Techniques in Functional Neuroanatomy Flashcards
Name 2 methods to identify neuron outputs
Retrograde tracing
Transynaptic retrograde viral tracing
Name 2 methods to identify neuron inputs
Anterograde tracing
Lesion neurons/axons
Name 5 methods to test the functionality of connections
C-fos
Electrophysiology - stimulation and recording
Calcium imaging
Optogenetics
Genetic manipulation of targeted neurons - ablation/silencing
What are the 2 main transgene insertion methods?
Genetic targeting
Viral vector targeting
What are the 3 genetic targeting approaches to transgene insertion?
Transgenic approach
Binary expression systems
Inducible systems
What are the 2 types of binary expression system?
Recombination-based - Cre-loxP
Transactivation-based - tTa-tetO
What are the 3 viral vector targeting approaches to transgene insertion?
Viral constructs
Engineered tropism
Axon transduction
Which 2 types of transgenes can be inserted for neural circuit studies?
Optogenetics
Chemogenetics - DREADDs
What are the components of a transgene cassette?
Exogenous gene
With/without promoter
Recombination sites
What are the 2 methods used in the transgenic approach?
Conventional - transgene cassette
BAC
What are the advantages of BAC over transgene cassette?
BAC is large - longer transgene
Can contain more regulatory elements - more complex expression regulation
What is the driver line in binary expression systems?
Expresses driver gene (e.g. Cre)
Controlled specific promoter - gives cell specificity
What is the reporter line in binary expression systems?
Expresses transgene of interest
Controlled by robust ubiquitous promoter - gives high expression levels
Which promoter is specific for excitatory neurons?
CAMKII
Which promoter is specific for inhibitory neurons?
NPY
How is Cre-lox used to cause a selective transgene deletion?
LoxP sites flank transgene - within promoters
Cre recombination - transgene deletion only where Cre expressed
How is Cre-lox used to cause a selective transgene knock-in?
Stop codon flanked by loxP sites - lox stop lox (LSL) - precedes transgene
Cre recombination - deletion of stop codon - transgene expressed only where Cre expressed
How is Cre-lox used to selectively convert a transgene from inactive to active?
FLEX-switch system
Transgene in antisense orientation - flanked by 2 pairs of loxP sites
Cre recombination - transgene flipped to sense orientation only where Cre expressed - transgene expressed
What is a benefit of the FLEX-switch system?
Can use 2 transgenes in cassette - opposite orientations - where Cre expressed switch one on and other off
How does CreER work?
CreER - Cre + ligand-binding domain of oestrogen receptor
CreER in cytoplasm
Add tamoxifen (oestrogen analogue) - Cre translocates to nucleus - acts on loxP sites
Cre active on-demand
What is tTA-tetO?
Transgene expressed in absence of tetracycline/doxycycline
Reversible
How does a viral construct work?
Insert transgene into viral vector
Vector infects host cells
Different virus types integrate/do not integrate into host DNA
Transgene transcribed
What is engineered tropism and what is its benefit?
Viral vector coated with protein - only infects cells expressing receptor for protein (TVA)
Enables host cell type-specific transgene expression
How does axon transduction work?
Transgene in recombinant rabies virus deficient in glycoprotein - infects axon terminals - cannot cross synapse
Reintroduce glycoprotein - virus crosses synapse - infects other cells
What is a disadvantage of axon transduction?
High cytotoxicity
Name 3 main viral vectors?
Recombinant adeno-associated viral vector
Retroviral vector
Gutless adenoviral vector
At what timescale does optogenetics allow the control of neuronal activity?
Millisecond
How can opsin expression be visualised?
Insert gene for reporter molecule after opsin gene in transgene cassette - all under cell-specific promoter
Name 2 reporter molecules
mCherry
tdTomato
What are DREADDs?
Designer receptors exclusively activated by designer drugs
Which DREADD is a Gq-coupled receptor, which ligand activates it, and what is its effect on neuronal activity?
hM3D
Activated by CNO
Activates neuron
Which DREADD is a Gi-coupled receptor, which ligand activates it, and what is its effect on neuronal activity?
hM4D
Activated by CNO
Silences neuron
What is a disadvantage of DREADDs?
Same agonist (CNO) activates hM3D and hM4D - cannot simulatenously express both in same neuron to switch on/off