Abstracts - Association for Chemoreception Sciences

#P39 POSTER SESSION I:
MULTIMODAL RECEPTION; CHEMOSENSATION
AND DISEASE; OLFACTION PERIPHERY
Evidence for a Cell Fate Refinement Mechanism in
Olfactory Sensory Neurons
Ishmail Abdus-Saboor, Benjamin Shykind
Weill Cornell Medical College Qatar/ Department of Cell and
Developmental Biology Doha, Qatar
Olfactory receptors (ORs) number more than 1,000 and comprise
the largest gene family in the mammalian genome. ORs reside
in heterochromatin and selection of one OR and from one
allele is thought to occur stochastically. ORs are expressed both
monogenically and monoallelically in olfactory sensory neurons
(OSNs) and the mechanism that controls their regulation is
largely unknown. Here we describe results for mice with a
‘monoclonal’ nose that express one OR M71in 95% of all mature
OSNs. M71 mice suppress expression of endogenous ORs, and
expression of the suppressed ORs is shifted to the immature
layer of the olfactory epithelium. We show that the suppressed
ORs were first selected and then turned off by M71. When we
introduced a second transgene into M71 mice that expressed
another OR in most mature OSNs, OSNs uncharacteristically
expressed both of the ORs. We hypothesize that unresolved OR
competition compromised the neuron’s ability to express only
one receptor. We further show that suppression of endogenous
ORs by M71 is not reversible, and that M71 does not need
to be continuously expressed for endogenous ORs to remain
suppressed. In these experiments, we have engineered OSNs
to express more than one OR in an OSN at a time, which is
normally a low probability event. We have shown that when
this event arises, a secondary refinement pathway is invoked
that turns off one OR to maintain singular expression. We
thus provide compelling evidence for a new paradigm of OR
regulation: post-selection shut down, which we hypothesize occurs
through a yet-to-be uncovered competitive mechanism.
#P40 POSTER SESSION I:
MULTIMODAL RECEPTION; CHEMOSENSATION
AND DISEASE; OLFACTION PERIPHERY
Odorant Receptor Dependent Spontaneous Firing Rates
Do Not Predict Sensory-evoked Firing Rates in Mouse
Olfactory Sensory Neurons
Timothy Connelly, Agnes Savigner, Minghong Ma
University of Pennsylvania/Department of Neuroscience Philadelphia,
PA, USA
Sensory systems need to tease out stimulation-evoked activity
against a background of spontaneous activity. In the olfactory
system, the odor response profile of an olfactory sensory neuron
(OSN) is dependent on the type of odorant receptor it expresses.
OSNs also exhibit spontaneous activity, which plays a role in
establishing proper synaptic connections and may also increase
the sensitivity of the cells. However, where the spontaneous
activity originates and whether it informs sensory-evoked activity
remain unclear. We addressed these questions by examining
patch-clamp recordings of genetically labeled mouse OSNs with
the defined odorant receptor M71 (n = 22), I7 (n = 21), SR1
(n = 11), mOR-EG (n = 24) or MOR23 (n = 16) in intact
olfactory epithelia. We show that OSNs expressing different
odorant receptors had significantly different rates of basal
activity. Additionally, OSNs expressing an inactive mutant I7
receptor completely lacked spontaneous activity (n = 34), despite
being able to fire action potentials in response to current injection
(n = 6). This finding strongly suggests that the spontaneous
firing of an OSN originates from the spontaneous activation
of its G-protein coupled odorant receptor. Lastly, we show
that the spontaneous firing rates of selected OSN types do not
correlate with the firing rates evoked by a near-saturating odorant
stimulus. This study reveals that neither the basal activity nor the
receptor type dictates the maximum odorant-evoked activity in
OSNs, which suggests that OSNs expressing the same receptor
type may send distinct information to the brain upon odorant
stimulation. Acknowledgements: This work was supported by
R01 grants from NIDCD/NIH (DC006213 and DC011554).
#P41 POSTER SESSION I:
MULTIMODAL RECEPTION; CHEMOSENSATION
AND DISEASE; OLFACTION PERIPHERY
How plastic is the peripheral olfactory system of
Drosophila melanogaster larvae?
MA Grillet, R Petersen, C McCrohan, M Cobb
University of Manchester Manchester, United Kingdom
During their larval stage, fruit flies are exposed to an odourrich
environment, in which they must choose between toxic
and edible substrates. For this they need an efficient olfactory
system with the capacity for both short and long term plasticity.
Drosophila larvae possess only 21 paired olfactory sensory
neurons (OSN), most of which express a single olfactory
receptor (OR) type together with the co-receptor Orco.
Information arising from each OSN is transmitted to a unique
glomerulus in the antennal lobe and then to the mushroom body
via projection neurons. Combinatorial coding in the periphery
allows larvae to detect and discriminate a large number of
odours. Previous studies have characterised the odour-response
profiles of 19 of the 21 OSNs and found that a given OSN’s
response to a given odour is often highly variable (Hoare et
al 2008, 2011). This raised the possibility that the peripheral
olfactory code exhibits plasticity and that this plasticity may
be directly involved in mediating behavioural adaptation and
learning. We are exploiting the UAS-Gal4 system to create single
OR lines in which only one identified OSN is functioning. We
are studying the effect of short and long-term adaptation on the
response of individual OSN classes to a panel of odours using
extracellular electrophysiology and behavioural assays. Our
preliminary results show that short-term adaptation to specific
odours may induce a decrease or an increase in OSN responses
depending on the odour used. We are currently exploring the
effect of longer-term adaptation on the peripheral olfactory code.
Acknowledgements: BBSRC UK grant BB/H009914/1
POSTER PRESENTATIONS
Abstracts are printed as submitted by the author(s).
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