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Optogenetics

Consolato Sergi, M.D., Ph.D.University of Alberta Hospital

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Signals

Single-electrode recordings - Limitations

- Intracellular recordings: Only a few neurons and difficult in vivo

- Extracellular recordings: No capture information about sub-

threshold activity, bias against small cells, poorly defined cell identity

2-deoxyglucose (2DG) imaging (H3 or C14) - Limitations

- Visualization of active brain areas or neurons (post-mortem)

- Temporal resolution in min or hrs, not msec.

- ‘One-shot’ or ‘two-shot’ ways.

PET/fMRI: poor spatio-temporal resolution, hemodynamic transformation, drug receptor activation patterns.

Optical Intrinsic Signal Imaging (OISI): hemodynamic response in local capillaries related to local activity.

Voltage Sensitive Dye Imaging (VSDI): membrane voltage, mostly sub-threshold activity in neurons and glia cells.

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Signals Cont’

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Optogenetics - Applications

Fast depolarization / hyperpolarization of specific cells in living animals

Precise control and study of cell population dynamics

The identification of causal positive and negative proof with cell specificity

Superior targeting & biocompatibility vs. electrical stimulation

Visual confirmation of target morphology using fluorescent labeling

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Zhang F, Wang L-P, Boyden ES and Deisseroth K (2006) Channelrhodopsin-2 and optical control of excitable cells. Nature Methods 3(10): 785–792.

Chlamydomonas reinhardtii- Wikipedia

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Zhang et al (2007) Multimodal fast optical interrogation of neural circuitry. Nature 446: 633–641.

Archaea – Wikipedia

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• Light-activated chloride pump

• Archaebacterium Natronomas pharaonis

• 22 mW/mm2 @ 560 +/- 27 nm• Inactivates after ~1 sec

Halorhodopsin (NpHR)

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Current Status of ApplicationsCurrent Status of Applications

Some published work in animals (e.g. mouse & zebrafish):

• Control and mapping of the function of motor cortex

• Expression restores light responses in retinal ganglion cells

• Dissection of Parkinson’s circuitry

• Dissection of role of DA neurons in behavioral conditioning

• Temporally precise in vivo control of intracellular signaling

• Potential control of epileptiform activity

• High-speed mapping of synaptic connectivity

• Dissection of a behavioral module in the spinal cord

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Take Home Message

Optogenetics is Nature Method of the Year 2010 and is going to have more biology applications in the future!!!

...but how much is there to be discovered?...but how much is there to be discovered?

More Information on Pub Med and on website of Dr. Chou Hung, Ph.D. vision.ym.edu.tw/courses/methods/Presentation2.ppt

…is it up to us?

Thank you