Abstracts - Association for Chemoreception Sciences

axons into the olfactory bulb where they face the challenge to
integrate into an existing neuronal circuitry. Synaptic contacts
to second-order neurons are formed in distinct target regions,
so-called glomeruli. In rodents, sensory neurons normally
project only into one specific glomerulus of the olfactory bulb.
We investigated the growth patterns of sensory neuron axons
in the developing olfactory system of the aquatic amphibian
Xenopus laevis. To address the question how connectivity is
reshaped during olfactory system maturation a range of larval
stages and young postmetamorphic animals were included
in the experiments. Fluophore-coupled dextrans or plasmid
DNA, encoding for fluorescent proteins, were introduced
into sensory neurons via electroporation. The main sensory
projection fields within the main- and accessory olfactory bulb
were visualized by electroporation of the whole olfactory organ.
During metamorphosis the main olfactory system is completely
reorganized, whereas the sensory neurons of the accessory
olfactory system are maintained. The axonal branching patterns
of sensory neurons, originating from both the vomeronasal and
main olfactory epithelium, were investigated by sparse staining
of sensory neurons. Synaptic connections were clearly visible as
tufted axonal endings. Most sensory neurons showed a branched
axonal pattern before terminating in tufted arborizations inside
glomeruli. Surprisingly, a high percentage of cells terminated in
multiple and not single glomerulus-like structures. This pattern
was comparable in sensory neurons originating from both the
vomeronasal and the main olfactory organ. Acknowledgements:
Supported by DFG Cluster of Excellence “Nanoscale
Microscopy and Molecular Physiology of the Brain” (CNMPB)
to I.M. and DFG Schwerpunktprogramm 1392 to I.M.
#P76 POSTER SESSION II:
OLFACTION DEVELOPMENT; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Activity-Dependent Expression of Odorant Receptors
in the Mouse Olfactory Epithelium
Shaohua Zhao 1,2 , Huikai Tian 1 , Rosemary Lewis 1 , Limei Ma 3 ,
Ying Yuan 1 , Congrong R Yu 3 , Minghong Ma 1
1
Department of Neuroscience, University of Pennsylvania School of
Medicine Philadelphia, PA, USA, 2 Department of Geriatric Cardiology,
Qilu Hospital of Shandong University Jinan, China, 3 Stowers Institute
for Medical Research Kansas City, MT, USA
Sensory experience plays critical roles in development and
maintenance of the olfactory system, which undergoes
considerable neurogenesis throughout life. In the mouse olfactory
epithelium, each primary olfactory sensory neuron (OSN) stably
expresses a single odorant receptor (OR) type out of a repertoire
of ~1200. All OSNs with the same OR identity are distributed
within one of the few broadly-defined zones. However, it remains
elusive whether such OR expression patterns are shaped by
sensory stimulation and/or neuronal activity. Here we addressed
this question by investigating OR gene or protein expression in
two surgically- or genetically-modified mouse models. Using in
situ hybridization, we examined the expression patterns of 15
selected OR genes in mice which underwent neonatal, unilateral
naris closure. After four-week occlusion, the expression level in
the closed side was significantly lower (for four ORs), similar
(for three ORs) or significantly higher (for eight ORs) than that
in the open side. In addition, using a specific OR antibody,
we demonstrated that this OR protein was upregulated in the
closed side but downregulated in the open side. Furthermore,
we examined the expression patterns of individual OR genes
in transgenic mice in which olfactory marker protein (OMP)
drives overexpression of the inward rectifying potassium channel
(Kir2.1) in most mature OSNs to reduce their neuronal activity.
The cell density for most OR genes (six out of seven tested) was
significantly reduced compared to wild-type controls. The results
suggest that sensory inputs have differential influence on OSNs
expressing different ORs and that neuronal activity is critical for
survival of OSNs. Acknowledgements: Supported by grants from
the NIDCD/NIH DC006213 and DC011554.
#P77 POSTER SESSION II:
OLFACTION DEVELOPMENT; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Optogenetic Investigation of GABAergic Circuitries in the
Rostral Nucleus of the Solitary Tract
James A. Corson, Robert M. Bradley
University of Michigan/ Biologic and Materials Sciences Ann Arbor,
MI, USA
The rostral nucleus of the solitary tract (rNTS) is the first central
target of primary gustatory nerve fibers and as such plays an
essential role in the processing and coding of peripheral taste
sensory information. The intrinsic circuitry within rNTS is likely
integral in shaping the incoming information into both ascending
and descending efferent signals. Substantial subpopulations of
interneurons in the rNTS are GABAergic and thus contribute
to the generation of hyperpolarization-activated changes in
repetitive firing patterns in projection neurons. Despite this
importance in shaping rNTS gustatory-evoked signaling, the
organization of rNTS GABAergic circuits is unknown. To
investigate the organization of GABAergic innervation onto
identified populations of neurons, we used a mouse model
in which channelrhodopsin was expressed under the control
of the vesicular GABA transporter. GABAergic interneurons
were activated in an in vitro slice preparation with 473 nm laser
illumination merged into the optic train of the microscope.
Focused laser illumination produced consistent saturated
photocurrents in GABAergic neurons with high temporal and
spatial resolution. While recording inhibitory postsynaptic
currents in either GABAergic or non-GABAergic neurons, the
laser spot was systematically scanned over discrete portions
of the rNTS to map out the GABAergic innervation onto the
recorded neuron. Neurons received inhibitory innervation
from wide expanses of rNTS, often with focal spots of strong
inhibition located in areas not immediately adjacent to the
recorded neuron. This suggests that in addition to a low level
of global inhibition, there are also specific subregions of rNTS
that are able to strongly hyperpolarize individual neurons and
possibly induce alterations in repetitive discharge patterns.
Acknowledgements: T32DC000011, RO1DC000288
POSTER PRESENTATIONS
Abstracts are printed as submitted by the author(s).
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