Animal Research Flashcards
Anatomy in animals
- tracers
Injecting tracers into localized areas and study transport along axons
- anterograde tracers
- retrograde traces
- monosynaptic connections
- polysynaptic tracers
Anterograde tracers
Label pathway from cellbody to termination site of axons
Tetrograde tracers
Label pathway from termination site to cell body
Monosynaptic connections
Projection to the first synapse
- tracers are monosynaptic
Polysynaptic tracers
Chains of connections –> transmitter across synapses
- virusses are polysynaptic
Why use animals instead of humans
Info on which of the 6 cortical layers receives or sends the connection (detail level not possible untill now)
Localization of tracers is not ethical in humans
Permanent lesions
Aspiration
Electrolytic
Excitotoxic/neurotoxic
Aspiration
- remove tissue by sunction through glass pipette
- visually guided
- only surface areas, but also fiber destruction
Electrolytic
- pass current through electrode head exposed tip and destroy adjacent tissue
- also areas at depth, also fiber destruction
Excitotoxic/neurotoxic
- selectivity destroy cells (or neurotransmitters) and spare fibers by infusion of chemical through a cannula
- also deep subcortical structures
- difficult to ensure the precise extent of the lesion
Reversible lesion
Pharmacological interventions
Cryogenic inactivation
Genetic-based approaches
Optogenetics
Chemogenetics
Pharmacological interventions
Infusion of non-toxic chemical t temporarily change neurtoransmission (re-uptake, synthesis, break-down)
- e.g. GABA agonist muscimol => increase local inhibition
- virtually any brain region can be targeted while sparing fibers of passage, but difficult to assess spread and efficacy of drugs
- typically 10-20 min to take fulle ffect and wear off after a few hours
Cryogenic inactivation
Transient cooling prevents synaptic transmission
- requires direct access to tissue, not well-suited for deep and subcrtical structures
Genetic-based approaches
Use of viral vectors to make cells express specific proteins
- proteins are selectively activated to alter cell function
- high spatial resolution: target individual structures, cell types or pathways
- high temporal reolution: precise control over timing of lesion (less reorganization)
Optogenetics
Combination of genetic and optical methods to achieve gain or loss of function of well-defined events in specific cells of living tissue with millisecond precision
Chemogenetics
Combination of genetics and drug-based methods to achieve gain or loss of function of well-defined events in specific cells of living tissue for minutes to hours
- DREADDS
DREADDS
Designer Receptors Exclusively Activated by Desgner Drugs
-??
Why use animals for lesions studies
- possivle to plce lesion in a single cytoarchitectonic area
- possible to remove grey matter while leaving underlying white matter undisturbed
- possible to place exactly the same lesion in several animals –> reliability of results
- possible to assess cognitive function both before and after lesion is induced
Recording neural activity
Activity patterns of neurons (single unit recordings) and neuron clusters (multi unit recordings) provide insight into a region’s function
- superior spatial and temporal resolution
Inducing neuronal activity
Stimulating neurons in the vicinity of the electrode provides inisghts into the function of an area and its projection regions => effective connectivity
Why use animals for neural recording
- possible to record/induce activity in any area
- possible to record/induce activity in a brain that is not abnormal
- possible to test each cell in a variety of conditions
Neuroimaging
Compare neuroimaging data between rodents, non-human primates and humans
Neuroimaging in rodents
- less variable brains => easier to place subcortical lesions
- especially for processes related brain structure, study of neurotransmitter systems, behavioral pharmacology
- due to eyes and paws and cognitive limitations: difficult to train to fixate central point
Marmosets
- new world monkey
Mature and age more quickly => speed up studies of disease that affect development/aging
- brain is less furrowed => easier to record activity from surface
Macaques
- old world monkey
Easier to train, better work ethics
- better knowledge on anatomical connections
- less smooth brains => easier to localize specific areas
Ethics in animal research
3R’s principle for the protection of animals used in research
- Replacement
- Reduction
- Refinement
Replacement
Absolute: replace with inanimate systems
Relative: replace with more sentient animals with animals with lower potential for pain reception
Reduction
Any strategy that results in fewer animals being used to obtain sufficient data
- maximize information obtained per animal => limit/avoid subsequent use fo additional animals
Refinement
- modify husbandry or experimental procedures to minimize pain and distress
- enhance welfare f animals from birth to death
