Origin, migration and fate of newly generated neurons in the adult rodent piriform cortex

Abstract

Newly generated neurons are continuously added to the olfactory epithelium and olfactory bulbs of adult mammals. Studies also report newly generated neurons in the piriform cortex, the primary cortical projection site of the olfactory bulbs. The current study used BrdU-injection paradigms, and in vivo and in vitro DiI tracing methods to address three fundamental issues of these cells: their origin, migratory route and fate. The results show that 1 day after a BrdU-injection, BrdU/DCX double-labeled cells appear deep to the ventricular subependyma, within the white matter. Such cells appear further ventral and caudal in the ensuing days, first appearing in the rostral piriform cortex of mice at 2 days after the BrdU-injection, and at 4 days in the rat. In the caudal piriform cortex, BrdU/DCX labeled cells first appear at 4 days after the injection in mice and 7 days in rats. The time it takes for these cells to appear in the piriform cortex and the temporal distribution pattern suggest that they migrate from outside this region. DiI tracing methods confirmed a migratory route to the piriform cortex from the ventricular subependyma. The presence of BrdU/NeuN labeled cells as early as 7 days after a BrdU injection in mice and 10 days in the rat and lasting as long as 41 days indicates that some of these cells have extended survival durations in the adult piriform cortex.

A Population of Prenatally Generated Cells in the Rat Paleocortex Maintains an Immature Neuronal Phenotype into Adulthood

“…Additionally, during the review process of the present study, a new report on adult neurogenesis in the rodent piriform cortex has been published by Ribak's group (Shapiro, Ng, Kinyamu, et al 2007). A previous study has described the presence of individual SVZ-derived neurons in the anterior olfactory nucleus and anterior olfactory cortex of perinatal mice (De Marchis et al 2004).…”

“…Moreover, there is discrepancy on the time of origin of these cells. Although some reports have failed to find adult neurogenesis in this region (Nacher et al 2002a;Bonfanti 2006), 3 recent studies have described the presence of newly generated neurons in the adult paleocortex (Pekcec et al 2006;Shapiro, Ng, Kinyamu, et al 2007;. In order to investigate in detail the phenotype of these putative immature cells in the paleocortex layer II, we have analyzed the expression of molecules commonly found in recently generated neurons and neuronal progenitor cells in the adult CNS, such as those found in the dentate gyrus and SVZ/olfactory bulb.…”

Noncanonical Sites of Adult Neurogenesis in the Mammalian Brain

“…Interestingly, the heterogeneous nature of parenchymal neurogenesis and the technical limitations of newborn neuron detection (see above) have inadvertently led to the discovery of noncanonical neurogenic mechanisms of plasticity. This is the case of the piriform cortex, which is one region in which neurogenesis was reported by different research groups and is refuted by others (see, for example, Bernier et al 2002;Pekcec et al 2006;Shapiro et al 2007;Gomez-Climent et al 2008). The piriform cortex is known to harbor a population of neurons immunoreactive for PSA-NCAM and DCX, which are two markers highly expressed in newborn neurons, but are also present in non-newly generated cells (Bonfanti 2006;Gomez-Climent et al 2008).…”

Effect of aging on neurogenesis in the canine brain

“…Doublecortinpositive or Ki-67-positive cells were counted in the subgranular zone and the granule cell layer of the hippocampal dentate gyrus. Therefore, a modified stereological-like method as recently described by Shapiro et al (2007) was used. In this adapted version, analysis of the immunoreactive cells was performed conventionally but not unbiased using the KS400 software.…”