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developing neuronal circuitry prior to sensory input. We used
Dlx-2 tdTomato (Dlx-2T) transgenic mice to identify the small
(4-8 um dia) GCs. This red dye uses the
Rosa26-Cag
promoter to
continuously label cells that have expressed the
Dlx-2
gene at the
neuroblast stage. We performed confocal Ca
2+
imaging on live
Dlx-2T OB slices from P2-P5 mice loaded with green membrane
permeant Ca
2+
indicator dye (Fluo-4 AM). We confirmed that
40 nM PACAP evokes either simple bursts or long term Ca
2+
oscillations in identified GCs. We determined the stage of neuronal
development of the Dlx-2T cells by using GABA, which is
excitatory in immature neurons under our recording
conditions. While at least half of the red Dlx-2T cells respond to
GABA alone, we discovered that some PACAP-responding cells
respond to GABA too, meaning they are neuroblasts in the process
of becoming mature neurons. The appearance of PACAP-induced
Ca
2+
activity before GCs are mature suggests a role for PACAP in
turning neuroblasts into mature GCs. Acknowledgements:
University of Utah Graduate Research Fellowship, Ruth L.
Kirschstein National Research Service Award NIDCD
1F31DC011686-01A to MAI, NIDCD R01 DC002994 to MTL
#P105
POSTER SESSION III:
OLFACTION DEVELOPMENT & CNS;
HUMAN PSYCHOPHYSICS; TASTE PERIPHERY
Kv1.3 Channel Activity and GABAergic Signaling are likely
Mediators of Glucosensing in Mitral Cells
Suk-Hee Cho
1,2
, Kristal Tucker
1,2
, Michael Henderson
2
,
Debra Ann Fadool
1,2,3
1
The Florida State University, Program in Neuroscience
Tallahassee, FL, USA,
2
The Florida State University, Department
of Biological Science Tallahassee, FL, USA,
3
The Florida State
University, Molecular Biophysics Tallahassee, FL, USA
Olfaction is not static and is modulated by consumption of meals
and metabolic disease states. The firing properties of mitral cells,
the principle neurons of the olfactory bulb, are modulated by
metabolic factors released from peripheral tissues and the central
nervous system. We previously reported that mice with diet-
induced obesity exhibit altered mitral cell intrinsic firing properties
and insulin resistance of the olfactory bulb. We hypothesized that
extracellular glucose levels may also be detected by a potassium
channel predominantly expressed in mitral cells, Kv1.3. Using a
heterologous expression system, Kv1.3 voltage-activated peak
currents were rapidly modulated by D- but not L-glucose in a
bell-shaped dose-dependent fashion. To examine the changes of
mitral cell firing patterns in response to different glucose
concentrations ranging from 0 to 22 mM, mitral cell evoked action
potential (AP) firing frequency, AP cluster and pause duration, and
AP shape and timing were recorded via slice electrophysiology in
postnatal (day 15-30) mice. The most prominent biophysical
change was in firing frequency that was inhibited in 12 of 23 mitral
cells in response to higher glucose. Modulation was not reversible
following subsequent bath substitution to the original glucose
concentration. Addition of synaptic blockers (NBQX, gabazine, and
AP5) prevented the glucose modulation, suggesting that mitral cell
intrinsic membrane properties are not glucose sensitive. Systematic
substitution of blockers revealed the involvement of GABAergic
synaptic transmission in the development of glucose sensitivity.
Glucose sensing was lost in mice with gene-targeted deletion of
Kv1.3, which could be attributed to loss of channel signaling or
persistently low fasting glucose in these mice. Acknowledgements:
R01 DC003387, F31 DC010097, and T32 DC00044 from the
NIH/NIDCD
#P106
POSTER SESSION III:
OLFACTION DEVELOPMENT & CNS;
HUMAN PSYCHOPHYSICS; TASTE PERIPHERY
Role of Intraglomerular Inhibition in Shaping Responses
to Dynamic Olfactory Input
Ryan M Carey
1
, William Erik Sherwood
2
, Alla Borisyuk
2
,
Matt Wachowiak
1,3
1
Department of Biomedical Engineering, Boston University Boston,
MA, USA,
2
Department of Mathematics, University of Utah Salt
Lake City, UT, USA,
3
Department of Physiology and Brain Institute,
University of Utah Salt Lake City, UT, USA
Odorant-evoked activity in the mammalian olfactory bulb (OB) is
dynamically shaped by sniffing behavior, with individual sniffs
eliciting bursts of activity across OB neuron populations.
Mitral/tufted cells (MCs) – the projection neurons – generally
maintain this sniff-patterning even at high sniff frequencies, while
olfactory receptor neuron (ORN) inputs attenuate and show less
patterning. Here, we investigate the glomerular circuitry that shapes
inhalation-driven dynamics in MCs. First, we tested the role of
glomerular inhibition using optogenetics. We injected a Cre-
dependent virus containing the proton pump Archaerhodopsin
into the dorsal OB of GAD2-Cre mice, targeting GAD65+
periglomerular (PG) interneurons. After three weeks, we obtained
extracellular recordings from MCs below the infected region while
controlling sniffing in the anesthetized animal and using light
stimulation to suppress activity in infected neurons. The most
prominent effect of optical stimulation was an increase in odorant-
evoked MC peak firing rates. However, there was little change in
fine-scale temporal dynamics, suggesting that inhibition from
infected interneurons may affect MC excitability but not be critical
in determining temporal response patterns. We next constructed a
computational model of a glomerular circuit, including an external
tufted (ET), PG, and mitral cell, each as a single-compartment,
Hodgkin-Huxley-style model, and using different connectivities
between these cell types. As input to the model we used signals
derived from ORN recordings imaged from awake, naturally-
sniffing rats. Preliminary modeling results suggest that synaptic
depression and ET cell bursting can strengthen MC patterning.
Ongoing work will further explore the contribution of
intraglomerular inhibition to the shaping of MC responses.
Acknowledgements: F31DC010312 (NIDCD NRSA), BU Center
for Neuroscience Seed Grant, and R01DC011423-01 (NIH CRCNS)
62 | AChemS Abstracts 2012
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