Page 52 - ACHEMS 2012 PROGRAM

#P73 POSTER SESSION II:
TRIGEMINAL SYSTEM; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Cholinergic modulation of sensory processing in the rodent
olfactory bulb
Markus Rothermel1, Ryan M. Carey2, Matt Wachowiak1
1Department of Physiology, University of Utah School of Medicine
Salt Lake City, UT, USA, 2Department of Biomedical Engineering,
Boston University Boston, MA, USA
The olfactory bulb (OB) receives centrifugal input from multiple
sources whose role in shaping early olfactory processing remains
unclear. Here, we examine how cholinergic projections from the
horizontal limb of the diagonal band of Broca (HDB) modulate
sensory neuron (ORN) input to and mitral/tufted cell (MT) output
from the OB using imaging, electrophysiological and optogenetic
approaches in vivo. First we tested whether HDB stimulation
affected ORN inputs by imaging transmitter release from ORN
terminals; we found no effect of HDB stimulation on ORN inputs.
Next we tested whether HDB stimulation affected MT cell
excitation by imaging from mice in which GCaMP3 was selectively
expressed in MT cells. HDB stimulation caused a transient increase
in excitation apparent as an increase both in the baseline
fluorescence and in the inhalation-evoked response. We confirmed
this effect with extracellular recordings from presumptive MT cells,
finding that HDB stimulation enhanced spontaneous as well as
inhalation-evoked spiking. Finally, to selectively examine the
influences of cholinergic (as opposed to GABA-ergic) projections
and to localize their site of action to the OB, we expressed
channelrhodopsin2 in cholinergic HDB neurons. Optical activation
of these neurons in HDB or their axon terminals in the OB led to
enhanced MT cell excitation that was qualitatively similar to that
seen with electrical HDB stimulation. In all of the above
experiments, the effects of cholinergic activation were blocked
by OB application of muscarinic ACh receptor antagonists.
Together, these experiments are consistent with the hypothesis that
cholinergic modulation enhances sensory-evoked MT responses
and implicate muscarinic receptor-mediated signaling in
superficial OB layers as an important step in this modulation.
Acknowledgements: Supported by DFG (MR) and NIDCD
(MW, RC).
#P74 POSTER SESSION II:
TRIGEMINAL SYSTEM; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Expression of the Nicotinic Acetylcholine Receptor Subtype
α7 in Adult-Born Periglomerular Cells
Zachary T. Frenchek1, 5, Elizabeth Myers6, Mary T. Lucero1, 3, 4,
Scott W. Rogers1, 2, 5
1Interdepartmental Program in Neuroscience, University of Utah
Salt Lake City, UT, USA, 2SLC-VA GRECC Salt Lake City, UT,
USA, 3 Department of Physiology, University of Utah School of
Medicine Salt Lake City, UT, USA, 4Brain Institute, University of
Utah Salt Lake City, UT, USA, 5Department of Neurobiology and
Anatomy, University of Utah School of Medicine Salt Lake City,
UT, USA, 6Division of Geriatrics, University of Utah School of
Medicine Salt Lake City, UT, USA
Adult neurogenesis is an ongoing process of neuronal replacement
in the brain that is subject to modification by environmental factors.
Two significant sites of ongoing neuronal replacement are in the
granule cells (GC) of the dentate gyrus and interneurons in the
main olfactory bulb. We are interested in how nicotine influences
these processes. Nicotine targets the nicotinic acetylcholine
receptors, of which the alpha7 (α7) subtype is being investigated
for its role in both neurogenesis and age-related changes in sensory
function. To measure α7 expression with spatial and temporal
sensitivity, we developed mouse (Mus musculus) strains in which
homologous recombination was used to introduced a bi-cistronic
IRES-tau:GFP reporter (α7GFP). Using immunohistochemistry,
we find α7GFP expression in the adult olfactory bulb is restricted
to a subset of periglomerular cells (PGC). Unexpectedly, these
cells do not co-label with markers of mature PGCs, including
parvalbumin, calbindin, calretinin, tyrosine hydroxyase, glutamic
acid decarboxylase, and somatostatin. In the dentate gyrus, α7 is
expressed only transiently by immature GCs where it participates in
mechanisms leading to final neuron differentiation. We examined
this possibility for PGCs. Pulse-chase experiments using 5-ethynyl-
2’-deoxyuridine (EdU) revealed labeled cells co-expressing α7GFP
prior to acquisition of maturation markers. Further, lineage analysis
indicates that all mature PGCs did express α7 in their history,
consistent with transient expression of α7GFP in PGCs prior to
differentiation. These results may provide a basis for correlations
between α7 expression level and olfactory discrimination abilities.
Ongoing experiments are defining the impact of exposure to
nicotine and other receptor ligands on α7 expression and PGC fate.
Acknowledgements: S.W.R. was supported by DA025057, Z.T.F.
was supported by T32-MH076693.
#P75 POSTER SESSION II:
TRIGEMINAL SYSTEM; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
α7-Nicotinic Acetylcholine Receptor: Role in Early Odor
Learning Preference in Mice
Jennifer L. Hellier1,2, Nicole L. Arevalo1,2, Lynelle Smith1,2,
Ka-Na Xiong1,2, Diego Restrepo1,2,3
1Cell & Developmental Biology, Univ. of Colorado-AMC Aurora,
CO, USA, 2Rocky Mountain Taste & Smell Center, Univ. of
Colorado-AMC Aurora, CO, USA, 3Center for Neuroscience,
Univ. of Colorado-AMC Aurora, CO, USA
Recently, mice with decreased expression of α7-nicotinic
acetylcholine receptors (α7) in the olfactory bulb were associated
with a deficit in odor discrimination compared to wild-type mice
(Hellier et al., 2010). However, it is unknown if mice with
decreased α7-receptor expression (i.e., α7 heterozygous knockouts
– HET; α7 homozygous knockouts – KO) also show a deficit in
early odor learning preference (ELP), an enhanced behavioral
response to odors with attractive value observed in rats. In this
study, we modified ELP methods performed in rats and
implemented similar conditions in mice. From post-natal days
5-18, wild-type mice were stroked simultaneously with an odor
presentation (conditioned odor) for 90 s daily. Control mice were
only stroked, exposed to odor, or neither. On the day of testing
(P21), mice that were stroked in concert with a conditioned odor
significantly investigated the conditioned odor compared to a novel
odor, as observed similarly in rats. However, mice with a decrease
in α7-receptor expression (i.e., HET mice but not KO mice) that
were stroked during a conditioned odor did not show a behavioral
response to that odorant. These results suggest that decreased
α7-receptor expression has a role in associative learning, olfactory
preference, and/or sensory processing deficits. Acknowledgements:
Funded by NIH grants MH06858, DC 04657, DC00566, and
DC008855 (DR).
52 | AChemS Abstracts 2012 Abstracts are printed as submitted by the author(s)
P O S T E R P R E S E N T AT I O N S