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reactivity after sciatic nerve injury. To test if TLR4 may also be
fundamental to microglial responses in the nTS, CT injury was
performed on TLR4 point-mutant mice (C3H/HeJ), which express
only a mutated and nonfunctional TLR4 protein. From 3-5 days
after CT damage, microglia still reacted in the nTS. In particular,
a cluster of microglial cells appeared in the CT terminal field and
microglia underwent typical transformations to display reactive
morphologies with shorter, thicker processes and an amoeboid
shape. Although deletion or blockade of TLR4 prevents microglial
reactivity after sciatic nerve injury, TLR4 signaling does not
appear to be required for microglial responses after CT injury.
This suggests that different signals activate microglia after CT
damage compared to pain models. Acknowledgements: Supported
by NIDCD grants R56DC000147 and P30DC004657 to T.E.F.
and D.R.
#P54
POSTER SESSION II:
TRIGEMINAL SYSTEM; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Biophysical, morphological, and synaptic properties of
intramedullary projection neurons in the rostral nucleus
of the solitary tract
James A. Corson, Robert M. Bradley
University of Michigan, School of Dentistry,
Biological and Material Sciences Ann Arbor, MI, USA
The efferent circuitry of the first-order gustatory nucleus, the
rostral nucleus of the solitary tract (rNST), arises from two major
pathways. Although much is known regarding the characteristics of
ascending projections to the pons, the biophysical, morphological,
and synaptic properties of the intramedullary descending
projections remain less clear. To identify rNTS descending
projection neurons, unilateral iontophoretic injections of DiI were
made into the reticular formation (the major target of this neuron
population). One to three days post-injection, 300-400mm coronal
or parasagittal (parallel to the solitary tract) brain slices containing
the rNST were prepared for whole cell patch clamp recording.
Retrogradely labeled neurons were bilaterally located in the ventral
and rostrocentral rNST subdivisions. The majority of neurons
responded to depolarizing current injection with a tonic firing
pattern, although initial burst and irregular firing patterns were also
observed. Descending projection neurons also exhibited a number
of different voltage activated currents, with some neurons
expressing post-inhibitory rebound spikes, Ih currents, and A-type
potassium currents. Small current pulses delivered to the rostral tip
of the solitary tract with a bipolar stimulating electrode evoked
monosynaptic excitatory post-synaptic currents in approximately
half of the neurons tested. The remainder responded with
postsynaptic currents with variable latency and reliability,
indicative of polysynaptic circuitry. The majority of neurons
recorded were multipolar with spiny dendrites extending into
multiple rNST subdivisions. This study has revealed that
descending rNST projections arise from heterogeneous
subpopulations of neurons, which may exert equally complex
control over oromotor reflexive behaviors. Acknowledgements:
NIH: R01DC000288-25, T32DC000011-33
#P55
POSTER SESSION II:
TRIGEMINAL SYSTEM; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Morphology and Distribution of GFAP Labeled Elements in the
Developing Solitary Tract and Nucleus of the Solitary Tract
Sara L Corson
1
, Robert M Bradley
1,2
, Charlotte M Mistretta
1
1
Department of Biologic and Materials Sciences, School of
Dentistry, University of Michigan Ann Arbor, MI, USA,
2
Department of Molecular and Integrative Physiology, School of
Medicine, University of Michigan Ann Arbor, MI, USA
Glial fibrillary acidic protein (GFAP) is a marker of intermediate
filaments that identifies cells of astrocytic origin in the developing
central nervous system. We surveyed GFAP expression in the
developing solitary tract (ST) and rostral nucleus of the solitary
tract (rNST) to characterize glial morphology and distribution in
this gustatory brainstem area. The ST consists of afferent fibers that
originate in the oral cavity and project to the rNST, the site of the
first synaptic relay in transmitting taste-related information to
higher brain areas. In horizontal sections of rat brainstem,
fasciculated GFAP labeled fibers were present in the ST as early as
embryonic day 14 (E14) and persisted throughout development.
At E18, radially oriented GFAP labeled fibers were observed in
addition to those found in the ST. There were no GFAP labeled
astrocytic-like cells in the presumptive rNST at any embryonic age
examined (E14, E15, E16 and E18). Postnatally (P1, P5 and P10),
GFAP labeled fibers persisted in the ST, but were less fasciculated.
A continued postnatal presence of radially oriented GFAP labeled
fibers was also noted. In addition, astrocytic-like cells appeared in
the rNST and were found more rostrally as development
progressed. In coronal sections, these astrocytic-like cells were
predominantly localized to the ventral subdivision of the rNST.
Interestingly, the initial, embryonic appearance of GFAP labeled
fibers was concurrent with the appearance of fibers labeled with
neuropilin 1 and neuropilin 2, transmembrane proteins that bind
semaphorins, suggesting a possible role for GFAP in axon guidance
and fasciculation. Labeling for GFAP with additional markers, such
as calbindin and neurofilament, will highlight potential interactions
between glia and neurons in the developing brainstem.
Acknowledgements: NIDCD, NIH Grant DC009982
#P56
POSTER SESSION II:
TRIGEMINAL SYSTEM; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Neuropilin 1, Neuropilin 2 and calbindin expression in
the developing rat solitary tract and rostral nucleus of the
solitary tract
Miwon Kim
1
, Sara L Corson
1
, Charlotte M Mistretta
1
,
Robert M Bradley
1,2
1
Department of Biologic and Materials Sciences, School of
Dentistry, University of Michigan Ann Arbor, MI, USA,
2
Department of Physiology, School of Medicine, University of
Michigan Ann Arbor, MI, USA
The rostral nucleus of the solitary tract (rNST) receives orosensory
information via cranial nerves VII, IX and X. These nerves enter
the brainstem, form the solitary tract (ST) and synapse with rNST
neurons. We studied development of ST and rNST in E
(embryonic) 13 to E18 rats. DiI was applied to VII and the
geniculate ganglion to identify ST. Immunolabeling of neuropilin 1
(Npn1) and 2 (Npn2), axon guidance receptors, was used to
investigate their contribution to ST formation. Calbindin was used
to label rNST neurons. At E13, DiI-labeled ST extends caudally in
46 | AChemS Abstracts 2012
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