Optogenetics
Optogenetics use of light to regulate the activity of nuerons
Cells are genetically engineers to posses light responsive ion channels
Cloned from Green algae Chlamydomonas (Channelrhodopsins let in positive ions)
Halobacteria(Archaerhodopsin-remove positive ions from the cells.
Virus carrying the opsin (channelrhodopsin) and identifier for a specific neuron type (promoter), are injected into a brain area to infect the cells of interest.
Types of Nuerons
Neuron activators Channelrhodopsin (ChR2)
NA and Calcium are let in
Stimulate with Bluet Light
Lets positive ions into the cell
Neuron Inhibitors: activated by orange/yellow light
Opsin should be tagged with a fluorescent tagged so that you can visualise the infected neurones. GFP or Mcherry
Function should always be checked using electrophysiology
NpHR halorhodopsin lets chlroide ions in
Arch(archaerhodposin)-proton pump: pumps positive ions out
Why use it optogenetics
Is specific to the neuron/circuit you are targeting.
Nueropharamcology affect all nuerons with that type of receptor in the area where the drug is administered
Electrical stimulation affects all nuerons in area- including fibres of passage
Can inject virus into cell bodies and then use the laser at projection areas to work out circuitry of the brain.
Can bidirectionally control nuerons infect with activator and inhibitor opsin but optogenitcs is only as good as your laser
Optogentic to understand anxiety
Amygdala is a key area in processing fear and anxiety especially the basolateral- alerted when emotional processing or an emotional response is required
CEM believe to drive anxiety
Activation of BLA-CEL reduced anxiety in the elevated plus maze and open field test
Anxiolytic effect linked to BLA activating the CEL to reduce CEM output
Inhibiting BLA-CEL with ENpHR3 activation enhanced anxiety
Activation of the BLA leads to glutamate release in the CEL which stimulates the GABA cells (RED) of the CEL. These GABA cells then inhibit the fear response that would normally be elicited by the CeM.
Optogentic activation of the BLA terminals in the CEL reduces anxiety by stopping the output of the CEM.
Activation of CHR2 on oxytocin terminals in the CEL of the central amygdala reduces fear in rats. Tested using oxytocin receptor antagonist.
VTA role in addiction receiving dopamine from the VTA
STh
Striatum
Oribtofrontal cortex -impulsitivity
Pre limbic cortex -Decision making
Nucelus accumbens -saliency motivation
Amygdala -context of drug use
Hippocampus -context memory of drug use
PFC and Nucleus accumbens
pre limbic cortex to vta and nucleus accumbens via Glutamate
VTA to pre limbic cortex and nucleus accumbens via dopamine
Somatic method-directly firing onto the place they inject
Hypoactive Pyramidal nueron of the PFC in rats willing to keep taking cocaine despite shock
Activation of the Pre-limbic cortex(somatic method) reduced cocaine seeking in shock resistant rats
Inhibition of the Pre-limbic cortex(somatic method) increases compulsive cocaine seeking in shock sensitive rats