Optogenetics

Question 1

Different regions?
Different cell types?
No. of nerve cells?
No. of connections per neuron ?

Answer 1

100
1000
billions
10,000

Question 2

neurotechnology invention is difficult why?

Answer 2

Because the brain is : dynamic
anatomically rich 
fragile 
high speed function 
inaccessibility of structures
heterogeneity of cells

Question 3

Green Algae

Answer 3

Chlamydomonas reinhardtii

Unicellular organisms

“Eye spot” located inside the cell to detect light and to swim toward it (phototaxis).

Unique photosensitive ion channel that converts a light signal into a voltage change (ion flow) that provides information to the algae.

Question 4

Optogenetic tools can…

Answer 4

Optogenetic” tools are genetically encoded molecules (Opsins) that, when targeted to specific neurons in the brain, enable their activity to be activated or silenced by light.

Control the electrical activity of specific neuron types embedded within intact brain circuits.
A light switch for neuronal activity

Question 5

Optogenetics

Answer 5

Integration of optics and genetics to control precisely defined events within specific cells of living tissue and freely moving animals

Question 6

Channelrodopsin

Answer 6

activated by blue light at 470nm

Orginates from The algae Chlamydomonas reinhardtii

opens Na+ channels, depolarising cells

Question 7

Halorodopsin

Answer 7

activated by yellow light at 580nm

orginates from The halobacterium Natronomonas pharaonis

opens Cl- channels hyperpolarises neurons

Question 8

Thy1 promoter

Answer 8

Is a 25–37 kDa heavily Nglycosylated, glycophosphatidylinositol (GPI) anchored conserved cell surface protein with a single V-like immunoglobulin domain, originally discovered as a thymocyte antigen. Thy-1 can be used as a marker for a variety of stem cells and for the axonal processes of mature neurons

Question 9

Neurons expressing Leptosphaeria maculans opsin (Mac) (fungus)

Answer 9

were silenced by blue and unaffected by red

Question 10

Optogenetic mapping of neuronal circuits

Optogenetic actuators

Optogenetic sensors/probes

Answer 10

Optogenetic actuators - channelrhodopsin, halorhodopsin, and archaerhodopsin conver precise neuronal control with high spatial and temporal resolution

Optogenetic sensors/probes - for
Ca+2 = Aequorin, Cameleon, GCaMP
Cl- = Clomeleon
membrane voltage = Mermaid

all give temporally-precise recordings of geneticaly defined population of neurons

Question 11

Jaws opsin

Answer 11

Red-shifted cruxhalorhodopsin, Jaws, derived from Haloarcula (Halobacterium) salinarum (strain Shark) and engineered to result in red light–induced photocurrents 3x better as earlier silencers

Question 12

sonogenetics

Answer 12

Worm with motor neurons that carried TRP-4 ion channels

But require gas-filled microbubbles around nematode to transduce the ultrasound wave