Abstracts - Association for Chemoreception Sciences

#35 SYMPOSIUM:
NEW APPROACHES TO PHYSIOLOGY
AND BEHAVIOR IN AWAKE RODENTS
Dramatic state-dependency of the activity of granule cells in
the mouse main olfactory bulb
Stephen D Shea, Brittany N Cazakoff, Kerensa L Crump, Billy Y Lau
Cold Spring Harbor Laboratory Cold Spring Harbor, NY, USA
It is becoming increasingly clear that olfactory representations in
the main olfactory bulb (MOB) are substantially reformatted in
awake rodents. In addition to elevated rates and altered temporal
structure in the spike discharge of mitral/tufted cells (MT),
the wakeful state is marked by a fusion of sensory input-driven
responses with activity that reflects attention, experience, and
behavioral task contingencies. It seems likely that as a key target
of many neuromodulatory systems and corticofugal feedback
pathways, the extensive network of inhibitory MOB granule
cells (GC) is instrumental in the state-dependent sculpting of
MT activity patterns. Despite this predicted critical role, few
published studies have demonstrably made electrophysiological
recordings from these small cells. Moreover, none have been
reported in awake animals. As a first step towards closing this
gap, we recently developed reliable methods for recording and
labeling GC in awake, head-fixed mice. Our preparation allows
us to directly compare the activity and sensory responses of
the same GC during wakefulness and inhalant anesthesia.
Our data reveal that GC in awake mice are dramatically more
spontaneously active, and exhibit stronger, more broadly-tuned
sensory responses that include both increases and decreases
in spike rate. Under either of two pharmacologically-distinct
anesthetics, many of these cells emit very few spontaneous
or stimulus-driven spikes. Those that have somewhat higher
spontaneous rates still exhibit little response to odors. We are
currently quantifying the variable respiratory coupling of GC in
awake animals, and assessing the effects of stimulus novelty or
familiarity on GC odor responses.
#36 SYMPOSIUM:
NEW APPROACHES TO PHYSIOLOGY
AND BEHAVIOR IN AWAKE RODENTS
Response properties of cortico-bulbar feedback and granule
cells in awake head-fixed mice
Dinu F Albeanu, Hong goo Chae, Gonzalo H Otazu
Cold Spring Harbor Laboratory Cold Spring Harbor, NY, USA
Sensory circuits integrate inputs from the environment, as well
as feedback signals from higher brain regions, in a close loop
manner. The interplay of feed-forward and feedback signals
has been proposed to be fundamental for learning and memory
recall. Though rich cortical feedback projections innervate
the mouse olfactory bulb, to date, little is known about their
contribution to olfactory processing. Cortico-bulbar feedback
primarily targets the granule cells (GC), which form extensive
dendro-dendritic synapses with the mitral/tufted cells. To
examine how cortical feedback shapes processing in the bulb,
we used genetically encoded calcium indicators (GCaMP3&5)
and multiphoton imaging to monitor the odor evoked responses
of feedback fibers and granule cells, in awake head-fixed mice.
GCs and feedback fibers showed rich spontaneous activity and
diverse excitatory and inhibitory odor responses. On average,
to our stimulus panel (up to 30 odors), we observed 54% purely
excitatory and only 17% purely inhibitory responses in the
GCs, while the two response types were equally common in
the feedback fibers. Interestingly, both GCs and feedback fibers,
that showed spontaneous activity, were inhibited upon odor
presentation, irrespective of stimulus identity. While inhibition
of feedback fibers was sparse and odor specific, GCs showed
both broad, and narrowly tuned inhibitory responses. Further,
a significant fraction (~25%) of GCs exhibited excitatory OFF
responses, independent of stimulus duration. We are currently
investigating how response properties of GCs and feedback
fibers are shaped by odor experience and during reinforcement
learning. Additionally, we are employing pharmacological and
optogenetic approaches to modulate the feedback fibers, while
simultaneously monitoring granule cell activity.
#37 SYMPOSIUM:
NEW APPROACHES TO PHYSIOLOGY
AND BEHAVIOR IN AWAKE RODENTS
Odor-guided behaviors in head-restrained and
freely-moving mice
Venkatesh N Murthy 1,2 , Dan Rokni 1,2 , David H. Gire 1,2 ,
Daniel Millman 1,2
1
Harvard University, Molecular & Cellular Biology Cambridge,
MA, USA, 2 Harvard University, Center for Brain Science Cambridge,
MA, USA
Olfaction plays a central role in guiding behavior in many
animals, including the common laboratory mammalian models
– rats and mice. There is a renewed excitement about studying
the neural basis of such behaviors, which entails developing
behavioral tasks under controlled conditions where neural
activity can be recorded and manipulated. We have trained mice
to perform odor tasks while their heads are restrained, which
allows stable electrophysiological recordings, high-resolution
optical imaging and optogenetic manipulation. In one such task,
head-restrained mice can be trained to recognize target odorants
embedded in unpredictable and variable background mixtures.
We have also developed strategies to study odor-guided behaviors
in freely moving animals, including spatial navigation. We will
present a detailed analysis of these behaviors in our talk, and
some initial efforts in recording and imaging neural activity
under these conditions. Acknowledgements: R01DC011291
ORAL ABSTRACTS
Abstracts are printed as submitted by the author(s).
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