Abstracts - Association for Chemoreception Sciences

etter characterize glomerular responses. Functional MRI and
intrinsic imaging share slow responses of complex origin which
are based on dynamic changes in oxy- and deoxy-hemoglobin.
Whereas fMRI can image the entire bulb, intrinsic and calcium
are limited to the dorsal regions but with high spatiotemporal
resolution. CBV-weighted fMRI was unsuccessful in bulb
imaging, as was the use of other anesthetics (Ex:domitor). In
seven rats we performed micro fMRI (BOLD, 120x120x300µm)
in dorsal orientation so that data could be compared to
subsequent calcium imaging of orthonasal responses in the
same subjects. In a few cases odor induced activation maps
showed strong overlap between the two imaging modalities.
We further apply these techniques in separate animals to define
retronasal dorsal and whole bulb responses and compare those
to orthonasal odorant presentations. We have found significant
effects of odor route on the response magnitude and timing.
Further, retronasal odor concentration affects response latency
in a direction depending on the odorant. We are evaluating
several methods of post-hoc co-registering across these methods
1) across functional maps (fMRI, intrinsic, calcium), 2) using
phantom markers on the skull, 3) using vasculature via venogram
MRI, and 4) using SWIFT-MRI for skull imaging. Due to the
partial volume effect and the relatively thin dorsal glomerular
layer we are also developing a miniature phased coil-array
allowing higher resolution and high quality dorsal functional
images. Our comparative approach shows the challenges
in obtaining and interpreting odor maps using different
methodologies. Acknowledgements: This work is supported by
NIH/NIDCD Grants R01DC009994 and R01DC011286.
#P68 POSTER SESSION II:
OLFACTION DEVELOPMENT; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Quantifying Bursting Olfactory Neuron Activity from Calcium
Signals Using Maximum Entropy Deconvolution
In Jun Park 1 , Yuriy V. Bobkov 2 , Barry W. Ache 2,3 , Jose C. Principe 1
1
Dept. of Electrical and Computer Engineering, University of Florida
Gainesville, FL, USA, 2 Whitney Laboratory, Center for Smell and
Taste, and McKnight Brain Institute St Augustine, FL, USA, 3 Depts. of
Biology and Neuroscience, University of Florida Gainesville, FL, USA
Advances in calcium imaging have enabled studies of the activity
dynamics of both individual neurons and neuronal assemblies.
However, inferring action potentials (spikes) from calcium signals
is still a challenging issue due to hidden nonlinearity in their
relationship, contamination by noise, and often the relatively
low temporal resolution of the calcium signal compared to the
time-scale of spike generation. Complex neuronal discharge,
as in the case of the bursting or rhythmically active neuronal
activity represents an even greater challenge for reconstructing
spike trains based on calcium signals. Here we propose doing this
using blind calcium signal deconvolution based on a theoretical
information approach. The basic idea is to maximize the output
entropy of a nonlinear filter where the nonlinearity is defined
by the cumulative distribution function of the spike signal.
We tested this maximum entropy (ME) algorithm on bursting
olfactory receptor neurons (bORNs) in the lobster olfactory
organ. The advantage of the ME algorithm is that the filter can
be trained online based only on the statistics of the spike signal
without making any assumptions about the spike-calcium signal
relation. We show that the ME method is able to reconstruct
the timing of the first and the last spike of a burst with higher
accuracy compared to other methods. Thus the ME method
should be a useful tool for inferring parameters of bursting
neurons, including bursting olfactory neurons, to help further
understand the mechanism and function of bursting-based
neuronal sensory coding. Acknowledgements: Supported by
award R21 DC011859 from the NIDCD
#P69 POSTER SESSION II:
OLFACTION DEVELOPMENT; TASTE CNS;
NEUROIMAGING; OLFACTION CNS
Allometric Growth of Olfactory Bulb and Brain in Female
Minks
Willi Bennegger 1 , Elke Weiler 1,2
1
Maria-von-Linden-Schule, Heckentalstraße 86 89518 Heidenheim,
Germany, 2 Faculty of Medicine, Institute of Anatomy,
Department of Neuroimmunology, University of Leipzig, Liebigstr.
13 04103 Leipzig, Germany
The olfactory bulb is the anterior part of the brain and
phylogenetically one of the oldest brain structures. During
postnatal development, when the animal grows, the brain
increases in size – and so does the olfactory bulb. However, in
some mammals, such as the American mink (Neovison vison) it is
known, that brain shows an overshoot development postnatally
with a subsequent reduction in size. Thus we were interested,
if this applies also to the olfactory bulb. Therefore we analyzed
morphometrically a total of 57 female minks ranging from
newborn (postnatal day 0, P0) to one year of age for their brain
and olfactory bulb size. The results reveal, that the volume of
one olfactory bulb in newborns is 1.26 ± 0.02 mm 3 , increasing
continuously (P30: 40.27 ± 8.77 mm 3 ; P90: 84.70 ± 1.87 mm 3 ) to
adult values (107.19 ± 4.15 mm 3 ) with no overshoot phenomena.
In contrast, the brain weight increases postnatally from P0 (0.29
± 0.06 g) up to P90 (10.18 ± 0.42 g) when maximal values are
reached, and decreasing afterwards more than 17% to the adult
size (8.43 ± 0.35 g). The olfactory bulb growth therefore does not
parallel the total brain growth but shows an allometric growth
pattern. On the other hand, the overall body growth increases
continuously to adult values resulting in an olfactory bulb/
body weight ratio of similar values among newborns, brain
overshoot age and adults (P0: 0.014±0.002 %; P90: 0.012±0.002
%, adult: 0.011±0.001 %) with higher values early postnatally
(P30: 0.047±0.013 %). This indicates that the olfactory bulb
is influenced by other factors than the cortical neurons for its
neuronal network growth and controlled by different stimuli for
its formation and connectivity. Further, no postnatal reduction
in size suggests a basic and important functional relevance of the
olfactory bulb.
POSTER PRESENTATIONS
Abstracts are printed as submitted by the author(s).
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