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motivated by experimental results, demonstrating intrinsic axon
ordering in the nerve fiber before reaching the OB. We show that
the model can successfully reproduce the ordering of the OSNs in
the developing OB and the formation of the glomeruli, provided
that some conditions are met. We demonstrate that the axon types
have to be arranged in the receptotopic space in a pattern where no
neighbors share the same set of local mosaic labels. We suggest
therefore that the arrangement of axon types in the receptotopic
space satisfies the so-called coloring constraint, such as in the four
color theorem. This is also motivated by experimental results,
showing sharp differences in the expression of the local molecular
labels in neighboring glomeruli. Using our model we reproduce
several experimental results of the olfactory map formation in
ephrin-A, Big2, Kir2/Kir3 and CNG knockout mice.
#P98
POSTER SESSION III:
OLFACTION DEVELOPMENT & CNS;
HUMAN PSYCHOPHYSICS; TASTE PERIPHERY
Composition of the Olfactory Bulb during Postnatal
Development in Mink
Willi Bennegger
1
, Elke Weiler
2
1
Maria-von-Linden-Schule, Heckentalstraße 86 D-89518
Heidenheim, Germany,
2
Faculty of Medicine, Institute of Anatomy,
Department of Neuroimmunology, University of Leipzig D-04103
Leipzig, Germany
The olfactory bulb is composed of neurons arranged in typical
layers accounting for specific functions. In mammals, the bulb
grows continuously until adulthood, thus we were interested if
the layers expand proportionally. We therefore investigated
histologically the olfactory bulb of the American mink (
Neovison
vison var. atratus
), a species born very altricial in which a major
part of development takes place postnatally. A total of 36 males
(newborns, postnatal day 1, P1, up to seven months, P210) were
analyzed. The total bulb increases in size continuously from
1.85±0.04 mm
3
at P1 to 152.00±9.14 mm
3
in adults, however the
composition pattern is highly significantly different. The
subependymal layer (P1: 7.43±0.42%; P210: 0.92±0.72%) and the
stratum album (P1: 16.98±0.47%; P210: 8.61±1.26%) decrease in
proportion possibly due to the retraction of the ventricle and
reduction of centrifugal migration, while the layer of the fila
olfactoria increases (P1: 15.92±1.08%; P210: 26.90±5.18%).
However, the fila layer increases not continuously but shows
significant reduction in relative proportion as well as in the
absolute volume in 60days intervals, which might be a result of the
lifespan of the sensory neurons. For the external plexiform, mitral
cell and internal plexiform layers the major changes happen within
the first three postnatal weeks, when mitral cells arrange from
several rows to a single row of somata and tufted cells probably
pass through the layers to reach their more outer position.
The increase of the glomerular layer (P1: 12.34±0.45%, P210:
14.28±1.31%) is small indicating the important function from birth
on. Thus, the layers of the olfactory bulb do not just expand
proportionally with bulb size but are a dynamic system and exhibit
specific developmental and functional compositions.
#P99
POSTER SESSION III:
OLFACTION DEVELOPMENT & CNS;
HUMAN PSYCHOPHYSICS; TASTE PERIPHERY
Postnatal requirement of Rac1 for mitral cell dendritic
development
Jason Estep, Matthew Mahavongtrakul, Christine Chaimanont,
Qizhi Gong
University of California at Davis, School of Medicine,
Department of Cell Biology and Human Anatomy Davis, CA, USA
Mitral cells in the mouse olfactory bulb bear a unique morphology
with a single non-branching apical dendrite targeting into a
glomerulus before elaborating terminal dendritic tufts. This mature
mitral cell dendritic morphology is achieved through a rapid
pruning process from an exuberant dendritic tree during early
postnatal stages. To investigate the molecular mechanisms of
dendritic pruning, we generated transgenic mice that express
Cre recombinase in postnatal mitral cells. TARSH gene was shown
to be specifically expressed in mitral and tufted cells and
developmentally regulated to turn on at P0 and to peak at postnatal
day 6. Using an 8kb TARSH promoter region to drive Cre
expression (TARSH-Cre), we generated and characterized three
transgenic lines. Among the three lines, two of them have Cre
expression in majority of the mitral and tufted cells at postnatal day
3 (P3), while one of TARSH-Cre line (TB) show Cre expression in
a subset of the mitral cells. TARSH-Cre transgenic lines were used
to knockout Rac1 expression specifically within mitral and tufted
cells in the olfactory bulb. Rac1 is shown to be specifically
required for dendritic development. Using a conditional Rac1
knockout (cKO) allele, we analyzed the requirement of Rac1 in
postnatal mitral cell morphology by Golgi impregnation. At P0,
mitral cell dendritic morphology did not significantly differ
between Rac1 cKO and their wildtype littermate. Mitral cells at this
stage have multiple apical dendrites. At P6, 78% of mitral cells in
wildtype littermates has single apical dendritic while 48% of mitral
cells in Rac1 cKO bears multiple apical dendrite. These data
suggest that Rac1 is required in postnatal mitral cells for their
dendritic pruning process. Acknowledgements: NIH DC011346
#P100
POSTER SESSION III:
OLFACTION DEVELOPMENT & CNS;
HUMAN PSYCHOPHYSICS; TASTE PERIPHERY
Using the mouse olfactory system as a new model to study
Traumatic Brain Injury
Elizabeth L. Steuer
1,2,3
, Michele L. Schaefer
1,2,3
,
Leonardo Belluscio
1,2,3
1
NIH/NINDS Bethesda, MD, USA,
2
Henry M. Jackson Foundation
Bethesda, MD, USA,
3
Center for Neuroscience and Regenerative
Medicine Bethesda, MD, USA
Loss of olfactory function is one of the earliest indicators of
Traumatic Brain Injury (TBI). The regenerative capacity and
well-defined neural maps within the olfactory system allow for
the investigation of neurodegeneration, regeneration, and possible
intervention following injury. Here we introduce an olfactory
system-based model that reproduces many hallmarks associated
with human brain trauma. We performed a unilateral penetrating
impact to the olfactory bulb (OB) and observed a gradation in cell
loss with ipsilateral showing a greater reduction than contralateral
and both significantly greater than control. We observed a glial
response on both the ipsilateral and contralateral bulb. Moreover,
cells in the olfactory epithelium (OE), including olfactory sensory
neurons (OSNs) that send axonal projections to the OB and
60 | AChemS Abstracts 2012
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