Figure 202

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October 30, 2007 Olfaction
Phenomonology General Organization Olfactory
reception olfactory epithelium
perireceptor events in olfaction olfactory
receptor cells, receptor proteins, and odor
transduction receptive-field in olfaction
molecular receptive range turnover of
olfactory receptor cells Olfactory bulb
layers glomeruli and their chemotopic
organization Higher-order olfactory pathways
(bypassing the thalamus!) Model Olfactory
Systems Nitric Oxide Commercial
Applications Human Olfaction - Pheromones
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The Lancet, May 14, 1881
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Humanolfactoryeiptheliumand olfactorybulb
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ORN Neurogenesis -ORNs are constantly turning
over, so unlike the auditory or visual system,
loss of peripheral cells does not cause a
permanent loss of sensation
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Fig. 32-4
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In-class Exercise
Describe what you expect the receptive fields of
olfactory receptor neurons to look like. Do you
expect all ORNs to have roughly similar receptive
fields?
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ORNs express only one type of olfactory receptor
protein (with some exceptions)
Couto et al, 2005
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Receptive Field of an ORN
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Stimulating Determinants of Olfactory Molecules
Courtesy of Gordon Shepherd
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The stereoisomers of carvone exhibit very
different perceptual qualities
Importance of stereochemistry in olfaction
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ORN specificity decreases as odor concentration
increases
Hallem et al., 2004
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Human olfactory bulb
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olfactory bulb
Illustration by Frank Netter
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Hamster olfactory bulb (coronal section)
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Projections of olfactory receptor axons
Mombaerts 1996
Mombaerts et al., 1996
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Functional Organization of a Glomerulus
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Within each glomerulus

• Cells types
• ORNs deliver info about odors in the environment
• Output Neurons Communicate to higher areas of
  processing from the olfactory bulb
• Inhibitory interneurons Refine neural responses
  within the olfactory bulb (both between and
  within glomeruli)

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_
Higher areas of processing
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If the visual system uses a retinotopic
organization, and the auditory system uses a
tonotopic organization, then the olfactory
system must use
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Odotopic Organization
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Anterior olfactory nucleus
Further olfactory processing (odor object
reconstruction)
Olfactory tubercle
Piriform cortex
Memory
Entorhinal cortex
Amygdala
Emotion
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Odor Object Reconstruction

ORNs

Olfactory bulb



OT AON
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Bombyx mori
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Manduca sexta (Lepidoptera Sphingidae) the
tobacco hornworm
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NO signaling enzymes in the AL
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Methods for Real-Time NO Imaging

• DAF-FM was dissolved in 20 Pluronic F-127,
  diluted to 10 mM in saline, and bath applied for
  1 hr. at room temp.
• We used a TILL Photonics imaging system and an
  Olympus upright microscope with a 10x lens (W
  0,30)
• Filter settings were dichroic500 nm emission LP
  515 nm excitation 488 nm.
• Sequences of 60 frames (4 frames/s, 200 ms) were
  recorded for each stimulus

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Linalool
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Linalool
Pheromone Blend
10 mg
10 ng
100 mg
100 ng
1 mg
1 mg
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In-Class Exercise
Increasing concentrations of an odorant result in
many more glomeruli being active. Why is this
the case? What does this imply about
discrimination of different odors at high
concentrations?
Is that what really happens?
What mechanisms might cause this effect?
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Commercial Applications
from National Geographic
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Human Behavioral Effects?
Chemosignals of Fear Enhance Cognitive
Performance in Humans Denise Chen, Ameeta Katdare
and Nadia Lucas Chem. Senses 31 415423, 2006
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What about Human pheromones?
National Geographic
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Potential Human Pheromone AND
4,16-androstadien-3-one found in human sweat,
10X higher in men than women
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