Transcript Dendritic organization of sensory input to cortical neurons in vivo

REPRESENTATIONS OF ODOR
IN THE PIRIFORM CORTEX
Dan D. Stettler and Richard Axel
Neuron 63, p. 854-864 (2009)
THE OLFACTORY BULB IS QUITE ORGANIZED
?
Cortex
What about the cortex?
THE PIRIFORM CORTEX
100μm
•
3-layered structure
•
On the ventral-lateral surface of the cerebral hemisphere
•
Pyramidal cells synapse with mitral cell afferents in layer 1
•
SL = pyramidal????
http://aups.org.au/Proceedings/38/9-14/
IMAGING METHOD
• For the calcium imaging the calcium sensitive fluorescent dye
Oregon Green 488 BAPTA-1 AM was used.
• The dye was injected into broad regions of layer 1, causing the
labeling of > 90% of the pyramidal cell bodies in layers 2 and 3
across wide regions in the piriform cortex.
• Imaging was done at multiple sites in more than 100 mice.
Baseline fluorescence
(air)
50μm
STIMULI
• Stimulation consisted of a 1sec??? puff of odorant at concentrations of 0.5-80ppm in
air.
• 20 different odors were used
ODORANT-EVOKED RESPONSES IN MOUSE PIRIFORM
USING IN VIVO TWO-PHOTON CALCIUM IMAGING
(Fox urine)
Fluorescence changes were elicited in 3-15% of the piriform
neurons
•
Each odorant activated a unique but dispersed ensemble of cells in layer 2.
•
Behaviorally different odors elicited the same type of response.
Adjacent cells can respond selectively to different odorants
Responses of the 5
marked cells to 5 odorants
50μm
DPG/air
ODORANT-EVOKED CALCIUM RESPONSES IN
PIRIFORM CORTEX ARE HIGHLY CONSISTENT
Odor puff
ODORANT-EVOKED CALCIUM RESPONSES IN
PIRIFORM CORTEX ARE HIGHLY CONSISTENT
Cells responsive to a given odorant within the same imaging field
exhibited a range of statistically significant positive responses
CONCENTRATION DEPENDENCE OF ODOR-EVOKED RESPONSES
ODORANTS EVOKE RESPONSES IN UNIQUE BUT
OVERLAPPING ENSEMBLES OF PIRIFORM NEURONS
ODORANTS EVOKE RESPONSES IN UNIQUE BUT
OVERLAPPING ENSEMBLES OF PIRIFORM NEURONS
DISTRIBUTED ODORANT REPRESENTATIONS EXTEND
ACROSS WIDE REGIONS OF PIRIFORM CORTEX
THE RESPONSE OF PIRIFORM CELLS TO A MIX OF ODORANTS
EXHIBITS STRONG SUPPRESSION AND WEAK SYNERGY
THE RESPONSE OF PIRIFORM CELLS TO A MIX OF ODORANTS
EXHIBITS STRONG SUPPRESSION AND WEAK SYNERGY
A MODEL OF PIRIFORM RESPONSES BASED UPON RANDOM
CONNECTIVITY BETWEEN THE BULB AND PIRIFORM CAN
GENERATE THE OBSERVED ODORANT REPRESENTATIONS
A MODEL OF PIRIFORM RESPONSES BASED UPON RANDOM
CONNECTIVITY BETWEEN THE BULB AND PIRIFORM CAN
GENERATE THE OBSERVED ODORANT REPRESENTATIONS
CONCLUSIONS
Unlike visual, auditory or somatosensory cortical sensory areas:
• The piriform cortex discards the spatial segregation and chemotopy
apparent in earlier stages of the olfactory system.
• The piriform shows a highly distributed organization - different odorants
activate unique but dispersed ensembles of cortical neurons.
• Neurons in the piriform cortex don’t have an apparent continuous
receptive fields (chemotopy, ….behavioral What else was checked?)
→ It should be remembered, though, that a relevant odors space still needs to be
defined, while in other senses this step is more straightforward.
Caveat – results are dependent on thresholds of imaging
GLUTAMATE BLOCKADE DIMINISHES ODORANTEVOKED RESPONSES
MONTE CARLO SIMULATIONS OF RESPONSIVE CELL DISTRIBUTIONS.
AUTO- AND CROSS- CORRELATION ANALYSIS REVEALS NO
CONSISTENT FINE-SCALE PATTERNING IN ODORANT RESPONSES.
MOTIVATION
 Measuring the input to neurons.
 In electrical measurements one finds:
• directional selectivity of the firing rate
• but no directional selectivity under hyperpolarization –
indicating a low tuning level of the inputs.
POSSIBILITIES OF INPUT TUNING AND ORGANIZATION:
Untuned
Tuned and clustered
 Investigating the activity under hyperpolarization
Tuned and dispersed
HETEROGENEOUS DISTRIBUTION OF PURETONE-ACTIVATED SPINES ALONG DENDRITES.
Xiaowei Chen, Ulrich Leischner, Nathalie L. Rochefort, Israel Nelken & Arthur Konnerth
Functional mapping of single spines in cortical neurons in vivo
Nature 475, 501–505
http://www.nobelprize.org/nobel_prizes/medicine/lau
reates/2004/illpres/2_olfactory.html
2-photon microscope
Practical theory of 2-photon microscopy
1. Near simultaneous absorption of the energy of two infrared
photons results in excitation of a fluorochrome that would
normally be excited by a single photon of twice the energy.
2. The probability of excitation depends on the square of the
infrared intensity and decreases rapidly with distance from the
focal volume.
Advantages of 2-photon microscopy
1.
2.
3.
4.
5.
Increased penetration of infrared light allows deeper imaging.
No out-of-focus fluorescence.
Photo-damage and bleaching are confined to diffraction- limited
spot.
Multiple fluorochrome excitation allows simultaneous, diffractionlimited, co-localization.
Imaging of UV-excited compounds with conventional optics.