[Abstract Title]. - Society for Neuroscience

Program#/Poster#: 231.6/B19
Topic: A.04.i. Dendritic growth and branching
Support: NIH Grant DC000210
NIH Grant DC006972
NIH Grant DC006291
Title: Role of TrkB in dendritic development of mitral cells in mouse olfactory bulb
Authors: *F. IMAMURA, C. GREER;
Dept. Neurosurg., Yale Univ,Sch Med., New Haven, CT
Abstract: Mature mitral and tufted cells in the mammalian olfactory bulb (OB) have a single
primary dendrite that arborizes within a single glomerulus. Here, we focused on factors
regulating the development of mitral/tufted cell dendritic arbors within a glomerulus, and test the
hypothesis that the neurotrophins are important determinants of this mechanism. First, we
visualized the development of glomerular tufts of mitral cells in mice using intracellular lucifer
yellow injections. We found that dendritic tufts in a glomerulus significantly increase their total
length and number of branching points during early postnatal days, especially from postnatal day
(P) 3 to 10. Second, using immunohistochemical analyses, we found that the full-length TrkB
(TrkB.FL) was expressed by thick dendritic trunks of mitral/tufted cells, while the truncated
isoform of TrkB (TrkB.T1) is localized at the tip of mitral/tufted cell dendrites including
dendritic tips in the glomerular tuft. Interestingly, the TrkB.T1 expression in glomeruli
colocalized with growth cone marker CDA 1, and was high during early postnatal days but
disappeared by P10. Therefore, this suggested that the TrkB.T1 was expressed in dendritic
growth cones when dendrites arborize in glomeruli. Third, to examine the role of TrkB in
dendritic development, we cultured mitral/tufted cells and treated them with neurotrophins:
BDNF, NT-3, and NT-4. In cultured mitral/tufted cells at 1 day in vitro (DIV), localization of the
TrkB.T1 at the tip of neurites was observed, while the TrkB.FL was seen in whole neurites.
When treated with TrkB ligands, BDNF or NT-4, from 0 to 4 DIV, mitral/tufted cells
significantly increased the number of primary neurites and branching points, as well as their total
neurite length compared with untreated controls. NT-3 treatment did not have a significant
effect. Our findings strongly suggest that the TrkB.T1 expression during dendritic development
plays a significant role in the elaboration of mitral/tufted cell glomerular dendritic arbors,
consistent with our working hypothesis that neurotrophins are determinants of olfactory bulb
circuitry.
Disclosures: F. Imamura, None; C. Greer, None.
Poster