled cells was estimated to be 38 microm/h, while that of radial migration, 7 to 25 microm/h. The present BrdU-labeling study, together with our previous immunohistochemical study (Kakuta et al., 2001), indicates that anterior subependymal cells differentiate into granule cells in the granule cell layer, into Van Gehuchten cells in the external plexiform layer, and into periglomerular and perinidal cells in the glomerular layer of the olfactory bulb in the musk shrew.

Sensory Deafferentation Transsynaptically Alters Neuronal GluR1 Expression in the External Plexiform Layer of the Adult Mouse Main Olfactory Bulb

“…In adults, only ;2% of EPL cells (neurons and glial cells) are generated after postnatal day 20 (Bayer 1983), and only ;7% of adult-generated interneurons derived from the subventricular zone are destined for the EPL (Luskin 1993). Most adult-generated interneurons are instead destined for the granule cell layer (GCL) and to a lesser extent for the GL (Kaplan et al 1985;Lois and Alvarez-Buylla 1994;Kato et al 2000;De Marchis et al 2001Wichterle et al 2001;Takei et al 2002;Ninkovic et al 2007). Recent studies show that PV-IR interneurons of the adult mouse EPL do not exhibit significant turnover (Young et al 2007).…”