Abstracts - Association for Chemoreception Sciences

appetite. Glucagon-like peptide-1 (GLP-1) is an incretin peptide
that also suppresses food intake, and in situ hybridization in
rat has suggested that both GLP-1 and its receptor are present
in the olfactory bulb (OB). Furthermore, GLP-1 modulation
of taste sensitivity has been reported for taste buds, prompting
us to speculate a similar role in the olfactory system. Using
transgenic mice expressing YFP under the preproglucagon (PPG)
promoter, we confirm that a population of YFP-immunoreactive
neurons exists in the granule cell layer (GCL) of the OB,
indicative of GLP-1 producing cells. The labeled neurons had
a typical granule cell morphology with a single axon projecting
into the adjacent mitral cell layer (MCL). We observed strong
immunoreactivity for the GLP-1 receptor in the MCL and in
sparse cells in the GCL in olfactory marker protein (OMP-GFP)
transgenic mice. Binding of biotinylated GLP-1 to the GLP-1
receptor was visualized within the same regions. We confirmed
the presence of functional GLP-1 receptors on mitral cells (MCs)
using whole-cell patch-clamp recordings in acute OB slices.
Bath perfusion of 1 µM GLP-1 or its stable analogue, exendin-4,
resulted in a significant increase in the evoked action potential
frequency (370% for GLP-1 and 170% for exendin-4) and a
concomitant decrease in the interburst interval in about 60% of
the sampled MCs. These results show that GLP-1 is synthesized
locally in the OB and directly affects the firing properties of
MCs, suggesting a potential paracrine modulation of olfactory
output with satiety. Acknowledgements: This work was
supported by R01 DC003387 from the NIH/NIDCD, a Creative
Research Council (CRC) award from FSU, a Project Grant
1025031 from NHMRC Australia, and MR/J013293/1 from the
MRC United Kingdom.
#P111 POSTER SESSION II:
OLFACTION DEVELOPMENT; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Enhanced Survival of Newly Formed Cells Contributes to
Restoration of Olfactory Bulb Volume Following Reversible
Deafferentation in Adult Zebrafish
Darcy M Trimpe, Christine A Byrd-Jacobs
Western Michigan University/Biological Sciences Kalamazoo, MI, USA
Our lab has shown that chronic partial deafferentation, achieved
through unilateral chemical ablation of the olfactory epithelium
with Triton X-100, results in a decrease in olfactory bulb
volume, while cessation of treatment allows bulb volume to
recover. We hypothesized that alterations in cell genesis and/
or survival would be involved in restoration of olfactory bulb
size. Bromodeoxyuridine (BrdU) administration was used to
examine newly formed cells in the brain of adult zebrafish,
with short-term survival allowing investigation of patterns of
cell proliferation and long-term survival allowing examination
of cell survival and fate. We first compared two methods of
BrdU administration: immersion of fish in the drug versus
intraperitoneal injection. While both methods revealed similar
numbers of newly formed cells, injection of the drug resulted
in loss of fewer fish during treatment. Next, we examined
potential alterations in cell genesis and/or cell survival resulting
from reversible partial deafferentation. Repeated detergent
treatment followed by BrdU exposure showed no difference in
the number of dividing cells in the olfactory bulb, indicating that
cell genesis is not affected. There was, however, an increase in
newly formed cells that survived when the detergent treatment
ceased, indicating that cell survival contributes to the restoration
of bulb volume during the period of reinnervation. When fish
were exposed to BrdU before the repeated detergent treatment,
there appeared to be no effect on the number of newly formed
cells. Thus, enhanced cell survival, rather than cell genesis,
appears to be a contributing factor in the restoration of olfactory
bulb volume following return of innervation in a reversible
deafferentation model. Acknowledgements: Supported by
NIH-NIDCD #011137 (CBJ)
#P112 POSTER SESSION II:
OLFACTION DEVELOPMENT; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Characterizing Olfactory Bulb Circuitry using Intrinsic
Flavoprotein Fluorescence Imaging
Cedric R Uytingco 1,2,4 , Adam C Puche 1,2,4 , Steven D Munger 1,2,3,4
1
Depatment of Anaotmy and Neurobiology Baltimore, MD, USA,
2
Program in Neuroscience Baltimore, MD, USA, 3 Department of
Medicine, Division of Endocrinology, Diabetes and Nutrition Baltimore,
MD, USA, 4 University of Maryland School of Medicine Baltimore,
MD, USA
The main olfactory system has distinct subsystems that differ
in the chemosensory stimuli to which they respond and the
connections they make to the brain. In contrast to the canonical
glomeruli of the main olfactory bulb (MOB), individual necklace
glomeruli (NGs) receive heterogeneous olfactory sensory neuron
(OSN) innervation [including semiochemical-sensitive OSNs
expressing guanylyl cyclase D (GC-D)] and display extensive
intrabulbar connections. This organization suggests that NGs
integrate multiple olfactory signals. To better understand the
functional circuitry associated with NGs, we examine the transsynaptic
spread of neuronal activity using intrinsic flavoprotein
fluorescence (FF) imaging. FF imaging measures the changes
in endogenous fluorescence produced by mitochondrial
flavoproteins that accompany increased metabolic demand. The
FF signals correspond to neuronal activity and can be followed
across synapses, thus facilitating the mapping of functional
circuits. Studies in horizontal MOB slices from 3-5 w.o. mice
exhibit robust FF signal spread from the glomerular layer
(GL) to the external plexiform layer (EPL) following electrical
stimulation (1-4 s, 10-50 Hz, 10-100 μA) of individual canonical
and necklace glomeruli. Bath application of 10 mM gabazine
increased lateral stimulus-dependent FF signal spread in the GL/
EPL, and resulted in a 2-fold increase in FF signal amplitude in
the EPL. Single NG stimulation (from mice expressing green
fluorescent protein under control of the gene encoding GC-
D) results in reduced FF signal amplitude but prolonged FA
signal duration compared to canonical glomeruli. The use of
FF imaging should help reveal basic strategies of information
processing in the MOB and its subsystems. Acknowledgements:
NIDCD (DC005633), NIGMS (GM008181), NINDS
(NS063391)
POSTER PRESENTATIONS
Abstracts are printed as submitted by the author(s).
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