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Conserved properties of dendritic trees in four cortical interneuron
subtypes
1,2 1,2 2,3 1,2
1
2 CREST 3
Dendritic trees influence synaptic integration and neuronal excitability, yet
appear to develop in rather arbitrary patterns. Using electron microscopy and
serial reconstructions, we analyzed the dendritic trees of four morphologically
distinct neocortical interneuron subtypes to reveal two underlying organizational
principles common to all. First, crosssectional areas at any given point within
a dendrite were proportional to the summed length of all dendritic segments
distal to that point. Consistent with this observation, total crosssectional area
was almost perfectly conserved at bifurcation points. Second, dendritic cross
sections became progressively more elliptical atmore proximal, larger diameter,
dendritic locations. Finally, computer simulations revealed that these conserved
morphological features limit distance dependent filtering of somatic EPSPs and
facilitate distribution of somatic depolarization into all dendritic compartments.
Because these features were shared by all interneurons studied, they may represent
common organizationalprinciples underlying the otherwise diverse morphology of
dendritic trees.
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FABP in astrocytes is involved in control of neuronal dendritic
formation
Majid Ebrahimi, Yshiteru Kagawa, Kazem Sharifi, Yasuhiro Adachi,
Tomoo Sawada, Nobuko Tokuda, Yuji Owada
Department of Organ Anatomy, Yamaguchi University Graduate School of
Medicine
Alteration of fatty acid homeostasis in brain is associated with human functional
psychosis. We previously showed that FABP7 braintype fatty acid binding
protein, a cellular fatty acid chaperon abundantly expressed in astrocytes, is
involved in control of emotional behavior. However, mechanism by which FABP7
in astrocytes modulates neuronal activity is still unknown.
Mixed cortical culture and neuron/astrocyte coculture were established from
wildtype WT and FABP7 KO KO mice, and morphology of pyramidal
neurons was evaluated by NeuronMetrics. GolgiCox staining was performed to
examine dendrite morphology of neurons in cerebral cortex of KO mice.
In mixed cortical culture, pyramidal neurons of KO mice showed decrease in
length and number of dendritic branches. In the WT neuron/KO astrocyte hybrid
coculture WTn/KOa such changes in dendrite morphology were also detected
compared to WTn/WTa coculture. Moreover, pyramidal neurons in prefrontal
cortex of KO mice showed aberrant dendrite formation.
FABP7 may regulate neuronal dendrite formation by modulation of lipid
homeostasis metabolism/signal transduction in astrocytes.
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FILIP
1 1 1 1 1 1
1,2 1
1
2
FILIP
A
FILIP
FILIP
P
CA
CA1
Thy1 GFP
9 2
mushroom type stubby type thin type
CA1 Western blot
BDNF PSD95
BDNF PSD95
BDNFPSD95
P
In vivo analysis of postsynaptic molecular dynamics in the
developing mouse cortex
Dynamic behavior of postsynaptic molecules is thought to play important
roles in synaptic transmission and plasticity. Postsynaptic densities PSDs and
spines are key elements in the process of postsynaptic signal transduction. We
previously reported differential dynamics of molecules present in PSDs and
spines in cultured hippocampal neurons. Photobleaching of actin, the prominent
cytoskeletal component in the spine cytoplasm, and PSD scaffolding proteins
PSD95 and Homer1c showed distinct mobility in the postsynaptic cytoplasm,
indicating independent regulation of molecular dynamics. To gain more insights in
the protein mobility at the postsynaptic sites and its regulation, information from
neurons in the native environment should be obtained. To monitor protein mobility
in vivo, we applied twophoton photoactivation/bleaching to pyramidal neurons
in the mouse cortex and monitored fluorescence decay/recovery in individual
spines at different developmental stages. Lifetime of PSD/spine structure was
much longer than resident times of individual protein molecules, indicating the
importance of protein network in maintenance of the postsynaptic structural
organization.
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Direct monitoring of AMPA receptor recycling and trafficking
Ayako Hayashi 1 , Daisuke Asanuma 2 , Mako Kamiya 3 , Yasuteru Urano 3 , Shigeo
Okabe 1
1
Department of Cellular Neurobiology, Graduate School of Medicine, The
university of Tokyo, 2 Department of Neurobiology, Graduate School of Medicine,
The university of Tokyo, 3 Department of Chemical Biology and Molecular
Imaging, Graduate School of Medicine, The university of Tokyo
Longlasting change of synaptic efficacy, such as LTP, is known to be correlated
with increase of postsynaptic response of AMPAtype glutamate receptors
AMPARs. AMPAR targeting is regulated by surface mobility and exo/
endocytosis. Although single particle tracking revealed contribution of AMPAR
lateral mobility in their trapping at the synaptic sites, dynamic recycling of
AMPARcontaining vesicles after plasticityinducing stimuli has not yet been
clarified. We expressed AMPAR subunit GluR1 tagged with ZIPbinding cassette
in primary hippocampal neurons and visualized cell surface AMPARs by labeling
with ZIP peptides conjugated with pH sensitive dye RhPM. RhPMlabeled
GluR1 increased its fluorescence after endocytosis, due to the acidification in
the endosomal compartment. To visualize the intracellular transport of GluR1
containing vesicles after endocytosis, we monitored both superecliptic pHluorin
tagged GluR1 and RhPMlabeled GluR1 simultaneously. We identified that GluR1
endocytosis occurred on dendritic shafts and also in larger spines. Reciprocal
signal change of SEP/RhPMlabeled receptors facilitates the identification of exo/
endocytotic events within dendritic spines.